Basin Research 202032587ndash612 | 587

EAGE

wileyonlinelibrarycomjournalbre

Received 30 June 2018 | Revised 17 May 2019 | Accepted 22 May 2019

DOI 101111bre12374

O R I G I N A L A R T I C L E

Relationships between tectonic activity and sedimentary source‐to‐sink system parameters in a lacustrine rift basin A quantitative case study of the Huanghekou Depression (Bohai Bay Basin E China)

Hao Liu1 | A J (Tom) van Loon2 | Jie Xu1 | Lixin Tian3 | Xiaofeng Du3 | Xintao Zhang3 | Danlei Chen1

copy 2019 The Authors Basin Research copy 2019 John Wiley amp Sons Ltd European Association of Geoscientists amp Engineers and International Association of Sedimentologists

1School of Ocean Sciences China University of Geosciences (Beijing) Beijing China2College of Earth Science and Engineering Shandong University of Science and Technology Qingdao China3Exploration amp Exploitation Research Institute Tianjin Branch of China National Offshore Oil Corporation Tianjin China

CorrespondenceHao Liu School of Ocean Sciences China University of Geosciences (Beijing) Beijing 100083 ChinaEmail lhcugb163com

Funding informationFundamental Research Funds for the Central Universities of China GrantAward Number 2652014037 National Natural Science Fundations of China GrantAward Number 41676050 National Science and Technology Major Project of China GrantAward Number 2016ZX05024-003-003

AbstractLacustrine rift basins commonly preserve a fairly complete record of the sediment source‐to‐sink (S2S) system and consequently may form an ideal natural laboratory for establishing quantitative relationships between the various elements within the S2S system The tectonic‐activity rate in the source (eg fault‐growth rate and fault‐activity rate) accommodation space and depositional system in the sink (eg areal extent and volume as well as the depositional dip of the fan‐ and braid‐deltas) are genetically related and their quantitative correlations are explored The Palaeogene succession on the southwestern margin of the Huanghekou Depressionin the Bohai Bay Basin one of the largest lacustrine rift basins in eastern China was chosen to study these relationships using 3‐D seismic core and well‐log data The tectonic activity was strongly related to the sediment supply accommodation space and mor-phology of the sink area Three different rates of tectonic activity are identified these led to changes in the basic features of the S2S system that influenced each other In Members 4 and 3 (lower unit) of the Shahejie Fm (4044ndash447 Ma) strong tectonic activity led to significant uplift resulting in the widest exposure of the provenance area to erosion to a high sediment‐supply rate to a steep slope and to a large accom-modation space which controlled the development of several fan‐deltas with steep progradational angles In Member 3 (upper unit) of Shahejie Fm (3789ndash4044 Ma) and Member 3 of Dongying Fm (302ndash3328 Ma) decreased tectonic activity led to slower uplifting resulting in a wider alluvial plain longer transport distances a lower sediment‐supply rate and less accommodation space so that braid‐deltas with larger volumes and a gentler slope developed In Members 1 and 2 of Shahejie Fm (3328ndash3789 Ma) and Member 2 of Dongying Fm (2671ndash302 Ma) still further decreasing tectonic activity led to a still lower sediment‐supply rate a more gentle depositional slope less accommodation space and the development of several braid‐deltas with a gentle angle The quantitative relationships established here advance our understanding of the relationships within lacustrine source‐to‐sink systems es-pecially for tectonically controlled rift basins

588 | EAGE

LIU et aL

1 | INTRODUCTION

The analysis of source‐to‐sink (S2S) systems systemati-cally studied in the past two decades (Walsh Wiberg Aalto Nittrouer amp Kuehl 2016) deals with erosion in the source area transport of the eroded particles and their final deposi-tion in the sink (eg Allen 2008a Anderson et al 2016 Anthony amp Julian 1999 Meade 1982 Soslashmme amp Jackson 2013 Soslashmme Jackson amp Vaksdal 2013) Studies of the ge-omorphological evolution and S2S system in a basin cannot only reveal the geological evolution sedimentary dynamics and their controlling factors (eg Allen 2008b Castelltort amp Van denDriessche 2003 Martinsen Soslashmme Thurmond Helland‐Hansen amp Lunt 2010 Metivier amp Gaudemer 1999 Soslashmme Helland‐Hansen Martinsen amp Thurmond 2009)but also provide effective methods for hydrocarbon exploration (eg Liu Meng Zhang amp Yang 2019 Martinsen Lien amp Jackson 2005 Liu Lin Guo Zhu amp Cui 2015b)

Most S2S system studies focus on modern and Quaternary systems because the elements of such S2S systems are still fairly completely preserved and their quantitative relation-ships are easily established (eg Bhattacharya Copeland Lawton amp Holbrook 2016 Covault Craddock Romans Fildani amp Gosai 2013 Covault Romans Graham Fildani amp Hilley 2011 Kertznus amp Kneller 2009 Soslashmme et al 2009 Syvitski amp Milliman 2007) There are several studies carried out to analyse the S2S system of ancient passive‐margin basins and reveal correlations between the various upstream source and downstream sink parameters (eg Blum amp Pecha 2014 Galloway Whiteaker amp Ganey‐Curry 2011 Milliken et al 2018 Snedden et al 2018 Xu Snedden Stockli Fulthorpe amp Galloway 2017) These studies indicate that the quantitative relationships between different elements of an S2S system also exist in ancient systems and can be reconstructed by detailed study of the tectonic‐climatic evolution in the source area of the sediment dispersal systems in the sink area

Sediment delivery from source to sink is however com-monly complicated for a large passive‐margin basin by the changes of provenance area sediment supply from several sources sediment stored temporarily somewhere on the pathway from source to sink etc (Hovius 1998 Romans Castelltort Covault Fildani amp Walsh 2016) Consequently the reconstruction of S2S system parameters (eg the catchment area sediment‐supply rate accommodation space geomor-phology and scale of the depositional systems etc)of ancient passive‐margin systems is usually associated with significant uncertainties

Ancient lacustrine basins which receive relatively little attention are commonly characterized by relatively simple S2S systems and tend to preserve the complete system (eg Lin Xia Shi amp Zhou 2015 Liu Meng amp Banerjee 2017) Tectonic activity is the most significant factor controlling the depositional pattern in tectonically active lacustrine basins such as the lacustrine rift basins in eastern China (eg Chen et al 2009 Hsiao Graham amp Tilander 2010 Katz amp Liu 1998 Lin et al 2001 Zhu Yang Liu amp Zhou 2014) Not only does it control the position of provenance areas and the morphology of the sink area but also significantly influences the accommodation space fluctuations in lake level (which tends to be also the base level) and even the local climate (eg Hadlari Midwinter Galloway Dewing amp Durbano 2016 Johnson Halfman Rosendahl amp Lister 1987 Leeder 2011 Williams 1993 Masini Manatschal Mohn Ghienne amp Lafont 2011 Ravnas amp Steel 1998)

Previous investigations have enhanced our understanding of the infilling process of active rift basins (eg Brown amp Fisher 1977 Leeder amp Gawthorpe 1987 Hadlari Rainbird amp Donaldson 2006 Scholz amp Rosendahl 1990 Strecker Steidtmann amp Smithson 1999) of the relationship between geomorphology and stratigraphic and facies patterns (eg Dill et al 2001 Galloway 1986 Gupta Cowie Dawers amp Underhill 1998 Martins‐Neto 1996 Obrist‐Farner amp Yang 2015) of the influence of the infilling process of rift basins on the reservoir quality of sand bodies and of the development of subtle hydrocarbons traps (Liu Wang Xin amp Wang 2006 Liu Xia et al 2015a) Although most current S2S system studies on ancient lacustrine basins are still immature they can provide valuable information that may help understand how each element of an S2S system responds to processes in other elements they may also help to establish quantitative

K E Y W O R D SBohai Bay Basin lacustrine sediments Palaeogene rift basin source‐to‐sink analysis

Highlightsbull An obvious control of tectonic activity on synsedi-

mentary rift in a tectonically active rift basinbull Tectonic activity is quantitatively related to

source‐to‐sink system parametersbull These quantitative relationships provide excellent

clues to make sequence stratigrapic analysisbull Differential tectonic activity leads to change of

source‐to‐sink system and the distribution of reservoir

| 589EAGE

LIU et aL

relationships in a relatively closed system Particularly for well‐studied lacustrine basins with a good coverage of data from drilling wells and seismic data it is relatively easy to identify and reconstruct the erosional provenance area and other S2S system parameters etc (Li et al 2017 Zhu et al 2018) In such cases it is relatively easy to establish the quan-titative relationship among the various elements of an S2S system and use such a quantitative relationship to predict the occurrences of reservoir sands in other basin with less data coverage (eg Liu et al 2017)

Based on previous research progress concerning lacustrine basins the present study chooses Palaeogene successions in the Huanghekou Depression (HD) in the Bohai Bay Basin eastern Chinato (a) establish the quantitative relationship be-tween tectonic subsidence and S2S system parameters and (b) explore the controlling effect of tectonics on the internal stacking pattern of the sedimentary successions

This work uses 2‐D and 3‐D seismic data core analysis and well log data to (a) document the sedimentary facies of the Palaeogene in the HD with emphasis on the seismic in-terpretation of the internal stacking pattern of the fan‐delta and braid‐delta complexes (b) estimate the development in time of the tectonic subsidence the main boundary faults and the S2S system parameters (c) establish the quantita-tive relationship between the intensity of the tectonics and the various S2S system parameters as well as to analyse the variation in the sizes of the sedimentary systems and their internal stacking patterns and (d) discuss the effects of the tectonic activity and the evolution of the S2S system on the scale of the sedimentary systems and the depositional process in the tectonically active lacustrine basin The quantitative relationships between the intensity of the tectonics and the various S2S system parameters established in the study can contribute to a better understanding of the different elements of S2S system responses to tectonic activity at a million‐year time scale In addition the established quantitative relation-ships are applicable to the analysis of many other rift basins which are the major hosts of hydrocarbon resources in China

2 | GEOLOGICAL BACKGROUND

The HD is a sub‐basin in the south‐eastern part of the Bohai Bay Basin It occupies about 3300 km2 and is bounded by the Kendong Structural High and the less elevated Laibei Structural High in the south and by the relatively low Bonan Structural High in the north (Figure 1a‐c) (Liu Xia et al 2015a Tian Yu Zhou Peng amp Wang 2009 Zhou Yu Tang Lv amp Wang 2010) Two sets of roughly E‐W‐ and NNE‐SSW‐oriented faults cross‐cut the Palaeogene of the HD The NNE‐SSW‐oriented faults represent the western branches of the Tanlu Fault Belt They are characterized by a right‐lateral strike‐slip displacement and run through the

entire Bohai Bay Basin thus largely controlling the formation of many sub‐basins (or depressions) in the Bohai Bay Basin (eg Glider Leloup amp Courtillot 1999 Hsiao Graham amp Tilander 2004 Schellart amp Lister 2005)

21 | The Palaeogene successionThe Bohai Bay Basin is a Cainozoic rift basin developed on top of the ancient Sino‐Korean Plateau It consists of two tectonic units the Palaeogene syn‐rift unit and the Neogene post‐rift unit The Palaeogene of the Bohai Bay Basin is built by from bottom to top the Kongdian Shahejie and Dongying Formations (Liu et al 2017) (Figure 2) The Shahejie Formation is subdivided into four members viz ndash from bottom to top (the member numbers reflect the stratigraphy based on borings) ndash Member 4 Member 3 which is subdivided into three informal units the upper one of which is absent in the study area because of ero-sion (the two informal units present in the study area will therefore be indicated in the following as the lower part and the middle part of Member 3 respectively) Member 2 and Member 1 The Dongying Formation is subdivided ndash again from bottom to top ndash into Member 3 Member 2 and Member 1

22 | Palaeogene tectonic evolutionThe Bohai Bay Basin which shows superimposed rifts and depressions is characterized by several stages and types of tectonism (Zhou et al 2010) The basin experienced rift‐related subsidence during the Palaeogene and post‐rift thermal subsidence during the Neogene‐Holocene The Palaeogene rifting was episodic and several sub‐basins developed within a distinct tectonic framework of highs and depressions (Figure 1d‐f) Four rifting phases can be deduced from the rift features that took place during four phases these phases correspond to the Kongdian Fm Member 4 of the Shahejie Fm (S‐4) Members 1ndash3 of the Shahejie Fm and the Dongying Fm The surface area of the basin experienced as a rule temporary regional uplift after each rifting phase which led to the erosion of earlier deposited sediments which thus became separated from each other by low‐angle unconformities or disconformities (Liu et al 2017) (Figure 2)

3 | DATA SETS AND METHODS

31 | Data sets and facies interpretationHigh‐quality seismic reflection data cores cutting logs and logging data have been provided by the Tianjin Branch of China National Offshore Oil Corporation (TBCNOOC) The seismic data include 2‐D seismic lines (Figure 1b) and

590 | EAGE

LIU et aL

F I G U R E 1 Schematic map of the Bohai Bay Basin and the Huanghekou Depression (HD) (a) Location of the Bohai Bay Basin within China The red solid line in the figure forms the boundary of the Bohai Bay Basin (b) Tectonic map showing sub‐basins of the Bohai Bay Basin The tectonic features in this figure are based on the interpretation of regional 2‐D seismic data of the lower boundary of the Palaeogene (modified from Zhou et al 2010 Liu Xia et al 2015a) The blue dotted line representing the present‐day coastline of China indicates the offshore part (Bohai Bay) of the Bohai Bay Basin Light‐gray dotted lines in this figure are regional 2‐D seismic lines near the HD Purple solid lines in figures B and C indicate the locations of the seismic lines shown in Figures 3 and 5 (c) Structural characteristics of the HD The tectonic characteristics of the HD are modified from results of Zhou et al (2010) and Liu Xia et al (2015a) The south‐western faults (F1 and F2) and the Kendong Structural High have been interpreted and validated through newly acquired 3‐D seismic data F1‐S1 F1‐S2 F1‐S3 F2‐S1 F2‐S2 and F2‐S3 are the calculation locations of faults F1 and F2 Circles (filling in yellow) represent drilling well locations (dndashf) Schematic structure and seismic profiles across the HD in the offshore part of the Bohay Bay Basin (for locations see Figure 1b‐c) The texts ldquoT2 T31 T32 hellip T8rdquo in the legend refer to the seismic surfaces (see Figure 2) The codes of formations and members are consistent with Figure 2

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over 5000 km2 of 3‐D seismic surveys in the HD Both the 2‐D and the 3‐D seismic data have a vertical sampling rate of 2 ms and were processed to zero phases They were dis-played as reversed polarities The 3‐D seismic data have a dominant frequency of 15ndash40 Hz and an average velocity of 3600 ms (calculated from Well W25) with a vertical resolu-tion of 22ndash60 m

Cutting log and logging data from 25 wells have been used for the present study Core data were made available for 11 wells with a total length of about 1000 m Integration of these well and seismic data helped establishing a regional stratigraphic framework through calibration of seismic syn-thetic records seismic units and interpretation of the sedimen-tary facies (Table 1) In total eight horizons were interpreted

respectively as T7 (dated at 447 Ma) T63 (4223 Ma) T62 (4044 Ma) T5 (3790 Ma) T3(3328 Ma) T31 (2671 Ma) and T2 (2338 Ma) The successions between these horizons represent different members of the Dongying and Shahejie Formations The codes and interpretation of these members are provided in Figure 2 The quantitative compilation of the sedimentary system and the palaeogeomorphological maps are based on these results

32 | Quantitative estimation of tectonic activityThe tectonic‐subsidence rate fault‐growth index and fault‐activity rate are used in the present contribution to detail

F I G U R E 2 Lithostratigraphy and sequences of the HD The lithological data and interpretations are based mainly on a combination of data from Wells W1 W18 and W25 Ages are based on data obtained from CNOOC Tianjin Branch The tectonic stages sedimentary environment and fossil associations are modified after Liu Xia et al (2015a) Note that newly acquired 3‐D seismic data indicate that the Kongdian Fm is possibly absent in the HD which differs from the results presented by Liu Xia et al (2015a) D‐1 = Member 1 of the Dongying Fm D‐2 = Member 2 of the Dongying Fm D‐3 = Member 3 of the Dongying Fm S‐1 amp 2 = Members 1 and 2 of the Shahejie Fm S‐3 = Member 3 of the Shahejie Fm S‐4 = Member 4 of the Shahejie Fm

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the tectonic history and intensity We have selected Well W25 (Figure 1c) because it is the only drilling well in the south‐eastern HD for simulation of the subsidence history This simulation is based on our reconstructed stratigraphic framework and age information provided by the TBCNOOC (Figure 2)

Correction for compaction is critical in quantitative sim-ulation of the subsidence history and rate The influence of the water depth during sedimentation is considered negligible since the Bohai Bay Basin was a lacustrine basin Differences in the acoustic travel times have been used to calculate the porosities at the corresponding depths (cf Wylliel Gregory amp Gardner 1958) Subsequently the porosities of the vari-ous types of lithology (mainly sandstone and mudstone) at different depths were determined by logging and the poros-itydepth relationship was established by statistic fitting (cf Athy 1930) Back‐stripping of the selected strata was per-formed layer‐by‐layer to calculate the top and bottom bound-ary depths at different times in the geological development (cf Perrie amp Qiublier 1974) thus distinguishing between the compaction history the tectonic subsidence and the total subsidence during the Palaeogene (Figure 3 Table 2 supple-mentary text)

The normal boundary faults (F1 amp F2) controlling depo-sition on the south‐western margin of the HD have been

selected to calculate the fault‐growth index and the fault‐ac-tivity rate (Figure 1c) The fault‐growth index sometimes also called the ldquoexpansion indexrdquo is the ratio between the stratigraphic thickness of the hanging wall and that of the footwall of a growth fault The fault‐activity rate is the ratio between the thicknesses of the sedimentary successions in the hanging wall and the foot wall resulting from fault activ-ity during a specific depositional phase corresponding to the length of the time‐span during which the investigated succes-sion accumulated ie (Zhou Niu amp Teng 2009)

where RF is the fault‐activity rate in mMa T is the length of the time‐span during which the investigated succession ac-cumulated (in Ma) STh is the stratigraphic thickness of the hanging wall (in m) and STf is the stratigraphic thickness of the footwall (in m) For the calculation of the stratigraphic thickness the conversion from two‐way travel time to depth was made by analysis of the P‐wave velocity in the wells The growth index and the activity rate of the main faults have thus been calculated for several locations (Table 2 Figure 1c) which was considered necessary because of the differ-ent successive stages in the morphological evolution of the

RF=ΔST∕T =

(

SThminusST

f

)

∕T

F I G U R E 3 Palaeogene burial history of the HD (a) Cumulative subsidence (b) Subsidence during the development of the individual members D‐1 = Member 1 of the Dongying Fm D‐2 = Member 2 of the Dongying Fm D‐3 = Member 3 of the Dongying Fm S‐1 amp 2 = Members 1 and 2 of the Shahejie Fm S‐3 = Member 3 of the Shahejie Fm S‐4 = Member 4 of the Shahejie Fm

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basin‐controlling faults and because of the changes in the intensity of the fault activity

33 | Quantitative calculation of S2S system parameters

331 | Area and volume of the sedimentary faciesQuantitative calculation of the dimensions of sedimentary facies requires reliable estimates of the lateral extent and thickness of the sediments involved For these calculations first the maxi-mum extent of the specific units under study (fan‐deltas braid‐deltas etc) at different times was determined in plan view based on the combined interpretation obtained from seismic facies lithofacies and the outer boundaries of the sediment bodies Subsequently the outcomes were digitalized and used as input for a 3‐D survey by GEOFRAME Detailed calculations of the sedi-ment bodies extents were conducted using the PLANIMETER tool in the BASEMAP window of GEOFRAME

This was followed by the selection of several seismic sec-tions across the sediment body in order to identify the lower

and upper boundaries as well as to calculate the maximum minimum and average thickness (see Amorosi Maselli amp Trincardi 2016 Liu et al 2017) Finally we used a colum-nar body with irregular base and the same height to represent the irregular sediment body The formula for volume calcu-lation is as follows (Figure 4 Table 3 supplementary text)

where VS is the volume of the sediment (in km3) AS is the horizontal surface area of the irregular base of the sediment (in km2) and H is the height (average thickness) of the sed-iment (in m) Detailed calculations of the thickness were conducted using the AREAL tool in the SEIS3DVSEIS2DV window of GEOFRAME

332 | Determination of the depositional dip of the delta surface due to progradationThe term ldquodepositional diprdquo is used here to indicate the inclination of a dipping sedimentary surface Horizon flat-tening was used to analyse and calculate the morphology of the underlying strata First the maximum flooding surface ndash approximately corresponding to the palaeo‐sedimentary surface (Lin et al 2012) ndash of each unit under study was interpreted it was subsequently flattened to calculate the original depositional dip (Figure 5d) with the formula

where DSD is the sedimentary dip (in degrees) dy is the verti-cal thickness between the lower boundary of the sedimentary unit and the ancient sedimentary surface in the depositional centre (in m) and dx is the distance from the apex of the delta to its depositional centre (in m)

Two to four seismic sections have been selected to calcu-late the average sedimentary dip of each individual delta with the following formula

where DSDA is the average sedimentary dip of a sediment (in degrees) and n is the number of seismic sections

The seismic progradational angle of the deltas interior has been calculated by the horizon‐flattening method (Figure 5e) which is expressed by the formula

VS=A

StimesH

DSD

= tanminus1 (dy∕dx)

DSDA

=

(

nsum

i=1

DSDi

)

∕n

DP= tan

minus1 (dy∕dx)

F I G U R E 4 Schematic diagram showing the calculation of the volume of a sediment (a) is an irregular sediment body Volume calculation of cuboids was used for reference to calculate the volume of an irregular sedimentary body ie the volume of an irregular sediment body equals the area of the irregular bottoms times height (b) 3ndash4 seismic lines along the sedimentary body are selected and the thickness of the sedimentary body is determined at intervals of 10 seismic traces (c) when a thickness grid covering the entire sedimentary body in space is acquired the average thickness of all counted thicknesses can be calculated as the height of the irregular sediment body (d)

594 | EAGE

LIU et aL

where DP is the seismic progradational dip (in degrees) The average dip angle is obtained from only one seismic sec-tion because of the variations in the progradational seismic event of the delta on the same seismic line

where DPA is the average seismic progradational dip in a spe-cific seismic section (in degrees) and n is the number of seis-mic progradational events

Based on the calculated average dip of one seismic sec-tion the average progradational dip of a specific sediment body can be calculated with the formula

DPA

=

(

nsum

i=1

DPi

)

∕n

F I G U R E 5 Detailed calculations of the sedimentary dip and the progradational seismic event dip of the delta interior taking the progradation seismic reflection of the delta developed in Member 3 of the Dongying Formation as an example The locations of the seismic lines are shown in Figure 1c Based on the interpretation of the stratigraphic and seismic facies visible in the original seismic lines (a) the topset or the maximum flooding surface (MFS) corresponding to the delta was flattened (b) Taking into account the water depth during sedimentation the sedimentary dip (d) and the progradational seismic event dip of the delta interior (e) can be calculated DSD = depositional dip in a specific seismic section DSDA = average depositional dip of a specific sedimentary unit DP = seismic progradational dip DPA = average seismic progradational dip

| 595EAGE

LIU et aL

TA

BL

E 1

In

terp

reta

tion

of th

e m

ain

sedi

men

tary

faci

es in

the

Pale

ogen

e of

the

Hua

nghe

kou

Dep

ress

ion

Evi

denc

e of

fan

delta

s and

bra

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s in

wel

ls W

1 an

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18 c

omes

from

Liu

Xia

et a

l (2

015a

)

Form

atio

n an

d m

embe

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ismic

faci

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ampl

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thof

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Wel

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Dep

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res-

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ualit

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D‐2

Seis

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Fac

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mod

erat

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ntin

uous

lo

w‐a

mpl

itude

and

a sh

ingl

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ke

prog

rada

tiona

l sei

smic

refle

ctio

n

Figu

re

Mul

tiple

upw

ard‐

coar

s-en

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litho

faci

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Gre

y m

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gre

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w

hite

pebb

ly fi

ne sa

ndst

ones

and

fin

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ndst

ones

T25

Bra

id d

elta

Mod

erat

e to

hi

gh

D‐3

Seis

mic

Fac

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con

tinuo

us m

oder

-at

e‐to

high

‐am

plitu

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nd o

bliq

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igm

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prog

rada

tiona

l sei

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flect

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Figu

re

Mul

tiple

upw

ard‐

coar

s-en

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litho

faci

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Gre

yish

whi

te to

whi

te fi

ne

sand

ston

es s

iltst

ones

and

gre

y m

udst

ones

T25

Bra

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Hig

h

Figu

re 7

e‐f

S‐1

+ 2

Seis

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Fac

ies 5

mod

erat

e co

ntin

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m

oder

ate‐

ampl

itude

and

shin

gled

‐like

pr

ogra

datio

nal s

eism

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flect

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Figu

re

Mul

tiple

upw

ard‐

coar

s-en

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litho

faci

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asso

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Dar

k gr

ey m

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ones

and

gre

yish

w

hite

to g

rey

mid

dle‐

to fi

ne‐

grai

ned

sand

ston

es

T25

Bra

id d

elta

Hig

h

S‐3

(mid

dle

unit)

Seis

mic

Fac

ies 3

har

dly

tom

oder

atel

y co

ntin

uous

low

‐am

plitu

de o

bliq

ue

prog

rada

tiona

l sei

smic

refle

ctio

n

Figu

re

Lith

ofac

ies 1

Gre

y to

gre

yish

whi

te sa

ndy

cong

lom

erat

esT2

5B

raid

del

taH

igh

Lith

ofac

ies 2

Thic

k gr

ey m

iddl

e‐to

fine

‐gra

ined

sa

ndst

ones

Figu

re 7

a‐d

Lith

ofac

ies 3

Gre

y m

udst

ones

inte

rbed

ded

with

gr

ey fi

ne sa

ndst

ones

and

gre

y m

uddy

silts

tone

s

Lith

ofac

ies 4

Thic

k da

rk g

rey

mud

ston

es

S‐3

(low

er

unit)

Seis

mic

Fac

ies 2

cha

otic

prog

rada

-tio

nal t

o ob

lique

pro

grad

atio

nal

seis

mic

faci

es

Figu

re

Pe

bbly

sand

ston

es in

terb

edde

d w

ith

thin

bro

wn‐

grey

mud

ston

esb

row

n sa

ndy

cong

lom

erat

ess

ands

tone

s in-

terb

edde

d w

ith th

in m

udst

ones

thic

k m

udst

ones

inte

rbed

ded

with

th

in sa

ndst

ones

or p

ebbl

y fin

e sa

ndst

ones

T1Fa

n de

ltaM

oder

ate

S‐4

Seis

mic

Fac

ies 1

dis

cont

inuo

us to

con

-tin

uous

low

‐tohi

gh‐a

mpl

itude

cha

otic

pr

ogra

datio

nal s

eism

ic re

flect

ion

Figu

re

Figu

re

Fig

ure

and

Fi

gure

Lith

ofac

ies 1

Gre

y pe

bbly

sand

ston

es c

oars

e sa

ndst

ones

T18

Fan

delta

sM

oder

ate

Lith

ofac

ies 2

Ash

‐bla

ck m

udst

ones

inte

rbed

-de

d w

ith th

in g

rey

fine‐

grai

ned

sand

ston

es

Lith

ofac

ies 3

Ash

‐bla

ck m

udst

ones

inte

rbed

ded

with

peb

bly

sand

ston

esa D

= D

ongy

ing

Fm

S =

Sha

hejie

Fm

The

num

ber i

ndic

ates

the

num

ber o

f the

mem

ber

596 | EAGE

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TA

BL

E 2

Es

timat

ion

stat

istic

s of t

he te

cton

ic‐s

ubsi

denc

e ra

te g

row

th in

dex

and

activ

ity ra

te o

f fau

lts F

1 an

d F2

S1

S2

and

S3 a

re th

e ca

lcul

atio

n lo

catio

ns o

f F1

and

F2 (s

ee F

igur

e 1c

) th

e co

rres

pond

ing

num

bers

are

F1‐

S1 F

1‐S2

F1‐

S3 F

2‐S1

F2‐

S2 a

nd F

2‐S3

res

pect

ivel

y

Form

atio

n an

d m

embe

raA

ge

(Ma)

R TS

(m

Ma)

b

Faul

t‐gro

wth

inde

xFa

ult‐a

ctiv

ity r

ate

(mM

a)

AFG

I F1‐

F2c

R FA

A‐F

1‐F2

d

S1S2

S3A

vera

geS1

S2S3

aver

age

F1F2

F1F2

F1F2

F1F2

F1F2

F1F2

F1F2

F1F2

D‐1

233

75ndash

267

1450

00

111

106

109

110

107

109

109

108

389

270

389

479

270

389

349

379

109

364

D‐2

267

14ndash

302

060

00

139

130

138

140

137

133

138

134

320

730

29

341

442

62

329

534

98

330

535

96

136

345

1

D‐3

302

0ndash33

278

190

002

002

052

102

342

032

052

042

1579

67

104

0010

372

111

3485

59

762

989

66

972

12

1093

44

S‐1

+ 2

332

78ndash

378

9250

00

145

136

142

147

155

145

148

143

122

211

36

105

915

78

587

176

39

5614

92

146

122

4

S‐3

(mid

dle

unit)

378

92ndash

404

3812

500

131

202

192

242

175

257

166

234

335

140

88

490

380

62

215

510

919

347

076

90

205

558

0

S‐3

(low

er

unit)

404

38ndash

422

3135

500

284

343

302

395

342

389

309

376

737

185

37

104

4016

956

742

820

480

841

315

324

343

118

69

S‐4

422

31ndash

447

300

002

512

921

584

173

023

332

373

4791

33

106

4357

58

151

8811

007

121

5186

33

126

612

9210

647

a D =

Don

gyin

g Fm

S

= S

hahe

jie F

m T

he n

umbe

r ind

icat

es th

e nu

mbe

r of t

he m

embe

r b R T

S = te

cton

ic‐s

ubsi

denc

e ra

te

c AFG

I F1‐

F2 =

ave

rage

faul

t‐gro

wth

inde

x of

F1

and

F2

d R FA

A‐F

1‐F2

= a

vera

ge fa

ult‐a

ctiv

ity ra

te o

f F1

and

F2

| 597EAGE

LIU et aL

TA

BL

E 3

C

alcu

latio

n ch

art o

f the

sedi

men

tary

‐fac

ies d

imen

sion

s and

the

inte

rnal

pro

grad

atio

nal s

eism

ic e

vent

dip

The

spat

ial e

xten

t is s

how

n in

Fig

ure

7

Form

atio

nand

mem

bera

Sedi

men

tary

faci

esSe

ismic

sect

ions

Thic

knes

s (m

)

Are

a (k

m2 )

Vol

ume

(km

3 )To

tal v

olum

e (k

m3 )

DPb

Max

M

in

Ave

rage

DPA

DPS

A

D‐2

Bra

id d

elta

Figu

re a

176

0075

00

107

7016

246

175

017

50

157

156

Figu

re b

174

0080

00

157

Figu

re c

218

0080

00

152

D‐3

Bra

id d

elta

Figu

re a

285

0011

400

200

5014

219

285

128

51

268

285

Figu

re b

295

0099

00

309

Figu

re c

296

0078

00

309

Figu

re d

284

0091

00

254

S‐1

+ 2

Bra

id d

elta

Figu

re a

178

0089

00

136

7512

023

164

416

44

172

177

Figu

re b

185

0095

00

176

Figu

re c

236

0010

500

193

Figu

re d

209

0011

400

166

S‐3

(mid

dle

unit)

Bra

id d

elta

Figu

re a

274

0010

100

223

7587

87

196

619

66

213

225

Figu

re b

279

0083

00

225

Figu

re c

292

0086

00

235

Figu

re d

296

0086

00

226

S‐3

(low

er u

nit)

Fan

delta

Figu

re a

428

8623

903

374

0062

89

235

223

52

301

305

Figu

re b

432

5522

071

325

Figu

re c

473

0920

583

312

Figu

re d

450

8325

500

283

S‐4

Fan

delta

1Fi

gure

a30

700

483

929

200

107

03

1221

26c

423

365

Figu

re b

350

0010

728

439

Fan

delta

2Fi

gure

a46

500

704

832

900

856

282

421

Figu

re b

379

0066

52

362

Fan

delta

3Fi

gure

a40

100

118

7841

100

186

27

654

21

Figu

re b

468

0016

718

309

Figu

re c

527

0015

127

387

Figu

re d

486

0014

844

297

Fan

delta

4Fi

gure

a42

800

151

2042

700

179

57

663

04

Figu

re b

512

0027

287

289

a D =

Don

gyin

g Fm

S

= S

hahe

jie F

m T

he n

umbe

r ind

icat

es th

e nu

mbe

r of t

he m

embe

r b D

P = se

ism

ic p

rogr

adat

iona

l dip

DPA

= a

vera

ge se

ism

ic p

rogr

adat

iona

l dip

DPS

A =

ave

rage

seis

mic

pro

grad

atio

nal d

ip o

fthe

sedi

men

t c 21

26

= to

tal j

oint

vol

umes

of f

an d

elta

s 1 2

3 a

nd 4

598 | EAGE

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where DPSA is the average seismic progradational dip of a sediment (in degrees) and n is the number of seismic sections

Detailed estimated results of the depositional dip and the seismic progradational dip of the delta are shown in Tables 3 and 4

333 | Provenance conditions and estimation of the sediment supplySystematic investigation by TBCNOOC of the regional uplift and provenance in the geological past has indicated that the main provenance areas around the HD existed alreadybefore the deposition of Member 3 of the Shahejie Fm (Zhou et al 2010) They include the Bonan Laibei and Kendong Highs (Figure 1b‐c Figure S1a‐b) However starting with the depo-sition of Members 1ndash2 of the Shahejie Fm (S‐1 + 2) (3789ndash3328 Ma) until the accumulation of the Dongying Formation (3328ndash2338 Ma) the Bonan and Laibei Highs subsided to below lake level and consequently stopped providing sedi-ment to the depression (Liu Xia et al 2015a) Only the Kendong High which remained a high for a long time re-mained a provenance area for the south‐western part of the

HD during this time‐span (Figure S1a) The Kendong High has therefore been selected as the site where the relationship between tectonics and depositional systems within the same provenance system could be studied best The distribution area of the Kendong High as the provenance area at different moments has been determined on the basis of numerous seis-mic interpretations through seismic terminations (eg onlap) and the absence of specific sediment units due to faulting

The sediment‐supply rate can be obtained by calculation of the volumes of the deltas and the duration of their forma-tion (cf Allen et al 2013 Lemons amp Chan 1999 Lemons Milligan amp Chan 1996) Although the stratigraphic ages are well‐known for each unit (Figure 2) there is no high‐resolu-tion age control for the top and base of each delta system The absolute age of the pertinent stratigraphic unit (Figure 2) is therefore used to represent the formation time of the individual deltas in the unit The thus calculated sediment‐supply rate rep-resents in our opinion the trend of the supply rate from bottom to top sufficiently well

334 | Estimation of the extent and accommodation space of the sink areaDetermination of the boundaries of the sink area is based on reconstructions of the morphology during the successive dep-ositional phases The extent of the sink area was estimated using the same calculations as for the area of the depositional system

DPSA

=

(

nsum

i=1

DPAi

)

∕n

F I G U R E 6 Vertical successions and representative examples of the various lithofacies (a) A fan‐delta in Well W18 (b‐e) Braid‐deltas in Well W25 (f) Grey to greyish white sandy conglomerate (deposits in braided channels) (g) Grey medium‐ to fine‐grained massive sandstone (mouth‐bar deposits) (h) Grey fine sandstone (distal sand bars) (i) Grey muddy siltstone with parallel bedding (prodelta) (j) Greyish white fine sandstone with convolute bedding (mouth bars) (k) Greyish white fine sandstone with boulders (mouth bars) Wireline logs show the spontaneous‐potential (SP) and gamma‐ray (GR) changes with depth Depth in metres For location of the cores see Figure 6bd

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Differences in base level and the original sedimentary sur-face define the accommodation space (Jervey 1988 Muto amp Steel 2000 Neal amp Abreu 2009 Wheeler 1964) The

accommodation space in the depositional area can be deter-mined on the basis of the thickness of the preserved sediments (Muto amp Steel 2000) This space is obviously controlled by

F I G U R E 7 Schematic morphology during the successive depositional phases The extent of the deltas the depositional sink area in the basin and the main features of the drainage systems are shown The extent of the deltas has been interpreted from seismic data and has been used for calculation of the surface area and volume of the various deltas (a) Shahejie Fm Member 4 (b) Shahejie Fm lower part of Member 3 (c) Shahejie Fm middle part of Member 3 (d) Shahejie Fm Members 1 and 2 (e) Dongying Fm Member 3 (f) Dongying Fm Member 2

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the rate of subsidence tectonic uplift and fluctuations of the lake level (Lemons amp Chan 1999) Changes in the lake level of the HD have not been investigated so that we take data on the tectonic‐subsidence rate as a proxy for changes in the accommodation space The total space is expressed in the equation (Table 4)

where AT represents the total accommodation space of the sink area (in km3) TS represents the tectonic subsidence (in m) and SA represents the surface area of the sink (in km2)

AT= TStimesSA∕1000

T A B L E 4 Estimation of the controlling factor parameters of the depositional system The distribution characteristics of the depositional sink in the basin are shown in Figure 7

Formation and membera

Sedimentary facies Seismic sections

DDb

RSSc(km3

Ma)Sink area (km2) AT

d(km3) ASeSource areaf(km2)DSD DSDA

D‐2 Braid delta Figure a 059 066 502 37542 7852 1195 58

Figure b 065

Figure c 074

D‐3 Braid delta Figure a 161 187 926 19823 11593 2051 252

Figure b 192

Figure c 215

Figure d 182

S‐1 + 2 Braid delta Figure a 086 096 356 28015 6463 1403 220

Figure b 094

Figure c 120

Figure d 083

S‐3 (middle unit) Braid delta Figure a 110 119 772 21756 6927 1619 355

Figure b 111

Figure c 129

Figure d 128

S‐3 (lower unit) Fan delta Figure a 307 303 1313 16506 10500 2705 482

Figure b 334

Figure c 332

Figure d 237

S‐4 Fan delta 1 Figure a 384 463g 861 14150 10481 3484 501

Figure b 379

Fan delta 2 Figure a 606

Figure b 498

Fan delta 3 Figure a 479

Figure b 499

Figure c 625

Figure d 553

Fan delta 4 Figure a 377

Figure b 226aD = Dongying Fm S = Shahejie Fm The number indicates the number of the member bDD = depositional dip DSD = depositional dip in a specific seismic section DSDA = average depositional dip of a specific sedimentary unit cRSS = sediment‐supply rate dAT = total accommodation space eAS = accommodation spacesediment supply fSource area = Denudation area within the seismic data coverage The complete erosional area cannot be estimated because of the limited data coverage g463 = the average depositional dip of fan deltas 1 2 3 and 4 Considering that the four fan deltas developed during S‐4 consist of sediment that was derived from the same provenance area and were deposited in the same time‐span the four fan deltas are taken as a whole when estimating the parameters of RSS the sink area AT and AS

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4 | ELEMENTS OF THE S2S SYSTEM

41 | Analysis of the seismic facies and stacking pattern of the main sedimentary faciesA comprehensive analysis of seismic data cores cutting log-gings and well‐logging curves by Liu Xia et al (2015a) in-dicated that the Palaeogene depositional systems of the HD included fan‐deltas braid‐deltas lake margins deep lakes etc The fan‐ and braid‐deltas have been chosen for a detailed seismic study that must reveal their internal texture and their stacking patterns Analysis of the progradational seismic‐re-flection types and of the seismic progradational dip is particu-larly helpful for a better understanding of the hydrodynamic conditions and sedimentary processes that resulted in these depositional systems Because the facies interpretation in this area has been done before and is not the focus of this work we here mainly describe the internal texture and their stack-ing patterns of the main sedimentary facies

The major facies of S‐4 is interpreted as a fan‐delta It is dominated by Seismic Facies 1 which is characterized by discontinuous to continuous low‐ to high‐amplitude and chaotic progradational seismic reflections (Figures S3ndashS6 Table 1) The average dip of the progradational seismic event is about 365deg (Table 3) Three lithofacies are associated with Seismic Facies 1 (Table 1) The coarser lithofacies 1 represents a fan‐delta front whereas the finer lithofacies 2 and 3 are prodelta deposits The overall coarsening‐upward succession facies stacking pattern (Figure 6a) discontinuous and chaotic seismic reflections and relatively steep slope of Seismic Facies 1 suggest a fan‐delta system developed under strong hydrodynamic conditions (Mitchum et al 1977)

The fan‐delta of the lower part of Member 3 of the Shahejie Fm (S‐3 [lower unit]) is dominated by Seismic Facies 2 which is characterized by chaotic progradational to oblique progradational seismic characteristics It has a typical wedge shape and is composed of two seismic‐reflection seg-ments (a) a moderately continuous low‐ to high‐amplitude chaotic seismic‐reflection segment located near boundary fault F2 and (b) a continuous moderate‐ to high‐amplitude and oblique progradational seismic reflection in a basinward direction (Figure S7 Table 1) No obvious upper or lower segments occur in SF 2 and the dip of the progradational seismic event in this segment is also relatively steep viz 305deg (Table 3)

The middle part of Member 3 of the Shahejie Fm (S‐3 [middle unit]) is characterized by a low‐ to moderate‐con-tinuous low‐amplitude and oblique progradational seismic reflection (Seismic Facies 3) and is interpreted as a braid‐delta (Figure S8 Table 1) The progradational seismic events are parallel or sub‐parallel to each other and dip less (aver-age 225deg) than Seismic Facies 1 and 2 (Table 3) Seismic

Facies 3 is associated with four lithofacies (Figure 6b Table 1) in Well T25 The complete succession of the braid‐delta consists of gravely to coarse‐grained sandstone (lithofacies 1) at the base (Figure 6f) massive bedded medium‐ to fine‐grained sandstones (lithofacies 2) and grey mudstones inter-bedded with grey fine sandstones and grey muddy siltstones (lithofacies 3) in the middle (Figures 6g and 6h) and thick dark grey mudstones (lithofacies 4) at the top (Figure 6i)

Member 3 of the Dongying Fm (D‐3) is characterized by Seismic Facies 4 a typically composite seismic progra-dation reflection configuration representing a braid‐delta system (Figure S9 Table 1) Seismic Facies 4 is composed of highly continuous moderate‐ to high‐amplitude and pro-gradational seismic reflections that represent well‐developed deltaic topsets and bottomsets The topset segments of SF 4 are nearly horizontal or dip only gently (Table 3) The foreset segments form thicker lenses with small depositional angles The oblique progradational part of this seismic facies is sim-ilar to that in Seismic Facies 3 and usually developed at the basinward front end of Seismic Facies 3 The lithology of Seismic Facies 4 is dominated by greyish white to white fine‐grained sandstones and siltstones The lithofacies association is characterized by coarsening‐upward sedimentary cycles (Figure 6c Table 1) Convolute bedding and abundant diam-ictites are present on top of the fine sandstones (Figure 6j‐k)

Both braid‐deltas in the Members 1 + 2 of th Shahejie Fm (S‐1 + 2) and Member 2 of the Dongying Fm (D‐2) show moderately continuous moderate‐amplitude and shin-gled‐like progradational seismic reflections (Seismic Facies 5 Figures S10ndashS11 Table 1) It shows a thin prograding seis-mic pattern commonly with parallel upper and lower bound-aries (cf Mitchum et al 1977) The successive internal progradational seismic events overlap each other between the upper and lower segments with a gentle dip of 152degndash193deg (Table 3) The lithofacies are mostly composed of several coarsening‐upward cycles (Figure 6d Table 1) Each cycle is composed of dark grey mudstones and grey to whitish‐grey medium‐ to fine‐grained sandstones Several coarsening‐up-ward lithofacies are mainly developed in D‐2 (Figure 6e Table 1)

42 | Analysis of the tectonic activityThe normal faults F1 and F2 selected to calculate the fault activity dipping to the north and running approximately E‐W are important boundary faults on the south‐western margin of the HD The tectonic‐subsidence rate fault‐growth index and fault‐activity rate were used as proxies to indicate the tectonic intensity (Figure 3 S2 Table 2) S‐4 and S‐3 (lower unit) have the highest subsidence rate (300ndash355 mMa) the highest fault‐growth index (292ndash343 mMa) and the highest fault‐activity rate (10647ndash11869 mMa) among the studied intervals whereas the overlying S‐3 (middle

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unit) and S‐1 + 2 are characterized by a much lower sub-sidence rate and fault‐growth index and fault‐activity rate D‐3 had again a high subsidence rate (190 mMa) and an average fault‐growth index (210 mMa) and fault‐activity rate (9344 mMa) The uppermost studied interval D‐2 had a much lower subsidence rate (60 mMa) growth index (136 mMa) and fault‐activity rate (3451 mMa) than the un-derlying unit Generally the analysis of the subsidence rate average fault‐growth index and fault‐activity rate indicates two phases of alternating strong tectonic activity and tectoni-cally stable conditions

43 | Palaeogeomorphology distribution and dimensions of the main depositional systemsDepositional systems of each depositional phase of the Palaeogene on the south‐western slope of the HD were com-piled through seismic facies identification of 3‐D seismic data and compilation of maps with the current thicknesses of the main target intervals based on the study by Liu Xia et al (2015a) that combined a correction for the depth of burial with an interpretation of the sedimentary facies The basins sink area on the south‐western slope of the HD was estimated on the basis of a palaeogeomorphological reconstruction The distribution of the depositional system is closely related to the evolution of the palaeogeomorphology and therefore we describe both the distribution of the depositional system and the palaeogeomorphology here

The palaeogeography of S‐4 is characterized by the larg-est extent of the uplifted areas of all studied intervals The depositional area is small and scattered (Figure 7a Table 4) Faults F1 and F2 mark the boundaries between erosional and depositional regions The elevated footwalls of the faults were erosional areas and located adjacent to the hanging walls whereas the hanging walls were low‐lying depositional areas The sedimentary facies analysis indicates a fan‐delta developed here (Figure 7a) Calculations indicate that the sedimentary dip of the four fan‐deltas was uncommonly high (about 463deg) The extent and thickness of the fan‐deltas di-minished towards the basin margin (Tables 34)

The tectonically‐induced morphology of S‐3 (lower unit) shows a similar pattern to that of the underlying S‐4 The depositional and erosional areas were also controlled by the active faults F1 and F2The HD deepened from west to east with the deepest area located just along the fault margin The depositional centre was located north of the hanging wall of F2 and became infilled by a fan‐delta (Figure 7b) The aver-age sedimentary dip of the fan‐delta is 303deg The extent of the fan‐delta was larger than that of S‐4 (Table 34)

During deposition of S‐3 (middle unit) the uplifted source area shifted southwards and the depression expanded A major depositional sink was located north of the hanging wall of F2 (Figure 7c Table 4) Elevation differences existed

between the footwalls and the hanging walls of F1 and F2 although the topography was obviously gentler during this time‐span A braided fluvial area developed at the footwalls of the faults whereas a braid‐delta developed mainly on the hanging wall of F2 and the northern depositional centre (Figure 7c) The braid‐delta had a fairly large extent and an average depositional dip of 119deg (Tables 34)

During S‐1 + 2 the elevated erosional area shifted farther southwards and the entire south‐western area had a low to-pography An alluvial plain developed south of the footwalls of the faults whereas a braid‐delta developed at the hanging walls and in the depression with a very gentle slope of 096deg (Table 4 Figure 7d) The depositional system was dominated by a fairly thin delta body and a braid‐delta with a much larger extent (Table 3)

During the deposition of D‐3 the topography of the foot-wall areas and of the area south of the provenance area was similar to that during the underlying S‐1 + 2 The slope was steep (187deg) in the hanging walls of the boundary faults however and the depositional area increased to 198 km2 which provided an excellent condition for the deposition of a large braid‐delta (Figure 7e Table 4) This braid‐delta had a NE‐SW orientation and covered an area of 142 km2 its average thickness is some 200 m which results in the largest delta volume in the Palaeogene on the south‐western slope of the HD (Table 3)

The palaeogeomorphological reconstruction of D‐2 shows a gentler topography in the entire south‐western HD with a sink area of 375 km2 (Table 4) The main body of the braid‐delta was dominated by imbricated progradational seis-mic reflections and developed in the hanging walls of F1 and F2 whereas an alluvial‐plain facies probably developed in the footwall areas of the faults and to the south‐west of the uplifted area (Figure 7f) Although the extent of the delta reached its maximum the thickness of the delta was limited due to the gentle topography resulting in a small delta vol-ume (Table 3)

5 | RELATIONSHIPS BETWEEN THE VARIOUS ELEMENTS OF THE S2S SYSTEM

Quantitative relationships between the various elements of the S2S system have been established through the above‐mentioned calculations A strong positive correlation is clearly present between the rate of tectonic subsidence the average fault activity and the average growth index of the boundary faults F1 and F2 (Figure 8ab) The rate of tectonic subsidence can therefore be used in the following as the pri-mary proxy to represent the intensity of the tectonic activity whereas the rate of fault activity and the growth index are used as secondary proxies

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The tectonic activity and the sediment‐supply rate show a positive relationship (Figures 8c 9a 10a) whereas the tec-tonic activity and the sink area of the basin show a negative relationship (Figures 8d 9b 10b) In contrast the tectonic activity has a positive relationship with the total accommo-dation space (Figures 8e 9c 10c Table 4) There is also a positive relationship between the average sedimentary dip of the fan‐ and braid‐deltas on the one hand and the tectonic activity on the other hand (Figures 8f 9d 10d)

The intensity of the tectonic activity correlates negatively with the extent of the sediment area but positively with the sediment volume (Figures 8g‐h 9e‐f 10e‐f) The different responses of the sediment area and the volume to the tectonic activity are caused by variations in the thicknesses of the sed-imentary units (Table 3)

There is also a positive relationship between the average seismic progradation dip of the fan‐ and braid‐deltas and the tectonic activity (Figures 8i 9g 10g) strong tectonic activ-ity usually formed deltas that are characterized by a chaotic progradational or oblique progradational seismic reflection such as SF 1 and 2 in S‐3 (lower unit) and S‐4 (Figures S3ndashS7) The minimum tectonic activity during Members S‐1 + 2 and D‐2 are reflected by dominantly shingled progradational seismic facies in the delta interior (Figures S10ndashS11)

In addition we find that the sediment area sediment vol-ume and average seismic progradation dip of the fan‐ and braid‐deltas correlate positively with the sediment‐supply rate (Figure 11a b and c) but negatively with the basin sink area (Figure 11d e and f) Both the sediment volume and the average seismic progradation dip of the fan‐ and braid‐deltas

F I G U R E 8 (a‐b) Relationships between the tectonic‐subsidence rate and tectonics (c‐i) Relationships between tectonic activity and sedimentary source‐to‐sink parameters Input data regarding the tectonic activity are from Table 2 those regarding the source‐to‐sink parameters data are from Tables 3 and 4 Regression‐line equations and coefficients of determination (R2) are shown for all diagrams

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show a positive relationship with the total accommodation space (Figure 11hi) However no obvious relationship ap-pears to be present between the sediment area and the total accommodation space (G) Both the sediment area and the average seismic progradation dip of the fan‐ and braid‐deltas correlate well with the average sedimentary dip of the fan‐ and braid‐deltas (Figure 11km) A poor correlation is found between the sediment volume and the average sedimentary dip of the fan‐ and braid‐deltas

6 | DISCUSSION

61 | Analysis of the influence of tectonic activity on the source area accommodation space geomorphology and sediment supplyA high relief and large drainage area usually can generate a large sediment supply (Leeder Harris amp Kirkby 1998 Syvitski amp Milliman 2007) Although the erosional area for the fan and delta system cannot be estimated because of the

limited data coverage the exposed area within the study area can be calculated The calculations show a generally decreas-ing trend of the source area from S‐4 (501 km2) to D‐2 (58 km2 Figure7 Table 4) The calculated exposed area cannot fully represent the true source area however but the evolu-tionary trend of the source area can be used as a proxy to indi-cate the relative influence on the change in sediment volume This trend is consistent with the decrease in sediment volume from S‐4 (2126 km3) to D‐2 (175 km3 Table 2) The relief is difficult to reconstruct in this case but variations in the fault‐activity rate (here taken as the tectonic‐subsidence rate) can create local elevation differences and can therefore be used as proxies for the trends in the relief development The relief shows an overall decreasing trend from S‐4 to D‐2 except for D‐3 this correlates well with the sediment volume (Figure 8h) Although the drainage area of D‐3 was smaller than that of D‐2 because of the high tectonic‐subsidence rate (result-ing in a high relief) D‐3 is thicker and shows a larger sedi-ment volume than the overlying D‐2 (Table 3) D‐3 is thinner than S‐4 + 3 but the larger source area resulted in a larger

F I G U R E 9 General relationships between the average fault‐growth index of F1 and F2 (AFGIF1‐F2) and sedimentary source‐to‐sink parameters The average fault‐growth index of F1 and F2 (AFGIF1‐F2) data in this figure are from Table 2 The source‐to‐sink parameters data are from Table 4 Regression‐line equations and the coefficients of determination are shown in each diagram

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sediment volume and supply rate (Table 3 Figure8ch) Therefore both the fault‐induced relief and the drainage area affected the sediment‐supply rate and the sediment volume in the sink

The changes in accommodation space during the vari-ous phases of the Palaeogene in the south‐western HD are clear from the estimated tectonic subsiding rate (Table 2) The correlations between the intensity of the tectonic activ-ity and the extent of the depositional sink area (Figures 8d 9b 10b) between the intensity of the tectonic activity and the total accommodation space and between the intensity of the tectonic activity and the morphology in the sink area (Figures 8e‐f 9c‐d 10c‐d) clearly show that strong tectonic activity resulted in a larger accommodation capacity of the sink

In particular the main subsiding area tended to form steeper slopes However the extent of the main subsiding sink area diminished (Figure 8d) with increasing tectonic activity which was possibly due to the relatively small sub-siding centre in the tectonically active basins It can thus be deduced that tectonic activity not only controlled the sedi-ment supply and the variation in accommodation space but

also determined the changes in the topography of the sedi-mentary basins and the extent of the main depositional areas in the tectonically active basins

62 | Analysis of the influence of tectonic activity on the size and internal stacking pattern of the delta depositional systemThe above data and considerations indicate that the tectonic activity was closely related to the sediment supply accom-modation space and morphology of the sink area which are possibly the most important factors affecting the extent and stacking pattern of the sedimentary facies (cf Cope et al 2010 DeCelles Kapp Ding amp Gehrels 2007 Leeder 2011 Olsen 1997 Simon et al 2017)

Statistical analysis indicates that the sediment‐supply rate has a strong positive correlation with the volume of the depositional system a moderate correlation with the seismic progradational dip in the depositional system and a poor cor-relation with the size of the depositional area (Figure 11a‐c) A larger sink area corresponded to a larger fanbraid‐delta a gentler seismic progradational angle and a reduced volume

F I G U R E 1 0 General relationships between average fault activity rate of F1 and F2 (RFAA‐F1‐F2) and sedimentary source‐to‐sink parameters The average fault activity rate of F1 and F2 (RFAA‐F1‐F2) data in this figure are from Table 2 The source‐to‐sink parameters data are from Table 4 Regression line equations and the coefficients of determination are shown in each diagram

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of the fan or braid‐delta which was possibly related to a re-duced sedimentary dip and thinner sediments (Figure 11d‐f) The total accommodation space in the basin correlates well

with the volume of the depositional system to some degree with the seismic progradational dip and poorly with the ex-tent of the depositional system area (Figure 11g‐i) These

FIGURE 11 Relationships between various parameters involved in the source‐to‐sink system (a‐c) Relationships between sediment supply and characteristics of the depositional system (extent volume and DPSA of the sediments) (d‐f) Relationships between the sink area of the basin and characteristics of the depositional system (g‐i) Relationships between the total accommodation space (AT) and the characteristics of the depositional system (j) Relationship between the accommodation‐spacesediment‐supply ratio (AS) and the DPSA of the sediments (k‐m) Relationships between the sedimentary dip and the characteristics of the depositional system The data regarding sediment supply basin sink area total accommodation space accommodation‐spacesediment‐supply ratio and sedimentary dips are from Table 4 The extent volume and DPSA of the sedimentary facies are from Table 3 Note the seemingly obvious polynomial (quadratic) relationship between the sedimentary dip and the sediment volume (L) The trend line in (L) suggests the following relationships between sediment volume and sedimentary slope in a rift or tectonically active basin (1) a very steep sedimentary slope is unfavourable for sediment accumulation (2) an appropriate sedimentary slope is favourable for preservation of depositional systems eg when the sedimentary slope in (L) is about 25degndash32deg the sediment volume reaches its largest value (3) a very gentle sedimentary slope will lead to a decrease of the sediment volume possibly due to weakening of the drainage system and thinner sediments

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relationships are clear evidence that the size of the sink area controlled the extent of the depositional system during the rifting of the lacustrine basin and that the rate of sediment supply and the accommodation space had a significant in-fluence on the total sedimentary volume as well as on the internal stacking pattern of the depositional system

We here use the ratio of the tectonic‐subsidence rate and the sediment‐supply rate as a proxy to indicate the ratio be-tween accommodation space and sediment‐supply rate (AS) (Table 4) AS has a strong influence on the internal stacking pattern of the depositional systems in the lacustrine rift basin (Figure 11j) This might be because the basin was small and because abundant and rapid material was supplied due

to intense tectonic activity (cf Catuneanu et al 2009 Liro 1993) and a favourable local climate (eg Bohacs Carroll Neal amp Mankiewicz 2000 Perlmutter amp Matthews 1989) The sediment supply still had a significant influence on the main subsidence area of the lacustrine basins and deposi-tional systems

In addition the basin slope significantly influenced the extent of the depositional system (Figure 11k) and had a polynomial relationship with its volume (Figure 11l) This relationship indicates that more intense tectonic activity and a steeper depositional slope were not favourable for sediment accumulation over a large extent in the lacustrine basin On the contrary these sediments were usually transported to a

F I G U R E 1 2 Tectonic differential activities and resulting patterns of the source‐to‐sink system on the south‐western slope of the HD during the Palaeogene (a) Development during phases of intense tectonics (Member 4 to the lower part of Member 3 of the Shahejie Fm) (b) Development during phases of somewhat less tectonic activity (middle part of Member 3 of the Shahejie Fm and Member 3 of the Dongying Fm) (c) Development during phases of weak tectonic activity (Members 1 and 2 of the Shahejie Fm and Member 2 of the Dongying Fm) The intensity of tectonic activity in the lacustrine rift basin had a significant influence on the development and extent of each unit of the source‐to‐sink system as well as on the type and dimensions of the depositional systems The present study indicates that probably sublacustrine fans developed (see for example Figure S4b) during phases with relatively strong tectonic activity This is not really clear from the seismic‐reflection data but possibly due to the small sizes of these sublacustrine fans Moreover lithofacies and core data are not available for the south‐western part of the study area The present contribution therefore focuses on the fan‐deltas and braid‐deltas regarding the sedimentary facies analysis the sublacustrine fans that probably developed in the deep or semi‐deep lake are presented just as a likely feature

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relatively small sink area with a fairly large accommodation space Finally stronger tectonic activity resulted in steeper depositional slopes (Figure 8f) which further controlled the hydrodynamic conditions and differential discharge when the sediments were deposited The strong correlation between the depositional slope and the deltas dip (Figure 11m) suggests that the differences in topography due to tectonics must be considered as one of the most critical factors that controlled the internal stacking pattern of the delta deposits

63 | Significance of the present study for other source‐to‐sink systems of lacustrine rift basins

631 | Summary of the source‐to‐sink systems in the HDIn lacustrine rift basins the tectonic setting is probably the main factor that determines the development of the S2S sys-tem but differential tectonic activities lead to variations in the basic characteristics of the S2S system Tectonic activity was most intense during S‐3 (lower unit) and during S‐4 and caused both a strong uplift of the source area and the devel-opment of depressions in the basin that formed a sink (Figure 12a) Strong tectonic activity in the S2S system during these time‐spans led to a high sediment‐supply rate steeper slopes a larger accommodation space and deposition of several fan‐deltas that are characterized by a fairly steep seismic progra-dational angle

The tectonic activity decreased during S‐3 (middle unit) and during D‐3 The S2S system that was present during this time‐span mainly concerned a rising area that shifted south-wards developing an alluvial plain between the erosional area and the sink area thus increasing the distance from source to sink (Figure 12b) Simultaneously the sediment‐supply rate and the accommodation space also changed and braid‐deltas could thus develop with larger volumes and gentler seismic progradational dips

Tectonic activity was clearly less intense during S‐1 + 2 and D‐2 The rising area had shifted further southwards cre-ating a wider alluvial plain connecting the source area to the sink in the HD (Figure 12c) At this stage stable tectonic activity led to relatively less sediment supply a gentle slope less accommodation space and the development of several braid‐deltas with a fairly gentle seismic progradational angle

632 | Wider implications and limitationsSoslashmme et al (2009) proposed that the elements of S2S sys-tems are genetically related and that quantitative correla-tions exist among these elements Other studies also suggest that the size of the drainage basin is correlated to the size of the fan developing on the basin floor (eg Blum et al

2017 Snedden et al 2018) and to the size of the river chan-nel (eg Milliken et al 2018) Helland‐Hansen Soslashmme Martinsen Lunt and Thurmond (2016) suggest a simplified subdivision of S2S systems into three main categories (a) Steep‐Short‐Deep (steep onshore and offshore gradients short distance between source and sink and deep offshore waters) (b) Wide‐Deep (low‐gradient shelf‐catchment area and deep offshore waters) and (c) Wide‐Shallow (relatively shallow offshore waters and a wide low‐gradient catchment area) systems

The present study indicates that the alluvial plain roughly corresponds to the alluvial‐shelf unit in marine basins al-though with a much smaller width and extent in the lacustrine rift basins than would have been the case on a continental shelf Faults F1 and F2 along the slope belt correspond to the slope of classical S2S systems whereas the shore‐shallow‐deep lake area can be compared with the basin floor (Soslashmme et al 2009) S‐4 and S‐3 (lower unit) can be roughly clas-sified as Steep‐Short‐Deep systems whereas the overlying S‐1 + 2and D‐2 can be classified as the Wide‐Shallow sys-tems that Helland‐Hansen et al (2016) defined During the deposition of S‐4 and S‐3 (lower unit) the strong tectonic activity caused a high relief of the source area a narrow allu-vial plain and a relatively deep lake The subsequently wan-ing tectonic activity resulted in a lower relief of the source area a wider alluvial plain and a shallower lake Although the absolute values of these elements in lacustrine basins are much smaller than those of marine basins the ratio between these elements in both settings is comparable Typically in a lacustrine basin a transformation from a Steep‐Short‐Deep system (S‐4 and S‐3 (lower unit)) to a Wide‐Shallow system (S‐1 + 2ampD‐2) occurs within a few million years Although the basin geomorphology has experienced signif-icant changes from S‐4 to D‐2 the quantitative relationships between tectonic activity sediment‐supply rate accommoda-tion space and sedimentary dip of the delta systems did not change significantly (eg Figures 8 and 11) The analytical approaches applied and quantitative relationship established here can help analyse other lacustrine basins worldwide and may even act as a reference for the analysis of marine basins

Our study focuses mainly on the influences of tectonic activity on the elements of the depositional sink Other pa-rameters (eg climate and lithology) were not considered in detail Studies on modern and ancient systems suggest that the climate and lithology also have a great influence on the sediment supply and distribution in the basin (eg Carroll Chetel amp Smith 2006 Hovius amp Leeder 1998 Syvitski amp Milliman 2007 Zhang et al 2018) For exam-ple climate variations between glacials and inter‐glacials have resulted in largely different sediment‐supply rates and in significant differences in the sizes of the Quaternary sub-marine fans in the north‐western Gulf of Mexico (Blum amp Hattier‐Womack 2009) We acknowledge the importance

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of climate and lithology for S2S systems and we are con-vinced that these elements can significantly affect the S2S systems in other cases(eg modern systems and systems influenced by glacialinterglacial alternations) These fac-tors were not really relevant for the present study however because no significant differences in lithology were present in the source areas and because we focus on the changes at a million‐year scale which implies that the tectonic ac-tivity has a first‐order control on the development of S2S elements in the investigated rift basin

7 | CONCLUSIONS

We have calculated the tectonic‐subsidence history the growth index and the activity rate of the main boundary faults (F1 and F2) and various S2S parameters of six Palaeogene rock units on the south‐western slope of the HD Based on the values found for these parameters quantitative corre-lation were established for the tectonic activity and other S2Sparameters in the basinal sink This leads to the follow-ing conclusions

1 The positive correlation between the intensity of fault activity and the tectonic‐subsidence rate is a strong indication for a distinct control by the tectonic activity of the syn‐depositional rifting of the tectonically active basin

2 The tectonic activity was quantitatively related to the sediment supply accommodation space and morphology of the sink area The relationship between tectonic activ-ity and depositional systems is reflected by changes in critical factors such as sediment supply accommodation space and dip of the sink area These critical factors were probably the most important factors that led to changes in the size and internal stacking pattern of the sedimentary facies

3 Differential tectonic activity led to changes in the char-acteristics of the S2S system on the south‐western slope of the HD The strongest tectonic activity which oc-curred during S‐3 (lower unit) and during S‐4 led to the largest provenance area adjacent to the sink area to a high sediment‐supply rate to steeper slopes to a larger accommodation space and controlled the development of several fan‐deltas Diminished tectonic activity dur-ing S‐3 (middle unit) and during D‐3 led to a decrease in uplift an increased width of the alluvial plain an in-creased transport distance a decrease in the sediment‐supply rate and accommodation space and resulted in the development of braid‐deltas with a large volume During S‐1 + 2 and D‐2 stable tectonic activity led to a lower sediment‐supply rate a gentle depositional slope and a smaller accommodation space resulting in the

development of several braid‐deltas with gentler seis-mic progradational angles

4 The analytical approaches applied and the quantitative re-lationships established here can help analyse other lacus-trine basins worldwide and may even act as a reference for the study of marine basins

ACKNOWLEDGEMENTS

We thank Dr Sarah Boulton and Dr Chenlin Gong as well as the Associate Editor of Basin Research Dr Craig Magee for their constructive comments on the manuscript This study was funded by the National Science and Technology Major Project (Exploration Technologies for Offshore Hidden OilGas) (project no 2016ZX05024‐003‐003) the National Natural Science Foundations of China (project no 41676050) and the Fundamental Research Funds for the Central Universities (2652014037)

REFERENCES

Allen P A (2008a) From landscapes into geological history Nature 451 274ndash276 https doiorg101038natur e06586

Allen P A (2008b) Time scales of tectonic landscapes and their sed-iment routing systems In Landscape evolution Denudation cli-mate and tectonics over different time and space scales (Ed by Gallagher K Jones S J amp Wainwright J) Geological Society London Special Publications 296 7ndash28

Allen P A Armitage J J Carter A Duller R A Michael N A Sinclair H D hellip Whittaker A C (2013) The Qs problem Sediment volumetric balance of proximal foreland basin systems Sedimentology 60 102ndash130

Amorosi A Maselli V amp Trincardi F (2016) Onshore to offshore anatomy of a late Quaternary source‐to‐sink system (Po Plain‐Adriatic Sea Italy) Earth‐Science Reviews 153 212ndash237 https doiorg101016jearsc irev201510010

Anderson J B Wallace D J Simms A R Rodriguez A B Weight R W R amp Taha Z P (2016) Recycling sediments between source and sink during a eustatic cycle Systems of late Quaternary northwestern Gulf of Mexico Basin Earth‐Science Reviews 153 111ndash138 https doiorg101016jearsc irev201510014

Anthony E J amp Julian M (1999) Source‐to‐sink sediment trans-fers environmental engineering and hazard mitigation in the steep Var River catchment French Riviera southeastern France Geomorphology 31 337ndash354 https doiorg101016S0169-555X(99)00088-4

Athy L F (1930) Density porosity and compaction of sedimentary rocks AAPG Bulletin 14 1ndash24

Bhattacharya J P Copeland P Lawton T F amp Holbrook J (2016) Estimation of source area river palaeo‐discharge palaeoslope and sediment budgets of linked deep‐time depositional systems and im-plications for hydrocarbon potential Earth‐Science Reviews 153 77ndash110

Blum M D amp Hattier‐Womack J (2009) Climate change sea‐level change and fluvial sediment supply to deepwater depositional

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relationships in a relatively closed system Particularly for well‐studied lacustrine basins with a good coverage of data from drilling wells and seismic data it is relatively easy to identify and reconstruct the erosional provenance area and other S2S system parameters etc (Li et al 2017 Zhu et al 2018) In such cases it is relatively easy to establish the quan-titative relationship among the various elements of an S2S system and use such a quantitative relationship to predict the occurrences of reservoir sands in other basin with less data coverage (eg Liu et al 2017)

Based on previous research progress concerning lacustrine basins the present study chooses Palaeogene successions in the Huanghekou Depression (HD) in the Bohai Bay Basin eastern Chinato (a) establish the quantitative relationship be-tween tectonic subsidence and S2S system parameters and (b) explore the controlling effect of tectonics on the internal stacking pattern of the sedimentary successions

This work uses 2‐D and 3‐D seismic data core analysis and well log data to (a) document the sedimentary facies of the Palaeogene in the HD with emphasis on the seismic in-terpretation of the internal stacking pattern of the fan‐delta and braid‐delta complexes (b) estimate the development in time of the tectonic subsidence the main boundary faults and the S2S system parameters (c) establish the quantita-tive relationship between the intensity of the tectonics and the various S2S system parameters as well as to analyse the variation in the sizes of the sedimentary systems and their internal stacking patterns and (d) discuss the effects of the tectonic activity and the evolution of the S2S system on the scale of the sedimentary systems and the depositional process in the tectonically active lacustrine basin The quantitative relationships between the intensity of the tectonics and the various S2S system parameters established in the study can contribute to a better understanding of the different elements of S2S system responses to tectonic activity at a million‐year time scale In addition the established quantitative relation-ships are applicable to the analysis of many other rift basins which are the major hosts of hydrocarbon resources in China

2 | GEOLOGICAL BACKGROUND

The HD is a sub‐basin in the south‐eastern part of the Bohai Bay Basin It occupies about 3300 km2 and is bounded by the Kendong Structural High and the less elevated Laibei Structural High in the south and by the relatively low Bonan Structural High in the north (Figure 1a‐c) (Liu Xia et al 2015a Tian Yu Zhou Peng amp Wang 2009 Zhou Yu Tang Lv amp Wang 2010) Two sets of roughly E‐W‐ and NNE‐SSW‐oriented faults cross‐cut the Palaeogene of the HD The NNE‐SSW‐oriented faults represent the western branches of the Tanlu Fault Belt They are characterized by a right‐lateral strike‐slip displacement and run through the

entire Bohai Bay Basin thus largely controlling the formation of many sub‐basins (or depressions) in the Bohai Bay Basin (eg Glider Leloup amp Courtillot 1999 Hsiao Graham amp Tilander 2004 Schellart amp Lister 2005)

21 | The Palaeogene successionThe Bohai Bay Basin is a Cainozoic rift basin developed on top of the ancient Sino‐Korean Plateau It consists of two tectonic units the Palaeogene syn‐rift unit and the Neogene post‐rift unit The Palaeogene of the Bohai Bay Basin is built by from bottom to top the Kongdian Shahejie and Dongying Formations (Liu et al 2017) (Figure 2) The Shahejie Formation is subdivided into four members viz ndash from bottom to top (the member numbers reflect the stratigraphy based on borings) ndash Member 4 Member 3 which is subdivided into three informal units the upper one of which is absent in the study area because of ero-sion (the two informal units present in the study area will therefore be indicated in the following as the lower part and the middle part of Member 3 respectively) Member 2 and Member 1 The Dongying Formation is subdivided ndash again from bottom to top ndash into Member 3 Member 2 and Member 1

22 | Palaeogene tectonic evolutionThe Bohai Bay Basin which shows superimposed rifts and depressions is characterized by several stages and types of tectonism (Zhou et al 2010) The basin experienced rift‐related subsidence during the Palaeogene and post‐rift thermal subsidence during the Neogene‐Holocene The Palaeogene rifting was episodic and several sub‐basins developed within a distinct tectonic framework of highs and depressions (Figure 1d‐f) Four rifting phases can be deduced from the rift features that took place during four phases these phases correspond to the Kongdian Fm Member 4 of the Shahejie Fm (S‐4) Members 1ndash3 of the Shahejie Fm and the Dongying Fm The surface area of the basin experienced as a rule temporary regional uplift after each rifting phase which led to the erosion of earlier deposited sediments which thus became separated from each other by low‐angle unconformities or disconformities (Liu et al 2017) (Figure 2)

3 | DATA SETS AND METHODS

31 | Data sets and facies interpretationHigh‐quality seismic reflection data cores cutting logs and logging data have been provided by the Tianjin Branch of China National Offshore Oil Corporation (TBCNOOC) The seismic data include 2‐D seismic lines (Figure 1b) and

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F I G U R E 1 Schematic map of the Bohai Bay Basin and the Huanghekou Depression (HD) (a) Location of the Bohai Bay Basin within China The red solid line in the figure forms the boundary of the Bohai Bay Basin (b) Tectonic map showing sub‐basins of the Bohai Bay Basin The tectonic features in this figure are based on the interpretation of regional 2‐D seismic data of the lower boundary of the Palaeogene (modified from Zhou et al 2010 Liu Xia et al 2015a) The blue dotted line representing the present‐day coastline of China indicates the offshore part (Bohai Bay) of the Bohai Bay Basin Light‐gray dotted lines in this figure are regional 2‐D seismic lines near the HD Purple solid lines in figures B and C indicate the locations of the seismic lines shown in Figures 3 and 5 (c) Structural characteristics of the HD The tectonic characteristics of the HD are modified from results of Zhou et al (2010) and Liu Xia et al (2015a) The south‐western faults (F1 and F2) and the Kendong Structural High have been interpreted and validated through newly acquired 3‐D seismic data F1‐S1 F1‐S2 F1‐S3 F2‐S1 F2‐S2 and F2‐S3 are the calculation locations of faults F1 and F2 Circles (filling in yellow) represent drilling well locations (dndashf) Schematic structure and seismic profiles across the HD in the offshore part of the Bohay Bay Basin (for locations see Figure 1b‐c) The texts ldquoT2 T31 T32 hellip T8rdquo in the legend refer to the seismic surfaces (see Figure 2) The codes of formations and members are consistent with Figure 2

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over 5000 km2 of 3‐D seismic surveys in the HD Both the 2‐D and the 3‐D seismic data have a vertical sampling rate of 2 ms and were processed to zero phases They were dis-played as reversed polarities The 3‐D seismic data have a dominant frequency of 15ndash40 Hz and an average velocity of 3600 ms (calculated from Well W25) with a vertical resolu-tion of 22ndash60 m

Cutting log and logging data from 25 wells have been used for the present study Core data were made available for 11 wells with a total length of about 1000 m Integration of these well and seismic data helped establishing a regional stratigraphic framework through calibration of seismic syn-thetic records seismic units and interpretation of the sedimen-tary facies (Table 1) In total eight horizons were interpreted

respectively as T7 (dated at 447 Ma) T63 (4223 Ma) T62 (4044 Ma) T5 (3790 Ma) T3(3328 Ma) T31 (2671 Ma) and T2 (2338 Ma) The successions between these horizons represent different members of the Dongying and Shahejie Formations The codes and interpretation of these members are provided in Figure 2 The quantitative compilation of the sedimentary system and the palaeogeomorphological maps are based on these results

32 | Quantitative estimation of tectonic activityThe tectonic‐subsidence rate fault‐growth index and fault‐activity rate are used in the present contribution to detail

F I G U R E 2 Lithostratigraphy and sequences of the HD The lithological data and interpretations are based mainly on a combination of data from Wells W1 W18 and W25 Ages are based on data obtained from CNOOC Tianjin Branch The tectonic stages sedimentary environment and fossil associations are modified after Liu Xia et al (2015a) Note that newly acquired 3‐D seismic data indicate that the Kongdian Fm is possibly absent in the HD which differs from the results presented by Liu Xia et al (2015a) D‐1 = Member 1 of the Dongying Fm D‐2 = Member 2 of the Dongying Fm D‐3 = Member 3 of the Dongying Fm S‐1 amp 2 = Members 1 and 2 of the Shahejie Fm S‐3 = Member 3 of the Shahejie Fm S‐4 = Member 4 of the Shahejie Fm

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the tectonic history and intensity We have selected Well W25 (Figure 1c) because it is the only drilling well in the south‐eastern HD for simulation of the subsidence history This simulation is based on our reconstructed stratigraphic framework and age information provided by the TBCNOOC (Figure 2)

Correction for compaction is critical in quantitative sim-ulation of the subsidence history and rate The influence of the water depth during sedimentation is considered negligible since the Bohai Bay Basin was a lacustrine basin Differences in the acoustic travel times have been used to calculate the porosities at the corresponding depths (cf Wylliel Gregory amp Gardner 1958) Subsequently the porosities of the vari-ous types of lithology (mainly sandstone and mudstone) at different depths were determined by logging and the poros-itydepth relationship was established by statistic fitting (cf Athy 1930) Back‐stripping of the selected strata was per-formed layer‐by‐layer to calculate the top and bottom bound-ary depths at different times in the geological development (cf Perrie amp Qiublier 1974) thus distinguishing between the compaction history the tectonic subsidence and the total subsidence during the Palaeogene (Figure 3 Table 2 supple-mentary text)

The normal boundary faults (F1 amp F2) controlling depo-sition on the south‐western margin of the HD have been

selected to calculate the fault‐growth index and the fault‐ac-tivity rate (Figure 1c) The fault‐growth index sometimes also called the ldquoexpansion indexrdquo is the ratio between the stratigraphic thickness of the hanging wall and that of the footwall of a growth fault The fault‐activity rate is the ratio between the thicknesses of the sedimentary successions in the hanging wall and the foot wall resulting from fault activ-ity during a specific depositional phase corresponding to the length of the time‐span during which the investigated succes-sion accumulated ie (Zhou Niu amp Teng 2009)

where RF is the fault‐activity rate in mMa T is the length of the time‐span during which the investigated succession ac-cumulated (in Ma) STh is the stratigraphic thickness of the hanging wall (in m) and STf is the stratigraphic thickness of the footwall (in m) For the calculation of the stratigraphic thickness the conversion from two‐way travel time to depth was made by analysis of the P‐wave velocity in the wells The growth index and the activity rate of the main faults have thus been calculated for several locations (Table 2 Figure 1c) which was considered necessary because of the differ-ent successive stages in the morphological evolution of the

RF=ΔST∕T =

(

SThminusST

f

)

∕T

F I G U R E 3 Palaeogene burial history of the HD (a) Cumulative subsidence (b) Subsidence during the development of the individual members D‐1 = Member 1 of the Dongying Fm D‐2 = Member 2 of the Dongying Fm D‐3 = Member 3 of the Dongying Fm S‐1 amp 2 = Members 1 and 2 of the Shahejie Fm S‐3 = Member 3 of the Shahejie Fm S‐4 = Member 4 of the Shahejie Fm

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basin‐controlling faults and because of the changes in the intensity of the fault activity

33 | Quantitative calculation of S2S system parameters

331 | Area and volume of the sedimentary faciesQuantitative calculation of the dimensions of sedimentary facies requires reliable estimates of the lateral extent and thickness of the sediments involved For these calculations first the maxi-mum extent of the specific units under study (fan‐deltas braid‐deltas etc) at different times was determined in plan view based on the combined interpretation obtained from seismic facies lithofacies and the outer boundaries of the sediment bodies Subsequently the outcomes were digitalized and used as input for a 3‐D survey by GEOFRAME Detailed calculations of the sedi-ment bodies extents were conducted using the PLANIMETER tool in the BASEMAP window of GEOFRAME

This was followed by the selection of several seismic sec-tions across the sediment body in order to identify the lower

and upper boundaries as well as to calculate the maximum minimum and average thickness (see Amorosi Maselli amp Trincardi 2016 Liu et al 2017) Finally we used a colum-nar body with irregular base and the same height to represent the irregular sediment body The formula for volume calcu-lation is as follows (Figure 4 Table 3 supplementary text)

where VS is the volume of the sediment (in km3) AS is the horizontal surface area of the irregular base of the sediment (in km2) and H is the height (average thickness) of the sed-iment (in m) Detailed calculations of the thickness were conducted using the AREAL tool in the SEIS3DVSEIS2DV window of GEOFRAME

332 | Determination of the depositional dip of the delta surface due to progradationThe term ldquodepositional diprdquo is used here to indicate the inclination of a dipping sedimentary surface Horizon flat-tening was used to analyse and calculate the morphology of the underlying strata First the maximum flooding surface ndash approximately corresponding to the palaeo‐sedimentary surface (Lin et al 2012) ndash of each unit under study was interpreted it was subsequently flattened to calculate the original depositional dip (Figure 5d) with the formula

where DSD is the sedimentary dip (in degrees) dy is the verti-cal thickness between the lower boundary of the sedimentary unit and the ancient sedimentary surface in the depositional centre (in m) and dx is the distance from the apex of the delta to its depositional centre (in m)

Two to four seismic sections have been selected to calcu-late the average sedimentary dip of each individual delta with the following formula

where DSDA is the average sedimentary dip of a sediment (in degrees) and n is the number of seismic sections

The seismic progradational angle of the deltas interior has been calculated by the horizon‐flattening method (Figure 5e) which is expressed by the formula

VS=A

StimesH

DSD

= tanminus1 (dy∕dx)

DSDA

=

(

nsum

i=1

DSDi

)

∕n

DP= tan

minus1 (dy∕dx)

F I G U R E 4 Schematic diagram showing the calculation of the volume of a sediment (a) is an irregular sediment body Volume calculation of cuboids was used for reference to calculate the volume of an irregular sedimentary body ie the volume of an irregular sediment body equals the area of the irregular bottoms times height (b) 3ndash4 seismic lines along the sedimentary body are selected and the thickness of the sedimentary body is determined at intervals of 10 seismic traces (c) when a thickness grid covering the entire sedimentary body in space is acquired the average thickness of all counted thicknesses can be calculated as the height of the irregular sediment body (d)

594 | EAGE

LIU et aL

where DP is the seismic progradational dip (in degrees) The average dip angle is obtained from only one seismic sec-tion because of the variations in the progradational seismic event of the delta on the same seismic line

where DPA is the average seismic progradational dip in a spe-cific seismic section (in degrees) and n is the number of seis-mic progradational events

Based on the calculated average dip of one seismic sec-tion the average progradational dip of a specific sediment body can be calculated with the formula

DPA

=

(

nsum

i=1

DPi

)

∕n

F I G U R E 5 Detailed calculations of the sedimentary dip and the progradational seismic event dip of the delta interior taking the progradation seismic reflection of the delta developed in Member 3 of the Dongying Formation as an example The locations of the seismic lines are shown in Figure 1c Based on the interpretation of the stratigraphic and seismic facies visible in the original seismic lines (a) the topset or the maximum flooding surface (MFS) corresponding to the delta was flattened (b) Taking into account the water depth during sedimentation the sedimentary dip (d) and the progradational seismic event dip of the delta interior (e) can be calculated DSD = depositional dip in a specific seismic section DSDA = average depositional dip of a specific sedimentary unit DP = seismic progradational dip DPA = average seismic progradational dip

| 595EAGE

LIU et aL

TA

BL

E 1

In

terp

reta

tion

of th

e m

ain

sedi

men

tary

faci

es in

the

Pale

ogen

e of

the

Hua

nghe

kou

Dep

ress

ion

Evi

denc

e of

fan

delta

s and

bra

id d

elta

s in

wel

ls W

1 an

d W

18 c

omes

from

Liu

Xia

et a

l (2

015a

)

Form

atio

n an

d m

embe

raSe

ismic

faci

esEx

ampl

esLi

thof

acie

sLi

thol

ogy

Wel

l amp c

ore

exam

ples

Dep

ositi

onal

en

viro

nmen

tPr

edic

ted

res-

ervo

ir q

ualit

y

D‐2

Seis

mic

Fac

ies 5

mod

erat

e co

ntin

uous

lo

w‐a

mpl

itude

and

a sh

ingl

ed‐li

ke

prog

rada

tiona

l sei

smic

refle

ctio

n

Figu

re

Mul

tiple

upw

ard‐

coar

s-en

ing

litho

faci

es

asso

ciat

ions

Gre

y m

udst

ones

gre

y to

gre

yish

w

hite

pebb

ly fi

ne sa

ndst

ones

and

fin

e sa

ndst

ones

T25

Bra

id d

elta

Mod

erat

e to

hi

gh

D‐3

Seis

mic

Fac

ies 4

con

tinuo

us m

oder

-at

e‐to

high

‐am

plitu

de a

nd o

bliq

ue‐

to‐s

igm

oid

prog

rada

tiona

l sei

smic

re

flect

ion

Figu

re

Mul

tiple

upw

ard‐

coar

s-en

ing

litho

faci

es

asso

ciat

ions

Gre

yish

whi

te to

whi

te fi

ne

sand

ston

es s

iltst

ones

and

gre

y m

udst

ones

T25

Bra

id d

elta

Hig

h

Figu

re 7

e‐f

S‐1

+ 2

Seis

mic

Fac

ies 5

mod

erat

e co

ntin

uous

m

oder

ate‐

ampl

itude

and

shin

gled

‐like

pr

ogra

datio

nal s

eism

ic re

flect

ion

Figu

re

Mul

tiple

upw

ard‐

coar

s-en

ing

litho

faci

es

asso

ciat

ions

Dar

k gr

ey m

udst

ones

and

gre

yish

w

hite

to g

rey

mid

dle‐

to fi

ne‐

grai

ned

sand

ston

es

T25

Bra

id d

elta

Hig

h

S‐3

(mid

dle

unit)

Seis

mic

Fac

ies 3

har

dly

tom

oder

atel

y co

ntin

uous

low

‐am

plitu

de o

bliq

ue

prog

rada

tiona

l sei

smic

refle

ctio

n

Figu

re

Lith

ofac

ies 1

Gre

y to

gre

yish

whi

te sa

ndy

cong

lom

erat

esT2

5B

raid

del

taH

igh

Lith

ofac

ies 2

Thic

k gr

ey m

iddl

e‐to

fine

‐gra

ined

sa

ndst

ones

Figu

re 7

a‐d

Lith

ofac

ies 3

Gre

y m

udst

ones

inte

rbed

ded

with

gr

ey fi

ne sa

ndst

ones

and

gre

y m

uddy

silts

tone

s

Lith

ofac

ies 4

Thic

k da

rk g

rey

mud

ston

es

S‐3

(low

er

unit)

Seis

mic

Fac

ies 2

cha

otic

prog

rada

-tio

nal t

o ob

lique

pro

grad

atio

nal

seis

mic

faci

es

Figu

re

Pe

bbly

sand

ston

es in

terb

edde

d w

ith

thin

bro

wn‐

grey

mud

ston

esb

row

n sa

ndy

cong

lom

erat

ess

ands

tone

s in-

terb

edde

d w

ith th

in m

udst

ones

thic

k m

udst

ones

inte

rbed

ded

with

th

in sa

ndst

ones

or p

ebbl

y fin

e sa

ndst

ones

T1Fa

n de

ltaM

oder

ate

S‐4

Seis

mic

Fac

ies 1

dis

cont

inuo

us to

con

-tin

uous

low

‐tohi

gh‐a

mpl

itude

cha

otic

pr

ogra

datio

nal s

eism

ic re

flect

ion

Figu

re

Figu

re

Fig

ure

and

Fi

gure

Lith

ofac

ies 1

Gre

y pe

bbly

sand

ston

es c

oars

e sa

ndst

ones

T18

Fan

delta

sM

oder

ate

Lith

ofac

ies 2

Ash

‐bla

ck m

udst

ones

inte

rbed

-de

d w

ith th

in g

rey

fine‐

grai

ned

sand

ston

es

Lith

ofac

ies 3

Ash

‐bla

ck m

udst

ones

inte

rbed

ded

with

peb

bly

sand

ston

esa D

= D

ongy

ing

Fm

S =

Sha

hejie

Fm

The

num

ber i

ndic

ates

the

num

ber o

f the

mem

ber

596 | EAGE

LIU et aL

TA

BL

E 2

Es

timat

ion

stat

istic

s of t

he te

cton

ic‐s

ubsi

denc

e ra

te g

row

th in

dex

and

activ

ity ra

te o

f fau

lts F

1 an

d F2

S1

S2

and

S3 a

re th

e ca

lcul

atio

n lo

catio

ns o

f F1

and

F2 (s

ee F

igur

e 1c

) th

e co

rres

pond

ing

num

bers

are

F1‐

S1 F

1‐S2

F1‐

S3 F

2‐S1

F2‐

S2 a

nd F

2‐S3

res

pect

ivel

y

Form

atio

n an

d m

embe

raA

ge

(Ma)

R TS

(m

Ma)

b

Faul

t‐gro

wth

inde

xFa

ult‐a

ctiv

ity r

ate

(mM

a)

AFG

I F1‐

F2c

R FA

A‐F

1‐F2

d

S1S2

S3A

vera

geS1

S2S3

aver

age

F1F2

F1F2

F1F2

F1F2

F1F2

F1F2

F1F2

F1F2

D‐1

233

75ndash

267

1450

00

111

106

109

110

107

109

109

108

389

270

389

479

270

389

349

379

109

364

D‐2

267

14ndash

302

060

00

139

130

138

140

137

133

138

134

320

730

29

341

442

62

329

534

98

330

535

96

136

345

1

D‐3

302

0ndash33

278

190

002

002

052

102

342

032

052

042

1579

67

104

0010

372

111

3485

59

762

989

66

972

12

1093

44

S‐1

+ 2

332

78ndash

378

9250

00

145

136

142

147

155

145

148

143

122

211

36

105

915

78

587

176

39

5614

92

146

122

4

S‐3

(mid

dle

unit)

378

92ndash

404

3812

500

131

202

192

242

175

257

166

234

335

140

88

490

380

62

215

510

919

347

076

90

205

558

0

S‐3

(low

er

unit)

404

38ndash

422

3135

500

284

343

302

395

342

389

309

376

737

185

37

104

4016

956

742

820

480

841

315

324

343

118

69

S‐4

422

31ndash

447

300

002

512

921

584

173

023

332

373

4791

33

106

4357

58

151

8811

007

121

5186

33

126

612

9210

647

a D =

Don

gyin

g Fm

S

= S

hahe

jie F

m T

he n

umbe

r ind

icat

es th

e nu

mbe

r of t

he m

embe

r b R T

S = te

cton

ic‐s

ubsi

denc

e ra

te

c AFG

I F1‐

F2 =

ave

rage

faul

t‐gro

wth

inde

x of

F1

and

F2

d R FA

A‐F

1‐F2

= a

vera

ge fa

ult‐a

ctiv

ity ra

te o

f F1

and

F2

| 597EAGE

LIU et aL

TA

BL

E 3

C

alcu

latio

n ch

art o

f the

sedi

men

tary

‐fac

ies d

imen

sion

s and

the

inte

rnal

pro

grad

atio

nal s

eism

ic e

vent

dip

The

spat

ial e

xten

t is s

how

n in

Fig

ure

7

Form

atio

nand

mem

bera

Sedi

men

tary

faci

esSe

ismic

sect

ions

Thic

knes

s (m

)

Are

a (k

m2 )

Vol

ume

(km

3 )To

tal v

olum

e (k

m3 )

DPb

Max

M

in

Ave

rage

DPA

DPS

A

D‐2

Bra

id d

elta

Figu

re a

176

0075

00

107

7016

246

175

017

50

157

156

Figu

re b

174

0080

00

157

Figu

re c

218

0080

00

152

D‐3

Bra

id d

elta

Figu

re a

285

0011

400

200

5014

219

285

128

51

268

285

Figu

re b

295

0099

00

309

Figu

re c

296

0078

00

309

Figu

re d

284

0091

00

254

S‐1

+ 2

Bra

id d

elta

Figu

re a

178

0089

00

136

7512

023

164

416

44

172

177

Figu

re b

185

0095

00

176

Figu

re c

236

0010

500

193

Figu

re d

209

0011

400

166

S‐3

(mid

dle

unit)

Bra

id d

elta

Figu

re a

274

0010

100

223

7587

87

196

619

66

213

225

Figu

re b

279

0083

00

225

Figu

re c

292

0086

00

235

Figu

re d

296

0086

00

226

S‐3

(low

er u

nit)

Fan

delta

Figu

re a

428

8623

903

374

0062

89

235

223

52

301

305

Figu

re b

432

5522

071

325

Figu

re c

473

0920

583

312

Figu

re d

450

8325

500

283

S‐4

Fan

delta

1Fi

gure

a30

700

483

929

200

107

03

1221

26c

423

365

Figu

re b

350

0010

728

439

Fan

delta

2Fi

gure

a46

500

704

832

900

856

282

421

Figu

re b

379

0066

52

362

Fan

delta

3Fi

gure

a40

100

118

7841

100

186

27

654

21

Figu

re b

468

0016

718

309

Figu

re c

527

0015

127

387

Figu

re d

486

0014

844

297

Fan

delta

4Fi

gure

a42

800

151

2042

700

179

57

663

04

Figu

re b

512

0027

287

289

a D =

Don

gyin

g Fm

S

= S

hahe

jie F

m T

he n

umbe

r ind

icat

es th

e nu

mbe

r of t

he m

embe

r b D

P = se

ism

ic p

rogr

adat

iona

l dip

DPA

= a

vera

ge se

ism

ic p

rogr

adat

iona

l dip

DPS

A =

ave

rage

seis

mic

pro

grad

atio

nal d

ip o

fthe

sedi

men

t c 21

26

= to

tal j

oint

vol

umes

of f

an d

elta

s 1 2

3 a

nd 4

598 | EAGE

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where DPSA is the average seismic progradational dip of a sediment (in degrees) and n is the number of seismic sections

Detailed estimated results of the depositional dip and the seismic progradational dip of the delta are shown in Tables 3 and 4

333 | Provenance conditions and estimation of the sediment supplySystematic investigation by TBCNOOC of the regional uplift and provenance in the geological past has indicated that the main provenance areas around the HD existed alreadybefore the deposition of Member 3 of the Shahejie Fm (Zhou et al 2010) They include the Bonan Laibei and Kendong Highs (Figure 1b‐c Figure S1a‐b) However starting with the depo-sition of Members 1ndash2 of the Shahejie Fm (S‐1 + 2) (3789ndash3328 Ma) until the accumulation of the Dongying Formation (3328ndash2338 Ma) the Bonan and Laibei Highs subsided to below lake level and consequently stopped providing sedi-ment to the depression (Liu Xia et al 2015a) Only the Kendong High which remained a high for a long time re-mained a provenance area for the south‐western part of the

HD during this time‐span (Figure S1a) The Kendong High has therefore been selected as the site where the relationship between tectonics and depositional systems within the same provenance system could be studied best The distribution area of the Kendong High as the provenance area at different moments has been determined on the basis of numerous seis-mic interpretations through seismic terminations (eg onlap) and the absence of specific sediment units due to faulting

The sediment‐supply rate can be obtained by calculation of the volumes of the deltas and the duration of their forma-tion (cf Allen et al 2013 Lemons amp Chan 1999 Lemons Milligan amp Chan 1996) Although the stratigraphic ages are well‐known for each unit (Figure 2) there is no high‐resolu-tion age control for the top and base of each delta system The absolute age of the pertinent stratigraphic unit (Figure 2) is therefore used to represent the formation time of the individual deltas in the unit The thus calculated sediment‐supply rate rep-resents in our opinion the trend of the supply rate from bottom to top sufficiently well

334 | Estimation of the extent and accommodation space of the sink areaDetermination of the boundaries of the sink area is based on reconstructions of the morphology during the successive dep-ositional phases The extent of the sink area was estimated using the same calculations as for the area of the depositional system

DPSA

=

(

nsum

i=1

DPAi

)

∕n

F I G U R E 6 Vertical successions and representative examples of the various lithofacies (a) A fan‐delta in Well W18 (b‐e) Braid‐deltas in Well W25 (f) Grey to greyish white sandy conglomerate (deposits in braided channels) (g) Grey medium‐ to fine‐grained massive sandstone (mouth‐bar deposits) (h) Grey fine sandstone (distal sand bars) (i) Grey muddy siltstone with parallel bedding (prodelta) (j) Greyish white fine sandstone with convolute bedding (mouth bars) (k) Greyish white fine sandstone with boulders (mouth bars) Wireline logs show the spontaneous‐potential (SP) and gamma‐ray (GR) changes with depth Depth in metres For location of the cores see Figure 6bd

| 599EAGE

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Differences in base level and the original sedimentary sur-face define the accommodation space (Jervey 1988 Muto amp Steel 2000 Neal amp Abreu 2009 Wheeler 1964) The

accommodation space in the depositional area can be deter-mined on the basis of the thickness of the preserved sediments (Muto amp Steel 2000) This space is obviously controlled by

F I G U R E 7 Schematic morphology during the successive depositional phases The extent of the deltas the depositional sink area in the basin and the main features of the drainage systems are shown The extent of the deltas has been interpreted from seismic data and has been used for calculation of the surface area and volume of the various deltas (a) Shahejie Fm Member 4 (b) Shahejie Fm lower part of Member 3 (c) Shahejie Fm middle part of Member 3 (d) Shahejie Fm Members 1 and 2 (e) Dongying Fm Member 3 (f) Dongying Fm Member 2

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the rate of subsidence tectonic uplift and fluctuations of the lake level (Lemons amp Chan 1999) Changes in the lake level of the HD have not been investigated so that we take data on the tectonic‐subsidence rate as a proxy for changes in the accommodation space The total space is expressed in the equation (Table 4)

where AT represents the total accommodation space of the sink area (in km3) TS represents the tectonic subsidence (in m) and SA represents the surface area of the sink (in km2)

AT= TStimesSA∕1000

T A B L E 4 Estimation of the controlling factor parameters of the depositional system The distribution characteristics of the depositional sink in the basin are shown in Figure 7

Formation and membera

Sedimentary facies Seismic sections

DDb

RSSc(km3

Ma)Sink area (km2) AT

d(km3) ASeSource areaf(km2)DSD DSDA

D‐2 Braid delta Figure a 059 066 502 37542 7852 1195 58

Figure b 065

Figure c 074

D‐3 Braid delta Figure a 161 187 926 19823 11593 2051 252

Figure b 192

Figure c 215

Figure d 182

S‐1 + 2 Braid delta Figure a 086 096 356 28015 6463 1403 220

Figure b 094

Figure c 120

Figure d 083

S‐3 (middle unit) Braid delta Figure a 110 119 772 21756 6927 1619 355

Figure b 111

Figure c 129

Figure d 128

S‐3 (lower unit) Fan delta Figure a 307 303 1313 16506 10500 2705 482

Figure b 334

Figure c 332

Figure d 237

S‐4 Fan delta 1 Figure a 384 463g 861 14150 10481 3484 501

Figure b 379

Fan delta 2 Figure a 606

Figure b 498

Fan delta 3 Figure a 479

Figure b 499

Figure c 625

Figure d 553

Fan delta 4 Figure a 377

Figure b 226aD = Dongying Fm S = Shahejie Fm The number indicates the number of the member bDD = depositional dip DSD = depositional dip in a specific seismic section DSDA = average depositional dip of a specific sedimentary unit cRSS = sediment‐supply rate dAT = total accommodation space eAS = accommodation spacesediment supply fSource area = Denudation area within the seismic data coverage The complete erosional area cannot be estimated because of the limited data coverage g463 = the average depositional dip of fan deltas 1 2 3 and 4 Considering that the four fan deltas developed during S‐4 consist of sediment that was derived from the same provenance area and were deposited in the same time‐span the four fan deltas are taken as a whole when estimating the parameters of RSS the sink area AT and AS

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4 | ELEMENTS OF THE S2S SYSTEM

41 | Analysis of the seismic facies and stacking pattern of the main sedimentary faciesA comprehensive analysis of seismic data cores cutting log-gings and well‐logging curves by Liu Xia et al (2015a) in-dicated that the Palaeogene depositional systems of the HD included fan‐deltas braid‐deltas lake margins deep lakes etc The fan‐ and braid‐deltas have been chosen for a detailed seismic study that must reveal their internal texture and their stacking patterns Analysis of the progradational seismic‐re-flection types and of the seismic progradational dip is particu-larly helpful for a better understanding of the hydrodynamic conditions and sedimentary processes that resulted in these depositional systems Because the facies interpretation in this area has been done before and is not the focus of this work we here mainly describe the internal texture and their stack-ing patterns of the main sedimentary facies

The major facies of S‐4 is interpreted as a fan‐delta It is dominated by Seismic Facies 1 which is characterized by discontinuous to continuous low‐ to high‐amplitude and chaotic progradational seismic reflections (Figures S3ndashS6 Table 1) The average dip of the progradational seismic event is about 365deg (Table 3) Three lithofacies are associated with Seismic Facies 1 (Table 1) The coarser lithofacies 1 represents a fan‐delta front whereas the finer lithofacies 2 and 3 are prodelta deposits The overall coarsening‐upward succession facies stacking pattern (Figure 6a) discontinuous and chaotic seismic reflections and relatively steep slope of Seismic Facies 1 suggest a fan‐delta system developed under strong hydrodynamic conditions (Mitchum et al 1977)

The fan‐delta of the lower part of Member 3 of the Shahejie Fm (S‐3 [lower unit]) is dominated by Seismic Facies 2 which is characterized by chaotic progradational to oblique progradational seismic characteristics It has a typical wedge shape and is composed of two seismic‐reflection seg-ments (a) a moderately continuous low‐ to high‐amplitude chaotic seismic‐reflection segment located near boundary fault F2 and (b) a continuous moderate‐ to high‐amplitude and oblique progradational seismic reflection in a basinward direction (Figure S7 Table 1) No obvious upper or lower segments occur in SF 2 and the dip of the progradational seismic event in this segment is also relatively steep viz 305deg (Table 3)

The middle part of Member 3 of the Shahejie Fm (S‐3 [middle unit]) is characterized by a low‐ to moderate‐con-tinuous low‐amplitude and oblique progradational seismic reflection (Seismic Facies 3) and is interpreted as a braid‐delta (Figure S8 Table 1) The progradational seismic events are parallel or sub‐parallel to each other and dip less (aver-age 225deg) than Seismic Facies 1 and 2 (Table 3) Seismic

Facies 3 is associated with four lithofacies (Figure 6b Table 1) in Well T25 The complete succession of the braid‐delta consists of gravely to coarse‐grained sandstone (lithofacies 1) at the base (Figure 6f) massive bedded medium‐ to fine‐grained sandstones (lithofacies 2) and grey mudstones inter-bedded with grey fine sandstones and grey muddy siltstones (lithofacies 3) in the middle (Figures 6g and 6h) and thick dark grey mudstones (lithofacies 4) at the top (Figure 6i)

Member 3 of the Dongying Fm (D‐3) is characterized by Seismic Facies 4 a typically composite seismic progra-dation reflection configuration representing a braid‐delta system (Figure S9 Table 1) Seismic Facies 4 is composed of highly continuous moderate‐ to high‐amplitude and pro-gradational seismic reflections that represent well‐developed deltaic topsets and bottomsets The topset segments of SF 4 are nearly horizontal or dip only gently (Table 3) The foreset segments form thicker lenses with small depositional angles The oblique progradational part of this seismic facies is sim-ilar to that in Seismic Facies 3 and usually developed at the basinward front end of Seismic Facies 3 The lithology of Seismic Facies 4 is dominated by greyish white to white fine‐grained sandstones and siltstones The lithofacies association is characterized by coarsening‐upward sedimentary cycles (Figure 6c Table 1) Convolute bedding and abundant diam-ictites are present on top of the fine sandstones (Figure 6j‐k)

Both braid‐deltas in the Members 1 + 2 of th Shahejie Fm (S‐1 + 2) and Member 2 of the Dongying Fm (D‐2) show moderately continuous moderate‐amplitude and shin-gled‐like progradational seismic reflections (Seismic Facies 5 Figures S10ndashS11 Table 1) It shows a thin prograding seis-mic pattern commonly with parallel upper and lower bound-aries (cf Mitchum et al 1977) The successive internal progradational seismic events overlap each other between the upper and lower segments with a gentle dip of 152degndash193deg (Table 3) The lithofacies are mostly composed of several coarsening‐upward cycles (Figure 6d Table 1) Each cycle is composed of dark grey mudstones and grey to whitish‐grey medium‐ to fine‐grained sandstones Several coarsening‐up-ward lithofacies are mainly developed in D‐2 (Figure 6e Table 1)

42 | Analysis of the tectonic activityThe normal faults F1 and F2 selected to calculate the fault activity dipping to the north and running approximately E‐W are important boundary faults on the south‐western margin of the HD The tectonic‐subsidence rate fault‐growth index and fault‐activity rate were used as proxies to indicate the tectonic intensity (Figure 3 S2 Table 2) S‐4 and S‐3 (lower unit) have the highest subsidence rate (300ndash355 mMa) the highest fault‐growth index (292ndash343 mMa) and the highest fault‐activity rate (10647ndash11869 mMa) among the studied intervals whereas the overlying S‐3 (middle

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unit) and S‐1 + 2 are characterized by a much lower sub-sidence rate and fault‐growth index and fault‐activity rate D‐3 had again a high subsidence rate (190 mMa) and an average fault‐growth index (210 mMa) and fault‐activity rate (9344 mMa) The uppermost studied interval D‐2 had a much lower subsidence rate (60 mMa) growth index (136 mMa) and fault‐activity rate (3451 mMa) than the un-derlying unit Generally the analysis of the subsidence rate average fault‐growth index and fault‐activity rate indicates two phases of alternating strong tectonic activity and tectoni-cally stable conditions

43 | Palaeogeomorphology distribution and dimensions of the main depositional systemsDepositional systems of each depositional phase of the Palaeogene on the south‐western slope of the HD were com-piled through seismic facies identification of 3‐D seismic data and compilation of maps with the current thicknesses of the main target intervals based on the study by Liu Xia et al (2015a) that combined a correction for the depth of burial with an interpretation of the sedimentary facies The basins sink area on the south‐western slope of the HD was estimated on the basis of a palaeogeomorphological reconstruction The distribution of the depositional system is closely related to the evolution of the palaeogeomorphology and therefore we describe both the distribution of the depositional system and the palaeogeomorphology here

The palaeogeography of S‐4 is characterized by the larg-est extent of the uplifted areas of all studied intervals The depositional area is small and scattered (Figure 7a Table 4) Faults F1 and F2 mark the boundaries between erosional and depositional regions The elevated footwalls of the faults were erosional areas and located adjacent to the hanging walls whereas the hanging walls were low‐lying depositional areas The sedimentary facies analysis indicates a fan‐delta developed here (Figure 7a) Calculations indicate that the sedimentary dip of the four fan‐deltas was uncommonly high (about 463deg) The extent and thickness of the fan‐deltas di-minished towards the basin margin (Tables 34)

The tectonically‐induced morphology of S‐3 (lower unit) shows a similar pattern to that of the underlying S‐4 The depositional and erosional areas were also controlled by the active faults F1 and F2The HD deepened from west to east with the deepest area located just along the fault margin The depositional centre was located north of the hanging wall of F2 and became infilled by a fan‐delta (Figure 7b) The aver-age sedimentary dip of the fan‐delta is 303deg The extent of the fan‐delta was larger than that of S‐4 (Table 34)

During deposition of S‐3 (middle unit) the uplifted source area shifted southwards and the depression expanded A major depositional sink was located north of the hanging wall of F2 (Figure 7c Table 4) Elevation differences existed

between the footwalls and the hanging walls of F1 and F2 although the topography was obviously gentler during this time‐span A braided fluvial area developed at the footwalls of the faults whereas a braid‐delta developed mainly on the hanging wall of F2 and the northern depositional centre (Figure 7c) The braid‐delta had a fairly large extent and an average depositional dip of 119deg (Tables 34)

During S‐1 + 2 the elevated erosional area shifted farther southwards and the entire south‐western area had a low to-pography An alluvial plain developed south of the footwalls of the faults whereas a braid‐delta developed at the hanging walls and in the depression with a very gentle slope of 096deg (Table 4 Figure 7d) The depositional system was dominated by a fairly thin delta body and a braid‐delta with a much larger extent (Table 3)

During the deposition of D‐3 the topography of the foot-wall areas and of the area south of the provenance area was similar to that during the underlying S‐1 + 2 The slope was steep (187deg) in the hanging walls of the boundary faults however and the depositional area increased to 198 km2 which provided an excellent condition for the deposition of a large braid‐delta (Figure 7e Table 4) This braid‐delta had a NE‐SW orientation and covered an area of 142 km2 its average thickness is some 200 m which results in the largest delta volume in the Palaeogene on the south‐western slope of the HD (Table 3)

The palaeogeomorphological reconstruction of D‐2 shows a gentler topography in the entire south‐western HD with a sink area of 375 km2 (Table 4) The main body of the braid‐delta was dominated by imbricated progradational seis-mic reflections and developed in the hanging walls of F1 and F2 whereas an alluvial‐plain facies probably developed in the footwall areas of the faults and to the south‐west of the uplifted area (Figure 7f) Although the extent of the delta reached its maximum the thickness of the delta was limited due to the gentle topography resulting in a small delta vol-ume (Table 3)

5 | RELATIONSHIPS BETWEEN THE VARIOUS ELEMENTS OF THE S2S SYSTEM

Quantitative relationships between the various elements of the S2S system have been established through the above‐mentioned calculations A strong positive correlation is clearly present between the rate of tectonic subsidence the average fault activity and the average growth index of the boundary faults F1 and F2 (Figure 8ab) The rate of tectonic subsidence can therefore be used in the following as the pri-mary proxy to represent the intensity of the tectonic activity whereas the rate of fault activity and the growth index are used as secondary proxies

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The tectonic activity and the sediment‐supply rate show a positive relationship (Figures 8c 9a 10a) whereas the tec-tonic activity and the sink area of the basin show a negative relationship (Figures 8d 9b 10b) In contrast the tectonic activity has a positive relationship with the total accommo-dation space (Figures 8e 9c 10c Table 4) There is also a positive relationship between the average sedimentary dip of the fan‐ and braid‐deltas on the one hand and the tectonic activity on the other hand (Figures 8f 9d 10d)

The intensity of the tectonic activity correlates negatively with the extent of the sediment area but positively with the sediment volume (Figures 8g‐h 9e‐f 10e‐f) The different responses of the sediment area and the volume to the tectonic activity are caused by variations in the thicknesses of the sed-imentary units (Table 3)

There is also a positive relationship between the average seismic progradation dip of the fan‐ and braid‐deltas and the tectonic activity (Figures 8i 9g 10g) strong tectonic activ-ity usually formed deltas that are characterized by a chaotic progradational or oblique progradational seismic reflection such as SF 1 and 2 in S‐3 (lower unit) and S‐4 (Figures S3ndashS7) The minimum tectonic activity during Members S‐1 + 2 and D‐2 are reflected by dominantly shingled progradational seismic facies in the delta interior (Figures S10ndashS11)

In addition we find that the sediment area sediment vol-ume and average seismic progradation dip of the fan‐ and braid‐deltas correlate positively with the sediment‐supply rate (Figure 11a b and c) but negatively with the basin sink area (Figure 11d e and f) Both the sediment volume and the average seismic progradation dip of the fan‐ and braid‐deltas

F I G U R E 8 (a‐b) Relationships between the tectonic‐subsidence rate and tectonics (c‐i) Relationships between tectonic activity and sedimentary source‐to‐sink parameters Input data regarding the tectonic activity are from Table 2 those regarding the source‐to‐sink parameters data are from Tables 3 and 4 Regression‐line equations and coefficients of determination (R2) are shown for all diagrams

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show a positive relationship with the total accommodation space (Figure 11hi) However no obvious relationship ap-pears to be present between the sediment area and the total accommodation space (G) Both the sediment area and the average seismic progradation dip of the fan‐ and braid‐deltas correlate well with the average sedimentary dip of the fan‐ and braid‐deltas (Figure 11km) A poor correlation is found between the sediment volume and the average sedimentary dip of the fan‐ and braid‐deltas

6 | DISCUSSION

61 | Analysis of the influence of tectonic activity on the source area accommodation space geomorphology and sediment supplyA high relief and large drainage area usually can generate a large sediment supply (Leeder Harris amp Kirkby 1998 Syvitski amp Milliman 2007) Although the erosional area for the fan and delta system cannot be estimated because of the

limited data coverage the exposed area within the study area can be calculated The calculations show a generally decreas-ing trend of the source area from S‐4 (501 km2) to D‐2 (58 km2 Figure7 Table 4) The calculated exposed area cannot fully represent the true source area however but the evolu-tionary trend of the source area can be used as a proxy to indi-cate the relative influence on the change in sediment volume This trend is consistent with the decrease in sediment volume from S‐4 (2126 km3) to D‐2 (175 km3 Table 2) The relief is difficult to reconstruct in this case but variations in the fault‐activity rate (here taken as the tectonic‐subsidence rate) can create local elevation differences and can therefore be used as proxies for the trends in the relief development The relief shows an overall decreasing trend from S‐4 to D‐2 except for D‐3 this correlates well with the sediment volume (Figure 8h) Although the drainage area of D‐3 was smaller than that of D‐2 because of the high tectonic‐subsidence rate (result-ing in a high relief) D‐3 is thicker and shows a larger sedi-ment volume than the overlying D‐2 (Table 3) D‐3 is thinner than S‐4 + 3 but the larger source area resulted in a larger

F I G U R E 9 General relationships between the average fault‐growth index of F1 and F2 (AFGIF1‐F2) and sedimentary source‐to‐sink parameters The average fault‐growth index of F1 and F2 (AFGIF1‐F2) data in this figure are from Table 2 The source‐to‐sink parameters data are from Table 4 Regression‐line equations and the coefficients of determination are shown in each diagram

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sediment volume and supply rate (Table 3 Figure8ch) Therefore both the fault‐induced relief and the drainage area affected the sediment‐supply rate and the sediment volume in the sink

The changes in accommodation space during the vari-ous phases of the Palaeogene in the south‐western HD are clear from the estimated tectonic subsiding rate (Table 2) The correlations between the intensity of the tectonic activ-ity and the extent of the depositional sink area (Figures 8d 9b 10b) between the intensity of the tectonic activity and the total accommodation space and between the intensity of the tectonic activity and the morphology in the sink area (Figures 8e‐f 9c‐d 10c‐d) clearly show that strong tectonic activity resulted in a larger accommodation capacity of the sink

In particular the main subsiding area tended to form steeper slopes However the extent of the main subsiding sink area diminished (Figure 8d) with increasing tectonic activity which was possibly due to the relatively small sub-siding centre in the tectonically active basins It can thus be deduced that tectonic activity not only controlled the sedi-ment supply and the variation in accommodation space but

also determined the changes in the topography of the sedi-mentary basins and the extent of the main depositional areas in the tectonically active basins

62 | Analysis of the influence of tectonic activity on the size and internal stacking pattern of the delta depositional systemThe above data and considerations indicate that the tectonic activity was closely related to the sediment supply accom-modation space and morphology of the sink area which are possibly the most important factors affecting the extent and stacking pattern of the sedimentary facies (cf Cope et al 2010 DeCelles Kapp Ding amp Gehrels 2007 Leeder 2011 Olsen 1997 Simon et al 2017)

Statistical analysis indicates that the sediment‐supply rate has a strong positive correlation with the volume of the depositional system a moderate correlation with the seismic progradational dip in the depositional system and a poor cor-relation with the size of the depositional area (Figure 11a‐c) A larger sink area corresponded to a larger fanbraid‐delta a gentler seismic progradational angle and a reduced volume

F I G U R E 1 0 General relationships between average fault activity rate of F1 and F2 (RFAA‐F1‐F2) and sedimentary source‐to‐sink parameters The average fault activity rate of F1 and F2 (RFAA‐F1‐F2) data in this figure are from Table 2 The source‐to‐sink parameters data are from Table 4 Regression line equations and the coefficients of determination are shown in each diagram

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of the fan or braid‐delta which was possibly related to a re-duced sedimentary dip and thinner sediments (Figure 11d‐f) The total accommodation space in the basin correlates well

with the volume of the depositional system to some degree with the seismic progradational dip and poorly with the ex-tent of the depositional system area (Figure 11g‐i) These

FIGURE 11 Relationships between various parameters involved in the source‐to‐sink system (a‐c) Relationships between sediment supply and characteristics of the depositional system (extent volume and DPSA of the sediments) (d‐f) Relationships between the sink area of the basin and characteristics of the depositional system (g‐i) Relationships between the total accommodation space (AT) and the characteristics of the depositional system (j) Relationship between the accommodation‐spacesediment‐supply ratio (AS) and the DPSA of the sediments (k‐m) Relationships between the sedimentary dip and the characteristics of the depositional system The data regarding sediment supply basin sink area total accommodation space accommodation‐spacesediment‐supply ratio and sedimentary dips are from Table 4 The extent volume and DPSA of the sedimentary facies are from Table 3 Note the seemingly obvious polynomial (quadratic) relationship between the sedimentary dip and the sediment volume (L) The trend line in (L) suggests the following relationships between sediment volume and sedimentary slope in a rift or tectonically active basin (1) a very steep sedimentary slope is unfavourable for sediment accumulation (2) an appropriate sedimentary slope is favourable for preservation of depositional systems eg when the sedimentary slope in (L) is about 25degndash32deg the sediment volume reaches its largest value (3) a very gentle sedimentary slope will lead to a decrease of the sediment volume possibly due to weakening of the drainage system and thinner sediments

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relationships are clear evidence that the size of the sink area controlled the extent of the depositional system during the rifting of the lacustrine basin and that the rate of sediment supply and the accommodation space had a significant in-fluence on the total sedimentary volume as well as on the internal stacking pattern of the depositional system

We here use the ratio of the tectonic‐subsidence rate and the sediment‐supply rate as a proxy to indicate the ratio be-tween accommodation space and sediment‐supply rate (AS) (Table 4) AS has a strong influence on the internal stacking pattern of the depositional systems in the lacustrine rift basin (Figure 11j) This might be because the basin was small and because abundant and rapid material was supplied due

to intense tectonic activity (cf Catuneanu et al 2009 Liro 1993) and a favourable local climate (eg Bohacs Carroll Neal amp Mankiewicz 2000 Perlmutter amp Matthews 1989) The sediment supply still had a significant influence on the main subsidence area of the lacustrine basins and deposi-tional systems

In addition the basin slope significantly influenced the extent of the depositional system (Figure 11k) and had a polynomial relationship with its volume (Figure 11l) This relationship indicates that more intense tectonic activity and a steeper depositional slope were not favourable for sediment accumulation over a large extent in the lacustrine basin On the contrary these sediments were usually transported to a

F I G U R E 1 2 Tectonic differential activities and resulting patterns of the source‐to‐sink system on the south‐western slope of the HD during the Palaeogene (a) Development during phases of intense tectonics (Member 4 to the lower part of Member 3 of the Shahejie Fm) (b) Development during phases of somewhat less tectonic activity (middle part of Member 3 of the Shahejie Fm and Member 3 of the Dongying Fm) (c) Development during phases of weak tectonic activity (Members 1 and 2 of the Shahejie Fm and Member 2 of the Dongying Fm) The intensity of tectonic activity in the lacustrine rift basin had a significant influence on the development and extent of each unit of the source‐to‐sink system as well as on the type and dimensions of the depositional systems The present study indicates that probably sublacustrine fans developed (see for example Figure S4b) during phases with relatively strong tectonic activity This is not really clear from the seismic‐reflection data but possibly due to the small sizes of these sublacustrine fans Moreover lithofacies and core data are not available for the south‐western part of the study area The present contribution therefore focuses on the fan‐deltas and braid‐deltas regarding the sedimentary facies analysis the sublacustrine fans that probably developed in the deep or semi‐deep lake are presented just as a likely feature

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relatively small sink area with a fairly large accommodation space Finally stronger tectonic activity resulted in steeper depositional slopes (Figure 8f) which further controlled the hydrodynamic conditions and differential discharge when the sediments were deposited The strong correlation between the depositional slope and the deltas dip (Figure 11m) suggests that the differences in topography due to tectonics must be considered as one of the most critical factors that controlled the internal stacking pattern of the delta deposits

63 | Significance of the present study for other source‐to‐sink systems of lacustrine rift basins

631 | Summary of the source‐to‐sink systems in the HDIn lacustrine rift basins the tectonic setting is probably the main factor that determines the development of the S2S sys-tem but differential tectonic activities lead to variations in the basic characteristics of the S2S system Tectonic activity was most intense during S‐3 (lower unit) and during S‐4 and caused both a strong uplift of the source area and the devel-opment of depressions in the basin that formed a sink (Figure 12a) Strong tectonic activity in the S2S system during these time‐spans led to a high sediment‐supply rate steeper slopes a larger accommodation space and deposition of several fan‐deltas that are characterized by a fairly steep seismic progra-dational angle

The tectonic activity decreased during S‐3 (middle unit) and during D‐3 The S2S system that was present during this time‐span mainly concerned a rising area that shifted south-wards developing an alluvial plain between the erosional area and the sink area thus increasing the distance from source to sink (Figure 12b) Simultaneously the sediment‐supply rate and the accommodation space also changed and braid‐deltas could thus develop with larger volumes and gentler seismic progradational dips

Tectonic activity was clearly less intense during S‐1 + 2 and D‐2 The rising area had shifted further southwards cre-ating a wider alluvial plain connecting the source area to the sink in the HD (Figure 12c) At this stage stable tectonic activity led to relatively less sediment supply a gentle slope less accommodation space and the development of several braid‐deltas with a fairly gentle seismic progradational angle

632 | Wider implications and limitationsSoslashmme et al (2009) proposed that the elements of S2S sys-tems are genetically related and that quantitative correla-tions exist among these elements Other studies also suggest that the size of the drainage basin is correlated to the size of the fan developing on the basin floor (eg Blum et al

2017 Snedden et al 2018) and to the size of the river chan-nel (eg Milliken et al 2018) Helland‐Hansen Soslashmme Martinsen Lunt and Thurmond (2016) suggest a simplified subdivision of S2S systems into three main categories (a) Steep‐Short‐Deep (steep onshore and offshore gradients short distance between source and sink and deep offshore waters) (b) Wide‐Deep (low‐gradient shelf‐catchment area and deep offshore waters) and (c) Wide‐Shallow (relatively shallow offshore waters and a wide low‐gradient catchment area) systems

The present study indicates that the alluvial plain roughly corresponds to the alluvial‐shelf unit in marine basins al-though with a much smaller width and extent in the lacustrine rift basins than would have been the case on a continental shelf Faults F1 and F2 along the slope belt correspond to the slope of classical S2S systems whereas the shore‐shallow‐deep lake area can be compared with the basin floor (Soslashmme et al 2009) S‐4 and S‐3 (lower unit) can be roughly clas-sified as Steep‐Short‐Deep systems whereas the overlying S‐1 + 2and D‐2 can be classified as the Wide‐Shallow sys-tems that Helland‐Hansen et al (2016) defined During the deposition of S‐4 and S‐3 (lower unit) the strong tectonic activity caused a high relief of the source area a narrow allu-vial plain and a relatively deep lake The subsequently wan-ing tectonic activity resulted in a lower relief of the source area a wider alluvial plain and a shallower lake Although the absolute values of these elements in lacustrine basins are much smaller than those of marine basins the ratio between these elements in both settings is comparable Typically in a lacustrine basin a transformation from a Steep‐Short‐Deep system (S‐4 and S‐3 (lower unit)) to a Wide‐Shallow system (S‐1 + 2ampD‐2) occurs within a few million years Although the basin geomorphology has experienced signif-icant changes from S‐4 to D‐2 the quantitative relationships between tectonic activity sediment‐supply rate accommoda-tion space and sedimentary dip of the delta systems did not change significantly (eg Figures 8 and 11) The analytical approaches applied and quantitative relationship established here can help analyse other lacustrine basins worldwide and may even act as a reference for the analysis of marine basins

Our study focuses mainly on the influences of tectonic activity on the elements of the depositional sink Other pa-rameters (eg climate and lithology) were not considered in detail Studies on modern and ancient systems suggest that the climate and lithology also have a great influence on the sediment supply and distribution in the basin (eg Carroll Chetel amp Smith 2006 Hovius amp Leeder 1998 Syvitski amp Milliman 2007 Zhang et al 2018) For exam-ple climate variations between glacials and inter‐glacials have resulted in largely different sediment‐supply rates and in significant differences in the sizes of the Quaternary sub-marine fans in the north‐western Gulf of Mexico (Blum amp Hattier‐Womack 2009) We acknowledge the importance

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of climate and lithology for S2S systems and we are con-vinced that these elements can significantly affect the S2S systems in other cases(eg modern systems and systems influenced by glacialinterglacial alternations) These fac-tors were not really relevant for the present study however because no significant differences in lithology were present in the source areas and because we focus on the changes at a million‐year scale which implies that the tectonic ac-tivity has a first‐order control on the development of S2S elements in the investigated rift basin

7 | CONCLUSIONS

We have calculated the tectonic‐subsidence history the growth index and the activity rate of the main boundary faults (F1 and F2) and various S2S parameters of six Palaeogene rock units on the south‐western slope of the HD Based on the values found for these parameters quantitative corre-lation were established for the tectonic activity and other S2Sparameters in the basinal sink This leads to the follow-ing conclusions

1 The positive correlation between the intensity of fault activity and the tectonic‐subsidence rate is a strong indication for a distinct control by the tectonic activity of the syn‐depositional rifting of the tectonically active basin

2 The tectonic activity was quantitatively related to the sediment supply accommodation space and morphology of the sink area The relationship between tectonic activ-ity and depositional systems is reflected by changes in critical factors such as sediment supply accommodation space and dip of the sink area These critical factors were probably the most important factors that led to changes in the size and internal stacking pattern of the sedimentary facies

3 Differential tectonic activity led to changes in the char-acteristics of the S2S system on the south‐western slope of the HD The strongest tectonic activity which oc-curred during S‐3 (lower unit) and during S‐4 led to the largest provenance area adjacent to the sink area to a high sediment‐supply rate to steeper slopes to a larger accommodation space and controlled the development of several fan‐deltas Diminished tectonic activity dur-ing S‐3 (middle unit) and during D‐3 led to a decrease in uplift an increased width of the alluvial plain an in-creased transport distance a decrease in the sediment‐supply rate and accommodation space and resulted in the development of braid‐deltas with a large volume During S‐1 + 2 and D‐2 stable tectonic activity led to a lower sediment‐supply rate a gentle depositional slope and a smaller accommodation space resulting in the

development of several braid‐deltas with gentler seis-mic progradational angles

4 The analytical approaches applied and the quantitative re-lationships established here can help analyse other lacus-trine basins worldwide and may even act as a reference for the study of marine basins

ACKNOWLEDGEMENTS

We thank Dr Sarah Boulton and Dr Chenlin Gong as well as the Associate Editor of Basin Research Dr Craig Magee for their constructive comments on the manuscript This study was funded by the National Science and Technology Major Project (Exploration Technologies for Offshore Hidden OilGas) (project no 2016ZX05024‐003‐003) the National Natural Science Foundations of China (project no 41676050) and the Fundamental Research Funds for the Central Universities (2652014037)

REFERENCES

Allen P A (2008a) From landscapes into geological history Nature 451 274ndash276 https doiorg101038natur e06586

Allen P A (2008b) Time scales of tectonic landscapes and their sed-iment routing systems In Landscape evolution Denudation cli-mate and tectonics over different time and space scales (Ed by Gallagher K Jones S J amp Wainwright J) Geological Society London Special Publications 296 7ndash28

Allen P A Armitage J J Carter A Duller R A Michael N A Sinclair H D hellip Whittaker A C (2013) The Qs problem Sediment volumetric balance of proximal foreland basin systems Sedimentology 60 102ndash130

Amorosi A Maselli V amp Trincardi F (2016) Onshore to offshore anatomy of a late Quaternary source‐to‐sink system (Po Plain‐Adriatic Sea Italy) Earth‐Science Reviews 153 212ndash237 https doiorg101016jearsc irev201510010

Anderson J B Wallace D J Simms A R Rodriguez A B Weight R W R amp Taha Z P (2016) Recycling sediments between source and sink during a eustatic cycle Systems of late Quaternary northwestern Gulf of Mexico Basin Earth‐Science Reviews 153 111ndash138 https doiorg101016jearsc irev201510014

Anthony E J amp Julian M (1999) Source‐to‐sink sediment trans-fers environmental engineering and hazard mitigation in the steep Var River catchment French Riviera southeastern France Geomorphology 31 337ndash354 https doiorg101016S0169-555X(99)00088-4

Athy L F (1930) Density porosity and compaction of sedimentary rocks AAPG Bulletin 14 1ndash24

Bhattacharya J P Copeland P Lawton T F amp Holbrook J (2016) Estimation of source area river palaeo‐discharge palaeoslope and sediment budgets of linked deep‐time depositional systems and im-plications for hydrocarbon potential Earth‐Science Reviews 153 77ndash110

Blum M D amp Hattier‐Womack J (2009) Climate change sea‐level change and fluvial sediment supply to deepwater depositional

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F I G U R E 1 Schematic map of the Bohai Bay Basin and the Huanghekou Depression (HD) (a) Location of the Bohai Bay Basin within China The red solid line in the figure forms the boundary of the Bohai Bay Basin (b) Tectonic map showing sub‐basins of the Bohai Bay Basin The tectonic features in this figure are based on the interpretation of regional 2‐D seismic data of the lower boundary of the Palaeogene (modified from Zhou et al 2010 Liu Xia et al 2015a) The blue dotted line representing the present‐day coastline of China indicates the offshore part (Bohai Bay) of the Bohai Bay Basin Light‐gray dotted lines in this figure are regional 2‐D seismic lines near the HD Purple solid lines in figures B and C indicate the locations of the seismic lines shown in Figures 3 and 5 (c) Structural characteristics of the HD The tectonic characteristics of the HD are modified from results of Zhou et al (2010) and Liu Xia et al (2015a) The south‐western faults (F1 and F2) and the Kendong Structural High have been interpreted and validated through newly acquired 3‐D seismic data F1‐S1 F1‐S2 F1‐S3 F2‐S1 F2‐S2 and F2‐S3 are the calculation locations of faults F1 and F2 Circles (filling in yellow) represent drilling well locations (dndashf) Schematic structure and seismic profiles across the HD in the offshore part of the Bohay Bay Basin (for locations see Figure 1b‐c) The texts ldquoT2 T31 T32 hellip T8rdquo in the legend refer to the seismic surfaces (see Figure 2) The codes of formations and members are consistent with Figure 2

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over 5000 km2 of 3‐D seismic surveys in the HD Both the 2‐D and the 3‐D seismic data have a vertical sampling rate of 2 ms and were processed to zero phases They were dis-played as reversed polarities The 3‐D seismic data have a dominant frequency of 15ndash40 Hz and an average velocity of 3600 ms (calculated from Well W25) with a vertical resolu-tion of 22ndash60 m

Cutting log and logging data from 25 wells have been used for the present study Core data were made available for 11 wells with a total length of about 1000 m Integration of these well and seismic data helped establishing a regional stratigraphic framework through calibration of seismic syn-thetic records seismic units and interpretation of the sedimen-tary facies (Table 1) In total eight horizons were interpreted

respectively as T7 (dated at 447 Ma) T63 (4223 Ma) T62 (4044 Ma) T5 (3790 Ma) T3(3328 Ma) T31 (2671 Ma) and T2 (2338 Ma) The successions between these horizons represent different members of the Dongying and Shahejie Formations The codes and interpretation of these members are provided in Figure 2 The quantitative compilation of the sedimentary system and the palaeogeomorphological maps are based on these results

32 | Quantitative estimation of tectonic activityThe tectonic‐subsidence rate fault‐growth index and fault‐activity rate are used in the present contribution to detail

F I G U R E 2 Lithostratigraphy and sequences of the HD The lithological data and interpretations are based mainly on a combination of data from Wells W1 W18 and W25 Ages are based on data obtained from CNOOC Tianjin Branch The tectonic stages sedimentary environment and fossil associations are modified after Liu Xia et al (2015a) Note that newly acquired 3‐D seismic data indicate that the Kongdian Fm is possibly absent in the HD which differs from the results presented by Liu Xia et al (2015a) D‐1 = Member 1 of the Dongying Fm D‐2 = Member 2 of the Dongying Fm D‐3 = Member 3 of the Dongying Fm S‐1 amp 2 = Members 1 and 2 of the Shahejie Fm S‐3 = Member 3 of the Shahejie Fm S‐4 = Member 4 of the Shahejie Fm

592 | EAGE

LIU et aL

the tectonic history and intensity We have selected Well W25 (Figure 1c) because it is the only drilling well in the south‐eastern HD for simulation of the subsidence history This simulation is based on our reconstructed stratigraphic framework and age information provided by the TBCNOOC (Figure 2)

Correction for compaction is critical in quantitative sim-ulation of the subsidence history and rate The influence of the water depth during sedimentation is considered negligible since the Bohai Bay Basin was a lacustrine basin Differences in the acoustic travel times have been used to calculate the porosities at the corresponding depths (cf Wylliel Gregory amp Gardner 1958) Subsequently the porosities of the vari-ous types of lithology (mainly sandstone and mudstone) at different depths were determined by logging and the poros-itydepth relationship was established by statistic fitting (cf Athy 1930) Back‐stripping of the selected strata was per-formed layer‐by‐layer to calculate the top and bottom bound-ary depths at different times in the geological development (cf Perrie amp Qiublier 1974) thus distinguishing between the compaction history the tectonic subsidence and the total subsidence during the Palaeogene (Figure 3 Table 2 supple-mentary text)

The normal boundary faults (F1 amp F2) controlling depo-sition on the south‐western margin of the HD have been

selected to calculate the fault‐growth index and the fault‐ac-tivity rate (Figure 1c) The fault‐growth index sometimes also called the ldquoexpansion indexrdquo is the ratio between the stratigraphic thickness of the hanging wall and that of the footwall of a growth fault The fault‐activity rate is the ratio between the thicknesses of the sedimentary successions in the hanging wall and the foot wall resulting from fault activ-ity during a specific depositional phase corresponding to the length of the time‐span during which the investigated succes-sion accumulated ie (Zhou Niu amp Teng 2009)

where RF is the fault‐activity rate in mMa T is the length of the time‐span during which the investigated succession ac-cumulated (in Ma) STh is the stratigraphic thickness of the hanging wall (in m) and STf is the stratigraphic thickness of the footwall (in m) For the calculation of the stratigraphic thickness the conversion from two‐way travel time to depth was made by analysis of the P‐wave velocity in the wells The growth index and the activity rate of the main faults have thus been calculated for several locations (Table 2 Figure 1c) which was considered necessary because of the differ-ent successive stages in the morphological evolution of the

RF=ΔST∕T =

(

SThminusST

f

)

∕T

F I G U R E 3 Palaeogene burial history of the HD (a) Cumulative subsidence (b) Subsidence during the development of the individual members D‐1 = Member 1 of the Dongying Fm D‐2 = Member 2 of the Dongying Fm D‐3 = Member 3 of the Dongying Fm S‐1 amp 2 = Members 1 and 2 of the Shahejie Fm S‐3 = Member 3 of the Shahejie Fm S‐4 = Member 4 of the Shahejie Fm

| 593EAGE

LIU et aL

basin‐controlling faults and because of the changes in the intensity of the fault activity

33 | Quantitative calculation of S2S system parameters

331 | Area and volume of the sedimentary faciesQuantitative calculation of the dimensions of sedimentary facies requires reliable estimates of the lateral extent and thickness of the sediments involved For these calculations first the maxi-mum extent of the specific units under study (fan‐deltas braid‐deltas etc) at different times was determined in plan view based on the combined interpretation obtained from seismic facies lithofacies and the outer boundaries of the sediment bodies Subsequently the outcomes were digitalized and used as input for a 3‐D survey by GEOFRAME Detailed calculations of the sedi-ment bodies extents were conducted using the PLANIMETER tool in the BASEMAP window of GEOFRAME

This was followed by the selection of several seismic sec-tions across the sediment body in order to identify the lower

and upper boundaries as well as to calculate the maximum minimum and average thickness (see Amorosi Maselli amp Trincardi 2016 Liu et al 2017) Finally we used a colum-nar body with irregular base and the same height to represent the irregular sediment body The formula for volume calcu-lation is as follows (Figure 4 Table 3 supplementary text)

where VS is the volume of the sediment (in km3) AS is the horizontal surface area of the irregular base of the sediment (in km2) and H is the height (average thickness) of the sed-iment (in m) Detailed calculations of the thickness were conducted using the AREAL tool in the SEIS3DVSEIS2DV window of GEOFRAME

332 | Determination of the depositional dip of the delta surface due to progradationThe term ldquodepositional diprdquo is used here to indicate the inclination of a dipping sedimentary surface Horizon flat-tening was used to analyse and calculate the morphology of the underlying strata First the maximum flooding surface ndash approximately corresponding to the palaeo‐sedimentary surface (Lin et al 2012) ndash of each unit under study was interpreted it was subsequently flattened to calculate the original depositional dip (Figure 5d) with the formula

where DSD is the sedimentary dip (in degrees) dy is the verti-cal thickness between the lower boundary of the sedimentary unit and the ancient sedimentary surface in the depositional centre (in m) and dx is the distance from the apex of the delta to its depositional centre (in m)

Two to four seismic sections have been selected to calcu-late the average sedimentary dip of each individual delta with the following formula

where DSDA is the average sedimentary dip of a sediment (in degrees) and n is the number of seismic sections

The seismic progradational angle of the deltas interior has been calculated by the horizon‐flattening method (Figure 5e) which is expressed by the formula

VS=A

StimesH

DSD

= tanminus1 (dy∕dx)

DSDA

=

(

nsum

i=1

DSDi

)

∕n

DP= tan

minus1 (dy∕dx)

F I G U R E 4 Schematic diagram showing the calculation of the volume of a sediment (a) is an irregular sediment body Volume calculation of cuboids was used for reference to calculate the volume of an irregular sedimentary body ie the volume of an irregular sediment body equals the area of the irregular bottoms times height (b) 3ndash4 seismic lines along the sedimentary body are selected and the thickness of the sedimentary body is determined at intervals of 10 seismic traces (c) when a thickness grid covering the entire sedimentary body in space is acquired the average thickness of all counted thicknesses can be calculated as the height of the irregular sediment body (d)

594 | EAGE

LIU et aL

where DP is the seismic progradational dip (in degrees) The average dip angle is obtained from only one seismic sec-tion because of the variations in the progradational seismic event of the delta on the same seismic line

where DPA is the average seismic progradational dip in a spe-cific seismic section (in degrees) and n is the number of seis-mic progradational events

Based on the calculated average dip of one seismic sec-tion the average progradational dip of a specific sediment body can be calculated with the formula

DPA

=

(

nsum

i=1

DPi

)

∕n

F I G U R E 5 Detailed calculations of the sedimentary dip and the progradational seismic event dip of the delta interior taking the progradation seismic reflection of the delta developed in Member 3 of the Dongying Formation as an example The locations of the seismic lines are shown in Figure 1c Based on the interpretation of the stratigraphic and seismic facies visible in the original seismic lines (a) the topset or the maximum flooding surface (MFS) corresponding to the delta was flattened (b) Taking into account the water depth during sedimentation the sedimentary dip (d) and the progradational seismic event dip of the delta interior (e) can be calculated DSD = depositional dip in a specific seismic section DSDA = average depositional dip of a specific sedimentary unit DP = seismic progradational dip DPA = average seismic progradational dip

| 595EAGE

LIU et aL

TA

BL

E 1

In

terp

reta

tion

of th

e m

ain

sedi

men

tary

faci

es in

the

Pale

ogen

e of

the

Hua

nghe

kou

Dep

ress

ion

Evi

denc

e of

fan

delta

s and

bra

id d

elta

s in

wel

ls W

1 an

d W

18 c

omes

from

Liu

Xia

et a

l (2

015a

)

Form

atio

n an

d m

embe

raSe

ismic

faci

esEx

ampl

esLi

thof

acie

sLi

thol

ogy

Wel

l amp c

ore

exam

ples

Dep

ositi

onal

en

viro

nmen

tPr

edic

ted

res-

ervo

ir q

ualit

y

D‐2

Seis

mic

Fac

ies 5

mod

erat

e co

ntin

uous

lo

w‐a

mpl

itude

and

a sh

ingl

ed‐li

ke

prog

rada

tiona

l sei

smic

refle

ctio

n

Figu

re

Mul

tiple

upw

ard‐

coar

s-en

ing

litho

faci

es

asso

ciat

ions

Gre

y m

udst

ones

gre

y to

gre

yish

w

hite

pebb

ly fi

ne sa

ndst

ones

and

fin

e sa

ndst

ones

T25

Bra

id d

elta

Mod

erat

e to

hi

gh

D‐3

Seis

mic

Fac

ies 4

con

tinuo

us m

oder

-at

e‐to

high

‐am

plitu

de a

nd o

bliq

ue‐

to‐s

igm

oid

prog

rada

tiona

l sei

smic

re

flect

ion

Figu

re

Mul

tiple

upw

ard‐

coar

s-en

ing

litho

faci

es

asso

ciat

ions

Gre

yish

whi

te to

whi

te fi

ne

sand

ston

es s

iltst

ones

and

gre

y m

udst

ones

T25

Bra

id d

elta

Hig

h

Figu

re 7

e‐f

S‐1

+ 2

Seis

mic

Fac

ies 5

mod

erat

e co

ntin

uous

m

oder

ate‐

ampl

itude

and

shin

gled

‐like

pr

ogra

datio

nal s

eism

ic re

flect

ion

Figu

re

Mul

tiple

upw

ard‐

coar

s-en

ing

litho

faci

es

asso

ciat

ions

Dar

k gr

ey m

udst

ones

and

gre

yish

w

hite

to g

rey

mid

dle‐

to fi

ne‐

grai

ned

sand

ston

es

T25

Bra

id d

elta

Hig

h

S‐3

(mid

dle

unit)

Seis

mic

Fac

ies 3

har

dly

tom

oder

atel

y co

ntin

uous

low

‐am

plitu

de o

bliq

ue

prog

rada

tiona

l sei

smic

refle

ctio

n

Figu

re

Lith

ofac

ies 1

Gre

y to

gre

yish

whi

te sa

ndy

cong

lom

erat

esT2

5B

raid

del

taH

igh

Lith

ofac

ies 2

Thic

k gr

ey m

iddl

e‐to

fine

‐gra

ined

sa

ndst

ones

Figu

re 7

a‐d

Lith

ofac

ies 3

Gre

y m

udst

ones

inte

rbed

ded

with

gr

ey fi

ne sa

ndst

ones

and

gre

y m

uddy

silts

tone

s

Lith

ofac

ies 4

Thic

k da

rk g

rey

mud

ston

es

S‐3

(low

er

unit)

Seis

mic

Fac

ies 2

cha

otic

prog

rada

-tio

nal t

o ob

lique

pro

grad

atio

nal

seis

mic

faci

es

Figu

re

Pe

bbly

sand

ston

es in

terb

edde

d w

ith

thin

bro

wn‐

grey

mud

ston

esb

row

n sa

ndy

cong

lom

erat

ess

ands

tone

s in-

terb

edde

d w

ith th

in m

udst

ones

thic

k m

udst

ones

inte

rbed

ded

with

th

in sa

ndst

ones

or p

ebbl

y fin

e sa

ndst

ones

T1Fa

n de

ltaM

oder

ate

S‐4

Seis

mic

Fac

ies 1

dis

cont

inuo

us to

con

-tin

uous

low

‐tohi

gh‐a

mpl

itude

cha

otic

pr

ogra

datio

nal s

eism

ic re

flect

ion

Figu

re

Figu

re

Fig

ure

and

Fi

gure

Lith

ofac

ies 1

Gre

y pe

bbly

sand

ston

es c

oars

e sa

ndst

ones

T18

Fan

delta

sM

oder

ate

Lith

ofac

ies 2

Ash

‐bla

ck m

udst

ones

inte

rbed

-de

d w

ith th

in g

rey

fine‐

grai

ned

sand

ston

es

Lith

ofac

ies 3

Ash

‐bla

ck m

udst

ones

inte

rbed

ded

with

peb

bly

sand

ston

esa D

= D

ongy

ing

Fm

S =

Sha

hejie

Fm

The

num

ber i

ndic

ates

the

num

ber o

f the

mem

ber

596 | EAGE

LIU et aL

TA

BL

E 2

Es

timat

ion

stat

istic

s of t

he te

cton

ic‐s

ubsi

denc

e ra

te g

row

th in

dex

and

activ

ity ra

te o

f fau

lts F

1 an

d F2

S1

S2

and

S3 a

re th

e ca

lcul

atio

n lo

catio

ns o

f F1

and

F2 (s

ee F

igur

e 1c

) th

e co

rres

pond

ing

num

bers

are

F1‐

S1 F

1‐S2

F1‐

S3 F

2‐S1

F2‐

S2 a

nd F

2‐S3

res

pect

ivel

y

Form

atio

n an

d m

embe

raA

ge

(Ma)

R TS

(m

Ma)

b

Faul

t‐gro

wth

inde

xFa

ult‐a

ctiv

ity r

ate

(mM

a)

AFG

I F1‐

F2c

R FA

A‐F

1‐F2

d

S1S2

S3A

vera

geS1

S2S3

aver

age

F1F2

F1F2

F1F2

F1F2

F1F2

F1F2

F1F2

F1F2

D‐1

233

75ndash

267

1450

00

111

106

109

110

107

109

109

108

389

270

389

479

270

389

349

379

109

364

D‐2

267

14ndash

302

060

00

139

130

138

140

137

133

138

134

320

730

29

341

442

62

329

534

98

330

535

96

136

345

1

D‐3

302

0ndash33

278

190

002

002

052

102

342

032

052

042

1579

67

104

0010

372

111

3485

59

762

989

66

972

12

1093

44

S‐1

+ 2

332

78ndash

378

9250

00

145

136

142

147

155

145

148

143

122

211

36

105

915

78

587

176

39

5614

92

146

122

4

S‐3

(mid

dle

unit)

378

92ndash

404

3812

500

131

202

192

242

175

257

166

234

335

140

88

490

380

62

215

510

919

347

076

90

205

558

0

S‐3

(low

er

unit)

404

38ndash

422

3135

500

284

343

302

395

342

389

309

376

737

185

37

104

4016

956

742

820

480

841

315

324

343

118

69

S‐4

422

31ndash

447

300

002

512

921

584

173

023

332

373

4791

33

106

4357

58

151

8811

007

121

5186

33

126

612

9210

647

a D =

Don

gyin

g Fm

S

= S

hahe

jie F

m T

he n

umbe

r ind

icat

es th

e nu

mbe

r of t

he m

embe

r b R T

S = te

cton

ic‐s

ubsi

denc

e ra

te

c AFG

I F1‐

F2 =

ave

rage

faul

t‐gro

wth

inde

x of

F1

and

F2

d R FA

A‐F

1‐F2

= a

vera

ge fa

ult‐a

ctiv

ity ra

te o

f F1

and

F2

| 597EAGE

LIU et aL

TA

BL

E 3

C

alcu

latio

n ch

art o

f the

sedi

men

tary

‐fac

ies d

imen

sion

s and

the

inte

rnal

pro

grad

atio

nal s

eism

ic e

vent

dip

The

spat

ial e

xten

t is s

how

n in

Fig

ure

7

Form

atio

nand

mem

bera

Sedi

men

tary

faci

esSe

ismic

sect

ions

Thic

knes

s (m

)

Are

a (k

m2 )

Vol

ume

(km

3 )To

tal v

olum

e (k

m3 )

DPb

Max

M

in

Ave

rage

DPA

DPS

A

D‐2

Bra

id d

elta

Figu

re a

176

0075

00

107

7016

246

175

017

50

157

156

Figu

re b

174

0080

00

157

Figu

re c

218

0080

00

152

D‐3

Bra

id d

elta

Figu

re a

285

0011

400

200

5014

219

285

128

51

268

285

Figu

re b

295

0099

00

309

Figu

re c

296

0078

00

309

Figu

re d

284

0091

00

254

S‐1

+ 2

Bra

id d

elta

Figu

re a

178

0089

00

136

7512

023

164

416

44

172

177

Figu

re b

185

0095

00

176

Figu

re c

236

0010

500

193

Figu

re d

209

0011

400

166

S‐3

(mid

dle

unit)

Bra

id d

elta

Figu

re a

274

0010

100

223

7587

87

196

619

66

213

225

Figu

re b

279

0083

00

225

Figu

re c

292

0086

00

235

Figu

re d

296

0086

00

226

S‐3

(low

er u

nit)

Fan

delta

Figu

re a

428

8623

903

374

0062

89

235

223

52

301

305

Figu

re b

432

5522

071

325

Figu

re c

473

0920

583

312

Figu

re d

450

8325

500

283

S‐4

Fan

delta

1Fi

gure

a30

700

483

929

200

107

03

1221

26c

423

365

Figu

re b

350

0010

728

439

Fan

delta

2Fi

gure

a46

500

704

832

900

856

282

421

Figu

re b

379

0066

52

362

Fan

delta

3Fi

gure

a40

100

118

7841

100

186

27

654

21

Figu

re b

468

0016

718

309

Figu

re c

527

0015

127

387

Figu

re d

486

0014

844

297

Fan

delta

4Fi

gure

a42

800

151

2042

700

179

57

663

04

Figu

re b

512

0027

287

289

a D =

Don

gyin

g Fm

S

= S

hahe

jie F

m T

he n

umbe

r ind

icat

es th

e nu

mbe

r of t

he m

embe

r b D

P = se

ism

ic p

rogr

adat

iona

l dip

DPA

= a

vera

ge se

ism

ic p

rogr

adat

iona

l dip

DPS

A =

ave

rage

seis

mic

pro

grad

atio

nal d

ip o

fthe

sedi

men

t c 21

26

= to

tal j

oint

vol

umes

of f

an d

elta

s 1 2

3 a

nd 4

598 | EAGE

LIU et aL

where DPSA is the average seismic progradational dip of a sediment (in degrees) and n is the number of seismic sections

Detailed estimated results of the depositional dip and the seismic progradational dip of the delta are shown in Tables 3 and 4

333 | Provenance conditions and estimation of the sediment supplySystematic investigation by TBCNOOC of the regional uplift and provenance in the geological past has indicated that the main provenance areas around the HD existed alreadybefore the deposition of Member 3 of the Shahejie Fm (Zhou et al 2010) They include the Bonan Laibei and Kendong Highs (Figure 1b‐c Figure S1a‐b) However starting with the depo-sition of Members 1ndash2 of the Shahejie Fm (S‐1 + 2) (3789ndash3328 Ma) until the accumulation of the Dongying Formation (3328ndash2338 Ma) the Bonan and Laibei Highs subsided to below lake level and consequently stopped providing sedi-ment to the depression (Liu Xia et al 2015a) Only the Kendong High which remained a high for a long time re-mained a provenance area for the south‐western part of the

HD during this time‐span (Figure S1a) The Kendong High has therefore been selected as the site where the relationship between tectonics and depositional systems within the same provenance system could be studied best The distribution area of the Kendong High as the provenance area at different moments has been determined on the basis of numerous seis-mic interpretations through seismic terminations (eg onlap) and the absence of specific sediment units due to faulting

The sediment‐supply rate can be obtained by calculation of the volumes of the deltas and the duration of their forma-tion (cf Allen et al 2013 Lemons amp Chan 1999 Lemons Milligan amp Chan 1996) Although the stratigraphic ages are well‐known for each unit (Figure 2) there is no high‐resolu-tion age control for the top and base of each delta system The absolute age of the pertinent stratigraphic unit (Figure 2) is therefore used to represent the formation time of the individual deltas in the unit The thus calculated sediment‐supply rate rep-resents in our opinion the trend of the supply rate from bottom to top sufficiently well

334 | Estimation of the extent and accommodation space of the sink areaDetermination of the boundaries of the sink area is based on reconstructions of the morphology during the successive dep-ositional phases The extent of the sink area was estimated using the same calculations as for the area of the depositional system

DPSA

=

(

nsum

i=1

DPAi

)

∕n

F I G U R E 6 Vertical successions and representative examples of the various lithofacies (a) A fan‐delta in Well W18 (b‐e) Braid‐deltas in Well W25 (f) Grey to greyish white sandy conglomerate (deposits in braided channels) (g) Grey medium‐ to fine‐grained massive sandstone (mouth‐bar deposits) (h) Grey fine sandstone (distal sand bars) (i) Grey muddy siltstone with parallel bedding (prodelta) (j) Greyish white fine sandstone with convolute bedding (mouth bars) (k) Greyish white fine sandstone with boulders (mouth bars) Wireline logs show the spontaneous‐potential (SP) and gamma‐ray (GR) changes with depth Depth in metres For location of the cores see Figure 6bd

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Differences in base level and the original sedimentary sur-face define the accommodation space (Jervey 1988 Muto amp Steel 2000 Neal amp Abreu 2009 Wheeler 1964) The

accommodation space in the depositional area can be deter-mined on the basis of the thickness of the preserved sediments (Muto amp Steel 2000) This space is obviously controlled by

F I G U R E 7 Schematic morphology during the successive depositional phases The extent of the deltas the depositional sink area in the basin and the main features of the drainage systems are shown The extent of the deltas has been interpreted from seismic data and has been used for calculation of the surface area and volume of the various deltas (a) Shahejie Fm Member 4 (b) Shahejie Fm lower part of Member 3 (c) Shahejie Fm middle part of Member 3 (d) Shahejie Fm Members 1 and 2 (e) Dongying Fm Member 3 (f) Dongying Fm Member 2

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the rate of subsidence tectonic uplift and fluctuations of the lake level (Lemons amp Chan 1999) Changes in the lake level of the HD have not been investigated so that we take data on the tectonic‐subsidence rate as a proxy for changes in the accommodation space The total space is expressed in the equation (Table 4)

where AT represents the total accommodation space of the sink area (in km3) TS represents the tectonic subsidence (in m) and SA represents the surface area of the sink (in km2)

AT= TStimesSA∕1000

T A B L E 4 Estimation of the controlling factor parameters of the depositional system The distribution characteristics of the depositional sink in the basin are shown in Figure 7

Formation and membera

Sedimentary facies Seismic sections

DDb

RSSc(km3

Ma)Sink area (km2) AT

d(km3) ASeSource areaf(km2)DSD DSDA

D‐2 Braid delta Figure a 059 066 502 37542 7852 1195 58

Figure b 065

Figure c 074

D‐3 Braid delta Figure a 161 187 926 19823 11593 2051 252

Figure b 192

Figure c 215

Figure d 182

S‐1 + 2 Braid delta Figure a 086 096 356 28015 6463 1403 220

Figure b 094

Figure c 120

Figure d 083

S‐3 (middle unit) Braid delta Figure a 110 119 772 21756 6927 1619 355

Figure b 111

Figure c 129

Figure d 128

S‐3 (lower unit) Fan delta Figure a 307 303 1313 16506 10500 2705 482

Figure b 334

Figure c 332

Figure d 237

S‐4 Fan delta 1 Figure a 384 463g 861 14150 10481 3484 501

Figure b 379

Fan delta 2 Figure a 606

Figure b 498

Fan delta 3 Figure a 479

Figure b 499

Figure c 625

Figure d 553

Fan delta 4 Figure a 377

Figure b 226aD = Dongying Fm S = Shahejie Fm The number indicates the number of the member bDD = depositional dip DSD = depositional dip in a specific seismic section DSDA = average depositional dip of a specific sedimentary unit cRSS = sediment‐supply rate dAT = total accommodation space eAS = accommodation spacesediment supply fSource area = Denudation area within the seismic data coverage The complete erosional area cannot be estimated because of the limited data coverage g463 = the average depositional dip of fan deltas 1 2 3 and 4 Considering that the four fan deltas developed during S‐4 consist of sediment that was derived from the same provenance area and were deposited in the same time‐span the four fan deltas are taken as a whole when estimating the parameters of RSS the sink area AT and AS

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4 | ELEMENTS OF THE S2S SYSTEM

41 | Analysis of the seismic facies and stacking pattern of the main sedimentary faciesA comprehensive analysis of seismic data cores cutting log-gings and well‐logging curves by Liu Xia et al (2015a) in-dicated that the Palaeogene depositional systems of the HD included fan‐deltas braid‐deltas lake margins deep lakes etc The fan‐ and braid‐deltas have been chosen for a detailed seismic study that must reveal their internal texture and their stacking patterns Analysis of the progradational seismic‐re-flection types and of the seismic progradational dip is particu-larly helpful for a better understanding of the hydrodynamic conditions and sedimentary processes that resulted in these depositional systems Because the facies interpretation in this area has been done before and is not the focus of this work we here mainly describe the internal texture and their stack-ing patterns of the main sedimentary facies

The major facies of S‐4 is interpreted as a fan‐delta It is dominated by Seismic Facies 1 which is characterized by discontinuous to continuous low‐ to high‐amplitude and chaotic progradational seismic reflections (Figures S3ndashS6 Table 1) The average dip of the progradational seismic event is about 365deg (Table 3) Three lithofacies are associated with Seismic Facies 1 (Table 1) The coarser lithofacies 1 represents a fan‐delta front whereas the finer lithofacies 2 and 3 are prodelta deposits The overall coarsening‐upward succession facies stacking pattern (Figure 6a) discontinuous and chaotic seismic reflections and relatively steep slope of Seismic Facies 1 suggest a fan‐delta system developed under strong hydrodynamic conditions (Mitchum et al 1977)

The fan‐delta of the lower part of Member 3 of the Shahejie Fm (S‐3 [lower unit]) is dominated by Seismic Facies 2 which is characterized by chaotic progradational to oblique progradational seismic characteristics It has a typical wedge shape and is composed of two seismic‐reflection seg-ments (a) a moderately continuous low‐ to high‐amplitude chaotic seismic‐reflection segment located near boundary fault F2 and (b) a continuous moderate‐ to high‐amplitude and oblique progradational seismic reflection in a basinward direction (Figure S7 Table 1) No obvious upper or lower segments occur in SF 2 and the dip of the progradational seismic event in this segment is also relatively steep viz 305deg (Table 3)

The middle part of Member 3 of the Shahejie Fm (S‐3 [middle unit]) is characterized by a low‐ to moderate‐con-tinuous low‐amplitude and oblique progradational seismic reflection (Seismic Facies 3) and is interpreted as a braid‐delta (Figure S8 Table 1) The progradational seismic events are parallel or sub‐parallel to each other and dip less (aver-age 225deg) than Seismic Facies 1 and 2 (Table 3) Seismic

Facies 3 is associated with four lithofacies (Figure 6b Table 1) in Well T25 The complete succession of the braid‐delta consists of gravely to coarse‐grained sandstone (lithofacies 1) at the base (Figure 6f) massive bedded medium‐ to fine‐grained sandstones (lithofacies 2) and grey mudstones inter-bedded with grey fine sandstones and grey muddy siltstones (lithofacies 3) in the middle (Figures 6g and 6h) and thick dark grey mudstones (lithofacies 4) at the top (Figure 6i)

Member 3 of the Dongying Fm (D‐3) is characterized by Seismic Facies 4 a typically composite seismic progra-dation reflection configuration representing a braid‐delta system (Figure S9 Table 1) Seismic Facies 4 is composed of highly continuous moderate‐ to high‐amplitude and pro-gradational seismic reflections that represent well‐developed deltaic topsets and bottomsets The topset segments of SF 4 are nearly horizontal or dip only gently (Table 3) The foreset segments form thicker lenses with small depositional angles The oblique progradational part of this seismic facies is sim-ilar to that in Seismic Facies 3 and usually developed at the basinward front end of Seismic Facies 3 The lithology of Seismic Facies 4 is dominated by greyish white to white fine‐grained sandstones and siltstones The lithofacies association is characterized by coarsening‐upward sedimentary cycles (Figure 6c Table 1) Convolute bedding and abundant diam-ictites are present on top of the fine sandstones (Figure 6j‐k)

Both braid‐deltas in the Members 1 + 2 of th Shahejie Fm (S‐1 + 2) and Member 2 of the Dongying Fm (D‐2) show moderately continuous moderate‐amplitude and shin-gled‐like progradational seismic reflections (Seismic Facies 5 Figures S10ndashS11 Table 1) It shows a thin prograding seis-mic pattern commonly with parallel upper and lower bound-aries (cf Mitchum et al 1977) The successive internal progradational seismic events overlap each other between the upper and lower segments with a gentle dip of 152degndash193deg (Table 3) The lithofacies are mostly composed of several coarsening‐upward cycles (Figure 6d Table 1) Each cycle is composed of dark grey mudstones and grey to whitish‐grey medium‐ to fine‐grained sandstones Several coarsening‐up-ward lithofacies are mainly developed in D‐2 (Figure 6e Table 1)

42 | Analysis of the tectonic activityThe normal faults F1 and F2 selected to calculate the fault activity dipping to the north and running approximately E‐W are important boundary faults on the south‐western margin of the HD The tectonic‐subsidence rate fault‐growth index and fault‐activity rate were used as proxies to indicate the tectonic intensity (Figure 3 S2 Table 2) S‐4 and S‐3 (lower unit) have the highest subsidence rate (300ndash355 mMa) the highest fault‐growth index (292ndash343 mMa) and the highest fault‐activity rate (10647ndash11869 mMa) among the studied intervals whereas the overlying S‐3 (middle

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unit) and S‐1 + 2 are characterized by a much lower sub-sidence rate and fault‐growth index and fault‐activity rate D‐3 had again a high subsidence rate (190 mMa) and an average fault‐growth index (210 mMa) and fault‐activity rate (9344 mMa) The uppermost studied interval D‐2 had a much lower subsidence rate (60 mMa) growth index (136 mMa) and fault‐activity rate (3451 mMa) than the un-derlying unit Generally the analysis of the subsidence rate average fault‐growth index and fault‐activity rate indicates two phases of alternating strong tectonic activity and tectoni-cally stable conditions

43 | Palaeogeomorphology distribution and dimensions of the main depositional systemsDepositional systems of each depositional phase of the Palaeogene on the south‐western slope of the HD were com-piled through seismic facies identification of 3‐D seismic data and compilation of maps with the current thicknesses of the main target intervals based on the study by Liu Xia et al (2015a) that combined a correction for the depth of burial with an interpretation of the sedimentary facies The basins sink area on the south‐western slope of the HD was estimated on the basis of a palaeogeomorphological reconstruction The distribution of the depositional system is closely related to the evolution of the palaeogeomorphology and therefore we describe both the distribution of the depositional system and the palaeogeomorphology here

The palaeogeography of S‐4 is characterized by the larg-est extent of the uplifted areas of all studied intervals The depositional area is small and scattered (Figure 7a Table 4) Faults F1 and F2 mark the boundaries between erosional and depositional regions The elevated footwalls of the faults were erosional areas and located adjacent to the hanging walls whereas the hanging walls were low‐lying depositional areas The sedimentary facies analysis indicates a fan‐delta developed here (Figure 7a) Calculations indicate that the sedimentary dip of the four fan‐deltas was uncommonly high (about 463deg) The extent and thickness of the fan‐deltas di-minished towards the basin margin (Tables 34)

The tectonically‐induced morphology of S‐3 (lower unit) shows a similar pattern to that of the underlying S‐4 The depositional and erosional areas were also controlled by the active faults F1 and F2The HD deepened from west to east with the deepest area located just along the fault margin The depositional centre was located north of the hanging wall of F2 and became infilled by a fan‐delta (Figure 7b) The aver-age sedimentary dip of the fan‐delta is 303deg The extent of the fan‐delta was larger than that of S‐4 (Table 34)

During deposition of S‐3 (middle unit) the uplifted source area shifted southwards and the depression expanded A major depositional sink was located north of the hanging wall of F2 (Figure 7c Table 4) Elevation differences existed

between the footwalls and the hanging walls of F1 and F2 although the topography was obviously gentler during this time‐span A braided fluvial area developed at the footwalls of the faults whereas a braid‐delta developed mainly on the hanging wall of F2 and the northern depositional centre (Figure 7c) The braid‐delta had a fairly large extent and an average depositional dip of 119deg (Tables 34)

During S‐1 + 2 the elevated erosional area shifted farther southwards and the entire south‐western area had a low to-pography An alluvial plain developed south of the footwalls of the faults whereas a braid‐delta developed at the hanging walls and in the depression with a very gentle slope of 096deg (Table 4 Figure 7d) The depositional system was dominated by a fairly thin delta body and a braid‐delta with a much larger extent (Table 3)

During the deposition of D‐3 the topography of the foot-wall areas and of the area south of the provenance area was similar to that during the underlying S‐1 + 2 The slope was steep (187deg) in the hanging walls of the boundary faults however and the depositional area increased to 198 km2 which provided an excellent condition for the deposition of a large braid‐delta (Figure 7e Table 4) This braid‐delta had a NE‐SW orientation and covered an area of 142 km2 its average thickness is some 200 m which results in the largest delta volume in the Palaeogene on the south‐western slope of the HD (Table 3)

The palaeogeomorphological reconstruction of D‐2 shows a gentler topography in the entire south‐western HD with a sink area of 375 km2 (Table 4) The main body of the braid‐delta was dominated by imbricated progradational seis-mic reflections and developed in the hanging walls of F1 and F2 whereas an alluvial‐plain facies probably developed in the footwall areas of the faults and to the south‐west of the uplifted area (Figure 7f) Although the extent of the delta reached its maximum the thickness of the delta was limited due to the gentle topography resulting in a small delta vol-ume (Table 3)

5 | RELATIONSHIPS BETWEEN THE VARIOUS ELEMENTS OF THE S2S SYSTEM

Quantitative relationships between the various elements of the S2S system have been established through the above‐mentioned calculations A strong positive correlation is clearly present between the rate of tectonic subsidence the average fault activity and the average growth index of the boundary faults F1 and F2 (Figure 8ab) The rate of tectonic subsidence can therefore be used in the following as the pri-mary proxy to represent the intensity of the tectonic activity whereas the rate of fault activity and the growth index are used as secondary proxies

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The tectonic activity and the sediment‐supply rate show a positive relationship (Figures 8c 9a 10a) whereas the tec-tonic activity and the sink area of the basin show a negative relationship (Figures 8d 9b 10b) In contrast the tectonic activity has a positive relationship with the total accommo-dation space (Figures 8e 9c 10c Table 4) There is also a positive relationship between the average sedimentary dip of the fan‐ and braid‐deltas on the one hand and the tectonic activity on the other hand (Figures 8f 9d 10d)

The intensity of the tectonic activity correlates negatively with the extent of the sediment area but positively with the sediment volume (Figures 8g‐h 9e‐f 10e‐f) The different responses of the sediment area and the volume to the tectonic activity are caused by variations in the thicknesses of the sed-imentary units (Table 3)

There is also a positive relationship between the average seismic progradation dip of the fan‐ and braid‐deltas and the tectonic activity (Figures 8i 9g 10g) strong tectonic activ-ity usually formed deltas that are characterized by a chaotic progradational or oblique progradational seismic reflection such as SF 1 and 2 in S‐3 (lower unit) and S‐4 (Figures S3ndashS7) The minimum tectonic activity during Members S‐1 + 2 and D‐2 are reflected by dominantly shingled progradational seismic facies in the delta interior (Figures S10ndashS11)

In addition we find that the sediment area sediment vol-ume and average seismic progradation dip of the fan‐ and braid‐deltas correlate positively with the sediment‐supply rate (Figure 11a b and c) but negatively with the basin sink area (Figure 11d e and f) Both the sediment volume and the average seismic progradation dip of the fan‐ and braid‐deltas

F I G U R E 8 (a‐b) Relationships between the tectonic‐subsidence rate and tectonics (c‐i) Relationships between tectonic activity and sedimentary source‐to‐sink parameters Input data regarding the tectonic activity are from Table 2 those regarding the source‐to‐sink parameters data are from Tables 3 and 4 Regression‐line equations and coefficients of determination (R2) are shown for all diagrams

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show a positive relationship with the total accommodation space (Figure 11hi) However no obvious relationship ap-pears to be present between the sediment area and the total accommodation space (G) Both the sediment area and the average seismic progradation dip of the fan‐ and braid‐deltas correlate well with the average sedimentary dip of the fan‐ and braid‐deltas (Figure 11km) A poor correlation is found between the sediment volume and the average sedimentary dip of the fan‐ and braid‐deltas

6 | DISCUSSION

61 | Analysis of the influence of tectonic activity on the source area accommodation space geomorphology and sediment supplyA high relief and large drainage area usually can generate a large sediment supply (Leeder Harris amp Kirkby 1998 Syvitski amp Milliman 2007) Although the erosional area for the fan and delta system cannot be estimated because of the

limited data coverage the exposed area within the study area can be calculated The calculations show a generally decreas-ing trend of the source area from S‐4 (501 km2) to D‐2 (58 km2 Figure7 Table 4) The calculated exposed area cannot fully represent the true source area however but the evolu-tionary trend of the source area can be used as a proxy to indi-cate the relative influence on the change in sediment volume This trend is consistent with the decrease in sediment volume from S‐4 (2126 km3) to D‐2 (175 km3 Table 2) The relief is difficult to reconstruct in this case but variations in the fault‐activity rate (here taken as the tectonic‐subsidence rate) can create local elevation differences and can therefore be used as proxies for the trends in the relief development The relief shows an overall decreasing trend from S‐4 to D‐2 except for D‐3 this correlates well with the sediment volume (Figure 8h) Although the drainage area of D‐3 was smaller than that of D‐2 because of the high tectonic‐subsidence rate (result-ing in a high relief) D‐3 is thicker and shows a larger sedi-ment volume than the overlying D‐2 (Table 3) D‐3 is thinner than S‐4 + 3 but the larger source area resulted in a larger

F I G U R E 9 General relationships between the average fault‐growth index of F1 and F2 (AFGIF1‐F2) and sedimentary source‐to‐sink parameters The average fault‐growth index of F1 and F2 (AFGIF1‐F2) data in this figure are from Table 2 The source‐to‐sink parameters data are from Table 4 Regression‐line equations and the coefficients of determination are shown in each diagram

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sediment volume and supply rate (Table 3 Figure8ch) Therefore both the fault‐induced relief and the drainage area affected the sediment‐supply rate and the sediment volume in the sink

The changes in accommodation space during the vari-ous phases of the Palaeogene in the south‐western HD are clear from the estimated tectonic subsiding rate (Table 2) The correlations between the intensity of the tectonic activ-ity and the extent of the depositional sink area (Figures 8d 9b 10b) between the intensity of the tectonic activity and the total accommodation space and between the intensity of the tectonic activity and the morphology in the sink area (Figures 8e‐f 9c‐d 10c‐d) clearly show that strong tectonic activity resulted in a larger accommodation capacity of the sink

In particular the main subsiding area tended to form steeper slopes However the extent of the main subsiding sink area diminished (Figure 8d) with increasing tectonic activity which was possibly due to the relatively small sub-siding centre in the tectonically active basins It can thus be deduced that tectonic activity not only controlled the sedi-ment supply and the variation in accommodation space but

also determined the changes in the topography of the sedi-mentary basins and the extent of the main depositional areas in the tectonically active basins

62 | Analysis of the influence of tectonic activity on the size and internal stacking pattern of the delta depositional systemThe above data and considerations indicate that the tectonic activity was closely related to the sediment supply accom-modation space and morphology of the sink area which are possibly the most important factors affecting the extent and stacking pattern of the sedimentary facies (cf Cope et al 2010 DeCelles Kapp Ding amp Gehrels 2007 Leeder 2011 Olsen 1997 Simon et al 2017)

Statistical analysis indicates that the sediment‐supply rate has a strong positive correlation with the volume of the depositional system a moderate correlation with the seismic progradational dip in the depositional system and a poor cor-relation with the size of the depositional area (Figure 11a‐c) A larger sink area corresponded to a larger fanbraid‐delta a gentler seismic progradational angle and a reduced volume

F I G U R E 1 0 General relationships between average fault activity rate of F1 and F2 (RFAA‐F1‐F2) and sedimentary source‐to‐sink parameters The average fault activity rate of F1 and F2 (RFAA‐F1‐F2) data in this figure are from Table 2 The source‐to‐sink parameters data are from Table 4 Regression line equations and the coefficients of determination are shown in each diagram

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of the fan or braid‐delta which was possibly related to a re-duced sedimentary dip and thinner sediments (Figure 11d‐f) The total accommodation space in the basin correlates well

with the volume of the depositional system to some degree with the seismic progradational dip and poorly with the ex-tent of the depositional system area (Figure 11g‐i) These

FIGURE 11 Relationships between various parameters involved in the source‐to‐sink system (a‐c) Relationships between sediment supply and characteristics of the depositional system (extent volume and DPSA of the sediments) (d‐f) Relationships between the sink area of the basin and characteristics of the depositional system (g‐i) Relationships between the total accommodation space (AT) and the characteristics of the depositional system (j) Relationship between the accommodation‐spacesediment‐supply ratio (AS) and the DPSA of the sediments (k‐m) Relationships between the sedimentary dip and the characteristics of the depositional system The data regarding sediment supply basin sink area total accommodation space accommodation‐spacesediment‐supply ratio and sedimentary dips are from Table 4 The extent volume and DPSA of the sedimentary facies are from Table 3 Note the seemingly obvious polynomial (quadratic) relationship between the sedimentary dip and the sediment volume (L) The trend line in (L) suggests the following relationships between sediment volume and sedimentary slope in a rift or tectonically active basin (1) a very steep sedimentary slope is unfavourable for sediment accumulation (2) an appropriate sedimentary slope is favourable for preservation of depositional systems eg when the sedimentary slope in (L) is about 25degndash32deg the sediment volume reaches its largest value (3) a very gentle sedimentary slope will lead to a decrease of the sediment volume possibly due to weakening of the drainage system and thinner sediments

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relationships are clear evidence that the size of the sink area controlled the extent of the depositional system during the rifting of the lacustrine basin and that the rate of sediment supply and the accommodation space had a significant in-fluence on the total sedimentary volume as well as on the internal stacking pattern of the depositional system

We here use the ratio of the tectonic‐subsidence rate and the sediment‐supply rate as a proxy to indicate the ratio be-tween accommodation space and sediment‐supply rate (AS) (Table 4) AS has a strong influence on the internal stacking pattern of the depositional systems in the lacustrine rift basin (Figure 11j) This might be because the basin was small and because abundant and rapid material was supplied due

to intense tectonic activity (cf Catuneanu et al 2009 Liro 1993) and a favourable local climate (eg Bohacs Carroll Neal amp Mankiewicz 2000 Perlmutter amp Matthews 1989) The sediment supply still had a significant influence on the main subsidence area of the lacustrine basins and deposi-tional systems

In addition the basin slope significantly influenced the extent of the depositional system (Figure 11k) and had a polynomial relationship with its volume (Figure 11l) This relationship indicates that more intense tectonic activity and a steeper depositional slope were not favourable for sediment accumulation over a large extent in the lacustrine basin On the contrary these sediments were usually transported to a

F I G U R E 1 2 Tectonic differential activities and resulting patterns of the source‐to‐sink system on the south‐western slope of the HD during the Palaeogene (a) Development during phases of intense tectonics (Member 4 to the lower part of Member 3 of the Shahejie Fm) (b) Development during phases of somewhat less tectonic activity (middle part of Member 3 of the Shahejie Fm and Member 3 of the Dongying Fm) (c) Development during phases of weak tectonic activity (Members 1 and 2 of the Shahejie Fm and Member 2 of the Dongying Fm) The intensity of tectonic activity in the lacustrine rift basin had a significant influence on the development and extent of each unit of the source‐to‐sink system as well as on the type and dimensions of the depositional systems The present study indicates that probably sublacustrine fans developed (see for example Figure S4b) during phases with relatively strong tectonic activity This is not really clear from the seismic‐reflection data but possibly due to the small sizes of these sublacustrine fans Moreover lithofacies and core data are not available for the south‐western part of the study area The present contribution therefore focuses on the fan‐deltas and braid‐deltas regarding the sedimentary facies analysis the sublacustrine fans that probably developed in the deep or semi‐deep lake are presented just as a likely feature

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relatively small sink area with a fairly large accommodation space Finally stronger tectonic activity resulted in steeper depositional slopes (Figure 8f) which further controlled the hydrodynamic conditions and differential discharge when the sediments were deposited The strong correlation between the depositional slope and the deltas dip (Figure 11m) suggests that the differences in topography due to tectonics must be considered as one of the most critical factors that controlled the internal stacking pattern of the delta deposits

63 | Significance of the present study for other source‐to‐sink systems of lacustrine rift basins

631 | Summary of the source‐to‐sink systems in the HDIn lacustrine rift basins the tectonic setting is probably the main factor that determines the development of the S2S sys-tem but differential tectonic activities lead to variations in the basic characteristics of the S2S system Tectonic activity was most intense during S‐3 (lower unit) and during S‐4 and caused both a strong uplift of the source area and the devel-opment of depressions in the basin that formed a sink (Figure 12a) Strong tectonic activity in the S2S system during these time‐spans led to a high sediment‐supply rate steeper slopes a larger accommodation space and deposition of several fan‐deltas that are characterized by a fairly steep seismic progra-dational angle

The tectonic activity decreased during S‐3 (middle unit) and during D‐3 The S2S system that was present during this time‐span mainly concerned a rising area that shifted south-wards developing an alluvial plain between the erosional area and the sink area thus increasing the distance from source to sink (Figure 12b) Simultaneously the sediment‐supply rate and the accommodation space also changed and braid‐deltas could thus develop with larger volumes and gentler seismic progradational dips

Tectonic activity was clearly less intense during S‐1 + 2 and D‐2 The rising area had shifted further southwards cre-ating a wider alluvial plain connecting the source area to the sink in the HD (Figure 12c) At this stage stable tectonic activity led to relatively less sediment supply a gentle slope less accommodation space and the development of several braid‐deltas with a fairly gentle seismic progradational angle

632 | Wider implications and limitationsSoslashmme et al (2009) proposed that the elements of S2S sys-tems are genetically related and that quantitative correla-tions exist among these elements Other studies also suggest that the size of the drainage basin is correlated to the size of the fan developing on the basin floor (eg Blum et al

2017 Snedden et al 2018) and to the size of the river chan-nel (eg Milliken et al 2018) Helland‐Hansen Soslashmme Martinsen Lunt and Thurmond (2016) suggest a simplified subdivision of S2S systems into three main categories (a) Steep‐Short‐Deep (steep onshore and offshore gradients short distance between source and sink and deep offshore waters) (b) Wide‐Deep (low‐gradient shelf‐catchment area and deep offshore waters) and (c) Wide‐Shallow (relatively shallow offshore waters and a wide low‐gradient catchment area) systems

The present study indicates that the alluvial plain roughly corresponds to the alluvial‐shelf unit in marine basins al-though with a much smaller width and extent in the lacustrine rift basins than would have been the case on a continental shelf Faults F1 and F2 along the slope belt correspond to the slope of classical S2S systems whereas the shore‐shallow‐deep lake area can be compared with the basin floor (Soslashmme et al 2009) S‐4 and S‐3 (lower unit) can be roughly clas-sified as Steep‐Short‐Deep systems whereas the overlying S‐1 + 2and D‐2 can be classified as the Wide‐Shallow sys-tems that Helland‐Hansen et al (2016) defined During the deposition of S‐4 and S‐3 (lower unit) the strong tectonic activity caused a high relief of the source area a narrow allu-vial plain and a relatively deep lake The subsequently wan-ing tectonic activity resulted in a lower relief of the source area a wider alluvial plain and a shallower lake Although the absolute values of these elements in lacustrine basins are much smaller than those of marine basins the ratio between these elements in both settings is comparable Typically in a lacustrine basin a transformation from a Steep‐Short‐Deep system (S‐4 and S‐3 (lower unit)) to a Wide‐Shallow system (S‐1 + 2ampD‐2) occurs within a few million years Although the basin geomorphology has experienced signif-icant changes from S‐4 to D‐2 the quantitative relationships between tectonic activity sediment‐supply rate accommoda-tion space and sedimentary dip of the delta systems did not change significantly (eg Figures 8 and 11) The analytical approaches applied and quantitative relationship established here can help analyse other lacustrine basins worldwide and may even act as a reference for the analysis of marine basins

Our study focuses mainly on the influences of tectonic activity on the elements of the depositional sink Other pa-rameters (eg climate and lithology) were not considered in detail Studies on modern and ancient systems suggest that the climate and lithology also have a great influence on the sediment supply and distribution in the basin (eg Carroll Chetel amp Smith 2006 Hovius amp Leeder 1998 Syvitski amp Milliman 2007 Zhang et al 2018) For exam-ple climate variations between glacials and inter‐glacials have resulted in largely different sediment‐supply rates and in significant differences in the sizes of the Quaternary sub-marine fans in the north‐western Gulf of Mexico (Blum amp Hattier‐Womack 2009) We acknowledge the importance

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of climate and lithology for S2S systems and we are con-vinced that these elements can significantly affect the S2S systems in other cases(eg modern systems and systems influenced by glacialinterglacial alternations) These fac-tors were not really relevant for the present study however because no significant differences in lithology were present in the source areas and because we focus on the changes at a million‐year scale which implies that the tectonic ac-tivity has a first‐order control on the development of S2S elements in the investigated rift basin

7 | CONCLUSIONS

We have calculated the tectonic‐subsidence history the growth index and the activity rate of the main boundary faults (F1 and F2) and various S2S parameters of six Palaeogene rock units on the south‐western slope of the HD Based on the values found for these parameters quantitative corre-lation were established for the tectonic activity and other S2Sparameters in the basinal sink This leads to the follow-ing conclusions

1 The positive correlation between the intensity of fault activity and the tectonic‐subsidence rate is a strong indication for a distinct control by the tectonic activity of the syn‐depositional rifting of the tectonically active basin

2 The tectonic activity was quantitatively related to the sediment supply accommodation space and morphology of the sink area The relationship between tectonic activ-ity and depositional systems is reflected by changes in critical factors such as sediment supply accommodation space and dip of the sink area These critical factors were probably the most important factors that led to changes in the size and internal stacking pattern of the sedimentary facies

3 Differential tectonic activity led to changes in the char-acteristics of the S2S system on the south‐western slope of the HD The strongest tectonic activity which oc-curred during S‐3 (lower unit) and during S‐4 led to the largest provenance area adjacent to the sink area to a high sediment‐supply rate to steeper slopes to a larger accommodation space and controlled the development of several fan‐deltas Diminished tectonic activity dur-ing S‐3 (middle unit) and during D‐3 led to a decrease in uplift an increased width of the alluvial plain an in-creased transport distance a decrease in the sediment‐supply rate and accommodation space and resulted in the development of braid‐deltas with a large volume During S‐1 + 2 and D‐2 stable tectonic activity led to a lower sediment‐supply rate a gentle depositional slope and a smaller accommodation space resulting in the

development of several braid‐deltas with gentler seis-mic progradational angles

4 The analytical approaches applied and the quantitative re-lationships established here can help analyse other lacus-trine basins worldwide and may even act as a reference for the study of marine basins

ACKNOWLEDGEMENTS

We thank Dr Sarah Boulton and Dr Chenlin Gong as well as the Associate Editor of Basin Research Dr Craig Magee for their constructive comments on the manuscript This study was funded by the National Science and Technology Major Project (Exploration Technologies for Offshore Hidden OilGas) (project no 2016ZX05024‐003‐003) the National Natural Science Foundations of China (project no 41676050) and the Fundamental Research Funds for the Central Universities (2652014037)

REFERENCES

Allen P A (2008a) From landscapes into geological history Nature 451 274ndash276 https doiorg101038natur e06586

Allen P A (2008b) Time scales of tectonic landscapes and their sed-iment routing systems In Landscape evolution Denudation cli-mate and tectonics over different time and space scales (Ed by Gallagher K Jones S J amp Wainwright J) Geological Society London Special Publications 296 7ndash28

Allen P A Armitage J J Carter A Duller R A Michael N A Sinclair H D hellip Whittaker A C (2013) The Qs problem Sediment volumetric balance of proximal foreland basin systems Sedimentology 60 102ndash130

Amorosi A Maselli V amp Trincardi F (2016) Onshore to offshore anatomy of a late Quaternary source‐to‐sink system (Po Plain‐Adriatic Sea Italy) Earth‐Science Reviews 153 212ndash237 https doiorg101016jearsc irev201510010

Anderson J B Wallace D J Simms A R Rodriguez A B Weight R W R amp Taha Z P (2016) Recycling sediments between source and sink during a eustatic cycle Systems of late Quaternary northwestern Gulf of Mexico Basin Earth‐Science Reviews 153 111ndash138 https doiorg101016jearsc irev201510014

Anthony E J amp Julian M (1999) Source‐to‐sink sediment trans-fers environmental engineering and hazard mitigation in the steep Var River catchment French Riviera southeastern France Geomorphology 31 337ndash354 https doiorg101016S0169-555X(99)00088-4

Athy L F (1930) Density porosity and compaction of sedimentary rocks AAPG Bulletin 14 1ndash24

Bhattacharya J P Copeland P Lawton T F amp Holbrook J (2016) Estimation of source area river palaeo‐discharge palaeoslope and sediment budgets of linked deep‐time depositional systems and im-plications for hydrocarbon potential Earth‐Science Reviews 153 77ndash110

Blum M D amp Hattier‐Womack J (2009) Climate change sea‐level change and fluvial sediment supply to deepwater depositional

| 591EAGE

LIU et aL

over 5000 km2 of 3‐D seismic surveys in the HD Both the 2‐D and the 3‐D seismic data have a vertical sampling rate of 2 ms and were processed to zero phases They were dis-played as reversed polarities The 3‐D seismic data have a dominant frequency of 15ndash40 Hz and an average velocity of 3600 ms (calculated from Well W25) with a vertical resolu-tion of 22ndash60 m

Cutting log and logging data from 25 wells have been used for the present study Core data were made available for 11 wells with a total length of about 1000 m Integration of these well and seismic data helped establishing a regional stratigraphic framework through calibration of seismic syn-thetic records seismic units and interpretation of the sedimen-tary facies (Table 1) In total eight horizons were interpreted

respectively as T7 (dated at 447 Ma) T63 (4223 Ma) T62 (4044 Ma) T5 (3790 Ma) T3(3328 Ma) T31 (2671 Ma) and T2 (2338 Ma) The successions between these horizons represent different members of the Dongying and Shahejie Formations The codes and interpretation of these members are provided in Figure 2 The quantitative compilation of the sedimentary system and the palaeogeomorphological maps are based on these results

32 | Quantitative estimation of tectonic activityThe tectonic‐subsidence rate fault‐growth index and fault‐activity rate are used in the present contribution to detail

F I G U R E 2 Lithostratigraphy and sequences of the HD The lithological data and interpretations are based mainly on a combination of data from Wells W1 W18 and W25 Ages are based on data obtained from CNOOC Tianjin Branch The tectonic stages sedimentary environment and fossil associations are modified after Liu Xia et al (2015a) Note that newly acquired 3‐D seismic data indicate that the Kongdian Fm is possibly absent in the HD which differs from the results presented by Liu Xia et al (2015a) D‐1 = Member 1 of the Dongying Fm D‐2 = Member 2 of the Dongying Fm D‐3 = Member 3 of the Dongying Fm S‐1 amp 2 = Members 1 and 2 of the Shahejie Fm S‐3 = Member 3 of the Shahejie Fm S‐4 = Member 4 of the Shahejie Fm

592 | EAGE

LIU et aL

the tectonic history and intensity We have selected Well W25 (Figure 1c) because it is the only drilling well in the south‐eastern HD for simulation of the subsidence history This simulation is based on our reconstructed stratigraphic framework and age information provided by the TBCNOOC (Figure 2)

Correction for compaction is critical in quantitative sim-ulation of the subsidence history and rate The influence of the water depth during sedimentation is considered negligible since the Bohai Bay Basin was a lacustrine basin Differences in the acoustic travel times have been used to calculate the porosities at the corresponding depths (cf Wylliel Gregory amp Gardner 1958) Subsequently the porosities of the vari-ous types of lithology (mainly sandstone and mudstone) at different depths were determined by logging and the poros-itydepth relationship was established by statistic fitting (cf Athy 1930) Back‐stripping of the selected strata was per-formed layer‐by‐layer to calculate the top and bottom bound-ary depths at different times in the geological development (cf Perrie amp Qiublier 1974) thus distinguishing between the compaction history the tectonic subsidence and the total subsidence during the Palaeogene (Figure 3 Table 2 supple-mentary text)

The normal boundary faults (F1 amp F2) controlling depo-sition on the south‐western margin of the HD have been

selected to calculate the fault‐growth index and the fault‐ac-tivity rate (Figure 1c) The fault‐growth index sometimes also called the ldquoexpansion indexrdquo is the ratio between the stratigraphic thickness of the hanging wall and that of the footwall of a growth fault The fault‐activity rate is the ratio between the thicknesses of the sedimentary successions in the hanging wall and the foot wall resulting from fault activ-ity during a specific depositional phase corresponding to the length of the time‐span during which the investigated succes-sion accumulated ie (Zhou Niu amp Teng 2009)

where RF is the fault‐activity rate in mMa T is the length of the time‐span during which the investigated succession ac-cumulated (in Ma) STh is the stratigraphic thickness of the hanging wall (in m) and STf is the stratigraphic thickness of the footwall (in m) For the calculation of the stratigraphic thickness the conversion from two‐way travel time to depth was made by analysis of the P‐wave velocity in the wells The growth index and the activity rate of the main faults have thus been calculated for several locations (Table 2 Figure 1c) which was considered necessary because of the differ-ent successive stages in the morphological evolution of the

RF=ΔST∕T =

(

SThminusST

f

)

∕T

F I G U R E 3 Palaeogene burial history of the HD (a) Cumulative subsidence (b) Subsidence during the development of the individual members D‐1 = Member 1 of the Dongying Fm D‐2 = Member 2 of the Dongying Fm D‐3 = Member 3 of the Dongying Fm S‐1 amp 2 = Members 1 and 2 of the Shahejie Fm S‐3 = Member 3 of the Shahejie Fm S‐4 = Member 4 of the Shahejie Fm

| 593EAGE

LIU et aL

basin‐controlling faults and because of the changes in the intensity of the fault activity

33 | Quantitative calculation of S2S system parameters

331 | Area and volume of the sedimentary faciesQuantitative calculation of the dimensions of sedimentary facies requires reliable estimates of the lateral extent and thickness of the sediments involved For these calculations first the maxi-mum extent of the specific units under study (fan‐deltas braid‐deltas etc) at different times was determined in plan view based on the combined interpretation obtained from seismic facies lithofacies and the outer boundaries of the sediment bodies Subsequently the outcomes were digitalized and used as input for a 3‐D survey by GEOFRAME Detailed calculations of the sedi-ment bodies extents were conducted using the PLANIMETER tool in the BASEMAP window of GEOFRAME

This was followed by the selection of several seismic sec-tions across the sediment body in order to identify the lower

and upper boundaries as well as to calculate the maximum minimum and average thickness (see Amorosi Maselli amp Trincardi 2016 Liu et al 2017) Finally we used a colum-nar body with irregular base and the same height to represent the irregular sediment body The formula for volume calcu-lation is as follows (Figure 4 Table 3 supplementary text)

where VS is the volume of the sediment (in km3) AS is the horizontal surface area of the irregular base of the sediment (in km2) and H is the height (average thickness) of the sed-iment (in m) Detailed calculations of the thickness were conducted using the AREAL tool in the SEIS3DVSEIS2DV window of GEOFRAME

332 | Determination of the depositional dip of the delta surface due to progradationThe term ldquodepositional diprdquo is used here to indicate the inclination of a dipping sedimentary surface Horizon flat-tening was used to analyse and calculate the morphology of the underlying strata First the maximum flooding surface ndash approximately corresponding to the palaeo‐sedimentary surface (Lin et al 2012) ndash of each unit under study was interpreted it was subsequently flattened to calculate the original depositional dip (Figure 5d) with the formula

where DSD is the sedimentary dip (in degrees) dy is the verti-cal thickness between the lower boundary of the sedimentary unit and the ancient sedimentary surface in the depositional centre (in m) and dx is the distance from the apex of the delta to its depositional centre (in m)

Two to four seismic sections have been selected to calcu-late the average sedimentary dip of each individual delta with the following formula

where DSDA is the average sedimentary dip of a sediment (in degrees) and n is the number of seismic sections

The seismic progradational angle of the deltas interior has been calculated by the horizon‐flattening method (Figure 5e) which is expressed by the formula

VS=A

StimesH

DSD

= tanminus1 (dy∕dx)

DSDA

=

(

nsum

i=1

DSDi

)

∕n

DP= tan

minus1 (dy∕dx)

F I G U R E 4 Schematic diagram showing the calculation of the volume of a sediment (a) is an irregular sediment body Volume calculation of cuboids was used for reference to calculate the volume of an irregular sedimentary body ie the volume of an irregular sediment body equals the area of the irregular bottoms times height (b) 3ndash4 seismic lines along the sedimentary body are selected and the thickness of the sedimentary body is determined at intervals of 10 seismic traces (c) when a thickness grid covering the entire sedimentary body in space is acquired the average thickness of all counted thicknesses can be calculated as the height of the irregular sediment body (d)

594 | EAGE

LIU et aL

where DP is the seismic progradational dip (in degrees) The average dip angle is obtained from only one seismic sec-tion because of the variations in the progradational seismic event of the delta on the same seismic line

where DPA is the average seismic progradational dip in a spe-cific seismic section (in degrees) and n is the number of seis-mic progradational events

Based on the calculated average dip of one seismic sec-tion the average progradational dip of a specific sediment body can be calculated with the formula

DPA

=

(

nsum

i=1

DPi

)

∕n

F I G U R E 5 Detailed calculations of the sedimentary dip and the progradational seismic event dip of the delta interior taking the progradation seismic reflection of the delta developed in Member 3 of the Dongying Formation as an example The locations of the seismic lines are shown in Figure 1c Based on the interpretation of the stratigraphic and seismic facies visible in the original seismic lines (a) the topset or the maximum flooding surface (MFS) corresponding to the delta was flattened (b) Taking into account the water depth during sedimentation the sedimentary dip (d) and the progradational seismic event dip of the delta interior (e) can be calculated DSD = depositional dip in a specific seismic section DSDA = average depositional dip of a specific sedimentary unit DP = seismic progradational dip DPA = average seismic progradational dip

| 595EAGE

LIU et aL

TA

BL

E 1

In

terp

reta

tion

of th

e m

ain

sedi

men

tary

faci

es in

the

Pale

ogen

e of

the

Hua

nghe

kou

Dep

ress

ion

Evi

denc

e of

fan

delta

s and

bra

id d

elta

s in

wel

ls W

1 an

d W

18 c

omes

from

Liu

Xia

et a

l (2

015a

)

Form

atio

n an

d m

embe

raSe

ismic

faci

esEx

ampl

esLi

thof

acie

sLi

thol

ogy

Wel

l amp c

ore

exam

ples

Dep

ositi

onal

en

viro

nmen

tPr

edic

ted

res-

ervo

ir q

ualit

y

D‐2

Seis

mic

Fac

ies 5

mod

erat

e co

ntin

uous

lo

w‐a

mpl

itude

and

a sh

ingl

ed‐li

ke

prog

rada

tiona

l sei

smic

refle

ctio

n

Figu

re

Mul

tiple

upw

ard‐

coar

s-en

ing

litho

faci

es

asso

ciat

ions

Gre

y m

udst

ones

gre

y to

gre

yish

w

hite

pebb

ly fi

ne sa

ndst

ones

and

fin

e sa

ndst

ones

T25

Bra

id d

elta

Mod

erat

e to

hi

gh

D‐3

Seis

mic

Fac

ies 4

con

tinuo

us m

oder

-at

e‐to

high

‐am

plitu

de a

nd o

bliq

ue‐

to‐s

igm

oid

prog

rada

tiona

l sei

smic

re

flect

ion

Figu

re

Mul

tiple

upw

ard‐

coar

s-en

ing

litho

faci

es

asso

ciat

ions

Gre

yish

whi

te to

whi

te fi

ne

sand

ston

es s

iltst

ones

and

gre

y m

udst

ones

T25

Bra

id d

elta

Hig

h

Figu

re 7

e‐f

S‐1

+ 2

Seis

mic

Fac

ies 5

mod

erat

e co

ntin

uous

m

oder

ate‐

ampl

itude

and

shin

gled

‐like

pr

ogra

datio

nal s

eism

ic re

flect

ion

Figu

re

Mul

tiple

upw

ard‐

coar

s-en

ing

litho

faci

es

asso

ciat

ions

Dar

k gr

ey m

udst

ones

and

gre

yish

w

hite

to g

rey

mid

dle‐

to fi

ne‐

grai

ned

sand

ston

es

T25

Bra

id d

elta

Hig

h

S‐3

(mid

dle

unit)

Seis

mic

Fac

ies 3

har

dly

tom

oder

atel

y co

ntin

uous

low

‐am

plitu

de o

bliq

ue

prog

rada

tiona

l sei

smic

refle

ctio

n

Figu

re

Lith

ofac

ies 1

Gre

y to

gre

yish

whi

te sa

ndy

cong

lom

erat

esT2

5B

raid

del

taH

igh

Lith

ofac

ies 2

Thic

k gr

ey m

iddl

e‐to

fine

‐gra

ined

sa

ndst

ones

Figu

re 7

a‐d

Lith

ofac

ies 3

Gre

y m

udst

ones

inte

rbed

ded

with

gr

ey fi

ne sa

ndst

ones

and

gre

y m

uddy

silts

tone

s

Lith

ofac

ies 4

Thic

k da

rk g

rey

mud

ston

es

S‐3

(low

er

unit)

Seis

mic

Fac

ies 2

cha

otic

prog

rada

-tio

nal t

o ob

lique

pro

grad

atio

nal

seis

mic

faci

es

Figu

re

Pe

bbly

sand

ston

es in

terb

edde

d w

ith

thin

bro

wn‐

grey

mud

ston

esb

row

n sa

ndy

cong

lom

erat

ess

ands

tone

s in-

terb

edde

d w

ith th

in m

udst

ones

thic

k m

udst

ones

inte

rbed

ded

with

th

in sa

ndst

ones

or p

ebbl

y fin

e sa

ndst

ones

T1Fa

n de

ltaM

oder

ate

S‐4

Seis

mic

Fac

ies 1

dis

cont

inuo

us to

con

-tin

uous

low

‐tohi

gh‐a

mpl

itude

cha

otic

pr

ogra

datio

nal s

eism

ic re

flect

ion

Figu

re

Figu

re

Fig

ure

and

Fi

gure

Lith

ofac

ies 1

Gre

y pe

bbly

sand

ston

es c

oars

e sa

ndst

ones

T18

Fan

delta

sM

oder

ate

Lith

ofac

ies 2

Ash

‐bla

ck m

udst

ones

inte

rbed

-de

d w

ith th

in g

rey

fine‐

grai

ned

sand

ston

es

Lith

ofac

ies 3

Ash

‐bla

ck m

udst

ones

inte

rbed

ded

with

peb

bly

sand

ston

esa D

= D

ongy

ing

Fm

S =

Sha

hejie

Fm

The

num

ber i

ndic

ates

the

num

ber o

f the

mem

ber

596 | EAGE

LIU et aL

TA

BL

E 2

Es

timat

ion

stat

istic

s of t

he te

cton

ic‐s

ubsi

denc

e ra

te g

row

th in

dex

and

activ

ity ra

te o

f fau

lts F

1 an

d F2

S1

S2

and

S3 a

re th

e ca

lcul

atio

n lo

catio

ns o

f F1

and

F2 (s

ee F

igur

e 1c

) th

e co

rres

pond

ing

num

bers

are

F1‐

S1 F

1‐S2

F1‐

S3 F

2‐S1

F2‐

S2 a

nd F

2‐S3

res

pect

ivel

y

Form

atio

n an

d m

embe

raA

ge

(Ma)

R TS

(m

Ma)

b

Faul

t‐gro

wth

inde

xFa

ult‐a

ctiv

ity r

ate

(mM

a)

AFG

I F1‐

F2c

R FA

A‐F

1‐F2

d

S1S2

S3A

vera

geS1

S2S3

aver

age

F1F2

F1F2

F1F2

F1F2

F1F2

F1F2

F1F2

F1F2

D‐1

233

75ndash

267

1450

00

111

106

109

110

107

109

109

108

389

270

389

479

270

389

349

379

109

364

D‐2

267

14ndash

302

060

00

139

130

138

140

137

133

138

134

320

730

29

341

442

62

329

534

98

330

535

96

136

345

1

D‐3

302

0ndash33

278

190

002

002

052

102

342

032

052

042

1579

67

104

0010

372

111

3485

59

762

989

66

972

12

1093

44

S‐1

+ 2

332

78ndash

378

9250

00

145

136

142

147

155

145

148

143

122

211

36

105

915

78

587

176

39

5614

92

146

122

4

S‐3

(mid

dle

unit)

378

92ndash

404

3812

500

131

202

192

242

175

257

166

234

335

140

88

490

380

62

215

510

919

347

076

90

205

558

0

S‐3

(low

er

unit)

404

38ndash

422

3135

500

284

343

302

395

342

389

309

376

737

185

37

104

4016

956

742

820

480

841

315

324

343

118

69

S‐4

422

31ndash

447

300

002

512

921

584

173

023

332

373

4791

33

106

4357

58

151

8811

007

121

5186

33

126

612

9210

647

a D =

Don

gyin

g Fm

S

= S

hahe

jie F

m T

he n

umbe

r ind

icat

es th

e nu

mbe

r of t

he m

embe

r b R T

S = te

cton

ic‐s

ubsi

denc

e ra

te

c AFG

I F1‐

F2 =

ave

rage

faul

t‐gro

wth

inde

x of

F1

and

F2

d R FA

A‐F

1‐F2

= a

vera

ge fa

ult‐a

ctiv

ity ra

te o

f F1

and

F2

| 597EAGE

LIU et aL

TA

BL

E 3

C

alcu

latio

n ch

art o

f the

sedi

men

tary

‐fac

ies d

imen

sion

s and

the

inte

rnal

pro

grad

atio

nal s

eism

ic e

vent

dip

The

spat

ial e

xten

t is s

how

n in

Fig

ure

7

Form

atio

nand

mem

bera

Sedi

men

tary

faci

esSe

ismic

sect

ions

Thic

knes

s (m

)

Are

a (k

m2 )

Vol

ume

(km

3 )To

tal v

olum

e (k

m3 )

DPb

Max

M

in

Ave

rage

DPA

DPS

A

D‐2

Bra

id d

elta

Figu

re a

176

0075

00

107

7016

246

175

017

50

157

156

Figu

re b

174

0080

00

157

Figu

re c

218

0080

00

152

D‐3

Bra

id d

elta

Figu

re a

285

0011

400

200

5014

219

285

128

51

268

285

Figu

re b

295

0099

00

309

Figu

re c

296

0078

00

309

Figu

re d

284

0091

00

254

S‐1

+ 2

Bra

id d

elta

Figu

re a

178

0089

00

136

7512

023

164

416

44

172

177

Figu

re b

185

0095

00

176

Figu

re c

236

0010

500

193

Figu

re d

209

0011

400

166

S‐3

(mid

dle

unit)

Bra

id d

elta

Figu

re a

274

0010

100

223

7587

87

196

619

66

213

225

Figu

re b

279

0083

00

225

Figu

re c

292

0086

00

235

Figu

re d

296

0086

00

226

S‐3

(low

er u

nit)

Fan

delta

Figu

re a

428

8623

903

374

0062

89

235

223

52

301

305

Figu

re b

432

5522

071

325

Figu

re c

473

0920

583

312

Figu

re d

450

8325

500

283

S‐4

Fan

delta

1Fi

gure

a30

700

483

929

200

107

03

1221

26c

423

365

Figu

re b

350

0010

728

439

Fan

delta

2Fi

gure

a46

500

704

832

900

856

282

421

Figu

re b

379

0066

52

362

Fan

delta

3Fi

gure

a40

100

118

7841

100

186

27

654

21

Figu

re b

468

0016

718

309

Figu

re c

527

0015

127

387

Figu

re d

486

0014

844

297

Fan

delta

4Fi

gure

a42

800

151

2042

700

179

57

663

04

Figu

re b

512

0027

287

289

a D =

Don

gyin

g Fm

S

= S

hahe

jie F

m T

he n

umbe

r ind

icat

es th

e nu

mbe

r of t

he m

embe

r b D

P = se

ism

ic p

rogr

adat

iona

l dip

DPA

= a

vera

ge se

ism

ic p

rogr

adat

iona

l dip

DPS

A =

ave

rage

seis

mic

pro

grad

atio

nal d

ip o

fthe

sedi

men

t c 21

26

= to

tal j

oint

vol

umes

of f

an d

elta

s 1 2

3 a

nd 4

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where DPSA is the average seismic progradational dip of a sediment (in degrees) and n is the number of seismic sections

Detailed estimated results of the depositional dip and the seismic progradational dip of the delta are shown in Tables 3 and 4

333 | Provenance conditions and estimation of the sediment supplySystematic investigation by TBCNOOC of the regional uplift and provenance in the geological past has indicated that the main provenance areas around the HD existed alreadybefore the deposition of Member 3 of the Shahejie Fm (Zhou et al 2010) They include the Bonan Laibei and Kendong Highs (Figure 1b‐c Figure S1a‐b) However starting with the depo-sition of Members 1ndash2 of the Shahejie Fm (S‐1 + 2) (3789ndash3328 Ma) until the accumulation of the Dongying Formation (3328ndash2338 Ma) the Bonan and Laibei Highs subsided to below lake level and consequently stopped providing sedi-ment to the depression (Liu Xia et al 2015a) Only the Kendong High which remained a high for a long time re-mained a provenance area for the south‐western part of the

HD during this time‐span (Figure S1a) The Kendong High has therefore been selected as the site where the relationship between tectonics and depositional systems within the same provenance system could be studied best The distribution area of the Kendong High as the provenance area at different moments has been determined on the basis of numerous seis-mic interpretations through seismic terminations (eg onlap) and the absence of specific sediment units due to faulting

The sediment‐supply rate can be obtained by calculation of the volumes of the deltas and the duration of their forma-tion (cf Allen et al 2013 Lemons amp Chan 1999 Lemons Milligan amp Chan 1996) Although the stratigraphic ages are well‐known for each unit (Figure 2) there is no high‐resolu-tion age control for the top and base of each delta system The absolute age of the pertinent stratigraphic unit (Figure 2) is therefore used to represent the formation time of the individual deltas in the unit The thus calculated sediment‐supply rate rep-resents in our opinion the trend of the supply rate from bottom to top sufficiently well

334 | Estimation of the extent and accommodation space of the sink areaDetermination of the boundaries of the sink area is based on reconstructions of the morphology during the successive dep-ositional phases The extent of the sink area was estimated using the same calculations as for the area of the depositional system

DPSA

=

(

nsum

i=1

DPAi

)

∕n

F I G U R E 6 Vertical successions and representative examples of the various lithofacies (a) A fan‐delta in Well W18 (b‐e) Braid‐deltas in Well W25 (f) Grey to greyish white sandy conglomerate (deposits in braided channels) (g) Grey medium‐ to fine‐grained massive sandstone (mouth‐bar deposits) (h) Grey fine sandstone (distal sand bars) (i) Grey muddy siltstone with parallel bedding (prodelta) (j) Greyish white fine sandstone with convolute bedding (mouth bars) (k) Greyish white fine sandstone with boulders (mouth bars) Wireline logs show the spontaneous‐potential (SP) and gamma‐ray (GR) changes with depth Depth in metres For location of the cores see Figure 6bd

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Differences in base level and the original sedimentary sur-face define the accommodation space (Jervey 1988 Muto amp Steel 2000 Neal amp Abreu 2009 Wheeler 1964) The

accommodation space in the depositional area can be deter-mined on the basis of the thickness of the preserved sediments (Muto amp Steel 2000) This space is obviously controlled by

F I G U R E 7 Schematic morphology during the successive depositional phases The extent of the deltas the depositional sink area in the basin and the main features of the drainage systems are shown The extent of the deltas has been interpreted from seismic data and has been used for calculation of the surface area and volume of the various deltas (a) Shahejie Fm Member 4 (b) Shahejie Fm lower part of Member 3 (c) Shahejie Fm middle part of Member 3 (d) Shahejie Fm Members 1 and 2 (e) Dongying Fm Member 3 (f) Dongying Fm Member 2

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the rate of subsidence tectonic uplift and fluctuations of the lake level (Lemons amp Chan 1999) Changes in the lake level of the HD have not been investigated so that we take data on the tectonic‐subsidence rate as a proxy for changes in the accommodation space The total space is expressed in the equation (Table 4)

where AT represents the total accommodation space of the sink area (in km3) TS represents the tectonic subsidence (in m) and SA represents the surface area of the sink (in km2)

AT= TStimesSA∕1000

T A B L E 4 Estimation of the controlling factor parameters of the depositional system The distribution characteristics of the depositional sink in the basin are shown in Figure 7

Formation and membera

Sedimentary facies Seismic sections

DDb

RSSc(km3

Ma)Sink area (km2) AT

d(km3) ASeSource areaf(km2)DSD DSDA

D‐2 Braid delta Figure a 059 066 502 37542 7852 1195 58

Figure b 065

Figure c 074

D‐3 Braid delta Figure a 161 187 926 19823 11593 2051 252

Figure b 192

Figure c 215

Figure d 182

S‐1 + 2 Braid delta Figure a 086 096 356 28015 6463 1403 220

Figure b 094

Figure c 120

Figure d 083

S‐3 (middle unit) Braid delta Figure a 110 119 772 21756 6927 1619 355

Figure b 111

Figure c 129

Figure d 128

S‐3 (lower unit) Fan delta Figure a 307 303 1313 16506 10500 2705 482

Figure b 334

Figure c 332

Figure d 237

S‐4 Fan delta 1 Figure a 384 463g 861 14150 10481 3484 501

Figure b 379

Fan delta 2 Figure a 606

Figure b 498

Fan delta 3 Figure a 479

Figure b 499

Figure c 625

Figure d 553

Fan delta 4 Figure a 377

Figure b 226aD = Dongying Fm S = Shahejie Fm The number indicates the number of the member bDD = depositional dip DSD = depositional dip in a specific seismic section DSDA = average depositional dip of a specific sedimentary unit cRSS = sediment‐supply rate dAT = total accommodation space eAS = accommodation spacesediment supply fSource area = Denudation area within the seismic data coverage The complete erosional area cannot be estimated because of the limited data coverage g463 = the average depositional dip of fan deltas 1 2 3 and 4 Considering that the four fan deltas developed during S‐4 consist of sediment that was derived from the same provenance area and were deposited in the same time‐span the four fan deltas are taken as a whole when estimating the parameters of RSS the sink area AT and AS

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4 | ELEMENTS OF THE S2S SYSTEM

41 | Analysis of the seismic facies and stacking pattern of the main sedimentary faciesA comprehensive analysis of seismic data cores cutting log-gings and well‐logging curves by Liu Xia et al (2015a) in-dicated that the Palaeogene depositional systems of the HD included fan‐deltas braid‐deltas lake margins deep lakes etc The fan‐ and braid‐deltas have been chosen for a detailed seismic study that must reveal their internal texture and their stacking patterns Analysis of the progradational seismic‐re-flection types and of the seismic progradational dip is particu-larly helpful for a better understanding of the hydrodynamic conditions and sedimentary processes that resulted in these depositional systems Because the facies interpretation in this area has been done before and is not the focus of this work we here mainly describe the internal texture and their stack-ing patterns of the main sedimentary facies

The major facies of S‐4 is interpreted as a fan‐delta It is dominated by Seismic Facies 1 which is characterized by discontinuous to continuous low‐ to high‐amplitude and chaotic progradational seismic reflections (Figures S3ndashS6 Table 1) The average dip of the progradational seismic event is about 365deg (Table 3) Three lithofacies are associated with Seismic Facies 1 (Table 1) The coarser lithofacies 1 represents a fan‐delta front whereas the finer lithofacies 2 and 3 are prodelta deposits The overall coarsening‐upward succession facies stacking pattern (Figure 6a) discontinuous and chaotic seismic reflections and relatively steep slope of Seismic Facies 1 suggest a fan‐delta system developed under strong hydrodynamic conditions (Mitchum et al 1977)

The fan‐delta of the lower part of Member 3 of the Shahejie Fm (S‐3 [lower unit]) is dominated by Seismic Facies 2 which is characterized by chaotic progradational to oblique progradational seismic characteristics It has a typical wedge shape and is composed of two seismic‐reflection seg-ments (a) a moderately continuous low‐ to high‐amplitude chaotic seismic‐reflection segment located near boundary fault F2 and (b) a continuous moderate‐ to high‐amplitude and oblique progradational seismic reflection in a basinward direction (Figure S7 Table 1) No obvious upper or lower segments occur in SF 2 and the dip of the progradational seismic event in this segment is also relatively steep viz 305deg (Table 3)

The middle part of Member 3 of the Shahejie Fm (S‐3 [middle unit]) is characterized by a low‐ to moderate‐con-tinuous low‐amplitude and oblique progradational seismic reflection (Seismic Facies 3) and is interpreted as a braid‐delta (Figure S8 Table 1) The progradational seismic events are parallel or sub‐parallel to each other and dip less (aver-age 225deg) than Seismic Facies 1 and 2 (Table 3) Seismic

Facies 3 is associated with four lithofacies (Figure 6b Table 1) in Well T25 The complete succession of the braid‐delta consists of gravely to coarse‐grained sandstone (lithofacies 1) at the base (Figure 6f) massive bedded medium‐ to fine‐grained sandstones (lithofacies 2) and grey mudstones inter-bedded with grey fine sandstones and grey muddy siltstones (lithofacies 3) in the middle (Figures 6g and 6h) and thick dark grey mudstones (lithofacies 4) at the top (Figure 6i)

Member 3 of the Dongying Fm (D‐3) is characterized by Seismic Facies 4 a typically composite seismic progra-dation reflection configuration representing a braid‐delta system (Figure S9 Table 1) Seismic Facies 4 is composed of highly continuous moderate‐ to high‐amplitude and pro-gradational seismic reflections that represent well‐developed deltaic topsets and bottomsets The topset segments of SF 4 are nearly horizontal or dip only gently (Table 3) The foreset segments form thicker lenses with small depositional angles The oblique progradational part of this seismic facies is sim-ilar to that in Seismic Facies 3 and usually developed at the basinward front end of Seismic Facies 3 The lithology of Seismic Facies 4 is dominated by greyish white to white fine‐grained sandstones and siltstones The lithofacies association is characterized by coarsening‐upward sedimentary cycles (Figure 6c Table 1) Convolute bedding and abundant diam-ictites are present on top of the fine sandstones (Figure 6j‐k)

Both braid‐deltas in the Members 1 + 2 of th Shahejie Fm (S‐1 + 2) and Member 2 of the Dongying Fm (D‐2) show moderately continuous moderate‐amplitude and shin-gled‐like progradational seismic reflections (Seismic Facies 5 Figures S10ndashS11 Table 1) It shows a thin prograding seis-mic pattern commonly with parallel upper and lower bound-aries (cf Mitchum et al 1977) The successive internal progradational seismic events overlap each other between the upper and lower segments with a gentle dip of 152degndash193deg (Table 3) The lithofacies are mostly composed of several coarsening‐upward cycles (Figure 6d Table 1) Each cycle is composed of dark grey mudstones and grey to whitish‐grey medium‐ to fine‐grained sandstones Several coarsening‐up-ward lithofacies are mainly developed in D‐2 (Figure 6e Table 1)

42 | Analysis of the tectonic activityThe normal faults F1 and F2 selected to calculate the fault activity dipping to the north and running approximately E‐W are important boundary faults on the south‐western margin of the HD The tectonic‐subsidence rate fault‐growth index and fault‐activity rate were used as proxies to indicate the tectonic intensity (Figure 3 S2 Table 2) S‐4 and S‐3 (lower unit) have the highest subsidence rate (300ndash355 mMa) the highest fault‐growth index (292ndash343 mMa) and the highest fault‐activity rate (10647ndash11869 mMa) among the studied intervals whereas the overlying S‐3 (middle

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unit) and S‐1 + 2 are characterized by a much lower sub-sidence rate and fault‐growth index and fault‐activity rate D‐3 had again a high subsidence rate (190 mMa) and an average fault‐growth index (210 mMa) and fault‐activity rate (9344 mMa) The uppermost studied interval D‐2 had a much lower subsidence rate (60 mMa) growth index (136 mMa) and fault‐activity rate (3451 mMa) than the un-derlying unit Generally the analysis of the subsidence rate average fault‐growth index and fault‐activity rate indicates two phases of alternating strong tectonic activity and tectoni-cally stable conditions

43 | Palaeogeomorphology distribution and dimensions of the main depositional systemsDepositional systems of each depositional phase of the Palaeogene on the south‐western slope of the HD were com-piled through seismic facies identification of 3‐D seismic data and compilation of maps with the current thicknesses of the main target intervals based on the study by Liu Xia et al (2015a) that combined a correction for the depth of burial with an interpretation of the sedimentary facies The basins sink area on the south‐western slope of the HD was estimated on the basis of a palaeogeomorphological reconstruction The distribution of the depositional system is closely related to the evolution of the palaeogeomorphology and therefore we describe both the distribution of the depositional system and the palaeogeomorphology here

The palaeogeography of S‐4 is characterized by the larg-est extent of the uplifted areas of all studied intervals The depositional area is small and scattered (Figure 7a Table 4) Faults F1 and F2 mark the boundaries between erosional and depositional regions The elevated footwalls of the faults were erosional areas and located adjacent to the hanging walls whereas the hanging walls were low‐lying depositional areas The sedimentary facies analysis indicates a fan‐delta developed here (Figure 7a) Calculations indicate that the sedimentary dip of the four fan‐deltas was uncommonly high (about 463deg) The extent and thickness of the fan‐deltas di-minished towards the basin margin (Tables 34)

The tectonically‐induced morphology of S‐3 (lower unit) shows a similar pattern to that of the underlying S‐4 The depositional and erosional areas were also controlled by the active faults F1 and F2The HD deepened from west to east with the deepest area located just along the fault margin The depositional centre was located north of the hanging wall of F2 and became infilled by a fan‐delta (Figure 7b) The aver-age sedimentary dip of the fan‐delta is 303deg The extent of the fan‐delta was larger than that of S‐4 (Table 34)

During deposition of S‐3 (middle unit) the uplifted source area shifted southwards and the depression expanded A major depositional sink was located north of the hanging wall of F2 (Figure 7c Table 4) Elevation differences existed

between the footwalls and the hanging walls of F1 and F2 although the topography was obviously gentler during this time‐span A braided fluvial area developed at the footwalls of the faults whereas a braid‐delta developed mainly on the hanging wall of F2 and the northern depositional centre (Figure 7c) The braid‐delta had a fairly large extent and an average depositional dip of 119deg (Tables 34)

During S‐1 + 2 the elevated erosional area shifted farther southwards and the entire south‐western area had a low to-pography An alluvial plain developed south of the footwalls of the faults whereas a braid‐delta developed at the hanging walls and in the depression with a very gentle slope of 096deg (Table 4 Figure 7d) The depositional system was dominated by a fairly thin delta body and a braid‐delta with a much larger extent (Table 3)

During the deposition of D‐3 the topography of the foot-wall areas and of the area south of the provenance area was similar to that during the underlying S‐1 + 2 The slope was steep (187deg) in the hanging walls of the boundary faults however and the depositional area increased to 198 km2 which provided an excellent condition for the deposition of a large braid‐delta (Figure 7e Table 4) This braid‐delta had a NE‐SW orientation and covered an area of 142 km2 its average thickness is some 200 m which results in the largest delta volume in the Palaeogene on the south‐western slope of the HD (Table 3)

The palaeogeomorphological reconstruction of D‐2 shows a gentler topography in the entire south‐western HD with a sink area of 375 km2 (Table 4) The main body of the braid‐delta was dominated by imbricated progradational seis-mic reflections and developed in the hanging walls of F1 and F2 whereas an alluvial‐plain facies probably developed in the footwall areas of the faults and to the south‐west of the uplifted area (Figure 7f) Although the extent of the delta reached its maximum the thickness of the delta was limited due to the gentle topography resulting in a small delta vol-ume (Table 3)

5 | RELATIONSHIPS BETWEEN THE VARIOUS ELEMENTS OF THE S2S SYSTEM

Quantitative relationships between the various elements of the S2S system have been established through the above‐mentioned calculations A strong positive correlation is clearly present between the rate of tectonic subsidence the average fault activity and the average growth index of the boundary faults F1 and F2 (Figure 8ab) The rate of tectonic subsidence can therefore be used in the following as the pri-mary proxy to represent the intensity of the tectonic activity whereas the rate of fault activity and the growth index are used as secondary proxies

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The tectonic activity and the sediment‐supply rate show a positive relationship (Figures 8c 9a 10a) whereas the tec-tonic activity and the sink area of the basin show a negative relationship (Figures 8d 9b 10b) In contrast the tectonic activity has a positive relationship with the total accommo-dation space (Figures 8e 9c 10c Table 4) There is also a positive relationship between the average sedimentary dip of the fan‐ and braid‐deltas on the one hand and the tectonic activity on the other hand (Figures 8f 9d 10d)

The intensity of the tectonic activity correlates negatively with the extent of the sediment area but positively with the sediment volume (Figures 8g‐h 9e‐f 10e‐f) The different responses of the sediment area and the volume to the tectonic activity are caused by variations in the thicknesses of the sed-imentary units (Table 3)

There is also a positive relationship between the average seismic progradation dip of the fan‐ and braid‐deltas and the tectonic activity (Figures 8i 9g 10g) strong tectonic activ-ity usually formed deltas that are characterized by a chaotic progradational or oblique progradational seismic reflection such as SF 1 and 2 in S‐3 (lower unit) and S‐4 (Figures S3ndashS7) The minimum tectonic activity during Members S‐1 + 2 and D‐2 are reflected by dominantly shingled progradational seismic facies in the delta interior (Figures S10ndashS11)

In addition we find that the sediment area sediment vol-ume and average seismic progradation dip of the fan‐ and braid‐deltas correlate positively with the sediment‐supply rate (Figure 11a b and c) but negatively with the basin sink area (Figure 11d e and f) Both the sediment volume and the average seismic progradation dip of the fan‐ and braid‐deltas

F I G U R E 8 (a‐b) Relationships between the tectonic‐subsidence rate and tectonics (c‐i) Relationships between tectonic activity and sedimentary source‐to‐sink parameters Input data regarding the tectonic activity are from Table 2 those regarding the source‐to‐sink parameters data are from Tables 3 and 4 Regression‐line equations and coefficients of determination (R2) are shown for all diagrams

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show a positive relationship with the total accommodation space (Figure 11hi) However no obvious relationship ap-pears to be present between the sediment area and the total accommodation space (G) Both the sediment area and the average seismic progradation dip of the fan‐ and braid‐deltas correlate well with the average sedimentary dip of the fan‐ and braid‐deltas (Figure 11km) A poor correlation is found between the sediment volume and the average sedimentary dip of the fan‐ and braid‐deltas

6 | DISCUSSION

61 | Analysis of the influence of tectonic activity on the source area accommodation space geomorphology and sediment supplyA high relief and large drainage area usually can generate a large sediment supply (Leeder Harris amp Kirkby 1998 Syvitski amp Milliman 2007) Although the erosional area for the fan and delta system cannot be estimated because of the

limited data coverage the exposed area within the study area can be calculated The calculations show a generally decreas-ing trend of the source area from S‐4 (501 km2) to D‐2 (58 km2 Figure7 Table 4) The calculated exposed area cannot fully represent the true source area however but the evolu-tionary trend of the source area can be used as a proxy to indi-cate the relative influence on the change in sediment volume This trend is consistent with the decrease in sediment volume from S‐4 (2126 km3) to D‐2 (175 km3 Table 2) The relief is difficult to reconstruct in this case but variations in the fault‐activity rate (here taken as the tectonic‐subsidence rate) can create local elevation differences and can therefore be used as proxies for the trends in the relief development The relief shows an overall decreasing trend from S‐4 to D‐2 except for D‐3 this correlates well with the sediment volume (Figure 8h) Although the drainage area of D‐3 was smaller than that of D‐2 because of the high tectonic‐subsidence rate (result-ing in a high relief) D‐3 is thicker and shows a larger sedi-ment volume than the overlying D‐2 (Table 3) D‐3 is thinner than S‐4 + 3 but the larger source area resulted in a larger

F I G U R E 9 General relationships between the average fault‐growth index of F1 and F2 (AFGIF1‐F2) and sedimentary source‐to‐sink parameters The average fault‐growth index of F1 and F2 (AFGIF1‐F2) data in this figure are from Table 2 The source‐to‐sink parameters data are from Table 4 Regression‐line equations and the coefficients of determination are shown in each diagram

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sediment volume and supply rate (Table 3 Figure8ch) Therefore both the fault‐induced relief and the drainage area affected the sediment‐supply rate and the sediment volume in the sink

The changes in accommodation space during the vari-ous phases of the Palaeogene in the south‐western HD are clear from the estimated tectonic subsiding rate (Table 2) The correlations between the intensity of the tectonic activ-ity and the extent of the depositional sink area (Figures 8d 9b 10b) between the intensity of the tectonic activity and the total accommodation space and between the intensity of the tectonic activity and the morphology in the sink area (Figures 8e‐f 9c‐d 10c‐d) clearly show that strong tectonic activity resulted in a larger accommodation capacity of the sink

In particular the main subsiding area tended to form steeper slopes However the extent of the main subsiding sink area diminished (Figure 8d) with increasing tectonic activity which was possibly due to the relatively small sub-siding centre in the tectonically active basins It can thus be deduced that tectonic activity not only controlled the sedi-ment supply and the variation in accommodation space but

also determined the changes in the topography of the sedi-mentary basins and the extent of the main depositional areas in the tectonically active basins

62 | Analysis of the influence of tectonic activity on the size and internal stacking pattern of the delta depositional systemThe above data and considerations indicate that the tectonic activity was closely related to the sediment supply accom-modation space and morphology of the sink area which are possibly the most important factors affecting the extent and stacking pattern of the sedimentary facies (cf Cope et al 2010 DeCelles Kapp Ding amp Gehrels 2007 Leeder 2011 Olsen 1997 Simon et al 2017)

Statistical analysis indicates that the sediment‐supply rate has a strong positive correlation with the volume of the depositional system a moderate correlation with the seismic progradational dip in the depositional system and a poor cor-relation with the size of the depositional area (Figure 11a‐c) A larger sink area corresponded to a larger fanbraid‐delta a gentler seismic progradational angle and a reduced volume

F I G U R E 1 0 General relationships between average fault activity rate of F1 and F2 (RFAA‐F1‐F2) and sedimentary source‐to‐sink parameters The average fault activity rate of F1 and F2 (RFAA‐F1‐F2) data in this figure are from Table 2 The source‐to‐sink parameters data are from Table 4 Regression line equations and the coefficients of determination are shown in each diagram

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of the fan or braid‐delta which was possibly related to a re-duced sedimentary dip and thinner sediments (Figure 11d‐f) The total accommodation space in the basin correlates well

with the volume of the depositional system to some degree with the seismic progradational dip and poorly with the ex-tent of the depositional system area (Figure 11g‐i) These

FIGURE 11 Relationships between various parameters involved in the source‐to‐sink system (a‐c) Relationships between sediment supply and characteristics of the depositional system (extent volume and DPSA of the sediments) (d‐f) Relationships between the sink area of the basin and characteristics of the depositional system (g‐i) Relationships between the total accommodation space (AT) and the characteristics of the depositional system (j) Relationship between the accommodation‐spacesediment‐supply ratio (AS) and the DPSA of the sediments (k‐m) Relationships between the sedimentary dip and the characteristics of the depositional system The data regarding sediment supply basin sink area total accommodation space accommodation‐spacesediment‐supply ratio and sedimentary dips are from Table 4 The extent volume and DPSA of the sedimentary facies are from Table 3 Note the seemingly obvious polynomial (quadratic) relationship between the sedimentary dip and the sediment volume (L) The trend line in (L) suggests the following relationships between sediment volume and sedimentary slope in a rift or tectonically active basin (1) a very steep sedimentary slope is unfavourable for sediment accumulation (2) an appropriate sedimentary slope is favourable for preservation of depositional systems eg when the sedimentary slope in (L) is about 25degndash32deg the sediment volume reaches its largest value (3) a very gentle sedimentary slope will lead to a decrease of the sediment volume possibly due to weakening of the drainage system and thinner sediments

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relationships are clear evidence that the size of the sink area controlled the extent of the depositional system during the rifting of the lacustrine basin and that the rate of sediment supply and the accommodation space had a significant in-fluence on the total sedimentary volume as well as on the internal stacking pattern of the depositional system

We here use the ratio of the tectonic‐subsidence rate and the sediment‐supply rate as a proxy to indicate the ratio be-tween accommodation space and sediment‐supply rate (AS) (Table 4) AS has a strong influence on the internal stacking pattern of the depositional systems in the lacustrine rift basin (Figure 11j) This might be because the basin was small and because abundant and rapid material was supplied due

to intense tectonic activity (cf Catuneanu et al 2009 Liro 1993) and a favourable local climate (eg Bohacs Carroll Neal amp Mankiewicz 2000 Perlmutter amp Matthews 1989) The sediment supply still had a significant influence on the main subsidence area of the lacustrine basins and deposi-tional systems

In addition the basin slope significantly influenced the extent of the depositional system (Figure 11k) and had a polynomial relationship with its volume (Figure 11l) This relationship indicates that more intense tectonic activity and a steeper depositional slope were not favourable for sediment accumulation over a large extent in the lacustrine basin On the contrary these sediments were usually transported to a

F I G U R E 1 2 Tectonic differential activities and resulting patterns of the source‐to‐sink system on the south‐western slope of the HD during the Palaeogene (a) Development during phases of intense tectonics (Member 4 to the lower part of Member 3 of the Shahejie Fm) (b) Development during phases of somewhat less tectonic activity (middle part of Member 3 of the Shahejie Fm and Member 3 of the Dongying Fm) (c) Development during phases of weak tectonic activity (Members 1 and 2 of the Shahejie Fm and Member 2 of the Dongying Fm) The intensity of tectonic activity in the lacustrine rift basin had a significant influence on the development and extent of each unit of the source‐to‐sink system as well as on the type and dimensions of the depositional systems The present study indicates that probably sublacustrine fans developed (see for example Figure S4b) during phases with relatively strong tectonic activity This is not really clear from the seismic‐reflection data but possibly due to the small sizes of these sublacustrine fans Moreover lithofacies and core data are not available for the south‐western part of the study area The present contribution therefore focuses on the fan‐deltas and braid‐deltas regarding the sedimentary facies analysis the sublacustrine fans that probably developed in the deep or semi‐deep lake are presented just as a likely feature

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relatively small sink area with a fairly large accommodation space Finally stronger tectonic activity resulted in steeper depositional slopes (Figure 8f) which further controlled the hydrodynamic conditions and differential discharge when the sediments were deposited The strong correlation between the depositional slope and the deltas dip (Figure 11m) suggests that the differences in topography due to tectonics must be considered as one of the most critical factors that controlled the internal stacking pattern of the delta deposits

63 | Significance of the present study for other source‐to‐sink systems of lacustrine rift basins

631 | Summary of the source‐to‐sink systems in the HDIn lacustrine rift basins the tectonic setting is probably the main factor that determines the development of the S2S sys-tem but differential tectonic activities lead to variations in the basic characteristics of the S2S system Tectonic activity was most intense during S‐3 (lower unit) and during S‐4 and caused both a strong uplift of the source area and the devel-opment of depressions in the basin that formed a sink (Figure 12a) Strong tectonic activity in the S2S system during these time‐spans led to a high sediment‐supply rate steeper slopes a larger accommodation space and deposition of several fan‐deltas that are characterized by a fairly steep seismic progra-dational angle

The tectonic activity decreased during S‐3 (middle unit) and during D‐3 The S2S system that was present during this time‐span mainly concerned a rising area that shifted south-wards developing an alluvial plain between the erosional area and the sink area thus increasing the distance from source to sink (Figure 12b) Simultaneously the sediment‐supply rate and the accommodation space also changed and braid‐deltas could thus develop with larger volumes and gentler seismic progradational dips

Tectonic activity was clearly less intense during S‐1 + 2 and D‐2 The rising area had shifted further southwards cre-ating a wider alluvial plain connecting the source area to the sink in the HD (Figure 12c) At this stage stable tectonic activity led to relatively less sediment supply a gentle slope less accommodation space and the development of several braid‐deltas with a fairly gentle seismic progradational angle

632 | Wider implications and limitationsSoslashmme et al (2009) proposed that the elements of S2S sys-tems are genetically related and that quantitative correla-tions exist among these elements Other studies also suggest that the size of the drainage basin is correlated to the size of the fan developing on the basin floor (eg Blum et al

2017 Snedden et al 2018) and to the size of the river chan-nel (eg Milliken et al 2018) Helland‐Hansen Soslashmme Martinsen Lunt and Thurmond (2016) suggest a simplified subdivision of S2S systems into three main categories (a) Steep‐Short‐Deep (steep onshore and offshore gradients short distance between source and sink and deep offshore waters) (b) Wide‐Deep (low‐gradient shelf‐catchment area and deep offshore waters) and (c) Wide‐Shallow (relatively shallow offshore waters and a wide low‐gradient catchment area) systems

The present study indicates that the alluvial plain roughly corresponds to the alluvial‐shelf unit in marine basins al-though with a much smaller width and extent in the lacustrine rift basins than would have been the case on a continental shelf Faults F1 and F2 along the slope belt correspond to the slope of classical S2S systems whereas the shore‐shallow‐deep lake area can be compared with the basin floor (Soslashmme et al 2009) S‐4 and S‐3 (lower unit) can be roughly clas-sified as Steep‐Short‐Deep systems whereas the overlying S‐1 + 2and D‐2 can be classified as the Wide‐Shallow sys-tems that Helland‐Hansen et al (2016) defined During the deposition of S‐4 and S‐3 (lower unit) the strong tectonic activity caused a high relief of the source area a narrow allu-vial plain and a relatively deep lake The subsequently wan-ing tectonic activity resulted in a lower relief of the source area a wider alluvial plain and a shallower lake Although the absolute values of these elements in lacustrine basins are much smaller than those of marine basins the ratio between these elements in both settings is comparable Typically in a lacustrine basin a transformation from a Steep‐Short‐Deep system (S‐4 and S‐3 (lower unit)) to a Wide‐Shallow system (S‐1 + 2ampD‐2) occurs within a few million years Although the basin geomorphology has experienced signif-icant changes from S‐4 to D‐2 the quantitative relationships between tectonic activity sediment‐supply rate accommoda-tion space and sedimentary dip of the delta systems did not change significantly (eg Figures 8 and 11) The analytical approaches applied and quantitative relationship established here can help analyse other lacustrine basins worldwide and may even act as a reference for the analysis of marine basins

Our study focuses mainly on the influences of tectonic activity on the elements of the depositional sink Other pa-rameters (eg climate and lithology) were not considered in detail Studies on modern and ancient systems suggest that the climate and lithology also have a great influence on the sediment supply and distribution in the basin (eg Carroll Chetel amp Smith 2006 Hovius amp Leeder 1998 Syvitski amp Milliman 2007 Zhang et al 2018) For exam-ple climate variations between glacials and inter‐glacials have resulted in largely different sediment‐supply rates and in significant differences in the sizes of the Quaternary sub-marine fans in the north‐western Gulf of Mexico (Blum amp Hattier‐Womack 2009) We acknowledge the importance

| 609EAGE

LIU et aL

of climate and lithology for S2S systems and we are con-vinced that these elements can significantly affect the S2S systems in other cases(eg modern systems and systems influenced by glacialinterglacial alternations) These fac-tors were not really relevant for the present study however because no significant differences in lithology were present in the source areas and because we focus on the changes at a million‐year scale which implies that the tectonic ac-tivity has a first‐order control on the development of S2S elements in the investigated rift basin

7 | CONCLUSIONS

We have calculated the tectonic‐subsidence history the growth index and the activity rate of the main boundary faults (F1 and F2) and various S2S parameters of six Palaeogene rock units on the south‐western slope of the HD Based on the values found for these parameters quantitative corre-lation were established for the tectonic activity and other S2Sparameters in the basinal sink This leads to the follow-ing conclusions

1 The positive correlation between the intensity of fault activity and the tectonic‐subsidence rate is a strong indication for a distinct control by the tectonic activity of the syn‐depositional rifting of the tectonically active basin

2 The tectonic activity was quantitatively related to the sediment supply accommodation space and morphology of the sink area The relationship between tectonic activ-ity and depositional systems is reflected by changes in critical factors such as sediment supply accommodation space and dip of the sink area These critical factors were probably the most important factors that led to changes in the size and internal stacking pattern of the sedimentary facies

3 Differential tectonic activity led to changes in the char-acteristics of the S2S system on the south‐western slope of the HD The strongest tectonic activity which oc-curred during S‐3 (lower unit) and during S‐4 led to the largest provenance area adjacent to the sink area to a high sediment‐supply rate to steeper slopes to a larger accommodation space and controlled the development of several fan‐deltas Diminished tectonic activity dur-ing S‐3 (middle unit) and during D‐3 led to a decrease in uplift an increased width of the alluvial plain an in-creased transport distance a decrease in the sediment‐supply rate and accommodation space and resulted in the development of braid‐deltas with a large volume During S‐1 + 2 and D‐2 stable tectonic activity led to a lower sediment‐supply rate a gentle depositional slope and a smaller accommodation space resulting in the

development of several braid‐deltas with gentler seis-mic progradational angles

4 The analytical approaches applied and the quantitative re-lationships established here can help analyse other lacus-trine basins worldwide and may even act as a reference for the study of marine basins

ACKNOWLEDGEMENTS

We thank Dr Sarah Boulton and Dr Chenlin Gong as well as the Associate Editor of Basin Research Dr Craig Magee for their constructive comments on the manuscript This study was funded by the National Science and Technology Major Project (Exploration Technologies for Offshore Hidden OilGas) (project no 2016ZX05024‐003‐003) the National Natural Science Foundations of China (project no 41676050) and the Fundamental Research Funds for the Central Universities (2652014037)

REFERENCES

Allen P A (2008a) From landscapes into geological history Nature 451 274ndash276 https doiorg101038natur e06586

Allen P A (2008b) Time scales of tectonic landscapes and their sed-iment routing systems In Landscape evolution Denudation cli-mate and tectonics over different time and space scales (Ed by Gallagher K Jones S J amp Wainwright J) Geological Society London Special Publications 296 7ndash28

Allen P A Armitage J J Carter A Duller R A Michael N A Sinclair H D hellip Whittaker A C (2013) The Qs problem Sediment volumetric balance of proximal foreland basin systems Sedimentology 60 102ndash130

Amorosi A Maselli V amp Trincardi F (2016) Onshore to offshore anatomy of a late Quaternary source‐to‐sink system (Po Plain‐Adriatic Sea Italy) Earth‐Science Reviews 153 212ndash237 https doiorg101016jearsc irev201510010

Anderson J B Wallace D J Simms A R Rodriguez A B Weight R W R amp Taha Z P (2016) Recycling sediments between source and sink during a eustatic cycle Systems of late Quaternary northwestern Gulf of Mexico Basin Earth‐Science Reviews 153 111ndash138 https doiorg101016jearsc irev201510014

Anthony E J amp Julian M (1999) Source‐to‐sink sediment trans-fers environmental engineering and hazard mitigation in the steep Var River catchment French Riviera southeastern France Geomorphology 31 337ndash354 https doiorg101016S0169-555X(99)00088-4

Athy L F (1930) Density porosity and compaction of sedimentary rocks AAPG Bulletin 14 1ndash24

Bhattacharya J P Copeland P Lawton T F amp Holbrook J (2016) Estimation of source area river palaeo‐discharge palaeoslope and sediment budgets of linked deep‐time depositional systems and im-plications for hydrocarbon potential Earth‐Science Reviews 153 77ndash110

Blum M D amp Hattier‐Womack J (2009) Climate change sea‐level change and fluvial sediment supply to deepwater depositional

592 | EAGE

LIU et aL

the tectonic history and intensity We have selected Well W25 (Figure 1c) because it is the only drilling well in the south‐eastern HD for simulation of the subsidence history This simulation is based on our reconstructed stratigraphic framework and age information provided by the TBCNOOC (Figure 2)

Correction for compaction is critical in quantitative sim-ulation of the subsidence history and rate The influence of the water depth during sedimentation is considered negligible since the Bohai Bay Basin was a lacustrine basin Differences in the acoustic travel times have been used to calculate the porosities at the corresponding depths (cf Wylliel Gregory amp Gardner 1958) Subsequently the porosities of the vari-ous types of lithology (mainly sandstone and mudstone) at different depths were determined by logging and the poros-itydepth relationship was established by statistic fitting (cf Athy 1930) Back‐stripping of the selected strata was per-formed layer‐by‐layer to calculate the top and bottom bound-ary depths at different times in the geological development (cf Perrie amp Qiublier 1974) thus distinguishing between the compaction history the tectonic subsidence and the total subsidence during the Palaeogene (Figure 3 Table 2 supple-mentary text)

The normal boundary faults (F1 amp F2) controlling depo-sition on the south‐western margin of the HD have been

selected to calculate the fault‐growth index and the fault‐ac-tivity rate (Figure 1c) The fault‐growth index sometimes also called the ldquoexpansion indexrdquo is the ratio between the stratigraphic thickness of the hanging wall and that of the footwall of a growth fault The fault‐activity rate is the ratio between the thicknesses of the sedimentary successions in the hanging wall and the foot wall resulting from fault activ-ity during a specific depositional phase corresponding to the length of the time‐span during which the investigated succes-sion accumulated ie (Zhou Niu amp Teng 2009)

where RF is the fault‐activity rate in mMa T is the length of the time‐span during which the investigated succession ac-cumulated (in Ma) STh is the stratigraphic thickness of the hanging wall (in m) and STf is the stratigraphic thickness of the footwall (in m) For the calculation of the stratigraphic thickness the conversion from two‐way travel time to depth was made by analysis of the P‐wave velocity in the wells The growth index and the activity rate of the main faults have thus been calculated for several locations (Table 2 Figure 1c) which was considered necessary because of the differ-ent successive stages in the morphological evolution of the

RF=ΔST∕T =

(

SThminusST

f

)

∕T

F I G U R E 3 Palaeogene burial history of the HD (a) Cumulative subsidence (b) Subsidence during the development of the individual members D‐1 = Member 1 of the Dongying Fm D‐2 = Member 2 of the Dongying Fm D‐3 = Member 3 of the Dongying Fm S‐1 amp 2 = Members 1 and 2 of the Shahejie Fm S‐3 = Member 3 of the Shahejie Fm S‐4 = Member 4 of the Shahejie Fm

| 593EAGE

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basin‐controlling faults and because of the changes in the intensity of the fault activity

33 | Quantitative calculation of S2S system parameters

331 | Area and volume of the sedimentary faciesQuantitative calculation of the dimensions of sedimentary facies requires reliable estimates of the lateral extent and thickness of the sediments involved For these calculations first the maxi-mum extent of the specific units under study (fan‐deltas braid‐deltas etc) at different times was determined in plan view based on the combined interpretation obtained from seismic facies lithofacies and the outer boundaries of the sediment bodies Subsequently the outcomes were digitalized and used as input for a 3‐D survey by GEOFRAME Detailed calculations of the sedi-ment bodies extents were conducted using the PLANIMETER tool in the BASEMAP window of GEOFRAME

This was followed by the selection of several seismic sec-tions across the sediment body in order to identify the lower

and upper boundaries as well as to calculate the maximum minimum and average thickness (see Amorosi Maselli amp Trincardi 2016 Liu et al 2017) Finally we used a colum-nar body with irregular base and the same height to represent the irregular sediment body The formula for volume calcu-lation is as follows (Figure 4 Table 3 supplementary text)

where VS is the volume of the sediment (in km3) AS is the horizontal surface area of the irregular base of the sediment (in km2) and H is the height (average thickness) of the sed-iment (in m) Detailed calculations of the thickness were conducted using the AREAL tool in the SEIS3DVSEIS2DV window of GEOFRAME

332 | Determination of the depositional dip of the delta surface due to progradationThe term ldquodepositional diprdquo is used here to indicate the inclination of a dipping sedimentary surface Horizon flat-tening was used to analyse and calculate the morphology of the underlying strata First the maximum flooding surface ndash approximately corresponding to the palaeo‐sedimentary surface (Lin et al 2012) ndash of each unit under study was interpreted it was subsequently flattened to calculate the original depositional dip (Figure 5d) with the formula

where DSD is the sedimentary dip (in degrees) dy is the verti-cal thickness between the lower boundary of the sedimentary unit and the ancient sedimentary surface in the depositional centre (in m) and dx is the distance from the apex of the delta to its depositional centre (in m)

Two to four seismic sections have been selected to calcu-late the average sedimentary dip of each individual delta with the following formula

where DSDA is the average sedimentary dip of a sediment (in degrees) and n is the number of seismic sections

The seismic progradational angle of the deltas interior has been calculated by the horizon‐flattening method (Figure 5e) which is expressed by the formula

VS=A

StimesH

DSD

= tanminus1 (dy∕dx)

DSDA

=

(

nsum

i=1

DSDi

)

∕n

DP= tan

minus1 (dy∕dx)

F I G U R E 4 Schematic diagram showing the calculation of the volume of a sediment (a) is an irregular sediment body Volume calculation of cuboids was used for reference to calculate the volume of an irregular sedimentary body ie the volume of an irregular sediment body equals the area of the irregular bottoms times height (b) 3ndash4 seismic lines along the sedimentary body are selected and the thickness of the sedimentary body is determined at intervals of 10 seismic traces (c) when a thickness grid covering the entire sedimentary body in space is acquired the average thickness of all counted thicknesses can be calculated as the height of the irregular sediment body (d)

594 | EAGE

LIU et aL

where DP is the seismic progradational dip (in degrees) The average dip angle is obtained from only one seismic sec-tion because of the variations in the progradational seismic event of the delta on the same seismic line

where DPA is the average seismic progradational dip in a spe-cific seismic section (in degrees) and n is the number of seis-mic progradational events

Based on the calculated average dip of one seismic sec-tion the average progradational dip of a specific sediment body can be calculated with the formula

DPA

=

(

nsum

i=1

DPi

)

∕n

F I G U R E 5 Detailed calculations of the sedimentary dip and the progradational seismic event dip of the delta interior taking the progradation seismic reflection of the delta developed in Member 3 of the Dongying Formation as an example The locations of the seismic lines are shown in Figure 1c Based on the interpretation of the stratigraphic and seismic facies visible in the original seismic lines (a) the topset or the maximum flooding surface (MFS) corresponding to the delta was flattened (b) Taking into account the water depth during sedimentation the sedimentary dip (d) and the progradational seismic event dip of the delta interior (e) can be calculated DSD = depositional dip in a specific seismic section DSDA = average depositional dip of a specific sedimentary unit DP = seismic progradational dip DPA = average seismic progradational dip

| 595EAGE

LIU et aL

TA

BL

E 1

In

terp

reta

tion

of th

e m

ain

sedi

men

tary

faci

es in

the

Pale

ogen

e of

the

Hua

nghe

kou

Dep

ress

ion

Evi

denc

e of

fan

delta

s and

bra

id d

elta

s in

wel

ls W

1 an

d W

18 c

omes

from

Liu

Xia

et a

l (2

015a

)

Form

atio

n an

d m

embe

raSe

ismic

faci

esEx

ampl

esLi

thof

acie

sLi

thol

ogy

Wel

l amp c

ore

exam

ples

Dep

ositi

onal

en

viro

nmen

tPr

edic

ted

res-

ervo

ir q

ualit

y

D‐2

Seis

mic

Fac

ies 5

mod

erat

e co

ntin

uous

lo

w‐a

mpl

itude

and

a sh

ingl

ed‐li

ke

prog

rada

tiona

l sei

smic

refle

ctio

n

Figu

re

Mul

tiple

upw

ard‐

coar

s-en

ing

litho

faci

es

asso

ciat

ions

Gre

y m

udst

ones

gre

y to

gre

yish

w

hite

pebb

ly fi

ne sa

ndst

ones

and

fin

e sa

ndst

ones

T25

Bra

id d

elta

Mod

erat

e to

hi

gh

D‐3

Seis

mic

Fac

ies 4

con

tinuo

us m

oder

-at

e‐to

high

‐am

plitu

de a

nd o

bliq

ue‐

to‐s

igm

oid

prog

rada

tiona

l sei

smic

re

flect

ion

Figu

re

Mul

tiple

upw

ard‐

coar

s-en

ing

litho

faci

es

asso

ciat

ions

Gre

yish

whi

te to

whi

te fi

ne

sand

ston

es s

iltst

ones

and

gre

y m

udst

ones

T25

Bra

id d

elta

Hig

h

Figu

re 7

e‐f

S‐1

+ 2

Seis

mic

Fac

ies 5

mod

erat

e co

ntin

uous

m

oder

ate‐

ampl

itude

and

shin

gled

‐like

pr

ogra

datio

nal s

eism

ic re

flect

ion

Figu

re

Mul

tiple

upw

ard‐

coar

s-en

ing

litho

faci

es

asso

ciat

ions

Dar

k gr

ey m

udst

ones

and

gre

yish

w

hite

to g

rey

mid

dle‐

to fi

ne‐

grai

ned

sand

ston

es

T25

Bra

id d

elta

Hig

h

S‐3

(mid

dle

unit)

Seis

mic

Fac

ies 3

har

dly

tom

oder

atel

y co

ntin

uous

low

‐am

plitu

de o

bliq

ue

prog

rada

tiona

l sei

smic

refle

ctio

n

Figu

re

Lith

ofac

ies 1

Gre

y to

gre

yish

whi

te sa

ndy

cong

lom

erat

esT2

5B

raid

del

taH

igh

Lith

ofac

ies 2

Thic

k gr

ey m

iddl

e‐to

fine

‐gra

ined

sa

ndst

ones

Figu

re 7

a‐d

Lith

ofac

ies 3

Gre

y m

udst

ones

inte

rbed

ded

with

gr

ey fi

ne sa

ndst

ones

and

gre

y m

uddy

silts

tone

s

Lith

ofac

ies 4

Thic

k da

rk g

rey

mud

ston

es

S‐3

(low

er

unit)

Seis

mic

Fac

ies 2

cha

otic

prog

rada

-tio

nal t

o ob

lique

pro

grad

atio

nal

seis

mic

faci

es

Figu

re

Pe

bbly

sand

ston

es in

terb

edde

d w

ith

thin

bro

wn‐

grey

mud

ston

esb

row

n sa

ndy

cong

lom

erat

ess

ands

tone

s in-

terb

edde

d w

ith th

in m

udst

ones

thic

k m

udst

ones

inte

rbed

ded

with

th

in sa

ndst

ones

or p

ebbl

y fin

e sa

ndst

ones

T1Fa

n de

ltaM

oder

ate

S‐4

Seis

mic

Fac

ies 1

dis

cont

inuo

us to

con

-tin

uous

low

‐tohi

gh‐a

mpl

itude

cha

otic

pr

ogra

datio

nal s

eism

ic re

flect

ion

Figu

re

Figu

re

Fig

ure

and

Fi

gure

Lith

ofac

ies 1

Gre

y pe

bbly

sand

ston

es c

oars

e sa

ndst

ones

T18

Fan

delta

sM

oder

ate

Lith

ofac

ies 2

Ash

‐bla

ck m

udst

ones

inte

rbed

-de

d w

ith th

in g

rey

fine‐

grai

ned

sand

ston

es

Lith

ofac

ies 3

Ash

‐bla

ck m

udst

ones

inte

rbed

ded

with

peb

bly

sand

ston

esa D

= D

ongy

ing

Fm

S =

Sha

hejie

Fm

The

num

ber i

ndic

ates

the

num

ber o

f the

mem

ber

596 | EAGE

LIU et aL

TA

BL

E 2

Es

timat

ion

stat

istic

s of t

he te

cton

ic‐s

ubsi

denc

e ra

te g

row

th in

dex

and

activ

ity ra

te o

f fau

lts F

1 an

d F2

S1

S2

and

S3 a

re th

e ca

lcul

atio

n lo

catio

ns o

f F1

and

F2 (s

ee F

igur

e 1c

) th

e co

rres

pond

ing

num

bers

are

F1‐

S1 F

1‐S2

F1‐

S3 F

2‐S1

F2‐

S2 a

nd F

2‐S3

res

pect

ivel

y

Form

atio

n an

d m

embe

raA

ge

(Ma)

R TS

(m

Ma)

b

Faul

t‐gro

wth

inde

xFa

ult‐a

ctiv

ity r

ate

(mM

a)

AFG

I F1‐

F2c

R FA

A‐F

1‐F2

d

S1S2

S3A

vera

geS1

S2S3

aver

age

F1F2

F1F2

F1F2

F1F2

F1F2

F1F2

F1F2

F1F2

D‐1

233

75ndash

267

1450

00

111

106

109

110

107

109

109

108

389

270

389

479

270

389

349

379

109

364

D‐2

267

14ndash

302

060

00

139

130

138

140

137

133

138

134

320

730

29

341

442

62

329

534

98

330

535

96

136

345

1

D‐3

302

0ndash33

278

190

002

002

052

102

342

032

052

042

1579

67

104

0010

372

111

3485

59

762

989

66

972

12

1093

44

S‐1

+ 2

332

78ndash

378

9250

00

145

136

142

147

155

145

148

143

122

211

36

105

915

78

587

176

39

5614

92

146

122

4

S‐3

(mid

dle

unit)

378

92ndash

404

3812

500

131

202

192

242

175

257

166

234

335

140

88

490

380

62

215

510

919

347

076

90

205

558

0

S‐3

(low

er

unit)

404

38ndash

422

3135

500

284

343

302

395

342

389

309

376

737

185

37

104

4016

956

742

820

480

841

315

324

343

118

69

S‐4

422

31ndash

447

300

002

512

921

584

173

023

332

373

4791

33

106

4357

58

151

8811

007

121

5186

33

126

612

9210

647

a D =

Don

gyin

g Fm

S

= S

hahe

jie F

m T

he n

umbe

r ind

icat

es th

e nu

mbe

r of t

he m

embe

r b R T

S = te

cton

ic‐s

ubsi

denc

e ra

te

c AFG

I F1‐

F2 =

ave

rage

faul

t‐gro

wth

inde

x of

F1

and

F2

d R FA

A‐F

1‐F2

= a

vera

ge fa

ult‐a

ctiv

ity ra

te o

f F1

and

F2

| 597EAGE

LIU et aL

TA

BL

E 3

C

alcu

latio

n ch

art o

f the

sedi

men

tary

‐fac

ies d

imen

sion

s and

the

inte

rnal

pro

grad

atio

nal s

eism

ic e

vent

dip

The

spat

ial e

xten

t is s

how

n in

Fig

ure

7

Form

atio

nand

mem

bera

Sedi

men

tary

faci

esSe

ismic

sect

ions

Thic

knes

s (m

)

Are

a (k

m2 )

Vol

ume

(km

3 )To

tal v

olum

e (k

m3 )

DPb

Max

M

in

Ave

rage

DPA

DPS

A

D‐2

Bra

id d

elta

Figu

re a

176

0075

00

107

7016

246

175

017

50

157

156

Figu

re b

174

0080

00

157

Figu

re c

218

0080

00

152

D‐3

Bra

id d

elta

Figu

re a

285

0011

400

200

5014

219

285

128

51

268

285

Figu

re b

295

0099

00

309

Figu

re c

296

0078

00

309

Figu

re d

284

0091

00

254

S‐1

+ 2

Bra

id d

elta

Figu

re a

178

0089

00

136

7512

023

164

416

44

172

177

Figu

re b

185

0095

00

176

Figu

re c

236

0010

500

193

Figu

re d

209

0011

400

166

S‐3

(mid

dle

unit)

Bra

id d

elta

Figu

re a

274

0010

100

223

7587

87

196

619

66

213

225

Figu

re b

279

0083

00

225

Figu

re c

292

0086

00

235

Figu

re d

296

0086

00

226

S‐3

(low

er u

nit)

Fan

delta

Figu

re a

428

8623

903

374

0062

89

235

223

52

301

305

Figu

re b

432

5522

071

325

Figu

re c

473

0920

583

312

Figu

re d

450

8325

500

283

S‐4

Fan

delta

1Fi

gure

a30

700

483

929

200

107

03

1221

26c

423

365

Figu

re b

350

0010

728

439

Fan

delta

2Fi

gure

a46

500

704

832

900

856

282

421

Figu

re b

379

0066

52

362

Fan

delta

3Fi

gure

a40

100

118

7841

100

186

27

654

21

Figu

re b

468

0016

718

309

Figu

re c

527

0015

127

387

Figu

re d

486

0014

844

297

Fan

delta

4Fi

gure

a42

800

151

2042

700

179

57

663

04

Figu

re b

512

0027

287

289

a D =

Don

gyin

g Fm

S

= S

hahe

jie F

m T

he n

umbe

r ind

icat

es th

e nu

mbe

r of t

he m

embe

r b D

P = se

ism

ic p

rogr

adat

iona

l dip

DPA

= a

vera

ge se

ism

ic p

rogr

adat

iona

l dip

DPS

A =

ave

rage

seis

mic

pro

grad

atio

nal d

ip o

fthe

sedi

men

t c 21

26

= to

tal j

oint

vol

umes

of f

an d

elta

s 1 2

3 a

nd 4

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where DPSA is the average seismic progradational dip of a sediment (in degrees) and n is the number of seismic sections

Detailed estimated results of the depositional dip and the seismic progradational dip of the delta are shown in Tables 3 and 4

333 | Provenance conditions and estimation of the sediment supplySystematic investigation by TBCNOOC of the regional uplift and provenance in the geological past has indicated that the main provenance areas around the HD existed alreadybefore the deposition of Member 3 of the Shahejie Fm (Zhou et al 2010) They include the Bonan Laibei and Kendong Highs (Figure 1b‐c Figure S1a‐b) However starting with the depo-sition of Members 1ndash2 of the Shahejie Fm (S‐1 + 2) (3789ndash3328 Ma) until the accumulation of the Dongying Formation (3328ndash2338 Ma) the Bonan and Laibei Highs subsided to below lake level and consequently stopped providing sedi-ment to the depression (Liu Xia et al 2015a) Only the Kendong High which remained a high for a long time re-mained a provenance area for the south‐western part of the

HD during this time‐span (Figure S1a) The Kendong High has therefore been selected as the site where the relationship between tectonics and depositional systems within the same provenance system could be studied best The distribution area of the Kendong High as the provenance area at different moments has been determined on the basis of numerous seis-mic interpretations through seismic terminations (eg onlap) and the absence of specific sediment units due to faulting

The sediment‐supply rate can be obtained by calculation of the volumes of the deltas and the duration of their forma-tion (cf Allen et al 2013 Lemons amp Chan 1999 Lemons Milligan amp Chan 1996) Although the stratigraphic ages are well‐known for each unit (Figure 2) there is no high‐resolu-tion age control for the top and base of each delta system The absolute age of the pertinent stratigraphic unit (Figure 2) is therefore used to represent the formation time of the individual deltas in the unit The thus calculated sediment‐supply rate rep-resents in our opinion the trend of the supply rate from bottom to top sufficiently well

334 | Estimation of the extent and accommodation space of the sink areaDetermination of the boundaries of the sink area is based on reconstructions of the morphology during the successive dep-ositional phases The extent of the sink area was estimated using the same calculations as for the area of the depositional system

DPSA

=

(

nsum

i=1

DPAi

)

∕n

F I G U R E 6 Vertical successions and representative examples of the various lithofacies (a) A fan‐delta in Well W18 (b‐e) Braid‐deltas in Well W25 (f) Grey to greyish white sandy conglomerate (deposits in braided channels) (g) Grey medium‐ to fine‐grained massive sandstone (mouth‐bar deposits) (h) Grey fine sandstone (distal sand bars) (i) Grey muddy siltstone with parallel bedding (prodelta) (j) Greyish white fine sandstone with convolute bedding (mouth bars) (k) Greyish white fine sandstone with boulders (mouth bars) Wireline logs show the spontaneous‐potential (SP) and gamma‐ray (GR) changes with depth Depth in metres For location of the cores see Figure 6bd

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Differences in base level and the original sedimentary sur-face define the accommodation space (Jervey 1988 Muto amp Steel 2000 Neal amp Abreu 2009 Wheeler 1964) The

accommodation space in the depositional area can be deter-mined on the basis of the thickness of the preserved sediments (Muto amp Steel 2000) This space is obviously controlled by

F I G U R E 7 Schematic morphology during the successive depositional phases The extent of the deltas the depositional sink area in the basin and the main features of the drainage systems are shown The extent of the deltas has been interpreted from seismic data and has been used for calculation of the surface area and volume of the various deltas (a) Shahejie Fm Member 4 (b) Shahejie Fm lower part of Member 3 (c) Shahejie Fm middle part of Member 3 (d) Shahejie Fm Members 1 and 2 (e) Dongying Fm Member 3 (f) Dongying Fm Member 2

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the rate of subsidence tectonic uplift and fluctuations of the lake level (Lemons amp Chan 1999) Changes in the lake level of the HD have not been investigated so that we take data on the tectonic‐subsidence rate as a proxy for changes in the accommodation space The total space is expressed in the equation (Table 4)

where AT represents the total accommodation space of the sink area (in km3) TS represents the tectonic subsidence (in m) and SA represents the surface area of the sink (in km2)

AT= TStimesSA∕1000

T A B L E 4 Estimation of the controlling factor parameters of the depositional system The distribution characteristics of the depositional sink in the basin are shown in Figure 7

Formation and membera

Sedimentary facies Seismic sections

DDb

RSSc(km3

Ma)Sink area (km2) AT

d(km3) ASeSource areaf(km2)DSD DSDA

D‐2 Braid delta Figure a 059 066 502 37542 7852 1195 58

Figure b 065

Figure c 074

D‐3 Braid delta Figure a 161 187 926 19823 11593 2051 252

Figure b 192

Figure c 215

Figure d 182

S‐1 + 2 Braid delta Figure a 086 096 356 28015 6463 1403 220

Figure b 094

Figure c 120

Figure d 083

S‐3 (middle unit) Braid delta Figure a 110 119 772 21756 6927 1619 355

Figure b 111

Figure c 129

Figure d 128

S‐3 (lower unit) Fan delta Figure a 307 303 1313 16506 10500 2705 482

Figure b 334

Figure c 332

Figure d 237

S‐4 Fan delta 1 Figure a 384 463g 861 14150 10481 3484 501

Figure b 379

Fan delta 2 Figure a 606

Figure b 498

Fan delta 3 Figure a 479

Figure b 499

Figure c 625

Figure d 553

Fan delta 4 Figure a 377

Figure b 226aD = Dongying Fm S = Shahejie Fm The number indicates the number of the member bDD = depositional dip DSD = depositional dip in a specific seismic section DSDA = average depositional dip of a specific sedimentary unit cRSS = sediment‐supply rate dAT = total accommodation space eAS = accommodation spacesediment supply fSource area = Denudation area within the seismic data coverage The complete erosional area cannot be estimated because of the limited data coverage g463 = the average depositional dip of fan deltas 1 2 3 and 4 Considering that the four fan deltas developed during S‐4 consist of sediment that was derived from the same provenance area and were deposited in the same time‐span the four fan deltas are taken as a whole when estimating the parameters of RSS the sink area AT and AS

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4 | ELEMENTS OF THE S2S SYSTEM

41 | Analysis of the seismic facies and stacking pattern of the main sedimentary faciesA comprehensive analysis of seismic data cores cutting log-gings and well‐logging curves by Liu Xia et al (2015a) in-dicated that the Palaeogene depositional systems of the HD included fan‐deltas braid‐deltas lake margins deep lakes etc The fan‐ and braid‐deltas have been chosen for a detailed seismic study that must reveal their internal texture and their stacking patterns Analysis of the progradational seismic‐re-flection types and of the seismic progradational dip is particu-larly helpful for a better understanding of the hydrodynamic conditions and sedimentary processes that resulted in these depositional systems Because the facies interpretation in this area has been done before and is not the focus of this work we here mainly describe the internal texture and their stack-ing patterns of the main sedimentary facies

The major facies of S‐4 is interpreted as a fan‐delta It is dominated by Seismic Facies 1 which is characterized by discontinuous to continuous low‐ to high‐amplitude and chaotic progradational seismic reflections (Figures S3ndashS6 Table 1) The average dip of the progradational seismic event is about 365deg (Table 3) Three lithofacies are associated with Seismic Facies 1 (Table 1) The coarser lithofacies 1 represents a fan‐delta front whereas the finer lithofacies 2 and 3 are prodelta deposits The overall coarsening‐upward succession facies stacking pattern (Figure 6a) discontinuous and chaotic seismic reflections and relatively steep slope of Seismic Facies 1 suggest a fan‐delta system developed under strong hydrodynamic conditions (Mitchum et al 1977)

The fan‐delta of the lower part of Member 3 of the Shahejie Fm (S‐3 [lower unit]) is dominated by Seismic Facies 2 which is characterized by chaotic progradational to oblique progradational seismic characteristics It has a typical wedge shape and is composed of two seismic‐reflection seg-ments (a) a moderately continuous low‐ to high‐amplitude chaotic seismic‐reflection segment located near boundary fault F2 and (b) a continuous moderate‐ to high‐amplitude and oblique progradational seismic reflection in a basinward direction (Figure S7 Table 1) No obvious upper or lower segments occur in SF 2 and the dip of the progradational seismic event in this segment is also relatively steep viz 305deg (Table 3)

The middle part of Member 3 of the Shahejie Fm (S‐3 [middle unit]) is characterized by a low‐ to moderate‐con-tinuous low‐amplitude and oblique progradational seismic reflection (Seismic Facies 3) and is interpreted as a braid‐delta (Figure S8 Table 1) The progradational seismic events are parallel or sub‐parallel to each other and dip less (aver-age 225deg) than Seismic Facies 1 and 2 (Table 3) Seismic

Facies 3 is associated with four lithofacies (Figure 6b Table 1) in Well T25 The complete succession of the braid‐delta consists of gravely to coarse‐grained sandstone (lithofacies 1) at the base (Figure 6f) massive bedded medium‐ to fine‐grained sandstones (lithofacies 2) and grey mudstones inter-bedded with grey fine sandstones and grey muddy siltstones (lithofacies 3) in the middle (Figures 6g and 6h) and thick dark grey mudstones (lithofacies 4) at the top (Figure 6i)

Member 3 of the Dongying Fm (D‐3) is characterized by Seismic Facies 4 a typically composite seismic progra-dation reflection configuration representing a braid‐delta system (Figure S9 Table 1) Seismic Facies 4 is composed of highly continuous moderate‐ to high‐amplitude and pro-gradational seismic reflections that represent well‐developed deltaic topsets and bottomsets The topset segments of SF 4 are nearly horizontal or dip only gently (Table 3) The foreset segments form thicker lenses with small depositional angles The oblique progradational part of this seismic facies is sim-ilar to that in Seismic Facies 3 and usually developed at the basinward front end of Seismic Facies 3 The lithology of Seismic Facies 4 is dominated by greyish white to white fine‐grained sandstones and siltstones The lithofacies association is characterized by coarsening‐upward sedimentary cycles (Figure 6c Table 1) Convolute bedding and abundant diam-ictites are present on top of the fine sandstones (Figure 6j‐k)

Both braid‐deltas in the Members 1 + 2 of th Shahejie Fm (S‐1 + 2) and Member 2 of the Dongying Fm (D‐2) show moderately continuous moderate‐amplitude and shin-gled‐like progradational seismic reflections (Seismic Facies 5 Figures S10ndashS11 Table 1) It shows a thin prograding seis-mic pattern commonly with parallel upper and lower bound-aries (cf Mitchum et al 1977) The successive internal progradational seismic events overlap each other between the upper and lower segments with a gentle dip of 152degndash193deg (Table 3) The lithofacies are mostly composed of several coarsening‐upward cycles (Figure 6d Table 1) Each cycle is composed of dark grey mudstones and grey to whitish‐grey medium‐ to fine‐grained sandstones Several coarsening‐up-ward lithofacies are mainly developed in D‐2 (Figure 6e Table 1)

42 | Analysis of the tectonic activityThe normal faults F1 and F2 selected to calculate the fault activity dipping to the north and running approximately E‐W are important boundary faults on the south‐western margin of the HD The tectonic‐subsidence rate fault‐growth index and fault‐activity rate were used as proxies to indicate the tectonic intensity (Figure 3 S2 Table 2) S‐4 and S‐3 (lower unit) have the highest subsidence rate (300ndash355 mMa) the highest fault‐growth index (292ndash343 mMa) and the highest fault‐activity rate (10647ndash11869 mMa) among the studied intervals whereas the overlying S‐3 (middle

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unit) and S‐1 + 2 are characterized by a much lower sub-sidence rate and fault‐growth index and fault‐activity rate D‐3 had again a high subsidence rate (190 mMa) and an average fault‐growth index (210 mMa) and fault‐activity rate (9344 mMa) The uppermost studied interval D‐2 had a much lower subsidence rate (60 mMa) growth index (136 mMa) and fault‐activity rate (3451 mMa) than the un-derlying unit Generally the analysis of the subsidence rate average fault‐growth index and fault‐activity rate indicates two phases of alternating strong tectonic activity and tectoni-cally stable conditions

43 | Palaeogeomorphology distribution and dimensions of the main depositional systemsDepositional systems of each depositional phase of the Palaeogene on the south‐western slope of the HD were com-piled through seismic facies identification of 3‐D seismic data and compilation of maps with the current thicknesses of the main target intervals based on the study by Liu Xia et al (2015a) that combined a correction for the depth of burial with an interpretation of the sedimentary facies The basins sink area on the south‐western slope of the HD was estimated on the basis of a palaeogeomorphological reconstruction The distribution of the depositional system is closely related to the evolution of the palaeogeomorphology and therefore we describe both the distribution of the depositional system and the palaeogeomorphology here

The palaeogeography of S‐4 is characterized by the larg-est extent of the uplifted areas of all studied intervals The depositional area is small and scattered (Figure 7a Table 4) Faults F1 and F2 mark the boundaries between erosional and depositional regions The elevated footwalls of the faults were erosional areas and located adjacent to the hanging walls whereas the hanging walls were low‐lying depositional areas The sedimentary facies analysis indicates a fan‐delta developed here (Figure 7a) Calculations indicate that the sedimentary dip of the four fan‐deltas was uncommonly high (about 463deg) The extent and thickness of the fan‐deltas di-minished towards the basin margin (Tables 34)

The tectonically‐induced morphology of S‐3 (lower unit) shows a similar pattern to that of the underlying S‐4 The depositional and erosional areas were also controlled by the active faults F1 and F2The HD deepened from west to east with the deepest area located just along the fault margin The depositional centre was located north of the hanging wall of F2 and became infilled by a fan‐delta (Figure 7b) The aver-age sedimentary dip of the fan‐delta is 303deg The extent of the fan‐delta was larger than that of S‐4 (Table 34)

During deposition of S‐3 (middle unit) the uplifted source area shifted southwards and the depression expanded A major depositional sink was located north of the hanging wall of F2 (Figure 7c Table 4) Elevation differences existed

between the footwalls and the hanging walls of F1 and F2 although the topography was obviously gentler during this time‐span A braided fluvial area developed at the footwalls of the faults whereas a braid‐delta developed mainly on the hanging wall of F2 and the northern depositional centre (Figure 7c) The braid‐delta had a fairly large extent and an average depositional dip of 119deg (Tables 34)

During S‐1 + 2 the elevated erosional area shifted farther southwards and the entire south‐western area had a low to-pography An alluvial plain developed south of the footwalls of the faults whereas a braid‐delta developed at the hanging walls and in the depression with a very gentle slope of 096deg (Table 4 Figure 7d) The depositional system was dominated by a fairly thin delta body and a braid‐delta with a much larger extent (Table 3)

During the deposition of D‐3 the topography of the foot-wall areas and of the area south of the provenance area was similar to that during the underlying S‐1 + 2 The slope was steep (187deg) in the hanging walls of the boundary faults however and the depositional area increased to 198 km2 which provided an excellent condition for the deposition of a large braid‐delta (Figure 7e Table 4) This braid‐delta had a NE‐SW orientation and covered an area of 142 km2 its average thickness is some 200 m which results in the largest delta volume in the Palaeogene on the south‐western slope of the HD (Table 3)

The palaeogeomorphological reconstruction of D‐2 shows a gentler topography in the entire south‐western HD with a sink area of 375 km2 (Table 4) The main body of the braid‐delta was dominated by imbricated progradational seis-mic reflections and developed in the hanging walls of F1 and F2 whereas an alluvial‐plain facies probably developed in the footwall areas of the faults and to the south‐west of the uplifted area (Figure 7f) Although the extent of the delta reached its maximum the thickness of the delta was limited due to the gentle topography resulting in a small delta vol-ume (Table 3)

5 | RELATIONSHIPS BETWEEN THE VARIOUS ELEMENTS OF THE S2S SYSTEM

Quantitative relationships between the various elements of the S2S system have been established through the above‐mentioned calculations A strong positive correlation is clearly present between the rate of tectonic subsidence the average fault activity and the average growth index of the boundary faults F1 and F2 (Figure 8ab) The rate of tectonic subsidence can therefore be used in the following as the pri-mary proxy to represent the intensity of the tectonic activity whereas the rate of fault activity and the growth index are used as secondary proxies

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The tectonic activity and the sediment‐supply rate show a positive relationship (Figures 8c 9a 10a) whereas the tec-tonic activity and the sink area of the basin show a negative relationship (Figures 8d 9b 10b) In contrast the tectonic activity has a positive relationship with the total accommo-dation space (Figures 8e 9c 10c Table 4) There is also a positive relationship between the average sedimentary dip of the fan‐ and braid‐deltas on the one hand and the tectonic activity on the other hand (Figures 8f 9d 10d)

The intensity of the tectonic activity correlates negatively with the extent of the sediment area but positively with the sediment volume (Figures 8g‐h 9e‐f 10e‐f) The different responses of the sediment area and the volume to the tectonic activity are caused by variations in the thicknesses of the sed-imentary units (Table 3)

There is also a positive relationship between the average seismic progradation dip of the fan‐ and braid‐deltas and the tectonic activity (Figures 8i 9g 10g) strong tectonic activ-ity usually formed deltas that are characterized by a chaotic progradational or oblique progradational seismic reflection such as SF 1 and 2 in S‐3 (lower unit) and S‐4 (Figures S3ndashS7) The minimum tectonic activity during Members S‐1 + 2 and D‐2 are reflected by dominantly shingled progradational seismic facies in the delta interior (Figures S10ndashS11)

In addition we find that the sediment area sediment vol-ume and average seismic progradation dip of the fan‐ and braid‐deltas correlate positively with the sediment‐supply rate (Figure 11a b and c) but negatively with the basin sink area (Figure 11d e and f) Both the sediment volume and the average seismic progradation dip of the fan‐ and braid‐deltas

F I G U R E 8 (a‐b) Relationships between the tectonic‐subsidence rate and tectonics (c‐i) Relationships between tectonic activity and sedimentary source‐to‐sink parameters Input data regarding the tectonic activity are from Table 2 those regarding the source‐to‐sink parameters data are from Tables 3 and 4 Regression‐line equations and coefficients of determination (R2) are shown for all diagrams

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show a positive relationship with the total accommodation space (Figure 11hi) However no obvious relationship ap-pears to be present between the sediment area and the total accommodation space (G) Both the sediment area and the average seismic progradation dip of the fan‐ and braid‐deltas correlate well with the average sedimentary dip of the fan‐ and braid‐deltas (Figure 11km) A poor correlation is found between the sediment volume and the average sedimentary dip of the fan‐ and braid‐deltas

6 | DISCUSSION

61 | Analysis of the influence of tectonic activity on the source area accommodation space geomorphology and sediment supplyA high relief and large drainage area usually can generate a large sediment supply (Leeder Harris amp Kirkby 1998 Syvitski amp Milliman 2007) Although the erosional area for the fan and delta system cannot be estimated because of the

limited data coverage the exposed area within the study area can be calculated The calculations show a generally decreas-ing trend of the source area from S‐4 (501 km2) to D‐2 (58 km2 Figure7 Table 4) The calculated exposed area cannot fully represent the true source area however but the evolu-tionary trend of the source area can be used as a proxy to indi-cate the relative influence on the change in sediment volume This trend is consistent with the decrease in sediment volume from S‐4 (2126 km3) to D‐2 (175 km3 Table 2) The relief is difficult to reconstruct in this case but variations in the fault‐activity rate (here taken as the tectonic‐subsidence rate) can create local elevation differences and can therefore be used as proxies for the trends in the relief development The relief shows an overall decreasing trend from S‐4 to D‐2 except for D‐3 this correlates well with the sediment volume (Figure 8h) Although the drainage area of D‐3 was smaller than that of D‐2 because of the high tectonic‐subsidence rate (result-ing in a high relief) D‐3 is thicker and shows a larger sedi-ment volume than the overlying D‐2 (Table 3) D‐3 is thinner than S‐4 + 3 but the larger source area resulted in a larger

F I G U R E 9 General relationships between the average fault‐growth index of F1 and F2 (AFGIF1‐F2) and sedimentary source‐to‐sink parameters The average fault‐growth index of F1 and F2 (AFGIF1‐F2) data in this figure are from Table 2 The source‐to‐sink parameters data are from Table 4 Regression‐line equations and the coefficients of determination are shown in each diagram

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sediment volume and supply rate (Table 3 Figure8ch) Therefore both the fault‐induced relief and the drainage area affected the sediment‐supply rate and the sediment volume in the sink

The changes in accommodation space during the vari-ous phases of the Palaeogene in the south‐western HD are clear from the estimated tectonic subsiding rate (Table 2) The correlations between the intensity of the tectonic activ-ity and the extent of the depositional sink area (Figures 8d 9b 10b) between the intensity of the tectonic activity and the total accommodation space and between the intensity of the tectonic activity and the morphology in the sink area (Figures 8e‐f 9c‐d 10c‐d) clearly show that strong tectonic activity resulted in a larger accommodation capacity of the sink

In particular the main subsiding area tended to form steeper slopes However the extent of the main subsiding sink area diminished (Figure 8d) with increasing tectonic activity which was possibly due to the relatively small sub-siding centre in the tectonically active basins It can thus be deduced that tectonic activity not only controlled the sedi-ment supply and the variation in accommodation space but

also determined the changes in the topography of the sedi-mentary basins and the extent of the main depositional areas in the tectonically active basins

62 | Analysis of the influence of tectonic activity on the size and internal stacking pattern of the delta depositional systemThe above data and considerations indicate that the tectonic activity was closely related to the sediment supply accom-modation space and morphology of the sink area which are possibly the most important factors affecting the extent and stacking pattern of the sedimentary facies (cf Cope et al 2010 DeCelles Kapp Ding amp Gehrels 2007 Leeder 2011 Olsen 1997 Simon et al 2017)

Statistical analysis indicates that the sediment‐supply rate has a strong positive correlation with the volume of the depositional system a moderate correlation with the seismic progradational dip in the depositional system and a poor cor-relation with the size of the depositional area (Figure 11a‐c) A larger sink area corresponded to a larger fanbraid‐delta a gentler seismic progradational angle and a reduced volume

F I G U R E 1 0 General relationships between average fault activity rate of F1 and F2 (RFAA‐F1‐F2) and sedimentary source‐to‐sink parameters The average fault activity rate of F1 and F2 (RFAA‐F1‐F2) data in this figure are from Table 2 The source‐to‐sink parameters data are from Table 4 Regression line equations and the coefficients of determination are shown in each diagram

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of the fan or braid‐delta which was possibly related to a re-duced sedimentary dip and thinner sediments (Figure 11d‐f) The total accommodation space in the basin correlates well

with the volume of the depositional system to some degree with the seismic progradational dip and poorly with the ex-tent of the depositional system area (Figure 11g‐i) These

FIGURE 11 Relationships between various parameters involved in the source‐to‐sink system (a‐c) Relationships between sediment supply and characteristics of the depositional system (extent volume and DPSA of the sediments) (d‐f) Relationships between the sink area of the basin and characteristics of the depositional system (g‐i) Relationships between the total accommodation space (AT) and the characteristics of the depositional system (j) Relationship between the accommodation‐spacesediment‐supply ratio (AS) and the DPSA of the sediments (k‐m) Relationships between the sedimentary dip and the characteristics of the depositional system The data regarding sediment supply basin sink area total accommodation space accommodation‐spacesediment‐supply ratio and sedimentary dips are from Table 4 The extent volume and DPSA of the sedimentary facies are from Table 3 Note the seemingly obvious polynomial (quadratic) relationship between the sedimentary dip and the sediment volume (L) The trend line in (L) suggests the following relationships between sediment volume and sedimentary slope in a rift or tectonically active basin (1) a very steep sedimentary slope is unfavourable for sediment accumulation (2) an appropriate sedimentary slope is favourable for preservation of depositional systems eg when the sedimentary slope in (L) is about 25degndash32deg the sediment volume reaches its largest value (3) a very gentle sedimentary slope will lead to a decrease of the sediment volume possibly due to weakening of the drainage system and thinner sediments

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relationships are clear evidence that the size of the sink area controlled the extent of the depositional system during the rifting of the lacustrine basin and that the rate of sediment supply and the accommodation space had a significant in-fluence on the total sedimentary volume as well as on the internal stacking pattern of the depositional system

We here use the ratio of the tectonic‐subsidence rate and the sediment‐supply rate as a proxy to indicate the ratio be-tween accommodation space and sediment‐supply rate (AS) (Table 4) AS has a strong influence on the internal stacking pattern of the depositional systems in the lacustrine rift basin (Figure 11j) This might be because the basin was small and because abundant and rapid material was supplied due

to intense tectonic activity (cf Catuneanu et al 2009 Liro 1993) and a favourable local climate (eg Bohacs Carroll Neal amp Mankiewicz 2000 Perlmutter amp Matthews 1989) The sediment supply still had a significant influence on the main subsidence area of the lacustrine basins and deposi-tional systems

In addition the basin slope significantly influenced the extent of the depositional system (Figure 11k) and had a polynomial relationship with its volume (Figure 11l) This relationship indicates that more intense tectonic activity and a steeper depositional slope were not favourable for sediment accumulation over a large extent in the lacustrine basin On the contrary these sediments were usually transported to a

F I G U R E 1 2 Tectonic differential activities and resulting patterns of the source‐to‐sink system on the south‐western slope of the HD during the Palaeogene (a) Development during phases of intense tectonics (Member 4 to the lower part of Member 3 of the Shahejie Fm) (b) Development during phases of somewhat less tectonic activity (middle part of Member 3 of the Shahejie Fm and Member 3 of the Dongying Fm) (c) Development during phases of weak tectonic activity (Members 1 and 2 of the Shahejie Fm and Member 2 of the Dongying Fm) The intensity of tectonic activity in the lacustrine rift basin had a significant influence on the development and extent of each unit of the source‐to‐sink system as well as on the type and dimensions of the depositional systems The present study indicates that probably sublacustrine fans developed (see for example Figure S4b) during phases with relatively strong tectonic activity This is not really clear from the seismic‐reflection data but possibly due to the small sizes of these sublacustrine fans Moreover lithofacies and core data are not available for the south‐western part of the study area The present contribution therefore focuses on the fan‐deltas and braid‐deltas regarding the sedimentary facies analysis the sublacustrine fans that probably developed in the deep or semi‐deep lake are presented just as a likely feature

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relatively small sink area with a fairly large accommodation space Finally stronger tectonic activity resulted in steeper depositional slopes (Figure 8f) which further controlled the hydrodynamic conditions and differential discharge when the sediments were deposited The strong correlation between the depositional slope and the deltas dip (Figure 11m) suggests that the differences in topography due to tectonics must be considered as one of the most critical factors that controlled the internal stacking pattern of the delta deposits

63 | Significance of the present study for other source‐to‐sink systems of lacustrine rift basins

631 | Summary of the source‐to‐sink systems in the HDIn lacustrine rift basins the tectonic setting is probably the main factor that determines the development of the S2S sys-tem but differential tectonic activities lead to variations in the basic characteristics of the S2S system Tectonic activity was most intense during S‐3 (lower unit) and during S‐4 and caused both a strong uplift of the source area and the devel-opment of depressions in the basin that formed a sink (Figure 12a) Strong tectonic activity in the S2S system during these time‐spans led to a high sediment‐supply rate steeper slopes a larger accommodation space and deposition of several fan‐deltas that are characterized by a fairly steep seismic progra-dational angle

The tectonic activity decreased during S‐3 (middle unit) and during D‐3 The S2S system that was present during this time‐span mainly concerned a rising area that shifted south-wards developing an alluvial plain between the erosional area and the sink area thus increasing the distance from source to sink (Figure 12b) Simultaneously the sediment‐supply rate and the accommodation space also changed and braid‐deltas could thus develop with larger volumes and gentler seismic progradational dips

Tectonic activity was clearly less intense during S‐1 + 2 and D‐2 The rising area had shifted further southwards cre-ating a wider alluvial plain connecting the source area to the sink in the HD (Figure 12c) At this stage stable tectonic activity led to relatively less sediment supply a gentle slope less accommodation space and the development of several braid‐deltas with a fairly gentle seismic progradational angle

632 | Wider implications and limitationsSoslashmme et al (2009) proposed that the elements of S2S sys-tems are genetically related and that quantitative correla-tions exist among these elements Other studies also suggest that the size of the drainage basin is correlated to the size of the fan developing on the basin floor (eg Blum et al

2017 Snedden et al 2018) and to the size of the river chan-nel (eg Milliken et al 2018) Helland‐Hansen Soslashmme Martinsen Lunt and Thurmond (2016) suggest a simplified subdivision of S2S systems into three main categories (a) Steep‐Short‐Deep (steep onshore and offshore gradients short distance between source and sink and deep offshore waters) (b) Wide‐Deep (low‐gradient shelf‐catchment area and deep offshore waters) and (c) Wide‐Shallow (relatively shallow offshore waters and a wide low‐gradient catchment area) systems

The present study indicates that the alluvial plain roughly corresponds to the alluvial‐shelf unit in marine basins al-though with a much smaller width and extent in the lacustrine rift basins than would have been the case on a continental shelf Faults F1 and F2 along the slope belt correspond to the slope of classical S2S systems whereas the shore‐shallow‐deep lake area can be compared with the basin floor (Soslashmme et al 2009) S‐4 and S‐3 (lower unit) can be roughly clas-sified as Steep‐Short‐Deep systems whereas the overlying S‐1 + 2and D‐2 can be classified as the Wide‐Shallow sys-tems that Helland‐Hansen et al (2016) defined During the deposition of S‐4 and S‐3 (lower unit) the strong tectonic activity caused a high relief of the source area a narrow allu-vial plain and a relatively deep lake The subsequently wan-ing tectonic activity resulted in a lower relief of the source area a wider alluvial plain and a shallower lake Although the absolute values of these elements in lacustrine basins are much smaller than those of marine basins the ratio between these elements in both settings is comparable Typically in a lacustrine basin a transformation from a Steep‐Short‐Deep system (S‐4 and S‐3 (lower unit)) to a Wide‐Shallow system (S‐1 + 2ampD‐2) occurs within a few million years Although the basin geomorphology has experienced signif-icant changes from S‐4 to D‐2 the quantitative relationships between tectonic activity sediment‐supply rate accommoda-tion space and sedimentary dip of the delta systems did not change significantly (eg Figures 8 and 11) The analytical approaches applied and quantitative relationship established here can help analyse other lacustrine basins worldwide and may even act as a reference for the analysis of marine basins

Our study focuses mainly on the influences of tectonic activity on the elements of the depositional sink Other pa-rameters (eg climate and lithology) were not considered in detail Studies on modern and ancient systems suggest that the climate and lithology also have a great influence on the sediment supply and distribution in the basin (eg Carroll Chetel amp Smith 2006 Hovius amp Leeder 1998 Syvitski amp Milliman 2007 Zhang et al 2018) For exam-ple climate variations between glacials and inter‐glacials have resulted in largely different sediment‐supply rates and in significant differences in the sizes of the Quaternary sub-marine fans in the north‐western Gulf of Mexico (Blum amp Hattier‐Womack 2009) We acknowledge the importance

| 609EAGE

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of climate and lithology for S2S systems and we are con-vinced that these elements can significantly affect the S2S systems in other cases(eg modern systems and systems influenced by glacialinterglacial alternations) These fac-tors were not really relevant for the present study however because no significant differences in lithology were present in the source areas and because we focus on the changes at a million‐year scale which implies that the tectonic ac-tivity has a first‐order control on the development of S2S elements in the investigated rift basin

7 | CONCLUSIONS

We have calculated the tectonic‐subsidence history the growth index and the activity rate of the main boundary faults (F1 and F2) and various S2S parameters of six Palaeogene rock units on the south‐western slope of the HD Based on the values found for these parameters quantitative corre-lation were established for the tectonic activity and other S2Sparameters in the basinal sink This leads to the follow-ing conclusions

1 The positive correlation between the intensity of fault activity and the tectonic‐subsidence rate is a strong indication for a distinct control by the tectonic activity of the syn‐depositional rifting of the tectonically active basin

2 The tectonic activity was quantitatively related to the sediment supply accommodation space and morphology of the sink area The relationship between tectonic activ-ity and depositional systems is reflected by changes in critical factors such as sediment supply accommodation space and dip of the sink area These critical factors were probably the most important factors that led to changes in the size and internal stacking pattern of the sedimentary facies

3 Differential tectonic activity led to changes in the char-acteristics of the S2S system on the south‐western slope of the HD The strongest tectonic activity which oc-curred during S‐3 (lower unit) and during S‐4 led to the largest provenance area adjacent to the sink area to a high sediment‐supply rate to steeper slopes to a larger accommodation space and controlled the development of several fan‐deltas Diminished tectonic activity dur-ing S‐3 (middle unit) and during D‐3 led to a decrease in uplift an increased width of the alluvial plain an in-creased transport distance a decrease in the sediment‐supply rate and accommodation space and resulted in the development of braid‐deltas with a large volume During S‐1 + 2 and D‐2 stable tectonic activity led to a lower sediment‐supply rate a gentle depositional slope and a smaller accommodation space resulting in the

development of several braid‐deltas with gentler seis-mic progradational angles

4 The analytical approaches applied and the quantitative re-lationships established here can help analyse other lacus-trine basins worldwide and may even act as a reference for the study of marine basins

ACKNOWLEDGEMENTS

We thank Dr Sarah Boulton and Dr Chenlin Gong as well as the Associate Editor of Basin Research Dr Craig Magee for their constructive comments on the manuscript This study was funded by the National Science and Technology Major Project (Exploration Technologies for Offshore Hidden OilGas) (project no 2016ZX05024‐003‐003) the National Natural Science Foundations of China (project no 41676050) and the Fundamental Research Funds for the Central Universities (2652014037)

REFERENCES

Allen P A (2008a) From landscapes into geological history Nature 451 274ndash276 https doiorg101038natur e06586

Allen P A (2008b) Time scales of tectonic landscapes and their sed-iment routing systems In Landscape evolution Denudation cli-mate and tectonics over different time and space scales (Ed by Gallagher K Jones S J amp Wainwright J) Geological Society London Special Publications 296 7ndash28

Allen P A Armitage J J Carter A Duller R A Michael N A Sinclair H D hellip Whittaker A C (2013) The Qs problem Sediment volumetric balance of proximal foreland basin systems Sedimentology 60 102ndash130

Amorosi A Maselli V amp Trincardi F (2016) Onshore to offshore anatomy of a late Quaternary source‐to‐sink system (Po Plain‐Adriatic Sea Italy) Earth‐Science Reviews 153 212ndash237 https doiorg101016jearsc irev201510010

Anderson J B Wallace D J Simms A R Rodriguez A B Weight R W R amp Taha Z P (2016) Recycling sediments between source and sink during a eustatic cycle Systems of late Quaternary northwestern Gulf of Mexico Basin Earth‐Science Reviews 153 111ndash138 https doiorg101016jearsc irev201510014

Anthony E J amp Julian M (1999) Source‐to‐sink sediment trans-fers environmental engineering and hazard mitigation in the steep Var River catchment French Riviera southeastern France Geomorphology 31 337ndash354 https doiorg101016S0169-555X(99)00088-4

Athy L F (1930) Density porosity and compaction of sedimentary rocks AAPG Bulletin 14 1ndash24

Bhattacharya J P Copeland P Lawton T F amp Holbrook J (2016) Estimation of source area river palaeo‐discharge palaeoslope and sediment budgets of linked deep‐time depositional systems and im-plications for hydrocarbon potential Earth‐Science Reviews 153 77ndash110

Blum M D amp Hattier‐Womack J (2009) Climate change sea‐level change and fluvial sediment supply to deepwater depositional

| 593EAGE

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basin‐controlling faults and because of the changes in the intensity of the fault activity

33 | Quantitative calculation of S2S system parameters

331 | Area and volume of the sedimentary faciesQuantitative calculation of the dimensions of sedimentary facies requires reliable estimates of the lateral extent and thickness of the sediments involved For these calculations first the maxi-mum extent of the specific units under study (fan‐deltas braid‐deltas etc) at different times was determined in plan view based on the combined interpretation obtained from seismic facies lithofacies and the outer boundaries of the sediment bodies Subsequently the outcomes were digitalized and used as input for a 3‐D survey by GEOFRAME Detailed calculations of the sedi-ment bodies extents were conducted using the PLANIMETER tool in the BASEMAP window of GEOFRAME

This was followed by the selection of several seismic sec-tions across the sediment body in order to identify the lower

and upper boundaries as well as to calculate the maximum minimum and average thickness (see Amorosi Maselli amp Trincardi 2016 Liu et al 2017) Finally we used a colum-nar body with irregular base and the same height to represent the irregular sediment body The formula for volume calcu-lation is as follows (Figure 4 Table 3 supplementary text)

where VS is the volume of the sediment (in km3) AS is the horizontal surface area of the irregular base of the sediment (in km2) and H is the height (average thickness) of the sed-iment (in m) Detailed calculations of the thickness were conducted using the AREAL tool in the SEIS3DVSEIS2DV window of GEOFRAME

332 | Determination of the depositional dip of the delta surface due to progradationThe term ldquodepositional diprdquo is used here to indicate the inclination of a dipping sedimentary surface Horizon flat-tening was used to analyse and calculate the morphology of the underlying strata First the maximum flooding surface ndash approximately corresponding to the palaeo‐sedimentary surface (Lin et al 2012) ndash of each unit under study was interpreted it was subsequently flattened to calculate the original depositional dip (Figure 5d) with the formula

where DSD is the sedimentary dip (in degrees) dy is the verti-cal thickness between the lower boundary of the sedimentary unit and the ancient sedimentary surface in the depositional centre (in m) and dx is the distance from the apex of the delta to its depositional centre (in m)

Two to four seismic sections have been selected to calcu-late the average sedimentary dip of each individual delta with the following formula

where DSDA is the average sedimentary dip of a sediment (in degrees) and n is the number of seismic sections

The seismic progradational angle of the deltas interior has been calculated by the horizon‐flattening method (Figure 5e) which is expressed by the formula

VS=A

StimesH

DSD

= tanminus1 (dy∕dx)

DSDA

=

(

nsum

i=1

DSDi

)

∕n

DP= tan

minus1 (dy∕dx)

F I G U R E 4 Schematic diagram showing the calculation of the volume of a sediment (a) is an irregular sediment body Volume calculation of cuboids was used for reference to calculate the volume of an irregular sedimentary body ie the volume of an irregular sediment body equals the area of the irregular bottoms times height (b) 3ndash4 seismic lines along the sedimentary body are selected and the thickness of the sedimentary body is determined at intervals of 10 seismic traces (c) when a thickness grid covering the entire sedimentary body in space is acquired the average thickness of all counted thicknesses can be calculated as the height of the irregular sediment body (d)

594 | EAGE

LIU et aL

where DP is the seismic progradational dip (in degrees) The average dip angle is obtained from only one seismic sec-tion because of the variations in the progradational seismic event of the delta on the same seismic line

where DPA is the average seismic progradational dip in a spe-cific seismic section (in degrees) and n is the number of seis-mic progradational events

Based on the calculated average dip of one seismic sec-tion the average progradational dip of a specific sediment body can be calculated with the formula

DPA

=

(

nsum

i=1

DPi

)

∕n

F I G U R E 5 Detailed calculations of the sedimentary dip and the progradational seismic event dip of the delta interior taking the progradation seismic reflection of the delta developed in Member 3 of the Dongying Formation as an example The locations of the seismic lines are shown in Figure 1c Based on the interpretation of the stratigraphic and seismic facies visible in the original seismic lines (a) the topset or the maximum flooding surface (MFS) corresponding to the delta was flattened (b) Taking into account the water depth during sedimentation the sedimentary dip (d) and the progradational seismic event dip of the delta interior (e) can be calculated DSD = depositional dip in a specific seismic section DSDA = average depositional dip of a specific sedimentary unit DP = seismic progradational dip DPA = average seismic progradational dip

| 595EAGE

LIU et aL

TA

BL

E 1

In

terp

reta

tion

of th

e m

ain

sedi

men

tary

faci

es in

the

Pale

ogen

e of

the

Hua

nghe

kou

Dep

ress

ion

Evi

denc

e of

fan

delta

s and

bra

id d

elta

s in

wel

ls W

1 an

d W

18 c

omes

from

Liu

Xia

et a

l (2

015a

)

Form

atio

n an

d m

embe

raSe

ismic

faci

esEx

ampl

esLi

thof

acie

sLi

thol

ogy

Wel

l amp c

ore

exam

ples

Dep

ositi

onal

en

viro

nmen

tPr

edic

ted

res-

ervo

ir q

ualit

y

D‐2

Seis

mic

Fac

ies 5

mod

erat

e co

ntin

uous

lo

w‐a

mpl

itude

and

a sh

ingl

ed‐li

ke

prog

rada

tiona

l sei

smic

refle

ctio

n

Figu

re

Mul

tiple

upw

ard‐

coar

s-en

ing

litho

faci

es

asso

ciat

ions

Gre

y m

udst

ones

gre

y to

gre

yish

w

hite

pebb

ly fi

ne sa

ndst

ones

and

fin

e sa

ndst

ones

T25

Bra

id d

elta

Mod

erat

e to

hi

gh

D‐3

Seis

mic

Fac

ies 4

con

tinuo

us m

oder

-at

e‐to

high

‐am

plitu

de a

nd o

bliq

ue‐

to‐s

igm

oid

prog

rada

tiona

l sei

smic

re

flect

ion

Figu

re

Mul

tiple

upw

ard‐

coar

s-en

ing

litho

faci

es

asso

ciat

ions

Gre

yish

whi

te to

whi

te fi

ne

sand

ston

es s

iltst

ones

and

gre

y m

udst

ones

T25

Bra

id d

elta

Hig

h

Figu

re 7

e‐f

S‐1

+ 2

Seis

mic

Fac

ies 5

mod

erat

e co

ntin

uous

m

oder

ate‐

ampl

itude

and

shin

gled

‐like

pr

ogra

datio

nal s

eism

ic re

flect

ion

Figu

re

Mul

tiple

upw

ard‐

coar

s-en

ing

litho

faci

es

asso

ciat

ions

Dar

k gr

ey m

udst

ones

and

gre

yish

w

hite

to g

rey

mid

dle‐

to fi

ne‐

grai

ned

sand

ston

es

T25

Bra

id d

elta

Hig

h

S‐3

(mid

dle

unit)

Seis

mic

Fac

ies 3

har

dly

tom

oder

atel

y co

ntin

uous

low

‐am

plitu

de o

bliq

ue

prog

rada

tiona

l sei

smic

refle

ctio

n

Figu

re

Lith

ofac

ies 1

Gre

y to

gre

yish

whi

te sa

ndy

cong

lom

erat

esT2

5B

raid

del

taH

igh

Lith

ofac

ies 2

Thic

k gr

ey m

iddl

e‐to

fine

‐gra

ined

sa

ndst

ones

Figu

re 7

a‐d

Lith

ofac

ies 3

Gre

y m

udst

ones

inte

rbed

ded

with

gr

ey fi

ne sa

ndst

ones

and

gre

y m

uddy

silts

tone

s

Lith

ofac

ies 4

Thic

k da

rk g

rey

mud

ston

es

S‐3

(low

er

unit)

Seis

mic

Fac

ies 2

cha

otic

prog

rada

-tio

nal t

o ob

lique

pro

grad

atio

nal

seis

mic

faci

es

Figu

re

Pe

bbly

sand

ston

es in

terb

edde

d w

ith

thin

bro

wn‐

grey

mud

ston

esb

row

n sa

ndy

cong

lom

erat

ess

ands

tone

s in-

terb

edde

d w

ith th

in m

udst

ones

thic

k m

udst

ones

inte

rbed

ded

with

th

in sa

ndst

ones

or p

ebbl

y fin

e sa

ndst

ones

T1Fa

n de

ltaM

oder

ate

S‐4

Seis

mic

Fac

ies 1

dis

cont

inuo

us to

con

-tin

uous

low

‐tohi

gh‐a

mpl

itude

cha

otic

pr

ogra

datio

nal s

eism

ic re

flect

ion

Figu

re

Figu

re

Fig

ure

and

Fi

gure

Lith

ofac

ies 1

Gre

y pe

bbly

sand

ston

es c

oars

e sa

ndst

ones

T18

Fan

delta

sM

oder

ate

Lith

ofac

ies 2

Ash

‐bla

ck m

udst

ones

inte

rbed

-de

d w

ith th

in g

rey

fine‐

grai

ned

sand

ston

es

Lith

ofac

ies 3

Ash

‐bla

ck m

udst

ones

inte

rbed

ded

with

peb

bly

sand

ston

esa D

= D

ongy

ing

Fm

S =

Sha

hejie

Fm

The

num

ber i

ndic

ates

the

num

ber o

f the

mem

ber

596 | EAGE

LIU et aL

TA

BL

E 2

Es

timat

ion

stat

istic

s of t

he te

cton

ic‐s

ubsi

denc

e ra

te g

row

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and

activ

ity ra

te o

f fau

lts F

1 an

d F2

S1

S2

and

S3 a

re th

e ca

lcul

atio

n lo

catio

ns o

f F1

and

F2 (s

ee F

igur

e 1c

) th

e co

rres

pond

ing

num

bers

are

F1‐

S1 F

1‐S2

F1‐

S3 F

2‐S1

F2‐

S2 a

nd F

2‐S3

res

pect

ivel

y

Form

atio

n an

d m

embe

raA

ge

(Ma)

R TS

(m

Ma)

b

Faul

t‐gro

wth

inde

xFa

ult‐a

ctiv

ity r

ate

(mM

a)

AFG

I F1‐

F2c

R FA

A‐F

1‐F2

d

S1S2

S3A

vera

geS1

S2S3

aver

age

F1F2

F1F2

F1F2

F1F2

F1F2

F1F2

F1F2

F1F2

D‐1

233

75ndash

267

1450

00

111

106

109

110

107

109

109

108

389

270

389

479

270

389

349

379

109

364

D‐2

267

14ndash

302

060

00

139

130

138

140

137

133

138

134

320

730

29

341

442

62

329

534

98

330

535

96

136

345

1

D‐3

302

0ndash33

278

190

002

002

052

102

342

032

052

042

1579

67

104

0010

372

111

3485

59

762

989

66

972

12

1093

44

S‐1

+ 2

332

78ndash

378

9250

00

145

136

142

147

155

145

148

143

122

211

36

105

915

78

587

176

39

5614

92

146

122

4

S‐3

(mid

dle

unit)

378

92ndash

404

3812

500

131

202

192

242

175

257

166

234

335

140

88

490

380

62

215

510

919

347

076

90

205

558

0

S‐3

(low

er

unit)

404

38ndash

422

3135

500

284

343

302

395

342

389

309

376

737

185

37

104

4016

956

742

820

480

841

315

324

343

118

69

S‐4

422

31ndash

447

300

002

512

921

584

173

023

332

373

4791

33

106

4357

58

151

8811

007

121

5186

33

126

612

9210

647

a D =

Don

gyin

g Fm

S

= S

hahe

jie F

m T

he n

umbe

r ind

icat

es th

e nu

mbe

r of t

he m

embe

r b R T

S = te

cton

ic‐s

ubsi

denc

e ra

te

c AFG

I F1‐

F2 =

ave

rage

faul

t‐gro

wth

inde

x of

F1

and

F2

d R FA

A‐F

1‐F2

= a

vera

ge fa

ult‐a

ctiv

ity ra

te o

f F1

and

F2

| 597EAGE

LIU et aL

TA

BL

E 3

C

alcu

latio

n ch

art o

f the

sedi

men

tary

‐fac

ies d

imen

sion

s and

the

inte

rnal

pro

grad

atio

nal s

eism

ic e

vent

dip

The

spat

ial e

xten

t is s

how

n in

Fig

ure

7

Form

atio

nand

mem

bera

Sedi

men

tary

faci

esSe

ismic

sect

ions

Thic

knes

s (m

)

Are

a (k

m2 )

Vol

ume

(km

3 )To

tal v

olum

e (k

m3 )

DPb

Max

M

in

Ave

rage

DPA

DPS

A

D‐2

Bra

id d

elta

Figu

re a

176

0075

00

107

7016

246

175

017

50

157

156

Figu

re b

174

0080

00

157

Figu

re c

218

0080

00

152

D‐3

Bra

id d

elta

Figu

re a

285

0011

400

200

5014

219

285

128

51

268

285

Figu

re b

295

0099

00

309

Figu

re c

296

0078

00

309

Figu

re d

284

0091

00

254

S‐1

+ 2

Bra

id d

elta

Figu

re a

178

0089

00

136

7512

023

164

416

44

172

177

Figu

re b

185

0095

00

176

Figu

re c

236

0010

500

193

Figu

re d

209

0011

400

166

S‐3

(mid

dle

unit)

Bra

id d

elta

Figu

re a

274

0010

100

223

7587

87

196

619

66

213

225

Figu

re b

279

0083

00

225

Figu

re c

292

0086

00

235

Figu

re d

296

0086

00

226

S‐3

(low

er u

nit)

Fan

delta

Figu

re a

428

8623

903

374

0062

89

235

223

52

301

305

Figu

re b

432

5522

071

325

Figu

re c

473

0920

583

312

Figu

re d

450

8325

500

283

S‐4

Fan

delta

1Fi

gure

a30

700

483

929

200

107

03

1221

26c

423

365

Figu

re b

350

0010

728

439

Fan

delta

2Fi

gure

a46

500

704

832

900

856

282

421

Figu

re b

379

0066

52

362

Fan

delta

3Fi

gure

a40

100

118

7841

100

186

27

654

21

Figu

re b

468

0016

718

309

Figu

re c

527

0015

127

387

Figu

re d

486

0014

844

297

Fan

delta

4Fi

gure

a42

800

151

2042

700

179

57

663

04

Figu

re b

512

0027

287

289

a D =

Don

gyin

g Fm

S

= S

hahe

jie F

m T

he n

umbe

r ind

icat

es th

e nu

mbe

r of t

he m

embe

r b D

P = se

ism

ic p

rogr

adat

iona

l dip

DPA

= a

vera

ge se

ism

ic p

rogr

adat

iona

l dip

DPS

A =

ave

rage

seis

mic

pro

grad

atio

nal d

ip o

fthe

sedi

men

t c 21

26

= to

tal j

oint

vol

umes

of f

an d

elta

s 1 2

3 a

nd 4

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where DPSA is the average seismic progradational dip of a sediment (in degrees) and n is the number of seismic sections

Detailed estimated results of the depositional dip and the seismic progradational dip of the delta are shown in Tables 3 and 4

333 | Provenance conditions and estimation of the sediment supplySystematic investigation by TBCNOOC of the regional uplift and provenance in the geological past has indicated that the main provenance areas around the HD existed alreadybefore the deposition of Member 3 of the Shahejie Fm (Zhou et al 2010) They include the Bonan Laibei and Kendong Highs (Figure 1b‐c Figure S1a‐b) However starting with the depo-sition of Members 1ndash2 of the Shahejie Fm (S‐1 + 2) (3789ndash3328 Ma) until the accumulation of the Dongying Formation (3328ndash2338 Ma) the Bonan and Laibei Highs subsided to below lake level and consequently stopped providing sedi-ment to the depression (Liu Xia et al 2015a) Only the Kendong High which remained a high for a long time re-mained a provenance area for the south‐western part of the

HD during this time‐span (Figure S1a) The Kendong High has therefore been selected as the site where the relationship between tectonics and depositional systems within the same provenance system could be studied best The distribution area of the Kendong High as the provenance area at different moments has been determined on the basis of numerous seis-mic interpretations through seismic terminations (eg onlap) and the absence of specific sediment units due to faulting

The sediment‐supply rate can be obtained by calculation of the volumes of the deltas and the duration of their forma-tion (cf Allen et al 2013 Lemons amp Chan 1999 Lemons Milligan amp Chan 1996) Although the stratigraphic ages are well‐known for each unit (Figure 2) there is no high‐resolu-tion age control for the top and base of each delta system The absolute age of the pertinent stratigraphic unit (Figure 2) is therefore used to represent the formation time of the individual deltas in the unit The thus calculated sediment‐supply rate rep-resents in our opinion the trend of the supply rate from bottom to top sufficiently well

334 | Estimation of the extent and accommodation space of the sink areaDetermination of the boundaries of the sink area is based on reconstructions of the morphology during the successive dep-ositional phases The extent of the sink area was estimated using the same calculations as for the area of the depositional system

DPSA

=

(

nsum

i=1

DPAi

)

∕n

F I G U R E 6 Vertical successions and representative examples of the various lithofacies (a) A fan‐delta in Well W18 (b‐e) Braid‐deltas in Well W25 (f) Grey to greyish white sandy conglomerate (deposits in braided channels) (g) Grey medium‐ to fine‐grained massive sandstone (mouth‐bar deposits) (h) Grey fine sandstone (distal sand bars) (i) Grey muddy siltstone with parallel bedding (prodelta) (j) Greyish white fine sandstone with convolute bedding (mouth bars) (k) Greyish white fine sandstone with boulders (mouth bars) Wireline logs show the spontaneous‐potential (SP) and gamma‐ray (GR) changes with depth Depth in metres For location of the cores see Figure 6bd

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Differences in base level and the original sedimentary sur-face define the accommodation space (Jervey 1988 Muto amp Steel 2000 Neal amp Abreu 2009 Wheeler 1964) The

accommodation space in the depositional area can be deter-mined on the basis of the thickness of the preserved sediments (Muto amp Steel 2000) This space is obviously controlled by

F I G U R E 7 Schematic morphology during the successive depositional phases The extent of the deltas the depositional sink area in the basin and the main features of the drainage systems are shown The extent of the deltas has been interpreted from seismic data and has been used for calculation of the surface area and volume of the various deltas (a) Shahejie Fm Member 4 (b) Shahejie Fm lower part of Member 3 (c) Shahejie Fm middle part of Member 3 (d) Shahejie Fm Members 1 and 2 (e) Dongying Fm Member 3 (f) Dongying Fm Member 2

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the rate of subsidence tectonic uplift and fluctuations of the lake level (Lemons amp Chan 1999) Changes in the lake level of the HD have not been investigated so that we take data on the tectonic‐subsidence rate as a proxy for changes in the accommodation space The total space is expressed in the equation (Table 4)

where AT represents the total accommodation space of the sink area (in km3) TS represents the tectonic subsidence (in m) and SA represents the surface area of the sink (in km2)

AT= TStimesSA∕1000

T A B L E 4 Estimation of the controlling factor parameters of the depositional system The distribution characteristics of the depositional sink in the basin are shown in Figure 7

Formation and membera

Sedimentary facies Seismic sections

DDb

RSSc(km3

Ma)Sink area (km2) AT

d(km3) ASeSource areaf(km2)DSD DSDA

D‐2 Braid delta Figure a 059 066 502 37542 7852 1195 58

Figure b 065

Figure c 074

D‐3 Braid delta Figure a 161 187 926 19823 11593 2051 252

Figure b 192

Figure c 215

Figure d 182

S‐1 + 2 Braid delta Figure a 086 096 356 28015 6463 1403 220

Figure b 094

Figure c 120

Figure d 083

S‐3 (middle unit) Braid delta Figure a 110 119 772 21756 6927 1619 355

Figure b 111

Figure c 129

Figure d 128

S‐3 (lower unit) Fan delta Figure a 307 303 1313 16506 10500 2705 482

Figure b 334

Figure c 332

Figure d 237

S‐4 Fan delta 1 Figure a 384 463g 861 14150 10481 3484 501

Figure b 379

Fan delta 2 Figure a 606

Figure b 498

Fan delta 3 Figure a 479

Figure b 499

Figure c 625

Figure d 553

Fan delta 4 Figure a 377

Figure b 226aD = Dongying Fm S = Shahejie Fm The number indicates the number of the member bDD = depositional dip DSD = depositional dip in a specific seismic section DSDA = average depositional dip of a specific sedimentary unit cRSS = sediment‐supply rate dAT = total accommodation space eAS = accommodation spacesediment supply fSource area = Denudation area within the seismic data coverage The complete erosional area cannot be estimated because of the limited data coverage g463 = the average depositional dip of fan deltas 1 2 3 and 4 Considering that the four fan deltas developed during S‐4 consist of sediment that was derived from the same provenance area and were deposited in the same time‐span the four fan deltas are taken as a whole when estimating the parameters of RSS the sink area AT and AS

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4 | ELEMENTS OF THE S2S SYSTEM

41 | Analysis of the seismic facies and stacking pattern of the main sedimentary faciesA comprehensive analysis of seismic data cores cutting log-gings and well‐logging curves by Liu Xia et al (2015a) in-dicated that the Palaeogene depositional systems of the HD included fan‐deltas braid‐deltas lake margins deep lakes etc The fan‐ and braid‐deltas have been chosen for a detailed seismic study that must reveal their internal texture and their stacking patterns Analysis of the progradational seismic‐re-flection types and of the seismic progradational dip is particu-larly helpful for a better understanding of the hydrodynamic conditions and sedimentary processes that resulted in these depositional systems Because the facies interpretation in this area has been done before and is not the focus of this work we here mainly describe the internal texture and their stack-ing patterns of the main sedimentary facies

The major facies of S‐4 is interpreted as a fan‐delta It is dominated by Seismic Facies 1 which is characterized by discontinuous to continuous low‐ to high‐amplitude and chaotic progradational seismic reflections (Figures S3ndashS6 Table 1) The average dip of the progradational seismic event is about 365deg (Table 3) Three lithofacies are associated with Seismic Facies 1 (Table 1) The coarser lithofacies 1 represents a fan‐delta front whereas the finer lithofacies 2 and 3 are prodelta deposits The overall coarsening‐upward succession facies stacking pattern (Figure 6a) discontinuous and chaotic seismic reflections and relatively steep slope of Seismic Facies 1 suggest a fan‐delta system developed under strong hydrodynamic conditions (Mitchum et al 1977)

The fan‐delta of the lower part of Member 3 of the Shahejie Fm (S‐3 [lower unit]) is dominated by Seismic Facies 2 which is characterized by chaotic progradational to oblique progradational seismic characteristics It has a typical wedge shape and is composed of two seismic‐reflection seg-ments (a) a moderately continuous low‐ to high‐amplitude chaotic seismic‐reflection segment located near boundary fault F2 and (b) a continuous moderate‐ to high‐amplitude and oblique progradational seismic reflection in a basinward direction (Figure S7 Table 1) No obvious upper or lower segments occur in SF 2 and the dip of the progradational seismic event in this segment is also relatively steep viz 305deg (Table 3)

The middle part of Member 3 of the Shahejie Fm (S‐3 [middle unit]) is characterized by a low‐ to moderate‐con-tinuous low‐amplitude and oblique progradational seismic reflection (Seismic Facies 3) and is interpreted as a braid‐delta (Figure S8 Table 1) The progradational seismic events are parallel or sub‐parallel to each other and dip less (aver-age 225deg) than Seismic Facies 1 and 2 (Table 3) Seismic

Facies 3 is associated with four lithofacies (Figure 6b Table 1) in Well T25 The complete succession of the braid‐delta consists of gravely to coarse‐grained sandstone (lithofacies 1) at the base (Figure 6f) massive bedded medium‐ to fine‐grained sandstones (lithofacies 2) and grey mudstones inter-bedded with grey fine sandstones and grey muddy siltstones (lithofacies 3) in the middle (Figures 6g and 6h) and thick dark grey mudstones (lithofacies 4) at the top (Figure 6i)

Member 3 of the Dongying Fm (D‐3) is characterized by Seismic Facies 4 a typically composite seismic progra-dation reflection configuration representing a braid‐delta system (Figure S9 Table 1) Seismic Facies 4 is composed of highly continuous moderate‐ to high‐amplitude and pro-gradational seismic reflections that represent well‐developed deltaic topsets and bottomsets The topset segments of SF 4 are nearly horizontal or dip only gently (Table 3) The foreset segments form thicker lenses with small depositional angles The oblique progradational part of this seismic facies is sim-ilar to that in Seismic Facies 3 and usually developed at the basinward front end of Seismic Facies 3 The lithology of Seismic Facies 4 is dominated by greyish white to white fine‐grained sandstones and siltstones The lithofacies association is characterized by coarsening‐upward sedimentary cycles (Figure 6c Table 1) Convolute bedding and abundant diam-ictites are present on top of the fine sandstones (Figure 6j‐k)

Both braid‐deltas in the Members 1 + 2 of th Shahejie Fm (S‐1 + 2) and Member 2 of the Dongying Fm (D‐2) show moderately continuous moderate‐amplitude and shin-gled‐like progradational seismic reflections (Seismic Facies 5 Figures S10ndashS11 Table 1) It shows a thin prograding seis-mic pattern commonly with parallel upper and lower bound-aries (cf Mitchum et al 1977) The successive internal progradational seismic events overlap each other between the upper and lower segments with a gentle dip of 152degndash193deg (Table 3) The lithofacies are mostly composed of several coarsening‐upward cycles (Figure 6d Table 1) Each cycle is composed of dark grey mudstones and grey to whitish‐grey medium‐ to fine‐grained sandstones Several coarsening‐up-ward lithofacies are mainly developed in D‐2 (Figure 6e Table 1)

42 | Analysis of the tectonic activityThe normal faults F1 and F2 selected to calculate the fault activity dipping to the north and running approximately E‐W are important boundary faults on the south‐western margin of the HD The tectonic‐subsidence rate fault‐growth index and fault‐activity rate were used as proxies to indicate the tectonic intensity (Figure 3 S2 Table 2) S‐4 and S‐3 (lower unit) have the highest subsidence rate (300ndash355 mMa) the highest fault‐growth index (292ndash343 mMa) and the highest fault‐activity rate (10647ndash11869 mMa) among the studied intervals whereas the overlying S‐3 (middle

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unit) and S‐1 + 2 are characterized by a much lower sub-sidence rate and fault‐growth index and fault‐activity rate D‐3 had again a high subsidence rate (190 mMa) and an average fault‐growth index (210 mMa) and fault‐activity rate (9344 mMa) The uppermost studied interval D‐2 had a much lower subsidence rate (60 mMa) growth index (136 mMa) and fault‐activity rate (3451 mMa) than the un-derlying unit Generally the analysis of the subsidence rate average fault‐growth index and fault‐activity rate indicates two phases of alternating strong tectonic activity and tectoni-cally stable conditions

43 | Palaeogeomorphology distribution and dimensions of the main depositional systemsDepositional systems of each depositional phase of the Palaeogene on the south‐western slope of the HD were com-piled through seismic facies identification of 3‐D seismic data and compilation of maps with the current thicknesses of the main target intervals based on the study by Liu Xia et al (2015a) that combined a correction for the depth of burial with an interpretation of the sedimentary facies The basins sink area on the south‐western slope of the HD was estimated on the basis of a palaeogeomorphological reconstruction The distribution of the depositional system is closely related to the evolution of the palaeogeomorphology and therefore we describe both the distribution of the depositional system and the palaeogeomorphology here

The palaeogeography of S‐4 is characterized by the larg-est extent of the uplifted areas of all studied intervals The depositional area is small and scattered (Figure 7a Table 4) Faults F1 and F2 mark the boundaries between erosional and depositional regions The elevated footwalls of the faults were erosional areas and located adjacent to the hanging walls whereas the hanging walls were low‐lying depositional areas The sedimentary facies analysis indicates a fan‐delta developed here (Figure 7a) Calculations indicate that the sedimentary dip of the four fan‐deltas was uncommonly high (about 463deg) The extent and thickness of the fan‐deltas di-minished towards the basin margin (Tables 34)

The tectonically‐induced morphology of S‐3 (lower unit) shows a similar pattern to that of the underlying S‐4 The depositional and erosional areas were also controlled by the active faults F1 and F2The HD deepened from west to east with the deepest area located just along the fault margin The depositional centre was located north of the hanging wall of F2 and became infilled by a fan‐delta (Figure 7b) The aver-age sedimentary dip of the fan‐delta is 303deg The extent of the fan‐delta was larger than that of S‐4 (Table 34)

During deposition of S‐3 (middle unit) the uplifted source area shifted southwards and the depression expanded A major depositional sink was located north of the hanging wall of F2 (Figure 7c Table 4) Elevation differences existed

between the footwalls and the hanging walls of F1 and F2 although the topography was obviously gentler during this time‐span A braided fluvial area developed at the footwalls of the faults whereas a braid‐delta developed mainly on the hanging wall of F2 and the northern depositional centre (Figure 7c) The braid‐delta had a fairly large extent and an average depositional dip of 119deg (Tables 34)

During S‐1 + 2 the elevated erosional area shifted farther southwards and the entire south‐western area had a low to-pography An alluvial plain developed south of the footwalls of the faults whereas a braid‐delta developed at the hanging walls and in the depression with a very gentle slope of 096deg (Table 4 Figure 7d) The depositional system was dominated by a fairly thin delta body and a braid‐delta with a much larger extent (Table 3)

During the deposition of D‐3 the topography of the foot-wall areas and of the area south of the provenance area was similar to that during the underlying S‐1 + 2 The slope was steep (187deg) in the hanging walls of the boundary faults however and the depositional area increased to 198 km2 which provided an excellent condition for the deposition of a large braid‐delta (Figure 7e Table 4) This braid‐delta had a NE‐SW orientation and covered an area of 142 km2 its average thickness is some 200 m which results in the largest delta volume in the Palaeogene on the south‐western slope of the HD (Table 3)

The palaeogeomorphological reconstruction of D‐2 shows a gentler topography in the entire south‐western HD with a sink area of 375 km2 (Table 4) The main body of the braid‐delta was dominated by imbricated progradational seis-mic reflections and developed in the hanging walls of F1 and F2 whereas an alluvial‐plain facies probably developed in the footwall areas of the faults and to the south‐west of the uplifted area (Figure 7f) Although the extent of the delta reached its maximum the thickness of the delta was limited due to the gentle topography resulting in a small delta vol-ume (Table 3)

5 | RELATIONSHIPS BETWEEN THE VARIOUS ELEMENTS OF THE S2S SYSTEM

Quantitative relationships between the various elements of the S2S system have been established through the above‐mentioned calculations A strong positive correlation is clearly present between the rate of tectonic subsidence the average fault activity and the average growth index of the boundary faults F1 and F2 (Figure 8ab) The rate of tectonic subsidence can therefore be used in the following as the pri-mary proxy to represent the intensity of the tectonic activity whereas the rate of fault activity and the growth index are used as secondary proxies

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The tectonic activity and the sediment‐supply rate show a positive relationship (Figures 8c 9a 10a) whereas the tec-tonic activity and the sink area of the basin show a negative relationship (Figures 8d 9b 10b) In contrast the tectonic activity has a positive relationship with the total accommo-dation space (Figures 8e 9c 10c Table 4) There is also a positive relationship between the average sedimentary dip of the fan‐ and braid‐deltas on the one hand and the tectonic activity on the other hand (Figures 8f 9d 10d)

The intensity of the tectonic activity correlates negatively with the extent of the sediment area but positively with the sediment volume (Figures 8g‐h 9e‐f 10e‐f) The different responses of the sediment area and the volume to the tectonic activity are caused by variations in the thicknesses of the sed-imentary units (Table 3)

There is also a positive relationship between the average seismic progradation dip of the fan‐ and braid‐deltas and the tectonic activity (Figures 8i 9g 10g) strong tectonic activ-ity usually formed deltas that are characterized by a chaotic progradational or oblique progradational seismic reflection such as SF 1 and 2 in S‐3 (lower unit) and S‐4 (Figures S3ndashS7) The minimum tectonic activity during Members S‐1 + 2 and D‐2 are reflected by dominantly shingled progradational seismic facies in the delta interior (Figures S10ndashS11)

In addition we find that the sediment area sediment vol-ume and average seismic progradation dip of the fan‐ and braid‐deltas correlate positively with the sediment‐supply rate (Figure 11a b and c) but negatively with the basin sink area (Figure 11d e and f) Both the sediment volume and the average seismic progradation dip of the fan‐ and braid‐deltas

F I G U R E 8 (a‐b) Relationships between the tectonic‐subsidence rate and tectonics (c‐i) Relationships between tectonic activity and sedimentary source‐to‐sink parameters Input data regarding the tectonic activity are from Table 2 those regarding the source‐to‐sink parameters data are from Tables 3 and 4 Regression‐line equations and coefficients of determination (R2) are shown for all diagrams

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show a positive relationship with the total accommodation space (Figure 11hi) However no obvious relationship ap-pears to be present between the sediment area and the total accommodation space (G) Both the sediment area and the average seismic progradation dip of the fan‐ and braid‐deltas correlate well with the average sedimentary dip of the fan‐ and braid‐deltas (Figure 11km) A poor correlation is found between the sediment volume and the average sedimentary dip of the fan‐ and braid‐deltas

6 | DISCUSSION

61 | Analysis of the influence of tectonic activity on the source area accommodation space geomorphology and sediment supplyA high relief and large drainage area usually can generate a large sediment supply (Leeder Harris amp Kirkby 1998 Syvitski amp Milliman 2007) Although the erosional area for the fan and delta system cannot be estimated because of the

limited data coverage the exposed area within the study area can be calculated The calculations show a generally decreas-ing trend of the source area from S‐4 (501 km2) to D‐2 (58 km2 Figure7 Table 4) The calculated exposed area cannot fully represent the true source area however but the evolu-tionary trend of the source area can be used as a proxy to indi-cate the relative influence on the change in sediment volume This trend is consistent with the decrease in sediment volume from S‐4 (2126 km3) to D‐2 (175 km3 Table 2) The relief is difficult to reconstruct in this case but variations in the fault‐activity rate (here taken as the tectonic‐subsidence rate) can create local elevation differences and can therefore be used as proxies for the trends in the relief development The relief shows an overall decreasing trend from S‐4 to D‐2 except for D‐3 this correlates well with the sediment volume (Figure 8h) Although the drainage area of D‐3 was smaller than that of D‐2 because of the high tectonic‐subsidence rate (result-ing in a high relief) D‐3 is thicker and shows a larger sedi-ment volume than the overlying D‐2 (Table 3) D‐3 is thinner than S‐4 + 3 but the larger source area resulted in a larger

F I G U R E 9 General relationships between the average fault‐growth index of F1 and F2 (AFGIF1‐F2) and sedimentary source‐to‐sink parameters The average fault‐growth index of F1 and F2 (AFGIF1‐F2) data in this figure are from Table 2 The source‐to‐sink parameters data are from Table 4 Regression‐line equations and the coefficients of determination are shown in each diagram

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sediment volume and supply rate (Table 3 Figure8ch) Therefore both the fault‐induced relief and the drainage area affected the sediment‐supply rate and the sediment volume in the sink

The changes in accommodation space during the vari-ous phases of the Palaeogene in the south‐western HD are clear from the estimated tectonic subsiding rate (Table 2) The correlations between the intensity of the tectonic activ-ity and the extent of the depositional sink area (Figures 8d 9b 10b) between the intensity of the tectonic activity and the total accommodation space and between the intensity of the tectonic activity and the morphology in the sink area (Figures 8e‐f 9c‐d 10c‐d) clearly show that strong tectonic activity resulted in a larger accommodation capacity of the sink

In particular the main subsiding area tended to form steeper slopes However the extent of the main subsiding sink area diminished (Figure 8d) with increasing tectonic activity which was possibly due to the relatively small sub-siding centre in the tectonically active basins It can thus be deduced that tectonic activity not only controlled the sedi-ment supply and the variation in accommodation space but

also determined the changes in the topography of the sedi-mentary basins and the extent of the main depositional areas in the tectonically active basins

62 | Analysis of the influence of tectonic activity on the size and internal stacking pattern of the delta depositional systemThe above data and considerations indicate that the tectonic activity was closely related to the sediment supply accom-modation space and morphology of the sink area which are possibly the most important factors affecting the extent and stacking pattern of the sedimentary facies (cf Cope et al 2010 DeCelles Kapp Ding amp Gehrels 2007 Leeder 2011 Olsen 1997 Simon et al 2017)

Statistical analysis indicates that the sediment‐supply rate has a strong positive correlation with the volume of the depositional system a moderate correlation with the seismic progradational dip in the depositional system and a poor cor-relation with the size of the depositional area (Figure 11a‐c) A larger sink area corresponded to a larger fanbraid‐delta a gentler seismic progradational angle and a reduced volume

F I G U R E 1 0 General relationships between average fault activity rate of F1 and F2 (RFAA‐F1‐F2) and sedimentary source‐to‐sink parameters The average fault activity rate of F1 and F2 (RFAA‐F1‐F2) data in this figure are from Table 2 The source‐to‐sink parameters data are from Table 4 Regression line equations and the coefficients of determination are shown in each diagram

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of the fan or braid‐delta which was possibly related to a re-duced sedimentary dip and thinner sediments (Figure 11d‐f) The total accommodation space in the basin correlates well

with the volume of the depositional system to some degree with the seismic progradational dip and poorly with the ex-tent of the depositional system area (Figure 11g‐i) These

FIGURE 11 Relationships between various parameters involved in the source‐to‐sink system (a‐c) Relationships between sediment supply and characteristics of the depositional system (extent volume and DPSA of the sediments) (d‐f) Relationships between the sink area of the basin and characteristics of the depositional system (g‐i) Relationships between the total accommodation space (AT) and the characteristics of the depositional system (j) Relationship between the accommodation‐spacesediment‐supply ratio (AS) and the DPSA of the sediments (k‐m) Relationships between the sedimentary dip and the characteristics of the depositional system The data regarding sediment supply basin sink area total accommodation space accommodation‐spacesediment‐supply ratio and sedimentary dips are from Table 4 The extent volume and DPSA of the sedimentary facies are from Table 3 Note the seemingly obvious polynomial (quadratic) relationship between the sedimentary dip and the sediment volume (L) The trend line in (L) suggests the following relationships between sediment volume and sedimentary slope in a rift or tectonically active basin (1) a very steep sedimentary slope is unfavourable for sediment accumulation (2) an appropriate sedimentary slope is favourable for preservation of depositional systems eg when the sedimentary slope in (L) is about 25degndash32deg the sediment volume reaches its largest value (3) a very gentle sedimentary slope will lead to a decrease of the sediment volume possibly due to weakening of the drainage system and thinner sediments

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relationships are clear evidence that the size of the sink area controlled the extent of the depositional system during the rifting of the lacustrine basin and that the rate of sediment supply and the accommodation space had a significant in-fluence on the total sedimentary volume as well as on the internal stacking pattern of the depositional system

We here use the ratio of the tectonic‐subsidence rate and the sediment‐supply rate as a proxy to indicate the ratio be-tween accommodation space and sediment‐supply rate (AS) (Table 4) AS has a strong influence on the internal stacking pattern of the depositional systems in the lacustrine rift basin (Figure 11j) This might be because the basin was small and because abundant and rapid material was supplied due

to intense tectonic activity (cf Catuneanu et al 2009 Liro 1993) and a favourable local climate (eg Bohacs Carroll Neal amp Mankiewicz 2000 Perlmutter amp Matthews 1989) The sediment supply still had a significant influence on the main subsidence area of the lacustrine basins and deposi-tional systems

In addition the basin slope significantly influenced the extent of the depositional system (Figure 11k) and had a polynomial relationship with its volume (Figure 11l) This relationship indicates that more intense tectonic activity and a steeper depositional slope were not favourable for sediment accumulation over a large extent in the lacustrine basin On the contrary these sediments were usually transported to a

F I G U R E 1 2 Tectonic differential activities and resulting patterns of the source‐to‐sink system on the south‐western slope of the HD during the Palaeogene (a) Development during phases of intense tectonics (Member 4 to the lower part of Member 3 of the Shahejie Fm) (b) Development during phases of somewhat less tectonic activity (middle part of Member 3 of the Shahejie Fm and Member 3 of the Dongying Fm) (c) Development during phases of weak tectonic activity (Members 1 and 2 of the Shahejie Fm and Member 2 of the Dongying Fm) The intensity of tectonic activity in the lacustrine rift basin had a significant influence on the development and extent of each unit of the source‐to‐sink system as well as on the type and dimensions of the depositional systems The present study indicates that probably sublacustrine fans developed (see for example Figure S4b) during phases with relatively strong tectonic activity This is not really clear from the seismic‐reflection data but possibly due to the small sizes of these sublacustrine fans Moreover lithofacies and core data are not available for the south‐western part of the study area The present contribution therefore focuses on the fan‐deltas and braid‐deltas regarding the sedimentary facies analysis the sublacustrine fans that probably developed in the deep or semi‐deep lake are presented just as a likely feature

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relatively small sink area with a fairly large accommodation space Finally stronger tectonic activity resulted in steeper depositional slopes (Figure 8f) which further controlled the hydrodynamic conditions and differential discharge when the sediments were deposited The strong correlation between the depositional slope and the deltas dip (Figure 11m) suggests that the differences in topography due to tectonics must be considered as one of the most critical factors that controlled the internal stacking pattern of the delta deposits

63 | Significance of the present study for other source‐to‐sink systems of lacustrine rift basins

631 | Summary of the source‐to‐sink systems in the HDIn lacustrine rift basins the tectonic setting is probably the main factor that determines the development of the S2S sys-tem but differential tectonic activities lead to variations in the basic characteristics of the S2S system Tectonic activity was most intense during S‐3 (lower unit) and during S‐4 and caused both a strong uplift of the source area and the devel-opment of depressions in the basin that formed a sink (Figure 12a) Strong tectonic activity in the S2S system during these time‐spans led to a high sediment‐supply rate steeper slopes a larger accommodation space and deposition of several fan‐deltas that are characterized by a fairly steep seismic progra-dational angle

The tectonic activity decreased during S‐3 (middle unit) and during D‐3 The S2S system that was present during this time‐span mainly concerned a rising area that shifted south-wards developing an alluvial plain between the erosional area and the sink area thus increasing the distance from source to sink (Figure 12b) Simultaneously the sediment‐supply rate and the accommodation space also changed and braid‐deltas could thus develop with larger volumes and gentler seismic progradational dips

Tectonic activity was clearly less intense during S‐1 + 2 and D‐2 The rising area had shifted further southwards cre-ating a wider alluvial plain connecting the source area to the sink in the HD (Figure 12c) At this stage stable tectonic activity led to relatively less sediment supply a gentle slope less accommodation space and the development of several braid‐deltas with a fairly gentle seismic progradational angle

632 | Wider implications and limitationsSoslashmme et al (2009) proposed that the elements of S2S sys-tems are genetically related and that quantitative correla-tions exist among these elements Other studies also suggest that the size of the drainage basin is correlated to the size of the fan developing on the basin floor (eg Blum et al

2017 Snedden et al 2018) and to the size of the river chan-nel (eg Milliken et al 2018) Helland‐Hansen Soslashmme Martinsen Lunt and Thurmond (2016) suggest a simplified subdivision of S2S systems into three main categories (a) Steep‐Short‐Deep (steep onshore and offshore gradients short distance between source and sink and deep offshore waters) (b) Wide‐Deep (low‐gradient shelf‐catchment area and deep offshore waters) and (c) Wide‐Shallow (relatively shallow offshore waters and a wide low‐gradient catchment area) systems

The present study indicates that the alluvial plain roughly corresponds to the alluvial‐shelf unit in marine basins al-though with a much smaller width and extent in the lacustrine rift basins than would have been the case on a continental shelf Faults F1 and F2 along the slope belt correspond to the slope of classical S2S systems whereas the shore‐shallow‐deep lake area can be compared with the basin floor (Soslashmme et al 2009) S‐4 and S‐3 (lower unit) can be roughly clas-sified as Steep‐Short‐Deep systems whereas the overlying S‐1 + 2and D‐2 can be classified as the Wide‐Shallow sys-tems that Helland‐Hansen et al (2016) defined During the deposition of S‐4 and S‐3 (lower unit) the strong tectonic activity caused a high relief of the source area a narrow allu-vial plain and a relatively deep lake The subsequently wan-ing tectonic activity resulted in a lower relief of the source area a wider alluvial plain and a shallower lake Although the absolute values of these elements in lacustrine basins are much smaller than those of marine basins the ratio between these elements in both settings is comparable Typically in a lacustrine basin a transformation from a Steep‐Short‐Deep system (S‐4 and S‐3 (lower unit)) to a Wide‐Shallow system (S‐1 + 2ampD‐2) occurs within a few million years Although the basin geomorphology has experienced signif-icant changes from S‐4 to D‐2 the quantitative relationships between tectonic activity sediment‐supply rate accommoda-tion space and sedimentary dip of the delta systems did not change significantly (eg Figures 8 and 11) The analytical approaches applied and quantitative relationship established here can help analyse other lacustrine basins worldwide and may even act as a reference for the analysis of marine basins

Our study focuses mainly on the influences of tectonic activity on the elements of the depositional sink Other pa-rameters (eg climate and lithology) were not considered in detail Studies on modern and ancient systems suggest that the climate and lithology also have a great influence on the sediment supply and distribution in the basin (eg Carroll Chetel amp Smith 2006 Hovius amp Leeder 1998 Syvitski amp Milliman 2007 Zhang et al 2018) For exam-ple climate variations between glacials and inter‐glacials have resulted in largely different sediment‐supply rates and in significant differences in the sizes of the Quaternary sub-marine fans in the north‐western Gulf of Mexico (Blum amp Hattier‐Womack 2009) We acknowledge the importance

| 609EAGE

LIU et aL

of climate and lithology for S2S systems and we are con-vinced that these elements can significantly affect the S2S systems in other cases(eg modern systems and systems influenced by glacialinterglacial alternations) These fac-tors were not really relevant for the present study however because no significant differences in lithology were present in the source areas and because we focus on the changes at a million‐year scale which implies that the tectonic ac-tivity has a first‐order control on the development of S2S elements in the investigated rift basin

7 | CONCLUSIONS

We have calculated the tectonic‐subsidence history the growth index and the activity rate of the main boundary faults (F1 and F2) and various S2S parameters of six Palaeogene rock units on the south‐western slope of the HD Based on the values found for these parameters quantitative corre-lation were established for the tectonic activity and other S2Sparameters in the basinal sink This leads to the follow-ing conclusions

1 The positive correlation between the intensity of fault activity and the tectonic‐subsidence rate is a strong indication for a distinct control by the tectonic activity of the syn‐depositional rifting of the tectonically active basin

2 The tectonic activity was quantitatively related to the sediment supply accommodation space and morphology of the sink area The relationship between tectonic activ-ity and depositional systems is reflected by changes in critical factors such as sediment supply accommodation space and dip of the sink area These critical factors were probably the most important factors that led to changes in the size and internal stacking pattern of the sedimentary facies

3 Differential tectonic activity led to changes in the char-acteristics of the S2S system on the south‐western slope of the HD The strongest tectonic activity which oc-curred during S‐3 (lower unit) and during S‐4 led to the largest provenance area adjacent to the sink area to a high sediment‐supply rate to steeper slopes to a larger accommodation space and controlled the development of several fan‐deltas Diminished tectonic activity dur-ing S‐3 (middle unit) and during D‐3 led to a decrease in uplift an increased width of the alluvial plain an in-creased transport distance a decrease in the sediment‐supply rate and accommodation space and resulted in the development of braid‐deltas with a large volume During S‐1 + 2 and D‐2 stable tectonic activity led to a lower sediment‐supply rate a gentle depositional slope and a smaller accommodation space resulting in the

development of several braid‐deltas with gentler seis-mic progradational angles

4 The analytical approaches applied and the quantitative re-lationships established here can help analyse other lacus-trine basins worldwide and may even act as a reference for the study of marine basins

ACKNOWLEDGEMENTS

We thank Dr Sarah Boulton and Dr Chenlin Gong as well as the Associate Editor of Basin Research Dr Craig Magee for their constructive comments on the manuscript This study was funded by the National Science and Technology Major Project (Exploration Technologies for Offshore Hidden OilGas) (project no 2016ZX05024‐003‐003) the National Natural Science Foundations of China (project no 41676050) and the Fundamental Research Funds for the Central Universities (2652014037)

REFERENCES

Allen P A (2008a) From landscapes into geological history Nature 451 274ndash276 https doiorg101038natur e06586

Allen P A (2008b) Time scales of tectonic landscapes and their sed-iment routing systems In Landscape evolution Denudation cli-mate and tectonics over different time and space scales (Ed by Gallagher K Jones S J amp Wainwright J) Geological Society London Special Publications 296 7ndash28

Allen P A Armitage J J Carter A Duller R A Michael N A Sinclair H D hellip Whittaker A C (2013) The Qs problem Sediment volumetric balance of proximal foreland basin systems Sedimentology 60 102ndash130

Amorosi A Maselli V amp Trincardi F (2016) Onshore to offshore anatomy of a late Quaternary source‐to‐sink system (Po Plain‐Adriatic Sea Italy) Earth‐Science Reviews 153 212ndash237 https doiorg101016jearsc irev201510010

Anderson J B Wallace D J Simms A R Rodriguez A B Weight R W R amp Taha Z P (2016) Recycling sediments between source and sink during a eustatic cycle Systems of late Quaternary northwestern Gulf of Mexico Basin Earth‐Science Reviews 153 111ndash138 https doiorg101016jearsc irev201510014

Anthony E J amp Julian M (1999) Source‐to‐sink sediment trans-fers environmental engineering and hazard mitigation in the steep Var River catchment French Riviera southeastern France Geomorphology 31 337ndash354 https doiorg101016S0169-555X(99)00088-4

Athy L F (1930) Density porosity and compaction of sedimentary rocks AAPG Bulletin 14 1ndash24

Bhattacharya J P Copeland P Lawton T F amp Holbrook J (2016) Estimation of source area river palaeo‐discharge palaeoslope and sediment budgets of linked deep‐time depositional systems and im-plications for hydrocarbon potential Earth‐Science Reviews 153 77ndash110

Blum M D amp Hattier‐Womack J (2009) Climate change sea‐level change and fluvial sediment supply to deepwater depositional

594 | EAGE

LIU et aL

where DP is the seismic progradational dip (in degrees) The average dip angle is obtained from only one seismic sec-tion because of the variations in the progradational seismic event of the delta on the same seismic line

where DPA is the average seismic progradational dip in a spe-cific seismic section (in degrees) and n is the number of seis-mic progradational events

Based on the calculated average dip of one seismic sec-tion the average progradational dip of a specific sediment body can be calculated with the formula

DPA

=

(

nsum

i=1

DPi

)

∕n

F I G U R E 5 Detailed calculations of the sedimentary dip and the progradational seismic event dip of the delta interior taking the progradation seismic reflection of the delta developed in Member 3 of the Dongying Formation as an example The locations of the seismic lines are shown in Figure 1c Based on the interpretation of the stratigraphic and seismic facies visible in the original seismic lines (a) the topset or the maximum flooding surface (MFS) corresponding to the delta was flattened (b) Taking into account the water depth during sedimentation the sedimentary dip (d) and the progradational seismic event dip of the delta interior (e) can be calculated DSD = depositional dip in a specific seismic section DSDA = average depositional dip of a specific sedimentary unit DP = seismic progradational dip DPA = average seismic progradational dip

| 595EAGE

LIU et aL

TA

BL

E 1

In

terp

reta

tion

of th

e m

ain

sedi

men

tary

faci

es in

the

Pale

ogen

e of

the

Hua

nghe

kou

Dep

ress

ion

Evi

denc

e of

fan

delta

s and

bra

id d

elta

s in

wel

ls W

1 an

d W

18 c

omes

from

Liu

Xia

et a

l (2

015a

)

Form

atio

n an

d m

embe

raSe

ismic

faci

esEx

ampl

esLi

thof

acie

sLi

thol

ogy

Wel

l amp c

ore

exam

ples

Dep

ositi

onal

en

viro

nmen

tPr

edic

ted

res-

ervo

ir q

ualit

y

D‐2

Seis

mic

Fac

ies 5

mod

erat

e co

ntin

uous

lo

w‐a

mpl

itude

and

a sh

ingl

ed‐li

ke

prog

rada

tiona

l sei

smic

refle

ctio

n

Figu

re

Mul

tiple

upw

ard‐

coar

s-en

ing

litho

faci

es

asso

ciat

ions

Gre

y m

udst

ones

gre

y to

gre

yish

w

hite

pebb

ly fi

ne sa

ndst

ones

and

fin

e sa

ndst

ones

T25

Bra

id d

elta

Mod

erat

e to

hi

gh

D‐3

Seis

mic

Fac

ies 4

con

tinuo

us m

oder

-at

e‐to

high

‐am

plitu

de a

nd o

bliq

ue‐

to‐s

igm

oid

prog

rada

tiona

l sei

smic

re

flect

ion

Figu

re

Mul

tiple

upw

ard‐

coar

s-en

ing

litho

faci

es

asso

ciat

ions

Gre

yish

whi

te to

whi

te fi

ne

sand

ston

es s

iltst

ones

and

gre

y m

udst

ones

T25

Bra

id d

elta

Hig

h

Figu

re 7

e‐f

S‐1

+ 2

Seis

mic

Fac

ies 5

mod

erat

e co

ntin

uous

m

oder

ate‐

ampl

itude

and

shin

gled

‐like

pr

ogra

datio

nal s

eism

ic re

flect

ion

Figu

re

Mul

tiple

upw

ard‐

coar

s-en

ing

litho

faci

es

asso

ciat

ions

Dar

k gr

ey m

udst

ones

and

gre

yish

w

hite

to g

rey

mid

dle‐

to fi

ne‐

grai

ned

sand

ston

es

T25

Bra

id d

elta

Hig

h

S‐3

(mid

dle

unit)

Seis

mic

Fac

ies 3

har

dly

tom

oder

atel

y co

ntin

uous

low

‐am

plitu

de o

bliq

ue

prog

rada

tiona

l sei

smic

refle

ctio

n

Figu

re

Lith

ofac

ies 1

Gre

y to

gre

yish

whi

te sa

ndy

cong

lom

erat

esT2

5B

raid

del

taH

igh

Lith

ofac

ies 2

Thic

k gr

ey m

iddl

e‐to

fine

‐gra

ined

sa

ndst

ones

Figu

re 7

a‐d

Lith

ofac

ies 3

Gre

y m

udst

ones

inte

rbed

ded

with

gr

ey fi

ne sa

ndst

ones

and

gre

y m

uddy

silts

tone

s

Lith

ofac

ies 4

Thic

k da

rk g

rey

mud

ston

es

S‐3

(low

er

unit)

Seis

mic

Fac

ies 2

cha

otic

prog

rada

-tio

nal t

o ob

lique

pro

grad

atio

nal

seis

mic

faci

es

Figu

re

Pe

bbly

sand

ston

es in

terb

edde

d w

ith

thin

bro

wn‐

grey

mud

ston

esb

row

n sa

ndy

cong

lom

erat

ess

ands

tone

s in-

terb

edde

d w

ith th

in m

udst

ones

thic

k m

udst

ones

inte

rbed

ded

with

th

in sa

ndst

ones

or p

ebbl

y fin

e sa

ndst

ones

T1Fa

n de

ltaM

oder

ate

S‐4

Seis

mic

Fac

ies 1

dis

cont

inuo

us to

con

-tin

uous

low

‐tohi

gh‐a

mpl

itude

cha

otic

pr

ogra

datio

nal s

eism

ic re

flect

ion

Figu

re

Figu

re

Fig

ure

and

Fi

gure

Lith

ofac

ies 1

Gre

y pe

bbly

sand

ston

es c

oars

e sa

ndst

ones

T18

Fan

delta

sM

oder

ate

Lith

ofac

ies 2

Ash

‐bla

ck m

udst

ones

inte

rbed

-de

d w

ith th

in g

rey

fine‐

grai

ned

sand

ston

es

Lith

ofac

ies 3

Ash

‐bla

ck m

udst

ones

inte

rbed

ded

with

peb

bly

sand

ston

esa D

= D

ongy

ing

Fm

S =

Sha

hejie

Fm

The

num

ber i

ndic

ates

the

num

ber o

f the

mem

ber

596 | EAGE

LIU et aL

TA

BL

E 2

Es

timat

ion

stat

istic

s of t

he te

cton

ic‐s

ubsi

denc

e ra

te g

row

th in

dex

and

activ

ity ra

te o

f fau

lts F

1 an

d F2

S1

S2

and

S3 a

re th

e ca

lcul

atio

n lo

catio

ns o

f F1

and

F2 (s

ee F

igur

e 1c

) th

e co

rres

pond

ing

num

bers

are

F1‐

S1 F

1‐S2

F1‐

S3 F

2‐S1

F2‐

S2 a

nd F

2‐S3

res

pect

ivel

y

Form

atio

n an

d m

embe

raA

ge

(Ma)

R TS

(m

Ma)

b

Faul

t‐gro

wth

inde

xFa

ult‐a

ctiv

ity r

ate

(mM

a)

AFG

I F1‐

F2c

R FA

A‐F

1‐F2

d

S1S2

S3A

vera

geS1

S2S3

aver

age

F1F2

F1F2

F1F2

F1F2

F1F2

F1F2

F1F2

F1F2

D‐1

233

75ndash

267

1450

00

111

106

109

110

107

109

109

108

389

270

389

479

270

389

349

379

109

364

D‐2

267

14ndash

302

060

00

139

130

138

140

137

133

138

134

320

730

29

341

442

62

329

534

98

330

535

96

136

345

1

D‐3

302

0ndash33

278

190

002

002

052

102

342

032

052

042

1579

67

104

0010

372

111

3485

59

762

989

66

972

12

1093

44

S‐1

+ 2

332

78ndash

378

9250

00

145

136

142

147

155

145

148

143

122

211

36

105

915

78

587

176

39

5614

92

146

122

4

S‐3

(mid

dle

unit)

378

92ndash

404

3812

500

131

202

192

242

175

257

166

234

335

140

88

490

380

62

215

510

919

347

076

90

205

558

0

S‐3

(low

er

unit)

404

38ndash

422

3135

500

284

343

302

395

342

389

309

376

737

185

37

104

4016

956

742

820

480

841

315

324

343

118

69

S‐4

422

31ndash

447

300

002

512

921

584

173

023

332

373

4791

33

106

4357

58

151

8811

007

121

5186

33

126

612

9210

647

a D =

Don

gyin

g Fm

S

= S

hahe

jie F

m T

he n

umbe

r ind

icat

es th

e nu

mbe

r of t

he m

embe

r b R T

S = te

cton

ic‐s

ubsi

denc

e ra

te

c AFG

I F1‐

F2 =

ave

rage

faul

t‐gro

wth

inde

x of

F1

and

F2

d R FA

A‐F

1‐F2

= a

vera

ge fa

ult‐a

ctiv

ity ra

te o

f F1

and

F2

| 597EAGE

LIU et aL

TA

BL

E 3

C

alcu

latio

n ch

art o

f the

sedi

men

tary

‐fac

ies d

imen

sion

s and

the

inte

rnal

pro

grad

atio

nal s

eism

ic e

vent

dip

The

spat

ial e

xten

t is s

how

n in

Fig

ure

7

Form

atio

nand

mem

bera

Sedi

men

tary

faci

esSe

ismic

sect

ions

Thic

knes

s (m

)

Are

a (k

m2 )

Vol

ume

(km

3 )To

tal v

olum

e (k

m3 )

DPb

Max

M

in

Ave

rage

DPA

DPS

A

D‐2

Bra

id d

elta

Figu

re a

176

0075

00

107

7016

246

175

017

50

157

156

Figu

re b

174

0080

00

157

Figu

re c

218

0080

00

152

D‐3

Bra

id d

elta

Figu

re a

285

0011

400

200

5014

219

285

128

51

268

285

Figu

re b

295

0099

00

309

Figu

re c

296

0078

00

309

Figu

re d

284

0091

00

254

S‐1

+ 2

Bra

id d

elta

Figu

re a

178

0089

00

136

7512

023

164

416

44

172

177

Figu

re b

185

0095

00

176

Figu

re c

236

0010

500

193

Figu

re d

209

0011

400

166

S‐3

(mid

dle

unit)

Bra

id d

elta

Figu

re a

274

0010

100

223

7587

87

196

619

66

213

225

Figu

re b

279

0083

00

225

Figu

re c

292

0086

00

235

Figu

re d

296

0086

00

226

S‐3

(low

er u

nit)

Fan

delta

Figu

re a

428

8623

903

374

0062

89

235

223

52

301

305

Figu

re b

432

5522

071

325

Figu

re c

473

0920

583

312

Figu

re d

450

8325

500

283

S‐4

Fan

delta

1Fi

gure

a30

700

483

929

200

107

03

1221

26c

423

365

Figu

re b

350

0010

728

439

Fan

delta

2Fi

gure

a46

500

704

832

900

856

282

421

Figu

re b

379

0066

52

362

Fan

delta

3Fi

gure

a40

100

118

7841

100

186

27

654

21

Figu

re b

468

0016

718

309

Figu

re c

527

0015

127

387

Figu

re d

486

0014

844

297

Fan

delta

4Fi

gure

a42

800

151

2042

700

179

57

663

04

Figu

re b

512

0027

287

289

a D =

Don

gyin

g Fm

S

= S

hahe

jie F

m T

he n

umbe

r ind

icat

es th

e nu

mbe

r of t

he m

embe

r b D

P = se

ism

ic p

rogr

adat

iona

l dip

DPA

= a

vera

ge se

ism

ic p

rogr

adat

iona

l dip

DPS

A =

ave

rage

seis

mic

pro

grad

atio

nal d

ip o

fthe

sedi

men

t c 21

26

= to

tal j

oint

vol

umes

of f

an d

elta

s 1 2

3 a

nd 4

598 | EAGE

LIU et aL

where DPSA is the average seismic progradational dip of a sediment (in degrees) and n is the number of seismic sections

Detailed estimated results of the depositional dip and the seismic progradational dip of the delta are shown in Tables 3 and 4

333 | Provenance conditions and estimation of the sediment supplySystematic investigation by TBCNOOC of the regional uplift and provenance in the geological past has indicated that the main provenance areas around the HD existed alreadybefore the deposition of Member 3 of the Shahejie Fm (Zhou et al 2010) They include the Bonan Laibei and Kendong Highs (Figure 1b‐c Figure S1a‐b) However starting with the depo-sition of Members 1ndash2 of the Shahejie Fm (S‐1 + 2) (3789ndash3328 Ma) until the accumulation of the Dongying Formation (3328ndash2338 Ma) the Bonan and Laibei Highs subsided to below lake level and consequently stopped providing sedi-ment to the depression (Liu Xia et al 2015a) Only the Kendong High which remained a high for a long time re-mained a provenance area for the south‐western part of the

HD during this time‐span (Figure S1a) The Kendong High has therefore been selected as the site where the relationship between tectonics and depositional systems within the same provenance system could be studied best The distribution area of the Kendong High as the provenance area at different moments has been determined on the basis of numerous seis-mic interpretations through seismic terminations (eg onlap) and the absence of specific sediment units due to faulting

The sediment‐supply rate can be obtained by calculation of the volumes of the deltas and the duration of their forma-tion (cf Allen et al 2013 Lemons amp Chan 1999 Lemons Milligan amp Chan 1996) Although the stratigraphic ages are well‐known for each unit (Figure 2) there is no high‐resolu-tion age control for the top and base of each delta system The absolute age of the pertinent stratigraphic unit (Figure 2) is therefore used to represent the formation time of the individual deltas in the unit The thus calculated sediment‐supply rate rep-resents in our opinion the trend of the supply rate from bottom to top sufficiently well

334 | Estimation of the extent and accommodation space of the sink areaDetermination of the boundaries of the sink area is based on reconstructions of the morphology during the successive dep-ositional phases The extent of the sink area was estimated using the same calculations as for the area of the depositional system

DPSA

=

(

nsum

i=1

DPAi

)

∕n

F I G U R E 6 Vertical successions and representative examples of the various lithofacies (a) A fan‐delta in Well W18 (b‐e) Braid‐deltas in Well W25 (f) Grey to greyish white sandy conglomerate (deposits in braided channels) (g) Grey medium‐ to fine‐grained massive sandstone (mouth‐bar deposits) (h) Grey fine sandstone (distal sand bars) (i) Grey muddy siltstone with parallel bedding (prodelta) (j) Greyish white fine sandstone with convolute bedding (mouth bars) (k) Greyish white fine sandstone with boulders (mouth bars) Wireline logs show the spontaneous‐potential (SP) and gamma‐ray (GR) changes with depth Depth in metres For location of the cores see Figure 6bd

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Differences in base level and the original sedimentary sur-face define the accommodation space (Jervey 1988 Muto amp Steel 2000 Neal amp Abreu 2009 Wheeler 1964) The

accommodation space in the depositional area can be deter-mined on the basis of the thickness of the preserved sediments (Muto amp Steel 2000) This space is obviously controlled by

F I G U R E 7 Schematic morphology during the successive depositional phases The extent of the deltas the depositional sink area in the basin and the main features of the drainage systems are shown The extent of the deltas has been interpreted from seismic data and has been used for calculation of the surface area and volume of the various deltas (a) Shahejie Fm Member 4 (b) Shahejie Fm lower part of Member 3 (c) Shahejie Fm middle part of Member 3 (d) Shahejie Fm Members 1 and 2 (e) Dongying Fm Member 3 (f) Dongying Fm Member 2

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the rate of subsidence tectonic uplift and fluctuations of the lake level (Lemons amp Chan 1999) Changes in the lake level of the HD have not been investigated so that we take data on the tectonic‐subsidence rate as a proxy for changes in the accommodation space The total space is expressed in the equation (Table 4)

where AT represents the total accommodation space of the sink area (in km3) TS represents the tectonic subsidence (in m) and SA represents the surface area of the sink (in km2)

AT= TStimesSA∕1000

T A B L E 4 Estimation of the controlling factor parameters of the depositional system The distribution characteristics of the depositional sink in the basin are shown in Figure 7

Formation and membera

Sedimentary facies Seismic sections

DDb

RSSc(km3

Ma)Sink area (km2) AT

d(km3) ASeSource areaf(km2)DSD DSDA

D‐2 Braid delta Figure a 059 066 502 37542 7852 1195 58

Figure b 065

Figure c 074

D‐3 Braid delta Figure a 161 187 926 19823 11593 2051 252

Figure b 192

Figure c 215

Figure d 182

S‐1 + 2 Braid delta Figure a 086 096 356 28015 6463 1403 220

Figure b 094

Figure c 120

Figure d 083

S‐3 (middle unit) Braid delta Figure a 110 119 772 21756 6927 1619 355

Figure b 111

Figure c 129

Figure d 128

S‐3 (lower unit) Fan delta Figure a 307 303 1313 16506 10500 2705 482

Figure b 334

Figure c 332

Figure d 237

S‐4 Fan delta 1 Figure a 384 463g 861 14150 10481 3484 501

Figure b 379

Fan delta 2 Figure a 606

Figure b 498

Fan delta 3 Figure a 479

Figure b 499

Figure c 625

Figure d 553

Fan delta 4 Figure a 377

Figure b 226aD = Dongying Fm S = Shahejie Fm The number indicates the number of the member bDD = depositional dip DSD = depositional dip in a specific seismic section DSDA = average depositional dip of a specific sedimentary unit cRSS = sediment‐supply rate dAT = total accommodation space eAS = accommodation spacesediment supply fSource area = Denudation area within the seismic data coverage The complete erosional area cannot be estimated because of the limited data coverage g463 = the average depositional dip of fan deltas 1 2 3 and 4 Considering that the four fan deltas developed during S‐4 consist of sediment that was derived from the same provenance area and were deposited in the same time‐span the four fan deltas are taken as a whole when estimating the parameters of RSS the sink area AT and AS

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4 | ELEMENTS OF THE S2S SYSTEM

41 | Analysis of the seismic facies and stacking pattern of the main sedimentary faciesA comprehensive analysis of seismic data cores cutting log-gings and well‐logging curves by Liu Xia et al (2015a) in-dicated that the Palaeogene depositional systems of the HD included fan‐deltas braid‐deltas lake margins deep lakes etc The fan‐ and braid‐deltas have been chosen for a detailed seismic study that must reveal their internal texture and their stacking patterns Analysis of the progradational seismic‐re-flection types and of the seismic progradational dip is particu-larly helpful for a better understanding of the hydrodynamic conditions and sedimentary processes that resulted in these depositional systems Because the facies interpretation in this area has been done before and is not the focus of this work we here mainly describe the internal texture and their stack-ing patterns of the main sedimentary facies

The major facies of S‐4 is interpreted as a fan‐delta It is dominated by Seismic Facies 1 which is characterized by discontinuous to continuous low‐ to high‐amplitude and chaotic progradational seismic reflections (Figures S3ndashS6 Table 1) The average dip of the progradational seismic event is about 365deg (Table 3) Three lithofacies are associated with Seismic Facies 1 (Table 1) The coarser lithofacies 1 represents a fan‐delta front whereas the finer lithofacies 2 and 3 are prodelta deposits The overall coarsening‐upward succession facies stacking pattern (Figure 6a) discontinuous and chaotic seismic reflections and relatively steep slope of Seismic Facies 1 suggest a fan‐delta system developed under strong hydrodynamic conditions (Mitchum et al 1977)

The fan‐delta of the lower part of Member 3 of the Shahejie Fm (S‐3 [lower unit]) is dominated by Seismic Facies 2 which is characterized by chaotic progradational to oblique progradational seismic characteristics It has a typical wedge shape and is composed of two seismic‐reflection seg-ments (a) a moderately continuous low‐ to high‐amplitude chaotic seismic‐reflection segment located near boundary fault F2 and (b) a continuous moderate‐ to high‐amplitude and oblique progradational seismic reflection in a basinward direction (Figure S7 Table 1) No obvious upper or lower segments occur in SF 2 and the dip of the progradational seismic event in this segment is also relatively steep viz 305deg (Table 3)

The middle part of Member 3 of the Shahejie Fm (S‐3 [middle unit]) is characterized by a low‐ to moderate‐con-tinuous low‐amplitude and oblique progradational seismic reflection (Seismic Facies 3) and is interpreted as a braid‐delta (Figure S8 Table 1) The progradational seismic events are parallel or sub‐parallel to each other and dip less (aver-age 225deg) than Seismic Facies 1 and 2 (Table 3) Seismic

Facies 3 is associated with four lithofacies (Figure 6b Table 1) in Well T25 The complete succession of the braid‐delta consists of gravely to coarse‐grained sandstone (lithofacies 1) at the base (Figure 6f) massive bedded medium‐ to fine‐grained sandstones (lithofacies 2) and grey mudstones inter-bedded with grey fine sandstones and grey muddy siltstones (lithofacies 3) in the middle (Figures 6g and 6h) and thick dark grey mudstones (lithofacies 4) at the top (Figure 6i)

Member 3 of the Dongying Fm (D‐3) is characterized by Seismic Facies 4 a typically composite seismic progra-dation reflection configuration representing a braid‐delta system (Figure S9 Table 1) Seismic Facies 4 is composed of highly continuous moderate‐ to high‐amplitude and pro-gradational seismic reflections that represent well‐developed deltaic topsets and bottomsets The topset segments of SF 4 are nearly horizontal or dip only gently (Table 3) The foreset segments form thicker lenses with small depositional angles The oblique progradational part of this seismic facies is sim-ilar to that in Seismic Facies 3 and usually developed at the basinward front end of Seismic Facies 3 The lithology of Seismic Facies 4 is dominated by greyish white to white fine‐grained sandstones and siltstones The lithofacies association is characterized by coarsening‐upward sedimentary cycles (Figure 6c Table 1) Convolute bedding and abundant diam-ictites are present on top of the fine sandstones (Figure 6j‐k)

Both braid‐deltas in the Members 1 + 2 of th Shahejie Fm (S‐1 + 2) and Member 2 of the Dongying Fm (D‐2) show moderately continuous moderate‐amplitude and shin-gled‐like progradational seismic reflections (Seismic Facies 5 Figures S10ndashS11 Table 1) It shows a thin prograding seis-mic pattern commonly with parallel upper and lower bound-aries (cf Mitchum et al 1977) The successive internal progradational seismic events overlap each other between the upper and lower segments with a gentle dip of 152degndash193deg (Table 3) The lithofacies are mostly composed of several coarsening‐upward cycles (Figure 6d Table 1) Each cycle is composed of dark grey mudstones and grey to whitish‐grey medium‐ to fine‐grained sandstones Several coarsening‐up-ward lithofacies are mainly developed in D‐2 (Figure 6e Table 1)

42 | Analysis of the tectonic activityThe normal faults F1 and F2 selected to calculate the fault activity dipping to the north and running approximately E‐W are important boundary faults on the south‐western margin of the HD The tectonic‐subsidence rate fault‐growth index and fault‐activity rate were used as proxies to indicate the tectonic intensity (Figure 3 S2 Table 2) S‐4 and S‐3 (lower unit) have the highest subsidence rate (300ndash355 mMa) the highest fault‐growth index (292ndash343 mMa) and the highest fault‐activity rate (10647ndash11869 mMa) among the studied intervals whereas the overlying S‐3 (middle

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unit) and S‐1 + 2 are characterized by a much lower sub-sidence rate and fault‐growth index and fault‐activity rate D‐3 had again a high subsidence rate (190 mMa) and an average fault‐growth index (210 mMa) and fault‐activity rate (9344 mMa) The uppermost studied interval D‐2 had a much lower subsidence rate (60 mMa) growth index (136 mMa) and fault‐activity rate (3451 mMa) than the un-derlying unit Generally the analysis of the subsidence rate average fault‐growth index and fault‐activity rate indicates two phases of alternating strong tectonic activity and tectoni-cally stable conditions

43 | Palaeogeomorphology distribution and dimensions of the main depositional systemsDepositional systems of each depositional phase of the Palaeogene on the south‐western slope of the HD were com-piled through seismic facies identification of 3‐D seismic data and compilation of maps with the current thicknesses of the main target intervals based on the study by Liu Xia et al (2015a) that combined a correction for the depth of burial with an interpretation of the sedimentary facies The basins sink area on the south‐western slope of the HD was estimated on the basis of a palaeogeomorphological reconstruction The distribution of the depositional system is closely related to the evolution of the palaeogeomorphology and therefore we describe both the distribution of the depositional system and the palaeogeomorphology here

The palaeogeography of S‐4 is characterized by the larg-est extent of the uplifted areas of all studied intervals The depositional area is small and scattered (Figure 7a Table 4) Faults F1 and F2 mark the boundaries between erosional and depositional regions The elevated footwalls of the faults were erosional areas and located adjacent to the hanging walls whereas the hanging walls were low‐lying depositional areas The sedimentary facies analysis indicates a fan‐delta developed here (Figure 7a) Calculations indicate that the sedimentary dip of the four fan‐deltas was uncommonly high (about 463deg) The extent and thickness of the fan‐deltas di-minished towards the basin margin (Tables 34)

The tectonically‐induced morphology of S‐3 (lower unit) shows a similar pattern to that of the underlying S‐4 The depositional and erosional areas were also controlled by the active faults F1 and F2The HD deepened from west to east with the deepest area located just along the fault margin The depositional centre was located north of the hanging wall of F2 and became infilled by a fan‐delta (Figure 7b) The aver-age sedimentary dip of the fan‐delta is 303deg The extent of the fan‐delta was larger than that of S‐4 (Table 34)

During deposition of S‐3 (middle unit) the uplifted source area shifted southwards and the depression expanded A major depositional sink was located north of the hanging wall of F2 (Figure 7c Table 4) Elevation differences existed

between the footwalls and the hanging walls of F1 and F2 although the topography was obviously gentler during this time‐span A braided fluvial area developed at the footwalls of the faults whereas a braid‐delta developed mainly on the hanging wall of F2 and the northern depositional centre (Figure 7c) The braid‐delta had a fairly large extent and an average depositional dip of 119deg (Tables 34)

During S‐1 + 2 the elevated erosional area shifted farther southwards and the entire south‐western area had a low to-pography An alluvial plain developed south of the footwalls of the faults whereas a braid‐delta developed at the hanging walls and in the depression with a very gentle slope of 096deg (Table 4 Figure 7d) The depositional system was dominated by a fairly thin delta body and a braid‐delta with a much larger extent (Table 3)

During the deposition of D‐3 the topography of the foot-wall areas and of the area south of the provenance area was similar to that during the underlying S‐1 + 2 The slope was steep (187deg) in the hanging walls of the boundary faults however and the depositional area increased to 198 km2 which provided an excellent condition for the deposition of a large braid‐delta (Figure 7e Table 4) This braid‐delta had a NE‐SW orientation and covered an area of 142 km2 its average thickness is some 200 m which results in the largest delta volume in the Palaeogene on the south‐western slope of the HD (Table 3)

The palaeogeomorphological reconstruction of D‐2 shows a gentler topography in the entire south‐western HD with a sink area of 375 km2 (Table 4) The main body of the braid‐delta was dominated by imbricated progradational seis-mic reflections and developed in the hanging walls of F1 and F2 whereas an alluvial‐plain facies probably developed in the footwall areas of the faults and to the south‐west of the uplifted area (Figure 7f) Although the extent of the delta reached its maximum the thickness of the delta was limited due to the gentle topography resulting in a small delta vol-ume (Table 3)

5 | RELATIONSHIPS BETWEEN THE VARIOUS ELEMENTS OF THE S2S SYSTEM

Quantitative relationships between the various elements of the S2S system have been established through the above‐mentioned calculations A strong positive correlation is clearly present between the rate of tectonic subsidence the average fault activity and the average growth index of the boundary faults F1 and F2 (Figure 8ab) The rate of tectonic subsidence can therefore be used in the following as the pri-mary proxy to represent the intensity of the tectonic activity whereas the rate of fault activity and the growth index are used as secondary proxies

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The tectonic activity and the sediment‐supply rate show a positive relationship (Figures 8c 9a 10a) whereas the tec-tonic activity and the sink area of the basin show a negative relationship (Figures 8d 9b 10b) In contrast the tectonic activity has a positive relationship with the total accommo-dation space (Figures 8e 9c 10c Table 4) There is also a positive relationship between the average sedimentary dip of the fan‐ and braid‐deltas on the one hand and the tectonic activity on the other hand (Figures 8f 9d 10d)

The intensity of the tectonic activity correlates negatively with the extent of the sediment area but positively with the sediment volume (Figures 8g‐h 9e‐f 10e‐f) The different responses of the sediment area and the volume to the tectonic activity are caused by variations in the thicknesses of the sed-imentary units (Table 3)

There is also a positive relationship between the average seismic progradation dip of the fan‐ and braid‐deltas and the tectonic activity (Figures 8i 9g 10g) strong tectonic activ-ity usually formed deltas that are characterized by a chaotic progradational or oblique progradational seismic reflection such as SF 1 and 2 in S‐3 (lower unit) and S‐4 (Figures S3ndashS7) The minimum tectonic activity during Members S‐1 + 2 and D‐2 are reflected by dominantly shingled progradational seismic facies in the delta interior (Figures S10ndashS11)

In addition we find that the sediment area sediment vol-ume and average seismic progradation dip of the fan‐ and braid‐deltas correlate positively with the sediment‐supply rate (Figure 11a b and c) but negatively with the basin sink area (Figure 11d e and f) Both the sediment volume and the average seismic progradation dip of the fan‐ and braid‐deltas

F I G U R E 8 (a‐b) Relationships between the tectonic‐subsidence rate and tectonics (c‐i) Relationships between tectonic activity and sedimentary source‐to‐sink parameters Input data regarding the tectonic activity are from Table 2 those regarding the source‐to‐sink parameters data are from Tables 3 and 4 Regression‐line equations and coefficients of determination (R2) are shown for all diagrams

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show a positive relationship with the total accommodation space (Figure 11hi) However no obvious relationship ap-pears to be present between the sediment area and the total accommodation space (G) Both the sediment area and the average seismic progradation dip of the fan‐ and braid‐deltas correlate well with the average sedimentary dip of the fan‐ and braid‐deltas (Figure 11km) A poor correlation is found between the sediment volume and the average sedimentary dip of the fan‐ and braid‐deltas

6 | DISCUSSION

61 | Analysis of the influence of tectonic activity on the source area accommodation space geomorphology and sediment supplyA high relief and large drainage area usually can generate a large sediment supply (Leeder Harris amp Kirkby 1998 Syvitski amp Milliman 2007) Although the erosional area for the fan and delta system cannot be estimated because of the

limited data coverage the exposed area within the study area can be calculated The calculations show a generally decreas-ing trend of the source area from S‐4 (501 km2) to D‐2 (58 km2 Figure7 Table 4) The calculated exposed area cannot fully represent the true source area however but the evolu-tionary trend of the source area can be used as a proxy to indi-cate the relative influence on the change in sediment volume This trend is consistent with the decrease in sediment volume from S‐4 (2126 km3) to D‐2 (175 km3 Table 2) The relief is difficult to reconstruct in this case but variations in the fault‐activity rate (here taken as the tectonic‐subsidence rate) can create local elevation differences and can therefore be used as proxies for the trends in the relief development The relief shows an overall decreasing trend from S‐4 to D‐2 except for D‐3 this correlates well with the sediment volume (Figure 8h) Although the drainage area of D‐3 was smaller than that of D‐2 because of the high tectonic‐subsidence rate (result-ing in a high relief) D‐3 is thicker and shows a larger sedi-ment volume than the overlying D‐2 (Table 3) D‐3 is thinner than S‐4 + 3 but the larger source area resulted in a larger

F I G U R E 9 General relationships between the average fault‐growth index of F1 and F2 (AFGIF1‐F2) and sedimentary source‐to‐sink parameters The average fault‐growth index of F1 and F2 (AFGIF1‐F2) data in this figure are from Table 2 The source‐to‐sink parameters data are from Table 4 Regression‐line equations and the coefficients of determination are shown in each diagram

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sediment volume and supply rate (Table 3 Figure8ch) Therefore both the fault‐induced relief and the drainage area affected the sediment‐supply rate and the sediment volume in the sink

The changes in accommodation space during the vari-ous phases of the Palaeogene in the south‐western HD are clear from the estimated tectonic subsiding rate (Table 2) The correlations between the intensity of the tectonic activ-ity and the extent of the depositional sink area (Figures 8d 9b 10b) between the intensity of the tectonic activity and the total accommodation space and between the intensity of the tectonic activity and the morphology in the sink area (Figures 8e‐f 9c‐d 10c‐d) clearly show that strong tectonic activity resulted in a larger accommodation capacity of the sink

In particular the main subsiding area tended to form steeper slopes However the extent of the main subsiding sink area diminished (Figure 8d) with increasing tectonic activity which was possibly due to the relatively small sub-siding centre in the tectonically active basins It can thus be deduced that tectonic activity not only controlled the sedi-ment supply and the variation in accommodation space but

also determined the changes in the topography of the sedi-mentary basins and the extent of the main depositional areas in the tectonically active basins

62 | Analysis of the influence of tectonic activity on the size and internal stacking pattern of the delta depositional systemThe above data and considerations indicate that the tectonic activity was closely related to the sediment supply accom-modation space and morphology of the sink area which are possibly the most important factors affecting the extent and stacking pattern of the sedimentary facies (cf Cope et al 2010 DeCelles Kapp Ding amp Gehrels 2007 Leeder 2011 Olsen 1997 Simon et al 2017)

Statistical analysis indicates that the sediment‐supply rate has a strong positive correlation with the volume of the depositional system a moderate correlation with the seismic progradational dip in the depositional system and a poor cor-relation with the size of the depositional area (Figure 11a‐c) A larger sink area corresponded to a larger fanbraid‐delta a gentler seismic progradational angle and a reduced volume

F I G U R E 1 0 General relationships between average fault activity rate of F1 and F2 (RFAA‐F1‐F2) and sedimentary source‐to‐sink parameters The average fault activity rate of F1 and F2 (RFAA‐F1‐F2) data in this figure are from Table 2 The source‐to‐sink parameters data are from Table 4 Regression line equations and the coefficients of determination are shown in each diagram

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of the fan or braid‐delta which was possibly related to a re-duced sedimentary dip and thinner sediments (Figure 11d‐f) The total accommodation space in the basin correlates well

with the volume of the depositional system to some degree with the seismic progradational dip and poorly with the ex-tent of the depositional system area (Figure 11g‐i) These

FIGURE 11 Relationships between various parameters involved in the source‐to‐sink system (a‐c) Relationships between sediment supply and characteristics of the depositional system (extent volume and DPSA of the sediments) (d‐f) Relationships between the sink area of the basin and characteristics of the depositional system (g‐i) Relationships between the total accommodation space (AT) and the characteristics of the depositional system (j) Relationship between the accommodation‐spacesediment‐supply ratio (AS) and the DPSA of the sediments (k‐m) Relationships between the sedimentary dip and the characteristics of the depositional system The data regarding sediment supply basin sink area total accommodation space accommodation‐spacesediment‐supply ratio and sedimentary dips are from Table 4 The extent volume and DPSA of the sedimentary facies are from Table 3 Note the seemingly obvious polynomial (quadratic) relationship between the sedimentary dip and the sediment volume (L) The trend line in (L) suggests the following relationships between sediment volume and sedimentary slope in a rift or tectonically active basin (1) a very steep sedimentary slope is unfavourable for sediment accumulation (2) an appropriate sedimentary slope is favourable for preservation of depositional systems eg when the sedimentary slope in (L) is about 25degndash32deg the sediment volume reaches its largest value (3) a very gentle sedimentary slope will lead to a decrease of the sediment volume possibly due to weakening of the drainage system and thinner sediments

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relationships are clear evidence that the size of the sink area controlled the extent of the depositional system during the rifting of the lacustrine basin and that the rate of sediment supply and the accommodation space had a significant in-fluence on the total sedimentary volume as well as on the internal stacking pattern of the depositional system

We here use the ratio of the tectonic‐subsidence rate and the sediment‐supply rate as a proxy to indicate the ratio be-tween accommodation space and sediment‐supply rate (AS) (Table 4) AS has a strong influence on the internal stacking pattern of the depositional systems in the lacustrine rift basin (Figure 11j) This might be because the basin was small and because abundant and rapid material was supplied due

to intense tectonic activity (cf Catuneanu et al 2009 Liro 1993) and a favourable local climate (eg Bohacs Carroll Neal amp Mankiewicz 2000 Perlmutter amp Matthews 1989) The sediment supply still had a significant influence on the main subsidence area of the lacustrine basins and deposi-tional systems

In addition the basin slope significantly influenced the extent of the depositional system (Figure 11k) and had a polynomial relationship with its volume (Figure 11l) This relationship indicates that more intense tectonic activity and a steeper depositional slope were not favourable for sediment accumulation over a large extent in the lacustrine basin On the contrary these sediments were usually transported to a

F I G U R E 1 2 Tectonic differential activities and resulting patterns of the source‐to‐sink system on the south‐western slope of the HD during the Palaeogene (a) Development during phases of intense tectonics (Member 4 to the lower part of Member 3 of the Shahejie Fm) (b) Development during phases of somewhat less tectonic activity (middle part of Member 3 of the Shahejie Fm and Member 3 of the Dongying Fm) (c) Development during phases of weak tectonic activity (Members 1 and 2 of the Shahejie Fm and Member 2 of the Dongying Fm) The intensity of tectonic activity in the lacustrine rift basin had a significant influence on the development and extent of each unit of the source‐to‐sink system as well as on the type and dimensions of the depositional systems The present study indicates that probably sublacustrine fans developed (see for example Figure S4b) during phases with relatively strong tectonic activity This is not really clear from the seismic‐reflection data but possibly due to the small sizes of these sublacustrine fans Moreover lithofacies and core data are not available for the south‐western part of the study area The present contribution therefore focuses on the fan‐deltas and braid‐deltas regarding the sedimentary facies analysis the sublacustrine fans that probably developed in the deep or semi‐deep lake are presented just as a likely feature

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relatively small sink area with a fairly large accommodation space Finally stronger tectonic activity resulted in steeper depositional slopes (Figure 8f) which further controlled the hydrodynamic conditions and differential discharge when the sediments were deposited The strong correlation between the depositional slope and the deltas dip (Figure 11m) suggests that the differences in topography due to tectonics must be considered as one of the most critical factors that controlled the internal stacking pattern of the delta deposits

63 | Significance of the present study for other source‐to‐sink systems of lacustrine rift basins

631 | Summary of the source‐to‐sink systems in the HDIn lacustrine rift basins the tectonic setting is probably the main factor that determines the development of the S2S sys-tem but differential tectonic activities lead to variations in the basic characteristics of the S2S system Tectonic activity was most intense during S‐3 (lower unit) and during S‐4 and caused both a strong uplift of the source area and the devel-opment of depressions in the basin that formed a sink (Figure 12a) Strong tectonic activity in the S2S system during these time‐spans led to a high sediment‐supply rate steeper slopes a larger accommodation space and deposition of several fan‐deltas that are characterized by a fairly steep seismic progra-dational angle

The tectonic activity decreased during S‐3 (middle unit) and during D‐3 The S2S system that was present during this time‐span mainly concerned a rising area that shifted south-wards developing an alluvial plain between the erosional area and the sink area thus increasing the distance from source to sink (Figure 12b) Simultaneously the sediment‐supply rate and the accommodation space also changed and braid‐deltas could thus develop with larger volumes and gentler seismic progradational dips

Tectonic activity was clearly less intense during S‐1 + 2 and D‐2 The rising area had shifted further southwards cre-ating a wider alluvial plain connecting the source area to the sink in the HD (Figure 12c) At this stage stable tectonic activity led to relatively less sediment supply a gentle slope less accommodation space and the development of several braid‐deltas with a fairly gentle seismic progradational angle

632 | Wider implications and limitationsSoslashmme et al (2009) proposed that the elements of S2S sys-tems are genetically related and that quantitative correla-tions exist among these elements Other studies also suggest that the size of the drainage basin is correlated to the size of the fan developing on the basin floor (eg Blum et al

2017 Snedden et al 2018) and to the size of the river chan-nel (eg Milliken et al 2018) Helland‐Hansen Soslashmme Martinsen Lunt and Thurmond (2016) suggest a simplified subdivision of S2S systems into three main categories (a) Steep‐Short‐Deep (steep onshore and offshore gradients short distance between source and sink and deep offshore waters) (b) Wide‐Deep (low‐gradient shelf‐catchment area and deep offshore waters) and (c) Wide‐Shallow (relatively shallow offshore waters and a wide low‐gradient catchment area) systems

The present study indicates that the alluvial plain roughly corresponds to the alluvial‐shelf unit in marine basins al-though with a much smaller width and extent in the lacustrine rift basins than would have been the case on a continental shelf Faults F1 and F2 along the slope belt correspond to the slope of classical S2S systems whereas the shore‐shallow‐deep lake area can be compared with the basin floor (Soslashmme et al 2009) S‐4 and S‐3 (lower unit) can be roughly clas-sified as Steep‐Short‐Deep systems whereas the overlying S‐1 + 2and D‐2 can be classified as the Wide‐Shallow sys-tems that Helland‐Hansen et al (2016) defined During the deposition of S‐4 and S‐3 (lower unit) the strong tectonic activity caused a high relief of the source area a narrow allu-vial plain and a relatively deep lake The subsequently wan-ing tectonic activity resulted in a lower relief of the source area a wider alluvial plain and a shallower lake Although the absolute values of these elements in lacustrine basins are much smaller than those of marine basins the ratio between these elements in both settings is comparable Typically in a lacustrine basin a transformation from a Steep‐Short‐Deep system (S‐4 and S‐3 (lower unit)) to a Wide‐Shallow system (S‐1 + 2ampD‐2) occurs within a few million years Although the basin geomorphology has experienced signif-icant changes from S‐4 to D‐2 the quantitative relationships between tectonic activity sediment‐supply rate accommoda-tion space and sedimentary dip of the delta systems did not change significantly (eg Figures 8 and 11) The analytical approaches applied and quantitative relationship established here can help analyse other lacustrine basins worldwide and may even act as a reference for the analysis of marine basins

Our study focuses mainly on the influences of tectonic activity on the elements of the depositional sink Other pa-rameters (eg climate and lithology) were not considered in detail Studies on modern and ancient systems suggest that the climate and lithology also have a great influence on the sediment supply and distribution in the basin (eg Carroll Chetel amp Smith 2006 Hovius amp Leeder 1998 Syvitski amp Milliman 2007 Zhang et al 2018) For exam-ple climate variations between glacials and inter‐glacials have resulted in largely different sediment‐supply rates and in significant differences in the sizes of the Quaternary sub-marine fans in the north‐western Gulf of Mexico (Blum amp Hattier‐Womack 2009) We acknowledge the importance

| 609EAGE

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of climate and lithology for S2S systems and we are con-vinced that these elements can significantly affect the S2S systems in other cases(eg modern systems and systems influenced by glacialinterglacial alternations) These fac-tors were not really relevant for the present study however because no significant differences in lithology were present in the source areas and because we focus on the changes at a million‐year scale which implies that the tectonic ac-tivity has a first‐order control on the development of S2S elements in the investigated rift basin

7 | CONCLUSIONS

We have calculated the tectonic‐subsidence history the growth index and the activity rate of the main boundary faults (F1 and F2) and various S2S parameters of six Palaeogene rock units on the south‐western slope of the HD Based on the values found for these parameters quantitative corre-lation were established for the tectonic activity and other S2Sparameters in the basinal sink This leads to the follow-ing conclusions

1 The positive correlation between the intensity of fault activity and the tectonic‐subsidence rate is a strong indication for a distinct control by the tectonic activity of the syn‐depositional rifting of the tectonically active basin

2 The tectonic activity was quantitatively related to the sediment supply accommodation space and morphology of the sink area The relationship between tectonic activ-ity and depositional systems is reflected by changes in critical factors such as sediment supply accommodation space and dip of the sink area These critical factors were probably the most important factors that led to changes in the size and internal stacking pattern of the sedimentary facies

3 Differential tectonic activity led to changes in the char-acteristics of the S2S system on the south‐western slope of the HD The strongest tectonic activity which oc-curred during S‐3 (lower unit) and during S‐4 led to the largest provenance area adjacent to the sink area to a high sediment‐supply rate to steeper slopes to a larger accommodation space and controlled the development of several fan‐deltas Diminished tectonic activity dur-ing S‐3 (middle unit) and during D‐3 led to a decrease in uplift an increased width of the alluvial plain an in-creased transport distance a decrease in the sediment‐supply rate and accommodation space and resulted in the development of braid‐deltas with a large volume During S‐1 + 2 and D‐2 stable tectonic activity led to a lower sediment‐supply rate a gentle depositional slope and a smaller accommodation space resulting in the

development of several braid‐deltas with gentler seis-mic progradational angles

4 The analytical approaches applied and the quantitative re-lationships established here can help analyse other lacus-trine basins worldwide and may even act as a reference for the study of marine basins

ACKNOWLEDGEMENTS

We thank Dr Sarah Boulton and Dr Chenlin Gong as well as the Associate Editor of Basin Research Dr Craig Magee for their constructive comments on the manuscript This study was funded by the National Science and Technology Major Project (Exploration Technologies for Offshore Hidden OilGas) (project no 2016ZX05024‐003‐003) the National Natural Science Foundations of China (project no 41676050) and the Fundamental Research Funds for the Central Universities (2652014037)

REFERENCES

Allen P A (2008a) From landscapes into geological history Nature 451 274ndash276 https doiorg101038natur e06586

Allen P A (2008b) Time scales of tectonic landscapes and their sed-iment routing systems In Landscape evolution Denudation cli-mate and tectonics over different time and space scales (Ed by Gallagher K Jones S J amp Wainwright J) Geological Society London Special Publications 296 7ndash28

Allen P A Armitage J J Carter A Duller R A Michael N A Sinclair H D hellip Whittaker A C (2013) The Qs problem Sediment volumetric balance of proximal foreland basin systems Sedimentology 60 102ndash130

Amorosi A Maselli V amp Trincardi F (2016) Onshore to offshore anatomy of a late Quaternary source‐to‐sink system (Po Plain‐Adriatic Sea Italy) Earth‐Science Reviews 153 212ndash237 https doiorg101016jearsc irev201510010

Anderson J B Wallace D J Simms A R Rodriguez A B Weight R W R amp Taha Z P (2016) Recycling sediments between source and sink during a eustatic cycle Systems of late Quaternary northwestern Gulf of Mexico Basin Earth‐Science Reviews 153 111ndash138 https doiorg101016jearsc irev201510014

Anthony E J amp Julian M (1999) Source‐to‐sink sediment trans-fers environmental engineering and hazard mitigation in the steep Var River catchment French Riviera southeastern France Geomorphology 31 337ndash354 https doiorg101016S0169-555X(99)00088-4

Athy L F (1930) Density porosity and compaction of sedimentary rocks AAPG Bulletin 14 1ndash24

Bhattacharya J P Copeland P Lawton T F amp Holbrook J (2016) Estimation of source area river palaeo‐discharge palaeoslope and sediment budgets of linked deep‐time depositional systems and im-plications for hydrocarbon potential Earth‐Science Reviews 153 77ndash110

Blum M D amp Hattier‐Womack J (2009) Climate change sea‐level change and fluvial sediment supply to deepwater depositional

| 595EAGE

LIU et aL

TA

BL

E 1

In

terp

reta

tion

of th

e m

ain

sedi

men

tary

faci

es in

the

Pale

ogen

e of

the

Hua

nghe

kou

Dep

ress

ion

Evi

denc

e of

fan

delta

s and

bra

id d

elta

s in

wel

ls W

1 an

d W

18 c

omes

from

Liu

Xia

et a

l (2

015a

)

Form

atio

n an

d m

embe

raSe

ismic

faci

esEx

ampl

esLi

thof

acie

sLi

thol

ogy

Wel

l amp c

ore

exam

ples

Dep

ositi

onal

en

viro

nmen

tPr

edic

ted

res-

ervo

ir q

ualit

y

D‐2

Seis

mic

Fac

ies 5

mod

erat

e co

ntin

uous

lo

w‐a

mpl

itude

and

a sh

ingl

ed‐li

ke

prog

rada

tiona

l sei

smic

refle

ctio

n

Figu

re

Mul

tiple

upw

ard‐

coar

s-en

ing

litho

faci

es

asso

ciat

ions

Gre

y m

udst

ones

gre

y to

gre

yish

w

hite

pebb

ly fi

ne sa

ndst

ones

and

fin

e sa

ndst

ones

T25

Bra

id d

elta

Mod

erat

e to

hi

gh

D‐3

Seis

mic

Fac

ies 4

con

tinuo

us m

oder

-at

e‐to

high

‐am

plitu

de a

nd o

bliq

ue‐

to‐s

igm

oid

prog

rada

tiona

l sei

smic

re

flect

ion

Figu

re

Mul

tiple

upw

ard‐

coar

s-en

ing

litho

faci

es

asso

ciat

ions

Gre

yish

whi

te to

whi

te fi

ne

sand

ston

es s

iltst

ones

and

gre

y m

udst

ones

T25

Bra

id d

elta

Hig

h

Figu

re 7

e‐f

S‐1

+ 2

Seis

mic

Fac

ies 5

mod

erat

e co

ntin

uous

m

oder

ate‐

ampl

itude

and

shin

gled

‐like

pr

ogra

datio

nal s

eism

ic re

flect

ion

Figu

re

Mul

tiple

upw

ard‐

coar

s-en

ing

litho

faci

es

asso

ciat

ions

Dar

k gr

ey m

udst

ones

and

gre

yish

w

hite

to g

rey

mid

dle‐

to fi

ne‐

grai

ned

sand

ston

es

T25

Bra

id d

elta

Hig

h

S‐3

(mid

dle

unit)

Seis

mic

Fac

ies 3

har

dly

tom

oder

atel

y co

ntin

uous

low

‐am

plitu

de o

bliq

ue

prog

rada

tiona

l sei

smic

refle

ctio

n

Figu

re

Lith

ofac

ies 1

Gre

y to

gre

yish

whi

te sa

ndy

cong

lom

erat

esT2

5B

raid

del

taH

igh

Lith

ofac

ies 2

Thic

k gr

ey m

iddl

e‐to

fine

‐gra

ined

sa

ndst

ones

Figu

re 7

a‐d

Lith

ofac

ies 3

Gre

y m

udst

ones

inte

rbed

ded

with

gr

ey fi

ne sa

ndst

ones

and

gre

y m

uddy

silts

tone

s

Lith

ofac

ies 4

Thic

k da

rk g

rey

mud

ston

es

S‐3

(low

er

unit)

Seis

mic

Fac

ies 2

cha

otic

prog

rada

-tio

nal t

o ob

lique

pro

grad

atio

nal

seis

mic

faci

es

Figu

re

Pe

bbly

sand

ston

es in

terb

edde

d w

ith

thin

bro

wn‐

grey

mud

ston

esb

row

n sa

ndy

cong

lom

erat

ess

ands

tone

s in-

terb

edde

d w

ith th

in m

udst

ones

thic

k m

udst

ones

inte

rbed

ded

with

th

in sa

ndst

ones

or p

ebbl

y fin

e sa

ndst

ones

T1Fa

n de

ltaM

oder

ate

S‐4

Seis

mic

Fac

ies 1

dis

cont

inuo

us to

con

-tin

uous

low

‐tohi

gh‐a

mpl

itude

cha

otic

pr

ogra

datio

nal s

eism

ic re

flect

ion

Figu

re

Figu

re

Fig

ure

and

Fi

gure

Lith

ofac

ies 1

Gre

y pe

bbly

sand

ston

es c

oars

e sa

ndst

ones

T18

Fan

delta

sM

oder

ate

Lith

ofac

ies 2

Ash

‐bla

ck m

udst

ones

inte

rbed

-de

d w

ith th

in g

rey

fine‐

grai

ned

sand

ston

es

Lith

ofac

ies 3

Ash

‐bla

ck m

udst

ones

inte

rbed

ded

with

peb

bly

sand

ston

esa D

= D

ongy

ing

Fm

S =

Sha

hejie

Fm

The

num

ber i

ndic

ates

the

num

ber o

f the

mem

ber

596 | EAGE

LIU et aL

TA

BL

E 2

Es

timat

ion

stat

istic

s of t

he te

cton

ic‐s

ubsi

denc

e ra

te g

row

th in

dex

and

activ

ity ra

te o

f fau

lts F

1 an

d F2

S1

S2

and

S3 a

re th

e ca

lcul

atio

n lo

catio

ns o

f F1

and

F2 (s

ee F

igur

e 1c

) th

e co

rres

pond

ing

num

bers

are

F1‐

S1 F

1‐S2

F1‐

S3 F

2‐S1

F2‐

S2 a

nd F

2‐S3

res

pect

ivel

y

Form

atio

n an

d m

embe

raA

ge

(Ma)

R TS

(m

Ma)

b

Faul

t‐gro

wth

inde

xFa

ult‐a

ctiv

ity r

ate

(mM

a)

AFG

I F1‐

F2c

R FA

A‐F

1‐F2

d

S1S2

S3A

vera

geS1

S2S3

aver

age

F1F2

F1F2

F1F2

F1F2

F1F2

F1F2

F1F2

F1F2

D‐1

233

75ndash

267

1450

00

111

106

109

110

107

109

109

108

389

270

389

479

270

389

349

379

109

364

D‐2

267

14ndash

302

060

00

139

130

138

140

137

133

138

134

320

730

29

341

442

62

329

534

98

330

535

96

136

345

1

D‐3

302

0ndash33

278

190

002

002

052

102

342

032

052

042

1579

67

104

0010

372

111

3485

59

762

989

66

972

12

1093

44

S‐1

+ 2

332

78ndash

378

9250

00

145

136

142

147

155

145

148

143

122

211

36

105

915

78

587

176

39

5614

92

146

122

4

S‐3

(mid

dle

unit)

378

92ndash

404

3812

500

131

202

192

242

175

257

166

234

335

140

88

490

380

62

215

510

919

347

076

90

205

558

0

S‐3

(low

er

unit)

404

38ndash

422

3135

500

284

343

302

395

342

389

309

376

737

185

37

104

4016

956

742

820

480

841

315

324

343

118

69

S‐4

422

31ndash

447

300

002

512

921

584

173

023

332

373

4791

33

106

4357

58

151

8811

007

121

5186

33

126

612

9210

647

a D =

Don

gyin

g Fm

S

= S

hahe

jie F

m T

he n

umbe

r ind

icat

es th

e nu

mbe

r of t

he m

embe

r b R T

S = te

cton

ic‐s

ubsi

denc

e ra

te

c AFG

I F1‐

F2 =

ave

rage

faul

t‐gro

wth

inde

x of

F1

and

F2

d R FA

A‐F

1‐F2

= a

vera

ge fa

ult‐a

ctiv

ity ra

te o

f F1

and

F2

| 597EAGE

LIU et aL

TA

BL

E 3

C

alcu

latio

n ch

art o

f the

sedi

men

tary

‐fac

ies d

imen

sion

s and

the

inte

rnal

pro

grad

atio

nal s

eism

ic e

vent

dip

The

spat

ial e

xten

t is s

how

n in

Fig

ure

7

Form

atio

nand

mem

bera

Sedi

men

tary

faci

esSe

ismic

sect

ions

Thic

knes

s (m

)

Are

a (k

m2 )

Vol

ume

(km

3 )To

tal v

olum

e (k

m3 )

DPb

Max

M

in

Ave

rage

DPA

DPS

A

D‐2

Bra

id d

elta

Figu

re a

176

0075

00

107

7016

246

175

017

50

157

156

Figu

re b

174

0080

00

157

Figu

re c

218

0080

00

152

D‐3

Bra

id d

elta

Figu

re a

285

0011

400

200

5014

219

285

128

51

268

285

Figu

re b

295

0099

00

309

Figu

re c

296

0078

00

309

Figu

re d

284

0091

00

254

S‐1

+ 2

Bra

id d

elta

Figu

re a

178

0089

00

136

7512

023

164

416

44

172

177

Figu

re b

185

0095

00

176

Figu

re c

236

0010

500

193

Figu

re d

209

0011

400

166

S‐3

(mid

dle

unit)

Bra

id d

elta

Figu

re a

274

0010

100

223

7587

87

196

619

66

213

225

Figu

re b

279

0083

00

225

Figu

re c

292

0086

00

235

Figu

re d

296

0086

00

226

S‐3

(low

er u

nit)

Fan

delta

Figu

re a

428

8623

903

374

0062

89

235

223

52

301

305

Figu

re b

432

5522

071

325

Figu

re c

473

0920

583

312

Figu

re d

450

8325

500

283

S‐4

Fan

delta

1Fi

gure

a30

700

483

929

200

107

03

1221

26c

423

365

Figu

re b

350

0010

728

439

Fan

delta

2Fi

gure

a46

500

704

832

900

856

282

421

Figu

re b

379

0066

52

362

Fan

delta

3Fi

gure

a40

100

118

7841

100

186

27

654

21

Figu

re b

468

0016

718

309

Figu

re c

527

0015

127

387

Figu

re d

486

0014

844

297

Fan

delta

4Fi

gure

a42

800

151

2042

700

179

57

663

04

Figu

re b

512

0027

287

289

a D =

Don

gyin

g Fm

S

= S

hahe

jie F

m T

he n

umbe

r ind

icat

es th

e nu

mbe

r of t

he m

embe

r b D

P = se

ism

ic p

rogr

adat

iona

l dip

DPA

= a

vera

ge se

ism

ic p

rogr

adat

iona

l dip

DPS

A =

ave

rage

seis

mic

pro

grad

atio

nal d

ip o

fthe

sedi

men

t c 21

26

= to

tal j

oint

vol

umes

of f

an d

elta

s 1 2

3 a

nd 4

598 | EAGE

LIU et aL

where DPSA is the average seismic progradational dip of a sediment (in degrees) and n is the number of seismic sections

Detailed estimated results of the depositional dip and the seismic progradational dip of the delta are shown in Tables 3 and 4

333 | Provenance conditions and estimation of the sediment supplySystematic investigation by TBCNOOC of the regional uplift and provenance in the geological past has indicated that the main provenance areas around the HD existed alreadybefore the deposition of Member 3 of the Shahejie Fm (Zhou et al 2010) They include the Bonan Laibei and Kendong Highs (Figure 1b‐c Figure S1a‐b) However starting with the depo-sition of Members 1ndash2 of the Shahejie Fm (S‐1 + 2) (3789ndash3328 Ma) until the accumulation of the Dongying Formation (3328ndash2338 Ma) the Bonan and Laibei Highs subsided to below lake level and consequently stopped providing sedi-ment to the depression (Liu Xia et al 2015a) Only the Kendong High which remained a high for a long time re-mained a provenance area for the south‐western part of the

HD during this time‐span (Figure S1a) The Kendong High has therefore been selected as the site where the relationship between tectonics and depositional systems within the same provenance system could be studied best The distribution area of the Kendong High as the provenance area at different moments has been determined on the basis of numerous seis-mic interpretations through seismic terminations (eg onlap) and the absence of specific sediment units due to faulting

The sediment‐supply rate can be obtained by calculation of the volumes of the deltas and the duration of their forma-tion (cf Allen et al 2013 Lemons amp Chan 1999 Lemons Milligan amp Chan 1996) Although the stratigraphic ages are well‐known for each unit (Figure 2) there is no high‐resolu-tion age control for the top and base of each delta system The absolute age of the pertinent stratigraphic unit (Figure 2) is therefore used to represent the formation time of the individual deltas in the unit The thus calculated sediment‐supply rate rep-resents in our opinion the trend of the supply rate from bottom to top sufficiently well

334 | Estimation of the extent and accommodation space of the sink areaDetermination of the boundaries of the sink area is based on reconstructions of the morphology during the successive dep-ositional phases The extent of the sink area was estimated using the same calculations as for the area of the depositional system

DPSA

=

(

nsum

i=1

DPAi

)

∕n

F I G U R E 6 Vertical successions and representative examples of the various lithofacies (a) A fan‐delta in Well W18 (b‐e) Braid‐deltas in Well W25 (f) Grey to greyish white sandy conglomerate (deposits in braided channels) (g) Grey medium‐ to fine‐grained massive sandstone (mouth‐bar deposits) (h) Grey fine sandstone (distal sand bars) (i) Grey muddy siltstone with parallel bedding (prodelta) (j) Greyish white fine sandstone with convolute bedding (mouth bars) (k) Greyish white fine sandstone with boulders (mouth bars) Wireline logs show the spontaneous‐potential (SP) and gamma‐ray (GR) changes with depth Depth in metres For location of the cores see Figure 6bd

| 599EAGE

LIU et aL

Differences in base level and the original sedimentary sur-face define the accommodation space (Jervey 1988 Muto amp Steel 2000 Neal amp Abreu 2009 Wheeler 1964) The

accommodation space in the depositional area can be deter-mined on the basis of the thickness of the preserved sediments (Muto amp Steel 2000) This space is obviously controlled by

F I G U R E 7 Schematic morphology during the successive depositional phases The extent of the deltas the depositional sink area in the basin and the main features of the drainage systems are shown The extent of the deltas has been interpreted from seismic data and has been used for calculation of the surface area and volume of the various deltas (a) Shahejie Fm Member 4 (b) Shahejie Fm lower part of Member 3 (c) Shahejie Fm middle part of Member 3 (d) Shahejie Fm Members 1 and 2 (e) Dongying Fm Member 3 (f) Dongying Fm Member 2

600 | EAGE

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the rate of subsidence tectonic uplift and fluctuations of the lake level (Lemons amp Chan 1999) Changes in the lake level of the HD have not been investigated so that we take data on the tectonic‐subsidence rate as a proxy for changes in the accommodation space The total space is expressed in the equation (Table 4)

where AT represents the total accommodation space of the sink area (in km3) TS represents the tectonic subsidence (in m) and SA represents the surface area of the sink (in km2)

AT= TStimesSA∕1000

T A B L E 4 Estimation of the controlling factor parameters of the depositional system The distribution characteristics of the depositional sink in the basin are shown in Figure 7

Formation and membera

Sedimentary facies Seismic sections

DDb

RSSc(km3

Ma)Sink area (km2) AT

d(km3) ASeSource areaf(km2)DSD DSDA

D‐2 Braid delta Figure a 059 066 502 37542 7852 1195 58

Figure b 065

Figure c 074

D‐3 Braid delta Figure a 161 187 926 19823 11593 2051 252

Figure b 192

Figure c 215

Figure d 182

S‐1 + 2 Braid delta Figure a 086 096 356 28015 6463 1403 220

Figure b 094

Figure c 120

Figure d 083

S‐3 (middle unit) Braid delta Figure a 110 119 772 21756 6927 1619 355

Figure b 111

Figure c 129

Figure d 128

S‐3 (lower unit) Fan delta Figure a 307 303 1313 16506 10500 2705 482

Figure b 334

Figure c 332

Figure d 237

S‐4 Fan delta 1 Figure a 384 463g 861 14150 10481 3484 501

Figure b 379

Fan delta 2 Figure a 606

Figure b 498

Fan delta 3 Figure a 479

Figure b 499

Figure c 625

Figure d 553

Fan delta 4 Figure a 377

Figure b 226aD = Dongying Fm S = Shahejie Fm The number indicates the number of the member bDD = depositional dip DSD = depositional dip in a specific seismic section DSDA = average depositional dip of a specific sedimentary unit cRSS = sediment‐supply rate dAT = total accommodation space eAS = accommodation spacesediment supply fSource area = Denudation area within the seismic data coverage The complete erosional area cannot be estimated because of the limited data coverage g463 = the average depositional dip of fan deltas 1 2 3 and 4 Considering that the four fan deltas developed during S‐4 consist of sediment that was derived from the same provenance area and were deposited in the same time‐span the four fan deltas are taken as a whole when estimating the parameters of RSS the sink area AT and AS

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4 | ELEMENTS OF THE S2S SYSTEM

41 | Analysis of the seismic facies and stacking pattern of the main sedimentary faciesA comprehensive analysis of seismic data cores cutting log-gings and well‐logging curves by Liu Xia et al (2015a) in-dicated that the Palaeogene depositional systems of the HD included fan‐deltas braid‐deltas lake margins deep lakes etc The fan‐ and braid‐deltas have been chosen for a detailed seismic study that must reveal their internal texture and their stacking patterns Analysis of the progradational seismic‐re-flection types and of the seismic progradational dip is particu-larly helpful for a better understanding of the hydrodynamic conditions and sedimentary processes that resulted in these depositional systems Because the facies interpretation in this area has been done before and is not the focus of this work we here mainly describe the internal texture and their stack-ing patterns of the main sedimentary facies

The major facies of S‐4 is interpreted as a fan‐delta It is dominated by Seismic Facies 1 which is characterized by discontinuous to continuous low‐ to high‐amplitude and chaotic progradational seismic reflections (Figures S3ndashS6 Table 1) The average dip of the progradational seismic event is about 365deg (Table 3) Three lithofacies are associated with Seismic Facies 1 (Table 1) The coarser lithofacies 1 represents a fan‐delta front whereas the finer lithofacies 2 and 3 are prodelta deposits The overall coarsening‐upward succession facies stacking pattern (Figure 6a) discontinuous and chaotic seismic reflections and relatively steep slope of Seismic Facies 1 suggest a fan‐delta system developed under strong hydrodynamic conditions (Mitchum et al 1977)

The fan‐delta of the lower part of Member 3 of the Shahejie Fm (S‐3 [lower unit]) is dominated by Seismic Facies 2 which is characterized by chaotic progradational to oblique progradational seismic characteristics It has a typical wedge shape and is composed of two seismic‐reflection seg-ments (a) a moderately continuous low‐ to high‐amplitude chaotic seismic‐reflection segment located near boundary fault F2 and (b) a continuous moderate‐ to high‐amplitude and oblique progradational seismic reflection in a basinward direction (Figure S7 Table 1) No obvious upper or lower segments occur in SF 2 and the dip of the progradational seismic event in this segment is also relatively steep viz 305deg (Table 3)

The middle part of Member 3 of the Shahejie Fm (S‐3 [middle unit]) is characterized by a low‐ to moderate‐con-tinuous low‐amplitude and oblique progradational seismic reflection (Seismic Facies 3) and is interpreted as a braid‐delta (Figure S8 Table 1) The progradational seismic events are parallel or sub‐parallel to each other and dip less (aver-age 225deg) than Seismic Facies 1 and 2 (Table 3) Seismic

Facies 3 is associated with four lithofacies (Figure 6b Table 1) in Well T25 The complete succession of the braid‐delta consists of gravely to coarse‐grained sandstone (lithofacies 1) at the base (Figure 6f) massive bedded medium‐ to fine‐grained sandstones (lithofacies 2) and grey mudstones inter-bedded with grey fine sandstones and grey muddy siltstones (lithofacies 3) in the middle (Figures 6g and 6h) and thick dark grey mudstones (lithofacies 4) at the top (Figure 6i)

Member 3 of the Dongying Fm (D‐3) is characterized by Seismic Facies 4 a typically composite seismic progra-dation reflection configuration representing a braid‐delta system (Figure S9 Table 1) Seismic Facies 4 is composed of highly continuous moderate‐ to high‐amplitude and pro-gradational seismic reflections that represent well‐developed deltaic topsets and bottomsets The topset segments of SF 4 are nearly horizontal or dip only gently (Table 3) The foreset segments form thicker lenses with small depositional angles The oblique progradational part of this seismic facies is sim-ilar to that in Seismic Facies 3 and usually developed at the basinward front end of Seismic Facies 3 The lithology of Seismic Facies 4 is dominated by greyish white to white fine‐grained sandstones and siltstones The lithofacies association is characterized by coarsening‐upward sedimentary cycles (Figure 6c Table 1) Convolute bedding and abundant diam-ictites are present on top of the fine sandstones (Figure 6j‐k)

Both braid‐deltas in the Members 1 + 2 of th Shahejie Fm (S‐1 + 2) and Member 2 of the Dongying Fm (D‐2) show moderately continuous moderate‐amplitude and shin-gled‐like progradational seismic reflections (Seismic Facies 5 Figures S10ndashS11 Table 1) It shows a thin prograding seis-mic pattern commonly with parallel upper and lower bound-aries (cf Mitchum et al 1977) The successive internal progradational seismic events overlap each other between the upper and lower segments with a gentle dip of 152degndash193deg (Table 3) The lithofacies are mostly composed of several coarsening‐upward cycles (Figure 6d Table 1) Each cycle is composed of dark grey mudstones and grey to whitish‐grey medium‐ to fine‐grained sandstones Several coarsening‐up-ward lithofacies are mainly developed in D‐2 (Figure 6e Table 1)

42 | Analysis of the tectonic activityThe normal faults F1 and F2 selected to calculate the fault activity dipping to the north and running approximately E‐W are important boundary faults on the south‐western margin of the HD The tectonic‐subsidence rate fault‐growth index and fault‐activity rate were used as proxies to indicate the tectonic intensity (Figure 3 S2 Table 2) S‐4 and S‐3 (lower unit) have the highest subsidence rate (300ndash355 mMa) the highest fault‐growth index (292ndash343 mMa) and the highest fault‐activity rate (10647ndash11869 mMa) among the studied intervals whereas the overlying S‐3 (middle

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unit) and S‐1 + 2 are characterized by a much lower sub-sidence rate and fault‐growth index and fault‐activity rate D‐3 had again a high subsidence rate (190 mMa) and an average fault‐growth index (210 mMa) and fault‐activity rate (9344 mMa) The uppermost studied interval D‐2 had a much lower subsidence rate (60 mMa) growth index (136 mMa) and fault‐activity rate (3451 mMa) than the un-derlying unit Generally the analysis of the subsidence rate average fault‐growth index and fault‐activity rate indicates two phases of alternating strong tectonic activity and tectoni-cally stable conditions

43 | Palaeogeomorphology distribution and dimensions of the main depositional systemsDepositional systems of each depositional phase of the Palaeogene on the south‐western slope of the HD were com-piled through seismic facies identification of 3‐D seismic data and compilation of maps with the current thicknesses of the main target intervals based on the study by Liu Xia et al (2015a) that combined a correction for the depth of burial with an interpretation of the sedimentary facies The basins sink area on the south‐western slope of the HD was estimated on the basis of a palaeogeomorphological reconstruction The distribution of the depositional system is closely related to the evolution of the palaeogeomorphology and therefore we describe both the distribution of the depositional system and the palaeogeomorphology here

The palaeogeography of S‐4 is characterized by the larg-est extent of the uplifted areas of all studied intervals The depositional area is small and scattered (Figure 7a Table 4) Faults F1 and F2 mark the boundaries between erosional and depositional regions The elevated footwalls of the faults were erosional areas and located adjacent to the hanging walls whereas the hanging walls were low‐lying depositional areas The sedimentary facies analysis indicates a fan‐delta developed here (Figure 7a) Calculations indicate that the sedimentary dip of the four fan‐deltas was uncommonly high (about 463deg) The extent and thickness of the fan‐deltas di-minished towards the basin margin (Tables 34)

The tectonically‐induced morphology of S‐3 (lower unit) shows a similar pattern to that of the underlying S‐4 The depositional and erosional areas were also controlled by the active faults F1 and F2The HD deepened from west to east with the deepest area located just along the fault margin The depositional centre was located north of the hanging wall of F2 and became infilled by a fan‐delta (Figure 7b) The aver-age sedimentary dip of the fan‐delta is 303deg The extent of the fan‐delta was larger than that of S‐4 (Table 34)

During deposition of S‐3 (middle unit) the uplifted source area shifted southwards and the depression expanded A major depositional sink was located north of the hanging wall of F2 (Figure 7c Table 4) Elevation differences existed

between the footwalls and the hanging walls of F1 and F2 although the topography was obviously gentler during this time‐span A braided fluvial area developed at the footwalls of the faults whereas a braid‐delta developed mainly on the hanging wall of F2 and the northern depositional centre (Figure 7c) The braid‐delta had a fairly large extent and an average depositional dip of 119deg (Tables 34)

During S‐1 + 2 the elevated erosional area shifted farther southwards and the entire south‐western area had a low to-pography An alluvial plain developed south of the footwalls of the faults whereas a braid‐delta developed at the hanging walls and in the depression with a very gentle slope of 096deg (Table 4 Figure 7d) The depositional system was dominated by a fairly thin delta body and a braid‐delta with a much larger extent (Table 3)

During the deposition of D‐3 the topography of the foot-wall areas and of the area south of the provenance area was similar to that during the underlying S‐1 + 2 The slope was steep (187deg) in the hanging walls of the boundary faults however and the depositional area increased to 198 km2 which provided an excellent condition for the deposition of a large braid‐delta (Figure 7e Table 4) This braid‐delta had a NE‐SW orientation and covered an area of 142 km2 its average thickness is some 200 m which results in the largest delta volume in the Palaeogene on the south‐western slope of the HD (Table 3)

The palaeogeomorphological reconstruction of D‐2 shows a gentler topography in the entire south‐western HD with a sink area of 375 km2 (Table 4) The main body of the braid‐delta was dominated by imbricated progradational seis-mic reflections and developed in the hanging walls of F1 and F2 whereas an alluvial‐plain facies probably developed in the footwall areas of the faults and to the south‐west of the uplifted area (Figure 7f) Although the extent of the delta reached its maximum the thickness of the delta was limited due to the gentle topography resulting in a small delta vol-ume (Table 3)

5 | RELATIONSHIPS BETWEEN THE VARIOUS ELEMENTS OF THE S2S SYSTEM

Quantitative relationships between the various elements of the S2S system have been established through the above‐mentioned calculations A strong positive correlation is clearly present between the rate of tectonic subsidence the average fault activity and the average growth index of the boundary faults F1 and F2 (Figure 8ab) The rate of tectonic subsidence can therefore be used in the following as the pri-mary proxy to represent the intensity of the tectonic activity whereas the rate of fault activity and the growth index are used as secondary proxies

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The tectonic activity and the sediment‐supply rate show a positive relationship (Figures 8c 9a 10a) whereas the tec-tonic activity and the sink area of the basin show a negative relationship (Figures 8d 9b 10b) In contrast the tectonic activity has a positive relationship with the total accommo-dation space (Figures 8e 9c 10c Table 4) There is also a positive relationship between the average sedimentary dip of the fan‐ and braid‐deltas on the one hand and the tectonic activity on the other hand (Figures 8f 9d 10d)

The intensity of the tectonic activity correlates negatively with the extent of the sediment area but positively with the sediment volume (Figures 8g‐h 9e‐f 10e‐f) The different responses of the sediment area and the volume to the tectonic activity are caused by variations in the thicknesses of the sed-imentary units (Table 3)

There is also a positive relationship between the average seismic progradation dip of the fan‐ and braid‐deltas and the tectonic activity (Figures 8i 9g 10g) strong tectonic activ-ity usually formed deltas that are characterized by a chaotic progradational or oblique progradational seismic reflection such as SF 1 and 2 in S‐3 (lower unit) and S‐4 (Figures S3ndashS7) The minimum tectonic activity during Members S‐1 + 2 and D‐2 are reflected by dominantly shingled progradational seismic facies in the delta interior (Figures S10ndashS11)

In addition we find that the sediment area sediment vol-ume and average seismic progradation dip of the fan‐ and braid‐deltas correlate positively with the sediment‐supply rate (Figure 11a b and c) but negatively with the basin sink area (Figure 11d e and f) Both the sediment volume and the average seismic progradation dip of the fan‐ and braid‐deltas

F I G U R E 8 (a‐b) Relationships between the tectonic‐subsidence rate and tectonics (c‐i) Relationships between tectonic activity and sedimentary source‐to‐sink parameters Input data regarding the tectonic activity are from Table 2 those regarding the source‐to‐sink parameters data are from Tables 3 and 4 Regression‐line equations and coefficients of determination (R2) are shown for all diagrams

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show a positive relationship with the total accommodation space (Figure 11hi) However no obvious relationship ap-pears to be present between the sediment area and the total accommodation space (G) Both the sediment area and the average seismic progradation dip of the fan‐ and braid‐deltas correlate well with the average sedimentary dip of the fan‐ and braid‐deltas (Figure 11km) A poor correlation is found between the sediment volume and the average sedimentary dip of the fan‐ and braid‐deltas

6 | DISCUSSION

61 | Analysis of the influence of tectonic activity on the source area accommodation space geomorphology and sediment supplyA high relief and large drainage area usually can generate a large sediment supply (Leeder Harris amp Kirkby 1998 Syvitski amp Milliman 2007) Although the erosional area for the fan and delta system cannot be estimated because of the

limited data coverage the exposed area within the study area can be calculated The calculations show a generally decreas-ing trend of the source area from S‐4 (501 km2) to D‐2 (58 km2 Figure7 Table 4) The calculated exposed area cannot fully represent the true source area however but the evolu-tionary trend of the source area can be used as a proxy to indi-cate the relative influence on the change in sediment volume This trend is consistent with the decrease in sediment volume from S‐4 (2126 km3) to D‐2 (175 km3 Table 2) The relief is difficult to reconstruct in this case but variations in the fault‐activity rate (here taken as the tectonic‐subsidence rate) can create local elevation differences and can therefore be used as proxies for the trends in the relief development The relief shows an overall decreasing trend from S‐4 to D‐2 except for D‐3 this correlates well with the sediment volume (Figure 8h) Although the drainage area of D‐3 was smaller than that of D‐2 because of the high tectonic‐subsidence rate (result-ing in a high relief) D‐3 is thicker and shows a larger sedi-ment volume than the overlying D‐2 (Table 3) D‐3 is thinner than S‐4 + 3 but the larger source area resulted in a larger

F I G U R E 9 General relationships between the average fault‐growth index of F1 and F2 (AFGIF1‐F2) and sedimentary source‐to‐sink parameters The average fault‐growth index of F1 and F2 (AFGIF1‐F2) data in this figure are from Table 2 The source‐to‐sink parameters data are from Table 4 Regression‐line equations and the coefficients of determination are shown in each diagram

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sediment volume and supply rate (Table 3 Figure8ch) Therefore both the fault‐induced relief and the drainage area affected the sediment‐supply rate and the sediment volume in the sink

The changes in accommodation space during the vari-ous phases of the Palaeogene in the south‐western HD are clear from the estimated tectonic subsiding rate (Table 2) The correlations between the intensity of the tectonic activ-ity and the extent of the depositional sink area (Figures 8d 9b 10b) between the intensity of the tectonic activity and the total accommodation space and between the intensity of the tectonic activity and the morphology in the sink area (Figures 8e‐f 9c‐d 10c‐d) clearly show that strong tectonic activity resulted in a larger accommodation capacity of the sink

In particular the main subsiding area tended to form steeper slopes However the extent of the main subsiding sink area diminished (Figure 8d) with increasing tectonic activity which was possibly due to the relatively small sub-siding centre in the tectonically active basins It can thus be deduced that tectonic activity not only controlled the sedi-ment supply and the variation in accommodation space but

also determined the changes in the topography of the sedi-mentary basins and the extent of the main depositional areas in the tectonically active basins

62 | Analysis of the influence of tectonic activity on the size and internal stacking pattern of the delta depositional systemThe above data and considerations indicate that the tectonic activity was closely related to the sediment supply accom-modation space and morphology of the sink area which are possibly the most important factors affecting the extent and stacking pattern of the sedimentary facies (cf Cope et al 2010 DeCelles Kapp Ding amp Gehrels 2007 Leeder 2011 Olsen 1997 Simon et al 2017)

Statistical analysis indicates that the sediment‐supply rate has a strong positive correlation with the volume of the depositional system a moderate correlation with the seismic progradational dip in the depositional system and a poor cor-relation with the size of the depositional area (Figure 11a‐c) A larger sink area corresponded to a larger fanbraid‐delta a gentler seismic progradational angle and a reduced volume

F I G U R E 1 0 General relationships between average fault activity rate of F1 and F2 (RFAA‐F1‐F2) and sedimentary source‐to‐sink parameters The average fault activity rate of F1 and F2 (RFAA‐F1‐F2) data in this figure are from Table 2 The source‐to‐sink parameters data are from Table 4 Regression line equations and the coefficients of determination are shown in each diagram

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of the fan or braid‐delta which was possibly related to a re-duced sedimentary dip and thinner sediments (Figure 11d‐f) The total accommodation space in the basin correlates well

with the volume of the depositional system to some degree with the seismic progradational dip and poorly with the ex-tent of the depositional system area (Figure 11g‐i) These

FIGURE 11 Relationships between various parameters involved in the source‐to‐sink system (a‐c) Relationships between sediment supply and characteristics of the depositional system (extent volume and DPSA of the sediments) (d‐f) Relationships between the sink area of the basin and characteristics of the depositional system (g‐i) Relationships between the total accommodation space (AT) and the characteristics of the depositional system (j) Relationship between the accommodation‐spacesediment‐supply ratio (AS) and the DPSA of the sediments (k‐m) Relationships between the sedimentary dip and the characteristics of the depositional system The data regarding sediment supply basin sink area total accommodation space accommodation‐spacesediment‐supply ratio and sedimentary dips are from Table 4 The extent volume and DPSA of the sedimentary facies are from Table 3 Note the seemingly obvious polynomial (quadratic) relationship between the sedimentary dip and the sediment volume (L) The trend line in (L) suggests the following relationships between sediment volume and sedimentary slope in a rift or tectonically active basin (1) a very steep sedimentary slope is unfavourable for sediment accumulation (2) an appropriate sedimentary slope is favourable for preservation of depositional systems eg when the sedimentary slope in (L) is about 25degndash32deg the sediment volume reaches its largest value (3) a very gentle sedimentary slope will lead to a decrease of the sediment volume possibly due to weakening of the drainage system and thinner sediments

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relationships are clear evidence that the size of the sink area controlled the extent of the depositional system during the rifting of the lacustrine basin and that the rate of sediment supply and the accommodation space had a significant in-fluence on the total sedimentary volume as well as on the internal stacking pattern of the depositional system

We here use the ratio of the tectonic‐subsidence rate and the sediment‐supply rate as a proxy to indicate the ratio be-tween accommodation space and sediment‐supply rate (AS) (Table 4) AS has a strong influence on the internal stacking pattern of the depositional systems in the lacustrine rift basin (Figure 11j) This might be because the basin was small and because abundant and rapid material was supplied due

to intense tectonic activity (cf Catuneanu et al 2009 Liro 1993) and a favourable local climate (eg Bohacs Carroll Neal amp Mankiewicz 2000 Perlmutter amp Matthews 1989) The sediment supply still had a significant influence on the main subsidence area of the lacustrine basins and deposi-tional systems

In addition the basin slope significantly influenced the extent of the depositional system (Figure 11k) and had a polynomial relationship with its volume (Figure 11l) This relationship indicates that more intense tectonic activity and a steeper depositional slope were not favourable for sediment accumulation over a large extent in the lacustrine basin On the contrary these sediments were usually transported to a

F I G U R E 1 2 Tectonic differential activities and resulting patterns of the source‐to‐sink system on the south‐western slope of the HD during the Palaeogene (a) Development during phases of intense tectonics (Member 4 to the lower part of Member 3 of the Shahejie Fm) (b) Development during phases of somewhat less tectonic activity (middle part of Member 3 of the Shahejie Fm and Member 3 of the Dongying Fm) (c) Development during phases of weak tectonic activity (Members 1 and 2 of the Shahejie Fm and Member 2 of the Dongying Fm) The intensity of tectonic activity in the lacustrine rift basin had a significant influence on the development and extent of each unit of the source‐to‐sink system as well as on the type and dimensions of the depositional systems The present study indicates that probably sublacustrine fans developed (see for example Figure S4b) during phases with relatively strong tectonic activity This is not really clear from the seismic‐reflection data but possibly due to the small sizes of these sublacustrine fans Moreover lithofacies and core data are not available for the south‐western part of the study area The present contribution therefore focuses on the fan‐deltas and braid‐deltas regarding the sedimentary facies analysis the sublacustrine fans that probably developed in the deep or semi‐deep lake are presented just as a likely feature

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relatively small sink area with a fairly large accommodation space Finally stronger tectonic activity resulted in steeper depositional slopes (Figure 8f) which further controlled the hydrodynamic conditions and differential discharge when the sediments were deposited The strong correlation between the depositional slope and the deltas dip (Figure 11m) suggests that the differences in topography due to tectonics must be considered as one of the most critical factors that controlled the internal stacking pattern of the delta deposits

63 | Significance of the present study for other source‐to‐sink systems of lacustrine rift basins

631 | Summary of the source‐to‐sink systems in the HDIn lacustrine rift basins the tectonic setting is probably the main factor that determines the development of the S2S sys-tem but differential tectonic activities lead to variations in the basic characteristics of the S2S system Tectonic activity was most intense during S‐3 (lower unit) and during S‐4 and caused both a strong uplift of the source area and the devel-opment of depressions in the basin that formed a sink (Figure 12a) Strong tectonic activity in the S2S system during these time‐spans led to a high sediment‐supply rate steeper slopes a larger accommodation space and deposition of several fan‐deltas that are characterized by a fairly steep seismic progra-dational angle

The tectonic activity decreased during S‐3 (middle unit) and during D‐3 The S2S system that was present during this time‐span mainly concerned a rising area that shifted south-wards developing an alluvial plain between the erosional area and the sink area thus increasing the distance from source to sink (Figure 12b) Simultaneously the sediment‐supply rate and the accommodation space also changed and braid‐deltas could thus develop with larger volumes and gentler seismic progradational dips

Tectonic activity was clearly less intense during S‐1 + 2 and D‐2 The rising area had shifted further southwards cre-ating a wider alluvial plain connecting the source area to the sink in the HD (Figure 12c) At this stage stable tectonic activity led to relatively less sediment supply a gentle slope less accommodation space and the development of several braid‐deltas with a fairly gentle seismic progradational angle

632 | Wider implications and limitationsSoslashmme et al (2009) proposed that the elements of S2S sys-tems are genetically related and that quantitative correla-tions exist among these elements Other studies also suggest that the size of the drainage basin is correlated to the size of the fan developing on the basin floor (eg Blum et al

2017 Snedden et al 2018) and to the size of the river chan-nel (eg Milliken et al 2018) Helland‐Hansen Soslashmme Martinsen Lunt and Thurmond (2016) suggest a simplified subdivision of S2S systems into three main categories (a) Steep‐Short‐Deep (steep onshore and offshore gradients short distance between source and sink and deep offshore waters) (b) Wide‐Deep (low‐gradient shelf‐catchment area and deep offshore waters) and (c) Wide‐Shallow (relatively shallow offshore waters and a wide low‐gradient catchment area) systems

The present study indicates that the alluvial plain roughly corresponds to the alluvial‐shelf unit in marine basins al-though with a much smaller width and extent in the lacustrine rift basins than would have been the case on a continental shelf Faults F1 and F2 along the slope belt correspond to the slope of classical S2S systems whereas the shore‐shallow‐deep lake area can be compared with the basin floor (Soslashmme et al 2009) S‐4 and S‐3 (lower unit) can be roughly clas-sified as Steep‐Short‐Deep systems whereas the overlying S‐1 + 2and D‐2 can be classified as the Wide‐Shallow sys-tems that Helland‐Hansen et al (2016) defined During the deposition of S‐4 and S‐3 (lower unit) the strong tectonic activity caused a high relief of the source area a narrow allu-vial plain and a relatively deep lake The subsequently wan-ing tectonic activity resulted in a lower relief of the source area a wider alluvial plain and a shallower lake Although the absolute values of these elements in lacustrine basins are much smaller than those of marine basins the ratio between these elements in both settings is comparable Typically in a lacustrine basin a transformation from a Steep‐Short‐Deep system (S‐4 and S‐3 (lower unit)) to a Wide‐Shallow system (S‐1 + 2ampD‐2) occurs within a few million years Although the basin geomorphology has experienced signif-icant changes from S‐4 to D‐2 the quantitative relationships between tectonic activity sediment‐supply rate accommoda-tion space and sedimentary dip of the delta systems did not change significantly (eg Figures 8 and 11) The analytical approaches applied and quantitative relationship established here can help analyse other lacustrine basins worldwide and may even act as a reference for the analysis of marine basins

Our study focuses mainly on the influences of tectonic activity on the elements of the depositional sink Other pa-rameters (eg climate and lithology) were not considered in detail Studies on modern and ancient systems suggest that the climate and lithology also have a great influence on the sediment supply and distribution in the basin (eg Carroll Chetel amp Smith 2006 Hovius amp Leeder 1998 Syvitski amp Milliman 2007 Zhang et al 2018) For exam-ple climate variations between glacials and inter‐glacials have resulted in largely different sediment‐supply rates and in significant differences in the sizes of the Quaternary sub-marine fans in the north‐western Gulf of Mexico (Blum amp Hattier‐Womack 2009) We acknowledge the importance

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of climate and lithology for S2S systems and we are con-vinced that these elements can significantly affect the S2S systems in other cases(eg modern systems and systems influenced by glacialinterglacial alternations) These fac-tors were not really relevant for the present study however because no significant differences in lithology were present in the source areas and because we focus on the changes at a million‐year scale which implies that the tectonic ac-tivity has a first‐order control on the development of S2S elements in the investigated rift basin

7 | CONCLUSIONS

We have calculated the tectonic‐subsidence history the growth index and the activity rate of the main boundary faults (F1 and F2) and various S2S parameters of six Palaeogene rock units on the south‐western slope of the HD Based on the values found for these parameters quantitative corre-lation were established for the tectonic activity and other S2Sparameters in the basinal sink This leads to the follow-ing conclusions

1 The positive correlation between the intensity of fault activity and the tectonic‐subsidence rate is a strong indication for a distinct control by the tectonic activity of the syn‐depositional rifting of the tectonically active basin

2 The tectonic activity was quantitatively related to the sediment supply accommodation space and morphology of the sink area The relationship between tectonic activ-ity and depositional systems is reflected by changes in critical factors such as sediment supply accommodation space and dip of the sink area These critical factors were probably the most important factors that led to changes in the size and internal stacking pattern of the sedimentary facies

3 Differential tectonic activity led to changes in the char-acteristics of the S2S system on the south‐western slope of the HD The strongest tectonic activity which oc-curred during S‐3 (lower unit) and during S‐4 led to the largest provenance area adjacent to the sink area to a high sediment‐supply rate to steeper slopes to a larger accommodation space and controlled the development of several fan‐deltas Diminished tectonic activity dur-ing S‐3 (middle unit) and during D‐3 led to a decrease in uplift an increased width of the alluvial plain an in-creased transport distance a decrease in the sediment‐supply rate and accommodation space and resulted in the development of braid‐deltas with a large volume During S‐1 + 2 and D‐2 stable tectonic activity led to a lower sediment‐supply rate a gentle depositional slope and a smaller accommodation space resulting in the

development of several braid‐deltas with gentler seis-mic progradational angles

4 The analytical approaches applied and the quantitative re-lationships established here can help analyse other lacus-trine basins worldwide and may even act as a reference for the study of marine basins

ACKNOWLEDGEMENTS

We thank Dr Sarah Boulton and Dr Chenlin Gong as well as the Associate Editor of Basin Research Dr Craig Magee for their constructive comments on the manuscript This study was funded by the National Science and Technology Major Project (Exploration Technologies for Offshore Hidden OilGas) (project no 2016ZX05024‐003‐003) the National Natural Science Foundations of China (project no 41676050) and the Fundamental Research Funds for the Central Universities (2652014037)

REFERENCES

Allen P A (2008a) From landscapes into geological history Nature 451 274ndash276 https doiorg101038natur e06586

Allen P A (2008b) Time scales of tectonic landscapes and their sed-iment routing systems In Landscape evolution Denudation cli-mate and tectonics over different time and space scales (Ed by Gallagher K Jones S J amp Wainwright J) Geological Society London Special Publications 296 7ndash28

Allen P A Armitage J J Carter A Duller R A Michael N A Sinclair H D hellip Whittaker A C (2013) The Qs problem Sediment volumetric balance of proximal foreland basin systems Sedimentology 60 102ndash130

Amorosi A Maselli V amp Trincardi F (2016) Onshore to offshore anatomy of a late Quaternary source‐to‐sink system (Po Plain‐Adriatic Sea Italy) Earth‐Science Reviews 153 212ndash237 https doiorg101016jearsc irev201510010

Anderson J B Wallace D J Simms A R Rodriguez A B Weight R W R amp Taha Z P (2016) Recycling sediments between source and sink during a eustatic cycle Systems of late Quaternary northwestern Gulf of Mexico Basin Earth‐Science Reviews 153 111ndash138 https doiorg101016jearsc irev201510014

Anthony E J amp Julian M (1999) Source‐to‐sink sediment trans-fers environmental engineering and hazard mitigation in the steep Var River catchment French Riviera southeastern France Geomorphology 31 337ndash354 https doiorg101016S0169-555X(99)00088-4

Athy L F (1930) Density porosity and compaction of sedimentary rocks AAPG Bulletin 14 1ndash24

Bhattacharya J P Copeland P Lawton T F amp Holbrook J (2016) Estimation of source area river palaeo‐discharge palaeoslope and sediment budgets of linked deep‐time depositional systems and im-plications for hydrocarbon potential Earth‐Science Reviews 153 77ndash110

Blum M D amp Hattier‐Womack J (2009) Climate change sea‐level change and fluvial sediment supply to deepwater depositional

596 | EAGE

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TA

BL

E 2

Es

timat

ion

stat

istic

s of t

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ic‐s

ubsi

denc

e ra

te g

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and

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lcul

atio

n lo

catio

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f F1

and

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ee F

igur

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) th

e co

rres

pond

ing

num

bers

are

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1‐S2

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2‐S1

F2‐

S2 a

nd F

2‐S3

res

pect

ivel

y

Form

atio

n an

d m

embe

raA

ge

(Ma)

R TS

(m

Ma)

b

Faul

t‐gro

wth

inde

xFa

ult‐a

ctiv

ity r

ate

(mM

a)

AFG

I F1‐

F2c

R FA

A‐F

1‐F2

d

S1S2

S3A

vera

geS1

S2S3

aver

age

F1F2

F1F2

F1F2

F1F2

F1F2

F1F2

F1F2

F1F2

D‐1

233

75ndash

267

1450

00

111

106

109

110

107

109

109

108

389

270

389

479

270

389

349

379

109

364

D‐2

267

14ndash

302

060

00

139

130

138

140

137

133

138

134

320

730

29

341

442

62

329

534

98

330

535

96

136

345

1

D‐3

302

0ndash33

278

190

002

002

052

102

342

032

052

042

1579

67

104

0010

372

111

3485

59

762

989

66

972

12

1093

44

S‐1

+ 2

332

78ndash

378

9250

00

145

136

142

147

155

145

148

143

122

211

36

105

915

78

587

176

39

5614

92

146

122

4

S‐3

(mid

dle

unit)

378

92ndash

404

3812

500

131

202

192

242

175

257

166

234

335

140

88

490

380

62

215

510

919

347

076

90

205

558

0

S‐3

(low

er

unit)

404

38ndash

422

3135

500

284

343

302

395

342

389

309

376

737

185

37

104

4016

956

742

820

480

841

315

324

343

118

69

S‐4

422

31ndash

447

300

002

512

921

584

173

023

332

373

4791

33

106

4357

58

151

8811

007

121

5186

33

126

612

9210

647

a D =

Don

gyin

g Fm

S

= S

hahe

jie F

m T

he n

umbe

r ind

icat

es th

e nu

mbe

r of t

he m

embe

r b R T

S = te

cton

ic‐s

ubsi

denc

e ra

te

c AFG

I F1‐

F2 =

ave

rage

faul

t‐gro

wth

inde

x of

F1

and

F2

d R FA

A‐F

1‐F2

= a

vera

ge fa

ult‐a

ctiv

ity ra

te o

f F1

and

F2

| 597EAGE

LIU et aL

TA

BL

E 3

C

alcu

latio

n ch

art o

f the

sedi

men

tary

‐fac

ies d

imen

sion

s and

the

inte

rnal

pro

grad

atio

nal s

eism

ic e

vent

dip

The

spat

ial e

xten

t is s

how

n in

Fig

ure

7

Form

atio

nand

mem

bera

Sedi

men

tary

faci

esSe

ismic

sect

ions

Thic

knes

s (m

)

Are

a (k

m2 )

Vol

ume

(km

3 )To

tal v

olum

e (k

m3 )

DPb

Max

M

in

Ave

rage

DPA

DPS

A

D‐2

Bra

id d

elta

Figu

re a

176

0075

00

107

7016

246

175

017

50

157

156

Figu

re b

174

0080

00

157

Figu

re c

218

0080

00

152

D‐3

Bra

id d

elta

Figu

re a

285

0011

400

200

5014

219

285

128

51

268

285

Figu

re b

295

0099

00

309

Figu

re c

296

0078

00

309

Figu

re d

284

0091

00

254

S‐1

+ 2

Bra

id d

elta

Figu

re a

178

0089

00

136

7512

023

164

416

44

172

177

Figu

re b

185

0095

00

176

Figu

re c

236

0010

500

193

Figu

re d

209

0011

400

166

S‐3

(mid

dle

unit)

Bra

id d

elta

Figu

re a

274

0010

100

223

7587

87

196

619

66

213

225

Figu

re b

279

0083

00

225

Figu

re c

292

0086

00

235

Figu

re d

296

0086

00

226

S‐3

(low

er u

nit)

Fan

delta

Figu

re a

428

8623

903

374

0062

89

235

223

52

301

305

Figu

re b

432

5522

071

325

Figu

re c

473

0920

583

312

Figu

re d

450

8325

500

283

S‐4

Fan

delta

1Fi

gure

a30

700

483

929

200

107

03

1221

26c

423

365

Figu

re b

350

0010

728

439

Fan

delta

2Fi

gure

a46

500

704

832

900

856

282

421

Figu

re b

379

0066

52

362

Fan

delta

3Fi

gure

a40

100

118

7841

100

186

27

654

21

Figu

re b

468

0016

718

309

Figu

re c

527

0015

127

387

Figu

re d

486

0014

844

297

Fan

delta

4Fi

gure

a42

800

151

2042

700

179

57

663

04

Figu

re b

512

0027

287

289

a D =

Don

gyin

g Fm

S

= S

hahe

jie F

m T

he n

umbe

r ind

icat

es th

e nu

mbe

r of t

he m

embe

r b D

P = se

ism

ic p

rogr

adat

iona

l dip

DPA

= a

vera

ge se

ism

ic p

rogr

adat

iona

l dip

DPS

A =

ave

rage

seis

mic

pro

grad

atio

nal d

ip o

fthe

sedi

men

t c 21

26

= to

tal j

oint

vol

umes

of f

an d

elta

s 1 2

3 a

nd 4

598 | EAGE

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where DPSA is the average seismic progradational dip of a sediment (in degrees) and n is the number of seismic sections

Detailed estimated results of the depositional dip and the seismic progradational dip of the delta are shown in Tables 3 and 4

333 | Provenance conditions and estimation of the sediment supplySystematic investigation by TBCNOOC of the regional uplift and provenance in the geological past has indicated that the main provenance areas around the HD existed alreadybefore the deposition of Member 3 of the Shahejie Fm (Zhou et al 2010) They include the Bonan Laibei and Kendong Highs (Figure 1b‐c Figure S1a‐b) However starting with the depo-sition of Members 1ndash2 of the Shahejie Fm (S‐1 + 2) (3789ndash3328 Ma) until the accumulation of the Dongying Formation (3328ndash2338 Ma) the Bonan and Laibei Highs subsided to below lake level and consequently stopped providing sedi-ment to the depression (Liu Xia et al 2015a) Only the Kendong High which remained a high for a long time re-mained a provenance area for the south‐western part of the

HD during this time‐span (Figure S1a) The Kendong High has therefore been selected as the site where the relationship between tectonics and depositional systems within the same provenance system could be studied best The distribution area of the Kendong High as the provenance area at different moments has been determined on the basis of numerous seis-mic interpretations through seismic terminations (eg onlap) and the absence of specific sediment units due to faulting

The sediment‐supply rate can be obtained by calculation of the volumes of the deltas and the duration of their forma-tion (cf Allen et al 2013 Lemons amp Chan 1999 Lemons Milligan amp Chan 1996) Although the stratigraphic ages are well‐known for each unit (Figure 2) there is no high‐resolu-tion age control for the top and base of each delta system The absolute age of the pertinent stratigraphic unit (Figure 2) is therefore used to represent the formation time of the individual deltas in the unit The thus calculated sediment‐supply rate rep-resents in our opinion the trend of the supply rate from bottom to top sufficiently well

334 | Estimation of the extent and accommodation space of the sink areaDetermination of the boundaries of the sink area is based on reconstructions of the morphology during the successive dep-ositional phases The extent of the sink area was estimated using the same calculations as for the area of the depositional system

DPSA

=

(

nsum

i=1

DPAi

)

∕n

F I G U R E 6 Vertical successions and representative examples of the various lithofacies (a) A fan‐delta in Well W18 (b‐e) Braid‐deltas in Well W25 (f) Grey to greyish white sandy conglomerate (deposits in braided channels) (g) Grey medium‐ to fine‐grained massive sandstone (mouth‐bar deposits) (h) Grey fine sandstone (distal sand bars) (i) Grey muddy siltstone with parallel bedding (prodelta) (j) Greyish white fine sandstone with convolute bedding (mouth bars) (k) Greyish white fine sandstone with boulders (mouth bars) Wireline logs show the spontaneous‐potential (SP) and gamma‐ray (GR) changes with depth Depth in metres For location of the cores see Figure 6bd

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Differences in base level and the original sedimentary sur-face define the accommodation space (Jervey 1988 Muto amp Steel 2000 Neal amp Abreu 2009 Wheeler 1964) The

accommodation space in the depositional area can be deter-mined on the basis of the thickness of the preserved sediments (Muto amp Steel 2000) This space is obviously controlled by

F I G U R E 7 Schematic morphology during the successive depositional phases The extent of the deltas the depositional sink area in the basin and the main features of the drainage systems are shown The extent of the deltas has been interpreted from seismic data and has been used for calculation of the surface area and volume of the various deltas (a) Shahejie Fm Member 4 (b) Shahejie Fm lower part of Member 3 (c) Shahejie Fm middle part of Member 3 (d) Shahejie Fm Members 1 and 2 (e) Dongying Fm Member 3 (f) Dongying Fm Member 2

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the rate of subsidence tectonic uplift and fluctuations of the lake level (Lemons amp Chan 1999) Changes in the lake level of the HD have not been investigated so that we take data on the tectonic‐subsidence rate as a proxy for changes in the accommodation space The total space is expressed in the equation (Table 4)

where AT represents the total accommodation space of the sink area (in km3) TS represents the tectonic subsidence (in m) and SA represents the surface area of the sink (in km2)

AT= TStimesSA∕1000

T A B L E 4 Estimation of the controlling factor parameters of the depositional system The distribution characteristics of the depositional sink in the basin are shown in Figure 7

Formation and membera

Sedimentary facies Seismic sections

DDb

RSSc(km3

Ma)Sink area (km2) AT

d(km3) ASeSource areaf(km2)DSD DSDA

D‐2 Braid delta Figure a 059 066 502 37542 7852 1195 58

Figure b 065

Figure c 074

D‐3 Braid delta Figure a 161 187 926 19823 11593 2051 252

Figure b 192

Figure c 215

Figure d 182

S‐1 + 2 Braid delta Figure a 086 096 356 28015 6463 1403 220

Figure b 094

Figure c 120

Figure d 083

S‐3 (middle unit) Braid delta Figure a 110 119 772 21756 6927 1619 355

Figure b 111

Figure c 129

Figure d 128

S‐3 (lower unit) Fan delta Figure a 307 303 1313 16506 10500 2705 482

Figure b 334

Figure c 332

Figure d 237

S‐4 Fan delta 1 Figure a 384 463g 861 14150 10481 3484 501

Figure b 379

Fan delta 2 Figure a 606

Figure b 498

Fan delta 3 Figure a 479

Figure b 499

Figure c 625

Figure d 553

Fan delta 4 Figure a 377

Figure b 226aD = Dongying Fm S = Shahejie Fm The number indicates the number of the member bDD = depositional dip DSD = depositional dip in a specific seismic section DSDA = average depositional dip of a specific sedimentary unit cRSS = sediment‐supply rate dAT = total accommodation space eAS = accommodation spacesediment supply fSource area = Denudation area within the seismic data coverage The complete erosional area cannot be estimated because of the limited data coverage g463 = the average depositional dip of fan deltas 1 2 3 and 4 Considering that the four fan deltas developed during S‐4 consist of sediment that was derived from the same provenance area and were deposited in the same time‐span the four fan deltas are taken as a whole when estimating the parameters of RSS the sink area AT and AS

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4 | ELEMENTS OF THE S2S SYSTEM

41 | Analysis of the seismic facies and stacking pattern of the main sedimentary faciesA comprehensive analysis of seismic data cores cutting log-gings and well‐logging curves by Liu Xia et al (2015a) in-dicated that the Palaeogene depositional systems of the HD included fan‐deltas braid‐deltas lake margins deep lakes etc The fan‐ and braid‐deltas have been chosen for a detailed seismic study that must reveal their internal texture and their stacking patterns Analysis of the progradational seismic‐re-flection types and of the seismic progradational dip is particu-larly helpful for a better understanding of the hydrodynamic conditions and sedimentary processes that resulted in these depositional systems Because the facies interpretation in this area has been done before and is not the focus of this work we here mainly describe the internal texture and their stack-ing patterns of the main sedimentary facies

The major facies of S‐4 is interpreted as a fan‐delta It is dominated by Seismic Facies 1 which is characterized by discontinuous to continuous low‐ to high‐amplitude and chaotic progradational seismic reflections (Figures S3ndashS6 Table 1) The average dip of the progradational seismic event is about 365deg (Table 3) Three lithofacies are associated with Seismic Facies 1 (Table 1) The coarser lithofacies 1 represents a fan‐delta front whereas the finer lithofacies 2 and 3 are prodelta deposits The overall coarsening‐upward succession facies stacking pattern (Figure 6a) discontinuous and chaotic seismic reflections and relatively steep slope of Seismic Facies 1 suggest a fan‐delta system developed under strong hydrodynamic conditions (Mitchum et al 1977)

The fan‐delta of the lower part of Member 3 of the Shahejie Fm (S‐3 [lower unit]) is dominated by Seismic Facies 2 which is characterized by chaotic progradational to oblique progradational seismic characteristics It has a typical wedge shape and is composed of two seismic‐reflection seg-ments (a) a moderately continuous low‐ to high‐amplitude chaotic seismic‐reflection segment located near boundary fault F2 and (b) a continuous moderate‐ to high‐amplitude and oblique progradational seismic reflection in a basinward direction (Figure S7 Table 1) No obvious upper or lower segments occur in SF 2 and the dip of the progradational seismic event in this segment is also relatively steep viz 305deg (Table 3)

The middle part of Member 3 of the Shahejie Fm (S‐3 [middle unit]) is characterized by a low‐ to moderate‐con-tinuous low‐amplitude and oblique progradational seismic reflection (Seismic Facies 3) and is interpreted as a braid‐delta (Figure S8 Table 1) The progradational seismic events are parallel or sub‐parallel to each other and dip less (aver-age 225deg) than Seismic Facies 1 and 2 (Table 3) Seismic

Facies 3 is associated with four lithofacies (Figure 6b Table 1) in Well T25 The complete succession of the braid‐delta consists of gravely to coarse‐grained sandstone (lithofacies 1) at the base (Figure 6f) massive bedded medium‐ to fine‐grained sandstones (lithofacies 2) and grey mudstones inter-bedded with grey fine sandstones and grey muddy siltstones (lithofacies 3) in the middle (Figures 6g and 6h) and thick dark grey mudstones (lithofacies 4) at the top (Figure 6i)

Member 3 of the Dongying Fm (D‐3) is characterized by Seismic Facies 4 a typically composite seismic progra-dation reflection configuration representing a braid‐delta system (Figure S9 Table 1) Seismic Facies 4 is composed of highly continuous moderate‐ to high‐amplitude and pro-gradational seismic reflections that represent well‐developed deltaic topsets and bottomsets The topset segments of SF 4 are nearly horizontal or dip only gently (Table 3) The foreset segments form thicker lenses with small depositional angles The oblique progradational part of this seismic facies is sim-ilar to that in Seismic Facies 3 and usually developed at the basinward front end of Seismic Facies 3 The lithology of Seismic Facies 4 is dominated by greyish white to white fine‐grained sandstones and siltstones The lithofacies association is characterized by coarsening‐upward sedimentary cycles (Figure 6c Table 1) Convolute bedding and abundant diam-ictites are present on top of the fine sandstones (Figure 6j‐k)

Both braid‐deltas in the Members 1 + 2 of th Shahejie Fm (S‐1 + 2) and Member 2 of the Dongying Fm (D‐2) show moderately continuous moderate‐amplitude and shin-gled‐like progradational seismic reflections (Seismic Facies 5 Figures S10ndashS11 Table 1) It shows a thin prograding seis-mic pattern commonly with parallel upper and lower bound-aries (cf Mitchum et al 1977) The successive internal progradational seismic events overlap each other between the upper and lower segments with a gentle dip of 152degndash193deg (Table 3) The lithofacies are mostly composed of several coarsening‐upward cycles (Figure 6d Table 1) Each cycle is composed of dark grey mudstones and grey to whitish‐grey medium‐ to fine‐grained sandstones Several coarsening‐up-ward lithofacies are mainly developed in D‐2 (Figure 6e Table 1)

42 | Analysis of the tectonic activityThe normal faults F1 and F2 selected to calculate the fault activity dipping to the north and running approximately E‐W are important boundary faults on the south‐western margin of the HD The tectonic‐subsidence rate fault‐growth index and fault‐activity rate were used as proxies to indicate the tectonic intensity (Figure 3 S2 Table 2) S‐4 and S‐3 (lower unit) have the highest subsidence rate (300ndash355 mMa) the highest fault‐growth index (292ndash343 mMa) and the highest fault‐activity rate (10647ndash11869 mMa) among the studied intervals whereas the overlying S‐3 (middle

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unit) and S‐1 + 2 are characterized by a much lower sub-sidence rate and fault‐growth index and fault‐activity rate D‐3 had again a high subsidence rate (190 mMa) and an average fault‐growth index (210 mMa) and fault‐activity rate (9344 mMa) The uppermost studied interval D‐2 had a much lower subsidence rate (60 mMa) growth index (136 mMa) and fault‐activity rate (3451 mMa) than the un-derlying unit Generally the analysis of the subsidence rate average fault‐growth index and fault‐activity rate indicates two phases of alternating strong tectonic activity and tectoni-cally stable conditions

43 | Palaeogeomorphology distribution and dimensions of the main depositional systemsDepositional systems of each depositional phase of the Palaeogene on the south‐western slope of the HD were com-piled through seismic facies identification of 3‐D seismic data and compilation of maps with the current thicknesses of the main target intervals based on the study by Liu Xia et al (2015a) that combined a correction for the depth of burial with an interpretation of the sedimentary facies The basins sink area on the south‐western slope of the HD was estimated on the basis of a palaeogeomorphological reconstruction The distribution of the depositional system is closely related to the evolution of the palaeogeomorphology and therefore we describe both the distribution of the depositional system and the palaeogeomorphology here

The palaeogeography of S‐4 is characterized by the larg-est extent of the uplifted areas of all studied intervals The depositional area is small and scattered (Figure 7a Table 4) Faults F1 and F2 mark the boundaries between erosional and depositional regions The elevated footwalls of the faults were erosional areas and located adjacent to the hanging walls whereas the hanging walls were low‐lying depositional areas The sedimentary facies analysis indicates a fan‐delta developed here (Figure 7a) Calculations indicate that the sedimentary dip of the four fan‐deltas was uncommonly high (about 463deg) The extent and thickness of the fan‐deltas di-minished towards the basin margin (Tables 34)

The tectonically‐induced morphology of S‐3 (lower unit) shows a similar pattern to that of the underlying S‐4 The depositional and erosional areas were also controlled by the active faults F1 and F2The HD deepened from west to east with the deepest area located just along the fault margin The depositional centre was located north of the hanging wall of F2 and became infilled by a fan‐delta (Figure 7b) The aver-age sedimentary dip of the fan‐delta is 303deg The extent of the fan‐delta was larger than that of S‐4 (Table 34)

During deposition of S‐3 (middle unit) the uplifted source area shifted southwards and the depression expanded A major depositional sink was located north of the hanging wall of F2 (Figure 7c Table 4) Elevation differences existed

between the footwalls and the hanging walls of F1 and F2 although the topography was obviously gentler during this time‐span A braided fluvial area developed at the footwalls of the faults whereas a braid‐delta developed mainly on the hanging wall of F2 and the northern depositional centre (Figure 7c) The braid‐delta had a fairly large extent and an average depositional dip of 119deg (Tables 34)

During S‐1 + 2 the elevated erosional area shifted farther southwards and the entire south‐western area had a low to-pography An alluvial plain developed south of the footwalls of the faults whereas a braid‐delta developed at the hanging walls and in the depression with a very gentle slope of 096deg (Table 4 Figure 7d) The depositional system was dominated by a fairly thin delta body and a braid‐delta with a much larger extent (Table 3)

During the deposition of D‐3 the topography of the foot-wall areas and of the area south of the provenance area was similar to that during the underlying S‐1 + 2 The slope was steep (187deg) in the hanging walls of the boundary faults however and the depositional area increased to 198 km2 which provided an excellent condition for the deposition of a large braid‐delta (Figure 7e Table 4) This braid‐delta had a NE‐SW orientation and covered an area of 142 km2 its average thickness is some 200 m which results in the largest delta volume in the Palaeogene on the south‐western slope of the HD (Table 3)

The palaeogeomorphological reconstruction of D‐2 shows a gentler topography in the entire south‐western HD with a sink area of 375 km2 (Table 4) The main body of the braid‐delta was dominated by imbricated progradational seis-mic reflections and developed in the hanging walls of F1 and F2 whereas an alluvial‐plain facies probably developed in the footwall areas of the faults and to the south‐west of the uplifted area (Figure 7f) Although the extent of the delta reached its maximum the thickness of the delta was limited due to the gentle topography resulting in a small delta vol-ume (Table 3)

5 | RELATIONSHIPS BETWEEN THE VARIOUS ELEMENTS OF THE S2S SYSTEM

Quantitative relationships between the various elements of the S2S system have been established through the above‐mentioned calculations A strong positive correlation is clearly present between the rate of tectonic subsidence the average fault activity and the average growth index of the boundary faults F1 and F2 (Figure 8ab) The rate of tectonic subsidence can therefore be used in the following as the pri-mary proxy to represent the intensity of the tectonic activity whereas the rate of fault activity and the growth index are used as secondary proxies

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The tectonic activity and the sediment‐supply rate show a positive relationship (Figures 8c 9a 10a) whereas the tec-tonic activity and the sink area of the basin show a negative relationship (Figures 8d 9b 10b) In contrast the tectonic activity has a positive relationship with the total accommo-dation space (Figures 8e 9c 10c Table 4) There is also a positive relationship between the average sedimentary dip of the fan‐ and braid‐deltas on the one hand and the tectonic activity on the other hand (Figures 8f 9d 10d)

The intensity of the tectonic activity correlates negatively with the extent of the sediment area but positively with the sediment volume (Figures 8g‐h 9e‐f 10e‐f) The different responses of the sediment area and the volume to the tectonic activity are caused by variations in the thicknesses of the sed-imentary units (Table 3)

There is also a positive relationship between the average seismic progradation dip of the fan‐ and braid‐deltas and the tectonic activity (Figures 8i 9g 10g) strong tectonic activ-ity usually formed deltas that are characterized by a chaotic progradational or oblique progradational seismic reflection such as SF 1 and 2 in S‐3 (lower unit) and S‐4 (Figures S3ndashS7) The minimum tectonic activity during Members S‐1 + 2 and D‐2 are reflected by dominantly shingled progradational seismic facies in the delta interior (Figures S10ndashS11)

In addition we find that the sediment area sediment vol-ume and average seismic progradation dip of the fan‐ and braid‐deltas correlate positively with the sediment‐supply rate (Figure 11a b and c) but negatively with the basin sink area (Figure 11d e and f) Both the sediment volume and the average seismic progradation dip of the fan‐ and braid‐deltas

F I G U R E 8 (a‐b) Relationships between the tectonic‐subsidence rate and tectonics (c‐i) Relationships between tectonic activity and sedimentary source‐to‐sink parameters Input data regarding the tectonic activity are from Table 2 those regarding the source‐to‐sink parameters data are from Tables 3 and 4 Regression‐line equations and coefficients of determination (R2) are shown for all diagrams

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show a positive relationship with the total accommodation space (Figure 11hi) However no obvious relationship ap-pears to be present between the sediment area and the total accommodation space (G) Both the sediment area and the average seismic progradation dip of the fan‐ and braid‐deltas correlate well with the average sedimentary dip of the fan‐ and braid‐deltas (Figure 11km) A poor correlation is found between the sediment volume and the average sedimentary dip of the fan‐ and braid‐deltas

6 | DISCUSSION

61 | Analysis of the influence of tectonic activity on the source area accommodation space geomorphology and sediment supplyA high relief and large drainage area usually can generate a large sediment supply (Leeder Harris amp Kirkby 1998 Syvitski amp Milliman 2007) Although the erosional area for the fan and delta system cannot be estimated because of the

limited data coverage the exposed area within the study area can be calculated The calculations show a generally decreas-ing trend of the source area from S‐4 (501 km2) to D‐2 (58 km2 Figure7 Table 4) The calculated exposed area cannot fully represent the true source area however but the evolu-tionary trend of the source area can be used as a proxy to indi-cate the relative influence on the change in sediment volume This trend is consistent with the decrease in sediment volume from S‐4 (2126 km3) to D‐2 (175 km3 Table 2) The relief is difficult to reconstruct in this case but variations in the fault‐activity rate (here taken as the tectonic‐subsidence rate) can create local elevation differences and can therefore be used as proxies for the trends in the relief development The relief shows an overall decreasing trend from S‐4 to D‐2 except for D‐3 this correlates well with the sediment volume (Figure 8h) Although the drainage area of D‐3 was smaller than that of D‐2 because of the high tectonic‐subsidence rate (result-ing in a high relief) D‐3 is thicker and shows a larger sedi-ment volume than the overlying D‐2 (Table 3) D‐3 is thinner than S‐4 + 3 but the larger source area resulted in a larger

F I G U R E 9 General relationships between the average fault‐growth index of F1 and F2 (AFGIF1‐F2) and sedimentary source‐to‐sink parameters The average fault‐growth index of F1 and F2 (AFGIF1‐F2) data in this figure are from Table 2 The source‐to‐sink parameters data are from Table 4 Regression‐line equations and the coefficients of determination are shown in each diagram

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sediment volume and supply rate (Table 3 Figure8ch) Therefore both the fault‐induced relief and the drainage area affected the sediment‐supply rate and the sediment volume in the sink

The changes in accommodation space during the vari-ous phases of the Palaeogene in the south‐western HD are clear from the estimated tectonic subsiding rate (Table 2) The correlations between the intensity of the tectonic activ-ity and the extent of the depositional sink area (Figures 8d 9b 10b) between the intensity of the tectonic activity and the total accommodation space and between the intensity of the tectonic activity and the morphology in the sink area (Figures 8e‐f 9c‐d 10c‐d) clearly show that strong tectonic activity resulted in a larger accommodation capacity of the sink

In particular the main subsiding area tended to form steeper slopes However the extent of the main subsiding sink area diminished (Figure 8d) with increasing tectonic activity which was possibly due to the relatively small sub-siding centre in the tectonically active basins It can thus be deduced that tectonic activity not only controlled the sedi-ment supply and the variation in accommodation space but

also determined the changes in the topography of the sedi-mentary basins and the extent of the main depositional areas in the tectonically active basins

62 | Analysis of the influence of tectonic activity on the size and internal stacking pattern of the delta depositional systemThe above data and considerations indicate that the tectonic activity was closely related to the sediment supply accom-modation space and morphology of the sink area which are possibly the most important factors affecting the extent and stacking pattern of the sedimentary facies (cf Cope et al 2010 DeCelles Kapp Ding amp Gehrels 2007 Leeder 2011 Olsen 1997 Simon et al 2017)

Statistical analysis indicates that the sediment‐supply rate has a strong positive correlation with the volume of the depositional system a moderate correlation with the seismic progradational dip in the depositional system and a poor cor-relation with the size of the depositional area (Figure 11a‐c) A larger sink area corresponded to a larger fanbraid‐delta a gentler seismic progradational angle and a reduced volume

F I G U R E 1 0 General relationships between average fault activity rate of F1 and F2 (RFAA‐F1‐F2) and sedimentary source‐to‐sink parameters The average fault activity rate of F1 and F2 (RFAA‐F1‐F2) data in this figure are from Table 2 The source‐to‐sink parameters data are from Table 4 Regression line equations and the coefficients of determination are shown in each diagram

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of the fan or braid‐delta which was possibly related to a re-duced sedimentary dip and thinner sediments (Figure 11d‐f) The total accommodation space in the basin correlates well

with the volume of the depositional system to some degree with the seismic progradational dip and poorly with the ex-tent of the depositional system area (Figure 11g‐i) These

FIGURE 11 Relationships between various parameters involved in the source‐to‐sink system (a‐c) Relationships between sediment supply and characteristics of the depositional system (extent volume and DPSA of the sediments) (d‐f) Relationships between the sink area of the basin and characteristics of the depositional system (g‐i) Relationships between the total accommodation space (AT) and the characteristics of the depositional system (j) Relationship between the accommodation‐spacesediment‐supply ratio (AS) and the DPSA of the sediments (k‐m) Relationships between the sedimentary dip and the characteristics of the depositional system The data regarding sediment supply basin sink area total accommodation space accommodation‐spacesediment‐supply ratio and sedimentary dips are from Table 4 The extent volume and DPSA of the sedimentary facies are from Table 3 Note the seemingly obvious polynomial (quadratic) relationship between the sedimentary dip and the sediment volume (L) The trend line in (L) suggests the following relationships between sediment volume and sedimentary slope in a rift or tectonically active basin (1) a very steep sedimentary slope is unfavourable for sediment accumulation (2) an appropriate sedimentary slope is favourable for preservation of depositional systems eg when the sedimentary slope in (L) is about 25degndash32deg the sediment volume reaches its largest value (3) a very gentle sedimentary slope will lead to a decrease of the sediment volume possibly due to weakening of the drainage system and thinner sediments

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relationships are clear evidence that the size of the sink area controlled the extent of the depositional system during the rifting of the lacustrine basin and that the rate of sediment supply and the accommodation space had a significant in-fluence on the total sedimentary volume as well as on the internal stacking pattern of the depositional system

We here use the ratio of the tectonic‐subsidence rate and the sediment‐supply rate as a proxy to indicate the ratio be-tween accommodation space and sediment‐supply rate (AS) (Table 4) AS has a strong influence on the internal stacking pattern of the depositional systems in the lacustrine rift basin (Figure 11j) This might be because the basin was small and because abundant and rapid material was supplied due

to intense tectonic activity (cf Catuneanu et al 2009 Liro 1993) and a favourable local climate (eg Bohacs Carroll Neal amp Mankiewicz 2000 Perlmutter amp Matthews 1989) The sediment supply still had a significant influence on the main subsidence area of the lacustrine basins and deposi-tional systems

In addition the basin slope significantly influenced the extent of the depositional system (Figure 11k) and had a polynomial relationship with its volume (Figure 11l) This relationship indicates that more intense tectonic activity and a steeper depositional slope were not favourable for sediment accumulation over a large extent in the lacustrine basin On the contrary these sediments were usually transported to a

F I G U R E 1 2 Tectonic differential activities and resulting patterns of the source‐to‐sink system on the south‐western slope of the HD during the Palaeogene (a) Development during phases of intense tectonics (Member 4 to the lower part of Member 3 of the Shahejie Fm) (b) Development during phases of somewhat less tectonic activity (middle part of Member 3 of the Shahejie Fm and Member 3 of the Dongying Fm) (c) Development during phases of weak tectonic activity (Members 1 and 2 of the Shahejie Fm and Member 2 of the Dongying Fm) The intensity of tectonic activity in the lacustrine rift basin had a significant influence on the development and extent of each unit of the source‐to‐sink system as well as on the type and dimensions of the depositional systems The present study indicates that probably sublacustrine fans developed (see for example Figure S4b) during phases with relatively strong tectonic activity This is not really clear from the seismic‐reflection data but possibly due to the small sizes of these sublacustrine fans Moreover lithofacies and core data are not available for the south‐western part of the study area The present contribution therefore focuses on the fan‐deltas and braid‐deltas regarding the sedimentary facies analysis the sublacustrine fans that probably developed in the deep or semi‐deep lake are presented just as a likely feature

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relatively small sink area with a fairly large accommodation space Finally stronger tectonic activity resulted in steeper depositional slopes (Figure 8f) which further controlled the hydrodynamic conditions and differential discharge when the sediments were deposited The strong correlation between the depositional slope and the deltas dip (Figure 11m) suggests that the differences in topography due to tectonics must be considered as one of the most critical factors that controlled the internal stacking pattern of the delta deposits

63 | Significance of the present study for other source‐to‐sink systems of lacustrine rift basins

631 | Summary of the source‐to‐sink systems in the HDIn lacustrine rift basins the tectonic setting is probably the main factor that determines the development of the S2S sys-tem but differential tectonic activities lead to variations in the basic characteristics of the S2S system Tectonic activity was most intense during S‐3 (lower unit) and during S‐4 and caused both a strong uplift of the source area and the devel-opment of depressions in the basin that formed a sink (Figure 12a) Strong tectonic activity in the S2S system during these time‐spans led to a high sediment‐supply rate steeper slopes a larger accommodation space and deposition of several fan‐deltas that are characterized by a fairly steep seismic progra-dational angle

The tectonic activity decreased during S‐3 (middle unit) and during D‐3 The S2S system that was present during this time‐span mainly concerned a rising area that shifted south-wards developing an alluvial plain between the erosional area and the sink area thus increasing the distance from source to sink (Figure 12b) Simultaneously the sediment‐supply rate and the accommodation space also changed and braid‐deltas could thus develop with larger volumes and gentler seismic progradational dips

Tectonic activity was clearly less intense during S‐1 + 2 and D‐2 The rising area had shifted further southwards cre-ating a wider alluvial plain connecting the source area to the sink in the HD (Figure 12c) At this stage stable tectonic activity led to relatively less sediment supply a gentle slope less accommodation space and the development of several braid‐deltas with a fairly gentle seismic progradational angle

632 | Wider implications and limitationsSoslashmme et al (2009) proposed that the elements of S2S sys-tems are genetically related and that quantitative correla-tions exist among these elements Other studies also suggest that the size of the drainage basin is correlated to the size of the fan developing on the basin floor (eg Blum et al

2017 Snedden et al 2018) and to the size of the river chan-nel (eg Milliken et al 2018) Helland‐Hansen Soslashmme Martinsen Lunt and Thurmond (2016) suggest a simplified subdivision of S2S systems into three main categories (a) Steep‐Short‐Deep (steep onshore and offshore gradients short distance between source and sink and deep offshore waters) (b) Wide‐Deep (low‐gradient shelf‐catchment area and deep offshore waters) and (c) Wide‐Shallow (relatively shallow offshore waters and a wide low‐gradient catchment area) systems

The present study indicates that the alluvial plain roughly corresponds to the alluvial‐shelf unit in marine basins al-though with a much smaller width and extent in the lacustrine rift basins than would have been the case on a continental shelf Faults F1 and F2 along the slope belt correspond to the slope of classical S2S systems whereas the shore‐shallow‐deep lake area can be compared with the basin floor (Soslashmme et al 2009) S‐4 and S‐3 (lower unit) can be roughly clas-sified as Steep‐Short‐Deep systems whereas the overlying S‐1 + 2and D‐2 can be classified as the Wide‐Shallow sys-tems that Helland‐Hansen et al (2016) defined During the deposition of S‐4 and S‐3 (lower unit) the strong tectonic activity caused a high relief of the source area a narrow allu-vial plain and a relatively deep lake The subsequently wan-ing tectonic activity resulted in a lower relief of the source area a wider alluvial plain and a shallower lake Although the absolute values of these elements in lacustrine basins are much smaller than those of marine basins the ratio between these elements in both settings is comparable Typically in a lacustrine basin a transformation from a Steep‐Short‐Deep system (S‐4 and S‐3 (lower unit)) to a Wide‐Shallow system (S‐1 + 2ampD‐2) occurs within a few million years Although the basin geomorphology has experienced signif-icant changes from S‐4 to D‐2 the quantitative relationships between tectonic activity sediment‐supply rate accommoda-tion space and sedimentary dip of the delta systems did not change significantly (eg Figures 8 and 11) The analytical approaches applied and quantitative relationship established here can help analyse other lacustrine basins worldwide and may even act as a reference for the analysis of marine basins

Our study focuses mainly on the influences of tectonic activity on the elements of the depositional sink Other pa-rameters (eg climate and lithology) were not considered in detail Studies on modern and ancient systems suggest that the climate and lithology also have a great influence on the sediment supply and distribution in the basin (eg Carroll Chetel amp Smith 2006 Hovius amp Leeder 1998 Syvitski amp Milliman 2007 Zhang et al 2018) For exam-ple climate variations between glacials and inter‐glacials have resulted in largely different sediment‐supply rates and in significant differences in the sizes of the Quaternary sub-marine fans in the north‐western Gulf of Mexico (Blum amp Hattier‐Womack 2009) We acknowledge the importance

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of climate and lithology for S2S systems and we are con-vinced that these elements can significantly affect the S2S systems in other cases(eg modern systems and systems influenced by glacialinterglacial alternations) These fac-tors were not really relevant for the present study however because no significant differences in lithology were present in the source areas and because we focus on the changes at a million‐year scale which implies that the tectonic ac-tivity has a first‐order control on the development of S2S elements in the investigated rift basin

7 | CONCLUSIONS

We have calculated the tectonic‐subsidence history the growth index and the activity rate of the main boundary faults (F1 and F2) and various S2S parameters of six Palaeogene rock units on the south‐western slope of the HD Based on the values found for these parameters quantitative corre-lation were established for the tectonic activity and other S2Sparameters in the basinal sink This leads to the follow-ing conclusions

1 The positive correlation between the intensity of fault activity and the tectonic‐subsidence rate is a strong indication for a distinct control by the tectonic activity of the syn‐depositional rifting of the tectonically active basin

2 The tectonic activity was quantitatively related to the sediment supply accommodation space and morphology of the sink area The relationship between tectonic activ-ity and depositional systems is reflected by changes in critical factors such as sediment supply accommodation space and dip of the sink area These critical factors were probably the most important factors that led to changes in the size and internal stacking pattern of the sedimentary facies

3 Differential tectonic activity led to changes in the char-acteristics of the S2S system on the south‐western slope of the HD The strongest tectonic activity which oc-curred during S‐3 (lower unit) and during S‐4 led to the largest provenance area adjacent to the sink area to a high sediment‐supply rate to steeper slopes to a larger accommodation space and controlled the development of several fan‐deltas Diminished tectonic activity dur-ing S‐3 (middle unit) and during D‐3 led to a decrease in uplift an increased width of the alluvial plain an in-creased transport distance a decrease in the sediment‐supply rate and accommodation space and resulted in the development of braid‐deltas with a large volume During S‐1 + 2 and D‐2 stable tectonic activity led to a lower sediment‐supply rate a gentle depositional slope and a smaller accommodation space resulting in the

development of several braid‐deltas with gentler seis-mic progradational angles

4 The analytical approaches applied and the quantitative re-lationships established here can help analyse other lacus-trine basins worldwide and may even act as a reference for the study of marine basins

ACKNOWLEDGEMENTS

We thank Dr Sarah Boulton and Dr Chenlin Gong as well as the Associate Editor of Basin Research Dr Craig Magee for their constructive comments on the manuscript This study was funded by the National Science and Technology Major Project (Exploration Technologies for Offshore Hidden OilGas) (project no 2016ZX05024‐003‐003) the National Natural Science Foundations of China (project no 41676050) and the Fundamental Research Funds for the Central Universities (2652014037)

REFERENCES

Allen P A (2008a) From landscapes into geological history Nature 451 274ndash276 https doiorg101038natur e06586

Allen P A (2008b) Time scales of tectonic landscapes and their sed-iment routing systems In Landscape evolution Denudation cli-mate and tectonics over different time and space scales (Ed by Gallagher K Jones S J amp Wainwright J) Geological Society London Special Publications 296 7ndash28

Allen P A Armitage J J Carter A Duller R A Michael N A Sinclair H D hellip Whittaker A C (2013) The Qs problem Sediment volumetric balance of proximal foreland basin systems Sedimentology 60 102ndash130

Amorosi A Maselli V amp Trincardi F (2016) Onshore to offshore anatomy of a late Quaternary source‐to‐sink system (Po Plain‐Adriatic Sea Italy) Earth‐Science Reviews 153 212ndash237 https doiorg101016jearsc irev201510010

Anderson J B Wallace D J Simms A R Rodriguez A B Weight R W R amp Taha Z P (2016) Recycling sediments between source and sink during a eustatic cycle Systems of late Quaternary northwestern Gulf of Mexico Basin Earth‐Science Reviews 153 111ndash138 https doiorg101016jearsc irev201510014

Anthony E J amp Julian M (1999) Source‐to‐sink sediment trans-fers environmental engineering and hazard mitigation in the steep Var River catchment French Riviera southeastern France Geomorphology 31 337ndash354 https doiorg101016S0169-555X(99)00088-4

Athy L F (1930) Density porosity and compaction of sedimentary rocks AAPG Bulletin 14 1ndash24

Bhattacharya J P Copeland P Lawton T F amp Holbrook J (2016) Estimation of source area river palaeo‐discharge palaeoslope and sediment budgets of linked deep‐time depositional systems and im-plications for hydrocarbon potential Earth‐Science Reviews 153 77ndash110

Blum M D amp Hattier‐Womack J (2009) Climate change sea‐level change and fluvial sediment supply to deepwater depositional

| 597EAGE

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Max

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Ave

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DPA

DPS

A

D‐2

Bra

id d

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Figu

re a

176

0075

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246

175

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50

157

156

Figu

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174

0080

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Figu

re c

218

0080

00

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Bra

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Figu

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285

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400

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295

0099

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Figu

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296

0078

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Figu

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284

0091

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S‐1

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Figu

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178

0089

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136

7512

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164

416

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172

177

Figu

re b

185

0095

00

176

Figu

re c

236

0010

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193

Figu

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209

0011

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166

S‐3

(mid

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Bra

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Figu

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274

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7587

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196

619

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213

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Figu

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279

0083

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Figu

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292

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Figu

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374

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89

235

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52

301

305

Figu

re b

432

5522

071

325

Figu

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473

0920

583

312

Figu

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450

8325

500

283

S‐4

Fan

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1Fi

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a30

700

483

929

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107

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423

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Figu

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Fan

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500

704

832

900

856

282

421

Figu

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379

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100

118

7841

100

186

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Figu

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468

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718

309

Figu

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527

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127

387

Figu

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486

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844

297

Fan

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4Fi

gure

a42

800

151

2042

700

179

57

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04

Figu

re b

512

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287

289

a D =

Don

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icat

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= a

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ave

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where DPSA is the average seismic progradational dip of a sediment (in degrees) and n is the number of seismic sections

Detailed estimated results of the depositional dip and the seismic progradational dip of the delta are shown in Tables 3 and 4

333 | Provenance conditions and estimation of the sediment supplySystematic investigation by TBCNOOC of the regional uplift and provenance in the geological past has indicated that the main provenance areas around the HD existed alreadybefore the deposition of Member 3 of the Shahejie Fm (Zhou et al 2010) They include the Bonan Laibei and Kendong Highs (Figure 1b‐c Figure S1a‐b) However starting with the depo-sition of Members 1ndash2 of the Shahejie Fm (S‐1 + 2) (3789ndash3328 Ma) until the accumulation of the Dongying Formation (3328ndash2338 Ma) the Bonan and Laibei Highs subsided to below lake level and consequently stopped providing sedi-ment to the depression (Liu Xia et al 2015a) Only the Kendong High which remained a high for a long time re-mained a provenance area for the south‐western part of the

HD during this time‐span (Figure S1a) The Kendong High has therefore been selected as the site where the relationship between tectonics and depositional systems within the same provenance system could be studied best The distribution area of the Kendong High as the provenance area at different moments has been determined on the basis of numerous seis-mic interpretations through seismic terminations (eg onlap) and the absence of specific sediment units due to faulting

The sediment‐supply rate can be obtained by calculation of the volumes of the deltas and the duration of their forma-tion (cf Allen et al 2013 Lemons amp Chan 1999 Lemons Milligan amp Chan 1996) Although the stratigraphic ages are well‐known for each unit (Figure 2) there is no high‐resolu-tion age control for the top and base of each delta system The absolute age of the pertinent stratigraphic unit (Figure 2) is therefore used to represent the formation time of the individual deltas in the unit The thus calculated sediment‐supply rate rep-resents in our opinion the trend of the supply rate from bottom to top sufficiently well

334 | Estimation of the extent and accommodation space of the sink areaDetermination of the boundaries of the sink area is based on reconstructions of the morphology during the successive dep-ositional phases The extent of the sink area was estimated using the same calculations as for the area of the depositional system

DPSA

=

(

nsum

i=1

DPAi

)

∕n

F I G U R E 6 Vertical successions and representative examples of the various lithofacies (a) A fan‐delta in Well W18 (b‐e) Braid‐deltas in Well W25 (f) Grey to greyish white sandy conglomerate (deposits in braided channels) (g) Grey medium‐ to fine‐grained massive sandstone (mouth‐bar deposits) (h) Grey fine sandstone (distal sand bars) (i) Grey muddy siltstone with parallel bedding (prodelta) (j) Greyish white fine sandstone with convolute bedding (mouth bars) (k) Greyish white fine sandstone with boulders (mouth bars) Wireline logs show the spontaneous‐potential (SP) and gamma‐ray (GR) changes with depth Depth in metres For location of the cores see Figure 6bd

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Differences in base level and the original sedimentary sur-face define the accommodation space (Jervey 1988 Muto amp Steel 2000 Neal amp Abreu 2009 Wheeler 1964) The

accommodation space in the depositional area can be deter-mined on the basis of the thickness of the preserved sediments (Muto amp Steel 2000) This space is obviously controlled by

F I G U R E 7 Schematic morphology during the successive depositional phases The extent of the deltas the depositional sink area in the basin and the main features of the drainage systems are shown The extent of the deltas has been interpreted from seismic data and has been used for calculation of the surface area and volume of the various deltas (a) Shahejie Fm Member 4 (b) Shahejie Fm lower part of Member 3 (c) Shahejie Fm middle part of Member 3 (d) Shahejie Fm Members 1 and 2 (e) Dongying Fm Member 3 (f) Dongying Fm Member 2

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the rate of subsidence tectonic uplift and fluctuations of the lake level (Lemons amp Chan 1999) Changes in the lake level of the HD have not been investigated so that we take data on the tectonic‐subsidence rate as a proxy for changes in the accommodation space The total space is expressed in the equation (Table 4)

where AT represents the total accommodation space of the sink area (in km3) TS represents the tectonic subsidence (in m) and SA represents the surface area of the sink (in km2)

AT= TStimesSA∕1000

T A B L E 4 Estimation of the controlling factor parameters of the depositional system The distribution characteristics of the depositional sink in the basin are shown in Figure 7

Formation and membera

Sedimentary facies Seismic sections

DDb

RSSc(km3

Ma)Sink area (km2) AT

d(km3) ASeSource areaf(km2)DSD DSDA

D‐2 Braid delta Figure a 059 066 502 37542 7852 1195 58

Figure b 065

Figure c 074

D‐3 Braid delta Figure a 161 187 926 19823 11593 2051 252

Figure b 192

Figure c 215

Figure d 182

S‐1 + 2 Braid delta Figure a 086 096 356 28015 6463 1403 220

Figure b 094

Figure c 120

Figure d 083

S‐3 (middle unit) Braid delta Figure a 110 119 772 21756 6927 1619 355

Figure b 111

Figure c 129

Figure d 128

S‐3 (lower unit) Fan delta Figure a 307 303 1313 16506 10500 2705 482

Figure b 334

Figure c 332

Figure d 237

S‐4 Fan delta 1 Figure a 384 463g 861 14150 10481 3484 501

Figure b 379

Fan delta 2 Figure a 606

Figure b 498

Fan delta 3 Figure a 479

Figure b 499

Figure c 625

Figure d 553

Fan delta 4 Figure a 377

Figure b 226aD = Dongying Fm S = Shahejie Fm The number indicates the number of the member bDD = depositional dip DSD = depositional dip in a specific seismic section DSDA = average depositional dip of a specific sedimentary unit cRSS = sediment‐supply rate dAT = total accommodation space eAS = accommodation spacesediment supply fSource area = Denudation area within the seismic data coverage The complete erosional area cannot be estimated because of the limited data coverage g463 = the average depositional dip of fan deltas 1 2 3 and 4 Considering that the four fan deltas developed during S‐4 consist of sediment that was derived from the same provenance area and were deposited in the same time‐span the four fan deltas are taken as a whole when estimating the parameters of RSS the sink area AT and AS

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4 | ELEMENTS OF THE S2S SYSTEM

41 | Analysis of the seismic facies and stacking pattern of the main sedimentary faciesA comprehensive analysis of seismic data cores cutting log-gings and well‐logging curves by Liu Xia et al (2015a) in-dicated that the Palaeogene depositional systems of the HD included fan‐deltas braid‐deltas lake margins deep lakes etc The fan‐ and braid‐deltas have been chosen for a detailed seismic study that must reveal their internal texture and their stacking patterns Analysis of the progradational seismic‐re-flection types and of the seismic progradational dip is particu-larly helpful for a better understanding of the hydrodynamic conditions and sedimentary processes that resulted in these depositional systems Because the facies interpretation in this area has been done before and is not the focus of this work we here mainly describe the internal texture and their stack-ing patterns of the main sedimentary facies

The major facies of S‐4 is interpreted as a fan‐delta It is dominated by Seismic Facies 1 which is characterized by discontinuous to continuous low‐ to high‐amplitude and chaotic progradational seismic reflections (Figures S3ndashS6 Table 1) The average dip of the progradational seismic event is about 365deg (Table 3) Three lithofacies are associated with Seismic Facies 1 (Table 1) The coarser lithofacies 1 represents a fan‐delta front whereas the finer lithofacies 2 and 3 are prodelta deposits The overall coarsening‐upward succession facies stacking pattern (Figure 6a) discontinuous and chaotic seismic reflections and relatively steep slope of Seismic Facies 1 suggest a fan‐delta system developed under strong hydrodynamic conditions (Mitchum et al 1977)

The fan‐delta of the lower part of Member 3 of the Shahejie Fm (S‐3 [lower unit]) is dominated by Seismic Facies 2 which is characterized by chaotic progradational to oblique progradational seismic characteristics It has a typical wedge shape and is composed of two seismic‐reflection seg-ments (a) a moderately continuous low‐ to high‐amplitude chaotic seismic‐reflection segment located near boundary fault F2 and (b) a continuous moderate‐ to high‐amplitude and oblique progradational seismic reflection in a basinward direction (Figure S7 Table 1) No obvious upper or lower segments occur in SF 2 and the dip of the progradational seismic event in this segment is also relatively steep viz 305deg (Table 3)

The middle part of Member 3 of the Shahejie Fm (S‐3 [middle unit]) is characterized by a low‐ to moderate‐con-tinuous low‐amplitude and oblique progradational seismic reflection (Seismic Facies 3) and is interpreted as a braid‐delta (Figure S8 Table 1) The progradational seismic events are parallel or sub‐parallel to each other and dip less (aver-age 225deg) than Seismic Facies 1 and 2 (Table 3) Seismic

Facies 3 is associated with four lithofacies (Figure 6b Table 1) in Well T25 The complete succession of the braid‐delta consists of gravely to coarse‐grained sandstone (lithofacies 1) at the base (Figure 6f) massive bedded medium‐ to fine‐grained sandstones (lithofacies 2) and grey mudstones inter-bedded with grey fine sandstones and grey muddy siltstones (lithofacies 3) in the middle (Figures 6g and 6h) and thick dark grey mudstones (lithofacies 4) at the top (Figure 6i)

Member 3 of the Dongying Fm (D‐3) is characterized by Seismic Facies 4 a typically composite seismic progra-dation reflection configuration representing a braid‐delta system (Figure S9 Table 1) Seismic Facies 4 is composed of highly continuous moderate‐ to high‐amplitude and pro-gradational seismic reflections that represent well‐developed deltaic topsets and bottomsets The topset segments of SF 4 are nearly horizontal or dip only gently (Table 3) The foreset segments form thicker lenses with small depositional angles The oblique progradational part of this seismic facies is sim-ilar to that in Seismic Facies 3 and usually developed at the basinward front end of Seismic Facies 3 The lithology of Seismic Facies 4 is dominated by greyish white to white fine‐grained sandstones and siltstones The lithofacies association is characterized by coarsening‐upward sedimentary cycles (Figure 6c Table 1) Convolute bedding and abundant diam-ictites are present on top of the fine sandstones (Figure 6j‐k)

Both braid‐deltas in the Members 1 + 2 of th Shahejie Fm (S‐1 + 2) and Member 2 of the Dongying Fm (D‐2) show moderately continuous moderate‐amplitude and shin-gled‐like progradational seismic reflections (Seismic Facies 5 Figures S10ndashS11 Table 1) It shows a thin prograding seis-mic pattern commonly with parallel upper and lower bound-aries (cf Mitchum et al 1977) The successive internal progradational seismic events overlap each other between the upper and lower segments with a gentle dip of 152degndash193deg (Table 3) The lithofacies are mostly composed of several coarsening‐upward cycles (Figure 6d Table 1) Each cycle is composed of dark grey mudstones and grey to whitish‐grey medium‐ to fine‐grained sandstones Several coarsening‐up-ward lithofacies are mainly developed in D‐2 (Figure 6e Table 1)

42 | Analysis of the tectonic activityThe normal faults F1 and F2 selected to calculate the fault activity dipping to the north and running approximately E‐W are important boundary faults on the south‐western margin of the HD The tectonic‐subsidence rate fault‐growth index and fault‐activity rate were used as proxies to indicate the tectonic intensity (Figure 3 S2 Table 2) S‐4 and S‐3 (lower unit) have the highest subsidence rate (300ndash355 mMa) the highest fault‐growth index (292ndash343 mMa) and the highest fault‐activity rate (10647ndash11869 mMa) among the studied intervals whereas the overlying S‐3 (middle

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unit) and S‐1 + 2 are characterized by a much lower sub-sidence rate and fault‐growth index and fault‐activity rate D‐3 had again a high subsidence rate (190 mMa) and an average fault‐growth index (210 mMa) and fault‐activity rate (9344 mMa) The uppermost studied interval D‐2 had a much lower subsidence rate (60 mMa) growth index (136 mMa) and fault‐activity rate (3451 mMa) than the un-derlying unit Generally the analysis of the subsidence rate average fault‐growth index and fault‐activity rate indicates two phases of alternating strong tectonic activity and tectoni-cally stable conditions

43 | Palaeogeomorphology distribution and dimensions of the main depositional systemsDepositional systems of each depositional phase of the Palaeogene on the south‐western slope of the HD were com-piled through seismic facies identification of 3‐D seismic data and compilation of maps with the current thicknesses of the main target intervals based on the study by Liu Xia et al (2015a) that combined a correction for the depth of burial with an interpretation of the sedimentary facies The basins sink area on the south‐western slope of the HD was estimated on the basis of a palaeogeomorphological reconstruction The distribution of the depositional system is closely related to the evolution of the palaeogeomorphology and therefore we describe both the distribution of the depositional system and the palaeogeomorphology here

The palaeogeography of S‐4 is characterized by the larg-est extent of the uplifted areas of all studied intervals The depositional area is small and scattered (Figure 7a Table 4) Faults F1 and F2 mark the boundaries between erosional and depositional regions The elevated footwalls of the faults were erosional areas and located adjacent to the hanging walls whereas the hanging walls were low‐lying depositional areas The sedimentary facies analysis indicates a fan‐delta developed here (Figure 7a) Calculations indicate that the sedimentary dip of the four fan‐deltas was uncommonly high (about 463deg) The extent and thickness of the fan‐deltas di-minished towards the basin margin (Tables 34)

The tectonically‐induced morphology of S‐3 (lower unit) shows a similar pattern to that of the underlying S‐4 The depositional and erosional areas were also controlled by the active faults F1 and F2The HD deepened from west to east with the deepest area located just along the fault margin The depositional centre was located north of the hanging wall of F2 and became infilled by a fan‐delta (Figure 7b) The aver-age sedimentary dip of the fan‐delta is 303deg The extent of the fan‐delta was larger than that of S‐4 (Table 34)

During deposition of S‐3 (middle unit) the uplifted source area shifted southwards and the depression expanded A major depositional sink was located north of the hanging wall of F2 (Figure 7c Table 4) Elevation differences existed

between the footwalls and the hanging walls of F1 and F2 although the topography was obviously gentler during this time‐span A braided fluvial area developed at the footwalls of the faults whereas a braid‐delta developed mainly on the hanging wall of F2 and the northern depositional centre (Figure 7c) The braid‐delta had a fairly large extent and an average depositional dip of 119deg (Tables 34)

During S‐1 + 2 the elevated erosional area shifted farther southwards and the entire south‐western area had a low to-pography An alluvial plain developed south of the footwalls of the faults whereas a braid‐delta developed at the hanging walls and in the depression with a very gentle slope of 096deg (Table 4 Figure 7d) The depositional system was dominated by a fairly thin delta body and a braid‐delta with a much larger extent (Table 3)

During the deposition of D‐3 the topography of the foot-wall areas and of the area south of the provenance area was similar to that during the underlying S‐1 + 2 The slope was steep (187deg) in the hanging walls of the boundary faults however and the depositional area increased to 198 km2 which provided an excellent condition for the deposition of a large braid‐delta (Figure 7e Table 4) This braid‐delta had a NE‐SW orientation and covered an area of 142 km2 its average thickness is some 200 m which results in the largest delta volume in the Palaeogene on the south‐western slope of the HD (Table 3)

The palaeogeomorphological reconstruction of D‐2 shows a gentler topography in the entire south‐western HD with a sink area of 375 km2 (Table 4) The main body of the braid‐delta was dominated by imbricated progradational seis-mic reflections and developed in the hanging walls of F1 and F2 whereas an alluvial‐plain facies probably developed in the footwall areas of the faults and to the south‐west of the uplifted area (Figure 7f) Although the extent of the delta reached its maximum the thickness of the delta was limited due to the gentle topography resulting in a small delta vol-ume (Table 3)

5 | RELATIONSHIPS BETWEEN THE VARIOUS ELEMENTS OF THE S2S SYSTEM

Quantitative relationships between the various elements of the S2S system have been established through the above‐mentioned calculations A strong positive correlation is clearly present between the rate of tectonic subsidence the average fault activity and the average growth index of the boundary faults F1 and F2 (Figure 8ab) The rate of tectonic subsidence can therefore be used in the following as the pri-mary proxy to represent the intensity of the tectonic activity whereas the rate of fault activity and the growth index are used as secondary proxies

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The tectonic activity and the sediment‐supply rate show a positive relationship (Figures 8c 9a 10a) whereas the tec-tonic activity and the sink area of the basin show a negative relationship (Figures 8d 9b 10b) In contrast the tectonic activity has a positive relationship with the total accommo-dation space (Figures 8e 9c 10c Table 4) There is also a positive relationship between the average sedimentary dip of the fan‐ and braid‐deltas on the one hand and the tectonic activity on the other hand (Figures 8f 9d 10d)

The intensity of the tectonic activity correlates negatively with the extent of the sediment area but positively with the sediment volume (Figures 8g‐h 9e‐f 10e‐f) The different responses of the sediment area and the volume to the tectonic activity are caused by variations in the thicknesses of the sed-imentary units (Table 3)

There is also a positive relationship between the average seismic progradation dip of the fan‐ and braid‐deltas and the tectonic activity (Figures 8i 9g 10g) strong tectonic activ-ity usually formed deltas that are characterized by a chaotic progradational or oblique progradational seismic reflection such as SF 1 and 2 in S‐3 (lower unit) and S‐4 (Figures S3ndashS7) The minimum tectonic activity during Members S‐1 + 2 and D‐2 are reflected by dominantly shingled progradational seismic facies in the delta interior (Figures S10ndashS11)

In addition we find that the sediment area sediment vol-ume and average seismic progradation dip of the fan‐ and braid‐deltas correlate positively with the sediment‐supply rate (Figure 11a b and c) but negatively with the basin sink area (Figure 11d e and f) Both the sediment volume and the average seismic progradation dip of the fan‐ and braid‐deltas

F I G U R E 8 (a‐b) Relationships between the tectonic‐subsidence rate and tectonics (c‐i) Relationships between tectonic activity and sedimentary source‐to‐sink parameters Input data regarding the tectonic activity are from Table 2 those regarding the source‐to‐sink parameters data are from Tables 3 and 4 Regression‐line equations and coefficients of determination (R2) are shown for all diagrams

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show a positive relationship with the total accommodation space (Figure 11hi) However no obvious relationship ap-pears to be present between the sediment area and the total accommodation space (G) Both the sediment area and the average seismic progradation dip of the fan‐ and braid‐deltas correlate well with the average sedimentary dip of the fan‐ and braid‐deltas (Figure 11km) A poor correlation is found between the sediment volume and the average sedimentary dip of the fan‐ and braid‐deltas

6 | DISCUSSION

61 | Analysis of the influence of tectonic activity on the source area accommodation space geomorphology and sediment supplyA high relief and large drainage area usually can generate a large sediment supply (Leeder Harris amp Kirkby 1998 Syvitski amp Milliman 2007) Although the erosional area for the fan and delta system cannot be estimated because of the

limited data coverage the exposed area within the study area can be calculated The calculations show a generally decreas-ing trend of the source area from S‐4 (501 km2) to D‐2 (58 km2 Figure7 Table 4) The calculated exposed area cannot fully represent the true source area however but the evolu-tionary trend of the source area can be used as a proxy to indi-cate the relative influence on the change in sediment volume This trend is consistent with the decrease in sediment volume from S‐4 (2126 km3) to D‐2 (175 km3 Table 2) The relief is difficult to reconstruct in this case but variations in the fault‐activity rate (here taken as the tectonic‐subsidence rate) can create local elevation differences and can therefore be used as proxies for the trends in the relief development The relief shows an overall decreasing trend from S‐4 to D‐2 except for D‐3 this correlates well with the sediment volume (Figure 8h) Although the drainage area of D‐3 was smaller than that of D‐2 because of the high tectonic‐subsidence rate (result-ing in a high relief) D‐3 is thicker and shows a larger sedi-ment volume than the overlying D‐2 (Table 3) D‐3 is thinner than S‐4 + 3 but the larger source area resulted in a larger

F I G U R E 9 General relationships between the average fault‐growth index of F1 and F2 (AFGIF1‐F2) and sedimentary source‐to‐sink parameters The average fault‐growth index of F1 and F2 (AFGIF1‐F2) data in this figure are from Table 2 The source‐to‐sink parameters data are from Table 4 Regression‐line equations and the coefficients of determination are shown in each diagram

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sediment volume and supply rate (Table 3 Figure8ch) Therefore both the fault‐induced relief and the drainage area affected the sediment‐supply rate and the sediment volume in the sink

The changes in accommodation space during the vari-ous phases of the Palaeogene in the south‐western HD are clear from the estimated tectonic subsiding rate (Table 2) The correlations between the intensity of the tectonic activ-ity and the extent of the depositional sink area (Figures 8d 9b 10b) between the intensity of the tectonic activity and the total accommodation space and between the intensity of the tectonic activity and the morphology in the sink area (Figures 8e‐f 9c‐d 10c‐d) clearly show that strong tectonic activity resulted in a larger accommodation capacity of the sink

In particular the main subsiding area tended to form steeper slopes However the extent of the main subsiding sink area diminished (Figure 8d) with increasing tectonic activity which was possibly due to the relatively small sub-siding centre in the tectonically active basins It can thus be deduced that tectonic activity not only controlled the sedi-ment supply and the variation in accommodation space but

also determined the changes in the topography of the sedi-mentary basins and the extent of the main depositional areas in the tectonically active basins

62 | Analysis of the influence of tectonic activity on the size and internal stacking pattern of the delta depositional systemThe above data and considerations indicate that the tectonic activity was closely related to the sediment supply accom-modation space and morphology of the sink area which are possibly the most important factors affecting the extent and stacking pattern of the sedimentary facies (cf Cope et al 2010 DeCelles Kapp Ding amp Gehrels 2007 Leeder 2011 Olsen 1997 Simon et al 2017)

Statistical analysis indicates that the sediment‐supply rate has a strong positive correlation with the volume of the depositional system a moderate correlation with the seismic progradational dip in the depositional system and a poor cor-relation with the size of the depositional area (Figure 11a‐c) A larger sink area corresponded to a larger fanbraid‐delta a gentler seismic progradational angle and a reduced volume

F I G U R E 1 0 General relationships between average fault activity rate of F1 and F2 (RFAA‐F1‐F2) and sedimentary source‐to‐sink parameters The average fault activity rate of F1 and F2 (RFAA‐F1‐F2) data in this figure are from Table 2 The source‐to‐sink parameters data are from Table 4 Regression line equations and the coefficients of determination are shown in each diagram

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of the fan or braid‐delta which was possibly related to a re-duced sedimentary dip and thinner sediments (Figure 11d‐f) The total accommodation space in the basin correlates well

with the volume of the depositional system to some degree with the seismic progradational dip and poorly with the ex-tent of the depositional system area (Figure 11g‐i) These

FIGURE 11 Relationships between various parameters involved in the source‐to‐sink system (a‐c) Relationships between sediment supply and characteristics of the depositional system (extent volume and DPSA of the sediments) (d‐f) Relationships between the sink area of the basin and characteristics of the depositional system (g‐i) Relationships between the total accommodation space (AT) and the characteristics of the depositional system (j) Relationship between the accommodation‐spacesediment‐supply ratio (AS) and the DPSA of the sediments (k‐m) Relationships between the sedimentary dip and the characteristics of the depositional system The data regarding sediment supply basin sink area total accommodation space accommodation‐spacesediment‐supply ratio and sedimentary dips are from Table 4 The extent volume and DPSA of the sedimentary facies are from Table 3 Note the seemingly obvious polynomial (quadratic) relationship between the sedimentary dip and the sediment volume (L) The trend line in (L) suggests the following relationships between sediment volume and sedimentary slope in a rift or tectonically active basin (1) a very steep sedimentary slope is unfavourable for sediment accumulation (2) an appropriate sedimentary slope is favourable for preservation of depositional systems eg when the sedimentary slope in (L) is about 25degndash32deg the sediment volume reaches its largest value (3) a very gentle sedimentary slope will lead to a decrease of the sediment volume possibly due to weakening of the drainage system and thinner sediments

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relationships are clear evidence that the size of the sink area controlled the extent of the depositional system during the rifting of the lacustrine basin and that the rate of sediment supply and the accommodation space had a significant in-fluence on the total sedimentary volume as well as on the internal stacking pattern of the depositional system

We here use the ratio of the tectonic‐subsidence rate and the sediment‐supply rate as a proxy to indicate the ratio be-tween accommodation space and sediment‐supply rate (AS) (Table 4) AS has a strong influence on the internal stacking pattern of the depositional systems in the lacustrine rift basin (Figure 11j) This might be because the basin was small and because abundant and rapid material was supplied due

to intense tectonic activity (cf Catuneanu et al 2009 Liro 1993) and a favourable local climate (eg Bohacs Carroll Neal amp Mankiewicz 2000 Perlmutter amp Matthews 1989) The sediment supply still had a significant influence on the main subsidence area of the lacustrine basins and deposi-tional systems

In addition the basin slope significantly influenced the extent of the depositional system (Figure 11k) and had a polynomial relationship with its volume (Figure 11l) This relationship indicates that more intense tectonic activity and a steeper depositional slope were not favourable for sediment accumulation over a large extent in the lacustrine basin On the contrary these sediments were usually transported to a

F I G U R E 1 2 Tectonic differential activities and resulting patterns of the source‐to‐sink system on the south‐western slope of the HD during the Palaeogene (a) Development during phases of intense tectonics (Member 4 to the lower part of Member 3 of the Shahejie Fm) (b) Development during phases of somewhat less tectonic activity (middle part of Member 3 of the Shahejie Fm and Member 3 of the Dongying Fm) (c) Development during phases of weak tectonic activity (Members 1 and 2 of the Shahejie Fm and Member 2 of the Dongying Fm) The intensity of tectonic activity in the lacustrine rift basin had a significant influence on the development and extent of each unit of the source‐to‐sink system as well as on the type and dimensions of the depositional systems The present study indicates that probably sublacustrine fans developed (see for example Figure S4b) during phases with relatively strong tectonic activity This is not really clear from the seismic‐reflection data but possibly due to the small sizes of these sublacustrine fans Moreover lithofacies and core data are not available for the south‐western part of the study area The present contribution therefore focuses on the fan‐deltas and braid‐deltas regarding the sedimentary facies analysis the sublacustrine fans that probably developed in the deep or semi‐deep lake are presented just as a likely feature

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relatively small sink area with a fairly large accommodation space Finally stronger tectonic activity resulted in steeper depositional slopes (Figure 8f) which further controlled the hydrodynamic conditions and differential discharge when the sediments were deposited The strong correlation between the depositional slope and the deltas dip (Figure 11m) suggests that the differences in topography due to tectonics must be considered as one of the most critical factors that controlled the internal stacking pattern of the delta deposits

63 | Significance of the present study for other source‐to‐sink systems of lacustrine rift basins

631 | Summary of the source‐to‐sink systems in the HDIn lacustrine rift basins the tectonic setting is probably the main factor that determines the development of the S2S sys-tem but differential tectonic activities lead to variations in the basic characteristics of the S2S system Tectonic activity was most intense during S‐3 (lower unit) and during S‐4 and caused both a strong uplift of the source area and the devel-opment of depressions in the basin that formed a sink (Figure 12a) Strong tectonic activity in the S2S system during these time‐spans led to a high sediment‐supply rate steeper slopes a larger accommodation space and deposition of several fan‐deltas that are characterized by a fairly steep seismic progra-dational angle

The tectonic activity decreased during S‐3 (middle unit) and during D‐3 The S2S system that was present during this time‐span mainly concerned a rising area that shifted south-wards developing an alluvial plain between the erosional area and the sink area thus increasing the distance from source to sink (Figure 12b) Simultaneously the sediment‐supply rate and the accommodation space also changed and braid‐deltas could thus develop with larger volumes and gentler seismic progradational dips

Tectonic activity was clearly less intense during S‐1 + 2 and D‐2 The rising area had shifted further southwards cre-ating a wider alluvial plain connecting the source area to the sink in the HD (Figure 12c) At this stage stable tectonic activity led to relatively less sediment supply a gentle slope less accommodation space and the development of several braid‐deltas with a fairly gentle seismic progradational angle

632 | Wider implications and limitationsSoslashmme et al (2009) proposed that the elements of S2S sys-tems are genetically related and that quantitative correla-tions exist among these elements Other studies also suggest that the size of the drainage basin is correlated to the size of the fan developing on the basin floor (eg Blum et al

2017 Snedden et al 2018) and to the size of the river chan-nel (eg Milliken et al 2018) Helland‐Hansen Soslashmme Martinsen Lunt and Thurmond (2016) suggest a simplified subdivision of S2S systems into three main categories (a) Steep‐Short‐Deep (steep onshore and offshore gradients short distance between source and sink and deep offshore waters) (b) Wide‐Deep (low‐gradient shelf‐catchment area and deep offshore waters) and (c) Wide‐Shallow (relatively shallow offshore waters and a wide low‐gradient catchment area) systems

The present study indicates that the alluvial plain roughly corresponds to the alluvial‐shelf unit in marine basins al-though with a much smaller width and extent in the lacustrine rift basins than would have been the case on a continental shelf Faults F1 and F2 along the slope belt correspond to the slope of classical S2S systems whereas the shore‐shallow‐deep lake area can be compared with the basin floor (Soslashmme et al 2009) S‐4 and S‐3 (lower unit) can be roughly clas-sified as Steep‐Short‐Deep systems whereas the overlying S‐1 + 2and D‐2 can be classified as the Wide‐Shallow sys-tems that Helland‐Hansen et al (2016) defined During the deposition of S‐4 and S‐3 (lower unit) the strong tectonic activity caused a high relief of the source area a narrow allu-vial plain and a relatively deep lake The subsequently wan-ing tectonic activity resulted in a lower relief of the source area a wider alluvial plain and a shallower lake Although the absolute values of these elements in lacustrine basins are much smaller than those of marine basins the ratio between these elements in both settings is comparable Typically in a lacustrine basin a transformation from a Steep‐Short‐Deep system (S‐4 and S‐3 (lower unit)) to a Wide‐Shallow system (S‐1 + 2ampD‐2) occurs within a few million years Although the basin geomorphology has experienced signif-icant changes from S‐4 to D‐2 the quantitative relationships between tectonic activity sediment‐supply rate accommoda-tion space and sedimentary dip of the delta systems did not change significantly (eg Figures 8 and 11) The analytical approaches applied and quantitative relationship established here can help analyse other lacustrine basins worldwide and may even act as a reference for the analysis of marine basins

Our study focuses mainly on the influences of tectonic activity on the elements of the depositional sink Other pa-rameters (eg climate and lithology) were not considered in detail Studies on modern and ancient systems suggest that the climate and lithology also have a great influence on the sediment supply and distribution in the basin (eg Carroll Chetel amp Smith 2006 Hovius amp Leeder 1998 Syvitski amp Milliman 2007 Zhang et al 2018) For exam-ple climate variations between glacials and inter‐glacials have resulted in largely different sediment‐supply rates and in significant differences in the sizes of the Quaternary sub-marine fans in the north‐western Gulf of Mexico (Blum amp Hattier‐Womack 2009) We acknowledge the importance

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of climate and lithology for S2S systems and we are con-vinced that these elements can significantly affect the S2S systems in other cases(eg modern systems and systems influenced by glacialinterglacial alternations) These fac-tors were not really relevant for the present study however because no significant differences in lithology were present in the source areas and because we focus on the changes at a million‐year scale which implies that the tectonic ac-tivity has a first‐order control on the development of S2S elements in the investigated rift basin

7 | CONCLUSIONS

We have calculated the tectonic‐subsidence history the growth index and the activity rate of the main boundary faults (F1 and F2) and various S2S parameters of six Palaeogene rock units on the south‐western slope of the HD Based on the values found for these parameters quantitative corre-lation were established for the tectonic activity and other S2Sparameters in the basinal sink This leads to the follow-ing conclusions

1 The positive correlation between the intensity of fault activity and the tectonic‐subsidence rate is a strong indication for a distinct control by the tectonic activity of the syn‐depositional rifting of the tectonically active basin

2 The tectonic activity was quantitatively related to the sediment supply accommodation space and morphology of the sink area The relationship between tectonic activ-ity and depositional systems is reflected by changes in critical factors such as sediment supply accommodation space and dip of the sink area These critical factors were probably the most important factors that led to changes in the size and internal stacking pattern of the sedimentary facies

3 Differential tectonic activity led to changes in the char-acteristics of the S2S system on the south‐western slope of the HD The strongest tectonic activity which oc-curred during S‐3 (lower unit) and during S‐4 led to the largest provenance area adjacent to the sink area to a high sediment‐supply rate to steeper slopes to a larger accommodation space and controlled the development of several fan‐deltas Diminished tectonic activity dur-ing S‐3 (middle unit) and during D‐3 led to a decrease in uplift an increased width of the alluvial plain an in-creased transport distance a decrease in the sediment‐supply rate and accommodation space and resulted in the development of braid‐deltas with a large volume During S‐1 + 2 and D‐2 stable tectonic activity led to a lower sediment‐supply rate a gentle depositional slope and a smaller accommodation space resulting in the

development of several braid‐deltas with gentler seis-mic progradational angles

4 The analytical approaches applied and the quantitative re-lationships established here can help analyse other lacus-trine basins worldwide and may even act as a reference for the study of marine basins

ACKNOWLEDGEMENTS

We thank Dr Sarah Boulton and Dr Chenlin Gong as well as the Associate Editor of Basin Research Dr Craig Magee for their constructive comments on the manuscript This study was funded by the National Science and Technology Major Project (Exploration Technologies for Offshore Hidden OilGas) (project no 2016ZX05024‐003‐003) the National Natural Science Foundations of China (project no 41676050) and the Fundamental Research Funds for the Central Universities (2652014037)

REFERENCES

Allen P A (2008a) From landscapes into geological history Nature 451 274ndash276 https doiorg101038natur e06586

Allen P A (2008b) Time scales of tectonic landscapes and their sed-iment routing systems In Landscape evolution Denudation cli-mate and tectonics over different time and space scales (Ed by Gallagher K Jones S J amp Wainwright J) Geological Society London Special Publications 296 7ndash28

Allen P A Armitage J J Carter A Duller R A Michael N A Sinclair H D hellip Whittaker A C (2013) The Qs problem Sediment volumetric balance of proximal foreland basin systems Sedimentology 60 102ndash130

Amorosi A Maselli V amp Trincardi F (2016) Onshore to offshore anatomy of a late Quaternary source‐to‐sink system (Po Plain‐Adriatic Sea Italy) Earth‐Science Reviews 153 212ndash237 https doiorg101016jearsc irev201510010

Anderson J B Wallace D J Simms A R Rodriguez A B Weight R W R amp Taha Z P (2016) Recycling sediments between source and sink during a eustatic cycle Systems of late Quaternary northwestern Gulf of Mexico Basin Earth‐Science Reviews 153 111ndash138 https doiorg101016jearsc irev201510014

Anthony E J amp Julian M (1999) Source‐to‐sink sediment trans-fers environmental engineering and hazard mitigation in the steep Var River catchment French Riviera southeastern France Geomorphology 31 337ndash354 https doiorg101016S0169-555X(99)00088-4

Athy L F (1930) Density porosity and compaction of sedimentary rocks AAPG Bulletin 14 1ndash24

Bhattacharya J P Copeland P Lawton T F amp Holbrook J (2016) Estimation of source area river palaeo‐discharge palaeoslope and sediment budgets of linked deep‐time depositional systems and im-plications for hydrocarbon potential Earth‐Science Reviews 153 77ndash110

Blum M D amp Hattier‐Womack J (2009) Climate change sea‐level change and fluvial sediment supply to deepwater depositional

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where DPSA is the average seismic progradational dip of a sediment (in degrees) and n is the number of seismic sections

Detailed estimated results of the depositional dip and the seismic progradational dip of the delta are shown in Tables 3 and 4

333 | Provenance conditions and estimation of the sediment supplySystematic investigation by TBCNOOC of the regional uplift and provenance in the geological past has indicated that the main provenance areas around the HD existed alreadybefore the deposition of Member 3 of the Shahejie Fm (Zhou et al 2010) They include the Bonan Laibei and Kendong Highs (Figure 1b‐c Figure S1a‐b) However starting with the depo-sition of Members 1ndash2 of the Shahejie Fm (S‐1 + 2) (3789ndash3328 Ma) until the accumulation of the Dongying Formation (3328ndash2338 Ma) the Bonan and Laibei Highs subsided to below lake level and consequently stopped providing sedi-ment to the depression (Liu Xia et al 2015a) Only the Kendong High which remained a high for a long time re-mained a provenance area for the south‐western part of the

HD during this time‐span (Figure S1a) The Kendong High has therefore been selected as the site where the relationship between tectonics and depositional systems within the same provenance system could be studied best The distribution area of the Kendong High as the provenance area at different moments has been determined on the basis of numerous seis-mic interpretations through seismic terminations (eg onlap) and the absence of specific sediment units due to faulting

The sediment‐supply rate can be obtained by calculation of the volumes of the deltas and the duration of their forma-tion (cf Allen et al 2013 Lemons amp Chan 1999 Lemons Milligan amp Chan 1996) Although the stratigraphic ages are well‐known for each unit (Figure 2) there is no high‐resolu-tion age control for the top and base of each delta system The absolute age of the pertinent stratigraphic unit (Figure 2) is therefore used to represent the formation time of the individual deltas in the unit The thus calculated sediment‐supply rate rep-resents in our opinion the trend of the supply rate from bottom to top sufficiently well

334 | Estimation of the extent and accommodation space of the sink areaDetermination of the boundaries of the sink area is based on reconstructions of the morphology during the successive dep-ositional phases The extent of the sink area was estimated using the same calculations as for the area of the depositional system

DPSA

=

(

nsum

i=1

DPAi

)

∕n

F I G U R E 6 Vertical successions and representative examples of the various lithofacies (a) A fan‐delta in Well W18 (b‐e) Braid‐deltas in Well W25 (f) Grey to greyish white sandy conglomerate (deposits in braided channels) (g) Grey medium‐ to fine‐grained massive sandstone (mouth‐bar deposits) (h) Grey fine sandstone (distal sand bars) (i) Grey muddy siltstone with parallel bedding (prodelta) (j) Greyish white fine sandstone with convolute bedding (mouth bars) (k) Greyish white fine sandstone with boulders (mouth bars) Wireline logs show the spontaneous‐potential (SP) and gamma‐ray (GR) changes with depth Depth in metres For location of the cores see Figure 6bd

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Differences in base level and the original sedimentary sur-face define the accommodation space (Jervey 1988 Muto amp Steel 2000 Neal amp Abreu 2009 Wheeler 1964) The

accommodation space in the depositional area can be deter-mined on the basis of the thickness of the preserved sediments (Muto amp Steel 2000) This space is obviously controlled by

F I G U R E 7 Schematic morphology during the successive depositional phases The extent of the deltas the depositional sink area in the basin and the main features of the drainage systems are shown The extent of the deltas has been interpreted from seismic data and has been used for calculation of the surface area and volume of the various deltas (a) Shahejie Fm Member 4 (b) Shahejie Fm lower part of Member 3 (c) Shahejie Fm middle part of Member 3 (d) Shahejie Fm Members 1 and 2 (e) Dongying Fm Member 3 (f) Dongying Fm Member 2

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the rate of subsidence tectonic uplift and fluctuations of the lake level (Lemons amp Chan 1999) Changes in the lake level of the HD have not been investigated so that we take data on the tectonic‐subsidence rate as a proxy for changes in the accommodation space The total space is expressed in the equation (Table 4)

where AT represents the total accommodation space of the sink area (in km3) TS represents the tectonic subsidence (in m) and SA represents the surface area of the sink (in km2)

AT= TStimesSA∕1000

T A B L E 4 Estimation of the controlling factor parameters of the depositional system The distribution characteristics of the depositional sink in the basin are shown in Figure 7

Formation and membera

Sedimentary facies Seismic sections

DDb

RSSc(km3

Ma)Sink area (km2) AT

d(km3) ASeSource areaf(km2)DSD DSDA

D‐2 Braid delta Figure a 059 066 502 37542 7852 1195 58

Figure b 065

Figure c 074

D‐3 Braid delta Figure a 161 187 926 19823 11593 2051 252

Figure b 192

Figure c 215

Figure d 182

S‐1 + 2 Braid delta Figure a 086 096 356 28015 6463 1403 220

Figure b 094

Figure c 120

Figure d 083

S‐3 (middle unit) Braid delta Figure a 110 119 772 21756 6927 1619 355

Figure b 111

Figure c 129

Figure d 128

S‐3 (lower unit) Fan delta Figure a 307 303 1313 16506 10500 2705 482

Figure b 334

Figure c 332

Figure d 237

S‐4 Fan delta 1 Figure a 384 463g 861 14150 10481 3484 501

Figure b 379

Fan delta 2 Figure a 606

Figure b 498

Fan delta 3 Figure a 479

Figure b 499

Figure c 625

Figure d 553

Fan delta 4 Figure a 377

Figure b 226aD = Dongying Fm S = Shahejie Fm The number indicates the number of the member bDD = depositional dip DSD = depositional dip in a specific seismic section DSDA = average depositional dip of a specific sedimentary unit cRSS = sediment‐supply rate dAT = total accommodation space eAS = accommodation spacesediment supply fSource area = Denudation area within the seismic data coverage The complete erosional area cannot be estimated because of the limited data coverage g463 = the average depositional dip of fan deltas 1 2 3 and 4 Considering that the four fan deltas developed during S‐4 consist of sediment that was derived from the same provenance area and were deposited in the same time‐span the four fan deltas are taken as a whole when estimating the parameters of RSS the sink area AT and AS

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4 | ELEMENTS OF THE S2S SYSTEM

41 | Analysis of the seismic facies and stacking pattern of the main sedimentary faciesA comprehensive analysis of seismic data cores cutting log-gings and well‐logging curves by Liu Xia et al (2015a) in-dicated that the Palaeogene depositional systems of the HD included fan‐deltas braid‐deltas lake margins deep lakes etc The fan‐ and braid‐deltas have been chosen for a detailed seismic study that must reveal their internal texture and their stacking patterns Analysis of the progradational seismic‐re-flection types and of the seismic progradational dip is particu-larly helpful for a better understanding of the hydrodynamic conditions and sedimentary processes that resulted in these depositional systems Because the facies interpretation in this area has been done before and is not the focus of this work we here mainly describe the internal texture and their stack-ing patterns of the main sedimentary facies

The major facies of S‐4 is interpreted as a fan‐delta It is dominated by Seismic Facies 1 which is characterized by discontinuous to continuous low‐ to high‐amplitude and chaotic progradational seismic reflections (Figures S3ndashS6 Table 1) The average dip of the progradational seismic event is about 365deg (Table 3) Three lithofacies are associated with Seismic Facies 1 (Table 1) The coarser lithofacies 1 represents a fan‐delta front whereas the finer lithofacies 2 and 3 are prodelta deposits The overall coarsening‐upward succession facies stacking pattern (Figure 6a) discontinuous and chaotic seismic reflections and relatively steep slope of Seismic Facies 1 suggest a fan‐delta system developed under strong hydrodynamic conditions (Mitchum et al 1977)

The fan‐delta of the lower part of Member 3 of the Shahejie Fm (S‐3 [lower unit]) is dominated by Seismic Facies 2 which is characterized by chaotic progradational to oblique progradational seismic characteristics It has a typical wedge shape and is composed of two seismic‐reflection seg-ments (a) a moderately continuous low‐ to high‐amplitude chaotic seismic‐reflection segment located near boundary fault F2 and (b) a continuous moderate‐ to high‐amplitude and oblique progradational seismic reflection in a basinward direction (Figure S7 Table 1) No obvious upper or lower segments occur in SF 2 and the dip of the progradational seismic event in this segment is also relatively steep viz 305deg (Table 3)

The middle part of Member 3 of the Shahejie Fm (S‐3 [middle unit]) is characterized by a low‐ to moderate‐con-tinuous low‐amplitude and oblique progradational seismic reflection (Seismic Facies 3) and is interpreted as a braid‐delta (Figure S8 Table 1) The progradational seismic events are parallel or sub‐parallel to each other and dip less (aver-age 225deg) than Seismic Facies 1 and 2 (Table 3) Seismic

Facies 3 is associated with four lithofacies (Figure 6b Table 1) in Well T25 The complete succession of the braid‐delta consists of gravely to coarse‐grained sandstone (lithofacies 1) at the base (Figure 6f) massive bedded medium‐ to fine‐grained sandstones (lithofacies 2) and grey mudstones inter-bedded with grey fine sandstones and grey muddy siltstones (lithofacies 3) in the middle (Figures 6g and 6h) and thick dark grey mudstones (lithofacies 4) at the top (Figure 6i)

Member 3 of the Dongying Fm (D‐3) is characterized by Seismic Facies 4 a typically composite seismic progra-dation reflection configuration representing a braid‐delta system (Figure S9 Table 1) Seismic Facies 4 is composed of highly continuous moderate‐ to high‐amplitude and pro-gradational seismic reflections that represent well‐developed deltaic topsets and bottomsets The topset segments of SF 4 are nearly horizontal or dip only gently (Table 3) The foreset segments form thicker lenses with small depositional angles The oblique progradational part of this seismic facies is sim-ilar to that in Seismic Facies 3 and usually developed at the basinward front end of Seismic Facies 3 The lithology of Seismic Facies 4 is dominated by greyish white to white fine‐grained sandstones and siltstones The lithofacies association is characterized by coarsening‐upward sedimentary cycles (Figure 6c Table 1) Convolute bedding and abundant diam-ictites are present on top of the fine sandstones (Figure 6j‐k)

Both braid‐deltas in the Members 1 + 2 of th Shahejie Fm (S‐1 + 2) and Member 2 of the Dongying Fm (D‐2) show moderately continuous moderate‐amplitude and shin-gled‐like progradational seismic reflections (Seismic Facies 5 Figures S10ndashS11 Table 1) It shows a thin prograding seis-mic pattern commonly with parallel upper and lower bound-aries (cf Mitchum et al 1977) The successive internal progradational seismic events overlap each other between the upper and lower segments with a gentle dip of 152degndash193deg (Table 3) The lithofacies are mostly composed of several coarsening‐upward cycles (Figure 6d Table 1) Each cycle is composed of dark grey mudstones and grey to whitish‐grey medium‐ to fine‐grained sandstones Several coarsening‐up-ward lithofacies are mainly developed in D‐2 (Figure 6e Table 1)

42 | Analysis of the tectonic activityThe normal faults F1 and F2 selected to calculate the fault activity dipping to the north and running approximately E‐W are important boundary faults on the south‐western margin of the HD The tectonic‐subsidence rate fault‐growth index and fault‐activity rate were used as proxies to indicate the tectonic intensity (Figure 3 S2 Table 2) S‐4 and S‐3 (lower unit) have the highest subsidence rate (300ndash355 mMa) the highest fault‐growth index (292ndash343 mMa) and the highest fault‐activity rate (10647ndash11869 mMa) among the studied intervals whereas the overlying S‐3 (middle

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unit) and S‐1 + 2 are characterized by a much lower sub-sidence rate and fault‐growth index and fault‐activity rate D‐3 had again a high subsidence rate (190 mMa) and an average fault‐growth index (210 mMa) and fault‐activity rate (9344 mMa) The uppermost studied interval D‐2 had a much lower subsidence rate (60 mMa) growth index (136 mMa) and fault‐activity rate (3451 mMa) than the un-derlying unit Generally the analysis of the subsidence rate average fault‐growth index and fault‐activity rate indicates two phases of alternating strong tectonic activity and tectoni-cally stable conditions

43 | Palaeogeomorphology distribution and dimensions of the main depositional systemsDepositional systems of each depositional phase of the Palaeogene on the south‐western slope of the HD were com-piled through seismic facies identification of 3‐D seismic data and compilation of maps with the current thicknesses of the main target intervals based on the study by Liu Xia et al (2015a) that combined a correction for the depth of burial with an interpretation of the sedimentary facies The basins sink area on the south‐western slope of the HD was estimated on the basis of a palaeogeomorphological reconstruction The distribution of the depositional system is closely related to the evolution of the palaeogeomorphology and therefore we describe both the distribution of the depositional system and the palaeogeomorphology here

The palaeogeography of S‐4 is characterized by the larg-est extent of the uplifted areas of all studied intervals The depositional area is small and scattered (Figure 7a Table 4) Faults F1 and F2 mark the boundaries between erosional and depositional regions The elevated footwalls of the faults were erosional areas and located adjacent to the hanging walls whereas the hanging walls were low‐lying depositional areas The sedimentary facies analysis indicates a fan‐delta developed here (Figure 7a) Calculations indicate that the sedimentary dip of the four fan‐deltas was uncommonly high (about 463deg) The extent and thickness of the fan‐deltas di-minished towards the basin margin (Tables 34)

The tectonically‐induced morphology of S‐3 (lower unit) shows a similar pattern to that of the underlying S‐4 The depositional and erosional areas were also controlled by the active faults F1 and F2The HD deepened from west to east with the deepest area located just along the fault margin The depositional centre was located north of the hanging wall of F2 and became infilled by a fan‐delta (Figure 7b) The aver-age sedimentary dip of the fan‐delta is 303deg The extent of the fan‐delta was larger than that of S‐4 (Table 34)

During deposition of S‐3 (middle unit) the uplifted source area shifted southwards and the depression expanded A major depositional sink was located north of the hanging wall of F2 (Figure 7c Table 4) Elevation differences existed

between the footwalls and the hanging walls of F1 and F2 although the topography was obviously gentler during this time‐span A braided fluvial area developed at the footwalls of the faults whereas a braid‐delta developed mainly on the hanging wall of F2 and the northern depositional centre (Figure 7c) The braid‐delta had a fairly large extent and an average depositional dip of 119deg (Tables 34)

During S‐1 + 2 the elevated erosional area shifted farther southwards and the entire south‐western area had a low to-pography An alluvial plain developed south of the footwalls of the faults whereas a braid‐delta developed at the hanging walls and in the depression with a very gentle slope of 096deg (Table 4 Figure 7d) The depositional system was dominated by a fairly thin delta body and a braid‐delta with a much larger extent (Table 3)

During the deposition of D‐3 the topography of the foot-wall areas and of the area south of the provenance area was similar to that during the underlying S‐1 + 2 The slope was steep (187deg) in the hanging walls of the boundary faults however and the depositional area increased to 198 km2 which provided an excellent condition for the deposition of a large braid‐delta (Figure 7e Table 4) This braid‐delta had a NE‐SW orientation and covered an area of 142 km2 its average thickness is some 200 m which results in the largest delta volume in the Palaeogene on the south‐western slope of the HD (Table 3)

The palaeogeomorphological reconstruction of D‐2 shows a gentler topography in the entire south‐western HD with a sink area of 375 km2 (Table 4) The main body of the braid‐delta was dominated by imbricated progradational seis-mic reflections and developed in the hanging walls of F1 and F2 whereas an alluvial‐plain facies probably developed in the footwall areas of the faults and to the south‐west of the uplifted area (Figure 7f) Although the extent of the delta reached its maximum the thickness of the delta was limited due to the gentle topography resulting in a small delta vol-ume (Table 3)

5 | RELATIONSHIPS BETWEEN THE VARIOUS ELEMENTS OF THE S2S SYSTEM

Quantitative relationships between the various elements of the S2S system have been established through the above‐mentioned calculations A strong positive correlation is clearly present between the rate of tectonic subsidence the average fault activity and the average growth index of the boundary faults F1 and F2 (Figure 8ab) The rate of tectonic subsidence can therefore be used in the following as the pri-mary proxy to represent the intensity of the tectonic activity whereas the rate of fault activity and the growth index are used as secondary proxies

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The tectonic activity and the sediment‐supply rate show a positive relationship (Figures 8c 9a 10a) whereas the tec-tonic activity and the sink area of the basin show a negative relationship (Figures 8d 9b 10b) In contrast the tectonic activity has a positive relationship with the total accommo-dation space (Figures 8e 9c 10c Table 4) There is also a positive relationship between the average sedimentary dip of the fan‐ and braid‐deltas on the one hand and the tectonic activity on the other hand (Figures 8f 9d 10d)

The intensity of the tectonic activity correlates negatively with the extent of the sediment area but positively with the sediment volume (Figures 8g‐h 9e‐f 10e‐f) The different responses of the sediment area and the volume to the tectonic activity are caused by variations in the thicknesses of the sed-imentary units (Table 3)

There is also a positive relationship between the average seismic progradation dip of the fan‐ and braid‐deltas and the tectonic activity (Figures 8i 9g 10g) strong tectonic activ-ity usually formed deltas that are characterized by a chaotic progradational or oblique progradational seismic reflection such as SF 1 and 2 in S‐3 (lower unit) and S‐4 (Figures S3ndashS7) The minimum tectonic activity during Members S‐1 + 2 and D‐2 are reflected by dominantly shingled progradational seismic facies in the delta interior (Figures S10ndashS11)

In addition we find that the sediment area sediment vol-ume and average seismic progradation dip of the fan‐ and braid‐deltas correlate positively with the sediment‐supply rate (Figure 11a b and c) but negatively with the basin sink area (Figure 11d e and f) Both the sediment volume and the average seismic progradation dip of the fan‐ and braid‐deltas

F I G U R E 8 (a‐b) Relationships between the tectonic‐subsidence rate and tectonics (c‐i) Relationships between tectonic activity and sedimentary source‐to‐sink parameters Input data regarding the tectonic activity are from Table 2 those regarding the source‐to‐sink parameters data are from Tables 3 and 4 Regression‐line equations and coefficients of determination (R2) are shown for all diagrams

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show a positive relationship with the total accommodation space (Figure 11hi) However no obvious relationship ap-pears to be present between the sediment area and the total accommodation space (G) Both the sediment area and the average seismic progradation dip of the fan‐ and braid‐deltas correlate well with the average sedimentary dip of the fan‐ and braid‐deltas (Figure 11km) A poor correlation is found between the sediment volume and the average sedimentary dip of the fan‐ and braid‐deltas

6 | DISCUSSION

61 | Analysis of the influence of tectonic activity on the source area accommodation space geomorphology and sediment supplyA high relief and large drainage area usually can generate a large sediment supply (Leeder Harris amp Kirkby 1998 Syvitski amp Milliman 2007) Although the erosional area for the fan and delta system cannot be estimated because of the

limited data coverage the exposed area within the study area can be calculated The calculations show a generally decreas-ing trend of the source area from S‐4 (501 km2) to D‐2 (58 km2 Figure7 Table 4) The calculated exposed area cannot fully represent the true source area however but the evolu-tionary trend of the source area can be used as a proxy to indi-cate the relative influence on the change in sediment volume This trend is consistent with the decrease in sediment volume from S‐4 (2126 km3) to D‐2 (175 km3 Table 2) The relief is difficult to reconstruct in this case but variations in the fault‐activity rate (here taken as the tectonic‐subsidence rate) can create local elevation differences and can therefore be used as proxies for the trends in the relief development The relief shows an overall decreasing trend from S‐4 to D‐2 except for D‐3 this correlates well with the sediment volume (Figure 8h) Although the drainage area of D‐3 was smaller than that of D‐2 because of the high tectonic‐subsidence rate (result-ing in a high relief) D‐3 is thicker and shows a larger sedi-ment volume than the overlying D‐2 (Table 3) D‐3 is thinner than S‐4 + 3 but the larger source area resulted in a larger

F I G U R E 9 General relationships between the average fault‐growth index of F1 and F2 (AFGIF1‐F2) and sedimentary source‐to‐sink parameters The average fault‐growth index of F1 and F2 (AFGIF1‐F2) data in this figure are from Table 2 The source‐to‐sink parameters data are from Table 4 Regression‐line equations and the coefficients of determination are shown in each diagram

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sediment volume and supply rate (Table 3 Figure8ch) Therefore both the fault‐induced relief and the drainage area affected the sediment‐supply rate and the sediment volume in the sink

The changes in accommodation space during the vari-ous phases of the Palaeogene in the south‐western HD are clear from the estimated tectonic subsiding rate (Table 2) The correlations between the intensity of the tectonic activ-ity and the extent of the depositional sink area (Figures 8d 9b 10b) between the intensity of the tectonic activity and the total accommodation space and between the intensity of the tectonic activity and the morphology in the sink area (Figures 8e‐f 9c‐d 10c‐d) clearly show that strong tectonic activity resulted in a larger accommodation capacity of the sink

In particular the main subsiding area tended to form steeper slopes However the extent of the main subsiding sink area diminished (Figure 8d) with increasing tectonic activity which was possibly due to the relatively small sub-siding centre in the tectonically active basins It can thus be deduced that tectonic activity not only controlled the sedi-ment supply and the variation in accommodation space but

also determined the changes in the topography of the sedi-mentary basins and the extent of the main depositional areas in the tectonically active basins

62 | Analysis of the influence of tectonic activity on the size and internal stacking pattern of the delta depositional systemThe above data and considerations indicate that the tectonic activity was closely related to the sediment supply accom-modation space and morphology of the sink area which are possibly the most important factors affecting the extent and stacking pattern of the sedimentary facies (cf Cope et al 2010 DeCelles Kapp Ding amp Gehrels 2007 Leeder 2011 Olsen 1997 Simon et al 2017)

Statistical analysis indicates that the sediment‐supply rate has a strong positive correlation with the volume of the depositional system a moderate correlation with the seismic progradational dip in the depositional system and a poor cor-relation with the size of the depositional area (Figure 11a‐c) A larger sink area corresponded to a larger fanbraid‐delta a gentler seismic progradational angle and a reduced volume

F I G U R E 1 0 General relationships between average fault activity rate of F1 and F2 (RFAA‐F1‐F2) and sedimentary source‐to‐sink parameters The average fault activity rate of F1 and F2 (RFAA‐F1‐F2) data in this figure are from Table 2 The source‐to‐sink parameters data are from Table 4 Regression line equations and the coefficients of determination are shown in each diagram

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of the fan or braid‐delta which was possibly related to a re-duced sedimentary dip and thinner sediments (Figure 11d‐f) The total accommodation space in the basin correlates well

with the volume of the depositional system to some degree with the seismic progradational dip and poorly with the ex-tent of the depositional system area (Figure 11g‐i) These

FIGURE 11 Relationships between various parameters involved in the source‐to‐sink system (a‐c) Relationships between sediment supply and characteristics of the depositional system (extent volume and DPSA of the sediments) (d‐f) Relationships between the sink area of the basin and characteristics of the depositional system (g‐i) Relationships between the total accommodation space (AT) and the characteristics of the depositional system (j) Relationship between the accommodation‐spacesediment‐supply ratio (AS) and the DPSA of the sediments (k‐m) Relationships between the sedimentary dip and the characteristics of the depositional system The data regarding sediment supply basin sink area total accommodation space accommodation‐spacesediment‐supply ratio and sedimentary dips are from Table 4 The extent volume and DPSA of the sedimentary facies are from Table 3 Note the seemingly obvious polynomial (quadratic) relationship between the sedimentary dip and the sediment volume (L) The trend line in (L) suggests the following relationships between sediment volume and sedimentary slope in a rift or tectonically active basin (1) a very steep sedimentary slope is unfavourable for sediment accumulation (2) an appropriate sedimentary slope is favourable for preservation of depositional systems eg when the sedimentary slope in (L) is about 25degndash32deg the sediment volume reaches its largest value (3) a very gentle sedimentary slope will lead to a decrease of the sediment volume possibly due to weakening of the drainage system and thinner sediments

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relationships are clear evidence that the size of the sink area controlled the extent of the depositional system during the rifting of the lacustrine basin and that the rate of sediment supply and the accommodation space had a significant in-fluence on the total sedimentary volume as well as on the internal stacking pattern of the depositional system

We here use the ratio of the tectonic‐subsidence rate and the sediment‐supply rate as a proxy to indicate the ratio be-tween accommodation space and sediment‐supply rate (AS) (Table 4) AS has a strong influence on the internal stacking pattern of the depositional systems in the lacustrine rift basin (Figure 11j) This might be because the basin was small and because abundant and rapid material was supplied due

to intense tectonic activity (cf Catuneanu et al 2009 Liro 1993) and a favourable local climate (eg Bohacs Carroll Neal amp Mankiewicz 2000 Perlmutter amp Matthews 1989) The sediment supply still had a significant influence on the main subsidence area of the lacustrine basins and deposi-tional systems

In addition the basin slope significantly influenced the extent of the depositional system (Figure 11k) and had a polynomial relationship with its volume (Figure 11l) This relationship indicates that more intense tectonic activity and a steeper depositional slope were not favourable for sediment accumulation over a large extent in the lacustrine basin On the contrary these sediments were usually transported to a

F I G U R E 1 2 Tectonic differential activities and resulting patterns of the source‐to‐sink system on the south‐western slope of the HD during the Palaeogene (a) Development during phases of intense tectonics (Member 4 to the lower part of Member 3 of the Shahejie Fm) (b) Development during phases of somewhat less tectonic activity (middle part of Member 3 of the Shahejie Fm and Member 3 of the Dongying Fm) (c) Development during phases of weak tectonic activity (Members 1 and 2 of the Shahejie Fm and Member 2 of the Dongying Fm) The intensity of tectonic activity in the lacustrine rift basin had a significant influence on the development and extent of each unit of the source‐to‐sink system as well as on the type and dimensions of the depositional systems The present study indicates that probably sublacustrine fans developed (see for example Figure S4b) during phases with relatively strong tectonic activity This is not really clear from the seismic‐reflection data but possibly due to the small sizes of these sublacustrine fans Moreover lithofacies and core data are not available for the south‐western part of the study area The present contribution therefore focuses on the fan‐deltas and braid‐deltas regarding the sedimentary facies analysis the sublacustrine fans that probably developed in the deep or semi‐deep lake are presented just as a likely feature

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relatively small sink area with a fairly large accommodation space Finally stronger tectonic activity resulted in steeper depositional slopes (Figure 8f) which further controlled the hydrodynamic conditions and differential discharge when the sediments were deposited The strong correlation between the depositional slope and the deltas dip (Figure 11m) suggests that the differences in topography due to tectonics must be considered as one of the most critical factors that controlled the internal stacking pattern of the delta deposits

63 | Significance of the present study for other source‐to‐sink systems of lacustrine rift basins

631 | Summary of the source‐to‐sink systems in the HDIn lacustrine rift basins the tectonic setting is probably the main factor that determines the development of the S2S sys-tem but differential tectonic activities lead to variations in the basic characteristics of the S2S system Tectonic activity was most intense during S‐3 (lower unit) and during S‐4 and caused both a strong uplift of the source area and the devel-opment of depressions in the basin that formed a sink (Figure 12a) Strong tectonic activity in the S2S system during these time‐spans led to a high sediment‐supply rate steeper slopes a larger accommodation space and deposition of several fan‐deltas that are characterized by a fairly steep seismic progra-dational angle

The tectonic activity decreased during S‐3 (middle unit) and during D‐3 The S2S system that was present during this time‐span mainly concerned a rising area that shifted south-wards developing an alluvial plain between the erosional area and the sink area thus increasing the distance from source to sink (Figure 12b) Simultaneously the sediment‐supply rate and the accommodation space also changed and braid‐deltas could thus develop with larger volumes and gentler seismic progradational dips

Tectonic activity was clearly less intense during S‐1 + 2 and D‐2 The rising area had shifted further southwards cre-ating a wider alluvial plain connecting the source area to the sink in the HD (Figure 12c) At this stage stable tectonic activity led to relatively less sediment supply a gentle slope less accommodation space and the development of several braid‐deltas with a fairly gentle seismic progradational angle

632 | Wider implications and limitationsSoslashmme et al (2009) proposed that the elements of S2S sys-tems are genetically related and that quantitative correla-tions exist among these elements Other studies also suggest that the size of the drainage basin is correlated to the size of the fan developing on the basin floor (eg Blum et al

2017 Snedden et al 2018) and to the size of the river chan-nel (eg Milliken et al 2018) Helland‐Hansen Soslashmme Martinsen Lunt and Thurmond (2016) suggest a simplified subdivision of S2S systems into three main categories (a) Steep‐Short‐Deep (steep onshore and offshore gradients short distance between source and sink and deep offshore waters) (b) Wide‐Deep (low‐gradient shelf‐catchment area and deep offshore waters) and (c) Wide‐Shallow (relatively shallow offshore waters and a wide low‐gradient catchment area) systems

The present study indicates that the alluvial plain roughly corresponds to the alluvial‐shelf unit in marine basins al-though with a much smaller width and extent in the lacustrine rift basins than would have been the case on a continental shelf Faults F1 and F2 along the slope belt correspond to the slope of classical S2S systems whereas the shore‐shallow‐deep lake area can be compared with the basin floor (Soslashmme et al 2009) S‐4 and S‐3 (lower unit) can be roughly clas-sified as Steep‐Short‐Deep systems whereas the overlying S‐1 + 2and D‐2 can be classified as the Wide‐Shallow sys-tems that Helland‐Hansen et al (2016) defined During the deposition of S‐4 and S‐3 (lower unit) the strong tectonic activity caused a high relief of the source area a narrow allu-vial plain and a relatively deep lake The subsequently wan-ing tectonic activity resulted in a lower relief of the source area a wider alluvial plain and a shallower lake Although the absolute values of these elements in lacustrine basins are much smaller than those of marine basins the ratio between these elements in both settings is comparable Typically in a lacustrine basin a transformation from a Steep‐Short‐Deep system (S‐4 and S‐3 (lower unit)) to a Wide‐Shallow system (S‐1 + 2ampD‐2) occurs within a few million years Although the basin geomorphology has experienced signif-icant changes from S‐4 to D‐2 the quantitative relationships between tectonic activity sediment‐supply rate accommoda-tion space and sedimentary dip of the delta systems did not change significantly (eg Figures 8 and 11) The analytical approaches applied and quantitative relationship established here can help analyse other lacustrine basins worldwide and may even act as a reference for the analysis of marine basins

Our study focuses mainly on the influences of tectonic activity on the elements of the depositional sink Other pa-rameters (eg climate and lithology) were not considered in detail Studies on modern and ancient systems suggest that the climate and lithology also have a great influence on the sediment supply and distribution in the basin (eg Carroll Chetel amp Smith 2006 Hovius amp Leeder 1998 Syvitski amp Milliman 2007 Zhang et al 2018) For exam-ple climate variations between glacials and inter‐glacials have resulted in largely different sediment‐supply rates and in significant differences in the sizes of the Quaternary sub-marine fans in the north‐western Gulf of Mexico (Blum amp Hattier‐Womack 2009) We acknowledge the importance

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of climate and lithology for S2S systems and we are con-vinced that these elements can significantly affect the S2S systems in other cases(eg modern systems and systems influenced by glacialinterglacial alternations) These fac-tors were not really relevant for the present study however because no significant differences in lithology were present in the source areas and because we focus on the changes at a million‐year scale which implies that the tectonic ac-tivity has a first‐order control on the development of S2S elements in the investigated rift basin

7 | CONCLUSIONS

We have calculated the tectonic‐subsidence history the growth index and the activity rate of the main boundary faults (F1 and F2) and various S2S parameters of six Palaeogene rock units on the south‐western slope of the HD Based on the values found for these parameters quantitative corre-lation were established for the tectonic activity and other S2Sparameters in the basinal sink This leads to the follow-ing conclusions

1 The positive correlation between the intensity of fault activity and the tectonic‐subsidence rate is a strong indication for a distinct control by the tectonic activity of the syn‐depositional rifting of the tectonically active basin

2 The tectonic activity was quantitatively related to the sediment supply accommodation space and morphology of the sink area The relationship between tectonic activ-ity and depositional systems is reflected by changes in critical factors such as sediment supply accommodation space and dip of the sink area These critical factors were probably the most important factors that led to changes in the size and internal stacking pattern of the sedimentary facies

3 Differential tectonic activity led to changes in the char-acteristics of the S2S system on the south‐western slope of the HD The strongest tectonic activity which oc-curred during S‐3 (lower unit) and during S‐4 led to the largest provenance area adjacent to the sink area to a high sediment‐supply rate to steeper slopes to a larger accommodation space and controlled the development of several fan‐deltas Diminished tectonic activity dur-ing S‐3 (middle unit) and during D‐3 led to a decrease in uplift an increased width of the alluvial plain an in-creased transport distance a decrease in the sediment‐supply rate and accommodation space and resulted in the development of braid‐deltas with a large volume During S‐1 + 2 and D‐2 stable tectonic activity led to a lower sediment‐supply rate a gentle depositional slope and a smaller accommodation space resulting in the

development of several braid‐deltas with gentler seis-mic progradational angles

4 The analytical approaches applied and the quantitative re-lationships established here can help analyse other lacus-trine basins worldwide and may even act as a reference for the study of marine basins

ACKNOWLEDGEMENTS

We thank Dr Sarah Boulton and Dr Chenlin Gong as well as the Associate Editor of Basin Research Dr Craig Magee for their constructive comments on the manuscript This study was funded by the National Science and Technology Major Project (Exploration Technologies for Offshore Hidden OilGas) (project no 2016ZX05024‐003‐003) the National Natural Science Foundations of China (project no 41676050) and the Fundamental Research Funds for the Central Universities (2652014037)

REFERENCES

Allen P A (2008a) From landscapes into geological history Nature 451 274ndash276 https doiorg101038natur e06586

Allen P A (2008b) Time scales of tectonic landscapes and their sed-iment routing systems In Landscape evolution Denudation cli-mate and tectonics over different time and space scales (Ed by Gallagher K Jones S J amp Wainwright J) Geological Society London Special Publications 296 7ndash28

Allen P A Armitage J J Carter A Duller R A Michael N A Sinclair H D hellip Whittaker A C (2013) The Qs problem Sediment volumetric balance of proximal foreland basin systems Sedimentology 60 102ndash130

Amorosi A Maselli V amp Trincardi F (2016) Onshore to offshore anatomy of a late Quaternary source‐to‐sink system (Po Plain‐Adriatic Sea Italy) Earth‐Science Reviews 153 212ndash237 https doiorg101016jearsc irev201510010

Anderson J B Wallace D J Simms A R Rodriguez A B Weight R W R amp Taha Z P (2016) Recycling sediments between source and sink during a eustatic cycle Systems of late Quaternary northwestern Gulf of Mexico Basin Earth‐Science Reviews 153 111ndash138 https doiorg101016jearsc irev201510014

Anthony E J amp Julian M (1999) Source‐to‐sink sediment trans-fers environmental engineering and hazard mitigation in the steep Var River catchment French Riviera southeastern France Geomorphology 31 337ndash354 https doiorg101016S0169-555X(99)00088-4

Athy L F (1930) Density porosity and compaction of sedimentary rocks AAPG Bulletin 14 1ndash24

Bhattacharya J P Copeland P Lawton T F amp Holbrook J (2016) Estimation of source area river palaeo‐discharge palaeoslope and sediment budgets of linked deep‐time depositional systems and im-plications for hydrocarbon potential Earth‐Science Reviews 153 77ndash110

Blum M D amp Hattier‐Womack J (2009) Climate change sea‐level change and fluvial sediment supply to deepwater depositional

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Differences in base level and the original sedimentary sur-face define the accommodation space (Jervey 1988 Muto amp Steel 2000 Neal amp Abreu 2009 Wheeler 1964) The

accommodation space in the depositional area can be deter-mined on the basis of the thickness of the preserved sediments (Muto amp Steel 2000) This space is obviously controlled by

F I G U R E 7 Schematic morphology during the successive depositional phases The extent of the deltas the depositional sink area in the basin and the main features of the drainage systems are shown The extent of the deltas has been interpreted from seismic data and has been used for calculation of the surface area and volume of the various deltas (a) Shahejie Fm Member 4 (b) Shahejie Fm lower part of Member 3 (c) Shahejie Fm middle part of Member 3 (d) Shahejie Fm Members 1 and 2 (e) Dongying Fm Member 3 (f) Dongying Fm Member 2

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the rate of subsidence tectonic uplift and fluctuations of the lake level (Lemons amp Chan 1999) Changes in the lake level of the HD have not been investigated so that we take data on the tectonic‐subsidence rate as a proxy for changes in the accommodation space The total space is expressed in the equation (Table 4)

where AT represents the total accommodation space of the sink area (in km3) TS represents the tectonic subsidence (in m) and SA represents the surface area of the sink (in km2)

AT= TStimesSA∕1000

T A B L E 4 Estimation of the controlling factor parameters of the depositional system The distribution characteristics of the depositional sink in the basin are shown in Figure 7

Formation and membera

Sedimentary facies Seismic sections

DDb

RSSc(km3

Ma)Sink area (km2) AT

d(km3) ASeSource areaf(km2)DSD DSDA

D‐2 Braid delta Figure a 059 066 502 37542 7852 1195 58

Figure b 065

Figure c 074

D‐3 Braid delta Figure a 161 187 926 19823 11593 2051 252

Figure b 192

Figure c 215

Figure d 182

S‐1 + 2 Braid delta Figure a 086 096 356 28015 6463 1403 220

Figure b 094

Figure c 120

Figure d 083

S‐3 (middle unit) Braid delta Figure a 110 119 772 21756 6927 1619 355

Figure b 111

Figure c 129

Figure d 128

S‐3 (lower unit) Fan delta Figure a 307 303 1313 16506 10500 2705 482

Figure b 334

Figure c 332

Figure d 237

S‐4 Fan delta 1 Figure a 384 463g 861 14150 10481 3484 501

Figure b 379

Fan delta 2 Figure a 606

Figure b 498

Fan delta 3 Figure a 479

Figure b 499

Figure c 625

Figure d 553

Fan delta 4 Figure a 377

Figure b 226aD = Dongying Fm S = Shahejie Fm The number indicates the number of the member bDD = depositional dip DSD = depositional dip in a specific seismic section DSDA = average depositional dip of a specific sedimentary unit cRSS = sediment‐supply rate dAT = total accommodation space eAS = accommodation spacesediment supply fSource area = Denudation area within the seismic data coverage The complete erosional area cannot be estimated because of the limited data coverage g463 = the average depositional dip of fan deltas 1 2 3 and 4 Considering that the four fan deltas developed during S‐4 consist of sediment that was derived from the same provenance area and were deposited in the same time‐span the four fan deltas are taken as a whole when estimating the parameters of RSS the sink area AT and AS

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4 | ELEMENTS OF THE S2S SYSTEM

41 | Analysis of the seismic facies and stacking pattern of the main sedimentary faciesA comprehensive analysis of seismic data cores cutting log-gings and well‐logging curves by Liu Xia et al (2015a) in-dicated that the Palaeogene depositional systems of the HD included fan‐deltas braid‐deltas lake margins deep lakes etc The fan‐ and braid‐deltas have been chosen for a detailed seismic study that must reveal their internal texture and their stacking patterns Analysis of the progradational seismic‐re-flection types and of the seismic progradational dip is particu-larly helpful for a better understanding of the hydrodynamic conditions and sedimentary processes that resulted in these depositional systems Because the facies interpretation in this area has been done before and is not the focus of this work we here mainly describe the internal texture and their stack-ing patterns of the main sedimentary facies

The major facies of S‐4 is interpreted as a fan‐delta It is dominated by Seismic Facies 1 which is characterized by discontinuous to continuous low‐ to high‐amplitude and chaotic progradational seismic reflections (Figures S3ndashS6 Table 1) The average dip of the progradational seismic event is about 365deg (Table 3) Three lithofacies are associated with Seismic Facies 1 (Table 1) The coarser lithofacies 1 represents a fan‐delta front whereas the finer lithofacies 2 and 3 are prodelta deposits The overall coarsening‐upward succession facies stacking pattern (Figure 6a) discontinuous and chaotic seismic reflections and relatively steep slope of Seismic Facies 1 suggest a fan‐delta system developed under strong hydrodynamic conditions (Mitchum et al 1977)

The fan‐delta of the lower part of Member 3 of the Shahejie Fm (S‐3 [lower unit]) is dominated by Seismic Facies 2 which is characterized by chaotic progradational to oblique progradational seismic characteristics It has a typical wedge shape and is composed of two seismic‐reflection seg-ments (a) a moderately continuous low‐ to high‐amplitude chaotic seismic‐reflection segment located near boundary fault F2 and (b) a continuous moderate‐ to high‐amplitude and oblique progradational seismic reflection in a basinward direction (Figure S7 Table 1) No obvious upper or lower segments occur in SF 2 and the dip of the progradational seismic event in this segment is also relatively steep viz 305deg (Table 3)

The middle part of Member 3 of the Shahejie Fm (S‐3 [middle unit]) is characterized by a low‐ to moderate‐con-tinuous low‐amplitude and oblique progradational seismic reflection (Seismic Facies 3) and is interpreted as a braid‐delta (Figure S8 Table 1) The progradational seismic events are parallel or sub‐parallel to each other and dip less (aver-age 225deg) than Seismic Facies 1 and 2 (Table 3) Seismic

Facies 3 is associated with four lithofacies (Figure 6b Table 1) in Well T25 The complete succession of the braid‐delta consists of gravely to coarse‐grained sandstone (lithofacies 1) at the base (Figure 6f) massive bedded medium‐ to fine‐grained sandstones (lithofacies 2) and grey mudstones inter-bedded with grey fine sandstones and grey muddy siltstones (lithofacies 3) in the middle (Figures 6g and 6h) and thick dark grey mudstones (lithofacies 4) at the top (Figure 6i)

Member 3 of the Dongying Fm (D‐3) is characterized by Seismic Facies 4 a typically composite seismic progra-dation reflection configuration representing a braid‐delta system (Figure S9 Table 1) Seismic Facies 4 is composed of highly continuous moderate‐ to high‐amplitude and pro-gradational seismic reflections that represent well‐developed deltaic topsets and bottomsets The topset segments of SF 4 are nearly horizontal or dip only gently (Table 3) The foreset segments form thicker lenses with small depositional angles The oblique progradational part of this seismic facies is sim-ilar to that in Seismic Facies 3 and usually developed at the basinward front end of Seismic Facies 3 The lithology of Seismic Facies 4 is dominated by greyish white to white fine‐grained sandstones and siltstones The lithofacies association is characterized by coarsening‐upward sedimentary cycles (Figure 6c Table 1) Convolute bedding and abundant diam-ictites are present on top of the fine sandstones (Figure 6j‐k)

Both braid‐deltas in the Members 1 + 2 of th Shahejie Fm (S‐1 + 2) and Member 2 of the Dongying Fm (D‐2) show moderately continuous moderate‐amplitude and shin-gled‐like progradational seismic reflections (Seismic Facies 5 Figures S10ndashS11 Table 1) It shows a thin prograding seis-mic pattern commonly with parallel upper and lower bound-aries (cf Mitchum et al 1977) The successive internal progradational seismic events overlap each other between the upper and lower segments with a gentle dip of 152degndash193deg (Table 3) The lithofacies are mostly composed of several coarsening‐upward cycles (Figure 6d Table 1) Each cycle is composed of dark grey mudstones and grey to whitish‐grey medium‐ to fine‐grained sandstones Several coarsening‐up-ward lithofacies are mainly developed in D‐2 (Figure 6e Table 1)

42 | Analysis of the tectonic activityThe normal faults F1 and F2 selected to calculate the fault activity dipping to the north and running approximately E‐W are important boundary faults on the south‐western margin of the HD The tectonic‐subsidence rate fault‐growth index and fault‐activity rate were used as proxies to indicate the tectonic intensity (Figure 3 S2 Table 2) S‐4 and S‐3 (lower unit) have the highest subsidence rate (300ndash355 mMa) the highest fault‐growth index (292ndash343 mMa) and the highest fault‐activity rate (10647ndash11869 mMa) among the studied intervals whereas the overlying S‐3 (middle

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unit) and S‐1 + 2 are characterized by a much lower sub-sidence rate and fault‐growth index and fault‐activity rate D‐3 had again a high subsidence rate (190 mMa) and an average fault‐growth index (210 mMa) and fault‐activity rate (9344 mMa) The uppermost studied interval D‐2 had a much lower subsidence rate (60 mMa) growth index (136 mMa) and fault‐activity rate (3451 mMa) than the un-derlying unit Generally the analysis of the subsidence rate average fault‐growth index and fault‐activity rate indicates two phases of alternating strong tectonic activity and tectoni-cally stable conditions

43 | Palaeogeomorphology distribution and dimensions of the main depositional systemsDepositional systems of each depositional phase of the Palaeogene on the south‐western slope of the HD were com-piled through seismic facies identification of 3‐D seismic data and compilation of maps with the current thicknesses of the main target intervals based on the study by Liu Xia et al (2015a) that combined a correction for the depth of burial with an interpretation of the sedimentary facies The basins sink area on the south‐western slope of the HD was estimated on the basis of a palaeogeomorphological reconstruction The distribution of the depositional system is closely related to the evolution of the palaeogeomorphology and therefore we describe both the distribution of the depositional system and the palaeogeomorphology here

The palaeogeography of S‐4 is characterized by the larg-est extent of the uplifted areas of all studied intervals The depositional area is small and scattered (Figure 7a Table 4) Faults F1 and F2 mark the boundaries between erosional and depositional regions The elevated footwalls of the faults were erosional areas and located adjacent to the hanging walls whereas the hanging walls were low‐lying depositional areas The sedimentary facies analysis indicates a fan‐delta developed here (Figure 7a) Calculations indicate that the sedimentary dip of the four fan‐deltas was uncommonly high (about 463deg) The extent and thickness of the fan‐deltas di-minished towards the basin margin (Tables 34)

The tectonically‐induced morphology of S‐3 (lower unit) shows a similar pattern to that of the underlying S‐4 The depositional and erosional areas were also controlled by the active faults F1 and F2The HD deepened from west to east with the deepest area located just along the fault margin The depositional centre was located north of the hanging wall of F2 and became infilled by a fan‐delta (Figure 7b) The aver-age sedimentary dip of the fan‐delta is 303deg The extent of the fan‐delta was larger than that of S‐4 (Table 34)

During deposition of S‐3 (middle unit) the uplifted source area shifted southwards and the depression expanded A major depositional sink was located north of the hanging wall of F2 (Figure 7c Table 4) Elevation differences existed

between the footwalls and the hanging walls of F1 and F2 although the topography was obviously gentler during this time‐span A braided fluvial area developed at the footwalls of the faults whereas a braid‐delta developed mainly on the hanging wall of F2 and the northern depositional centre (Figure 7c) The braid‐delta had a fairly large extent and an average depositional dip of 119deg (Tables 34)

During S‐1 + 2 the elevated erosional area shifted farther southwards and the entire south‐western area had a low to-pography An alluvial plain developed south of the footwalls of the faults whereas a braid‐delta developed at the hanging walls and in the depression with a very gentle slope of 096deg (Table 4 Figure 7d) The depositional system was dominated by a fairly thin delta body and a braid‐delta with a much larger extent (Table 3)

During the deposition of D‐3 the topography of the foot-wall areas and of the area south of the provenance area was similar to that during the underlying S‐1 + 2 The slope was steep (187deg) in the hanging walls of the boundary faults however and the depositional area increased to 198 km2 which provided an excellent condition for the deposition of a large braid‐delta (Figure 7e Table 4) This braid‐delta had a NE‐SW orientation and covered an area of 142 km2 its average thickness is some 200 m which results in the largest delta volume in the Palaeogene on the south‐western slope of the HD (Table 3)

The palaeogeomorphological reconstruction of D‐2 shows a gentler topography in the entire south‐western HD with a sink area of 375 km2 (Table 4) The main body of the braid‐delta was dominated by imbricated progradational seis-mic reflections and developed in the hanging walls of F1 and F2 whereas an alluvial‐plain facies probably developed in the footwall areas of the faults and to the south‐west of the uplifted area (Figure 7f) Although the extent of the delta reached its maximum the thickness of the delta was limited due to the gentle topography resulting in a small delta vol-ume (Table 3)

5 | RELATIONSHIPS BETWEEN THE VARIOUS ELEMENTS OF THE S2S SYSTEM

Quantitative relationships between the various elements of the S2S system have been established through the above‐mentioned calculations A strong positive correlation is clearly present between the rate of tectonic subsidence the average fault activity and the average growth index of the boundary faults F1 and F2 (Figure 8ab) The rate of tectonic subsidence can therefore be used in the following as the pri-mary proxy to represent the intensity of the tectonic activity whereas the rate of fault activity and the growth index are used as secondary proxies

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The tectonic activity and the sediment‐supply rate show a positive relationship (Figures 8c 9a 10a) whereas the tec-tonic activity and the sink area of the basin show a negative relationship (Figures 8d 9b 10b) In contrast the tectonic activity has a positive relationship with the total accommo-dation space (Figures 8e 9c 10c Table 4) There is also a positive relationship between the average sedimentary dip of the fan‐ and braid‐deltas on the one hand and the tectonic activity on the other hand (Figures 8f 9d 10d)

The intensity of the tectonic activity correlates negatively with the extent of the sediment area but positively with the sediment volume (Figures 8g‐h 9e‐f 10e‐f) The different responses of the sediment area and the volume to the tectonic activity are caused by variations in the thicknesses of the sed-imentary units (Table 3)

There is also a positive relationship between the average seismic progradation dip of the fan‐ and braid‐deltas and the tectonic activity (Figures 8i 9g 10g) strong tectonic activ-ity usually formed deltas that are characterized by a chaotic progradational or oblique progradational seismic reflection such as SF 1 and 2 in S‐3 (lower unit) and S‐4 (Figures S3ndashS7) The minimum tectonic activity during Members S‐1 + 2 and D‐2 are reflected by dominantly shingled progradational seismic facies in the delta interior (Figures S10ndashS11)

In addition we find that the sediment area sediment vol-ume and average seismic progradation dip of the fan‐ and braid‐deltas correlate positively with the sediment‐supply rate (Figure 11a b and c) but negatively with the basin sink area (Figure 11d e and f) Both the sediment volume and the average seismic progradation dip of the fan‐ and braid‐deltas

F I G U R E 8 (a‐b) Relationships between the tectonic‐subsidence rate and tectonics (c‐i) Relationships between tectonic activity and sedimentary source‐to‐sink parameters Input data regarding the tectonic activity are from Table 2 those regarding the source‐to‐sink parameters data are from Tables 3 and 4 Regression‐line equations and coefficients of determination (R2) are shown for all diagrams

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show a positive relationship with the total accommodation space (Figure 11hi) However no obvious relationship ap-pears to be present between the sediment area and the total accommodation space (G) Both the sediment area and the average seismic progradation dip of the fan‐ and braid‐deltas correlate well with the average sedimentary dip of the fan‐ and braid‐deltas (Figure 11km) A poor correlation is found between the sediment volume and the average sedimentary dip of the fan‐ and braid‐deltas

6 | DISCUSSION

61 | Analysis of the influence of tectonic activity on the source area accommodation space geomorphology and sediment supplyA high relief and large drainage area usually can generate a large sediment supply (Leeder Harris amp Kirkby 1998 Syvitski amp Milliman 2007) Although the erosional area for the fan and delta system cannot be estimated because of the

limited data coverage the exposed area within the study area can be calculated The calculations show a generally decreas-ing trend of the source area from S‐4 (501 km2) to D‐2 (58 km2 Figure7 Table 4) The calculated exposed area cannot fully represent the true source area however but the evolu-tionary trend of the source area can be used as a proxy to indi-cate the relative influence on the change in sediment volume This trend is consistent with the decrease in sediment volume from S‐4 (2126 km3) to D‐2 (175 km3 Table 2) The relief is difficult to reconstruct in this case but variations in the fault‐activity rate (here taken as the tectonic‐subsidence rate) can create local elevation differences and can therefore be used as proxies for the trends in the relief development The relief shows an overall decreasing trend from S‐4 to D‐2 except for D‐3 this correlates well with the sediment volume (Figure 8h) Although the drainage area of D‐3 was smaller than that of D‐2 because of the high tectonic‐subsidence rate (result-ing in a high relief) D‐3 is thicker and shows a larger sedi-ment volume than the overlying D‐2 (Table 3) D‐3 is thinner than S‐4 + 3 but the larger source area resulted in a larger

F I G U R E 9 General relationships between the average fault‐growth index of F1 and F2 (AFGIF1‐F2) and sedimentary source‐to‐sink parameters The average fault‐growth index of F1 and F2 (AFGIF1‐F2) data in this figure are from Table 2 The source‐to‐sink parameters data are from Table 4 Regression‐line equations and the coefficients of determination are shown in each diagram

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sediment volume and supply rate (Table 3 Figure8ch) Therefore both the fault‐induced relief and the drainage area affected the sediment‐supply rate and the sediment volume in the sink

The changes in accommodation space during the vari-ous phases of the Palaeogene in the south‐western HD are clear from the estimated tectonic subsiding rate (Table 2) The correlations between the intensity of the tectonic activ-ity and the extent of the depositional sink area (Figures 8d 9b 10b) between the intensity of the tectonic activity and the total accommodation space and between the intensity of the tectonic activity and the morphology in the sink area (Figures 8e‐f 9c‐d 10c‐d) clearly show that strong tectonic activity resulted in a larger accommodation capacity of the sink

In particular the main subsiding area tended to form steeper slopes However the extent of the main subsiding sink area diminished (Figure 8d) with increasing tectonic activity which was possibly due to the relatively small sub-siding centre in the tectonically active basins It can thus be deduced that tectonic activity not only controlled the sedi-ment supply and the variation in accommodation space but

also determined the changes in the topography of the sedi-mentary basins and the extent of the main depositional areas in the tectonically active basins

62 | Analysis of the influence of tectonic activity on the size and internal stacking pattern of the delta depositional systemThe above data and considerations indicate that the tectonic activity was closely related to the sediment supply accom-modation space and morphology of the sink area which are possibly the most important factors affecting the extent and stacking pattern of the sedimentary facies (cf Cope et al 2010 DeCelles Kapp Ding amp Gehrels 2007 Leeder 2011 Olsen 1997 Simon et al 2017)

Statistical analysis indicates that the sediment‐supply rate has a strong positive correlation with the volume of the depositional system a moderate correlation with the seismic progradational dip in the depositional system and a poor cor-relation with the size of the depositional area (Figure 11a‐c) A larger sink area corresponded to a larger fanbraid‐delta a gentler seismic progradational angle and a reduced volume

F I G U R E 1 0 General relationships between average fault activity rate of F1 and F2 (RFAA‐F1‐F2) and sedimentary source‐to‐sink parameters The average fault activity rate of F1 and F2 (RFAA‐F1‐F2) data in this figure are from Table 2 The source‐to‐sink parameters data are from Table 4 Regression line equations and the coefficients of determination are shown in each diagram

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of the fan or braid‐delta which was possibly related to a re-duced sedimentary dip and thinner sediments (Figure 11d‐f) The total accommodation space in the basin correlates well

with the volume of the depositional system to some degree with the seismic progradational dip and poorly with the ex-tent of the depositional system area (Figure 11g‐i) These

FIGURE 11 Relationships between various parameters involved in the source‐to‐sink system (a‐c) Relationships between sediment supply and characteristics of the depositional system (extent volume and DPSA of the sediments) (d‐f) Relationships between the sink area of the basin and characteristics of the depositional system (g‐i) Relationships between the total accommodation space (AT) and the characteristics of the depositional system (j) Relationship between the accommodation‐spacesediment‐supply ratio (AS) and the DPSA of the sediments (k‐m) Relationships between the sedimentary dip and the characteristics of the depositional system The data regarding sediment supply basin sink area total accommodation space accommodation‐spacesediment‐supply ratio and sedimentary dips are from Table 4 The extent volume and DPSA of the sedimentary facies are from Table 3 Note the seemingly obvious polynomial (quadratic) relationship between the sedimentary dip and the sediment volume (L) The trend line in (L) suggests the following relationships between sediment volume and sedimentary slope in a rift or tectonically active basin (1) a very steep sedimentary slope is unfavourable for sediment accumulation (2) an appropriate sedimentary slope is favourable for preservation of depositional systems eg when the sedimentary slope in (L) is about 25degndash32deg the sediment volume reaches its largest value (3) a very gentle sedimentary slope will lead to a decrease of the sediment volume possibly due to weakening of the drainage system and thinner sediments

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relationships are clear evidence that the size of the sink area controlled the extent of the depositional system during the rifting of the lacustrine basin and that the rate of sediment supply and the accommodation space had a significant in-fluence on the total sedimentary volume as well as on the internal stacking pattern of the depositional system

We here use the ratio of the tectonic‐subsidence rate and the sediment‐supply rate as a proxy to indicate the ratio be-tween accommodation space and sediment‐supply rate (AS) (Table 4) AS has a strong influence on the internal stacking pattern of the depositional systems in the lacustrine rift basin (Figure 11j) This might be because the basin was small and because abundant and rapid material was supplied due

to intense tectonic activity (cf Catuneanu et al 2009 Liro 1993) and a favourable local climate (eg Bohacs Carroll Neal amp Mankiewicz 2000 Perlmutter amp Matthews 1989) The sediment supply still had a significant influence on the main subsidence area of the lacustrine basins and deposi-tional systems

In addition the basin slope significantly influenced the extent of the depositional system (Figure 11k) and had a polynomial relationship with its volume (Figure 11l) This relationship indicates that more intense tectonic activity and a steeper depositional slope were not favourable for sediment accumulation over a large extent in the lacustrine basin On the contrary these sediments were usually transported to a

F I G U R E 1 2 Tectonic differential activities and resulting patterns of the source‐to‐sink system on the south‐western slope of the HD during the Palaeogene (a) Development during phases of intense tectonics (Member 4 to the lower part of Member 3 of the Shahejie Fm) (b) Development during phases of somewhat less tectonic activity (middle part of Member 3 of the Shahejie Fm and Member 3 of the Dongying Fm) (c) Development during phases of weak tectonic activity (Members 1 and 2 of the Shahejie Fm and Member 2 of the Dongying Fm) The intensity of tectonic activity in the lacustrine rift basin had a significant influence on the development and extent of each unit of the source‐to‐sink system as well as on the type and dimensions of the depositional systems The present study indicates that probably sublacustrine fans developed (see for example Figure S4b) during phases with relatively strong tectonic activity This is not really clear from the seismic‐reflection data but possibly due to the small sizes of these sublacustrine fans Moreover lithofacies and core data are not available for the south‐western part of the study area The present contribution therefore focuses on the fan‐deltas and braid‐deltas regarding the sedimentary facies analysis the sublacustrine fans that probably developed in the deep or semi‐deep lake are presented just as a likely feature

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relatively small sink area with a fairly large accommodation space Finally stronger tectonic activity resulted in steeper depositional slopes (Figure 8f) which further controlled the hydrodynamic conditions and differential discharge when the sediments were deposited The strong correlation between the depositional slope and the deltas dip (Figure 11m) suggests that the differences in topography due to tectonics must be considered as one of the most critical factors that controlled the internal stacking pattern of the delta deposits

63 | Significance of the present study for other source‐to‐sink systems of lacustrine rift basins

631 | Summary of the source‐to‐sink systems in the HDIn lacustrine rift basins the tectonic setting is probably the main factor that determines the development of the S2S sys-tem but differential tectonic activities lead to variations in the basic characteristics of the S2S system Tectonic activity was most intense during S‐3 (lower unit) and during S‐4 and caused both a strong uplift of the source area and the devel-opment of depressions in the basin that formed a sink (Figure 12a) Strong tectonic activity in the S2S system during these time‐spans led to a high sediment‐supply rate steeper slopes a larger accommodation space and deposition of several fan‐deltas that are characterized by a fairly steep seismic progra-dational angle

The tectonic activity decreased during S‐3 (middle unit) and during D‐3 The S2S system that was present during this time‐span mainly concerned a rising area that shifted south-wards developing an alluvial plain between the erosional area and the sink area thus increasing the distance from source to sink (Figure 12b) Simultaneously the sediment‐supply rate and the accommodation space also changed and braid‐deltas could thus develop with larger volumes and gentler seismic progradational dips

Tectonic activity was clearly less intense during S‐1 + 2 and D‐2 The rising area had shifted further southwards cre-ating a wider alluvial plain connecting the source area to the sink in the HD (Figure 12c) At this stage stable tectonic activity led to relatively less sediment supply a gentle slope less accommodation space and the development of several braid‐deltas with a fairly gentle seismic progradational angle

632 | Wider implications and limitationsSoslashmme et al (2009) proposed that the elements of S2S sys-tems are genetically related and that quantitative correla-tions exist among these elements Other studies also suggest that the size of the drainage basin is correlated to the size of the fan developing on the basin floor (eg Blum et al

2017 Snedden et al 2018) and to the size of the river chan-nel (eg Milliken et al 2018) Helland‐Hansen Soslashmme Martinsen Lunt and Thurmond (2016) suggest a simplified subdivision of S2S systems into three main categories (a) Steep‐Short‐Deep (steep onshore and offshore gradients short distance between source and sink and deep offshore waters) (b) Wide‐Deep (low‐gradient shelf‐catchment area and deep offshore waters) and (c) Wide‐Shallow (relatively shallow offshore waters and a wide low‐gradient catchment area) systems

The present study indicates that the alluvial plain roughly corresponds to the alluvial‐shelf unit in marine basins al-though with a much smaller width and extent in the lacustrine rift basins than would have been the case on a continental shelf Faults F1 and F2 along the slope belt correspond to the slope of classical S2S systems whereas the shore‐shallow‐deep lake area can be compared with the basin floor (Soslashmme et al 2009) S‐4 and S‐3 (lower unit) can be roughly clas-sified as Steep‐Short‐Deep systems whereas the overlying S‐1 + 2and D‐2 can be classified as the Wide‐Shallow sys-tems that Helland‐Hansen et al (2016) defined During the deposition of S‐4 and S‐3 (lower unit) the strong tectonic activity caused a high relief of the source area a narrow allu-vial plain and a relatively deep lake The subsequently wan-ing tectonic activity resulted in a lower relief of the source area a wider alluvial plain and a shallower lake Although the absolute values of these elements in lacustrine basins are much smaller than those of marine basins the ratio between these elements in both settings is comparable Typically in a lacustrine basin a transformation from a Steep‐Short‐Deep system (S‐4 and S‐3 (lower unit)) to a Wide‐Shallow system (S‐1 + 2ampD‐2) occurs within a few million years Although the basin geomorphology has experienced signif-icant changes from S‐4 to D‐2 the quantitative relationships between tectonic activity sediment‐supply rate accommoda-tion space and sedimentary dip of the delta systems did not change significantly (eg Figures 8 and 11) The analytical approaches applied and quantitative relationship established here can help analyse other lacustrine basins worldwide and may even act as a reference for the analysis of marine basins

Our study focuses mainly on the influences of tectonic activity on the elements of the depositional sink Other pa-rameters (eg climate and lithology) were not considered in detail Studies on modern and ancient systems suggest that the climate and lithology also have a great influence on the sediment supply and distribution in the basin (eg Carroll Chetel amp Smith 2006 Hovius amp Leeder 1998 Syvitski amp Milliman 2007 Zhang et al 2018) For exam-ple climate variations between glacials and inter‐glacials have resulted in largely different sediment‐supply rates and in significant differences in the sizes of the Quaternary sub-marine fans in the north‐western Gulf of Mexico (Blum amp Hattier‐Womack 2009) We acknowledge the importance

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of climate and lithology for S2S systems and we are con-vinced that these elements can significantly affect the S2S systems in other cases(eg modern systems and systems influenced by glacialinterglacial alternations) These fac-tors were not really relevant for the present study however because no significant differences in lithology were present in the source areas and because we focus on the changes at a million‐year scale which implies that the tectonic ac-tivity has a first‐order control on the development of S2S elements in the investigated rift basin

7 | CONCLUSIONS

We have calculated the tectonic‐subsidence history the growth index and the activity rate of the main boundary faults (F1 and F2) and various S2S parameters of six Palaeogene rock units on the south‐western slope of the HD Based on the values found for these parameters quantitative corre-lation were established for the tectonic activity and other S2Sparameters in the basinal sink This leads to the follow-ing conclusions

1 The positive correlation between the intensity of fault activity and the tectonic‐subsidence rate is a strong indication for a distinct control by the tectonic activity of the syn‐depositional rifting of the tectonically active basin

2 The tectonic activity was quantitatively related to the sediment supply accommodation space and morphology of the sink area The relationship between tectonic activ-ity and depositional systems is reflected by changes in critical factors such as sediment supply accommodation space and dip of the sink area These critical factors were probably the most important factors that led to changes in the size and internal stacking pattern of the sedimentary facies

3 Differential tectonic activity led to changes in the char-acteristics of the S2S system on the south‐western slope of the HD The strongest tectonic activity which oc-curred during S‐3 (lower unit) and during S‐4 led to the largest provenance area adjacent to the sink area to a high sediment‐supply rate to steeper slopes to a larger accommodation space and controlled the development of several fan‐deltas Diminished tectonic activity dur-ing S‐3 (middle unit) and during D‐3 led to a decrease in uplift an increased width of the alluvial plain an in-creased transport distance a decrease in the sediment‐supply rate and accommodation space and resulted in the development of braid‐deltas with a large volume During S‐1 + 2 and D‐2 stable tectonic activity led to a lower sediment‐supply rate a gentle depositional slope and a smaller accommodation space resulting in the

development of several braid‐deltas with gentler seis-mic progradational angles

4 The analytical approaches applied and the quantitative re-lationships established here can help analyse other lacus-trine basins worldwide and may even act as a reference for the study of marine basins

ACKNOWLEDGEMENTS

We thank Dr Sarah Boulton and Dr Chenlin Gong as well as the Associate Editor of Basin Research Dr Craig Magee for their constructive comments on the manuscript This study was funded by the National Science and Technology Major Project (Exploration Technologies for Offshore Hidden OilGas) (project no 2016ZX05024‐003‐003) the National Natural Science Foundations of China (project no 41676050) and the Fundamental Research Funds for the Central Universities (2652014037)

REFERENCES

Allen P A (2008a) From landscapes into geological history Nature 451 274ndash276 https doiorg101038natur e06586

Allen P A (2008b) Time scales of tectonic landscapes and their sed-iment routing systems In Landscape evolution Denudation cli-mate and tectonics over different time and space scales (Ed by Gallagher K Jones S J amp Wainwright J) Geological Society London Special Publications 296 7ndash28

Allen P A Armitage J J Carter A Duller R A Michael N A Sinclair H D hellip Whittaker A C (2013) The Qs problem Sediment volumetric balance of proximal foreland basin systems Sedimentology 60 102ndash130

Amorosi A Maselli V amp Trincardi F (2016) Onshore to offshore anatomy of a late Quaternary source‐to‐sink system (Po Plain‐Adriatic Sea Italy) Earth‐Science Reviews 153 212ndash237 https doiorg101016jearsc irev201510010

Anderson J B Wallace D J Simms A R Rodriguez A B Weight R W R amp Taha Z P (2016) Recycling sediments between source and sink during a eustatic cycle Systems of late Quaternary northwestern Gulf of Mexico Basin Earth‐Science Reviews 153 111ndash138 https doiorg101016jearsc irev201510014

Anthony E J amp Julian M (1999) Source‐to‐sink sediment trans-fers environmental engineering and hazard mitigation in the steep Var River catchment French Riviera southeastern France Geomorphology 31 337ndash354 https doiorg101016S0169-555X(99)00088-4

Athy L F (1930) Density porosity and compaction of sedimentary rocks AAPG Bulletin 14 1ndash24

Bhattacharya J P Copeland P Lawton T F amp Holbrook J (2016) Estimation of source area river palaeo‐discharge palaeoslope and sediment budgets of linked deep‐time depositional systems and im-plications for hydrocarbon potential Earth‐Science Reviews 153 77ndash110

Blum M D amp Hattier‐Womack J (2009) Climate change sea‐level change and fluvial sediment supply to deepwater depositional

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the rate of subsidence tectonic uplift and fluctuations of the lake level (Lemons amp Chan 1999) Changes in the lake level of the HD have not been investigated so that we take data on the tectonic‐subsidence rate as a proxy for changes in the accommodation space The total space is expressed in the equation (Table 4)

where AT represents the total accommodation space of the sink area (in km3) TS represents the tectonic subsidence (in m) and SA represents the surface area of the sink (in km2)

AT= TStimesSA∕1000

T A B L E 4 Estimation of the controlling factor parameters of the depositional system The distribution characteristics of the depositional sink in the basin are shown in Figure 7

Formation and membera

Sedimentary facies Seismic sections

DDb

RSSc(km3

Ma)Sink area (km2) AT

d(km3) ASeSource areaf(km2)DSD DSDA

D‐2 Braid delta Figure a 059 066 502 37542 7852 1195 58

Figure b 065

Figure c 074

D‐3 Braid delta Figure a 161 187 926 19823 11593 2051 252

Figure b 192

Figure c 215

Figure d 182

S‐1 + 2 Braid delta Figure a 086 096 356 28015 6463 1403 220

Figure b 094

Figure c 120

Figure d 083

S‐3 (middle unit) Braid delta Figure a 110 119 772 21756 6927 1619 355

Figure b 111

Figure c 129

Figure d 128

S‐3 (lower unit) Fan delta Figure a 307 303 1313 16506 10500 2705 482

Figure b 334

Figure c 332

Figure d 237

S‐4 Fan delta 1 Figure a 384 463g 861 14150 10481 3484 501

Figure b 379

Fan delta 2 Figure a 606

Figure b 498

Fan delta 3 Figure a 479

Figure b 499

Figure c 625

Figure d 553

Fan delta 4 Figure a 377

Figure b 226aD = Dongying Fm S = Shahejie Fm The number indicates the number of the member bDD = depositional dip DSD = depositional dip in a specific seismic section DSDA = average depositional dip of a specific sedimentary unit cRSS = sediment‐supply rate dAT = total accommodation space eAS = accommodation spacesediment supply fSource area = Denudation area within the seismic data coverage The complete erosional area cannot be estimated because of the limited data coverage g463 = the average depositional dip of fan deltas 1 2 3 and 4 Considering that the four fan deltas developed during S‐4 consist of sediment that was derived from the same provenance area and were deposited in the same time‐span the four fan deltas are taken as a whole when estimating the parameters of RSS the sink area AT and AS

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4 | ELEMENTS OF THE S2S SYSTEM

41 | Analysis of the seismic facies and stacking pattern of the main sedimentary faciesA comprehensive analysis of seismic data cores cutting log-gings and well‐logging curves by Liu Xia et al (2015a) in-dicated that the Palaeogene depositional systems of the HD included fan‐deltas braid‐deltas lake margins deep lakes etc The fan‐ and braid‐deltas have been chosen for a detailed seismic study that must reveal their internal texture and their stacking patterns Analysis of the progradational seismic‐re-flection types and of the seismic progradational dip is particu-larly helpful for a better understanding of the hydrodynamic conditions and sedimentary processes that resulted in these depositional systems Because the facies interpretation in this area has been done before and is not the focus of this work we here mainly describe the internal texture and their stack-ing patterns of the main sedimentary facies

The major facies of S‐4 is interpreted as a fan‐delta It is dominated by Seismic Facies 1 which is characterized by discontinuous to continuous low‐ to high‐amplitude and chaotic progradational seismic reflections (Figures S3ndashS6 Table 1) The average dip of the progradational seismic event is about 365deg (Table 3) Three lithofacies are associated with Seismic Facies 1 (Table 1) The coarser lithofacies 1 represents a fan‐delta front whereas the finer lithofacies 2 and 3 are prodelta deposits The overall coarsening‐upward succession facies stacking pattern (Figure 6a) discontinuous and chaotic seismic reflections and relatively steep slope of Seismic Facies 1 suggest a fan‐delta system developed under strong hydrodynamic conditions (Mitchum et al 1977)

The fan‐delta of the lower part of Member 3 of the Shahejie Fm (S‐3 [lower unit]) is dominated by Seismic Facies 2 which is characterized by chaotic progradational to oblique progradational seismic characteristics It has a typical wedge shape and is composed of two seismic‐reflection seg-ments (a) a moderately continuous low‐ to high‐amplitude chaotic seismic‐reflection segment located near boundary fault F2 and (b) a continuous moderate‐ to high‐amplitude and oblique progradational seismic reflection in a basinward direction (Figure S7 Table 1) No obvious upper or lower segments occur in SF 2 and the dip of the progradational seismic event in this segment is also relatively steep viz 305deg (Table 3)

The middle part of Member 3 of the Shahejie Fm (S‐3 [middle unit]) is characterized by a low‐ to moderate‐con-tinuous low‐amplitude and oblique progradational seismic reflection (Seismic Facies 3) and is interpreted as a braid‐delta (Figure S8 Table 1) The progradational seismic events are parallel or sub‐parallel to each other and dip less (aver-age 225deg) than Seismic Facies 1 and 2 (Table 3) Seismic

Facies 3 is associated with four lithofacies (Figure 6b Table 1) in Well T25 The complete succession of the braid‐delta consists of gravely to coarse‐grained sandstone (lithofacies 1) at the base (Figure 6f) massive bedded medium‐ to fine‐grained sandstones (lithofacies 2) and grey mudstones inter-bedded with grey fine sandstones and grey muddy siltstones (lithofacies 3) in the middle (Figures 6g and 6h) and thick dark grey mudstones (lithofacies 4) at the top (Figure 6i)

Member 3 of the Dongying Fm (D‐3) is characterized by Seismic Facies 4 a typically composite seismic progra-dation reflection configuration representing a braid‐delta system (Figure S9 Table 1) Seismic Facies 4 is composed of highly continuous moderate‐ to high‐amplitude and pro-gradational seismic reflections that represent well‐developed deltaic topsets and bottomsets The topset segments of SF 4 are nearly horizontal or dip only gently (Table 3) The foreset segments form thicker lenses with small depositional angles The oblique progradational part of this seismic facies is sim-ilar to that in Seismic Facies 3 and usually developed at the basinward front end of Seismic Facies 3 The lithology of Seismic Facies 4 is dominated by greyish white to white fine‐grained sandstones and siltstones The lithofacies association is characterized by coarsening‐upward sedimentary cycles (Figure 6c Table 1) Convolute bedding and abundant diam-ictites are present on top of the fine sandstones (Figure 6j‐k)

Both braid‐deltas in the Members 1 + 2 of th Shahejie Fm (S‐1 + 2) and Member 2 of the Dongying Fm (D‐2) show moderately continuous moderate‐amplitude and shin-gled‐like progradational seismic reflections (Seismic Facies 5 Figures S10ndashS11 Table 1) It shows a thin prograding seis-mic pattern commonly with parallel upper and lower bound-aries (cf Mitchum et al 1977) The successive internal progradational seismic events overlap each other between the upper and lower segments with a gentle dip of 152degndash193deg (Table 3) The lithofacies are mostly composed of several coarsening‐upward cycles (Figure 6d Table 1) Each cycle is composed of dark grey mudstones and grey to whitish‐grey medium‐ to fine‐grained sandstones Several coarsening‐up-ward lithofacies are mainly developed in D‐2 (Figure 6e Table 1)

42 | Analysis of the tectonic activityThe normal faults F1 and F2 selected to calculate the fault activity dipping to the north and running approximately E‐W are important boundary faults on the south‐western margin of the HD The tectonic‐subsidence rate fault‐growth index and fault‐activity rate were used as proxies to indicate the tectonic intensity (Figure 3 S2 Table 2) S‐4 and S‐3 (lower unit) have the highest subsidence rate (300ndash355 mMa) the highest fault‐growth index (292ndash343 mMa) and the highest fault‐activity rate (10647ndash11869 mMa) among the studied intervals whereas the overlying S‐3 (middle

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unit) and S‐1 + 2 are characterized by a much lower sub-sidence rate and fault‐growth index and fault‐activity rate D‐3 had again a high subsidence rate (190 mMa) and an average fault‐growth index (210 mMa) and fault‐activity rate (9344 mMa) The uppermost studied interval D‐2 had a much lower subsidence rate (60 mMa) growth index (136 mMa) and fault‐activity rate (3451 mMa) than the un-derlying unit Generally the analysis of the subsidence rate average fault‐growth index and fault‐activity rate indicates two phases of alternating strong tectonic activity and tectoni-cally stable conditions

43 | Palaeogeomorphology distribution and dimensions of the main depositional systemsDepositional systems of each depositional phase of the Palaeogene on the south‐western slope of the HD were com-piled through seismic facies identification of 3‐D seismic data and compilation of maps with the current thicknesses of the main target intervals based on the study by Liu Xia et al (2015a) that combined a correction for the depth of burial with an interpretation of the sedimentary facies The basins sink area on the south‐western slope of the HD was estimated on the basis of a palaeogeomorphological reconstruction The distribution of the depositional system is closely related to the evolution of the palaeogeomorphology and therefore we describe both the distribution of the depositional system and the palaeogeomorphology here

The palaeogeography of S‐4 is characterized by the larg-est extent of the uplifted areas of all studied intervals The depositional area is small and scattered (Figure 7a Table 4) Faults F1 and F2 mark the boundaries between erosional and depositional regions The elevated footwalls of the faults were erosional areas and located adjacent to the hanging walls whereas the hanging walls were low‐lying depositional areas The sedimentary facies analysis indicates a fan‐delta developed here (Figure 7a) Calculations indicate that the sedimentary dip of the four fan‐deltas was uncommonly high (about 463deg) The extent and thickness of the fan‐deltas di-minished towards the basin margin (Tables 34)

The tectonically‐induced morphology of S‐3 (lower unit) shows a similar pattern to that of the underlying S‐4 The depositional and erosional areas were also controlled by the active faults F1 and F2The HD deepened from west to east with the deepest area located just along the fault margin The depositional centre was located north of the hanging wall of F2 and became infilled by a fan‐delta (Figure 7b) The aver-age sedimentary dip of the fan‐delta is 303deg The extent of the fan‐delta was larger than that of S‐4 (Table 34)

During deposition of S‐3 (middle unit) the uplifted source area shifted southwards and the depression expanded A major depositional sink was located north of the hanging wall of F2 (Figure 7c Table 4) Elevation differences existed

between the footwalls and the hanging walls of F1 and F2 although the topography was obviously gentler during this time‐span A braided fluvial area developed at the footwalls of the faults whereas a braid‐delta developed mainly on the hanging wall of F2 and the northern depositional centre (Figure 7c) The braid‐delta had a fairly large extent and an average depositional dip of 119deg (Tables 34)

During S‐1 + 2 the elevated erosional area shifted farther southwards and the entire south‐western area had a low to-pography An alluvial plain developed south of the footwalls of the faults whereas a braid‐delta developed at the hanging walls and in the depression with a very gentle slope of 096deg (Table 4 Figure 7d) The depositional system was dominated by a fairly thin delta body and a braid‐delta with a much larger extent (Table 3)

During the deposition of D‐3 the topography of the foot-wall areas and of the area south of the provenance area was similar to that during the underlying S‐1 + 2 The slope was steep (187deg) in the hanging walls of the boundary faults however and the depositional area increased to 198 km2 which provided an excellent condition for the deposition of a large braid‐delta (Figure 7e Table 4) This braid‐delta had a NE‐SW orientation and covered an area of 142 km2 its average thickness is some 200 m which results in the largest delta volume in the Palaeogene on the south‐western slope of the HD (Table 3)

The palaeogeomorphological reconstruction of D‐2 shows a gentler topography in the entire south‐western HD with a sink area of 375 km2 (Table 4) The main body of the braid‐delta was dominated by imbricated progradational seis-mic reflections and developed in the hanging walls of F1 and F2 whereas an alluvial‐plain facies probably developed in the footwall areas of the faults and to the south‐west of the uplifted area (Figure 7f) Although the extent of the delta reached its maximum the thickness of the delta was limited due to the gentle topography resulting in a small delta vol-ume (Table 3)

5 | RELATIONSHIPS BETWEEN THE VARIOUS ELEMENTS OF THE S2S SYSTEM

Quantitative relationships between the various elements of the S2S system have been established through the above‐mentioned calculations A strong positive correlation is clearly present between the rate of tectonic subsidence the average fault activity and the average growth index of the boundary faults F1 and F2 (Figure 8ab) The rate of tectonic subsidence can therefore be used in the following as the pri-mary proxy to represent the intensity of the tectonic activity whereas the rate of fault activity and the growth index are used as secondary proxies

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The tectonic activity and the sediment‐supply rate show a positive relationship (Figures 8c 9a 10a) whereas the tec-tonic activity and the sink area of the basin show a negative relationship (Figures 8d 9b 10b) In contrast the tectonic activity has a positive relationship with the total accommo-dation space (Figures 8e 9c 10c Table 4) There is also a positive relationship between the average sedimentary dip of the fan‐ and braid‐deltas on the one hand and the tectonic activity on the other hand (Figures 8f 9d 10d)

The intensity of the tectonic activity correlates negatively with the extent of the sediment area but positively with the sediment volume (Figures 8g‐h 9e‐f 10e‐f) The different responses of the sediment area and the volume to the tectonic activity are caused by variations in the thicknesses of the sed-imentary units (Table 3)

There is also a positive relationship between the average seismic progradation dip of the fan‐ and braid‐deltas and the tectonic activity (Figures 8i 9g 10g) strong tectonic activ-ity usually formed deltas that are characterized by a chaotic progradational or oblique progradational seismic reflection such as SF 1 and 2 in S‐3 (lower unit) and S‐4 (Figures S3ndashS7) The minimum tectonic activity during Members S‐1 + 2 and D‐2 are reflected by dominantly shingled progradational seismic facies in the delta interior (Figures S10ndashS11)

In addition we find that the sediment area sediment vol-ume and average seismic progradation dip of the fan‐ and braid‐deltas correlate positively with the sediment‐supply rate (Figure 11a b and c) but negatively with the basin sink area (Figure 11d e and f) Both the sediment volume and the average seismic progradation dip of the fan‐ and braid‐deltas

F I G U R E 8 (a‐b) Relationships between the tectonic‐subsidence rate and tectonics (c‐i) Relationships between tectonic activity and sedimentary source‐to‐sink parameters Input data regarding the tectonic activity are from Table 2 those regarding the source‐to‐sink parameters data are from Tables 3 and 4 Regression‐line equations and coefficients of determination (R2) are shown for all diagrams

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show a positive relationship with the total accommodation space (Figure 11hi) However no obvious relationship ap-pears to be present between the sediment area and the total accommodation space (G) Both the sediment area and the average seismic progradation dip of the fan‐ and braid‐deltas correlate well with the average sedimentary dip of the fan‐ and braid‐deltas (Figure 11km) A poor correlation is found between the sediment volume and the average sedimentary dip of the fan‐ and braid‐deltas

6 | DISCUSSION

61 | Analysis of the influence of tectonic activity on the source area accommodation space geomorphology and sediment supplyA high relief and large drainage area usually can generate a large sediment supply (Leeder Harris amp Kirkby 1998 Syvitski amp Milliman 2007) Although the erosional area for the fan and delta system cannot be estimated because of the

limited data coverage the exposed area within the study area can be calculated The calculations show a generally decreas-ing trend of the source area from S‐4 (501 km2) to D‐2 (58 km2 Figure7 Table 4) The calculated exposed area cannot fully represent the true source area however but the evolu-tionary trend of the source area can be used as a proxy to indi-cate the relative influence on the change in sediment volume This trend is consistent with the decrease in sediment volume from S‐4 (2126 km3) to D‐2 (175 km3 Table 2) The relief is difficult to reconstruct in this case but variations in the fault‐activity rate (here taken as the tectonic‐subsidence rate) can create local elevation differences and can therefore be used as proxies for the trends in the relief development The relief shows an overall decreasing trend from S‐4 to D‐2 except for D‐3 this correlates well with the sediment volume (Figure 8h) Although the drainage area of D‐3 was smaller than that of D‐2 because of the high tectonic‐subsidence rate (result-ing in a high relief) D‐3 is thicker and shows a larger sedi-ment volume than the overlying D‐2 (Table 3) D‐3 is thinner than S‐4 + 3 but the larger source area resulted in a larger

F I G U R E 9 General relationships between the average fault‐growth index of F1 and F2 (AFGIF1‐F2) and sedimentary source‐to‐sink parameters The average fault‐growth index of F1 and F2 (AFGIF1‐F2) data in this figure are from Table 2 The source‐to‐sink parameters data are from Table 4 Regression‐line equations and the coefficients of determination are shown in each diagram

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sediment volume and supply rate (Table 3 Figure8ch) Therefore both the fault‐induced relief and the drainage area affected the sediment‐supply rate and the sediment volume in the sink

The changes in accommodation space during the vari-ous phases of the Palaeogene in the south‐western HD are clear from the estimated tectonic subsiding rate (Table 2) The correlations between the intensity of the tectonic activ-ity and the extent of the depositional sink area (Figures 8d 9b 10b) between the intensity of the tectonic activity and the total accommodation space and between the intensity of the tectonic activity and the morphology in the sink area (Figures 8e‐f 9c‐d 10c‐d) clearly show that strong tectonic activity resulted in a larger accommodation capacity of the sink

In particular the main subsiding area tended to form steeper slopes However the extent of the main subsiding sink area diminished (Figure 8d) with increasing tectonic activity which was possibly due to the relatively small sub-siding centre in the tectonically active basins It can thus be deduced that tectonic activity not only controlled the sedi-ment supply and the variation in accommodation space but

also determined the changes in the topography of the sedi-mentary basins and the extent of the main depositional areas in the tectonically active basins

62 | Analysis of the influence of tectonic activity on the size and internal stacking pattern of the delta depositional systemThe above data and considerations indicate that the tectonic activity was closely related to the sediment supply accom-modation space and morphology of the sink area which are possibly the most important factors affecting the extent and stacking pattern of the sedimentary facies (cf Cope et al 2010 DeCelles Kapp Ding amp Gehrels 2007 Leeder 2011 Olsen 1997 Simon et al 2017)

Statistical analysis indicates that the sediment‐supply rate has a strong positive correlation with the volume of the depositional system a moderate correlation with the seismic progradational dip in the depositional system and a poor cor-relation with the size of the depositional area (Figure 11a‐c) A larger sink area corresponded to a larger fanbraid‐delta a gentler seismic progradational angle and a reduced volume

F I G U R E 1 0 General relationships between average fault activity rate of F1 and F2 (RFAA‐F1‐F2) and sedimentary source‐to‐sink parameters The average fault activity rate of F1 and F2 (RFAA‐F1‐F2) data in this figure are from Table 2 The source‐to‐sink parameters data are from Table 4 Regression line equations and the coefficients of determination are shown in each diagram

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of the fan or braid‐delta which was possibly related to a re-duced sedimentary dip and thinner sediments (Figure 11d‐f) The total accommodation space in the basin correlates well

with the volume of the depositional system to some degree with the seismic progradational dip and poorly with the ex-tent of the depositional system area (Figure 11g‐i) These

FIGURE 11 Relationships between various parameters involved in the source‐to‐sink system (a‐c) Relationships between sediment supply and characteristics of the depositional system (extent volume and DPSA of the sediments) (d‐f) Relationships between the sink area of the basin and characteristics of the depositional system (g‐i) Relationships between the total accommodation space (AT) and the characteristics of the depositional system (j) Relationship between the accommodation‐spacesediment‐supply ratio (AS) and the DPSA of the sediments (k‐m) Relationships between the sedimentary dip and the characteristics of the depositional system The data regarding sediment supply basin sink area total accommodation space accommodation‐spacesediment‐supply ratio and sedimentary dips are from Table 4 The extent volume and DPSA of the sedimentary facies are from Table 3 Note the seemingly obvious polynomial (quadratic) relationship between the sedimentary dip and the sediment volume (L) The trend line in (L) suggests the following relationships between sediment volume and sedimentary slope in a rift or tectonically active basin (1) a very steep sedimentary slope is unfavourable for sediment accumulation (2) an appropriate sedimentary slope is favourable for preservation of depositional systems eg when the sedimentary slope in (L) is about 25degndash32deg the sediment volume reaches its largest value (3) a very gentle sedimentary slope will lead to a decrease of the sediment volume possibly due to weakening of the drainage system and thinner sediments

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relationships are clear evidence that the size of the sink area controlled the extent of the depositional system during the rifting of the lacustrine basin and that the rate of sediment supply and the accommodation space had a significant in-fluence on the total sedimentary volume as well as on the internal stacking pattern of the depositional system

We here use the ratio of the tectonic‐subsidence rate and the sediment‐supply rate as a proxy to indicate the ratio be-tween accommodation space and sediment‐supply rate (AS) (Table 4) AS has a strong influence on the internal stacking pattern of the depositional systems in the lacustrine rift basin (Figure 11j) This might be because the basin was small and because abundant and rapid material was supplied due

to intense tectonic activity (cf Catuneanu et al 2009 Liro 1993) and a favourable local climate (eg Bohacs Carroll Neal amp Mankiewicz 2000 Perlmutter amp Matthews 1989) The sediment supply still had a significant influence on the main subsidence area of the lacustrine basins and deposi-tional systems

In addition the basin slope significantly influenced the extent of the depositional system (Figure 11k) and had a polynomial relationship with its volume (Figure 11l) This relationship indicates that more intense tectonic activity and a steeper depositional slope were not favourable for sediment accumulation over a large extent in the lacustrine basin On the contrary these sediments were usually transported to a

F I G U R E 1 2 Tectonic differential activities and resulting patterns of the source‐to‐sink system on the south‐western slope of the HD during the Palaeogene (a) Development during phases of intense tectonics (Member 4 to the lower part of Member 3 of the Shahejie Fm) (b) Development during phases of somewhat less tectonic activity (middle part of Member 3 of the Shahejie Fm and Member 3 of the Dongying Fm) (c) Development during phases of weak tectonic activity (Members 1 and 2 of the Shahejie Fm and Member 2 of the Dongying Fm) The intensity of tectonic activity in the lacustrine rift basin had a significant influence on the development and extent of each unit of the source‐to‐sink system as well as on the type and dimensions of the depositional systems The present study indicates that probably sublacustrine fans developed (see for example Figure S4b) during phases with relatively strong tectonic activity This is not really clear from the seismic‐reflection data but possibly due to the small sizes of these sublacustrine fans Moreover lithofacies and core data are not available for the south‐western part of the study area The present contribution therefore focuses on the fan‐deltas and braid‐deltas regarding the sedimentary facies analysis the sublacustrine fans that probably developed in the deep or semi‐deep lake are presented just as a likely feature

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relatively small sink area with a fairly large accommodation space Finally stronger tectonic activity resulted in steeper depositional slopes (Figure 8f) which further controlled the hydrodynamic conditions and differential discharge when the sediments were deposited The strong correlation between the depositional slope and the deltas dip (Figure 11m) suggests that the differences in topography due to tectonics must be considered as one of the most critical factors that controlled the internal stacking pattern of the delta deposits

63 | Significance of the present study for other source‐to‐sink systems of lacustrine rift basins

631 | Summary of the source‐to‐sink systems in the HDIn lacustrine rift basins the tectonic setting is probably the main factor that determines the development of the S2S sys-tem but differential tectonic activities lead to variations in the basic characteristics of the S2S system Tectonic activity was most intense during S‐3 (lower unit) and during S‐4 and caused both a strong uplift of the source area and the devel-opment of depressions in the basin that formed a sink (Figure 12a) Strong tectonic activity in the S2S system during these time‐spans led to a high sediment‐supply rate steeper slopes a larger accommodation space and deposition of several fan‐deltas that are characterized by a fairly steep seismic progra-dational angle

The tectonic activity decreased during S‐3 (middle unit) and during D‐3 The S2S system that was present during this time‐span mainly concerned a rising area that shifted south-wards developing an alluvial plain between the erosional area and the sink area thus increasing the distance from source to sink (Figure 12b) Simultaneously the sediment‐supply rate and the accommodation space also changed and braid‐deltas could thus develop with larger volumes and gentler seismic progradational dips

Tectonic activity was clearly less intense during S‐1 + 2 and D‐2 The rising area had shifted further southwards cre-ating a wider alluvial plain connecting the source area to the sink in the HD (Figure 12c) At this stage stable tectonic activity led to relatively less sediment supply a gentle slope less accommodation space and the development of several braid‐deltas with a fairly gentle seismic progradational angle

632 | Wider implications and limitationsSoslashmme et al (2009) proposed that the elements of S2S sys-tems are genetically related and that quantitative correla-tions exist among these elements Other studies also suggest that the size of the drainage basin is correlated to the size of the fan developing on the basin floor (eg Blum et al

2017 Snedden et al 2018) and to the size of the river chan-nel (eg Milliken et al 2018) Helland‐Hansen Soslashmme Martinsen Lunt and Thurmond (2016) suggest a simplified subdivision of S2S systems into three main categories (a) Steep‐Short‐Deep (steep onshore and offshore gradients short distance between source and sink and deep offshore waters) (b) Wide‐Deep (low‐gradient shelf‐catchment area and deep offshore waters) and (c) Wide‐Shallow (relatively shallow offshore waters and a wide low‐gradient catchment area) systems

The present study indicates that the alluvial plain roughly corresponds to the alluvial‐shelf unit in marine basins al-though with a much smaller width and extent in the lacustrine rift basins than would have been the case on a continental shelf Faults F1 and F2 along the slope belt correspond to the slope of classical S2S systems whereas the shore‐shallow‐deep lake area can be compared with the basin floor (Soslashmme et al 2009) S‐4 and S‐3 (lower unit) can be roughly clas-sified as Steep‐Short‐Deep systems whereas the overlying S‐1 + 2and D‐2 can be classified as the Wide‐Shallow sys-tems that Helland‐Hansen et al (2016) defined During the deposition of S‐4 and S‐3 (lower unit) the strong tectonic activity caused a high relief of the source area a narrow allu-vial plain and a relatively deep lake The subsequently wan-ing tectonic activity resulted in a lower relief of the source area a wider alluvial plain and a shallower lake Although the absolute values of these elements in lacustrine basins are much smaller than those of marine basins the ratio between these elements in both settings is comparable Typically in a lacustrine basin a transformation from a Steep‐Short‐Deep system (S‐4 and S‐3 (lower unit)) to a Wide‐Shallow system (S‐1 + 2ampD‐2) occurs within a few million years Although the basin geomorphology has experienced signif-icant changes from S‐4 to D‐2 the quantitative relationships between tectonic activity sediment‐supply rate accommoda-tion space and sedimentary dip of the delta systems did not change significantly (eg Figures 8 and 11) The analytical approaches applied and quantitative relationship established here can help analyse other lacustrine basins worldwide and may even act as a reference for the analysis of marine basins

Our study focuses mainly on the influences of tectonic activity on the elements of the depositional sink Other pa-rameters (eg climate and lithology) were not considered in detail Studies on modern and ancient systems suggest that the climate and lithology also have a great influence on the sediment supply and distribution in the basin (eg Carroll Chetel amp Smith 2006 Hovius amp Leeder 1998 Syvitski amp Milliman 2007 Zhang et al 2018) For exam-ple climate variations between glacials and inter‐glacials have resulted in largely different sediment‐supply rates and in significant differences in the sizes of the Quaternary sub-marine fans in the north‐western Gulf of Mexico (Blum amp Hattier‐Womack 2009) We acknowledge the importance

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of climate and lithology for S2S systems and we are con-vinced that these elements can significantly affect the S2S systems in other cases(eg modern systems and systems influenced by glacialinterglacial alternations) These fac-tors were not really relevant for the present study however because no significant differences in lithology were present in the source areas and because we focus on the changes at a million‐year scale which implies that the tectonic ac-tivity has a first‐order control on the development of S2S elements in the investigated rift basin

7 | CONCLUSIONS

We have calculated the tectonic‐subsidence history the growth index and the activity rate of the main boundary faults (F1 and F2) and various S2S parameters of six Palaeogene rock units on the south‐western slope of the HD Based on the values found for these parameters quantitative corre-lation were established for the tectonic activity and other S2Sparameters in the basinal sink This leads to the follow-ing conclusions

1 The positive correlation between the intensity of fault activity and the tectonic‐subsidence rate is a strong indication for a distinct control by the tectonic activity of the syn‐depositional rifting of the tectonically active basin

2 The tectonic activity was quantitatively related to the sediment supply accommodation space and morphology of the sink area The relationship between tectonic activ-ity and depositional systems is reflected by changes in critical factors such as sediment supply accommodation space and dip of the sink area These critical factors were probably the most important factors that led to changes in the size and internal stacking pattern of the sedimentary facies

3 Differential tectonic activity led to changes in the char-acteristics of the S2S system on the south‐western slope of the HD The strongest tectonic activity which oc-curred during S‐3 (lower unit) and during S‐4 led to the largest provenance area adjacent to the sink area to a high sediment‐supply rate to steeper slopes to a larger accommodation space and controlled the development of several fan‐deltas Diminished tectonic activity dur-ing S‐3 (middle unit) and during D‐3 led to a decrease in uplift an increased width of the alluvial plain an in-creased transport distance a decrease in the sediment‐supply rate and accommodation space and resulted in the development of braid‐deltas with a large volume During S‐1 + 2 and D‐2 stable tectonic activity led to a lower sediment‐supply rate a gentle depositional slope and a smaller accommodation space resulting in the

development of several braid‐deltas with gentler seis-mic progradational angles

4 The analytical approaches applied and the quantitative re-lationships established here can help analyse other lacus-trine basins worldwide and may even act as a reference for the study of marine basins

ACKNOWLEDGEMENTS

We thank Dr Sarah Boulton and Dr Chenlin Gong as well as the Associate Editor of Basin Research Dr Craig Magee for their constructive comments on the manuscript This study was funded by the National Science and Technology Major Project (Exploration Technologies for Offshore Hidden OilGas) (project no 2016ZX05024‐003‐003) the National Natural Science Foundations of China (project no 41676050) and the Fundamental Research Funds for the Central Universities (2652014037)

REFERENCES

Allen P A (2008a) From landscapes into geological history Nature 451 274ndash276 https doiorg101038natur e06586

Allen P A (2008b) Time scales of tectonic landscapes and their sed-iment routing systems In Landscape evolution Denudation cli-mate and tectonics over different time and space scales (Ed by Gallagher K Jones S J amp Wainwright J) Geological Society London Special Publications 296 7ndash28

Allen P A Armitage J J Carter A Duller R A Michael N A Sinclair H D hellip Whittaker A C (2013) The Qs problem Sediment volumetric balance of proximal foreland basin systems Sedimentology 60 102ndash130

Amorosi A Maselli V amp Trincardi F (2016) Onshore to offshore anatomy of a late Quaternary source‐to‐sink system (Po Plain‐Adriatic Sea Italy) Earth‐Science Reviews 153 212ndash237 https doiorg101016jearsc irev201510010

Anderson J B Wallace D J Simms A R Rodriguez A B Weight R W R amp Taha Z P (2016) Recycling sediments between source and sink during a eustatic cycle Systems of late Quaternary northwestern Gulf of Mexico Basin Earth‐Science Reviews 153 111ndash138 https doiorg101016jearsc irev201510014

Anthony E J amp Julian M (1999) Source‐to‐sink sediment trans-fers environmental engineering and hazard mitigation in the steep Var River catchment French Riviera southeastern France Geomorphology 31 337ndash354 https doiorg101016S0169-555X(99)00088-4

Athy L F (1930) Density porosity and compaction of sedimentary rocks AAPG Bulletin 14 1ndash24

Bhattacharya J P Copeland P Lawton T F amp Holbrook J (2016) Estimation of source area river palaeo‐discharge palaeoslope and sediment budgets of linked deep‐time depositional systems and im-plications for hydrocarbon potential Earth‐Science Reviews 153 77ndash110

Blum M D amp Hattier‐Womack J (2009) Climate change sea‐level change and fluvial sediment supply to deepwater depositional

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4 | ELEMENTS OF THE S2S SYSTEM

41 | Analysis of the seismic facies and stacking pattern of the main sedimentary faciesA comprehensive analysis of seismic data cores cutting log-gings and well‐logging curves by Liu Xia et al (2015a) in-dicated that the Palaeogene depositional systems of the HD included fan‐deltas braid‐deltas lake margins deep lakes etc The fan‐ and braid‐deltas have been chosen for a detailed seismic study that must reveal their internal texture and their stacking patterns Analysis of the progradational seismic‐re-flection types and of the seismic progradational dip is particu-larly helpful for a better understanding of the hydrodynamic conditions and sedimentary processes that resulted in these depositional systems Because the facies interpretation in this area has been done before and is not the focus of this work we here mainly describe the internal texture and their stack-ing patterns of the main sedimentary facies

The major facies of S‐4 is interpreted as a fan‐delta It is dominated by Seismic Facies 1 which is characterized by discontinuous to continuous low‐ to high‐amplitude and chaotic progradational seismic reflections (Figures S3ndashS6 Table 1) The average dip of the progradational seismic event is about 365deg (Table 3) Three lithofacies are associated with Seismic Facies 1 (Table 1) The coarser lithofacies 1 represents a fan‐delta front whereas the finer lithofacies 2 and 3 are prodelta deposits The overall coarsening‐upward succession facies stacking pattern (Figure 6a) discontinuous and chaotic seismic reflections and relatively steep slope of Seismic Facies 1 suggest a fan‐delta system developed under strong hydrodynamic conditions (Mitchum et al 1977)

The fan‐delta of the lower part of Member 3 of the Shahejie Fm (S‐3 [lower unit]) is dominated by Seismic Facies 2 which is characterized by chaotic progradational to oblique progradational seismic characteristics It has a typical wedge shape and is composed of two seismic‐reflection seg-ments (a) a moderately continuous low‐ to high‐amplitude chaotic seismic‐reflection segment located near boundary fault F2 and (b) a continuous moderate‐ to high‐amplitude and oblique progradational seismic reflection in a basinward direction (Figure S7 Table 1) No obvious upper or lower segments occur in SF 2 and the dip of the progradational seismic event in this segment is also relatively steep viz 305deg (Table 3)

The middle part of Member 3 of the Shahejie Fm (S‐3 [middle unit]) is characterized by a low‐ to moderate‐con-tinuous low‐amplitude and oblique progradational seismic reflection (Seismic Facies 3) and is interpreted as a braid‐delta (Figure S8 Table 1) The progradational seismic events are parallel or sub‐parallel to each other and dip less (aver-age 225deg) than Seismic Facies 1 and 2 (Table 3) Seismic

Facies 3 is associated with four lithofacies (Figure 6b Table 1) in Well T25 The complete succession of the braid‐delta consists of gravely to coarse‐grained sandstone (lithofacies 1) at the base (Figure 6f) massive bedded medium‐ to fine‐grained sandstones (lithofacies 2) and grey mudstones inter-bedded with grey fine sandstones and grey muddy siltstones (lithofacies 3) in the middle (Figures 6g and 6h) and thick dark grey mudstones (lithofacies 4) at the top (Figure 6i)

Member 3 of the Dongying Fm (D‐3) is characterized by Seismic Facies 4 a typically composite seismic progra-dation reflection configuration representing a braid‐delta system (Figure S9 Table 1) Seismic Facies 4 is composed of highly continuous moderate‐ to high‐amplitude and pro-gradational seismic reflections that represent well‐developed deltaic topsets and bottomsets The topset segments of SF 4 are nearly horizontal or dip only gently (Table 3) The foreset segments form thicker lenses with small depositional angles The oblique progradational part of this seismic facies is sim-ilar to that in Seismic Facies 3 and usually developed at the basinward front end of Seismic Facies 3 The lithology of Seismic Facies 4 is dominated by greyish white to white fine‐grained sandstones and siltstones The lithofacies association is characterized by coarsening‐upward sedimentary cycles (Figure 6c Table 1) Convolute bedding and abundant diam-ictites are present on top of the fine sandstones (Figure 6j‐k)

Both braid‐deltas in the Members 1 + 2 of th Shahejie Fm (S‐1 + 2) and Member 2 of the Dongying Fm (D‐2) show moderately continuous moderate‐amplitude and shin-gled‐like progradational seismic reflections (Seismic Facies 5 Figures S10ndashS11 Table 1) It shows a thin prograding seis-mic pattern commonly with parallel upper and lower bound-aries (cf Mitchum et al 1977) The successive internal progradational seismic events overlap each other between the upper and lower segments with a gentle dip of 152degndash193deg (Table 3) The lithofacies are mostly composed of several coarsening‐upward cycles (Figure 6d Table 1) Each cycle is composed of dark grey mudstones and grey to whitish‐grey medium‐ to fine‐grained sandstones Several coarsening‐up-ward lithofacies are mainly developed in D‐2 (Figure 6e Table 1)

42 | Analysis of the tectonic activityThe normal faults F1 and F2 selected to calculate the fault activity dipping to the north and running approximately E‐W are important boundary faults on the south‐western margin of the HD The tectonic‐subsidence rate fault‐growth index and fault‐activity rate were used as proxies to indicate the tectonic intensity (Figure 3 S2 Table 2) S‐4 and S‐3 (lower unit) have the highest subsidence rate (300ndash355 mMa) the highest fault‐growth index (292ndash343 mMa) and the highest fault‐activity rate (10647ndash11869 mMa) among the studied intervals whereas the overlying S‐3 (middle

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unit) and S‐1 + 2 are characterized by a much lower sub-sidence rate and fault‐growth index and fault‐activity rate D‐3 had again a high subsidence rate (190 mMa) and an average fault‐growth index (210 mMa) and fault‐activity rate (9344 mMa) The uppermost studied interval D‐2 had a much lower subsidence rate (60 mMa) growth index (136 mMa) and fault‐activity rate (3451 mMa) than the un-derlying unit Generally the analysis of the subsidence rate average fault‐growth index and fault‐activity rate indicates two phases of alternating strong tectonic activity and tectoni-cally stable conditions

43 | Palaeogeomorphology distribution and dimensions of the main depositional systemsDepositional systems of each depositional phase of the Palaeogene on the south‐western slope of the HD were com-piled through seismic facies identification of 3‐D seismic data and compilation of maps with the current thicknesses of the main target intervals based on the study by Liu Xia et al (2015a) that combined a correction for the depth of burial with an interpretation of the sedimentary facies The basins sink area on the south‐western slope of the HD was estimated on the basis of a palaeogeomorphological reconstruction The distribution of the depositional system is closely related to the evolution of the palaeogeomorphology and therefore we describe both the distribution of the depositional system and the palaeogeomorphology here

The palaeogeography of S‐4 is characterized by the larg-est extent of the uplifted areas of all studied intervals The depositional area is small and scattered (Figure 7a Table 4) Faults F1 and F2 mark the boundaries between erosional and depositional regions The elevated footwalls of the faults were erosional areas and located adjacent to the hanging walls whereas the hanging walls were low‐lying depositional areas The sedimentary facies analysis indicates a fan‐delta developed here (Figure 7a) Calculations indicate that the sedimentary dip of the four fan‐deltas was uncommonly high (about 463deg) The extent and thickness of the fan‐deltas di-minished towards the basin margin (Tables 34)

The tectonically‐induced morphology of S‐3 (lower unit) shows a similar pattern to that of the underlying S‐4 The depositional and erosional areas were also controlled by the active faults F1 and F2The HD deepened from west to east with the deepest area located just along the fault margin The depositional centre was located north of the hanging wall of F2 and became infilled by a fan‐delta (Figure 7b) The aver-age sedimentary dip of the fan‐delta is 303deg The extent of the fan‐delta was larger than that of S‐4 (Table 34)

During deposition of S‐3 (middle unit) the uplifted source area shifted southwards and the depression expanded A major depositional sink was located north of the hanging wall of F2 (Figure 7c Table 4) Elevation differences existed

between the footwalls and the hanging walls of F1 and F2 although the topography was obviously gentler during this time‐span A braided fluvial area developed at the footwalls of the faults whereas a braid‐delta developed mainly on the hanging wall of F2 and the northern depositional centre (Figure 7c) The braid‐delta had a fairly large extent and an average depositional dip of 119deg (Tables 34)

During S‐1 + 2 the elevated erosional area shifted farther southwards and the entire south‐western area had a low to-pography An alluvial plain developed south of the footwalls of the faults whereas a braid‐delta developed at the hanging walls and in the depression with a very gentle slope of 096deg (Table 4 Figure 7d) The depositional system was dominated by a fairly thin delta body and a braid‐delta with a much larger extent (Table 3)

During the deposition of D‐3 the topography of the foot-wall areas and of the area south of the provenance area was similar to that during the underlying S‐1 + 2 The slope was steep (187deg) in the hanging walls of the boundary faults however and the depositional area increased to 198 km2 which provided an excellent condition for the deposition of a large braid‐delta (Figure 7e Table 4) This braid‐delta had a NE‐SW orientation and covered an area of 142 km2 its average thickness is some 200 m which results in the largest delta volume in the Palaeogene on the south‐western slope of the HD (Table 3)

The palaeogeomorphological reconstruction of D‐2 shows a gentler topography in the entire south‐western HD with a sink area of 375 km2 (Table 4) The main body of the braid‐delta was dominated by imbricated progradational seis-mic reflections and developed in the hanging walls of F1 and F2 whereas an alluvial‐plain facies probably developed in the footwall areas of the faults and to the south‐west of the uplifted area (Figure 7f) Although the extent of the delta reached its maximum the thickness of the delta was limited due to the gentle topography resulting in a small delta vol-ume (Table 3)

5 | RELATIONSHIPS BETWEEN THE VARIOUS ELEMENTS OF THE S2S SYSTEM

Quantitative relationships between the various elements of the S2S system have been established through the above‐mentioned calculations A strong positive correlation is clearly present between the rate of tectonic subsidence the average fault activity and the average growth index of the boundary faults F1 and F2 (Figure 8ab) The rate of tectonic subsidence can therefore be used in the following as the pri-mary proxy to represent the intensity of the tectonic activity whereas the rate of fault activity and the growth index are used as secondary proxies

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The tectonic activity and the sediment‐supply rate show a positive relationship (Figures 8c 9a 10a) whereas the tec-tonic activity and the sink area of the basin show a negative relationship (Figures 8d 9b 10b) In contrast the tectonic activity has a positive relationship with the total accommo-dation space (Figures 8e 9c 10c Table 4) There is also a positive relationship between the average sedimentary dip of the fan‐ and braid‐deltas on the one hand and the tectonic activity on the other hand (Figures 8f 9d 10d)

The intensity of the tectonic activity correlates negatively with the extent of the sediment area but positively with the sediment volume (Figures 8g‐h 9e‐f 10e‐f) The different responses of the sediment area and the volume to the tectonic activity are caused by variations in the thicknesses of the sed-imentary units (Table 3)

There is also a positive relationship between the average seismic progradation dip of the fan‐ and braid‐deltas and the tectonic activity (Figures 8i 9g 10g) strong tectonic activ-ity usually formed deltas that are characterized by a chaotic progradational or oblique progradational seismic reflection such as SF 1 and 2 in S‐3 (lower unit) and S‐4 (Figures S3ndashS7) The minimum tectonic activity during Members S‐1 + 2 and D‐2 are reflected by dominantly shingled progradational seismic facies in the delta interior (Figures S10ndashS11)

In addition we find that the sediment area sediment vol-ume and average seismic progradation dip of the fan‐ and braid‐deltas correlate positively with the sediment‐supply rate (Figure 11a b and c) but negatively with the basin sink area (Figure 11d e and f) Both the sediment volume and the average seismic progradation dip of the fan‐ and braid‐deltas

F I G U R E 8 (a‐b) Relationships between the tectonic‐subsidence rate and tectonics (c‐i) Relationships between tectonic activity and sedimentary source‐to‐sink parameters Input data regarding the tectonic activity are from Table 2 those regarding the source‐to‐sink parameters data are from Tables 3 and 4 Regression‐line equations and coefficients of determination (R2) are shown for all diagrams

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show a positive relationship with the total accommodation space (Figure 11hi) However no obvious relationship ap-pears to be present between the sediment area and the total accommodation space (G) Both the sediment area and the average seismic progradation dip of the fan‐ and braid‐deltas correlate well with the average sedimentary dip of the fan‐ and braid‐deltas (Figure 11km) A poor correlation is found between the sediment volume and the average sedimentary dip of the fan‐ and braid‐deltas

6 | DISCUSSION

61 | Analysis of the influence of tectonic activity on the source area accommodation space geomorphology and sediment supplyA high relief and large drainage area usually can generate a large sediment supply (Leeder Harris amp Kirkby 1998 Syvitski amp Milliman 2007) Although the erosional area for the fan and delta system cannot be estimated because of the

limited data coverage the exposed area within the study area can be calculated The calculations show a generally decreas-ing trend of the source area from S‐4 (501 km2) to D‐2 (58 km2 Figure7 Table 4) The calculated exposed area cannot fully represent the true source area however but the evolu-tionary trend of the source area can be used as a proxy to indi-cate the relative influence on the change in sediment volume This trend is consistent with the decrease in sediment volume from S‐4 (2126 km3) to D‐2 (175 km3 Table 2) The relief is difficult to reconstruct in this case but variations in the fault‐activity rate (here taken as the tectonic‐subsidence rate) can create local elevation differences and can therefore be used as proxies for the trends in the relief development The relief shows an overall decreasing trend from S‐4 to D‐2 except for D‐3 this correlates well with the sediment volume (Figure 8h) Although the drainage area of D‐3 was smaller than that of D‐2 because of the high tectonic‐subsidence rate (result-ing in a high relief) D‐3 is thicker and shows a larger sedi-ment volume than the overlying D‐2 (Table 3) D‐3 is thinner than S‐4 + 3 but the larger source area resulted in a larger

F I G U R E 9 General relationships between the average fault‐growth index of F1 and F2 (AFGIF1‐F2) and sedimentary source‐to‐sink parameters The average fault‐growth index of F1 and F2 (AFGIF1‐F2) data in this figure are from Table 2 The source‐to‐sink parameters data are from Table 4 Regression‐line equations and the coefficients of determination are shown in each diagram

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sediment volume and supply rate (Table 3 Figure8ch) Therefore both the fault‐induced relief and the drainage area affected the sediment‐supply rate and the sediment volume in the sink

The changes in accommodation space during the vari-ous phases of the Palaeogene in the south‐western HD are clear from the estimated tectonic subsiding rate (Table 2) The correlations between the intensity of the tectonic activ-ity and the extent of the depositional sink area (Figures 8d 9b 10b) between the intensity of the tectonic activity and the total accommodation space and between the intensity of the tectonic activity and the morphology in the sink area (Figures 8e‐f 9c‐d 10c‐d) clearly show that strong tectonic activity resulted in a larger accommodation capacity of the sink

In particular the main subsiding area tended to form steeper slopes However the extent of the main subsiding sink area diminished (Figure 8d) with increasing tectonic activity which was possibly due to the relatively small sub-siding centre in the tectonically active basins It can thus be deduced that tectonic activity not only controlled the sedi-ment supply and the variation in accommodation space but

also determined the changes in the topography of the sedi-mentary basins and the extent of the main depositional areas in the tectonically active basins

62 | Analysis of the influence of tectonic activity on the size and internal stacking pattern of the delta depositional systemThe above data and considerations indicate that the tectonic activity was closely related to the sediment supply accom-modation space and morphology of the sink area which are possibly the most important factors affecting the extent and stacking pattern of the sedimentary facies (cf Cope et al 2010 DeCelles Kapp Ding amp Gehrels 2007 Leeder 2011 Olsen 1997 Simon et al 2017)

Statistical analysis indicates that the sediment‐supply rate has a strong positive correlation with the volume of the depositional system a moderate correlation with the seismic progradational dip in the depositional system and a poor cor-relation with the size of the depositional area (Figure 11a‐c) A larger sink area corresponded to a larger fanbraid‐delta a gentler seismic progradational angle and a reduced volume

F I G U R E 1 0 General relationships between average fault activity rate of F1 and F2 (RFAA‐F1‐F2) and sedimentary source‐to‐sink parameters The average fault activity rate of F1 and F2 (RFAA‐F1‐F2) data in this figure are from Table 2 The source‐to‐sink parameters data are from Table 4 Regression line equations and the coefficients of determination are shown in each diagram

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of the fan or braid‐delta which was possibly related to a re-duced sedimentary dip and thinner sediments (Figure 11d‐f) The total accommodation space in the basin correlates well

with the volume of the depositional system to some degree with the seismic progradational dip and poorly with the ex-tent of the depositional system area (Figure 11g‐i) These

FIGURE 11 Relationships between various parameters involved in the source‐to‐sink system (a‐c) Relationships between sediment supply and characteristics of the depositional system (extent volume and DPSA of the sediments) (d‐f) Relationships between the sink area of the basin and characteristics of the depositional system (g‐i) Relationships between the total accommodation space (AT) and the characteristics of the depositional system (j) Relationship between the accommodation‐spacesediment‐supply ratio (AS) and the DPSA of the sediments (k‐m) Relationships between the sedimentary dip and the characteristics of the depositional system The data regarding sediment supply basin sink area total accommodation space accommodation‐spacesediment‐supply ratio and sedimentary dips are from Table 4 The extent volume and DPSA of the sedimentary facies are from Table 3 Note the seemingly obvious polynomial (quadratic) relationship between the sedimentary dip and the sediment volume (L) The trend line in (L) suggests the following relationships between sediment volume and sedimentary slope in a rift or tectonically active basin (1) a very steep sedimentary slope is unfavourable for sediment accumulation (2) an appropriate sedimentary slope is favourable for preservation of depositional systems eg when the sedimentary slope in (L) is about 25degndash32deg the sediment volume reaches its largest value (3) a very gentle sedimentary slope will lead to a decrease of the sediment volume possibly due to weakening of the drainage system and thinner sediments

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relationships are clear evidence that the size of the sink area controlled the extent of the depositional system during the rifting of the lacustrine basin and that the rate of sediment supply and the accommodation space had a significant in-fluence on the total sedimentary volume as well as on the internal stacking pattern of the depositional system

We here use the ratio of the tectonic‐subsidence rate and the sediment‐supply rate as a proxy to indicate the ratio be-tween accommodation space and sediment‐supply rate (AS) (Table 4) AS has a strong influence on the internal stacking pattern of the depositional systems in the lacustrine rift basin (Figure 11j) This might be because the basin was small and because abundant and rapid material was supplied due

to intense tectonic activity (cf Catuneanu et al 2009 Liro 1993) and a favourable local climate (eg Bohacs Carroll Neal amp Mankiewicz 2000 Perlmutter amp Matthews 1989) The sediment supply still had a significant influence on the main subsidence area of the lacustrine basins and deposi-tional systems

In addition the basin slope significantly influenced the extent of the depositional system (Figure 11k) and had a polynomial relationship with its volume (Figure 11l) This relationship indicates that more intense tectonic activity and a steeper depositional slope were not favourable for sediment accumulation over a large extent in the lacustrine basin On the contrary these sediments were usually transported to a

F I G U R E 1 2 Tectonic differential activities and resulting patterns of the source‐to‐sink system on the south‐western slope of the HD during the Palaeogene (a) Development during phases of intense tectonics (Member 4 to the lower part of Member 3 of the Shahejie Fm) (b) Development during phases of somewhat less tectonic activity (middle part of Member 3 of the Shahejie Fm and Member 3 of the Dongying Fm) (c) Development during phases of weak tectonic activity (Members 1 and 2 of the Shahejie Fm and Member 2 of the Dongying Fm) The intensity of tectonic activity in the lacustrine rift basin had a significant influence on the development and extent of each unit of the source‐to‐sink system as well as on the type and dimensions of the depositional systems The present study indicates that probably sublacustrine fans developed (see for example Figure S4b) during phases with relatively strong tectonic activity This is not really clear from the seismic‐reflection data but possibly due to the small sizes of these sublacustrine fans Moreover lithofacies and core data are not available for the south‐western part of the study area The present contribution therefore focuses on the fan‐deltas and braid‐deltas regarding the sedimentary facies analysis the sublacustrine fans that probably developed in the deep or semi‐deep lake are presented just as a likely feature

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relatively small sink area with a fairly large accommodation space Finally stronger tectonic activity resulted in steeper depositional slopes (Figure 8f) which further controlled the hydrodynamic conditions and differential discharge when the sediments were deposited The strong correlation between the depositional slope and the deltas dip (Figure 11m) suggests that the differences in topography due to tectonics must be considered as one of the most critical factors that controlled the internal stacking pattern of the delta deposits

63 | Significance of the present study for other source‐to‐sink systems of lacustrine rift basins

631 | Summary of the source‐to‐sink systems in the HDIn lacustrine rift basins the tectonic setting is probably the main factor that determines the development of the S2S sys-tem but differential tectonic activities lead to variations in the basic characteristics of the S2S system Tectonic activity was most intense during S‐3 (lower unit) and during S‐4 and caused both a strong uplift of the source area and the devel-opment of depressions in the basin that formed a sink (Figure 12a) Strong tectonic activity in the S2S system during these time‐spans led to a high sediment‐supply rate steeper slopes a larger accommodation space and deposition of several fan‐deltas that are characterized by a fairly steep seismic progra-dational angle

The tectonic activity decreased during S‐3 (middle unit) and during D‐3 The S2S system that was present during this time‐span mainly concerned a rising area that shifted south-wards developing an alluvial plain between the erosional area and the sink area thus increasing the distance from source to sink (Figure 12b) Simultaneously the sediment‐supply rate and the accommodation space also changed and braid‐deltas could thus develop with larger volumes and gentler seismic progradational dips

Tectonic activity was clearly less intense during S‐1 + 2 and D‐2 The rising area had shifted further southwards cre-ating a wider alluvial plain connecting the source area to the sink in the HD (Figure 12c) At this stage stable tectonic activity led to relatively less sediment supply a gentle slope less accommodation space and the development of several braid‐deltas with a fairly gentle seismic progradational angle

632 | Wider implications and limitationsSoslashmme et al (2009) proposed that the elements of S2S sys-tems are genetically related and that quantitative correla-tions exist among these elements Other studies also suggest that the size of the drainage basin is correlated to the size of the fan developing on the basin floor (eg Blum et al

2017 Snedden et al 2018) and to the size of the river chan-nel (eg Milliken et al 2018) Helland‐Hansen Soslashmme Martinsen Lunt and Thurmond (2016) suggest a simplified subdivision of S2S systems into three main categories (a) Steep‐Short‐Deep (steep onshore and offshore gradients short distance between source and sink and deep offshore waters) (b) Wide‐Deep (low‐gradient shelf‐catchment area and deep offshore waters) and (c) Wide‐Shallow (relatively shallow offshore waters and a wide low‐gradient catchment area) systems

The present study indicates that the alluvial plain roughly corresponds to the alluvial‐shelf unit in marine basins al-though with a much smaller width and extent in the lacustrine rift basins than would have been the case on a continental shelf Faults F1 and F2 along the slope belt correspond to the slope of classical S2S systems whereas the shore‐shallow‐deep lake area can be compared with the basin floor (Soslashmme et al 2009) S‐4 and S‐3 (lower unit) can be roughly clas-sified as Steep‐Short‐Deep systems whereas the overlying S‐1 + 2and D‐2 can be classified as the Wide‐Shallow sys-tems that Helland‐Hansen et al (2016) defined During the deposition of S‐4 and S‐3 (lower unit) the strong tectonic activity caused a high relief of the source area a narrow allu-vial plain and a relatively deep lake The subsequently wan-ing tectonic activity resulted in a lower relief of the source area a wider alluvial plain and a shallower lake Although the absolute values of these elements in lacustrine basins are much smaller than those of marine basins the ratio between these elements in both settings is comparable Typically in a lacustrine basin a transformation from a Steep‐Short‐Deep system (S‐4 and S‐3 (lower unit)) to a Wide‐Shallow system (S‐1 + 2ampD‐2) occurs within a few million years Although the basin geomorphology has experienced signif-icant changes from S‐4 to D‐2 the quantitative relationships between tectonic activity sediment‐supply rate accommoda-tion space and sedimentary dip of the delta systems did not change significantly (eg Figures 8 and 11) The analytical approaches applied and quantitative relationship established here can help analyse other lacustrine basins worldwide and may even act as a reference for the analysis of marine basins

Our study focuses mainly on the influences of tectonic activity on the elements of the depositional sink Other pa-rameters (eg climate and lithology) were not considered in detail Studies on modern and ancient systems suggest that the climate and lithology also have a great influence on the sediment supply and distribution in the basin (eg Carroll Chetel amp Smith 2006 Hovius amp Leeder 1998 Syvitski amp Milliman 2007 Zhang et al 2018) For exam-ple climate variations between glacials and inter‐glacials have resulted in largely different sediment‐supply rates and in significant differences in the sizes of the Quaternary sub-marine fans in the north‐western Gulf of Mexico (Blum amp Hattier‐Womack 2009) We acknowledge the importance

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of climate and lithology for S2S systems and we are con-vinced that these elements can significantly affect the S2S systems in other cases(eg modern systems and systems influenced by glacialinterglacial alternations) These fac-tors were not really relevant for the present study however because no significant differences in lithology were present in the source areas and because we focus on the changes at a million‐year scale which implies that the tectonic ac-tivity has a first‐order control on the development of S2S elements in the investigated rift basin

7 | CONCLUSIONS

We have calculated the tectonic‐subsidence history the growth index and the activity rate of the main boundary faults (F1 and F2) and various S2S parameters of six Palaeogene rock units on the south‐western slope of the HD Based on the values found for these parameters quantitative corre-lation were established for the tectonic activity and other S2Sparameters in the basinal sink This leads to the follow-ing conclusions

1 The positive correlation between the intensity of fault activity and the tectonic‐subsidence rate is a strong indication for a distinct control by the tectonic activity of the syn‐depositional rifting of the tectonically active basin

2 The tectonic activity was quantitatively related to the sediment supply accommodation space and morphology of the sink area The relationship between tectonic activ-ity and depositional systems is reflected by changes in critical factors such as sediment supply accommodation space and dip of the sink area These critical factors were probably the most important factors that led to changes in the size and internal stacking pattern of the sedimentary facies

3 Differential tectonic activity led to changes in the char-acteristics of the S2S system on the south‐western slope of the HD The strongest tectonic activity which oc-curred during S‐3 (lower unit) and during S‐4 led to the largest provenance area adjacent to the sink area to a high sediment‐supply rate to steeper slopes to a larger accommodation space and controlled the development of several fan‐deltas Diminished tectonic activity dur-ing S‐3 (middle unit) and during D‐3 led to a decrease in uplift an increased width of the alluvial plain an in-creased transport distance a decrease in the sediment‐supply rate and accommodation space and resulted in the development of braid‐deltas with a large volume During S‐1 + 2 and D‐2 stable tectonic activity led to a lower sediment‐supply rate a gentle depositional slope and a smaller accommodation space resulting in the

development of several braid‐deltas with gentler seis-mic progradational angles

4 The analytical approaches applied and the quantitative re-lationships established here can help analyse other lacus-trine basins worldwide and may even act as a reference for the study of marine basins

ACKNOWLEDGEMENTS

We thank Dr Sarah Boulton and Dr Chenlin Gong as well as the Associate Editor of Basin Research Dr Craig Magee for their constructive comments on the manuscript This study was funded by the National Science and Technology Major Project (Exploration Technologies for Offshore Hidden OilGas) (project no 2016ZX05024‐003‐003) the National Natural Science Foundations of China (project no 41676050) and the Fundamental Research Funds for the Central Universities (2652014037)

REFERENCES

Allen P A (2008a) From landscapes into geological history Nature 451 274ndash276 https doiorg101038natur e06586

Allen P A (2008b) Time scales of tectonic landscapes and their sed-iment routing systems In Landscape evolution Denudation cli-mate and tectonics over different time and space scales (Ed by Gallagher K Jones S J amp Wainwright J) Geological Society London Special Publications 296 7ndash28

Allen P A Armitage J J Carter A Duller R A Michael N A Sinclair H D hellip Whittaker A C (2013) The Qs problem Sediment volumetric balance of proximal foreland basin systems Sedimentology 60 102ndash130

Amorosi A Maselli V amp Trincardi F (2016) Onshore to offshore anatomy of a late Quaternary source‐to‐sink system (Po Plain‐Adriatic Sea Italy) Earth‐Science Reviews 153 212ndash237 https doiorg101016jearsc irev201510010

Anderson J B Wallace D J Simms A R Rodriguez A B Weight R W R amp Taha Z P (2016) Recycling sediments between source and sink during a eustatic cycle Systems of late Quaternary northwestern Gulf of Mexico Basin Earth‐Science Reviews 153 111ndash138 https doiorg101016jearsc irev201510014

Anthony E J amp Julian M (1999) Source‐to‐sink sediment trans-fers environmental engineering and hazard mitigation in the steep Var River catchment French Riviera southeastern France Geomorphology 31 337ndash354 https doiorg101016S0169-555X(99)00088-4

Athy L F (1930) Density porosity and compaction of sedimentary rocks AAPG Bulletin 14 1ndash24

Bhattacharya J P Copeland P Lawton T F amp Holbrook J (2016) Estimation of source area river palaeo‐discharge palaeoslope and sediment budgets of linked deep‐time depositional systems and im-plications for hydrocarbon potential Earth‐Science Reviews 153 77ndash110

Blum M D amp Hattier‐Womack J (2009) Climate change sea‐level change and fluvial sediment supply to deepwater depositional

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unit) and S‐1 + 2 are characterized by a much lower sub-sidence rate and fault‐growth index and fault‐activity rate D‐3 had again a high subsidence rate (190 mMa) and an average fault‐growth index (210 mMa) and fault‐activity rate (9344 mMa) The uppermost studied interval D‐2 had a much lower subsidence rate (60 mMa) growth index (136 mMa) and fault‐activity rate (3451 mMa) than the un-derlying unit Generally the analysis of the subsidence rate average fault‐growth index and fault‐activity rate indicates two phases of alternating strong tectonic activity and tectoni-cally stable conditions

43 | Palaeogeomorphology distribution and dimensions of the main depositional systemsDepositional systems of each depositional phase of the Palaeogene on the south‐western slope of the HD were com-piled through seismic facies identification of 3‐D seismic data and compilation of maps with the current thicknesses of the main target intervals based on the study by Liu Xia et al (2015a) that combined a correction for the depth of burial with an interpretation of the sedimentary facies The basins sink area on the south‐western slope of the HD was estimated on the basis of a palaeogeomorphological reconstruction The distribution of the depositional system is closely related to the evolution of the palaeogeomorphology and therefore we describe both the distribution of the depositional system and the palaeogeomorphology here

The palaeogeography of S‐4 is characterized by the larg-est extent of the uplifted areas of all studied intervals The depositional area is small and scattered (Figure 7a Table 4) Faults F1 and F2 mark the boundaries between erosional and depositional regions The elevated footwalls of the faults were erosional areas and located adjacent to the hanging walls whereas the hanging walls were low‐lying depositional areas The sedimentary facies analysis indicates a fan‐delta developed here (Figure 7a) Calculations indicate that the sedimentary dip of the four fan‐deltas was uncommonly high (about 463deg) The extent and thickness of the fan‐deltas di-minished towards the basin margin (Tables 34)

The tectonically‐induced morphology of S‐3 (lower unit) shows a similar pattern to that of the underlying S‐4 The depositional and erosional areas were also controlled by the active faults F1 and F2The HD deepened from west to east with the deepest area located just along the fault margin The depositional centre was located north of the hanging wall of F2 and became infilled by a fan‐delta (Figure 7b) The aver-age sedimentary dip of the fan‐delta is 303deg The extent of the fan‐delta was larger than that of S‐4 (Table 34)

During deposition of S‐3 (middle unit) the uplifted source area shifted southwards and the depression expanded A major depositional sink was located north of the hanging wall of F2 (Figure 7c Table 4) Elevation differences existed

between the footwalls and the hanging walls of F1 and F2 although the topography was obviously gentler during this time‐span A braided fluvial area developed at the footwalls of the faults whereas a braid‐delta developed mainly on the hanging wall of F2 and the northern depositional centre (Figure 7c) The braid‐delta had a fairly large extent and an average depositional dip of 119deg (Tables 34)

During S‐1 + 2 the elevated erosional area shifted farther southwards and the entire south‐western area had a low to-pography An alluvial plain developed south of the footwalls of the faults whereas a braid‐delta developed at the hanging walls and in the depression with a very gentle slope of 096deg (Table 4 Figure 7d) The depositional system was dominated by a fairly thin delta body and a braid‐delta with a much larger extent (Table 3)

During the deposition of D‐3 the topography of the foot-wall areas and of the area south of the provenance area was similar to that during the underlying S‐1 + 2 The slope was steep (187deg) in the hanging walls of the boundary faults however and the depositional area increased to 198 km2 which provided an excellent condition for the deposition of a large braid‐delta (Figure 7e Table 4) This braid‐delta had a NE‐SW orientation and covered an area of 142 km2 its average thickness is some 200 m which results in the largest delta volume in the Palaeogene on the south‐western slope of the HD (Table 3)

The palaeogeomorphological reconstruction of D‐2 shows a gentler topography in the entire south‐western HD with a sink area of 375 km2 (Table 4) The main body of the braid‐delta was dominated by imbricated progradational seis-mic reflections and developed in the hanging walls of F1 and F2 whereas an alluvial‐plain facies probably developed in the footwall areas of the faults and to the south‐west of the uplifted area (Figure 7f) Although the extent of the delta reached its maximum the thickness of the delta was limited due to the gentle topography resulting in a small delta vol-ume (Table 3)

5 | RELATIONSHIPS BETWEEN THE VARIOUS ELEMENTS OF THE S2S SYSTEM

Quantitative relationships between the various elements of the S2S system have been established through the above‐mentioned calculations A strong positive correlation is clearly present between the rate of tectonic subsidence the average fault activity and the average growth index of the boundary faults F1 and F2 (Figure 8ab) The rate of tectonic subsidence can therefore be used in the following as the pri-mary proxy to represent the intensity of the tectonic activity whereas the rate of fault activity and the growth index are used as secondary proxies

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The tectonic activity and the sediment‐supply rate show a positive relationship (Figures 8c 9a 10a) whereas the tec-tonic activity and the sink area of the basin show a negative relationship (Figures 8d 9b 10b) In contrast the tectonic activity has a positive relationship with the total accommo-dation space (Figures 8e 9c 10c Table 4) There is also a positive relationship between the average sedimentary dip of the fan‐ and braid‐deltas on the one hand and the tectonic activity on the other hand (Figures 8f 9d 10d)

The intensity of the tectonic activity correlates negatively with the extent of the sediment area but positively with the sediment volume (Figures 8g‐h 9e‐f 10e‐f) The different responses of the sediment area and the volume to the tectonic activity are caused by variations in the thicknesses of the sed-imentary units (Table 3)

There is also a positive relationship between the average seismic progradation dip of the fan‐ and braid‐deltas and the tectonic activity (Figures 8i 9g 10g) strong tectonic activ-ity usually formed deltas that are characterized by a chaotic progradational or oblique progradational seismic reflection such as SF 1 and 2 in S‐3 (lower unit) and S‐4 (Figures S3ndashS7) The minimum tectonic activity during Members S‐1 + 2 and D‐2 are reflected by dominantly shingled progradational seismic facies in the delta interior (Figures S10ndashS11)

In addition we find that the sediment area sediment vol-ume and average seismic progradation dip of the fan‐ and braid‐deltas correlate positively with the sediment‐supply rate (Figure 11a b and c) but negatively with the basin sink area (Figure 11d e and f) Both the sediment volume and the average seismic progradation dip of the fan‐ and braid‐deltas

F I G U R E 8 (a‐b) Relationships between the tectonic‐subsidence rate and tectonics (c‐i) Relationships between tectonic activity and sedimentary source‐to‐sink parameters Input data regarding the tectonic activity are from Table 2 those regarding the source‐to‐sink parameters data are from Tables 3 and 4 Regression‐line equations and coefficients of determination (R2) are shown for all diagrams

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show a positive relationship with the total accommodation space (Figure 11hi) However no obvious relationship ap-pears to be present between the sediment area and the total accommodation space (G) Both the sediment area and the average seismic progradation dip of the fan‐ and braid‐deltas correlate well with the average sedimentary dip of the fan‐ and braid‐deltas (Figure 11km) A poor correlation is found between the sediment volume and the average sedimentary dip of the fan‐ and braid‐deltas

6 | DISCUSSION

61 | Analysis of the influence of tectonic activity on the source area accommodation space geomorphology and sediment supplyA high relief and large drainage area usually can generate a large sediment supply (Leeder Harris amp Kirkby 1998 Syvitski amp Milliman 2007) Although the erosional area for the fan and delta system cannot be estimated because of the

limited data coverage the exposed area within the study area can be calculated The calculations show a generally decreas-ing trend of the source area from S‐4 (501 km2) to D‐2 (58 km2 Figure7 Table 4) The calculated exposed area cannot fully represent the true source area however but the evolu-tionary trend of the source area can be used as a proxy to indi-cate the relative influence on the change in sediment volume This trend is consistent with the decrease in sediment volume from S‐4 (2126 km3) to D‐2 (175 km3 Table 2) The relief is difficult to reconstruct in this case but variations in the fault‐activity rate (here taken as the tectonic‐subsidence rate) can create local elevation differences and can therefore be used as proxies for the trends in the relief development The relief shows an overall decreasing trend from S‐4 to D‐2 except for D‐3 this correlates well with the sediment volume (Figure 8h) Although the drainage area of D‐3 was smaller than that of D‐2 because of the high tectonic‐subsidence rate (result-ing in a high relief) D‐3 is thicker and shows a larger sedi-ment volume than the overlying D‐2 (Table 3) D‐3 is thinner than S‐4 + 3 but the larger source area resulted in a larger

F I G U R E 9 General relationships between the average fault‐growth index of F1 and F2 (AFGIF1‐F2) and sedimentary source‐to‐sink parameters The average fault‐growth index of F1 and F2 (AFGIF1‐F2) data in this figure are from Table 2 The source‐to‐sink parameters data are from Table 4 Regression‐line equations and the coefficients of determination are shown in each diagram

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sediment volume and supply rate (Table 3 Figure8ch) Therefore both the fault‐induced relief and the drainage area affected the sediment‐supply rate and the sediment volume in the sink

The changes in accommodation space during the vari-ous phases of the Palaeogene in the south‐western HD are clear from the estimated tectonic subsiding rate (Table 2) The correlations between the intensity of the tectonic activ-ity and the extent of the depositional sink area (Figures 8d 9b 10b) between the intensity of the tectonic activity and the total accommodation space and between the intensity of the tectonic activity and the morphology in the sink area (Figures 8e‐f 9c‐d 10c‐d) clearly show that strong tectonic activity resulted in a larger accommodation capacity of the sink

In particular the main subsiding area tended to form steeper slopes However the extent of the main subsiding sink area diminished (Figure 8d) with increasing tectonic activity which was possibly due to the relatively small sub-siding centre in the tectonically active basins It can thus be deduced that tectonic activity not only controlled the sedi-ment supply and the variation in accommodation space but

also determined the changes in the topography of the sedi-mentary basins and the extent of the main depositional areas in the tectonically active basins

62 | Analysis of the influence of tectonic activity on the size and internal stacking pattern of the delta depositional systemThe above data and considerations indicate that the tectonic activity was closely related to the sediment supply accom-modation space and morphology of the sink area which are possibly the most important factors affecting the extent and stacking pattern of the sedimentary facies (cf Cope et al 2010 DeCelles Kapp Ding amp Gehrels 2007 Leeder 2011 Olsen 1997 Simon et al 2017)

Statistical analysis indicates that the sediment‐supply rate has a strong positive correlation with the volume of the depositional system a moderate correlation with the seismic progradational dip in the depositional system and a poor cor-relation with the size of the depositional area (Figure 11a‐c) A larger sink area corresponded to a larger fanbraid‐delta a gentler seismic progradational angle and a reduced volume

F I G U R E 1 0 General relationships between average fault activity rate of F1 and F2 (RFAA‐F1‐F2) and sedimentary source‐to‐sink parameters The average fault activity rate of F1 and F2 (RFAA‐F1‐F2) data in this figure are from Table 2 The source‐to‐sink parameters data are from Table 4 Regression line equations and the coefficients of determination are shown in each diagram

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of the fan or braid‐delta which was possibly related to a re-duced sedimentary dip and thinner sediments (Figure 11d‐f) The total accommodation space in the basin correlates well

with the volume of the depositional system to some degree with the seismic progradational dip and poorly with the ex-tent of the depositional system area (Figure 11g‐i) These

FIGURE 11 Relationships between various parameters involved in the source‐to‐sink system (a‐c) Relationships between sediment supply and characteristics of the depositional system (extent volume and DPSA of the sediments) (d‐f) Relationships between the sink area of the basin and characteristics of the depositional system (g‐i) Relationships between the total accommodation space (AT) and the characteristics of the depositional system (j) Relationship between the accommodation‐spacesediment‐supply ratio (AS) and the DPSA of the sediments (k‐m) Relationships between the sedimentary dip and the characteristics of the depositional system The data regarding sediment supply basin sink area total accommodation space accommodation‐spacesediment‐supply ratio and sedimentary dips are from Table 4 The extent volume and DPSA of the sedimentary facies are from Table 3 Note the seemingly obvious polynomial (quadratic) relationship between the sedimentary dip and the sediment volume (L) The trend line in (L) suggests the following relationships between sediment volume and sedimentary slope in a rift or tectonically active basin (1) a very steep sedimentary slope is unfavourable for sediment accumulation (2) an appropriate sedimentary slope is favourable for preservation of depositional systems eg when the sedimentary slope in (L) is about 25degndash32deg the sediment volume reaches its largest value (3) a very gentle sedimentary slope will lead to a decrease of the sediment volume possibly due to weakening of the drainage system and thinner sediments

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relationships are clear evidence that the size of the sink area controlled the extent of the depositional system during the rifting of the lacustrine basin and that the rate of sediment supply and the accommodation space had a significant in-fluence on the total sedimentary volume as well as on the internal stacking pattern of the depositional system

We here use the ratio of the tectonic‐subsidence rate and the sediment‐supply rate as a proxy to indicate the ratio be-tween accommodation space and sediment‐supply rate (AS) (Table 4) AS has a strong influence on the internal stacking pattern of the depositional systems in the lacustrine rift basin (Figure 11j) This might be because the basin was small and because abundant and rapid material was supplied due

to intense tectonic activity (cf Catuneanu et al 2009 Liro 1993) and a favourable local climate (eg Bohacs Carroll Neal amp Mankiewicz 2000 Perlmutter amp Matthews 1989) The sediment supply still had a significant influence on the main subsidence area of the lacustrine basins and deposi-tional systems

In addition the basin slope significantly influenced the extent of the depositional system (Figure 11k) and had a polynomial relationship with its volume (Figure 11l) This relationship indicates that more intense tectonic activity and a steeper depositional slope were not favourable for sediment accumulation over a large extent in the lacustrine basin On the contrary these sediments were usually transported to a

F I G U R E 1 2 Tectonic differential activities and resulting patterns of the source‐to‐sink system on the south‐western slope of the HD during the Palaeogene (a) Development during phases of intense tectonics (Member 4 to the lower part of Member 3 of the Shahejie Fm) (b) Development during phases of somewhat less tectonic activity (middle part of Member 3 of the Shahejie Fm and Member 3 of the Dongying Fm) (c) Development during phases of weak tectonic activity (Members 1 and 2 of the Shahejie Fm and Member 2 of the Dongying Fm) The intensity of tectonic activity in the lacustrine rift basin had a significant influence on the development and extent of each unit of the source‐to‐sink system as well as on the type and dimensions of the depositional systems The present study indicates that probably sublacustrine fans developed (see for example Figure S4b) during phases with relatively strong tectonic activity This is not really clear from the seismic‐reflection data but possibly due to the small sizes of these sublacustrine fans Moreover lithofacies and core data are not available for the south‐western part of the study area The present contribution therefore focuses on the fan‐deltas and braid‐deltas regarding the sedimentary facies analysis the sublacustrine fans that probably developed in the deep or semi‐deep lake are presented just as a likely feature

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relatively small sink area with a fairly large accommodation space Finally stronger tectonic activity resulted in steeper depositional slopes (Figure 8f) which further controlled the hydrodynamic conditions and differential discharge when the sediments were deposited The strong correlation between the depositional slope and the deltas dip (Figure 11m) suggests that the differences in topography due to tectonics must be considered as one of the most critical factors that controlled the internal stacking pattern of the delta deposits

63 | Significance of the present study for other source‐to‐sink systems of lacustrine rift basins

631 | Summary of the source‐to‐sink systems in the HDIn lacustrine rift basins the tectonic setting is probably the main factor that determines the development of the S2S sys-tem but differential tectonic activities lead to variations in the basic characteristics of the S2S system Tectonic activity was most intense during S‐3 (lower unit) and during S‐4 and caused both a strong uplift of the source area and the devel-opment of depressions in the basin that formed a sink (Figure 12a) Strong tectonic activity in the S2S system during these time‐spans led to a high sediment‐supply rate steeper slopes a larger accommodation space and deposition of several fan‐deltas that are characterized by a fairly steep seismic progra-dational angle

The tectonic activity decreased during S‐3 (middle unit) and during D‐3 The S2S system that was present during this time‐span mainly concerned a rising area that shifted south-wards developing an alluvial plain between the erosional area and the sink area thus increasing the distance from source to sink (Figure 12b) Simultaneously the sediment‐supply rate and the accommodation space also changed and braid‐deltas could thus develop with larger volumes and gentler seismic progradational dips

Tectonic activity was clearly less intense during S‐1 + 2 and D‐2 The rising area had shifted further southwards cre-ating a wider alluvial plain connecting the source area to the sink in the HD (Figure 12c) At this stage stable tectonic activity led to relatively less sediment supply a gentle slope less accommodation space and the development of several braid‐deltas with a fairly gentle seismic progradational angle

632 | Wider implications and limitationsSoslashmme et al (2009) proposed that the elements of S2S sys-tems are genetically related and that quantitative correla-tions exist among these elements Other studies also suggest that the size of the drainage basin is correlated to the size of the fan developing on the basin floor (eg Blum et al

2017 Snedden et al 2018) and to the size of the river chan-nel (eg Milliken et al 2018) Helland‐Hansen Soslashmme Martinsen Lunt and Thurmond (2016) suggest a simplified subdivision of S2S systems into three main categories (a) Steep‐Short‐Deep (steep onshore and offshore gradients short distance between source and sink and deep offshore waters) (b) Wide‐Deep (low‐gradient shelf‐catchment area and deep offshore waters) and (c) Wide‐Shallow (relatively shallow offshore waters and a wide low‐gradient catchment area) systems

The present study indicates that the alluvial plain roughly corresponds to the alluvial‐shelf unit in marine basins al-though with a much smaller width and extent in the lacustrine rift basins than would have been the case on a continental shelf Faults F1 and F2 along the slope belt correspond to the slope of classical S2S systems whereas the shore‐shallow‐deep lake area can be compared with the basin floor (Soslashmme et al 2009) S‐4 and S‐3 (lower unit) can be roughly clas-sified as Steep‐Short‐Deep systems whereas the overlying S‐1 + 2and D‐2 can be classified as the Wide‐Shallow sys-tems that Helland‐Hansen et al (2016) defined During the deposition of S‐4 and S‐3 (lower unit) the strong tectonic activity caused a high relief of the source area a narrow allu-vial plain and a relatively deep lake The subsequently wan-ing tectonic activity resulted in a lower relief of the source area a wider alluvial plain and a shallower lake Although the absolute values of these elements in lacustrine basins are much smaller than those of marine basins the ratio between these elements in both settings is comparable Typically in a lacustrine basin a transformation from a Steep‐Short‐Deep system (S‐4 and S‐3 (lower unit)) to a Wide‐Shallow system (S‐1 + 2ampD‐2) occurs within a few million years Although the basin geomorphology has experienced signif-icant changes from S‐4 to D‐2 the quantitative relationships between tectonic activity sediment‐supply rate accommoda-tion space and sedimentary dip of the delta systems did not change significantly (eg Figures 8 and 11) The analytical approaches applied and quantitative relationship established here can help analyse other lacustrine basins worldwide and may even act as a reference for the analysis of marine basins

Our study focuses mainly on the influences of tectonic activity on the elements of the depositional sink Other pa-rameters (eg climate and lithology) were not considered in detail Studies on modern and ancient systems suggest that the climate and lithology also have a great influence on the sediment supply and distribution in the basin (eg Carroll Chetel amp Smith 2006 Hovius amp Leeder 1998 Syvitski amp Milliman 2007 Zhang et al 2018) For exam-ple climate variations between glacials and inter‐glacials have resulted in largely different sediment‐supply rates and in significant differences in the sizes of the Quaternary sub-marine fans in the north‐western Gulf of Mexico (Blum amp Hattier‐Womack 2009) We acknowledge the importance

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of climate and lithology for S2S systems and we are con-vinced that these elements can significantly affect the S2S systems in other cases(eg modern systems and systems influenced by glacialinterglacial alternations) These fac-tors were not really relevant for the present study however because no significant differences in lithology were present in the source areas and because we focus on the changes at a million‐year scale which implies that the tectonic ac-tivity has a first‐order control on the development of S2S elements in the investigated rift basin

7 | CONCLUSIONS

We have calculated the tectonic‐subsidence history the growth index and the activity rate of the main boundary faults (F1 and F2) and various S2S parameters of six Palaeogene rock units on the south‐western slope of the HD Based on the values found for these parameters quantitative corre-lation were established for the tectonic activity and other S2Sparameters in the basinal sink This leads to the follow-ing conclusions

1 The positive correlation between the intensity of fault activity and the tectonic‐subsidence rate is a strong indication for a distinct control by the tectonic activity of the syn‐depositional rifting of the tectonically active basin

2 The tectonic activity was quantitatively related to the sediment supply accommodation space and morphology of the sink area The relationship between tectonic activ-ity and depositional systems is reflected by changes in critical factors such as sediment supply accommodation space and dip of the sink area These critical factors were probably the most important factors that led to changes in the size and internal stacking pattern of the sedimentary facies

3 Differential tectonic activity led to changes in the char-acteristics of the S2S system on the south‐western slope of the HD The strongest tectonic activity which oc-curred during S‐3 (lower unit) and during S‐4 led to the largest provenance area adjacent to the sink area to a high sediment‐supply rate to steeper slopes to a larger accommodation space and controlled the development of several fan‐deltas Diminished tectonic activity dur-ing S‐3 (middle unit) and during D‐3 led to a decrease in uplift an increased width of the alluvial plain an in-creased transport distance a decrease in the sediment‐supply rate and accommodation space and resulted in the development of braid‐deltas with a large volume During S‐1 + 2 and D‐2 stable tectonic activity led to a lower sediment‐supply rate a gentle depositional slope and a smaller accommodation space resulting in the

development of several braid‐deltas with gentler seis-mic progradational angles

4 The analytical approaches applied and the quantitative re-lationships established here can help analyse other lacus-trine basins worldwide and may even act as a reference for the study of marine basins

ACKNOWLEDGEMENTS

We thank Dr Sarah Boulton and Dr Chenlin Gong as well as the Associate Editor of Basin Research Dr Craig Magee for their constructive comments on the manuscript This study was funded by the National Science and Technology Major Project (Exploration Technologies for Offshore Hidden OilGas) (project no 2016ZX05024‐003‐003) the National Natural Science Foundations of China (project no 41676050) and the Fundamental Research Funds for the Central Universities (2652014037)

REFERENCES

Allen P A (2008a) From landscapes into geological history Nature 451 274ndash276 https doiorg101038natur e06586

Allen P A (2008b) Time scales of tectonic landscapes and their sed-iment routing systems In Landscape evolution Denudation cli-mate and tectonics over different time and space scales (Ed by Gallagher K Jones S J amp Wainwright J) Geological Society London Special Publications 296 7ndash28

Allen P A Armitage J J Carter A Duller R A Michael N A Sinclair H D hellip Whittaker A C (2013) The Qs problem Sediment volumetric balance of proximal foreland basin systems Sedimentology 60 102ndash130

Amorosi A Maselli V amp Trincardi F (2016) Onshore to offshore anatomy of a late Quaternary source‐to‐sink system (Po Plain‐Adriatic Sea Italy) Earth‐Science Reviews 153 212ndash237 https doiorg101016jearsc irev201510010

Anderson J B Wallace D J Simms A R Rodriguez A B Weight R W R amp Taha Z P (2016) Recycling sediments between source and sink during a eustatic cycle Systems of late Quaternary northwestern Gulf of Mexico Basin Earth‐Science Reviews 153 111ndash138 https doiorg101016jearsc irev201510014

Anthony E J amp Julian M (1999) Source‐to‐sink sediment trans-fers environmental engineering and hazard mitigation in the steep Var River catchment French Riviera southeastern France Geomorphology 31 337ndash354 https doiorg101016S0169-555X(99)00088-4

Athy L F (1930) Density porosity and compaction of sedimentary rocks AAPG Bulletin 14 1ndash24

Bhattacharya J P Copeland P Lawton T F amp Holbrook J (2016) Estimation of source area river palaeo‐discharge palaeoslope and sediment budgets of linked deep‐time depositional systems and im-plications for hydrocarbon potential Earth‐Science Reviews 153 77ndash110

Blum M D amp Hattier‐Womack J (2009) Climate change sea‐level change and fluvial sediment supply to deepwater depositional

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The tectonic activity and the sediment‐supply rate show a positive relationship (Figures 8c 9a 10a) whereas the tec-tonic activity and the sink area of the basin show a negative relationship (Figures 8d 9b 10b) In contrast the tectonic activity has a positive relationship with the total accommo-dation space (Figures 8e 9c 10c Table 4) There is also a positive relationship between the average sedimentary dip of the fan‐ and braid‐deltas on the one hand and the tectonic activity on the other hand (Figures 8f 9d 10d)

The intensity of the tectonic activity correlates negatively with the extent of the sediment area but positively with the sediment volume (Figures 8g‐h 9e‐f 10e‐f) The different responses of the sediment area and the volume to the tectonic activity are caused by variations in the thicknesses of the sed-imentary units (Table 3)

There is also a positive relationship between the average seismic progradation dip of the fan‐ and braid‐deltas and the tectonic activity (Figures 8i 9g 10g) strong tectonic activ-ity usually formed deltas that are characterized by a chaotic progradational or oblique progradational seismic reflection such as SF 1 and 2 in S‐3 (lower unit) and S‐4 (Figures S3ndashS7) The minimum tectonic activity during Members S‐1 + 2 and D‐2 are reflected by dominantly shingled progradational seismic facies in the delta interior (Figures S10ndashS11)

In addition we find that the sediment area sediment vol-ume and average seismic progradation dip of the fan‐ and braid‐deltas correlate positively with the sediment‐supply rate (Figure 11a b and c) but negatively with the basin sink area (Figure 11d e and f) Both the sediment volume and the average seismic progradation dip of the fan‐ and braid‐deltas

F I G U R E 8 (a‐b) Relationships between the tectonic‐subsidence rate and tectonics (c‐i) Relationships between tectonic activity and sedimentary source‐to‐sink parameters Input data regarding the tectonic activity are from Table 2 those regarding the source‐to‐sink parameters data are from Tables 3 and 4 Regression‐line equations and coefficients of determination (R2) are shown for all diagrams

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show a positive relationship with the total accommodation space (Figure 11hi) However no obvious relationship ap-pears to be present between the sediment area and the total accommodation space (G) Both the sediment area and the average seismic progradation dip of the fan‐ and braid‐deltas correlate well with the average sedimentary dip of the fan‐ and braid‐deltas (Figure 11km) A poor correlation is found between the sediment volume and the average sedimentary dip of the fan‐ and braid‐deltas

6 | DISCUSSION

61 | Analysis of the influence of tectonic activity on the source area accommodation space geomorphology and sediment supplyA high relief and large drainage area usually can generate a large sediment supply (Leeder Harris amp Kirkby 1998 Syvitski amp Milliman 2007) Although the erosional area for the fan and delta system cannot be estimated because of the

limited data coverage the exposed area within the study area can be calculated The calculations show a generally decreas-ing trend of the source area from S‐4 (501 km2) to D‐2 (58 km2 Figure7 Table 4) The calculated exposed area cannot fully represent the true source area however but the evolu-tionary trend of the source area can be used as a proxy to indi-cate the relative influence on the change in sediment volume This trend is consistent with the decrease in sediment volume from S‐4 (2126 km3) to D‐2 (175 km3 Table 2) The relief is difficult to reconstruct in this case but variations in the fault‐activity rate (here taken as the tectonic‐subsidence rate) can create local elevation differences and can therefore be used as proxies for the trends in the relief development The relief shows an overall decreasing trend from S‐4 to D‐2 except for D‐3 this correlates well with the sediment volume (Figure 8h) Although the drainage area of D‐3 was smaller than that of D‐2 because of the high tectonic‐subsidence rate (result-ing in a high relief) D‐3 is thicker and shows a larger sedi-ment volume than the overlying D‐2 (Table 3) D‐3 is thinner than S‐4 + 3 but the larger source area resulted in a larger

F I G U R E 9 General relationships between the average fault‐growth index of F1 and F2 (AFGIF1‐F2) and sedimentary source‐to‐sink parameters The average fault‐growth index of F1 and F2 (AFGIF1‐F2) data in this figure are from Table 2 The source‐to‐sink parameters data are from Table 4 Regression‐line equations and the coefficients of determination are shown in each diagram

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sediment volume and supply rate (Table 3 Figure8ch) Therefore both the fault‐induced relief and the drainage area affected the sediment‐supply rate and the sediment volume in the sink

The changes in accommodation space during the vari-ous phases of the Palaeogene in the south‐western HD are clear from the estimated tectonic subsiding rate (Table 2) The correlations between the intensity of the tectonic activ-ity and the extent of the depositional sink area (Figures 8d 9b 10b) between the intensity of the tectonic activity and the total accommodation space and between the intensity of the tectonic activity and the morphology in the sink area (Figures 8e‐f 9c‐d 10c‐d) clearly show that strong tectonic activity resulted in a larger accommodation capacity of the sink

In particular the main subsiding area tended to form steeper slopes However the extent of the main subsiding sink area diminished (Figure 8d) with increasing tectonic activity which was possibly due to the relatively small sub-siding centre in the tectonically active basins It can thus be deduced that tectonic activity not only controlled the sedi-ment supply and the variation in accommodation space but

also determined the changes in the topography of the sedi-mentary basins and the extent of the main depositional areas in the tectonically active basins

62 | Analysis of the influence of tectonic activity on the size and internal stacking pattern of the delta depositional systemThe above data and considerations indicate that the tectonic activity was closely related to the sediment supply accom-modation space and morphology of the sink area which are possibly the most important factors affecting the extent and stacking pattern of the sedimentary facies (cf Cope et al 2010 DeCelles Kapp Ding amp Gehrels 2007 Leeder 2011 Olsen 1997 Simon et al 2017)

Statistical analysis indicates that the sediment‐supply rate has a strong positive correlation with the volume of the depositional system a moderate correlation with the seismic progradational dip in the depositional system and a poor cor-relation with the size of the depositional area (Figure 11a‐c) A larger sink area corresponded to a larger fanbraid‐delta a gentler seismic progradational angle and a reduced volume

F I G U R E 1 0 General relationships between average fault activity rate of F1 and F2 (RFAA‐F1‐F2) and sedimentary source‐to‐sink parameters The average fault activity rate of F1 and F2 (RFAA‐F1‐F2) data in this figure are from Table 2 The source‐to‐sink parameters data are from Table 4 Regression line equations and the coefficients of determination are shown in each diagram

606 | EAGE

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of the fan or braid‐delta which was possibly related to a re-duced sedimentary dip and thinner sediments (Figure 11d‐f) The total accommodation space in the basin correlates well

with the volume of the depositional system to some degree with the seismic progradational dip and poorly with the ex-tent of the depositional system area (Figure 11g‐i) These

FIGURE 11 Relationships between various parameters involved in the source‐to‐sink system (a‐c) Relationships between sediment supply and characteristics of the depositional system (extent volume and DPSA of the sediments) (d‐f) Relationships between the sink area of the basin and characteristics of the depositional system (g‐i) Relationships between the total accommodation space (AT) and the characteristics of the depositional system (j) Relationship between the accommodation‐spacesediment‐supply ratio (AS) and the DPSA of the sediments (k‐m) Relationships between the sedimentary dip and the characteristics of the depositional system The data regarding sediment supply basin sink area total accommodation space accommodation‐spacesediment‐supply ratio and sedimentary dips are from Table 4 The extent volume and DPSA of the sedimentary facies are from Table 3 Note the seemingly obvious polynomial (quadratic) relationship between the sedimentary dip and the sediment volume (L) The trend line in (L) suggests the following relationships between sediment volume and sedimentary slope in a rift or tectonically active basin (1) a very steep sedimentary slope is unfavourable for sediment accumulation (2) an appropriate sedimentary slope is favourable for preservation of depositional systems eg when the sedimentary slope in (L) is about 25degndash32deg the sediment volume reaches its largest value (3) a very gentle sedimentary slope will lead to a decrease of the sediment volume possibly due to weakening of the drainage system and thinner sediments

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relationships are clear evidence that the size of the sink area controlled the extent of the depositional system during the rifting of the lacustrine basin and that the rate of sediment supply and the accommodation space had a significant in-fluence on the total sedimentary volume as well as on the internal stacking pattern of the depositional system

We here use the ratio of the tectonic‐subsidence rate and the sediment‐supply rate as a proxy to indicate the ratio be-tween accommodation space and sediment‐supply rate (AS) (Table 4) AS has a strong influence on the internal stacking pattern of the depositional systems in the lacustrine rift basin (Figure 11j) This might be because the basin was small and because abundant and rapid material was supplied due

to intense tectonic activity (cf Catuneanu et al 2009 Liro 1993) and a favourable local climate (eg Bohacs Carroll Neal amp Mankiewicz 2000 Perlmutter amp Matthews 1989) The sediment supply still had a significant influence on the main subsidence area of the lacustrine basins and deposi-tional systems

In addition the basin slope significantly influenced the extent of the depositional system (Figure 11k) and had a polynomial relationship with its volume (Figure 11l) This relationship indicates that more intense tectonic activity and a steeper depositional slope were not favourable for sediment accumulation over a large extent in the lacustrine basin On the contrary these sediments were usually transported to a

F I G U R E 1 2 Tectonic differential activities and resulting patterns of the source‐to‐sink system on the south‐western slope of the HD during the Palaeogene (a) Development during phases of intense tectonics (Member 4 to the lower part of Member 3 of the Shahejie Fm) (b) Development during phases of somewhat less tectonic activity (middle part of Member 3 of the Shahejie Fm and Member 3 of the Dongying Fm) (c) Development during phases of weak tectonic activity (Members 1 and 2 of the Shahejie Fm and Member 2 of the Dongying Fm) The intensity of tectonic activity in the lacustrine rift basin had a significant influence on the development and extent of each unit of the source‐to‐sink system as well as on the type and dimensions of the depositional systems The present study indicates that probably sublacustrine fans developed (see for example Figure S4b) during phases with relatively strong tectonic activity This is not really clear from the seismic‐reflection data but possibly due to the small sizes of these sublacustrine fans Moreover lithofacies and core data are not available for the south‐western part of the study area The present contribution therefore focuses on the fan‐deltas and braid‐deltas regarding the sedimentary facies analysis the sublacustrine fans that probably developed in the deep or semi‐deep lake are presented just as a likely feature

608 | EAGE

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relatively small sink area with a fairly large accommodation space Finally stronger tectonic activity resulted in steeper depositional slopes (Figure 8f) which further controlled the hydrodynamic conditions and differential discharge when the sediments were deposited The strong correlation between the depositional slope and the deltas dip (Figure 11m) suggests that the differences in topography due to tectonics must be considered as one of the most critical factors that controlled the internal stacking pattern of the delta deposits

63 | Significance of the present study for other source‐to‐sink systems of lacustrine rift basins

631 | Summary of the source‐to‐sink systems in the HDIn lacustrine rift basins the tectonic setting is probably the main factor that determines the development of the S2S sys-tem but differential tectonic activities lead to variations in the basic characteristics of the S2S system Tectonic activity was most intense during S‐3 (lower unit) and during S‐4 and caused both a strong uplift of the source area and the devel-opment of depressions in the basin that formed a sink (Figure 12a) Strong tectonic activity in the S2S system during these time‐spans led to a high sediment‐supply rate steeper slopes a larger accommodation space and deposition of several fan‐deltas that are characterized by a fairly steep seismic progra-dational angle

The tectonic activity decreased during S‐3 (middle unit) and during D‐3 The S2S system that was present during this time‐span mainly concerned a rising area that shifted south-wards developing an alluvial plain between the erosional area and the sink area thus increasing the distance from source to sink (Figure 12b) Simultaneously the sediment‐supply rate and the accommodation space also changed and braid‐deltas could thus develop with larger volumes and gentler seismic progradational dips

Tectonic activity was clearly less intense during S‐1 + 2 and D‐2 The rising area had shifted further southwards cre-ating a wider alluvial plain connecting the source area to the sink in the HD (Figure 12c) At this stage stable tectonic activity led to relatively less sediment supply a gentle slope less accommodation space and the development of several braid‐deltas with a fairly gentle seismic progradational angle

632 | Wider implications and limitationsSoslashmme et al (2009) proposed that the elements of S2S sys-tems are genetically related and that quantitative correla-tions exist among these elements Other studies also suggest that the size of the drainage basin is correlated to the size of the fan developing on the basin floor (eg Blum et al

2017 Snedden et al 2018) and to the size of the river chan-nel (eg Milliken et al 2018) Helland‐Hansen Soslashmme Martinsen Lunt and Thurmond (2016) suggest a simplified subdivision of S2S systems into three main categories (a) Steep‐Short‐Deep (steep onshore and offshore gradients short distance between source and sink and deep offshore waters) (b) Wide‐Deep (low‐gradient shelf‐catchment area and deep offshore waters) and (c) Wide‐Shallow (relatively shallow offshore waters and a wide low‐gradient catchment area) systems

The present study indicates that the alluvial plain roughly corresponds to the alluvial‐shelf unit in marine basins al-though with a much smaller width and extent in the lacustrine rift basins than would have been the case on a continental shelf Faults F1 and F2 along the slope belt correspond to the slope of classical S2S systems whereas the shore‐shallow‐deep lake area can be compared with the basin floor (Soslashmme et al 2009) S‐4 and S‐3 (lower unit) can be roughly clas-sified as Steep‐Short‐Deep systems whereas the overlying S‐1 + 2and D‐2 can be classified as the Wide‐Shallow sys-tems that Helland‐Hansen et al (2016) defined During the deposition of S‐4 and S‐3 (lower unit) the strong tectonic activity caused a high relief of the source area a narrow allu-vial plain and a relatively deep lake The subsequently wan-ing tectonic activity resulted in a lower relief of the source area a wider alluvial plain and a shallower lake Although the absolute values of these elements in lacustrine basins are much smaller than those of marine basins the ratio between these elements in both settings is comparable Typically in a lacustrine basin a transformation from a Steep‐Short‐Deep system (S‐4 and S‐3 (lower unit)) to a Wide‐Shallow system (S‐1 + 2ampD‐2) occurs within a few million years Although the basin geomorphology has experienced signif-icant changes from S‐4 to D‐2 the quantitative relationships between tectonic activity sediment‐supply rate accommoda-tion space and sedimentary dip of the delta systems did not change significantly (eg Figures 8 and 11) The analytical approaches applied and quantitative relationship established here can help analyse other lacustrine basins worldwide and may even act as a reference for the analysis of marine basins

Our study focuses mainly on the influences of tectonic activity on the elements of the depositional sink Other pa-rameters (eg climate and lithology) were not considered in detail Studies on modern and ancient systems suggest that the climate and lithology also have a great influence on the sediment supply and distribution in the basin (eg Carroll Chetel amp Smith 2006 Hovius amp Leeder 1998 Syvitski amp Milliman 2007 Zhang et al 2018) For exam-ple climate variations between glacials and inter‐glacials have resulted in largely different sediment‐supply rates and in significant differences in the sizes of the Quaternary sub-marine fans in the north‐western Gulf of Mexico (Blum amp Hattier‐Womack 2009) We acknowledge the importance

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of climate and lithology for S2S systems and we are con-vinced that these elements can significantly affect the S2S systems in other cases(eg modern systems and systems influenced by glacialinterglacial alternations) These fac-tors were not really relevant for the present study however because no significant differences in lithology were present in the source areas and because we focus on the changes at a million‐year scale which implies that the tectonic ac-tivity has a first‐order control on the development of S2S elements in the investigated rift basin

7 | CONCLUSIONS

We have calculated the tectonic‐subsidence history the growth index and the activity rate of the main boundary faults (F1 and F2) and various S2S parameters of six Palaeogene rock units on the south‐western slope of the HD Based on the values found for these parameters quantitative corre-lation were established for the tectonic activity and other S2Sparameters in the basinal sink This leads to the follow-ing conclusions

1 The positive correlation between the intensity of fault activity and the tectonic‐subsidence rate is a strong indication for a distinct control by the tectonic activity of the syn‐depositional rifting of the tectonically active basin

2 The tectonic activity was quantitatively related to the sediment supply accommodation space and morphology of the sink area The relationship between tectonic activ-ity and depositional systems is reflected by changes in critical factors such as sediment supply accommodation space and dip of the sink area These critical factors were probably the most important factors that led to changes in the size and internal stacking pattern of the sedimentary facies

3 Differential tectonic activity led to changes in the char-acteristics of the S2S system on the south‐western slope of the HD The strongest tectonic activity which oc-curred during S‐3 (lower unit) and during S‐4 led to the largest provenance area adjacent to the sink area to a high sediment‐supply rate to steeper slopes to a larger accommodation space and controlled the development of several fan‐deltas Diminished tectonic activity dur-ing S‐3 (middle unit) and during D‐3 led to a decrease in uplift an increased width of the alluvial plain an in-creased transport distance a decrease in the sediment‐supply rate and accommodation space and resulted in the development of braid‐deltas with a large volume During S‐1 + 2 and D‐2 stable tectonic activity led to a lower sediment‐supply rate a gentle depositional slope and a smaller accommodation space resulting in the

development of several braid‐deltas with gentler seis-mic progradational angles

4 The analytical approaches applied and the quantitative re-lationships established here can help analyse other lacus-trine basins worldwide and may even act as a reference for the study of marine basins

ACKNOWLEDGEMENTS

We thank Dr Sarah Boulton and Dr Chenlin Gong as well as the Associate Editor of Basin Research Dr Craig Magee for their constructive comments on the manuscript This study was funded by the National Science and Technology Major Project (Exploration Technologies for Offshore Hidden OilGas) (project no 2016ZX05024‐003‐003) the National Natural Science Foundations of China (project no 41676050) and the Fundamental Research Funds for the Central Universities (2652014037)

REFERENCES

Allen P A (2008a) From landscapes into geological history Nature 451 274ndash276 https doiorg101038natur e06586

Allen P A (2008b) Time scales of tectonic landscapes and their sed-iment routing systems In Landscape evolution Denudation cli-mate and tectonics over different time and space scales (Ed by Gallagher K Jones S J amp Wainwright J) Geological Society London Special Publications 296 7ndash28

Allen P A Armitage J J Carter A Duller R A Michael N A Sinclair H D hellip Whittaker A C (2013) The Qs problem Sediment volumetric balance of proximal foreland basin systems Sedimentology 60 102ndash130

Amorosi A Maselli V amp Trincardi F (2016) Onshore to offshore anatomy of a late Quaternary source‐to‐sink system (Po Plain‐Adriatic Sea Italy) Earth‐Science Reviews 153 212ndash237 https doiorg101016jearsc irev201510010

Anderson J B Wallace D J Simms A R Rodriguez A B Weight R W R amp Taha Z P (2016) Recycling sediments between source and sink during a eustatic cycle Systems of late Quaternary northwestern Gulf of Mexico Basin Earth‐Science Reviews 153 111ndash138 https doiorg101016jearsc irev201510014

Anthony E J amp Julian M (1999) Source‐to‐sink sediment trans-fers environmental engineering and hazard mitigation in the steep Var River catchment French Riviera southeastern France Geomorphology 31 337ndash354 https doiorg101016S0169-555X(99)00088-4

Athy L F (1930) Density porosity and compaction of sedimentary rocks AAPG Bulletin 14 1ndash24

Bhattacharya J P Copeland P Lawton T F amp Holbrook J (2016) Estimation of source area river palaeo‐discharge palaeoslope and sediment budgets of linked deep‐time depositional systems and im-plications for hydrocarbon potential Earth‐Science Reviews 153 77ndash110

Blum M D amp Hattier‐Womack J (2009) Climate change sea‐level change and fluvial sediment supply to deepwater depositional

604 | EAGE

LIU et aL

show a positive relationship with the total accommodation space (Figure 11hi) However no obvious relationship ap-pears to be present between the sediment area and the total accommodation space (G) Both the sediment area and the average seismic progradation dip of the fan‐ and braid‐deltas correlate well with the average sedimentary dip of the fan‐ and braid‐deltas (Figure 11km) A poor correlation is found between the sediment volume and the average sedimentary dip of the fan‐ and braid‐deltas

6 | DISCUSSION

61 | Analysis of the influence of tectonic activity on the source area accommodation space geomorphology and sediment supplyA high relief and large drainage area usually can generate a large sediment supply (Leeder Harris amp Kirkby 1998 Syvitski amp Milliman 2007) Although the erosional area for the fan and delta system cannot be estimated because of the

limited data coverage the exposed area within the study area can be calculated The calculations show a generally decreas-ing trend of the source area from S‐4 (501 km2) to D‐2 (58 km2 Figure7 Table 4) The calculated exposed area cannot fully represent the true source area however but the evolu-tionary trend of the source area can be used as a proxy to indi-cate the relative influence on the change in sediment volume This trend is consistent with the decrease in sediment volume from S‐4 (2126 km3) to D‐2 (175 km3 Table 2) The relief is difficult to reconstruct in this case but variations in the fault‐activity rate (here taken as the tectonic‐subsidence rate) can create local elevation differences and can therefore be used as proxies for the trends in the relief development The relief shows an overall decreasing trend from S‐4 to D‐2 except for D‐3 this correlates well with the sediment volume (Figure 8h) Although the drainage area of D‐3 was smaller than that of D‐2 because of the high tectonic‐subsidence rate (result-ing in a high relief) D‐3 is thicker and shows a larger sedi-ment volume than the overlying D‐2 (Table 3) D‐3 is thinner than S‐4 + 3 but the larger source area resulted in a larger

F I G U R E 9 General relationships between the average fault‐growth index of F1 and F2 (AFGIF1‐F2) and sedimentary source‐to‐sink parameters The average fault‐growth index of F1 and F2 (AFGIF1‐F2) data in this figure are from Table 2 The source‐to‐sink parameters data are from Table 4 Regression‐line equations and the coefficients of determination are shown in each diagram

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sediment volume and supply rate (Table 3 Figure8ch) Therefore both the fault‐induced relief and the drainage area affected the sediment‐supply rate and the sediment volume in the sink

The changes in accommodation space during the vari-ous phases of the Palaeogene in the south‐western HD are clear from the estimated tectonic subsiding rate (Table 2) The correlations between the intensity of the tectonic activ-ity and the extent of the depositional sink area (Figures 8d 9b 10b) between the intensity of the tectonic activity and the total accommodation space and between the intensity of the tectonic activity and the morphology in the sink area (Figures 8e‐f 9c‐d 10c‐d) clearly show that strong tectonic activity resulted in a larger accommodation capacity of the sink

In particular the main subsiding area tended to form steeper slopes However the extent of the main subsiding sink area diminished (Figure 8d) with increasing tectonic activity which was possibly due to the relatively small sub-siding centre in the tectonically active basins It can thus be deduced that tectonic activity not only controlled the sedi-ment supply and the variation in accommodation space but

also determined the changes in the topography of the sedi-mentary basins and the extent of the main depositional areas in the tectonically active basins

62 | Analysis of the influence of tectonic activity on the size and internal stacking pattern of the delta depositional systemThe above data and considerations indicate that the tectonic activity was closely related to the sediment supply accom-modation space and morphology of the sink area which are possibly the most important factors affecting the extent and stacking pattern of the sedimentary facies (cf Cope et al 2010 DeCelles Kapp Ding amp Gehrels 2007 Leeder 2011 Olsen 1997 Simon et al 2017)

Statistical analysis indicates that the sediment‐supply rate has a strong positive correlation with the volume of the depositional system a moderate correlation with the seismic progradational dip in the depositional system and a poor cor-relation with the size of the depositional area (Figure 11a‐c) A larger sink area corresponded to a larger fanbraid‐delta a gentler seismic progradational angle and a reduced volume

F I G U R E 1 0 General relationships between average fault activity rate of F1 and F2 (RFAA‐F1‐F2) and sedimentary source‐to‐sink parameters The average fault activity rate of F1 and F2 (RFAA‐F1‐F2) data in this figure are from Table 2 The source‐to‐sink parameters data are from Table 4 Regression line equations and the coefficients of determination are shown in each diagram

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of the fan or braid‐delta which was possibly related to a re-duced sedimentary dip and thinner sediments (Figure 11d‐f) The total accommodation space in the basin correlates well

with the volume of the depositional system to some degree with the seismic progradational dip and poorly with the ex-tent of the depositional system area (Figure 11g‐i) These

FIGURE 11 Relationships between various parameters involved in the source‐to‐sink system (a‐c) Relationships between sediment supply and characteristics of the depositional system (extent volume and DPSA of the sediments) (d‐f) Relationships between the sink area of the basin and characteristics of the depositional system (g‐i) Relationships between the total accommodation space (AT) and the characteristics of the depositional system (j) Relationship between the accommodation‐spacesediment‐supply ratio (AS) and the DPSA of the sediments (k‐m) Relationships between the sedimentary dip and the characteristics of the depositional system The data regarding sediment supply basin sink area total accommodation space accommodation‐spacesediment‐supply ratio and sedimentary dips are from Table 4 The extent volume and DPSA of the sedimentary facies are from Table 3 Note the seemingly obvious polynomial (quadratic) relationship between the sedimentary dip and the sediment volume (L) The trend line in (L) suggests the following relationships between sediment volume and sedimentary slope in a rift or tectonically active basin (1) a very steep sedimentary slope is unfavourable for sediment accumulation (2) an appropriate sedimentary slope is favourable for preservation of depositional systems eg when the sedimentary slope in (L) is about 25degndash32deg the sediment volume reaches its largest value (3) a very gentle sedimentary slope will lead to a decrease of the sediment volume possibly due to weakening of the drainage system and thinner sediments

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relationships are clear evidence that the size of the sink area controlled the extent of the depositional system during the rifting of the lacustrine basin and that the rate of sediment supply and the accommodation space had a significant in-fluence on the total sedimentary volume as well as on the internal stacking pattern of the depositional system

We here use the ratio of the tectonic‐subsidence rate and the sediment‐supply rate as a proxy to indicate the ratio be-tween accommodation space and sediment‐supply rate (AS) (Table 4) AS has a strong influence on the internal stacking pattern of the depositional systems in the lacustrine rift basin (Figure 11j) This might be because the basin was small and because abundant and rapid material was supplied due

to intense tectonic activity (cf Catuneanu et al 2009 Liro 1993) and a favourable local climate (eg Bohacs Carroll Neal amp Mankiewicz 2000 Perlmutter amp Matthews 1989) The sediment supply still had a significant influence on the main subsidence area of the lacustrine basins and deposi-tional systems

In addition the basin slope significantly influenced the extent of the depositional system (Figure 11k) and had a polynomial relationship with its volume (Figure 11l) This relationship indicates that more intense tectonic activity and a steeper depositional slope were not favourable for sediment accumulation over a large extent in the lacustrine basin On the contrary these sediments were usually transported to a

F I G U R E 1 2 Tectonic differential activities and resulting patterns of the source‐to‐sink system on the south‐western slope of the HD during the Palaeogene (a) Development during phases of intense tectonics (Member 4 to the lower part of Member 3 of the Shahejie Fm) (b) Development during phases of somewhat less tectonic activity (middle part of Member 3 of the Shahejie Fm and Member 3 of the Dongying Fm) (c) Development during phases of weak tectonic activity (Members 1 and 2 of the Shahejie Fm and Member 2 of the Dongying Fm) The intensity of tectonic activity in the lacustrine rift basin had a significant influence on the development and extent of each unit of the source‐to‐sink system as well as on the type and dimensions of the depositional systems The present study indicates that probably sublacustrine fans developed (see for example Figure S4b) during phases with relatively strong tectonic activity This is not really clear from the seismic‐reflection data but possibly due to the small sizes of these sublacustrine fans Moreover lithofacies and core data are not available for the south‐western part of the study area The present contribution therefore focuses on the fan‐deltas and braid‐deltas regarding the sedimentary facies analysis the sublacustrine fans that probably developed in the deep or semi‐deep lake are presented just as a likely feature

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relatively small sink area with a fairly large accommodation space Finally stronger tectonic activity resulted in steeper depositional slopes (Figure 8f) which further controlled the hydrodynamic conditions and differential discharge when the sediments were deposited The strong correlation between the depositional slope and the deltas dip (Figure 11m) suggests that the differences in topography due to tectonics must be considered as one of the most critical factors that controlled the internal stacking pattern of the delta deposits

63 | Significance of the present study for other source‐to‐sink systems of lacustrine rift basins

631 | Summary of the source‐to‐sink systems in the HDIn lacustrine rift basins the tectonic setting is probably the main factor that determines the development of the S2S sys-tem but differential tectonic activities lead to variations in the basic characteristics of the S2S system Tectonic activity was most intense during S‐3 (lower unit) and during S‐4 and caused both a strong uplift of the source area and the devel-opment of depressions in the basin that formed a sink (Figure 12a) Strong tectonic activity in the S2S system during these time‐spans led to a high sediment‐supply rate steeper slopes a larger accommodation space and deposition of several fan‐deltas that are characterized by a fairly steep seismic progra-dational angle

The tectonic activity decreased during S‐3 (middle unit) and during D‐3 The S2S system that was present during this time‐span mainly concerned a rising area that shifted south-wards developing an alluvial plain between the erosional area and the sink area thus increasing the distance from source to sink (Figure 12b) Simultaneously the sediment‐supply rate and the accommodation space also changed and braid‐deltas could thus develop with larger volumes and gentler seismic progradational dips

Tectonic activity was clearly less intense during S‐1 + 2 and D‐2 The rising area had shifted further southwards cre-ating a wider alluvial plain connecting the source area to the sink in the HD (Figure 12c) At this stage stable tectonic activity led to relatively less sediment supply a gentle slope less accommodation space and the development of several braid‐deltas with a fairly gentle seismic progradational angle

632 | Wider implications and limitationsSoslashmme et al (2009) proposed that the elements of S2S sys-tems are genetically related and that quantitative correla-tions exist among these elements Other studies also suggest that the size of the drainage basin is correlated to the size of the fan developing on the basin floor (eg Blum et al

2017 Snedden et al 2018) and to the size of the river chan-nel (eg Milliken et al 2018) Helland‐Hansen Soslashmme Martinsen Lunt and Thurmond (2016) suggest a simplified subdivision of S2S systems into three main categories (a) Steep‐Short‐Deep (steep onshore and offshore gradients short distance between source and sink and deep offshore waters) (b) Wide‐Deep (low‐gradient shelf‐catchment area and deep offshore waters) and (c) Wide‐Shallow (relatively shallow offshore waters and a wide low‐gradient catchment area) systems

The present study indicates that the alluvial plain roughly corresponds to the alluvial‐shelf unit in marine basins al-though with a much smaller width and extent in the lacustrine rift basins than would have been the case on a continental shelf Faults F1 and F2 along the slope belt correspond to the slope of classical S2S systems whereas the shore‐shallow‐deep lake area can be compared with the basin floor (Soslashmme et al 2009) S‐4 and S‐3 (lower unit) can be roughly clas-sified as Steep‐Short‐Deep systems whereas the overlying S‐1 + 2and D‐2 can be classified as the Wide‐Shallow sys-tems that Helland‐Hansen et al (2016) defined During the deposition of S‐4 and S‐3 (lower unit) the strong tectonic activity caused a high relief of the source area a narrow allu-vial plain and a relatively deep lake The subsequently wan-ing tectonic activity resulted in a lower relief of the source area a wider alluvial plain and a shallower lake Although the absolute values of these elements in lacustrine basins are much smaller than those of marine basins the ratio between these elements in both settings is comparable Typically in a lacustrine basin a transformation from a Steep‐Short‐Deep system (S‐4 and S‐3 (lower unit)) to a Wide‐Shallow system (S‐1 + 2ampD‐2) occurs within a few million years Although the basin geomorphology has experienced signif-icant changes from S‐4 to D‐2 the quantitative relationships between tectonic activity sediment‐supply rate accommoda-tion space and sedimentary dip of the delta systems did not change significantly (eg Figures 8 and 11) The analytical approaches applied and quantitative relationship established here can help analyse other lacustrine basins worldwide and may even act as a reference for the analysis of marine basins

Our study focuses mainly on the influences of tectonic activity on the elements of the depositional sink Other pa-rameters (eg climate and lithology) were not considered in detail Studies on modern and ancient systems suggest that the climate and lithology also have a great influence on the sediment supply and distribution in the basin (eg Carroll Chetel amp Smith 2006 Hovius amp Leeder 1998 Syvitski amp Milliman 2007 Zhang et al 2018) For exam-ple climate variations between glacials and inter‐glacials have resulted in largely different sediment‐supply rates and in significant differences in the sizes of the Quaternary sub-marine fans in the north‐western Gulf of Mexico (Blum amp Hattier‐Womack 2009) We acknowledge the importance

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of climate and lithology for S2S systems and we are con-vinced that these elements can significantly affect the S2S systems in other cases(eg modern systems and systems influenced by glacialinterglacial alternations) These fac-tors were not really relevant for the present study however because no significant differences in lithology were present in the source areas and because we focus on the changes at a million‐year scale which implies that the tectonic ac-tivity has a first‐order control on the development of S2S elements in the investigated rift basin

7 | CONCLUSIONS

We have calculated the tectonic‐subsidence history the growth index and the activity rate of the main boundary faults (F1 and F2) and various S2S parameters of six Palaeogene rock units on the south‐western slope of the HD Based on the values found for these parameters quantitative corre-lation were established for the tectonic activity and other S2Sparameters in the basinal sink This leads to the follow-ing conclusions

1 The positive correlation between the intensity of fault activity and the tectonic‐subsidence rate is a strong indication for a distinct control by the tectonic activity of the syn‐depositional rifting of the tectonically active basin

2 The tectonic activity was quantitatively related to the sediment supply accommodation space and morphology of the sink area The relationship between tectonic activ-ity and depositional systems is reflected by changes in critical factors such as sediment supply accommodation space and dip of the sink area These critical factors were probably the most important factors that led to changes in the size and internal stacking pattern of the sedimentary facies

3 Differential tectonic activity led to changes in the char-acteristics of the S2S system on the south‐western slope of the HD The strongest tectonic activity which oc-curred during S‐3 (lower unit) and during S‐4 led to the largest provenance area adjacent to the sink area to a high sediment‐supply rate to steeper slopes to a larger accommodation space and controlled the development of several fan‐deltas Diminished tectonic activity dur-ing S‐3 (middle unit) and during D‐3 led to a decrease in uplift an increased width of the alluvial plain an in-creased transport distance a decrease in the sediment‐supply rate and accommodation space and resulted in the development of braid‐deltas with a large volume During S‐1 + 2 and D‐2 stable tectonic activity led to a lower sediment‐supply rate a gentle depositional slope and a smaller accommodation space resulting in the

development of several braid‐deltas with gentler seis-mic progradational angles

4 The analytical approaches applied and the quantitative re-lationships established here can help analyse other lacus-trine basins worldwide and may even act as a reference for the study of marine basins

ACKNOWLEDGEMENTS

We thank Dr Sarah Boulton and Dr Chenlin Gong as well as the Associate Editor of Basin Research Dr Craig Magee for their constructive comments on the manuscript This study was funded by the National Science and Technology Major Project (Exploration Technologies for Offshore Hidden OilGas) (project no 2016ZX05024‐003‐003) the National Natural Science Foundations of China (project no 41676050) and the Fundamental Research Funds for the Central Universities (2652014037)

REFERENCES

Allen P A (2008a) From landscapes into geological history Nature 451 274ndash276 https doiorg101038natur e06586

Allen P A (2008b) Time scales of tectonic landscapes and their sed-iment routing systems In Landscape evolution Denudation cli-mate and tectonics over different time and space scales (Ed by Gallagher K Jones S J amp Wainwright J) Geological Society London Special Publications 296 7ndash28

Allen P A Armitage J J Carter A Duller R A Michael N A Sinclair H D hellip Whittaker A C (2013) The Qs problem Sediment volumetric balance of proximal foreland basin systems Sedimentology 60 102ndash130

Amorosi A Maselli V amp Trincardi F (2016) Onshore to offshore anatomy of a late Quaternary source‐to‐sink system (Po Plain‐Adriatic Sea Italy) Earth‐Science Reviews 153 212ndash237 https doiorg101016jearsc irev201510010

Anderson J B Wallace D J Simms A R Rodriguez A B Weight R W R amp Taha Z P (2016) Recycling sediments between source and sink during a eustatic cycle Systems of late Quaternary northwestern Gulf of Mexico Basin Earth‐Science Reviews 153 111ndash138 https doiorg101016jearsc irev201510014

Anthony E J amp Julian M (1999) Source‐to‐sink sediment trans-fers environmental engineering and hazard mitigation in the steep Var River catchment French Riviera southeastern France Geomorphology 31 337ndash354 https doiorg101016S0169-555X(99)00088-4

Athy L F (1930) Density porosity and compaction of sedimentary rocks AAPG Bulletin 14 1ndash24

Bhattacharya J P Copeland P Lawton T F amp Holbrook J (2016) Estimation of source area river palaeo‐discharge palaeoslope and sediment budgets of linked deep‐time depositional systems and im-plications for hydrocarbon potential Earth‐Science Reviews 153 77ndash110

Blum M D amp Hattier‐Womack J (2009) Climate change sea‐level change and fluvial sediment supply to deepwater depositional

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sediment volume and supply rate (Table 3 Figure8ch) Therefore both the fault‐induced relief and the drainage area affected the sediment‐supply rate and the sediment volume in the sink

The changes in accommodation space during the vari-ous phases of the Palaeogene in the south‐western HD are clear from the estimated tectonic subsiding rate (Table 2) The correlations between the intensity of the tectonic activ-ity and the extent of the depositional sink area (Figures 8d 9b 10b) between the intensity of the tectonic activity and the total accommodation space and between the intensity of the tectonic activity and the morphology in the sink area (Figures 8e‐f 9c‐d 10c‐d) clearly show that strong tectonic activity resulted in a larger accommodation capacity of the sink

In particular the main subsiding area tended to form steeper slopes However the extent of the main subsiding sink area diminished (Figure 8d) with increasing tectonic activity which was possibly due to the relatively small sub-siding centre in the tectonically active basins It can thus be deduced that tectonic activity not only controlled the sedi-ment supply and the variation in accommodation space but

also determined the changes in the topography of the sedi-mentary basins and the extent of the main depositional areas in the tectonically active basins

62 | Analysis of the influence of tectonic activity on the size and internal stacking pattern of the delta depositional systemThe above data and considerations indicate that the tectonic activity was closely related to the sediment supply accom-modation space and morphology of the sink area which are possibly the most important factors affecting the extent and stacking pattern of the sedimentary facies (cf Cope et al 2010 DeCelles Kapp Ding amp Gehrels 2007 Leeder 2011 Olsen 1997 Simon et al 2017)

Statistical analysis indicates that the sediment‐supply rate has a strong positive correlation with the volume of the depositional system a moderate correlation with the seismic progradational dip in the depositional system and a poor cor-relation with the size of the depositional area (Figure 11a‐c) A larger sink area corresponded to a larger fanbraid‐delta a gentler seismic progradational angle and a reduced volume

F I G U R E 1 0 General relationships between average fault activity rate of F1 and F2 (RFAA‐F1‐F2) and sedimentary source‐to‐sink parameters The average fault activity rate of F1 and F2 (RFAA‐F1‐F2) data in this figure are from Table 2 The source‐to‐sink parameters data are from Table 4 Regression line equations and the coefficients of determination are shown in each diagram

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of the fan or braid‐delta which was possibly related to a re-duced sedimentary dip and thinner sediments (Figure 11d‐f) The total accommodation space in the basin correlates well

with the volume of the depositional system to some degree with the seismic progradational dip and poorly with the ex-tent of the depositional system area (Figure 11g‐i) These

FIGURE 11 Relationships between various parameters involved in the source‐to‐sink system (a‐c) Relationships between sediment supply and characteristics of the depositional system (extent volume and DPSA of the sediments) (d‐f) Relationships between the sink area of the basin and characteristics of the depositional system (g‐i) Relationships between the total accommodation space (AT) and the characteristics of the depositional system (j) Relationship between the accommodation‐spacesediment‐supply ratio (AS) and the DPSA of the sediments (k‐m) Relationships between the sedimentary dip and the characteristics of the depositional system The data regarding sediment supply basin sink area total accommodation space accommodation‐spacesediment‐supply ratio and sedimentary dips are from Table 4 The extent volume and DPSA of the sedimentary facies are from Table 3 Note the seemingly obvious polynomial (quadratic) relationship between the sedimentary dip and the sediment volume (L) The trend line in (L) suggests the following relationships between sediment volume and sedimentary slope in a rift or tectonically active basin (1) a very steep sedimentary slope is unfavourable for sediment accumulation (2) an appropriate sedimentary slope is favourable for preservation of depositional systems eg when the sedimentary slope in (L) is about 25degndash32deg the sediment volume reaches its largest value (3) a very gentle sedimentary slope will lead to a decrease of the sediment volume possibly due to weakening of the drainage system and thinner sediments

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relationships are clear evidence that the size of the sink area controlled the extent of the depositional system during the rifting of the lacustrine basin and that the rate of sediment supply and the accommodation space had a significant in-fluence on the total sedimentary volume as well as on the internal stacking pattern of the depositional system

We here use the ratio of the tectonic‐subsidence rate and the sediment‐supply rate as a proxy to indicate the ratio be-tween accommodation space and sediment‐supply rate (AS) (Table 4) AS has a strong influence on the internal stacking pattern of the depositional systems in the lacustrine rift basin (Figure 11j) This might be because the basin was small and because abundant and rapid material was supplied due

to intense tectonic activity (cf Catuneanu et al 2009 Liro 1993) and a favourable local climate (eg Bohacs Carroll Neal amp Mankiewicz 2000 Perlmutter amp Matthews 1989) The sediment supply still had a significant influence on the main subsidence area of the lacustrine basins and deposi-tional systems

In addition the basin slope significantly influenced the extent of the depositional system (Figure 11k) and had a polynomial relationship with its volume (Figure 11l) This relationship indicates that more intense tectonic activity and a steeper depositional slope were not favourable for sediment accumulation over a large extent in the lacustrine basin On the contrary these sediments were usually transported to a

F I G U R E 1 2 Tectonic differential activities and resulting patterns of the source‐to‐sink system on the south‐western slope of the HD during the Palaeogene (a) Development during phases of intense tectonics (Member 4 to the lower part of Member 3 of the Shahejie Fm) (b) Development during phases of somewhat less tectonic activity (middle part of Member 3 of the Shahejie Fm and Member 3 of the Dongying Fm) (c) Development during phases of weak tectonic activity (Members 1 and 2 of the Shahejie Fm and Member 2 of the Dongying Fm) The intensity of tectonic activity in the lacustrine rift basin had a significant influence on the development and extent of each unit of the source‐to‐sink system as well as on the type and dimensions of the depositional systems The present study indicates that probably sublacustrine fans developed (see for example Figure S4b) during phases with relatively strong tectonic activity This is not really clear from the seismic‐reflection data but possibly due to the small sizes of these sublacustrine fans Moreover lithofacies and core data are not available for the south‐western part of the study area The present contribution therefore focuses on the fan‐deltas and braid‐deltas regarding the sedimentary facies analysis the sublacustrine fans that probably developed in the deep or semi‐deep lake are presented just as a likely feature

608 | EAGE

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relatively small sink area with a fairly large accommodation space Finally stronger tectonic activity resulted in steeper depositional slopes (Figure 8f) which further controlled the hydrodynamic conditions and differential discharge when the sediments were deposited The strong correlation between the depositional slope and the deltas dip (Figure 11m) suggests that the differences in topography due to tectonics must be considered as one of the most critical factors that controlled the internal stacking pattern of the delta deposits

63 | Significance of the present study for other source‐to‐sink systems of lacustrine rift basins

631 | Summary of the source‐to‐sink systems in the HDIn lacustrine rift basins the tectonic setting is probably the main factor that determines the development of the S2S sys-tem but differential tectonic activities lead to variations in the basic characteristics of the S2S system Tectonic activity was most intense during S‐3 (lower unit) and during S‐4 and caused both a strong uplift of the source area and the devel-opment of depressions in the basin that formed a sink (Figure 12a) Strong tectonic activity in the S2S system during these time‐spans led to a high sediment‐supply rate steeper slopes a larger accommodation space and deposition of several fan‐deltas that are characterized by a fairly steep seismic progra-dational angle

The tectonic activity decreased during S‐3 (middle unit) and during D‐3 The S2S system that was present during this time‐span mainly concerned a rising area that shifted south-wards developing an alluvial plain between the erosional area and the sink area thus increasing the distance from source to sink (Figure 12b) Simultaneously the sediment‐supply rate and the accommodation space also changed and braid‐deltas could thus develop with larger volumes and gentler seismic progradational dips

Tectonic activity was clearly less intense during S‐1 + 2 and D‐2 The rising area had shifted further southwards cre-ating a wider alluvial plain connecting the source area to the sink in the HD (Figure 12c) At this stage stable tectonic activity led to relatively less sediment supply a gentle slope less accommodation space and the development of several braid‐deltas with a fairly gentle seismic progradational angle

632 | Wider implications and limitationsSoslashmme et al (2009) proposed that the elements of S2S sys-tems are genetically related and that quantitative correla-tions exist among these elements Other studies also suggest that the size of the drainage basin is correlated to the size of the fan developing on the basin floor (eg Blum et al

2017 Snedden et al 2018) and to the size of the river chan-nel (eg Milliken et al 2018) Helland‐Hansen Soslashmme Martinsen Lunt and Thurmond (2016) suggest a simplified subdivision of S2S systems into three main categories (a) Steep‐Short‐Deep (steep onshore and offshore gradients short distance between source and sink and deep offshore waters) (b) Wide‐Deep (low‐gradient shelf‐catchment area and deep offshore waters) and (c) Wide‐Shallow (relatively shallow offshore waters and a wide low‐gradient catchment area) systems

The present study indicates that the alluvial plain roughly corresponds to the alluvial‐shelf unit in marine basins al-though with a much smaller width and extent in the lacustrine rift basins than would have been the case on a continental shelf Faults F1 and F2 along the slope belt correspond to the slope of classical S2S systems whereas the shore‐shallow‐deep lake area can be compared with the basin floor (Soslashmme et al 2009) S‐4 and S‐3 (lower unit) can be roughly clas-sified as Steep‐Short‐Deep systems whereas the overlying S‐1 + 2and D‐2 can be classified as the Wide‐Shallow sys-tems that Helland‐Hansen et al (2016) defined During the deposition of S‐4 and S‐3 (lower unit) the strong tectonic activity caused a high relief of the source area a narrow allu-vial plain and a relatively deep lake The subsequently wan-ing tectonic activity resulted in a lower relief of the source area a wider alluvial plain and a shallower lake Although the absolute values of these elements in lacustrine basins are much smaller than those of marine basins the ratio between these elements in both settings is comparable Typically in a lacustrine basin a transformation from a Steep‐Short‐Deep system (S‐4 and S‐3 (lower unit)) to a Wide‐Shallow system (S‐1 + 2ampD‐2) occurs within a few million years Although the basin geomorphology has experienced signif-icant changes from S‐4 to D‐2 the quantitative relationships between tectonic activity sediment‐supply rate accommoda-tion space and sedimentary dip of the delta systems did not change significantly (eg Figures 8 and 11) The analytical approaches applied and quantitative relationship established here can help analyse other lacustrine basins worldwide and may even act as a reference for the analysis of marine basins

Our study focuses mainly on the influences of tectonic activity on the elements of the depositional sink Other pa-rameters (eg climate and lithology) were not considered in detail Studies on modern and ancient systems suggest that the climate and lithology also have a great influence on the sediment supply and distribution in the basin (eg Carroll Chetel amp Smith 2006 Hovius amp Leeder 1998 Syvitski amp Milliman 2007 Zhang et al 2018) For exam-ple climate variations between glacials and inter‐glacials have resulted in largely different sediment‐supply rates and in significant differences in the sizes of the Quaternary sub-marine fans in the north‐western Gulf of Mexico (Blum amp Hattier‐Womack 2009) We acknowledge the importance

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of climate and lithology for S2S systems and we are con-vinced that these elements can significantly affect the S2S systems in other cases(eg modern systems and systems influenced by glacialinterglacial alternations) These fac-tors were not really relevant for the present study however because no significant differences in lithology were present in the source areas and because we focus on the changes at a million‐year scale which implies that the tectonic ac-tivity has a first‐order control on the development of S2S elements in the investigated rift basin

7 | CONCLUSIONS

We have calculated the tectonic‐subsidence history the growth index and the activity rate of the main boundary faults (F1 and F2) and various S2S parameters of six Palaeogene rock units on the south‐western slope of the HD Based on the values found for these parameters quantitative corre-lation were established for the tectonic activity and other S2Sparameters in the basinal sink This leads to the follow-ing conclusions

1 The positive correlation between the intensity of fault activity and the tectonic‐subsidence rate is a strong indication for a distinct control by the tectonic activity of the syn‐depositional rifting of the tectonically active basin

2 The tectonic activity was quantitatively related to the sediment supply accommodation space and morphology of the sink area The relationship between tectonic activ-ity and depositional systems is reflected by changes in critical factors such as sediment supply accommodation space and dip of the sink area These critical factors were probably the most important factors that led to changes in the size and internal stacking pattern of the sedimentary facies

3 Differential tectonic activity led to changes in the char-acteristics of the S2S system on the south‐western slope of the HD The strongest tectonic activity which oc-curred during S‐3 (lower unit) and during S‐4 led to the largest provenance area adjacent to the sink area to a high sediment‐supply rate to steeper slopes to a larger accommodation space and controlled the development of several fan‐deltas Diminished tectonic activity dur-ing S‐3 (middle unit) and during D‐3 led to a decrease in uplift an increased width of the alluvial plain an in-creased transport distance a decrease in the sediment‐supply rate and accommodation space and resulted in the development of braid‐deltas with a large volume During S‐1 + 2 and D‐2 stable tectonic activity led to a lower sediment‐supply rate a gentle depositional slope and a smaller accommodation space resulting in the

development of several braid‐deltas with gentler seis-mic progradational angles

4 The analytical approaches applied and the quantitative re-lationships established here can help analyse other lacus-trine basins worldwide and may even act as a reference for the study of marine basins

ACKNOWLEDGEMENTS

We thank Dr Sarah Boulton and Dr Chenlin Gong as well as the Associate Editor of Basin Research Dr Craig Magee for their constructive comments on the manuscript This study was funded by the National Science and Technology Major Project (Exploration Technologies for Offshore Hidden OilGas) (project no 2016ZX05024‐003‐003) the National Natural Science Foundations of China (project no 41676050) and the Fundamental Research Funds for the Central Universities (2652014037)

REFERENCES

Allen P A (2008a) From landscapes into geological history Nature 451 274ndash276 https doiorg101038natur e06586

Allen P A (2008b) Time scales of tectonic landscapes and their sed-iment routing systems In Landscape evolution Denudation cli-mate and tectonics over different time and space scales (Ed by Gallagher K Jones S J amp Wainwright J) Geological Society London Special Publications 296 7ndash28

Allen P A Armitage J J Carter A Duller R A Michael N A Sinclair H D hellip Whittaker A C (2013) The Qs problem Sediment volumetric balance of proximal foreland basin systems Sedimentology 60 102ndash130

Amorosi A Maselli V amp Trincardi F (2016) Onshore to offshore anatomy of a late Quaternary source‐to‐sink system (Po Plain‐Adriatic Sea Italy) Earth‐Science Reviews 153 212ndash237 https doiorg101016jearsc irev201510010

Anderson J B Wallace D J Simms A R Rodriguez A B Weight R W R amp Taha Z P (2016) Recycling sediments between source and sink during a eustatic cycle Systems of late Quaternary northwestern Gulf of Mexico Basin Earth‐Science Reviews 153 111ndash138 https doiorg101016jearsc irev201510014

Anthony E J amp Julian M (1999) Source‐to‐sink sediment trans-fers environmental engineering and hazard mitigation in the steep Var River catchment French Riviera southeastern France Geomorphology 31 337ndash354 https doiorg101016S0169-555X(99)00088-4

Athy L F (1930) Density porosity and compaction of sedimentary rocks AAPG Bulletin 14 1ndash24

Bhattacharya J P Copeland P Lawton T F amp Holbrook J (2016) Estimation of source area river palaeo‐discharge palaeoslope and sediment budgets of linked deep‐time depositional systems and im-plications for hydrocarbon potential Earth‐Science Reviews 153 77ndash110

Blum M D amp Hattier‐Womack J (2009) Climate change sea‐level change and fluvial sediment supply to deepwater depositional

606 | EAGE

LIU et aL

of the fan or braid‐delta which was possibly related to a re-duced sedimentary dip and thinner sediments (Figure 11d‐f) The total accommodation space in the basin correlates well

with the volume of the depositional system to some degree with the seismic progradational dip and poorly with the ex-tent of the depositional system area (Figure 11g‐i) These

FIGURE 11 Relationships between various parameters involved in the source‐to‐sink system (a‐c) Relationships between sediment supply and characteristics of the depositional system (extent volume and DPSA of the sediments) (d‐f) Relationships between the sink area of the basin and characteristics of the depositional system (g‐i) Relationships between the total accommodation space (AT) and the characteristics of the depositional system (j) Relationship between the accommodation‐spacesediment‐supply ratio (AS) and the DPSA of the sediments (k‐m) Relationships between the sedimentary dip and the characteristics of the depositional system The data regarding sediment supply basin sink area total accommodation space accommodation‐spacesediment‐supply ratio and sedimentary dips are from Table 4 The extent volume and DPSA of the sedimentary facies are from Table 3 Note the seemingly obvious polynomial (quadratic) relationship between the sedimentary dip and the sediment volume (L) The trend line in (L) suggests the following relationships between sediment volume and sedimentary slope in a rift or tectonically active basin (1) a very steep sedimentary slope is unfavourable for sediment accumulation (2) an appropriate sedimentary slope is favourable for preservation of depositional systems eg when the sedimentary slope in (L) is about 25degndash32deg the sediment volume reaches its largest value (3) a very gentle sedimentary slope will lead to a decrease of the sediment volume possibly due to weakening of the drainage system and thinner sediments

| 607EAGE

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relationships are clear evidence that the size of the sink area controlled the extent of the depositional system during the rifting of the lacustrine basin and that the rate of sediment supply and the accommodation space had a significant in-fluence on the total sedimentary volume as well as on the internal stacking pattern of the depositional system

We here use the ratio of the tectonic‐subsidence rate and the sediment‐supply rate as a proxy to indicate the ratio be-tween accommodation space and sediment‐supply rate (AS) (Table 4) AS has a strong influence on the internal stacking pattern of the depositional systems in the lacustrine rift basin (Figure 11j) This might be because the basin was small and because abundant and rapid material was supplied due

to intense tectonic activity (cf Catuneanu et al 2009 Liro 1993) and a favourable local climate (eg Bohacs Carroll Neal amp Mankiewicz 2000 Perlmutter amp Matthews 1989) The sediment supply still had a significant influence on the main subsidence area of the lacustrine basins and deposi-tional systems

In addition the basin slope significantly influenced the extent of the depositional system (Figure 11k) and had a polynomial relationship with its volume (Figure 11l) This relationship indicates that more intense tectonic activity and a steeper depositional slope were not favourable for sediment accumulation over a large extent in the lacustrine basin On the contrary these sediments were usually transported to a

F I G U R E 1 2 Tectonic differential activities and resulting patterns of the source‐to‐sink system on the south‐western slope of the HD during the Palaeogene (a) Development during phases of intense tectonics (Member 4 to the lower part of Member 3 of the Shahejie Fm) (b) Development during phases of somewhat less tectonic activity (middle part of Member 3 of the Shahejie Fm and Member 3 of the Dongying Fm) (c) Development during phases of weak tectonic activity (Members 1 and 2 of the Shahejie Fm and Member 2 of the Dongying Fm) The intensity of tectonic activity in the lacustrine rift basin had a significant influence on the development and extent of each unit of the source‐to‐sink system as well as on the type and dimensions of the depositional systems The present study indicates that probably sublacustrine fans developed (see for example Figure S4b) during phases with relatively strong tectonic activity This is not really clear from the seismic‐reflection data but possibly due to the small sizes of these sublacustrine fans Moreover lithofacies and core data are not available for the south‐western part of the study area The present contribution therefore focuses on the fan‐deltas and braid‐deltas regarding the sedimentary facies analysis the sublacustrine fans that probably developed in the deep or semi‐deep lake are presented just as a likely feature

608 | EAGE

LIU et aL

relatively small sink area with a fairly large accommodation space Finally stronger tectonic activity resulted in steeper depositional slopes (Figure 8f) which further controlled the hydrodynamic conditions and differential discharge when the sediments were deposited The strong correlation between the depositional slope and the deltas dip (Figure 11m) suggests that the differences in topography due to tectonics must be considered as one of the most critical factors that controlled the internal stacking pattern of the delta deposits

63 | Significance of the present study for other source‐to‐sink systems of lacustrine rift basins

631 | Summary of the source‐to‐sink systems in the HDIn lacustrine rift basins the tectonic setting is probably the main factor that determines the development of the S2S sys-tem but differential tectonic activities lead to variations in the basic characteristics of the S2S system Tectonic activity was most intense during S‐3 (lower unit) and during S‐4 and caused both a strong uplift of the source area and the devel-opment of depressions in the basin that formed a sink (Figure 12a) Strong tectonic activity in the S2S system during these time‐spans led to a high sediment‐supply rate steeper slopes a larger accommodation space and deposition of several fan‐deltas that are characterized by a fairly steep seismic progra-dational angle

The tectonic activity decreased during S‐3 (middle unit) and during D‐3 The S2S system that was present during this time‐span mainly concerned a rising area that shifted south-wards developing an alluvial plain between the erosional area and the sink area thus increasing the distance from source to sink (Figure 12b) Simultaneously the sediment‐supply rate and the accommodation space also changed and braid‐deltas could thus develop with larger volumes and gentler seismic progradational dips

Tectonic activity was clearly less intense during S‐1 + 2 and D‐2 The rising area had shifted further southwards cre-ating a wider alluvial plain connecting the source area to the sink in the HD (Figure 12c) At this stage stable tectonic activity led to relatively less sediment supply a gentle slope less accommodation space and the development of several braid‐deltas with a fairly gentle seismic progradational angle

632 | Wider implications and limitationsSoslashmme et al (2009) proposed that the elements of S2S sys-tems are genetically related and that quantitative correla-tions exist among these elements Other studies also suggest that the size of the drainage basin is correlated to the size of the fan developing on the basin floor (eg Blum et al

2017 Snedden et al 2018) and to the size of the river chan-nel (eg Milliken et al 2018) Helland‐Hansen Soslashmme Martinsen Lunt and Thurmond (2016) suggest a simplified subdivision of S2S systems into three main categories (a) Steep‐Short‐Deep (steep onshore and offshore gradients short distance between source and sink and deep offshore waters) (b) Wide‐Deep (low‐gradient shelf‐catchment area and deep offshore waters) and (c) Wide‐Shallow (relatively shallow offshore waters and a wide low‐gradient catchment area) systems

The present study indicates that the alluvial plain roughly corresponds to the alluvial‐shelf unit in marine basins al-though with a much smaller width and extent in the lacustrine rift basins than would have been the case on a continental shelf Faults F1 and F2 along the slope belt correspond to the slope of classical S2S systems whereas the shore‐shallow‐deep lake area can be compared with the basin floor (Soslashmme et al 2009) S‐4 and S‐3 (lower unit) can be roughly clas-sified as Steep‐Short‐Deep systems whereas the overlying S‐1 + 2and D‐2 can be classified as the Wide‐Shallow sys-tems that Helland‐Hansen et al (2016) defined During the deposition of S‐4 and S‐3 (lower unit) the strong tectonic activity caused a high relief of the source area a narrow allu-vial plain and a relatively deep lake The subsequently wan-ing tectonic activity resulted in a lower relief of the source area a wider alluvial plain and a shallower lake Although the absolute values of these elements in lacustrine basins are much smaller than those of marine basins the ratio between these elements in both settings is comparable Typically in a lacustrine basin a transformation from a Steep‐Short‐Deep system (S‐4 and S‐3 (lower unit)) to a Wide‐Shallow system (S‐1 + 2ampD‐2) occurs within a few million years Although the basin geomorphology has experienced signif-icant changes from S‐4 to D‐2 the quantitative relationships between tectonic activity sediment‐supply rate accommoda-tion space and sedimentary dip of the delta systems did not change significantly (eg Figures 8 and 11) The analytical approaches applied and quantitative relationship established here can help analyse other lacustrine basins worldwide and may even act as a reference for the analysis of marine basins

Our study focuses mainly on the influences of tectonic activity on the elements of the depositional sink Other pa-rameters (eg climate and lithology) were not considered in detail Studies on modern and ancient systems suggest that the climate and lithology also have a great influence on the sediment supply and distribution in the basin (eg Carroll Chetel amp Smith 2006 Hovius amp Leeder 1998 Syvitski amp Milliman 2007 Zhang et al 2018) For exam-ple climate variations between glacials and inter‐glacials have resulted in largely different sediment‐supply rates and in significant differences in the sizes of the Quaternary sub-marine fans in the north‐western Gulf of Mexico (Blum amp Hattier‐Womack 2009) We acknowledge the importance

| 609EAGE

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of climate and lithology for S2S systems and we are con-vinced that these elements can significantly affect the S2S systems in other cases(eg modern systems and systems influenced by glacialinterglacial alternations) These fac-tors were not really relevant for the present study however because no significant differences in lithology were present in the source areas and because we focus on the changes at a million‐year scale which implies that the tectonic ac-tivity has a first‐order control on the development of S2S elements in the investigated rift basin

7 | CONCLUSIONS

We have calculated the tectonic‐subsidence history the growth index and the activity rate of the main boundary faults (F1 and F2) and various S2S parameters of six Palaeogene rock units on the south‐western slope of the HD Based on the values found for these parameters quantitative corre-lation were established for the tectonic activity and other S2Sparameters in the basinal sink This leads to the follow-ing conclusions

1 The positive correlation between the intensity of fault activity and the tectonic‐subsidence rate is a strong indication for a distinct control by the tectonic activity of the syn‐depositional rifting of the tectonically active basin

2 The tectonic activity was quantitatively related to the sediment supply accommodation space and morphology of the sink area The relationship between tectonic activ-ity and depositional systems is reflected by changes in critical factors such as sediment supply accommodation space and dip of the sink area These critical factors were probably the most important factors that led to changes in the size and internal stacking pattern of the sedimentary facies

3 Differential tectonic activity led to changes in the char-acteristics of the S2S system on the south‐western slope of the HD The strongest tectonic activity which oc-curred during S‐3 (lower unit) and during S‐4 led to the largest provenance area adjacent to the sink area to a high sediment‐supply rate to steeper slopes to a larger accommodation space and controlled the development of several fan‐deltas Diminished tectonic activity dur-ing S‐3 (middle unit) and during D‐3 led to a decrease in uplift an increased width of the alluvial plain an in-creased transport distance a decrease in the sediment‐supply rate and accommodation space and resulted in the development of braid‐deltas with a large volume During S‐1 + 2 and D‐2 stable tectonic activity led to a lower sediment‐supply rate a gentle depositional slope and a smaller accommodation space resulting in the

development of several braid‐deltas with gentler seis-mic progradational angles

4 The analytical approaches applied and the quantitative re-lationships established here can help analyse other lacus-trine basins worldwide and may even act as a reference for the study of marine basins

ACKNOWLEDGEMENTS

We thank Dr Sarah Boulton and Dr Chenlin Gong as well as the Associate Editor of Basin Research Dr Craig Magee for their constructive comments on the manuscript This study was funded by the National Science and Technology Major Project (Exploration Technologies for Offshore Hidden OilGas) (project no 2016ZX05024‐003‐003) the National Natural Science Foundations of China (project no 41676050) and the Fundamental Research Funds for the Central Universities (2652014037)

REFERENCES

Allen P A (2008a) From landscapes into geological history Nature 451 274ndash276 https doiorg101038natur e06586

Allen P A (2008b) Time scales of tectonic landscapes and their sed-iment routing systems In Landscape evolution Denudation cli-mate and tectonics over different time and space scales (Ed by Gallagher K Jones S J amp Wainwright J) Geological Society London Special Publications 296 7ndash28

Allen P A Armitage J J Carter A Duller R A Michael N A Sinclair H D hellip Whittaker A C (2013) The Qs problem Sediment volumetric balance of proximal foreland basin systems Sedimentology 60 102ndash130

Amorosi A Maselli V amp Trincardi F (2016) Onshore to offshore anatomy of a late Quaternary source‐to‐sink system (Po Plain‐Adriatic Sea Italy) Earth‐Science Reviews 153 212ndash237 https doiorg101016jearsc irev201510010

Anderson J B Wallace D J Simms A R Rodriguez A B Weight R W R amp Taha Z P (2016) Recycling sediments between source and sink during a eustatic cycle Systems of late Quaternary northwestern Gulf of Mexico Basin Earth‐Science Reviews 153 111ndash138 https doiorg101016jearsc irev201510014

Anthony E J amp Julian M (1999) Source‐to‐sink sediment trans-fers environmental engineering and hazard mitigation in the steep Var River catchment French Riviera southeastern France Geomorphology 31 337ndash354 https doiorg101016S0169-555X(99)00088-4

Athy L F (1930) Density porosity and compaction of sedimentary rocks AAPG Bulletin 14 1ndash24

Bhattacharya J P Copeland P Lawton T F amp Holbrook J (2016) Estimation of source area river palaeo‐discharge palaeoslope and sediment budgets of linked deep‐time depositional systems and im-plications for hydrocarbon potential Earth‐Science Reviews 153 77ndash110

Blum M D amp Hattier‐Womack J (2009) Climate change sea‐level change and fluvial sediment supply to deepwater depositional

| 607EAGE

LIU et aL

relationships are clear evidence that the size of the sink area controlled the extent of the depositional system during the rifting of the lacustrine basin and that the rate of sediment supply and the accommodation space had a significant in-fluence on the total sedimentary volume as well as on the internal stacking pattern of the depositional system

We here use the ratio of the tectonic‐subsidence rate and the sediment‐supply rate as a proxy to indicate the ratio be-tween accommodation space and sediment‐supply rate (AS) (Table 4) AS has a strong influence on the internal stacking pattern of the depositional systems in the lacustrine rift basin (Figure 11j) This might be because the basin was small and because abundant and rapid material was supplied due

to intense tectonic activity (cf Catuneanu et al 2009 Liro 1993) and a favourable local climate (eg Bohacs Carroll Neal amp Mankiewicz 2000 Perlmutter amp Matthews 1989) The sediment supply still had a significant influence on the main subsidence area of the lacustrine basins and deposi-tional systems

In addition the basin slope significantly influenced the extent of the depositional system (Figure 11k) and had a polynomial relationship with its volume (Figure 11l) This relationship indicates that more intense tectonic activity and a steeper depositional slope were not favourable for sediment accumulation over a large extent in the lacustrine basin On the contrary these sediments were usually transported to a

F I G U R E 1 2 Tectonic differential activities and resulting patterns of the source‐to‐sink system on the south‐western slope of the HD during the Palaeogene (a) Development during phases of intense tectonics (Member 4 to the lower part of Member 3 of the Shahejie Fm) (b) Development during phases of somewhat less tectonic activity (middle part of Member 3 of the Shahejie Fm and Member 3 of the Dongying Fm) (c) Development during phases of weak tectonic activity (Members 1 and 2 of the Shahejie Fm and Member 2 of the Dongying Fm) The intensity of tectonic activity in the lacustrine rift basin had a significant influence on the development and extent of each unit of the source‐to‐sink system as well as on the type and dimensions of the depositional systems The present study indicates that probably sublacustrine fans developed (see for example Figure S4b) during phases with relatively strong tectonic activity This is not really clear from the seismic‐reflection data but possibly due to the small sizes of these sublacustrine fans Moreover lithofacies and core data are not available for the south‐western part of the study area The present contribution therefore focuses on the fan‐deltas and braid‐deltas regarding the sedimentary facies analysis the sublacustrine fans that probably developed in the deep or semi‐deep lake are presented just as a likely feature

608 | EAGE

LIU et aL

relatively small sink area with a fairly large accommodation space Finally stronger tectonic activity resulted in steeper depositional slopes (Figure 8f) which further controlled the hydrodynamic conditions and differential discharge when the sediments were deposited The strong correlation between the depositional slope and the deltas dip (Figure 11m) suggests that the differences in topography due to tectonics must be considered as one of the most critical factors that controlled the internal stacking pattern of the delta deposits

63 | Significance of the present study for other source‐to‐sink systems of lacustrine rift basins

631 | Summary of the source‐to‐sink systems in the HDIn lacustrine rift basins the tectonic setting is probably the main factor that determines the development of the S2S sys-tem but differential tectonic activities lead to variations in the basic characteristics of the S2S system Tectonic activity was most intense during S‐3 (lower unit) and during S‐4 and caused both a strong uplift of the source area and the devel-opment of depressions in the basin that formed a sink (Figure 12a) Strong tectonic activity in the S2S system during these time‐spans led to a high sediment‐supply rate steeper slopes a larger accommodation space and deposition of several fan‐deltas that are characterized by a fairly steep seismic progra-dational angle

The tectonic activity decreased during S‐3 (middle unit) and during D‐3 The S2S system that was present during this time‐span mainly concerned a rising area that shifted south-wards developing an alluvial plain between the erosional area and the sink area thus increasing the distance from source to sink (Figure 12b) Simultaneously the sediment‐supply rate and the accommodation space also changed and braid‐deltas could thus develop with larger volumes and gentler seismic progradational dips

Tectonic activity was clearly less intense during S‐1 + 2 and D‐2 The rising area had shifted further southwards cre-ating a wider alluvial plain connecting the source area to the sink in the HD (Figure 12c) At this stage stable tectonic activity led to relatively less sediment supply a gentle slope less accommodation space and the development of several braid‐deltas with a fairly gentle seismic progradational angle

632 | Wider implications and limitationsSoslashmme et al (2009) proposed that the elements of S2S sys-tems are genetically related and that quantitative correla-tions exist among these elements Other studies also suggest that the size of the drainage basin is correlated to the size of the fan developing on the basin floor (eg Blum et al

2017 Snedden et al 2018) and to the size of the river chan-nel (eg Milliken et al 2018) Helland‐Hansen Soslashmme Martinsen Lunt and Thurmond (2016) suggest a simplified subdivision of S2S systems into three main categories (a) Steep‐Short‐Deep (steep onshore and offshore gradients short distance between source and sink and deep offshore waters) (b) Wide‐Deep (low‐gradient shelf‐catchment area and deep offshore waters) and (c) Wide‐Shallow (relatively shallow offshore waters and a wide low‐gradient catchment area) systems

The present study indicates that the alluvial plain roughly corresponds to the alluvial‐shelf unit in marine basins al-though with a much smaller width and extent in the lacustrine rift basins than would have been the case on a continental shelf Faults F1 and F2 along the slope belt correspond to the slope of classical S2S systems whereas the shore‐shallow‐deep lake area can be compared with the basin floor (Soslashmme et al 2009) S‐4 and S‐3 (lower unit) can be roughly clas-sified as Steep‐Short‐Deep systems whereas the overlying S‐1 + 2and D‐2 can be classified as the Wide‐Shallow sys-tems that Helland‐Hansen et al (2016) defined During the deposition of S‐4 and S‐3 (lower unit) the strong tectonic activity caused a high relief of the source area a narrow allu-vial plain and a relatively deep lake The subsequently wan-ing tectonic activity resulted in a lower relief of the source area a wider alluvial plain and a shallower lake Although the absolute values of these elements in lacustrine basins are much smaller than those of marine basins the ratio between these elements in both settings is comparable Typically in a lacustrine basin a transformation from a Steep‐Short‐Deep system (S‐4 and S‐3 (lower unit)) to a Wide‐Shallow system (S‐1 + 2ampD‐2) occurs within a few million years Although the basin geomorphology has experienced signif-icant changes from S‐4 to D‐2 the quantitative relationships between tectonic activity sediment‐supply rate accommoda-tion space and sedimentary dip of the delta systems did not change significantly (eg Figures 8 and 11) The analytical approaches applied and quantitative relationship established here can help analyse other lacustrine basins worldwide and may even act as a reference for the analysis of marine basins

Our study focuses mainly on the influences of tectonic activity on the elements of the depositional sink Other pa-rameters (eg climate and lithology) were not considered in detail Studies on modern and ancient systems suggest that the climate and lithology also have a great influence on the sediment supply and distribution in the basin (eg Carroll Chetel amp Smith 2006 Hovius amp Leeder 1998 Syvitski amp Milliman 2007 Zhang et al 2018) For exam-ple climate variations between glacials and inter‐glacials have resulted in largely different sediment‐supply rates and in significant differences in the sizes of the Quaternary sub-marine fans in the north‐western Gulf of Mexico (Blum amp Hattier‐Womack 2009) We acknowledge the importance

| 609EAGE

LIU et aL

of climate and lithology for S2S systems and we are con-vinced that these elements can significantly affect the S2S systems in other cases(eg modern systems and systems influenced by glacialinterglacial alternations) These fac-tors were not really relevant for the present study however because no significant differences in lithology were present in the source areas and because we focus on the changes at a million‐year scale which implies that the tectonic ac-tivity has a first‐order control on the development of S2S elements in the investigated rift basin

7 | CONCLUSIONS

We have calculated the tectonic‐subsidence history the growth index and the activity rate of the main boundary faults (F1 and F2) and various S2S parameters of six Palaeogene rock units on the south‐western slope of the HD Based on the values found for these parameters quantitative corre-lation were established for the tectonic activity and other S2Sparameters in the basinal sink This leads to the follow-ing conclusions

1 The positive correlation between the intensity of fault activity and the tectonic‐subsidence rate is a strong indication for a distinct control by the tectonic activity of the syn‐depositional rifting of the tectonically active basin

2 The tectonic activity was quantitatively related to the sediment supply accommodation space and morphology of the sink area The relationship between tectonic activ-ity and depositional systems is reflected by changes in critical factors such as sediment supply accommodation space and dip of the sink area These critical factors were probably the most important factors that led to changes in the size and internal stacking pattern of the sedimentary facies

3 Differential tectonic activity led to changes in the char-acteristics of the S2S system on the south‐western slope of the HD The strongest tectonic activity which oc-curred during S‐3 (lower unit) and during S‐4 led to the largest provenance area adjacent to the sink area to a high sediment‐supply rate to steeper slopes to a larger accommodation space and controlled the development of several fan‐deltas Diminished tectonic activity dur-ing S‐3 (middle unit) and during D‐3 led to a decrease in uplift an increased width of the alluvial plain an in-creased transport distance a decrease in the sediment‐supply rate and accommodation space and resulted in the development of braid‐deltas with a large volume During S‐1 + 2 and D‐2 stable tectonic activity led to a lower sediment‐supply rate a gentle depositional slope and a smaller accommodation space resulting in the

development of several braid‐deltas with gentler seis-mic progradational angles

4 The analytical approaches applied and the quantitative re-lationships established here can help analyse other lacus-trine basins worldwide and may even act as a reference for the study of marine basins

ACKNOWLEDGEMENTS

We thank Dr Sarah Boulton and Dr Chenlin Gong as well as the Associate Editor of Basin Research Dr Craig Magee for their constructive comments on the manuscript This study was funded by the National Science and Technology Major Project (Exploration Technologies for Offshore Hidden OilGas) (project no 2016ZX05024‐003‐003) the National Natural Science Foundations of China (project no 41676050) and the Fundamental Research Funds for the Central Universities (2652014037)

REFERENCES

Allen P A (2008a) From landscapes into geological history Nature 451 274ndash276 https doiorg101038natur e06586

Allen P A (2008b) Time scales of tectonic landscapes and their sed-iment routing systems In Landscape evolution Denudation cli-mate and tectonics over different time and space scales (Ed by Gallagher K Jones S J amp Wainwright J) Geological Society London Special Publications 296 7ndash28

Allen P A Armitage J J Carter A Duller R A Michael N A Sinclair H D hellip Whittaker A C (2013) The Qs problem Sediment volumetric balance of proximal foreland basin systems Sedimentology 60 102ndash130

Amorosi A Maselli V amp Trincardi F (2016) Onshore to offshore anatomy of a late Quaternary source‐to‐sink system (Po Plain‐Adriatic Sea Italy) Earth‐Science Reviews 153 212ndash237 https doiorg101016jearsc irev201510010

Anderson J B Wallace D J Simms A R Rodriguez A B Weight R W R amp Taha Z P (2016) Recycling sediments between source and sink during a eustatic cycle Systems of late Quaternary northwestern Gulf of Mexico Basin Earth‐Science Reviews 153 111ndash138 https doiorg101016jearsc irev201510014

Anthony E J amp Julian M (1999) Source‐to‐sink sediment trans-fers environmental engineering and hazard mitigation in the steep Var River catchment French Riviera southeastern France Geomorphology 31 337ndash354 https doiorg101016S0169-555X(99)00088-4

Athy L F (1930) Density porosity and compaction of sedimentary rocks AAPG Bulletin 14 1ndash24

Bhattacharya J P Copeland P Lawton T F amp Holbrook J (2016) Estimation of source area river palaeo‐discharge palaeoslope and sediment budgets of linked deep‐time depositional systems and im-plications for hydrocarbon potential Earth‐Science Reviews 153 77ndash110

Blum M D amp Hattier‐Womack J (2009) Climate change sea‐level change and fluvial sediment supply to deepwater depositional

608 | EAGE

LIU et aL

relatively small sink area with a fairly large accommodation space Finally stronger tectonic activity resulted in steeper depositional slopes (Figure 8f) which further controlled the hydrodynamic conditions and differential discharge when the sediments were deposited The strong correlation between the depositional slope and the deltas dip (Figure 11m) suggests that the differences in topography due to tectonics must be considered as one of the most critical factors that controlled the internal stacking pattern of the delta deposits

63 | Significance of the present study for other source‐to‐sink systems of lacustrine rift basins

631 | Summary of the source‐to‐sink systems in the HDIn lacustrine rift basins the tectonic setting is probably the main factor that determines the development of the S2S sys-tem but differential tectonic activities lead to variations in the basic characteristics of the S2S system Tectonic activity was most intense during S‐3 (lower unit) and during S‐4 and caused both a strong uplift of the source area and the devel-opment of depressions in the basin that formed a sink (Figure 12a) Strong tectonic activity in the S2S system during these time‐spans led to a high sediment‐supply rate steeper slopes a larger accommodation space and deposition of several fan‐deltas that are characterized by a fairly steep seismic progra-dational angle

The tectonic activity decreased during S‐3 (middle unit) and during D‐3 The S2S system that was present during this time‐span mainly concerned a rising area that shifted south-wards developing an alluvial plain between the erosional area and the sink area thus increasing the distance from source to sink (Figure 12b) Simultaneously the sediment‐supply rate and the accommodation space also changed and braid‐deltas could thus develop with larger volumes and gentler seismic progradational dips

Tectonic activity was clearly less intense during S‐1 + 2 and D‐2 The rising area had shifted further southwards cre-ating a wider alluvial plain connecting the source area to the sink in the HD (Figure 12c) At this stage stable tectonic activity led to relatively less sediment supply a gentle slope less accommodation space and the development of several braid‐deltas with a fairly gentle seismic progradational angle

632 | Wider implications and limitationsSoslashmme et al (2009) proposed that the elements of S2S sys-tems are genetically related and that quantitative correla-tions exist among these elements Other studies also suggest that the size of the drainage basin is correlated to the size of the fan developing on the basin floor (eg Blum et al

2017 Snedden et al 2018) and to the size of the river chan-nel (eg Milliken et al 2018) Helland‐Hansen Soslashmme Martinsen Lunt and Thurmond (2016) suggest a simplified subdivision of S2S systems into three main categories (a) Steep‐Short‐Deep (steep onshore and offshore gradients short distance between source and sink and deep offshore waters) (b) Wide‐Deep (low‐gradient shelf‐catchment area and deep offshore waters) and (c) Wide‐Shallow (relatively shallow offshore waters and a wide low‐gradient catchment area) systems

The present study indicates that the alluvial plain roughly corresponds to the alluvial‐shelf unit in marine basins al-though with a much smaller width and extent in the lacustrine rift basins than would have been the case on a continental shelf Faults F1 and F2 along the slope belt correspond to the slope of classical S2S systems whereas the shore‐shallow‐deep lake area can be compared with the basin floor (Soslashmme et al 2009) S‐4 and S‐3 (lower unit) can be roughly clas-sified as Steep‐Short‐Deep systems whereas the overlying S‐1 + 2and D‐2 can be classified as the Wide‐Shallow sys-tems that Helland‐Hansen et al (2016) defined During the deposition of S‐4 and S‐3 (lower unit) the strong tectonic activity caused a high relief of the source area a narrow allu-vial plain and a relatively deep lake The subsequently wan-ing tectonic activity resulted in a lower relief of the source area a wider alluvial plain and a shallower lake Although the absolute values of these elements in lacustrine basins are much smaller than those of marine basins the ratio between these elements in both settings is comparable Typically in a lacustrine basin a transformation from a Steep‐Short‐Deep system (S‐4 and S‐3 (lower unit)) to a Wide‐Shallow system (S‐1 + 2ampD‐2) occurs within a few million years Although the basin geomorphology has experienced signif-icant changes from S‐4 to D‐2 the quantitative relationships between tectonic activity sediment‐supply rate accommoda-tion space and sedimentary dip of the delta systems did not change significantly (eg Figures 8 and 11) The analytical approaches applied and quantitative relationship established here can help analyse other lacustrine basins worldwide and may even act as a reference for the analysis of marine basins

Our study focuses mainly on the influences of tectonic activity on the elements of the depositional sink Other pa-rameters (eg climate and lithology) were not considered in detail Studies on modern and ancient systems suggest that the climate and lithology also have a great influence on the sediment supply and distribution in the basin (eg Carroll Chetel amp Smith 2006 Hovius amp Leeder 1998 Syvitski amp Milliman 2007 Zhang et al 2018) For exam-ple climate variations between glacials and inter‐glacials have resulted in largely different sediment‐supply rates and in significant differences in the sizes of the Quaternary sub-marine fans in the north‐western Gulf of Mexico (Blum amp Hattier‐Womack 2009) We acknowledge the importance

| 609EAGE

LIU et aL

of climate and lithology for S2S systems and we are con-vinced that these elements can significantly affect the S2S systems in other cases(eg modern systems and systems influenced by glacialinterglacial alternations) These fac-tors were not really relevant for the present study however because no significant differences in lithology were present in the source areas and because we focus on the changes at a million‐year scale which implies that the tectonic ac-tivity has a first‐order control on the development of S2S elements in the investigated rift basin

7 | CONCLUSIONS

We have calculated the tectonic‐subsidence history the growth index and the activity rate of the main boundary faults (F1 and F2) and various S2S parameters of six Palaeogene rock units on the south‐western slope of the HD Based on the values found for these parameters quantitative corre-lation were established for the tectonic activity and other S2Sparameters in the basinal sink This leads to the follow-ing conclusions

1 The positive correlation between the intensity of fault activity and the tectonic‐subsidence rate is a strong indication for a distinct control by the tectonic activity of the syn‐depositional rifting of the tectonically active basin

2 The tectonic activity was quantitatively related to the sediment supply accommodation space and morphology of the sink area The relationship between tectonic activ-ity and depositional systems is reflected by changes in critical factors such as sediment supply accommodation space and dip of the sink area These critical factors were probably the most important factors that led to changes in the size and internal stacking pattern of the sedimentary facies

3 Differential tectonic activity led to changes in the char-acteristics of the S2S system on the south‐western slope of the HD The strongest tectonic activity which oc-curred during S‐3 (lower unit) and during S‐4 led to the largest provenance area adjacent to the sink area to a high sediment‐supply rate to steeper slopes to a larger accommodation space and controlled the development of several fan‐deltas Diminished tectonic activity dur-ing S‐3 (middle unit) and during D‐3 led to a decrease in uplift an increased width of the alluvial plain an in-creased transport distance a decrease in the sediment‐supply rate and accommodation space and resulted in the development of braid‐deltas with a large volume During S‐1 + 2 and D‐2 stable tectonic activity led to a lower sediment‐supply rate a gentle depositional slope and a smaller accommodation space resulting in the

development of several braid‐deltas with gentler seis-mic progradational angles

4 The analytical approaches applied and the quantitative re-lationships established here can help analyse other lacus-trine basins worldwide and may even act as a reference for the study of marine basins

ACKNOWLEDGEMENTS

We thank Dr Sarah Boulton and Dr Chenlin Gong as well as the Associate Editor of Basin Research Dr Craig Magee for their constructive comments on the manuscript This study was funded by the National Science and Technology Major Project (Exploration Technologies for Offshore Hidden OilGas) (project no 2016ZX05024‐003‐003) the National Natural Science Foundations of China (project no 41676050) and the Fundamental Research Funds for the Central Universities (2652014037)

REFERENCES

Allen P A (2008a) From landscapes into geological history Nature 451 274ndash276 https doiorg101038natur e06586

Allen P A (2008b) Time scales of tectonic landscapes and their sed-iment routing systems In Landscape evolution Denudation cli-mate and tectonics over different time and space scales (Ed by Gallagher K Jones S J amp Wainwright J) Geological Society London Special Publications 296 7ndash28

Allen P A Armitage J J Carter A Duller R A Michael N A Sinclair H D hellip Whittaker A C (2013) The Qs problem Sediment volumetric balance of proximal foreland basin systems Sedimentology 60 102ndash130

Amorosi A Maselli V amp Trincardi F (2016) Onshore to offshore anatomy of a late Quaternary source‐to‐sink system (Po Plain‐Adriatic Sea Italy) Earth‐Science Reviews 153 212ndash237 https doiorg101016jearsc irev201510010

Anderson J B Wallace D J Simms A R Rodriguez A B Weight R W R amp Taha Z P (2016) Recycling sediments between source and sink during a eustatic cycle Systems of late Quaternary northwestern Gulf of Mexico Basin Earth‐Science Reviews 153 111ndash138 https doiorg101016jearsc irev201510014

Anthony E J amp Julian M (1999) Source‐to‐sink sediment trans-fers environmental engineering and hazard mitigation in the steep Var River catchment French Riviera southeastern France Geomorphology 31 337ndash354 https doiorg101016S0169-555X(99)00088-4

Athy L F (1930) Density porosity and compaction of sedimentary rocks AAPG Bulletin 14 1ndash24

Bhattacharya J P Copeland P Lawton T F amp Holbrook J (2016) Estimation of source area river palaeo‐discharge palaeoslope and sediment budgets of linked deep‐time depositional systems and im-plications for hydrocarbon potential Earth‐Science Reviews 153 77ndash110

Blum M D amp Hattier‐Womack J (2009) Climate change sea‐level change and fluvial sediment supply to deepwater depositional

| 609EAGE

LIU et aL

of climate and lithology for S2S systems and we are con-vinced that these elements can significantly affect the S2S systems in other cases(eg modern systems and systems influenced by glacialinterglacial alternations) These fac-tors were not really relevant for the present study however because no significant differences in lithology were present in the source areas and because we focus on the changes at a million‐year scale which implies that the tectonic ac-tivity has a first‐order control on the development of S2S elements in the investigated rift basin

7 | CONCLUSIONS

We have calculated the tectonic‐subsidence history the growth index and the activity rate of the main boundary faults (F1 and F2) and various S2S parameters of six Palaeogene rock units on the south‐western slope of the HD Based on the values found for these parameters quantitative corre-lation were established for the tectonic activity and other S2Sparameters in the basinal sink This leads to the follow-ing conclusions

1 The positive correlation between the intensity of fault activity and the tectonic‐subsidence rate is a strong indication for a distinct control by the tectonic activity of the syn‐depositional rifting of the tectonically active basin

2 The tectonic activity was quantitatively related to the sediment supply accommodation space and morphology of the sink area The relationship between tectonic activ-ity and depositional systems is reflected by changes in critical factors such as sediment supply accommodation space and dip of the sink area These critical factors were probably the most important factors that led to changes in the size and internal stacking pattern of the sedimentary facies

3 Differential tectonic activity led to changes in the char-acteristics of the S2S system on the south‐western slope of the HD The strongest tectonic activity which oc-curred during S‐3 (lower unit) and during S‐4 led to the largest provenance area adjacent to the sink area to a high sediment‐supply rate to steeper slopes to a larger accommodation space and controlled the development of several fan‐deltas Diminished tectonic activity dur-ing S‐3 (middle unit) and during D‐3 led to a decrease in uplift an increased width of the alluvial plain an in-creased transport distance a decrease in the sediment‐supply rate and accommodation space and resulted in the development of braid‐deltas with a large volume During S‐1 + 2 and D‐2 stable tectonic activity led to a lower sediment‐supply rate a gentle depositional slope and a smaller accommodation space resulting in the

development of several braid‐deltas with gentler seis-mic progradational angles

4 The analytical approaches applied and the quantitative re-lationships established here can help analyse other lacus-trine basins worldwide and may even act as a reference for the study of marine basins

ACKNOWLEDGEMENTS

We thank Dr Sarah Boulton and Dr Chenlin Gong as well as the Associate Editor of Basin Research Dr Craig Magee for their constructive comments on the manuscript This study was funded by the National Science and Technology Major Project (Exploration Technologies for Offshore Hidden OilGas) (project no 2016ZX05024‐003‐003) the National Natural Science Foundations of China (project no 41676050) and the Fundamental Research Funds for the Central Universities (2652014037)

REFERENCES

Allen P A (2008a) From landscapes into geological history Nature 451 274ndash276 https doiorg101038natur e06586

Allen P A (2008b) Time scales of tectonic landscapes and their sed-iment routing systems In Landscape evolution Denudation cli-mate and tectonics over different time and space scales (Ed by Gallagher K Jones S J amp Wainwright J) Geological Society London Special Publications 296 7ndash28

Allen P A Armitage J J Carter A Duller R A Michael N A Sinclair H D hellip Whittaker A C (2013) The Qs problem Sediment volumetric balance of proximal foreland basin systems Sedimentology 60 102ndash130

Amorosi A Maselli V amp Trincardi F (2016) Onshore to offshore anatomy of a late Quaternary source‐to‐sink system (Po Plain‐Adriatic Sea Italy) Earth‐Science Reviews 153 212ndash237 https doiorg101016jearsc irev201510010

Anderson J B Wallace D J Simms A R Rodriguez A B Weight R W R amp Taha Z P (2016) Recycling sediments between source and sink during a eustatic cycle Systems of late Quaternary northwestern Gulf of Mexico Basin Earth‐Science Reviews 153 111ndash138 https doiorg101016jearsc irev201510014

Anthony E J amp Julian M (1999) Source‐to‐sink sediment trans-fers environmental engineering and hazard mitigation in the steep Var River catchment French Riviera southeastern France Geomorphology 31 337ndash354 https doiorg101016S0169-555X(99)00088-4

Athy L F (1930) Density porosity and compaction of sedimentary rocks AAPG Bulletin 14 1ndash24

Bhattacharya J P Copeland P Lawton T F amp Holbrook J (2016) Estimation of source area river palaeo‐discharge palaeoslope and sediment budgets of linked deep‐time depositional systems and im-plications for hydrocarbon potential Earth‐Science Reviews 153 77ndash110

Blum M D amp Hattier‐Womack J (2009) Climate change sea‐level change and fluvial sediment supply to deepwater depositional

610 | EAGE

LIU et aL

systems External Controls on Deep Water Depositional Systems SEPM Special Publication 92 15ndash39

Blum M D Milliken K T Pecha M A Snedden J W Frederick B C amp Galloway W E (2017) Detrital-zircon records of Cenomanian Paleocene and Oligocene Gulf of Mexico drain-age integration and sediment routing Implications for scales of basin-floor fans Geosphere 13 2169ndash2205 https doi101130GES01 4101

Blum M amp Pecha M (2014) Mid‐Cretaceous to Paleocene North American drainage reorganization from detrital zircons Geology 42 607ndash610 https doiorg101130G355131

Bohacs K M Carroll A R Neal J E amp Mankiewicz P J (2000) Lake‐basin type source potential and hydrocarbon character An integrated‐sequence stratigraphic‐geochemical framework In Lake basins through space and time (Ed by Gierlowski‐Kordesch E H Kelts K R) AAPG Studies in Geology 46 3ndash34

Brown L F Jr amp Fisher W L (1977) Seismic‐stratigraphic inter-pretation of depositional systems examples from Brazilian rift and Pull‐Apart Basin In Seismic stratigraphy ndash Applications to hydro-carbon exploration Tulsa Oklahoma USA (Ed by Payton CE) AAPG Memoir 26 213ndash248

Carroll A R Chetel L M amp Smith M E (2006) Feast to fam-ine Sediment supply control on Laramide Basin fill Geology 34 197ndash200 https doiorg101130G221481

Castelltort S amp Van denDriessche J (2003) How plausible are high‐frequency sediment supply‐driven cycles in the stratigraphic record Sedimentary Geology 157 3ndash13 https doiorg101016S0037-0738(03)00066-6

Catuneanu O Abreu V Bhattacharya J P Blum M D Dalrymple R W Eriksson P G hellip Winker C (2009) Towards the standard-ization of sequence stratigraphy Earth‐Science Reviews 92 1ndash33 https doiorg101016jearsc irev200810003

Chen D Pang X Jiang Z Zeng J Qiu N amp Li M (2009) Reservoir characteristics and their effects on hydrocarbon accumu-lation in lacustrine turbidites in the Jiyang Super‐depression Bohai Bay Basin China Marine and Petroleum Geology 26 149ndash162 https doiorg101016jmarpe tgeo200803003

Cope T Luo P Zhang X Zhang X J Song J M Zhou G amp Shultz M R (2010) Structural controls on facies distribution in a small half‐graben basin Luanping Basin northeast China Basin Research 22 33ndash44 https doiorg101111j1365-2117200900417x

Covault J A Craddock W H Romans B W Fildani A amp Gosai M (2013) Spatial and temporal variations in landscape evolution Historic and longer‐term sediment flux through global catchments The Journal of Geology 121 35ndash56 https doiorg101086668680

Covault J A Romans B W Graham S A Fildani A amp Hilley G E (2011) Terrestrial source to deep‐sea sink sediment budgets at high and low sea levels Insights from tectonically active southern California Geology 39 619ndash622 https doiorg101130G318011

DeCelles P G Kapp P Ding L amp Gehrels G E (2007) Late creta-ceous to mid‐tertiary basin evolution in the central Tibetan plateau Changing environments in response to tectonic partitioning aridifi-cation and regional elevation gain Geological Society of America Bulletin 119 654ndash680

Dill F G Kharel B D Singh V K Piys B Busch K amp Geyh M (2001) Sedimentology and palaeogeography evolution of the intermontane Kathmandu Basin Nepal during the Pliocene and Quaternary Implication for formation of deposits of economic in-terest Journal of Asian Earth Sciences 19 777ndash804

Galloway W E (1986) Growth faults and fault‐related structures of prograding terrigenous clastic continental margins Gulf Coast Association of Geological Societies Transactions 36 121ndash128

Galloway W E Whiteaker T L amp Ganey‐Curry P E (2011) History of Cenozoic North American drainage basin evolution sediment yield and accumulation in the Gulf of Mexico basin Geosphere 7 938ndash973 https doiorg101130GES00 6471

Glider S A Leloup P H amp Courtillot V (1999) Tectonic evolu-tion of Tancheng ‐Lujiang (Tan‐Lu) fault via Middle Triassic to Early Cenozoic paleomagnetic Journal of Geophysical Research 104(B7) 15365ndash15390

Gupta S Cowie P A Dawers N H amp Underhill J R (1998) A mechanism to explain rift-basin subsidence and stratigraphic pat-terns through fault-array evolution Geology 26 595ndash598 httpsdoi 1011300091-7613(1998)026lt0595AMTERBgt23CO2

Hadlari T Midwinter D Galloway J M Dewing K amp Durbano A M (2016) Mesozoic rift to post‐rift tectonostratigraphy of the Sverdrup Basin Canadian Arctic Marine and Petroleum Geology 76 148ndash158 https doiorg101016jmarpe tgeo201605008

Hadlari T Rainbird R H amp Donaldson J A (2006) Alluvial eo-lian and lacustrine sedimentology of a Paleoproterozoic half‐graben Baker Lake Basin Nunavut Canada Sedimentary Geology 190 47ndash70 https doiorg101016jsedgeo200605005

Helland‐Hansen W Soslashmme T O Martinsen O J Lunt I amp Thurmond J (2016) Deciphering earths natural hourglasses Perspectives on source‐to‐sink analysis Journal of Sedimentary Research 86 1008ndash1033 https doiorg102110jsr201656

Hovius N (1998) Controls on sediment supply by large rivers In Relative role of eustasy climate and tectonism in continental rocks Tulsa Oklahoma (Ed By Shanley KW amp McCabe P J) SEPM Special Publication 59 2ndash16

Hovius N amp Leeder M (1998) Clastic sediment supply to basins Basin research 10 1ndash5 https doiorg101046j1365-2117199800061x

Hsiao L Y Graham S A amp Tilander N (2004) Seismic reflection imaging of a major strike‐slip fault zone in a rift system Palaeogene structure and evolution of the Tan ‐Lu fault system Liaodong Bay Bohai offshore China AAPG Bulletin 88 71ndash97

Hsiao L Y Graham S A amp Tilander N (2010) Stratigraphy and sedi-mentation in a rift basin modified by synchronous strikendashslip deforma-tion Southern Xialiao basin Bohai offshore China Basin Research 22 61ndash78 https doiorg101111j1365-2117200900449x

Jervey M T (1988) Quantitative geological modeling of siliciclas-tic rock sequences and their seismic expression In Sea‐level changes An integrated approach (Ed by Wilgus C K Hastings B S Kendall C G St C Posamentier H W Ross C A amp Van Wagoner J C) Society of Economic Paleontologists and Mineralogists Special Publication 42 47ndash69

Johnson T C Halfman J D Rosendahl B R amp Lister G S (1987) Climatic and tectonic effects on sedimentation in a rift‐valley lake evidence from high‐resolution seismic profiles Lake Turkana Kenya Geological Society of America Bulletin 98 439ndash447 https doiorg1011300016-7606(1987)98lt439CATEO Sgt20CO2

Katz B J amp Liu X C (1998) Summary of the AAPG research sym-posium on lacustrine basin exploration in China and Southeast Asia AAPG Bulletin 82 1300ndash1307

Kertznus V amp Kneller B (2009) Clinoform quantification for assessing the effects of external forcing on continental mar-gin development Basin Research 21 738ndash758 https doiorg101111j1365-2117200900411x

| 611EAGE

LIU et aL

Leeder M R amp Gawthorpe R L (1987) Sedimentary models for ex-tensionin tilt‐blockhalf‐graben basins In Extensional tectonics (Ed By Coward M P Dewey J F amp Hancock P L) Geological Society London Special Publications 28 139ndash152

Leeder M R (2011) Tectonic sedimentology Sediment systems deci-phering global to local tectonics Sedimentology 58 2ndash56 https doiorg101111j1365-3091201001207x

Leeder M R Harris T amp Kirkby M J (1998) Sediment supply and climatechange Implications for basin stratigraphy Basin Research 10 7ndash18 https doiorg101046j1365-2117199800054x

Lemons D R amp Chan M A (1999) Facies architecture and sequence stratigraphy of fine‐grained lacustrine deltas along the eastern mar-gin of late Pleistocene Lake Bonneville northern Utah and southern Idaho AAPG Bulletin 83 635ndash665

Lemons D R Milligan M R amp Chan M A (1996) Paleoclimatic implications of late Pleistocene sediment yield rates for the Bonneville basin northern Utah Palaeogeography Palaeoclimatology Palaeoecology 123 147ndash159 https doiorg1010160031-0182(95)00117-4

Li S L Zhu X M Liu Q H Xu C G Du X F amp Li H Y (2017) Evaluation and prediction of favorable reservoirs in source‐to‐sink systems of the Palaeogene Shaleitian Uplift Earth Science 42 1994ndash2009

Lin C S Kenneth E Li S T Wan Y X Ren J Y amp Zhang Y M (2001) Sequence architecture depositional systems and controls on development of lacustrine basin fills in part of the Erlian basin northeast China AAPG Bulletin 85 2017ndash2043

Lin C S Xia Q L Shi H S amp Zhou X H (2015) Geomorphological evolution source to sink system and basin analysis Earth Science Frontier 22 9ndash22 (in Chinese with English abstract)

Lin C S Yang H J Liu J Y Rui Z F Cai Z Z amp Zhu Y F (2012) Distribution and erosion of the Paleozoic tectonic uncon-formities in the Tarim Basin Northwest China Significance for the evolution of paleo‐uplifts and tectonic geography during de-formation Journal of Asian Earth Sciences 46 1ndash19 https doiorg101016jjseaes201110004

Liro L M (1993) Sequence stratigraphy of a lacustrine system Upper Fort Union Formation (Paleocene) Wind River Basin Wyoming USA In Siliciclastic sequence stratigraphy Recent developments and applications (Ed By Weimer P amp Posamentier H W) AAPG Memoir 58 317ndash334

Liu H Lin C S Guo R B Zhu M amp Cui Y Q (2015b) Characteristics of the Palaeozoic slope break system and its control on stratigraphic‐lithologic traps An example from the Tarim Basin western China Journal of Palaeogeography 4 284ndash304

Liu H Meng J amp Banerjee S (2017) Estimation of palaeo‐slope and sediment volume of a lacustrine rift basin A semi‐quantitative study on the southern steep slope of the Shijiutuo Uplift Bohai Offshore Basin China Journal of Asian Earth Sciences 147 148ndash163 https doiorg101016jjseaes201707028

Liu H Meng J Zhang Y Z amp Yang L (2019) Pliocene seismic stratigraphy and deep‐water sedimentation in the Qiongdongnan Basin South China Sea Source‐to‐sink systems and hydrocarbon accumulation significance Geological Journal 54 392ndash408 https doiorg101002gj3188

Liu H Wang Y M Xin R C amp Wang Y (2006) Study on the slope break belts in the Jurassic down‐warped lacustrine basin in western‐margin area Junggar Basin northwestern China Marine and Petroleum Geology 23 913ndash930

Liu H Xia Q L Somerville I D Wang Y Zhou X H Niu C M hellip Zhang X T (2015a) Palaeogene of the Huanghekou Sag in the Bohai Bay Basin NE China Deposition‐erosion response to a slope break system of rift lacustrine basins Geological Journal 50 71ndash92

Martinsen O J Lien T amp Jackson C (2005) Cretaceous and Palaeogeneturbidite systems in the North Sea and Norwegian Sea basins-source staging area and basin physiography controls on reservoirdevelop-ment In PetroleumGeology North‐West Europe and Global Perspectives Proceedingsof the 6th Petroleum Geology Conference (Ed By Doreacute A G amp Vining B A) Geological Society London 1147ndash1164

Martinsen O J Soslashmme T O Thurmond J B Helland‐Hansen W amp Lunt I (2010) Source‐to‐sink systems on passive margins Theory and practice with an example from the Norwegian conti-nental margin Geological Society London Petroleum Geology Conference Series 7 913ndash920 https doiorg1011440070913

Martins‐Neto M A (1996) Lacustrine fan‐deltaic sedimentation in a Proterozoic rift basin The Sopa‐BrumadinhoTectonosequence southeastern Brazil Sedimentary Geology 106 65ndash96 https doiorg1010160037-0738(95)00152-2

Masini E Manatschal G Mohn G Ghienne J F amp Lafont F (2011) The tectono‐sedimentary evolution of a supra‐de-tachment rift basin at a deep‐water magma‐poor rifted margin The example of the Samedan Basin preserved in the Err nappe in SE Switzerland Basin Research 23 652ndash677 https doiorg101111j1365-2117201100509x

Meade R H (1982) Source sinks and storage of river sediment in the Atlantic drainage of the United States The Journal of Geology 90 235ndash252

Metivier F amp Gaudemer Y (1999) Stability of output fluxes of large rivers in south and East Asia during the last 2 million years Implications on floodplain processes Basin Research 11 293ndash303 https doiorg101046j1365-2117199900101x

Milliken K T Blum M D Snedden J W amp Galloway W E (2018) Application of fluvial scaling relationships to reconstruct drain-age‐basin evolution and sediment routing for the Cretaceous and Paleocene of the Gulf of Mexico Geosphere 14 1ndash19 https doiorg101130GES01 3741

Mitchum R M Jr Vail P R amp Sangree J B (1977) Part Six Stratigraphic interpretation of seismic reflection patterns in depo-sitional sequence In Seismic stratigraphy ndash Applications to hydro-carbon exploration Tulsa Oklahoma USA (Ed By Payton C E) AAPG Memoir 26 117ndash134

Muto T amp Steel R J (2000) The accommodation concept in sequence stratigraphy Some dimensional problems and possible redefini-tion Sedimentary Geology 130 1ndash10 https doiorg101016S0037-0738(99)00107-4

Neal J amp Abreu V (2009) Sequence stratigraphy hierarchy and the accommodation succession method Geology 37 779ndash782 https doiorg101130G2572 2A1

Obrist‐Farner J Yang W amp Hu X‐F (2015) Nonmarine time‐stratigraphy in a rift setting An example from the Mid‐Permian lower Quanzijie low‐order cycle Bogda Mountains NW China Journal of Palaeogeography 4 27ndash51 https doiorg103724SPJ1261201500066

Olsen P E (1997) Stratigraphic record of the early Mesozoic breakup of Pangea in the Laurasia‐Gondwana rift system Annual Reviews of Earth and Planetary Science 25 337ndash401 https doiorg101146annur evearth251337

612 | EAGE

LIU et aL

Perlmutter M A amp Matthews M D (1989) Global cyclostratigraphy A model quantitative dynamic stratigraphy In T A Cross (Ed) Quantitative dynamic stratigraphy (pp 233ndash260) New Jersey Prentice‐Hall Englewood Cliffs

Perrie R amp Qiublier J (1974) Thickness changes in sedimentary lay-ers during compaction history methods for quantitative evolution AAPG Bulletin 58 507ndash520

Ravnas R amp Steel R J (1998) Architecture of marine rift‐basin suc-cessions AAPG Bulletin 82 110ndash146

Romans B W Castelltort S Covault J A Fildani A amp Walsh J P (2016) Environmental signal propagation in sedimentary systems across timescales Earth‐Science Reviews 153 7ndash29 https doiorg101016jearsc irev201507012

Schellart W P amp Lister G S (2005) The role of East Asian active margin in widespread and strike‐slip deformation in East Asia Journal of the Geological Society 162 959ndash972

Scholz C A amp Rosendahl B R (1990) Coarse‐clastic facies and stratigraphic sequence models from lakes Malawi and Tanganyika East Africa In Lacustrine basin exploration Case studies and modern analogs (Ed By Katz B J) AAPG Memoir 50 137ndash149

Simon B Guillocheau F Robin C Dauteuil O Nalpas T Pickford M hellip Bez M (2017) Deformation and sedimentary evolution of the Lake Albert Rift (Uganda East African Rift System) Marine and Petroleum Geology 86 17ndash37 https doiorg101016jmarpe tgeo201705006

Snedden J W Galloway W E Milliken K T Xu J Whiteaker T amp Blum M D (2018) Validation of empirical source‐to‐sink scaling relationships in a continental‐scale system The Gulf of Mexico basin Cenozoic record Geosphere 14 768ndash784 https doiorg101130GES01 4521

Soslashmme T O Helland‐Hansen W Martinsen O J amp Thurmond J B (2009) Relationships between morphological and sed-imentological parameters in source‐to‐sink systems A basis for predicting semi‐quantitative characteristics in subsur-face systems Basin Research 21 361ndash387 https doiorg101111j1365-2117200900397x

Soslashmme T O amp Jackson C‐ A‐L (2013) Source‐to‐sink analysis of ancient sedimentary systems using a subsurface case study from the Moslashre‐Troslashndelag area of southern Norway Part 2 ndash Sediment disper-sal and forcing mechanisms Basin Research 25 512ndash531 https doiorg101111bre12014

Soslashmme T O Jackson C‐ A‐L amp Vaksdal M (2013) Source‐to‐sink analysis of ancient sedimentary systems using a subsurface case study from the Moslashre‐Troslashndelag area of southern Norway Part 1‐depositional setting and fan evolution Basin Research 25 489ndash511 https doiorg101111bre12013

Strecker U Steidtmann J R amp Smithson S B (1999) A conceptual tectonostratigraphic model for seismic facies migrations on a fluvio‐lacustrine extensional basin AAPG Bulletin 83 43ndash61

Syvitski J P M amp Milliman J D (2007) Geology geography and humans battle for dominance over the delivery of fluvial sediment to the coastal ocean Journal of Geology 115 1ndash19 https doiorg101086509246

Tian L Yu H Zhou X Peng W amp Wang Y (2009) Major control factors of petroleum accumulation in Huanghekou Sag

Xinjiang Petroleum Geology 30 319ndash321 (in Chinese with English abstract)

Walsh J P Wiberg P L Aalto R Nittrouer C A amp Kuehl S A (2016) Source‐to‐sink research Economy of the Earths surface and its strata Earth‐Science Reviews 153 1ndash6 https doiorg101016jearsc irev201511010

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Xu J Snedden J W Stockli D F Fulthorpe C S amp Galloway W E (2017) Early Miocene continental‐scale sediment supply to the Gulf of Mexico Basin based on detrital zircon analysis Geological Society of America Bulletin 129 3ndash22 https doiorg101130B314651

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SUPPORTING INFORMATION

Additional supporting information may be found online in the Supporting Information section at the end of the article

How to cite this article Liu H van Loon AJ Xu J et al Relationships between tectonic activity and sedimentary source‐to‐sink system parameters in a lacustrine rift basin A quantitative case study of the Huanghekou Depression (Bohai Bay Basin E China) Basin Res 202032587ndash612 https doiorg101111bre12374