sedimentology, petrology and geochemistry of an upper ...84522:3/component/diskurs:84521... ·...
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F A C U L T Y O F S C I E N C E
U N I V E R S I T Y O F C O P E N H A G E N
Master
Sedimentology, Petrology and Geochemistry
of an Upper Maastrichtian Cyclic Chalk-Marl
Interval
An integrated study of the Rørdal Member in the Dalbyover-1 core, Denmark
Academic advisor: Lars Stemmerik (SNM)
Co – advisor: Peter Frykman (GEUS)
Submitted: 00/00/00
Master’s Thesis
Carl Nicolai Strandrud Holtskog
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Institutnavn: Statens Naturhistoriske Museum
Name of department: The Natural History Museum of Denmark
Author: Carl Nicolai Strandrud Holtskog
Titel: Sedimentologi, Petrologi og Geokemi af en øvre Maastrichtian
Cyclisk Kalk-Mergl Interval
Et integreret studie af Rørdal Leddet I Dalbyover-1 kernen,
Danmark
Title: Sedimentology, Petrology and Geochemistry of an upper
Maastrichtian Cyclic Chalk – Marl interval
An integrated study of the Rørdal Member in the Dalbyover-1
core, Denmark
Subject description: A cyclic chalk – marl interval from a core in northern Jutland has been
studied in detail. Petrophysical, geochemical and sedimentological studies has been
integrated in order to evaluate the depositional history and the palaeo-environment of the
succession.
Academic advisor: Lars Stemmerik
Co – advisor: Peter Frykman
Submitted: 27.02.2015
Grade:
2
ABSTRACT
A cyclic chalk-marl succession belonging to the upper Maastrichtian Rørdal Member has
been studied in a shallow core drilled in eastern Jutland, Denmark. The studied section,
displays large perturbations in the natural gamma ray log (NGR) that coincide with observed
marl beds and higher values of insoluble residue. The 36.7m core interval has been under
sedimentological, geochemical and petrophysical analysis. Sonic velocity log, gamma ray log,
porosity and permeability measurements from plugs have resulted in a palaeo-burial profile
correlation with the adjacent Stevns-1 reference section. This shows that the studied section
has experienced a maximum burial depth of ~634-671m. A selected interval of 6m is tested
in a new XRF core scanner in order to evaluate depositional setting, clay content and
correlation with the NGR. XRF results suggests that the main clay minerals of this interval is
smectite, and that marl might indicate a slight oxygen depletion, which is in accordance with
spectral gamma ray results and the ichnology of the core section. Stable δ18O and δ13C
isotope measurements of the interval strongly suggests that the interval is the intrabasinal
Rørdal Member and that it represents a period of cooling in the otherwise warm Cretaceous
epeiric sea of the Danish Basin.
Keywords: Cyclicity, chalk, marl, Rørdal Member, stable isotopes, Gamma ray, Denmark.
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Acknowledgements
My gratitude and appreciations are expressed to my two supervisors, Professor Lars
Stemmerik (SNM) and Peter Frykman (GEUS) for all the patience with me, for useful
information, and for guiding me in the right direction towards this result, and my graduation.
Additional thanks to John Boserup for lending me his camera, to Bodil Wesenberg Lauridsen
for help with identifying trace fossils, Myriam Boushenou for introducing us to chalk
sedimentology. Thank you to Anders Lundsgaard Ebbesen and Bo Pettersen at IGN for the
work with the isotope samples, to the GEUS core Laboratory personel Claus Kjøller and Hans
Jørgen Lorentzen for introducing us to the procedures of the lab and to Marie-Louise
Siggaard-Andersen for always being helpful with both the XRF scanning, and the following
programming. Thanks to Michelle Strand, Trine Arp and Kristian Gram Sloth for good support
during the scanning and plugging procedure and for assisting with data when needed. My
gratitude to Tassos Perdiou for useful comments and information, to Tone Sorento Drøhse
for letting me live in her apartment, to Kasper “Lean” Høy Blinkenberg and Niklas “Bra”
Edvardsen for good conversations over a sandwich or a round of alufoil-sports. To my
parents and grandparents whose support has been invaluable, and finally to Maren; tusen
takk for all støtte, motivasjon og at du har tatt av din tid når jeg ikke hadde noe.
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CONTENTS ABSTRACT ............................................................................................................................... 2
List of figures .................................................................................................................... 6
List of tables ..................................................................................................................... 7
INTRODUCTION ................................................................................................................ 8
1.1 GEOLOGICAL SETTING ................................................................................................. 9
1.2 STRATIGRAPHY .......................................................................................................... 10
1.2.1 THE RØRDAL MEMBER ....................................................................................... 10
MATERIALS AND METHODS ............................................................................................ 12
2.0.1 CORE DESCRIPTION ............................................................................................ 12
2.0.2 GEUS CORE SCANNER ......................................................................................... 12
2.0.3 WIRELINE LOGGING ............................................................................................ 13
2.0.4 SNM XRF CORE SCANNER ................................................................................... 14
2.0.5 PERMEABILITY AND POROSITY ........................................................................... 15
2.0.6 INSOLUBLE RESIDUE ........................................................................................... 16
2.0.7 ISOTOPES ............................................................................................................ 17
RESULTS ......................................................................................................................... 18
3.1 CORE DESCRIPTION AND OBSERVATIONS ................................................................. 18
3.1.1 ICHNOLOGY ............................................................................................................. 23
3.1.2 SEDIMENTARY FACIES ........................................................................................ 27
3.1.3 PETROPHYSICAL RESULTS ................................................................................... 30
3.1.4 GEOCHEMICAL RESULTS ..................................................................................... 34
3.1.5 PLUGGING .......................................................................................................... 36
5
3.1.6 BULK δ13C AND δ18O ISOTOPES .......................................................................... 41
DISCUSSION .................................................................................................................... 43
4.1 SEDIMENTARY FACIES ................................................................................................ 43
4.1.1 LITHOLOGY ......................................................................................................... 43
4.1.2 CHALK-MARL CYCLICITY ...................................................................................... 44
4.1.3 ICHNOLOGY ........................................................................................................ 44
4.2 THICKNESS ................................................................................................................. 45
4.3 GAMMA LOG ............................................................................................................. 46
4.4 X-RAY FLUORESCENSE ............................................................................................... 46
4.5 STABLE δ18O AND δ13C ISOTOPES .............................................................................. 47
4.6 POROSITY AND PERMEABILITY .................................................................................. 51
4.6.1 Burial anomaly and porosity .............................................................................. 53
CONCLUSION .................................................................................................................. 59
FURTHER INVESTIGATIONS ............................................................................................. 60
6.0.1 Sampling frequency and selection .......................................................................... 60
6.0.2 Macrofossil investigation ........................................................................................ 60
6.0.3 XRF core-scanning ................................................................................................... 60
6.0.4 SEM analysis ............................................................................................................ 60
BIBLIOGRAPHY ................................................................................................................ 61
7 ..................................................................................................................................... 69
APPENDICES ................................................................................................................... 69
Appendix 1 ............................................................................................................................ 69
Appendix 2 ............................................................................................................................ 74
Appendix 3 ........................................................................................................................ 90
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List of figures
Figure 1.1: Map showing Chalk Group thickness and structural elements of the Danish Basin
and a detailed locality map ...................................................................................................... 10
Figure 1.2: Lithostratigraphic correlation of the Danish Basin and surrounding northern
Europe lithostratigraphic schemes. ......................................................................................... 11
Figure 3.1: A Selection of flints found in the studied interval. ................................................ 19
Figure 3.2: Pressure solution seams. ........................................................................................ 20
Figure 3.3: Fractures. ................................................................................................................ 21
Figure 3.4: Macrofossils observed in this study. ...................................................................... 23
Figure 3.5: Trace fossils of the studied interval. ...................................................................... 27
Figure 3.6: The wireline log results without casing of the studied interval. ............................ 31
Figure 3.7: Core scan log of the studied interval showing the total gamma response, K , U
and Th concentrations. ............................................................................................................. 32
Figure 3.8: The scanned and the wireline NGR logs compared. .............................................. 33
Figure 3.9: The results of the XRF compared with the scanned NGR and IR. .......................... 35
Figure 3.10: Plotted measured porosity in percentage. .......................................................... 37
Figure 3.11: Permeability-curve over the studied interval. ..................................................... 39
Figure 3.12: Insoluble residue over the studied interval. ........................................................ 41
Figure 4.1: Natural Gamma radiation, Insoluble residue, and manually entered lithological
facies throughout the studied section ..................................................................................... 43
Figure 4.2: Calculated palaeotemperatures of the Rørdal Member in the Dalbyover-1 core. 49
Figure 4.3: Cross-plot of carbon- and oxygen-isotope relations for bulk samples of the
studied interval of the Dalbyover-1 core.. ............................................................................... 50
Figure 4.4: The measured porosities against the measured permeability of the studied
section, and other Danish Maastrichtian chalk sections. ........................................................ 51
Figure 4.5: insoluble residue and porosity of the studied section plotted against each other.
.................................................................................................................................................. 52
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Figure 4.6: Permeability measurements against the scanned (mean 25) Natural Gamma
radiation ................................................................................................................................... 53
Figure 4.7: The porosity curve of the Stevns-1 core with calculated corrected values in
comparrisson with the Dalbyover-1 burial depth. ................................................................... 55
Figure 4.8: The Sonic velocity log of Dalbyover-1 fitted to the Chalk Group velocity-depth
curve of Japsen (2000). ............................................................................................................ 56
Figure 4.9: Porosity data of the lowest 161.90 meters (350.61 – 188.72m) of the Dalbyover-1
core. .......................................................................................................................................... 56
Figure 4.10: Permeability data of the lowest 161.90 meters (350.61 – 188.72m) of the
Dalbyover-1 core.. .................................................................................................................... 57
Figure 4.11: Facies of the Dalbyover-1 Rørdal Member along with the scanned NGR log,
sonic velocity log, porosity, permeability, δ18O, δ13C and insoluble (IR) values over height 58
List of tables
Table 1: All the observed Macrofossils, physical measurements, abundance and which facies
they are represented in with number of observations. ........................................................... 22
Table 2: Porosity results from plugs of the studied interval. ................................................... 36
Table 3: Permeability results from plugs of the studied interval. ............................................ 38
Table 4: Insoluble residue results from the plugs of the studied interval. .............................. 40
Table 5: Bulk stable isotopes, the outlier sample is marked grey. .......................................... 42
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1
INTRODUCTION
A 36.70m upper Maastrichtian cyclic chalk–marl succession belonging to the upper
Maastrichtian Rørdal Member that was drilled in eastern Jutland, Denmark, is in this study
investigated in detail. The section is part of the 350m long Dalbyover-1 core, and is
characterised by distinct cyclic perturbations in natural gamma ray values. The cyclicity of
the interbedded chalk–marl succession is linked to palaeocenographic cycles as a response
to a late Maastrichtian cooling event that in turn is controlled by the Earth’s orbital
perturbations – the Milankovitch cycles (Lauridsen and Surlyk, 2008; Lauridsen et al., 2011).
The depositional signature of marl beds in the Rørdal Member has been a subject of
discussion, different interpretations suggests both oxygen depletion, and well oxygenised
bottom conditions with enhanced terrestrial runoff (Lauridsen and Surlyk, 2008; Surlyk et al.,
2010; Lauridsen et al., 2011). Chalk is of major economic interest as it is an important
groundwater reservoir in northern Jutland and eastern Zealand and the main hydrocarbon
reservoir rock in the Danish North Sea (Surlyk et al., 2013). Lateral correlation is a useful tool
to understand depositional setting and mechanisms that affect reservoir quality of the chalk.
A series of methods has been incorporated in this study such as multiple wireline logging
tools, natural gamma ray core scanning, X-ray fluorescence, sedimentological logging,
porosity, permeability and clay content. The aim of this study is to integrate a series of
results in order to compare new data with previous results, improve the intra-basinal
correlation of Maastrichtian outcrops of northern Jutland and other cored section in
Zealand, Denmark, and to make an interpretation of the depositional environment and
burial history.
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1.1 GEOLOGICAL SETTING
The Dalbyover limestone quarry in which the 350 meter long Dalbyover-1 core is drilled is
located north of Randers, north-western Denmark and hence in the middle of the Danish
Basin (Fig.1.1). The Danish Basin was part of an Epeiric Sea, which flooded large parts of the
continental Europe during the Cretaceous. Calcareous algaes bloomed in this epeiric sea, and
resulted in deposition of a thick and extensive chalk successions (Madsen and Stemmerik,
2010). The Danish Basin is bordered in the north - north-east by the northwest – southeast
trending Sorgenfrei – Tornquist fault Zone that separates the Danish basin from a crystalline
Baltic shield. A west – northwest – east -southeast trending basement structural high named
the Ringkøbing – Fyn High, borders the basin in the south. The basin was formed by rifting in
the early Permian and modified by later rifting events in the Jurassic. Subsequently, from
Cretaceous times, thermal contraction dominated. Neogene uplift affected the whole
western Scandinavia and contributed to an approximately 320 m uplift of the study area.
During Maastrichtian times, the Danish Basin was situated approximately at 45◦ north and
was undergoing a slight northward drift. The Late Cretaceous was characterised by relative
high sea level due to combined basin subsidence and high eustatic sea level. (Anderskouv et
al., 2007). Data from seismics, other studied outcrops and cores, such as the Rørdal quarry,
Stevns -1 core and Karlslunde – 1 core, confirm that, the Danish Basin was a site of deep-
water chalk deposition. The basin had the highest sedimentation rates and deepest settings
along the basin axis, and shallower, less expanded settings on the Ringkøbing – Fyn High
(Esmerode et al., 2007; Lykke-Andersen and Surlyk 2004; Madsen and Stemmerik, 2010).
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Figure 1.1: Map showing Chalk Group thickness and structural elements of the Danish Basin (left). All reference localities are marked red, the green outline indicates the detailed locality map (right). Modified from Surlyk et al., (2013).
1.2 STRATIGRAPHY
The Dalbyover-1 core comprises most of the Maastrichtian Møns Klint
Formation from the upper Rørdal Member and up in to the Danian sediments exposed in the
Dalbyover quarry, Randers, Denmark. Focus in this study is the Rørdal Member of the Møns
Klint Formation (Fig.1.2).
1.2.1 THE RØRDAL MEMBER
The Rørdal Member has its name after its type section in Rørdal quarry in Aalborg, northern
Jutland. The reference sections are the boreholes Stevns-1 (105-76m), Stevns-2 (118.22-
88.25m) and Karslunde-1 (201.4-165m) south of Copenhagen (Fig.1.1) (Surlyk et al., 2010;
Surlyk et al., 2013). It deviates from the surrounding rather monotonous chalk with its
seemingly cyclic alternating chalk and marl beds that are suggested to represent shifts in
sedimentation related to astronomical forced periodicity within the Milankovitch frequency
band (Lauridsen and Surlyk 2008; Lauridsen et al., 2011). The studied section is 36.7m thick,
from 350.7- 314.0m, and comprises ten distinct peaks on the natural gamma ray log that
correlate with twenty-one observed marl beds in the core. The lower boundary of the
member might be below the base of the Dalbyover-1 core, so the thickness of the Rørdal
11
Member is not certain at this locality. The upper boundary is in this study defined at an
abrupt decrease in the alternating low-high gamma ray response at 314m. The member is
completely biomottled and the ichnospecies Chondrites, Planolites, Thalassinoides,
Zoophychos and Taenidium dominate the trace fossil assemblage.
Figure 1.2: Lithostratigraphic correlation of the Danish Basin and surrounding northern Europe lithostratigraphic schemes. Modified from Surlyk et al. (2013).
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2
MATERIALS AND METHODS
The Dalbyover-1 core (DGU 59. 459) was drilled in December 2013 at Dalbyover limestone
quarry, Randers, Jutland, Denmark by Faxe Kalk A/S for the Geological Survey of Denmark
and Greenland (GEUS) for scientific purposes. The core has a diameter of 5.6cm and is
350.7m long. It starts in mid-Danian chalk and penetrates into the upper Maastrictian Rørdal
Member of the Møns Klint formation. In this study, the lowermost 36.7m of the Dalbyover-1
core; equivalent to the upper Rørdal Member have been studied.
2.0.1 CORE DESCRIPTION
Macroscopic studies of the unslabbed core using water and a hand lens were made in order
xto create a sedimentological log in a scale of 1:10 (appendix 2). The study was executed
during June and September 2014. In order to clean the core for impurities and enhance
contrast and visibility of depositional characteristics, water was used. The description
focuses on changes in lithology, ichnology, diagenetic features and macrofossils. Both full
core photography and macrophotography were applied in the photo laboratory at GEUS,
using the EOS Utility 2.7 software. Core photos were taken using a camera with a 50mm
focal length. Macrophotos of certain features were also made using a camera with a 60mm
focal length.
2.0.2 GEUS CORE SCANNER
A scanner at GEUS Core Laboratory in Copenhagen measured the core as it was transported
through a lead shielded tunnel, where it passed a gamma ray source and a detector
assembly, at a constant speed of 1cm/min on a conveyor belt. The core was placed
untreated on U-shaped PVC and crushed parts where gathered in plastic sleeves in order to
maintain as even thickness as possible. The scanner measured the natural gamma radiation
13
(K, U and Th) and the bulk density of the core with readings every 1cm. Results of the
scanning are given as a function of depth (m) and the measured concentration parameters
are based on a mass parameter, which is calculated from the measured bulk density
parameter and the core diameter.
Results is given as following:
Total gamma (cps)
K (wt%)
U (ppm)
Th (ppm)
Bulk density (g/ml)
The water content influences the concentration results, and an air-filled pore section will
result in higher K, U and Th values than a section which contain water in its pores (Olsen,
2012). A potential bias in the collected data from this tool is the mechanical uncertainty of
the conveyor belts velocity, giving a potential error of up to 3%. The results are presented in
section 3.1.2 (Fig.3.7).
2.0.3 WIRELINE LOGGING
Two wireline logs have been produced by GEUS, one with a casing in order to secure a full
depth log (appendix 3), and one without casing, approximately 5 months later. Both logs
were carried out with a logging speed of 3m/min and a sampling interval of 1 cm with a
natural gamma probe, receiving decay products of stable Uranium (U), Potassium (K) and
Thorium (Th) as it passes a censor in the wire logging tool.
The latter wireline logging also conducted a sonic log. It measures travel time with pulses of
sound, and receives first arrival time in m/s in order to investigate velocities at different
depths to correlate with seismic data. The sonic log can also be used to calculate porosities
using a rewritten ‘Wyllie time average’ equation:
Ø =Δt − Δt𝑚𝑎
Δt𝑓𝑙 − Δt𝑚𝑎
14
Where Ø = porosity; Δt = tool measured compressional slowness (interval transit time); Δt𝑚𝑎
= slowness (compressional) of matrix material; Δt𝑓𝑙 = slowness (compressional) of interstitial
fluid. This equation is an empirical based equation and is used because there is no universal
relationship between linking sonic slowness and porosity (Rider and Kennedy, 2011). Other
measurements done with the wireline tool are fluid temperature (◦C), Fluid Conductivity of
pore fluid (mS/m) and Electric conductivity formations (mS/m).
2.0.4 SNM XRF CORE SCANNER
At the Natural History Museum of Denmark (SNM), an ITRAX Core scanner made by COX
Analytical Systems has been used in order to perform X-ray fluorescence (XRF) analysis of a
selected 6m interval of the Dalbyover-1 core. The studied section is from 326.7 - 332.7m.
This interval is between two depth markers, without larger damage, and shows pronounced
lithological variations on the gamma ray log. The core scanner is able to scan at high
resolution as fine as 200µm (Croudace et al., 2006; Rothwell et al., 2006). An intense micro-
X-ray beam was focused on the top of the core, as it moved through the scanner in order to
excite the atoms to ionize. This ionization ejected one or more electrons from the atoms
inner orbital, making the atom unstable, leading electrons from an outer shell to fill in the
void in the lower order shell. The result is a release of energy in form of emission of a
characteristic radiation, a signature emission. This emission is a fluorescent radiation that is
received at different wavelengths, making it possible to identify the chemical components of
the target. Before the core section was placed in the scanner, it was thoroughly cleaned with
a scalpel on top where the X-ray beam would target. The scanner started the process doing a
topographic laser scan in order to ensure even positioning of the XRF detector, making a
constant sample distance, and avoid collision with the sediment when scanning. In order to
avoid larger holes in the data set, because of the beam and censors angle, all irregularities
such as cracks and dissolution holes where taped over using a plastic tape. As this process
was running, a high resolution optical image was produced by a camera in the scanner. The
data were sent to a COX software named Q-Spec, where they were fitted in relation to a
standard deviation. The data were exported as a Microsoft Excel file, and further analysed
using Matlab coding. These results are discussed later in section 3.2.2. A test with X-
15
Radiographic imaging was also made, but the results will not be discussed in this study. The
scanning was carried out with a Rhodium tube at 30kV and 50mA.
2.0.5 PERMEABILITY AND POROSITY
Every second meter, a one inch plug was drilled from the core, to measure porosity and
permeability. Core sections with very high marl content were avoided and this induces a
slight bias in the analyses done on the plug material. They were labelled and then cleansed
for about 4 days in heated methanol to avoid any impurities like salt to cause inaccurate
readings in the permeability and porosity measurements. In the permeability test, the plugs
where put into a chamber, where a constant stream of nitrogen gas entered the chamber on
one side and measured the flow rate in cm3/s on the other side of the chamber. This
differential pressure where then plotted into the WinPOPE 3 software that calculated the
permeability.
Following Darcy’s law:
𝐾 = 2000 × Q ×𝐿
𝐴× 𝜇 ×
𝑃𝑎𝑡𝑚
𝑃12 − 𝑃2
2
Where K = permeability (mD); 𝜇 = nitrogen viscosity; L = length (cm); A = area (cm2); Patm =
ambient air pressure (atm); Q flowrate (cm3/s); P1 = inlet pressure (atm) and P2 = outlet
pressure (atm).
The porosity and grain density was analysed in the same plugs. They where first dried at
60◦C, before cooled off and temperature stabilised. The plug was placed in a cabinet of the
porosimeter, where a He-gas with a pressure of 7000 mbar was distributed between a
reference cell and the sample cell, using the equilibrium pressure between these cells as a
measure on the sample volume in the sample cell using Boyle’s law:
𝑃 × 𝑉 = 𝑁 × 𝑅 × 𝑇
𝑉 = 𝐾
𝑃
𝑉𝑡𝑜𝑡 − 𝑉𝐺 = 𝐾
𝑃
16
𝑉𝐺 = 𝑉𝑡𝑜𝑡 − 𝐾
𝑃
And further calculating the porosity in percent:
Ø% = 𝑉𝑃 × 100
𝑉𝐵
P = pressure in atm; V = volume; N = moles of gas; R = the gas constant 0.0821 (1 × atm / K
× mol); K = slope of the calibration curve; 𝑉𝐺 = grain volume; Ø% = porosity in percent; 𝑉𝑃 =
pore volume in cm3 = 𝑉𝐵 - 𝑉𝐺; 𝑉𝐺 = grain volume in cm3 from He-porosity measurement and
𝑉𝐵 = bulk volume in cm3.
Bulk volume was measured by putting the plugs in a bath of Hg, using Archimedes principle.
It was calculated as follows:
𝐵𝑉 = 𝐼𝑚𝑚𝑒𝑟𝑠𝑒𝑑 𝑤𝑒𝑖𝑔ℎ𝑡
𝐻𝑔 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑓𝑎𝑐𝑡𝑜𝑟
Hg temperature factor is the density of Hg at measurement temperature
Grain density – dg calculation:
𝑑𝑔 = 𝑊𝐷
𝑉𝐵 − 𝑉𝑃
WD = weight of the dry plug.
2.0.6 INSOLUBLE RESIDUE
Nineteen samples were crushed to smaller than 2mm powder and weighted. The samples
were washed in milli-Q water and stirred with a magnet. A 5ml acetic acid was added in the
solution until a stable pH value of 4.5 was reached, the solution was then allowed to settle
and excess solvent was removed. The precipitate was again allowed to settle, and further
centrifuged in 3000 rpm in a varifuge S. The sample was distributed in four centrifugal
glasses with a maximum deviation of ±0.5g before it was cleansed with a 50% ethanol
solution and dried at room temperature. Differential weight between the original powder
and the final product was then calculated in percent. A check for rests of calcium carbonate
(CaCO3) in the insoluble residue was then determined with an XRD analysis.
17
2.0.7 ISOTOPES
Samples from the core were retrieved, cleansed, powdered and weighted into 0.6 ± 0.2 mg
samples in preparation for the mass spectrometry routine. The powdered samples were
then sealed in small vials and flushed in helium in order to remove atmospheric gasses. 50
microlitres of phosphoric acid were added with a needle to the carbonate in order for it
dissolve to CO2 and attain an isotopic equilibrium with the acid. The vials are further kept at
72.0 ± 0.1°C in an aluminium tray 90 minutes prior to and during mass spectrometry in
accordance with Spötl and Vennemann (2003). The system setup at the Department of
Geosciences and Natural Resource Management, University of Copenhagen, consists of a
Micromass IsoPrime triple collector mass spectrometer and uses a Carrera marble as in-
house standard. Both carbon and oxygen isotope values are measured. The long-term
external reproducibility is 0.08‰ for δ13C and 0.18‰ for δ18O with double standard
deviations.
18
3
RESULTS
3.1 CORE DESCRIPTION AND OBSERVATIONS
This section presents the different elements of the core that have an impact on the
environmental and burial history interpretation, as well as the physical results.
Flint
Flint is the name of chert in Chalk. It consists of biogenic silica originated α-quartz crystals
that are mostly only a few microns across (Hancock, 1975). At the first stage it was a hydrous
and amorphous gel named Opal-A. Later, at low temperature, this Opal-A changes into Opal-
CT (porcellanite, lussatite or low-temperature cristobalite) (Hancock, 1975). The precipitated
amorphous silica is believed to originate from the dissolution of sponge spicules or siliceous
plankton (DeMaster, 2004; Tucker 2003). When the amorphous silica is precipitated, and
there is slow or nondeposition, at a redox boundary microbial activity results in a lowering of
the pH, dissolute the carbonates, liberates hydroxyl complexes and flocculate dissolved silica
in the pore water until there is enough silica to form the flint precursor (Madsen &
Stemmerik, 2010). In the studied section of Dalbyover – 1 core, flint is only observed in a few
levels. At 348.45m, a 7cm thick black flint band is covering the full width of the core, hence it
is not possible to determine the original horizontal extend of the flint band (Fig.3.1B). The
flint band is interpreted to represent a Thalasinoides burrow, and has light grey spots to a
light grey rim, which is a response of the levels of silicifiaction. At 348.65m a 5cm long and
4cm thick flint nodule with all of the similar features as the flint band it is also believed to
originate from a Thalasinoides burrow. (Fig3.1A). Two flint nodules found at close proximity
at 345.05m and 344.84m respectively, have a more complex reburrowing pattern where one
is disrupted by a distinct white egg-shaped silicified feature between the more common dark
coloured flint with grey spots, and the other seems to be completely reburrowed by
Taenidium and has a lighter grey colour (Fig.1.3C). At 315.0m there is three small patches of
19
what appears grey, but has a dark colour when scratched, one also have what appears to be
oxidised pyrite (Fig.3.1E), the origin of these are uncertain.
Figure 3.1: A Selection of flints found in the studied interval. A: Black silicified Thalassinoides burrow with a lighter rim (Depth: 348.65m). B: Black flintband with a larger white patch (Depth: 348.22m). C: Densely re-burrowed Thalassinoides-flint with a light- grey egg-shaped flint within, origin of egg-shaped burrow is unknown (Depth: 345.05). D: Light grey silicified Taenidium burrow (Depth: 344.84m). E: A ‘grainy’ grey flint, likely oxidised pyrite in the centre, the flint is black in fresh cuts (ruler scale is in mm, Depth: 315.0m).
Pressure solution seams
Pressure solution seams are present throughout the studied interval. They are to a high
degree found in relation to marl facies. Pressure solution seams are present both as smooth
sinusoidal features, and as sharper and more spikey protostylolites, being a precursor to
better developed stylolites. It is believed to be feature characteristics of burial between 200
and 2000 meters. They are the result of both mechanical and chemical compaction, and
contain a higher concentration of clay minerals than the surroundings (Frykman et al., 1999;
Fabricius, 2003). The protostylolites are more commonly present in facies of purer carbonate
and are associated with slickenside fractures with clay drapes. Individual dissolution seams
and protostylolites are between 0.04mm and 0.1mm thick.
20
Figure 3.2: Pressure solution seams. A: Solution seams merging into a marl bed (Depth: 339.55m). B: Protostylolites (Depth: 340.75m).
Fractures
Slickensides and hairline fractures are the two types of fractures recognised. There are
twelve slickensides throughout the studied interval, and they have distinct dark clay-smear
striations (Fig.3.3). Some slickensides are related to the protostylolites. Eighteen Hairline
fractures throughout the studied interval appear as thin fractures, usually less than 0.07mm
thick, all of which displace surrounding features. Slickensides are indicators of stress related
strike-slip movement (Wennberg et al., 2013). Hairline fractures are the result of a very early
dewatering and minor compaction of the sediment (soft sediment deformation) (Frykman et
al., 1999).
21
Figure 3.3: Fractures. A: High angle Slickenside fracture with clearly visible dark striated clay smear (B) (ruler scale in mm, Depth: 319.40m). C: Vertical Hairline fracture displacing a horizontal Zoophycos trace fossil approximately 2mm (Depth: 343.33m).
Macrofossils
Macrofossils are defined as remnants from animals or plants that are visible without a
microscope (Pickerill and Brenchley, 1991). Macrofossils have been incorporated in this
study in order to validate whether there are any greater changes between the different
facies. The macrofossils that have been observed are listed in table1, and in Fig.3.4. There
has not been focused on species recognition.
22
Macrofossil Measurements Abundance Facies Depth Figure
Bryozoa 0.1 – 40 mm >100 All All 3.4A
Porifera 5 – 75 mm >100 All All 3.4C
Mollusca
9 – 35 mm 4 Light + dark marly
chalk
348.70m, 321.12m, 320.11m, 316.3m
3.4J
Cnidaria (Coral)
~ 6 mm 5 Light + dark marly
chalk
350.31m, 349.8m,
349.10m, 341.63m, 317.4m
3.4H
Echinodermata (Crinoidea)
2.5 – 6.5 mm 10 Light marly chalk
All 3.4E
Serpiludae (tube worm)
5.5 mm 1 Light marly chalk
348.80m 3.4G
Brachiopoda 4 – 6 mm 5
Light + dark marly
chalk & Chalky marl
336.0m, 335.25m, 329.33m, 328.65m, 328.70m
3.4K
Ostreidae (Oyster)
5mm 1 Dark marly chalk
321.11m 3.4I
Table 1: All the observed Macrofossils, physical measurements, abundance and which facies they are represented in with number of observations.
Throughout the studied section, there is a very high abundance of both Porifera and Bryozoa
in all facies, although they are observed to a lesser extent in marl facies. The other five
identified macrofossils except for perhaps Crinoidea, are not observed in such extent that it
is reasonable to statistically use these data for any environmental interpretation.
23
Figure 3.4: Macrofossils observed in this study. A and B: Bryozoa (Depths: 348.13m and 348.58), C and D: Porifera (sponge, Depths 347.35m and 334.0m), E and F: Echinodermata (Crinoidea, Depths: 348.70m and 316.30m), G: Serpiludae, (tube worm, Depth: 348.78m), H: Cnidaria (Coral, Depth: 341.56m), I: Ostreidae (Oyster, Depth: 321.11m), J: Mollusca (Depth 316.27m), K: Brachiopoda (Depth 328.65m), L: Possible shell fragments of unknown origin (Depth 328.56). The scale in figure D is in mm; hence, the length of the sponge is here ~3.5cm.
3.1.1 ICHNOLOGY
Trace fossils are important as a utility to reconstruct the original depositional environment,
such as paleobathymetry, sedimentation and hydraulic regime during deposition (Bromley
and Ekdale 1984). The studied core section is completely biomottled, thus no primary
sedimentary structures have been recognised. The Rørdal Member of Dalbyover-1, consists
of five types of trace fossils, namely Chondrites, Planolites, Taenidium, Thalassinoides and
Zoophycos. Burrow generations and burrow cross cutting have not been investigated in
detail, ichnology in this study is solely meant as a supplement of the general environmental
description. Figure 3.5 shows a representation of all the observed trace fossils.
24
Chondrites
This trace fossil is a result of an unknown endobenthic deposit feeder making a complicated
but regularly branched burrow system. It resembles a root system that angles 30 – 40
degrees up to fifth or sixth order branching from higher order y-form branches (Pemberton
et al., 2009). It is known as a facies breaker that has a burrow system that was produced
deep within the sediment and has a shaft or tunnel system that has a uniform diameter
between ~ 0.5 and ~5 mm in this study, and an infaunal abyssal nematode is suggested
(Bromley and Ekdale, 1984). The Chondrites trace fossil appears as clusters of tens of circular
to oval traces. It often has a slightly darker colour than its surroundings, but also appears
lighter when it is within other trace fossils such as Thalassinoides, Zoophycos, and Planolites,
or it penetrates a darker coloured facies. Because it is such a deep burial system, it is usually
the last traces in its respective depth. The Chondrites is divided into “large” and “small”
solely based on its diameter where small Chondrites is approximately below 1mm and all
above is recognised as large Chondrites. They have no observed internal structure and there
has not been a quantitative study of them.
Planolites
The Planolites ichnogenera is divided into two; Planolites A and Planolites B mainly based on
Lauridsen et al., (2011). Planolites A is commonly found within Planolites B and differentiates
in colour and size where Planolites B is usually larger with a diameter of 10-20 mm and
Planolites A has a diameter 3-10 mm. Planolites A has a lighter active fill than its surrounding
sediment whilst Planolites B is has a darker active fill than its surrounding sediment, both
structureless. Planolites has an elliptic shape and has been found in a total of 177 instances
in the core section and 80.8% is found in the “light marly chalk” facies. The tracemaker is
considered to be a wandering shallow tier deposit feeder or grazing feeder that was
backfilling and may be classified as a pascichnion (Bromley 1996), and is probably infaunal
polychaetes or other worm-like organisms (Pemberton et al., 2009).
25
Taenidium
The Taenidium ichnospecies is a burrow with an alternating dark and light meniscate packet
and internal menisci (Bromley et al., 1999). It is typically interpreted as a vagile pascichnia
deposit feeder, but the alternation between the meniscate packing has led to some
suggestions that this originates from ambient and above-laying sediments and hence might
not be a pascichnia, but originates from a nonvagile worm stuffing its tunnels with both
ambient and near-surface sediments. The feeding strategy is not fully understood (Locklair
and Savrda 1998). Pedersen and Surlyk (1983) reported that the trace fossil is part of a 45 -
90 degrees angle branching tube-system, but no such system has been identified in this
study. Taenidium is predominantly horizontal to subhorizontal (Bromley et al., 1999), but
vertical examples are also found (Fig.3.5). The trace fossil is found evenly distributed
throughout the section in 34 instances of varying confidence. It is only found in the “light
marly chalk” facies and in the “dark marly chalk” facies. One of the specimens is silicified as
flint (Fig 3.1D), it is 4 – 7cm long and 1 – 2 cm thick. The specific ichnospecies is likely to be
Taenidium crassum based on its asymmetrically relatively deep chevron-shaped menisci
spreite and geographical origin in accordance to Bromley et al., (1999).
Thalassinoides
The large trace fossil of Thalassinoides is cylindrical shaped burrow that is believed to have
been made from a type of crustacean. More specific a decapod which is closely related to
the present Norway lobster (Heinberg, 2000 and Yanin and Baraboshkin, 2013). It is 2 – 7 cm
thick and from 1 cm to comprise the entire cores width. Four of the flints or silicified
features of the investigated section is interpreted to be silicified Thalassinoides burrows. In
this study 99 Thalassinoides has been identified, but no internal structures are found, mostly
due to reburrowing from other trace fossils, chiefly Chondrites. There is not identified any
Thalassinoides in the “chalky marl” facies or the “marl” facies throughout the section.
26
Zoophycos
What is believed to be an echiuran (spoon worm) originated burrow, named Zoophycos
consists of a complex deep-tier system (deep in the strata), up to half a meter deep burrows
is not uncommon (Ekdale and Bromley, 1984; Bromley, 1996; Heinberg 2000). It exhibits a
concave spreite made from an open tube system moving and feeding its way horizontally
around a vertical centre. When a 360◦ rotation around its own axis is reached, it has shifted
slightly down in order to avoid its own defecation which is believed to be the spreite along
with redundant sediment (Heinberg, 2000). The traces is in this study commonly observed as
horizontally traces that terminates on two sides, or it covers the entire width of the core
indicating a larger circumference. Measured to be between 2 and 7 mm thick, and is found
in 80 instances, but since it is highly likely that many of these is connected as being traces of
the same individual, it is difficult to propose any precise tendency in terms of abundance,
although it seems to decrease with depth. The Zoophycos traces are highly abundant in the
“light marly chalk” facies and appear remarkably darker than their surroundings.
27
Figure 3.5: Trace fossils of the studied interval. A: Large Chondrites appears dark in chalk and dark when it re-burrows other trace fossils (upper right, Depth: 341.80m). B: Three burrows generations, large dark grey represents a Thalassinoides crosscut, inside a lighter Planolites A and small darker spots within are small Chondrites (Depth: 334.15m). C: Planolites B (Depth: 341.75m) D: One of two observed semi-vertical Taenidium (Depth 334.30m). E: A Zoophycos network, probably from the same individual tracemaker as it works its way down the sediment in a circular motion (Depth: 333.90m). F: Close-up of where the trace enters into the sediment and its spreite (Depth: 333.90).
3.1.2 SEDIMENTARY FACIES
Four sedimentary facies are observed and described in this study based on the Dunham
(1962) classification system for limestone. The described facies have been classified with
respect to their visual colour properties. The entire studied interval consists of what is
defined as carbonate mudstone, meaning it is mud-supported and contains less than 10%
grains (larger than 62microns) (Tucker and Wright, 1990).
Marlstone
Description: The marlstone facies forms a distinct dark grey clay-rich carbonate mudstone
ranging in thickness from 1 – 23 cm with an average of 6.29cm. It comprises 3.61% (132 cm)
of the studied core section. Twenty-one marl beds have been identified throughout the
studied section, and are typically associated with bands of laminated pressure solution
seams compressed tightly together. One exception is a 23 cm thick bed which is slightly
lighter in colour than the other marl bands, but undoubtedly has a high clay content due to
its clay swelling caused by moistening in order to enhance structures within the core. The
twenty other marl bands show little or none clay swelling. The boundaries are transitional to
a other facies with a decreasing amount of pressure solution seams to the adjacent facies
and abrupt. Except from the pressure solution seams, primary sedimentary structures have
not been identified within the facies. Some of the marl bands apparently have different
mechanical properties than the surroundings since they easily got detached on the borders
between marl and the adjacent facies. No flint are found in a marl facies of this section. Six
of the marl beds also contain what is believed to be pyrite. Two slickensides are found in
close proximity to the third marl bed.
Trace - and body fossils: Trace fossils are only found in a few beds and are limited to small
Chondrites, occasionally Zoophycos and Planolites B, biota findings are restricted to
Bryozoans and Porifera to a few beds.
28
Interpretation: The marl facies has due to extensive bioturbation, no primary lamination, and
is probably a hemipelagite. It is most likely deposited in relatively deep, quiet water
unaffected by turbidity currents and below the storm-wave base, this is further backed by
the presence of Zoophycos (Savrda 2012). The marl beds occur in a cyclic manner which is
believed to be a response of astronomical forcing (Lauridsen and Surlyk, 2008; Lauridsen et
al., 2011). The marl beds most likely represent a period of enhanced freshwater runoff and
colder climate (Boulila et al., 2010) with less carbon production and dysoxic to anoxic
conditions also supported by the presence of pyrite at some depths.
Chalky Marlstone
Description: The Chalky marlstone is a grey – dark grey carbonate mudstone and appears to
be a mixture between chalk and marl in most beds, but shows a few pressure solution seams
in two of the beds whereof one part appears flaser-like and has what appears to be a
network of hairline fractures. Four intervals of 46, 31, 15 and 28cm thicknesses respectively
are defined visually as chalky marlstone, and comprise 3.28% (120 cm) of the studied
section. This facies is interbedded with dark marly chalk and more rarely marlstone. None of
the four intervals contains any flint. In the lowermost, thickest bed, black pyrite needles are
observed in the top and bottom, and one green potential glauconitic spot is seen.
Trace - and body fossils: Trace fossils are scarce, but Planolites B and Chondrites have been
identified in the shallowest of the four beds and some uncertain trace fossils are also
observed in the facies. In both the deepest and the shallowest interval, we find biota in form
of bryozoans and Porifera, the deepest interval also has two Brachiopods, no biota is found
in the two chalky marl beds in between.
Interpretation: The structureless bioturbated marly chalk is interpreted as a facies were
accumulation rates are slow enough for the infauna to burrow sediments and destroy any
primary structures although benthic oxic conditions were non-ideal. The presence of pyrite
at certain depths, indicate potentially dysoxic benthic conditions (Wignall et al., 2005), but
this might just be local or very limited in time due to the small extend of this. The
depositional environment might be explained by sufficiently oxic environment, and slow
29
enough accumulation rates for a complete biomottling of the seafloor (Anderskouv and
Surlyk, 2011) a combination of these two is not unlikely. This facies has a considerable
amount of terrigeneous material, which most likely is a result of an enhanced runoff from
adjacent land areas.
Dark marly chalk
Description: Dark marly chalk is a grey – light grey mix between chalk and clay, which visually
looks as it contains less clay than chalky marlstone and less chalk than light marly chalk. It is
interbedded with marl or chalky marlstone. Many of the marly chalk beds comprise a
significant amount of pressure solution seams as a natural transition to the marl beds.
Trace - and body fossils: The facies is generally heavily bioturbated and all the trace fossils
are represented in this facies. No flint is found at any of the beds. Only one of the beds in the
facies includes a slickenside fracture, but hairline fractures are not uncommon. Bryozoans,
Porifera, Oestriade and a few unidentified biograins are found in this facies. The total
percentage of the facies in the studied section is 18.66% (683 cm).
Interpretation: The dark marly chalk facies is interpreted to be a hemipelagic clay rich
carbonate (Anderskouv and Surlyk, 2011), and is a transitional facies to the marly facies. It is
because of the completely biomottled nature, believed to be a result well-oxygenated
benthic conditions (Anderskouv and Surlyk, 2011).
Light marly chalk
Description: The facies which by far represents the majority of the studied section it is a
light, heavily bioturbated marly chalk. It representes 2752 cm (75.17%) of the total 3661 cm
and is a light grey –whitish facies distributed over 21 beds. In the lower half of the studied
section it is interbedded with marlstone beds. Further up it is more commonly interbedded
with dark marly chalk beds, and more rarely marl beds. The transition between marlstone
and the light marly chalk is associated with increasing pressure solution seams towards the
marl bed, pressure solution seams are observed to a lesser extend elsewhere. No primary
structures are observed. All of the recognised flint is found within this facies.
30
Trace - and body fossils: Bryozoans, Porifera, Anthozoa, Serpulidae, Spondyalite, Crinoidea,
Mollusca and many unidentified biograins are represented in these sections. All of the
different types of observed trace fossils are also found in the light marly chalk.
Interpretation: The facies is interpreted to be the lithology with the least terrigenous
material, and hence is furthest away from a source of such kind or it represents longer
periods of limited input and is interpreted as a highstand deposition. The high degree of
bioturbation along with the biota, suggest a sufficient oxygenated sea bottom with a
sufficiently slow accumulation to disturb primary structures and is most likely a
hemipelagite.
3.1.3 PETROPHYSICAL RESULTS
Wireline log
The data from the wireline log presented in Fig. 3.6, and was recorded without a casing
about five months after initial wireline log (with casing). Full-lenght borehole wireline record
with casing is presented in appendix 3.
The sonic log displays a stable around 2500 𝑚
𝑠 signal with a slightly more elevated signal in
the interval above ~334m than below. Positive excursions tends to be associated with
positive excursions or just below positive excursions in the NGR log.
About 0.60⁰C decrease in the fluid temperature log registered from the deepest part of the
core, from ~13.40⁰C to ~12.80⁰C.
The Fluid elctric conductivity log measures the capability of the subsurface fluids to conduct
electric currents and is measured in milliSievert per meter (𝑚𝑆
𝑚). The deepest ~two meters
display a signal that rapidly increase about 1000 𝑚𝑆
𝑚, it is likely to be a mechanical distorted
signal, and not a petrophysical signal. Disregarding the deepest two meters, the signal
displays a stable upward decrease from 3875 𝑚𝑆
𝑚 to 3770
𝑚𝑆
𝑚.
Electric conductivity of formations (ECF) log is a measurement of the subsurface rocks to
conduct electricity, measuremts are in 𝑚𝑆
𝑚. The ECF-log displays an inverse signal in relation
31
to the NGR-log. Using the NGR-log as a proxy for lithology where peaks represents marly
beds, it is apparent that higher clay content has a negative effect of the ECF.
Figure 3.6: The wireline log results without casing of the studied interval.
GEUS core scanner
The analysis in the GEUS core scanner resulted in a spectral gamma ray log (Fig.3.7).The
spectral gamma radiation gives a volume fraction of the individual contributing radioactive
element of the total gamma ray signal. They come from naturally occurring uranium (U),
thorium (Th) and potassium (K) in the core (Rider and Kennedy, 2011).
32
Figure 3.7: Core scan log of the studied interval showing the total gamma response (black) and K (red), U (purple) and Th (light green) concentrations. An average over 25cm of the Th signal is also presented (dark-green).
The total gamma response in Fig.3.7 displays signals between -0.02 cps and 2.82 cps, with a
mean of 0.78 cps. Peaks corresponds to the marly beds. Because the Th signal displays large
alternating signals, a mean over 25 cm curve is displayed in Fig.3.7 for an easier correlation
to the remaning signals. The larger peaks at ~343.5m, ~340.0m and from ~328.5m and up,
have uranium as the largest contributor to the total gamma response, while the other four
larger total gamma peaks have potassium and thorium as the main contributors. The overall
total gamma response dispalys a small increase from the deepest to the highest part, it is
slightly increased in the middle part of the studied interval with larger positive perturbation
in this section than that of the deepest and highest sections. Negative values in the spectral
gamma ray log might be a result of slight variations in signal during the calibration
procedure.
33
Scanned and wireline gamma ray log
The natural gamma ray (NGR) results of the wireline logging are compared with those of the
core scanning in Fig.3.8. The gamma ray logs are scaled in American Petroleum Institute
(API) units. Since the studied section is the end section of the Dalbyover-1 core, the wireline
has not measured the deepest ~1m in order to avoid that the logging tools in the borehole
got injured or jammed. The wireline log results displays larger perturbation than the results
from the scanning and has a depth deviation in the lower section of ~0.7m.
Figure 3.8: The scanned and the wireline NGR logs compared, note that there is a difference in depth for the two signals, this is probably a result of the elasticity of the wire attached to the logging tool. The wireline log is without casing, measured five months after the core was drilled.
34
3.1.4 GEOCHEMICAL RESULTS
A total of 6m of the studied interval has been scanned with an X-ray fluorescence (XRF)
scanner at SNM. The scanner is in this study tested for the first time on limestone of any
kind. The results should therefore be considered as test results. The interval chosen is
between two depth markers (332.7m – 326.7m). The core has only minor damage, and
displays marl in both the sedimentological log and the NGR log. Because plastic tape was
used in order to smoothen up all irregularities, such as cracks and holes, these sections gave
highly biased results, so these has been removed from the original dataset. The XRF core-
scanner provides a variety of element signals. Elements used in this study have been chosen
based on their relevance to terrestrial clay-mineral content (Si, Al, Fe, Cr), Calcium carbonate
(Ca), and to look for signals that might be a proxy for anaerobic conditions (S, Fe, Mn) (Schulz
and Zabel, 2006). A correlation with the NGR log and core photography is also included
(Fig.3.9). Measurements are divided with coherence which is the specter of the elastic
scatter from the XRF-beam. The XRF results display an inverted signal between Si and Ca,
where Ca decreases with increased NGR signal, this also correlates well with the darker marl
beds of the core photography. Fe, Cr and Al tend to peak close to or at the marl beds. Mn
and S show no convincing trend in relation to the lithology.
35
Figure 3.9: The results of the XRF compared with the scanned NGR mean 25 results along with the insoluble residue (%) results from this interval (orange dots) and an optical image of the scanned interval.
36
3.1.5 PLUGGING
The core has been plugged every ~2m, plugs are 25.4 mm diameter and the material has
been used to determine porosity, permeability and insoluble residue. Marl beds were
purposely avoided as these beds tended to fracture easily and hence would have resulted in
poor data quality of permeability and porosity. Another consequence of this is that the
insoluble residue (IR) might not show the maximum content of clay.
POROSITY
The porosity measurements of the studied interval are given in table 2. The porosity is
measured in percentage (%), ranges from 22.94% to 37.31% and averages 30.62%.
Depth (m) Porosity (%)
315,87 36,15
317,90 30,73
319,87 27,32
321,87 31,03
323,90 27,84
325,95 24,99
327,74 27,31
329,69 29,34
331,84 22,94
333,80 31,23
335,70 26,28
337,48 29,96
339,27 29,24
341,25 35,10
343,14 34,70
345,00 33,48
346,95 32,45
348,82 37,31
350,63 34,35 Table 2: Porosity results from plugs of the studied interval.
37
Figure 3.10 shows the data from Table 2 plotted. The signal of the studied interval is
fluctuating with an overall declining trend from 350.63m to its lowest point at 331.84m
followed by a general increase in porosity.
Figure 3.10: Plotted measured porosity in percentage.
PERMEABILITY
Results of the measurements of single point gas permeability are listed in Table 3. The
permeability is given in millidarcy (mD) and ranges from 0.09mD to 2.92mD, it averages
1.17mD.
38
Depth (m) Permeability
(mD)
315,87 2,31
317,90 0,61
319,87 0,23
321,87 0,86
323,90 0,48
325,95 0,13
327,74 0,31
329,69 0,54
331,84 0,09
333,80 0,52
335,70 2,26
337,48 0,41
339,27 1,49
341,25 2,11
343,14 2,92
345,00 1,20
346,95 1,63
348,82 2,57
350,63 1,64 Table 3: Permeability results from plugs of the studied interval.
Figure 3.11 shows the data from Table3 plotted. The signal of the studied interval gives
similar trends as the porosity curve and it is fluctuating with an overall declining trend from
350.63m to its lowest point at 331.84m followed by a vague increase in permeability before
a large positive shift from 0.61 to 2.31mD between 317.90m and 315.87m.
39
Figure 3.11: Permeability-curve over the studied interval.
INSOLUBLE RESIDUE
Table 4 lists the results of the insoluble residue (IR) analysis. From XRD analysis of the IR, it is
established that the samples contain dominantly opal-CT and quartz. The results are given in
weight percentage (wt%) and range from 5.72wt% to 23.79wt.% and averages 12.94wt%.
40
Figure 3.12 shows the data from Table 4. The signal of the studied interval is highly
fluctuating. The first five (350.63m-343.14m) measurements are rather stable around
10wt%. The signal is fluctuating between 341.25m and 335.70m. Above it shows a steady
increase to a maximum at 321.87m.
Depth (m)
Sample weight (grams)
Insoluble residue (grams)
Insoluble residue (wt%)
315,87 20,26 2,50 12,34
317,90 17,46 2,89 16,55
319,87 17,08 3,76 22,01
321,87 18,37 4,37 23,79
323,90 17,67 2,04 11,54
325,95 19,99 2,98 14,91
327,74 22,07 2,69 12,19
329,69 20,18 3,23 16,01
331,84 22,14 3,35 15,13
333,80 19,66 2,58 13,12
335,70 22,68 1,39 6,13
337,48 20,54 2,89 14,07
339,27 22,01 1,26 5,72
341,25 16,77 1,90 11,33
343,14 17,09 1,70 9,95
345,00 15,69 1,54 9,82
346,95 18,19 1,85 10,17
348,82 18,51 1,94 10,48
350,63 19,41 2,05 10,56 Table 4: Insoluble residue results from the plugs of the studied interval.
41
Figure 3.12: Insoluble residue over the studied interval.
3.1.6 BULK δ13C AND δ18O ISOTOPES
Bulk samples have been taken every ~1m in the studied interval in order to measure Carbon
and Oxygen isotopes. The values are expressed in per mil (‰) relative to the Vienna- Pee
Dee Belemnite (V-PDB) standard reference. One sample at 341.25m has a large anomaly,
+4.87‰ and +5.38‰ for δ13C and δ18O respectively (table 5). This outlier is removed in
Fig.4.11, as it is interpreted to represent a non-normal measurement, and hence would bias
the data significantly. The analytical precision is estimated to be 0.1‰ for oxygen and
0.05‰ for carbon.
The δ13C values of the studied interval ranges between +2.02 and +2.40‰, averaging at
2.26‰ (table 5, Fig.4.11).The δ13C profile is characterised by small ±0.15‰ fluctuations with
no prominent excursions. The overall signal is stable and shows no apparent trend.
The δ18O signature varies between- 1.48 and -0.34‰, averaging at -1.03‰ (table 5,
Fig.4.11). A initial decreasing signal from 350.63m (-0.75‰) to 339.27m (-1.40‰) is followed
by a slightly more positive series of strong fluctuations, including five positive excursions
above -0.60‰, and five negative excursions below -1.25‰ with no apparent overall trend.
42
Sample ID δ13C (‰) δ18O (‰) wt. (mg) Depth (m)
2001 2,38 -0,75 0,66 350,63
2002 2,25 -1,08 0,66 349,72
2003 2,26 -1,05 0,61 348,82
2004 2,26 -1,29 0,66 347,82
2005 2,25 -1,11 0,62 346,95
2006 2,40 -1,04 0,64 345,98
2007 2,38 -1,03 0,6 345,00
2008 2,35 -0,90 0,64 344,10
2009 2,26 -1,17 0,61 343,14
2010 2,27 -1,12 0,69 342,19
2011 4,87 5,38 0,65 341,25
2012 2,13 -1,31 0,68 340,26
2013 2,26 -1,40 0,68 339,27
2014 2,30 -0,93 0,67 338,48
2015 2,21 -1,14 0,64 337,48
2016 2,22 -0,65 0,68 336,49
2017 2,20 -1,40 0,66 335,70
2018 2,31 -0,96 0,64 334,70
2019 2,22 -1,04 0,67 333,80
2020 2,24 -0,47 0,66 332,80
2021 2,16 -1,09 0,68 331,84
2022 2,24 -1,35 0,64 330,81
2023 2,21 -1,35 0,67 329,74
2024 2,35 -0,41 0,65 328,69
2025 2,24 -1,27 0,64 327,74
2026 2,16 -1,18 0,67 326,65
2027 2,26 -0,88 0,65 325,95
2028 2,36 -0,34 0,66 324,95
2029 2,24 -1,30 0,68 323,90
2030 2,33 -1,07 0,6 322,87
2031 2,21 -1,21 0,68 321,87
2032 2,28 -0,47 0,61 320,87
2033 2,12 -1,48 0,61 319,87
2034 2,31 -0,78 0,69 318,88
2035 2,02 -1,25 0,64 317,90
2036 2,30 -1,00 0,62 316,88
2037 2,33 -0,96 0,63 315,87
2038 2,22 -0,82 0,64 314,92
Table 5: Bulk stable isotopes, the outlier sample is marked grey.
43
4
DISCUSSION
4.1 SEDIMENTARY FACIES
4.1.1 LITHOLOGY
The studied interval consists of a grey carbonate mudstone with darker grey clay-rich
intervals and dark grey marl layers that coincides with significant peaks in the GR log.
Macrofossils are scattered throughout the studied interval, is dominated by Bryozoans and
Porifera, and they show no indications of transportation. The sedimentary log and facies
analysis shows an upwards increasing clay content to approximately 325m before it starts to
decrease at the top of the interval. The Natural Gamma log averaged over 25cm (mean 25)
and partly the insoluble residue data support this observation (Fig.4.1). Insoluble residue
was only sampled every 2m ± 0.2m, marl was avoided during the procedure and hence
should the data only be used as an indicative together with other datasets.
Figure 4.1: Mean 25 Natural Gamma radiation, Insoluble residue, and manually entered lithological facies throughout the studied section were 1 = “light marly chalk”; 2 = “dark marly chalk”; 3 = “chalky marl” and 4 = “marl beds”. The indifferences in the trend is likely to be due to low sampling frequency of the insoluble residue.
44
4.1.2 CHALK-MARL CYCLICITY
The alternating chalk-marl beds in the studied section coincide with the Natural Gamma ray
log (FIG.4.1). There is twenty-one marl beds at ten intervals. The distance between the marl
beds ranges from 0.95 to 4.37m averaging at ~3m. The amplitude of the GR signal has a
general increase up to ~324.74m. This increase is stepwise divided in two, where it peaks at
341m before it re-enters an increase from a smaller perturbation and stepwise increases
again in three pulses. The signal reaches a maximum at 324.74m before the pulses decrease
stepwise towards the top of the studied section. Increased content of fine terrigeneous
material in the calcareous biogenic sediments indicates enhanced freshwater runoff from
adjacent land areas as a response of colder climate and increased precipitation. The
alternating chalk-marl of the Rørdal Member has a distinct cyclic manner. Sedimentation
rates of the upper Maastrichtian Danish Basin show great variability and have been
suggested from a mean of 2.0cm/kyr (Rørdal-1) (Thibault et al., 2011), a mean of 6.0cm/kyr
(Rørdal quarry) (Lauridsen and Surlyk, 2008), and up to 10cm/kyr (Surlyk and Lykke-
Andersen, 2007). The uncertainty of the sedimentation rates makes it difficult to conclude
what the cyclic manner of the studied section is a response to. Cyclicity of marl beds in the
Rørdal Member is suggested to indicate climatic changes due to the orbital precession
forced periodicity within the Milankovitch frequency band (Lauridsen and Surlyk, 2008;
Lauridsen et al., 2011). If all NGR perturbation is a signal of the Milankovitch cycles and an
average sedimentation rate of 6cm /kyr as suggested in Lauridsen and Surlyk (2008) the NGR
signal might represent a combined ~20.000 year precession and 41.000 year obliquity forced
cyclicity. The entire core interval will, if compaction is excluded, represent a time span of
610,000 years.
4.1.3 ICHNOLOGY
The thoroughly bioturbated nature of the studied section displays little variation in the trace
fossil assemblage. The lack of primary sedimentary structures and the high level of
bioturbation shows that biogenic reworking exceeded the sedimentation rate (Lauridsen et
al., 2011). The presence of Chondrites, Planolites and Taenidium, Zoophycos and
Thalassinoides in the section indicates a well-oxygenated depositional setting in a shelf-sea
or epeiric sea and are interpreted to represent the Zoophycos ichnofacies (Savrda, 2012;
45
Mac Eachern et al., 2010). Zoophycos ichnofacies predominates in chalks, marly chalks, and
marls in quiet, relatively deep settings below storm-wave base. Lauridsen et al., (2011)
concluded that the visibility increases with higher clay content in respect to trace fossils, and
does not necessarily indicate ecological stress. No Thalassinoides are observed in the two
facies with the highest clay content (“chalky marl” and “marl”). As Thalassinoides are large
shallow-tier structures that normally are the first burrow structures to be excluded as
benthic oxygenation decreases (Savrda, 2012), it is thus possible that the “chalky marl” and
the “marl” facies represent some ecological stress or a slight decrease in the benthic
oxygenation.
4.2 THICKNESS
The Rørdal Member in the Dalbyover-1 core is in this study defined as ten distinctive peaks
of cyclic character in the Natural Gamma radiation wireline log combined with visual
identification of marl-bands in the sedimentological log below the petrophysical wireline log.
The distinctive cyclical peaks of the Natural Gamma ray wireline log terminates at ~314m,
and the first observed marl-band is at 350.65m giving the member a thickness of 36.65m.
There is uncertainty linked to the actual thickness of the Rørdal Member at the location,
both since the borehole does not penetrate deeper than 350.7m and hence there is no
obtained data from below this point, and also since marl layers are observed further up,
although not with the same rhythmicity as observed in the studied section. There is
nonetheless reason to believe that the studied interval comprise all of the Rørdal Member as
the signals of the Natural Gamma radiation wireline log seems to indicate a rather rapid
decrease in the clay content at the lower end of the core, and as abovementioned, a lack of
cyclic signal above the studied section. The Rørdal Member is 29.0m (Stevns-1) and 29.97m
(Stevns-2) on the Ringkøbing-Fyn High and 36.4m in Karlslunde-1 at the southern margin of
the Danish Basin. The reference sections situated at the Ringkøbing-Fyn Hight of the Danish
basin (Fig.1.1), displays ~22% less thickness of the member in correlation with the
Karlslunde-1 and Dalbyover-1 sections in which is situated in the basin. One other possible
explanation for the slight change of thickness could be that winnowing processes
transported the sediments down to the basin from the highs.
46
4.3 GAMMA LOG
Larger positive perturbation of the spectral gamma ray log have mainly two different
contributing element compositions (Fig.3.7), suggesting different compositions of the marl
bed in the studied section. Potassium is an important indicator of the mineralogical
composition, minerals such as illite, muscovite, plagioclase and K-feldspar, but results in a
negative correlation of radioactivity and clay content when the clay fraction is rich in K-poor
smectite, derived from basaltic volcanic material (Fabricius et al., 2003). Thorium is also
associated with clay content, typically displaying 5-30 ppm in pure clay, but it is not proven
that clays are responsible for Th enrichment. The Th content correlates well with high K
peaks. In the upper part of the core-section, U peaks correlates with the Th peaks better.
Uranium is usually related to organic carbon preserved under reducing conditions, with
accessory minerals and colloidal iron-oxide/hydroxide coatings on mineral grains. It is also
found adsorbed onto clay minerals (Fabricius et al., 2003). Because the perturbations of the
total gamma radiation is associated with marl beds (Fig.4.1), it is reasonable to interpret the
origin of radioactive elements to be from clay minerals. Surlyk et al., (2010) suggested a
common source area for the marl beds of the Rørdal quarry, the NGR signals of the Rørdal
Member in Dalbyover-1 however, might suggest two source areas, one of K-rich clay
minerals, and one of K-depleted clay minerals. The first, second, fifth and sixth marl bed
being the K-rich beds. Alternatively, there are two separate mechanisms for the Cyclicity,
one with reduced conditions, and one with input of terrestrial clay.
4.4 X-RAY FLUORESCENSE
The results of the 6m XRF scanned interval are in Fig.3.9 compared with the scanned NGR
mean over 25cm and the insoluble residue in order to test the validity of the assumption of
that Gamma ray peaks are related to higher clay content. The insoluble residue results are
here of little significance due to too low sampling frequency and due to the presence of both
clay and disperced silica in the IR material. Calcium (Ca) is a main component in chalk
(CaCO3) and is thus in this result used as a proxy for the relative content of chalk. Ca displays
elevated signal outside of the two marl layers in the section and decreases closer to the
marl, with the lowest values in these layers. Silica (Si) is used as a proxy for terrigeneous
Phyllosilicate minerals, and displays an inverse curve of that of Ca. Biogenic silica from
47
siliceous sponges is also a potential influential factor of the Si signal, but no flint is observed
in this interval. However, from the IR analysis we know that dispersed silica is a dominant
component of the residue, and therefore the Si signal is not reliable solely as a clay-proxy,
but is here used as a strong clay indicator. Aluminium (Al) shows slight positive excursions in
the marl layers. Chromium (Cr) is an element that is entirely connected with the clay fraction
in chalk (Kunzendorf and Sørensen, 1989). Cr displays along with Fe, Al and Si elevated
signals in the two marl layers in the scanned interval (Fig.3.9), and this strongly suggests that
the marl layers contain terrigeneous clay, and it is likely to be smectite minerals. Smectite
has the potential of isomorphous substitution and these elements are both main
constituents, and substitutes of smectite (Krauskopf and Bird, 1995). Sulphur (S) and
Manganese (Mn) were used as indicators for anaerobic sea bottom condition, and an
expected signal of low Mn should correlate with anaerobic conditions (Yarincik et al., 2000).
This is not observed in this interval. Sulphur correlates with Fe in intervals of observed pyrite
(~328.5m), this is also a depth where Uranium is the major contributor of the total gamma
ray. There is no reason to believe that the sea bottom conditions were anoxic or sulfidic
except from in local areas although these proxies might suggest slightly less oxygenated
conditions when the marl was formed. The Gamma ray signals correlate well with the marl
sections in this interval and it is therefore interpreted that elevated Gamma ray signals in
this interval correlate with higher clay content in the chalk.
4.5 STABLE δ18O AND δ13C ISOTOPES
Carbon isotopes are regarded a strong stratigraphic tool for regional correlation because
they are significantly less sensitive to alteration from diagenesis than Oxygen isotopes and
are not temperature-dependent (Thibault et al., 2012). Since the chalk of the Danish Basin
and thus the studied interval is primarily composed of calcareous nannofossils, the δ13C
values of bulk samples reflect primary sea-surface values. Diagenetic effects of the section
will therefore affect all values in a consistent manner (Thibault et al., 2012). The stable δ13C
isotope curve shows little variation and has no overall trending signal. The values are stable
around 2.26‰, with small perturbations of ~ ± 0.14‰ except from one value of 2.02‰
(Fig.4.11). The δ13C values in the Rørdal Member of Dalbyover-1 are approximately 0.1‰
48
more positive than those recorded in Rørdal quarry and ~0.1‰ more negative than in
Stevns-1 and Karlslunde-1 (Schovsbo et al., 2008).
The δ18O signal of the studied sections averages -1.03‰ and shows larger negative
perturbations of down to -1.48‰ and positive excursions up to -0.34‰. No overall trending
signal is noted. Following the palaeotemperature equation of Anderson and Arthur (1983),
calcite δ18O is controlled both by temperature and by seawater δ18O. Due to the continental
ice-free world of the Cretaceous (Shackleton and Kennett, 1975; Barron, 1983; Jenkyns et al.,
2004; Beltran et al., 2007; Zhou et al., 2008), the δ18O of seawater is assumed to be -1.0‰
The positive perturbations of the δ18O and δ13C signals are closely related to the samples
that have been taken in close proximity to marl-bands, δ18O and δ13C signals tend to
correlate with the scanned Gamma-ray (mean 25) profile (Fig.4.11). Isotope data acquired
from adjacent areas (Stevns-1, Karlslunde-1 and the Rørdal section) display the same overall
pattern as the Dalbyover-1 section (Fig. 3, Schovsbo et al., 2008; Fig.3, Surlyk et al., 2010).
A seawater temperature curve can be calculated using the original version of the
palaeotemperature equation of Anderson and Arthur (1983):
𝑇°𝐶 = 16.0 − 4.14 (𝛿18𝑂𝐶𝐶 − 𝛿18𝑂𝑆𝑊) + 0.13 (𝛿18𝑂𝐶𝐶 − 𝛿18𝑂𝑆𝑊)2
Were δ18OCC is the δ18O value of calcite given against the VPDB standard and δ18OSW is the
estimated value for the Vienna Standard Mean Ocean Water (VSMOW) δ18O value of the
Cretaceous ice-free world and equals -1.0‰.
A shift of 0.1‰ in this equation represents a shift of 0.39 degrees Celsius, the calculated
palaeotemperature curve of the studied interval displays temperatures between 18.02⁰C
and 13.32⁰C, a maximum difference of 4.70 ⁰C (Fig.4.2). Both the range and the perturbation
in palaeotemperature, are within what is observed of the Late Cretaceous in other studies
(Zachos et al., 2001; Jenkyns et al., 2004). Positive perturbations of the δ18O isotope curve
represent periods of cooler climate, but only if these signals are not results of diagenetic
alteration.
49
Figure 4.2: Calculated palaeotemperatures of the Rørdal Member in the Dalbyover-1 core calculated with the equation of Anderson and Arthur (1983), displaying colder climate at levels of positive excursions in the δ18O curve.
A cross-plot of carbon and oxygen isotopes is a commonly used method to test a possible
diagenetic overprint since it will result in a positive correlation between these two ratios
(Mitchell et al., 1997; Thibault et al., 2012). The scatterplot in Fig.4.3 displays a coefficient of
determination (R2) of 0.25 (Fig.4.3). This explains 25% of the vertical scatter of the straight-
line relationship between the δ18O isotope curve and the δ13C values. This indicates that
diagenetic alteration might be present and that the δ18O curve might not exclusively
50
represent a palaeotemperature signal. If diagenesis has affected the δ18O values, and thus
the quantification of palaeotemperatures of the seawater masses, the general trends
observed in the δ18O may still be qualitatively useful (Gómez-Adday et al., 2004).
Figure 4.3: Cross-plot of carbon- and oxygen-isotope relations for bulk samples of the studied interval of the Dalbyover-1 core displaying a coefficient of determination of 0.25.
The studied 9m interval of the Rørdal quarry section was sampled at a high resolution (63
bulk samples) (Surlyk et al., 2010), the samples were also taken in the marl layers of the
member (L. Stemmerik 2015, pers. comm., 2.Jan.). The studied interval of the Dalbyover-1
core is sampled at a lower resolution (every ~1m), and marl layers where systematically
avoided. This is most likely the reason for larger perturbation of the δ18O curve in the Rørdal
quarry sections than is displayed in this study.
51
4.6 POROSITY AND PERMEABILITY
The porosity and the permeability in the Rørdal Member of the Dalbyover-1 core are highly
fluctuating and seem to display an inverse general trend in relation to the insoluble residue
and the Natural gamma radiation curve (mean 25) from the gamma core-scanning (Fig.4.11).
Both permeability and porosity decrease towards the middle of the studied interval before
they increase again at the top. Except from one higher reading of the permeability of 2.26mD
on a porosity of 26.28%, increase in permeability correlates well with increased porosity and
is, although in the lower perimeter, within, what is observed in other Maastrichtian Chalk
sections in the Danish Basin (Fig.4.4).
Figure 4.4: The measured porosities against the measured permeability of the studied section, and other Danish Maastrichtian chalk sections. Permeability increases as porosity values increases except from one distinct higher permeability reading that breaks the overall trend of the studied section. The exponential linear regression displays a coefficient of determination (R2) of 0.65 in the Dalbyover-1 Rørdal Member.
52
Although an expected inverse general trend is observed between porosity and insoluble
residue over depth (Fig.4.11), they do not display any convincing relations when plotted
against each other (Fig.4.5). A decrease in porosity with an increase of insoluble residue is
expected. When plotting the scanned Natural Gamma radiation (NGR) (mean 25) against the
permeability, it seems that the highest NGR measurements correspond to levels of low
permeability (Fig. 4.6), but samples of lower NGR display a larger variety of permeability
results, this relation depends on a match between core depth of the sample and the depth
of the NGR log. As mentioned in section 2.0.5, marl layers were avoided during sampling and
samples were taken in a low resolution (every ~2m) during plugging. These two factors are
likely to be the main contribution for the missing trend.
Figure 4.5: insoluble residue and porosity of the studied section plotted against each other.
53
Figure 4.6: Permeability measurements against the scanned (mean 25) Natural Gamma radiation
.
4.6.1 Burial anomaly and porosity
The studied section is a section of higher clay content predominantly as marl layers and
argillaceous chalk than what is found above. The difference between the lower porosity in
the studied section and the more porous Rørdal Member of the Stevns-1 core is likely to be a
difference in the burial depth, the dissimilarity to the section overlying the studied interval is
believed to be both by burial depth and by the high content of clay minerals. As burial leads
to mechanical and subsequently to chemical compaction, clay minerals promote chemical
compaction (Fabricius, 2007; Anderskouv and Surlyk, 2012). Clay seems to have a larger
negative effect on the permeability than on the porosity, most likely because the chemical
compaction chokes the pore connections. A comparison with the original porosity data of
the Rørdal Member of Stevns-1, and the Rørdal Member of Dalbyover-1(Figs.3.10, 4.7),
reveals that porosity is up to 10% higher in the reference Stevns-1 section (105 – 76 m)
(Surlyk et al., 2013). Nielsen et al. (2011) estimated that the Stevns peninsula has had an
additional overburden of ~ 450-500m based on integrated data from refraction seismic
velocity, porosity, gamma and sonic log. The Dalbyover-1 section is estimated to have been
buried additionally 320m when correcting data from the sonic log and fit it with a velocity-
54
depth curve of Japsen (2000) (Fig.4.8). The Rørdal Member was thus at maximum burial
depth of ~526/576m – 555/605m (450m/500m burial anomaly) in the Stevns-1, and ~634-
671m in Dalbyover-1. The difference in maximum burial is 108m (top) – 116m (deepest),
averaging 112m. When the porosity data of the Rørdal Member in Stevns-1 is shifted 112m
down along the linear trend line of the entire dataset, the porosity values range from 28.30%
- 37.60% averaging 33.94%, these values are comparable with the porosity values in the
studied interval, and thus indicates that the estimated palaeo-burial depth is within the
correct magnitude. An important aspect of the palaeo-burial estimates between the two
cores, is that in the estimation of the burial anomaly on the Stevns peninsula, clay content is
accounted for (Nielsen et al., 2011), whilst the velocity-depth curve of Japsen (2000) is based
on an average of the Chalk Group velocities in the Danish Basin without any consideration of
clay content. This is a potential cause of erroneously estimate in the studied section because
high clay content may result in reduced velocities resulting in an underestimation of burial
anomaly and uplift, whilst the presence of moderate clay content may lead to an over-
estimation of uplift (Nielsen et al.,2011). It does however seems that the velocity-depth
curve of Japsen (2000) is a valid burial proxy in this study.
55
Figure 4.7: The porosity curve of the Stevns-1 core. Black points displays the original porosity measurements of the Rørdal Member in the core, and green points displays the same Rørdal Member measurements corrected 112 meters additional burial following the linear trend line (light blue) of the entire dataset assuming a maximum burial of 450m in this area. On the right margin: the respective datasets magnified.
56
Figure 4.8: The Sonic velocity log of Dalbyover-1 fitted to the Chalk Group velocity-depth curve of Japsen (2000). A correction of ~-320m is needed to fit the velocity-depth curve. Figure by Peter Frykman (2014).
Figure 4.9: Porosity data of the lowest 161.90 meters (350.61 – 188.72m) of the Dalbyover-1 core.
57
Figure 4.10: Permeability data of the lowest 161.90 meters (350.61 – 188.72m) of the Dalbyover-1 core. Note the logarithmic scale on the permeability axis.
Comparison with porosity and permeability data from further up of the Dalbyover-1 core
(Figs. 4.9, 4.10) reveals that these data also is significantly lower in the studied interval.
58
Figure 4.11: Facies of the Dalbyover-1 Rørdal Member along with the scanned NGR log, sonic velocity log, porosity, permeability, δ18O, δ13C and insoluble (IR) values over height
59
5
CONCLUSION
Following main conclusions based on the sedimentological, petrophysical and geochemical
results of the studied Dalbyover-1 core section are presented below.
The studied interval is, based on Carbon isotope data, Natural Gamma ray signal,
thickness and its physical sedimentology, recognised as the Maastrichtian Rørdal
Member of the Danish Basin.
The marl cyclicity signal is complicated, and probably represent both precession- and
obliquity-forced periodicity within the Milankovitch frequency band.
Spectral gamma ray results suggests that the origin of the marl bed materials are
either from two separate sources, or a result of two mechanisms, one being
terrestrial input, and the other being reduced oxic bottom conditions, or a
combination of these.
Results of observed ichnology in combination with XRF data and the spectral gamma
ray log suggests that chalky marl and marl facies might represent some ecological
stress such as a slight benthic oxygen depletion.
The Rørdal Member of Dalbyover-1 has experienced a maximum palaeo burial depth
of ~634-671m, and hence has a burial anomaly of about 320m.
Difference in porosity values between the studied interval and the reference interval
of Stevns-1 is more a result of different burial depth than clay chemistry.
60
6
FURTHER INVESTIGATIONS
Along with interesting results of the studied Dalbyover-1 core interval, some interesting
suggestions for further work has been raised.
6.0.1 Sampling frequency and selection
The studied core section is an interval of rapid changes in sedimentology with depth. Plug
samples every ~2m is not sufficient when the aim is to investigate these changes. A higher
sampling frequency and samples within the marl beds is considered to be beneficial for
these purposes.
6.0.2 Macrofossil investigation
A detailed investigation of the macrofossils of the Dalbyover-1 Rørdal Member can
supplement the depositional and palaeoecological setting, and result in a more accurate age
determination.
6.0.3 XRF core-scanning
The XRF core scanner is a useful tool in order to evaluate the geochemistry and its changes
of the scanned interval. Scanning longer sections, improve the software coding and test
more elements is likely to result in better understanding of the chemical processes and
signals.
6.0.4 SEM analysis
To obtain a more direct knowledge of the affects the clay content has on the chalk, and the
degree of cementation that alters porosity, permeability and geochemistry, SEM-analysis is
desirable.
61
BIBLIOGRAPHY
Anderskouv, K., Damholt, T., Surlyk, F., 2007. Late Maastrichtian chalk mounds, Stevns Klint,
Denmark e combined physical and biogenic structures. Sedimentary Geology 200, 57-72.
Anderskouv, K., Surlyk, F., 2011. Upper Cretaceous chalk facies and depositional history
recorded in the Mona-1 core, Mona Ridge, Danish North Sea. Geological Survey of
Denmark and Greenland Bulletin 25, 1-60.
Anderskouv, K., Surlyk, F., 2012. The influence of depositional processes on the porosity of
chalk. Journal of the Geological Society, London 169, 311-325.
http://dx.doi.org/10.1144/0016-76492011-079.
Anderson, T.F., Arthur, M.A., 1983. Stable isotopes of oxygen and carbon and their
application to sedimentologic and environmental problems. In: Arthur, M.A., Anderson,
T.F., Kaplan, I.R., Veizer, J., Land, L.S. (Eds.), Stable Isotopes in Sedimentary Geology. Soc.
Econ. Paleontol. Mineral. Short Course 10, Chap. 1.
BARRON E.J. (1983).- A warm equable Cretaceous: the nature of the problem.- Earth-Science
Reviews, Amsterdam, vol. 19, p. 305-338.
BELTRAN C., RAFÉLIS M. de, RENARD M., MOULLADE M. & TRONCHETTI G. (2007).-
Environmental changes during marl limestone formation: evidence from the Gargasian
(Middle Aptian) of La Marcouline Quarry (Cassis, SE France).- Carnets de Géologie /
Notebooks on Geology, Brest, Article 2007/01 (CG2007_A01)
62
Beltran, C., de Rafélis, M., Moullade, M., Tronchetti, G., 2007. Environmental changes during
marl-limestone formation: evidence from the Gargasian (Middle Aptian) of La Marcouline
Quarry (Cassis, SE France).
Bromley Richard G. Trace Fossils; Biology, Taphonomy and Apllications, Second Edition,
Chapman & Hall, 1996.
Bromley, R. G., Ekdale, A. A. & Richter, B., 1984. Chondrites: a trace fossil indicator of anoxia
in sediments. Science, 224(4651), 872-874.
Bromley, R. G., Ekdale, A. A. & Richter, B., 1999. New Taenidium (trace fossil) in the Upper
Cretaceous chalk of northwestern Europe. Bulletin of the Geological Society of Denmark,
46, 47–51.
DeMaster, D.J., 2004. The diagenesis of biogenic silica: chemical transformations occurring in
the water column, seabed, and crust, in Holland, H.D., and Turekian,
Dunham, R.J., 1962. Classification of carbonate rocks according to their depositional texture.
In: Ham, W.E. (Ed.), Classification of Carbonate Rocks. American Association of Petroleum
Geologists Memoir, vol. 1, pp. 108–121.
Ekdale, A. A.,Bromley, R.G., 1984. Comparative Ichnology of Shelf-Sea and Deep-Sea Chalk
Journal of Paleontology, 58, 322-332.
63
Esmerode, E.V., Lykke-Andersen, H., Surlyk, F., 2007. Ridge and valley systems in the Upper
Cretaceous chalk of the Danish Basin: contourites in an epeiric sea. In: Viana, A.R.,
Rebesco, M. (Eds.), Economic and Palaeoceanographic Significance of Contourite
deposits, Geological Society, London, Special Publications, 276, pp. 265-282.
Fabricius, I. L., 2003. How burial diagenesis of chalk sediments controls sonic velocity and
porosity. AAPG Bulletin, 87, 1755-1778.
Fabricius, I. L., Fazladic, L. D., Steinholm, A., Korsbech, U., 2003. The use of spectral natural
gamma-ray analysis in reservoir evaluation of siliciclastic sediments: a case study from the
Middle Jurassic of the Harald Field, Danish Central Graben. Geological Survey of Denmark
Bulletin, 1, 349-366.
Fabricius, I.L., 2007. Chalk: composition, diagenesis and physical properties. Bulletin of the
Geological Society of Denmark, 55, 97-128.
Frykman, P., Andersen, G., 1999. Characterisation and multistep upscaling of fractured chalk
reservoirs. In: JCR Phase V, Project No. 3, 6 pp.
Goméz-Alday, J. J., López, G., Elorza, J., 2004. Evidence of climatic cooling at the Early/Late
Maastrichtian boundary from inoceramid distribution and isotopes: Sopelana sections,
Basque County, Spain. Cretaceous Research, 25, 649-668.
Hancock, J., 1976. Petrology of the Chalk. Procedings of the Geologist Association 86, 499-
535.
Heinberg, C., 2000. Livet I Kridthavet. Varv, 4, 16-20.
64
Japsen, P., 2000b. Investigation of multi-phase erosion using reconstructed shale trends
based on sonic data. Sole Pit axis, North Sea. Global and Planetary Change 24, 189–210.
Jenkyns, C. J., Forster, A., Schouten, S., Sinninghe Damsté, J. S., 2004. High temperatures in
the Late Cretaceous Arctic Ocean. Nature, 432, 888-892.
K.K., eds., Treatise on Geochemistry, 87–98.
Kraunskopf, K. B., Bird, D. K., 2003. Introduction to Geochemistry. Third Edition, New York,
McGraw-Hill, Inc., 647pp.
Kunzendorf, H., Sørensen, P., 1989. Geochemical Criteria for Reservoir Quality Variations in
Chalk from The North Sea. Risø National Laboratory, 3-99.
Lauridsen, B.W., Surlyk, F., 2008. Benthic faunal response to late Maastrichtian chalk–marl
cyclicity at Rørdal, Denmark. Palaeogeography, Palaeoclimatology, Palaeoecology, 269,
38–53.
Lauridsen, B.W., Surlyk, F., Bromley, R.G., 2011. Trace fossils of a cyclic chalk-marl
succession; the upper Maastrichtian Rørdal Member, Denmark. Cretaceous Research, 32,
194-202.
Locklair, R. E. & Savrda, C. E. 1998. Ichnology of rhythmically bedded Demopolis Chalk
(Upper Cretaceous, Alabama): implications for paleoenvironment, depositional cycle
origins, and tracemaker behavior. Palaios 13, 423–438.
Lykke-Andersen, H., Surlyk, F., 2004. The Cretaceous_Palaeogene boundary at
Maastrichtian chalk at Stevns Klint, Denmark. the Geological Society, London 161, 343-352.
65
MacEachern, Pemberton, Gingras, Bram, 2010: Ichnology and Facies Models. In: James, N. P.
& Dalrymple, R. W. (eds): Facies Models 4. Geological Association of Canada: GEOtext 6,
201-232.
Madsen, H.B., Stemmerik, L., 2010. Diagenesis of flint and porcellanite in the Maastrichtian
Chalk at Stevns Klint, Denmark. Journal of Sedimentary Research80, 578-588.
Mitchell, S. F., Ball, J. D., Crowley, S. F., Marshall, J. D., Paul, C. R. C., Veltkamp, C. J., Samir,
Ashraf. Isotope data from Cretaceous chalks and foraminifera: Environmental or
diagenetic signals?. Geology, 25, 691-694.
Nielsen, L., Boldreel, L.O., Hansen, T.M., Lykke-Andersen, H., Stemmerik, L., Surlyk, F., Thybo,
H., 2011. Integrated seismic analysis of the Chalk Group in eastern Denmark e
implications for estimates of post-depositional uplift in southwest Scandinavia.
Tectonophysics 511, 14-26.
Olsen, D., 2012. Introduction to GEUS Core Gamma Scanner, 1-11.
Pedersen, G. K., Surlyk, F., 1983. The Fur Formation, a late Paleocene ash-bearing diatomite
from northern Denmark. Bulletin of the Geological Society of Denmark, 32, 43-65.
Pemberton, S. G., MacEachern, J. A., Gingras, M. K., Bann, K. L., 2009. Trace fossil atlas; the
recognition of common trace fossils in cores. 300.
Pickerill, R., K., Brenchley, P., J., 1991. Benthic macrofossils as paleoenvironmental indicators
in marine siliciclastic facies. Geoscience Canada, 18, 19- 138.
Rider M., Kennedy, M., 2011. The Geological Interpretation of Well Logs, Third edition.
Glasgow, Rider-French, 432 pp.
66
Savrda, C. E., 2012. Chalk and Related Deep-Marine Carbonates. Developments in
Sedimentology, 64, 777-806.
Schovsbo, N.H., Rasmussen, S.L., Sheldon, E., Stemmerik, L., 2008. Correlation of carbon
isotope events in the Danish Upper Cretaceous chalk. Geological Survey of Denmark and
Greenland Bulletin 15, 13-16.
Schulz, H. D., Zabel, M., 2006. Marine Geochemistry. Second Edition, New York, Springer,
574 pp.
Shackleton, N.J., Kennett, J.P., 1975. Paleotemperature history of he Cenozoic and the
initiation of Antarctic glaciation: oxygen and carbon isotope analyses in DSDP Sites 277,
279, and 281. In: Kennett, J.P. et al. _Eds.., Init. Rpts. DSDP 29, U.S. Govt. Printing Office,
Washington, DC, 743–755.
Spötl, C., Vennemann, T. W., 2003. Continous-flow isotope ratio mass spectrometric analysis
of carbonate minerals. Rapid Communications in Mass Spectrometry, 17, 1004-1006.
Stevns Klint, Denmark: Inversion tectonics or sea-floor topography? Journal of
Stratigraphy and Geological Correlation,21, 280–290.
Surlyk, F., Lykke-Andersen, H., 2007. Contourite drifts, moats and channels in the Upper
Cretaceous chalk of the Danish Basin. Sedimentology 54, 405-422.
Surlyk, F., Rasmussen, S. L., Boussaha, M., Schiøler, P., Schovsbo, N. H., Sheldon, E.,
Stemmerik, L., Thibault, Nicolas., 2013. Upper Campanian-Maastrichtion holostratigraphy
of the eastern Danish Basin. Cretaceous Research, 46, 232-256.
67
Surlyk, F., Stemmerik, L., Ahlborn, M., Harlou, R., Lauridsen, B.W., Rasmussen, S.L., Schovsbo,
N., Sheldon, E., Thibault, N., 2010. The cyclic Rørdal Member - a new lithostratigraphic
unit of chronostratigraphic and palaeoclimatic importance in the upper Maastrichtian of
Denmark. Bulletin of the Geological Society of Denmark 58, 89-98.
Thibault, N., Harlou, R., Schovsbo, N., Schiøler, P., Minoletti, F., Galbrun, B., Lauridsen, B.W.,
Sheldon, E., Stemmerik, L., Surlyk, F., 2012. Upper Campanian Maastrichtian nannofossil
biostratigraphy and high-resolution carbon-isotope stratigraphy of the Danish Basin:
towards a standard d13C curve for the Boreal Realm. Cretaceous Research 33, 72-90.
Thibault, N., Schovsbo, N., Harlou, R., Stemmerik, L., Surlyk, F., 2011. An age-calibrated
record of upper Campanian-Maastrichtian climate change in the Boreal Realm. In:
Abstract, 2011 Fall Meeting, AGU, San Fransisco, Calif., 5-9 Dec.
Tucker, M.E. and Wright, V.P. (eds) ,1990. Carbonate Sedimentology. Blackwell, Oxford, 482
pp.
Wennberg, O. P., Casini, G., Jahanpanah, A., Lapponi, F., Ineson, J., Wall, B. G., Gillespie, P.,
2013. Deformationbands in chalk, examples from the Shetland Group of the oseberg field,
North Sea, Norway. Journal of Structural Geology, 56, 103-117.
Wignall, P. B., Newton, R., Brookfield, M. E., 2005. Pyrite framboid evidence for oxygen-poor
deposition during the Permian-Triassic crisis in Kashmir. Palaeogeography,
Palaeoclimatology, Palaeoecology, 216, 183-188.
Yanin B. T., Baraboshkin, E. Yu., 2013. Thalassinoides Burrows (Decapoda Dwelling
Structures). Lower Cretaceous Sections of Southwestern and Central Crimea, Stratigraphy
and Geological Correlation, 3, 280-290.
68
Yarincik, K.M., Murray, R.W., Lyons, T.W., Peterson, L.C. and Haug, G.H. (2000). Oxygenation
history of bottom waters in the Cariaco Basin, Venezuela, over the past 578,000
years: Results from redox-sensitive metals (Mo, V, Mn, and Fe). Paleoceanography 15:
doi: 10.1029/1999PA000401. issn: 0883-8305.
Yarincik, K.M., Murray, R.W., Peterson, L.C., 2000. Climatically sensitive eolian and
hemipelagic deposition in the Cariaco Basin, Venezuela, over the past 578,000 years:
results from Al/Ti and K/ Al. Paleoceanography 15, 210–228.
Zachos, J., Pagani, M., Sloan, L., Thomas, E., Billups, K., 2001. Trends, Rythms, and
Abberations in Global Climate 65 Ma to Present. Science, 292, 686-693.
Zhou, J., C. J. Poulsen, D. Pollard, and T. S. White (2008), Simulation of modern and middle
Cretaceous marine d18O with an ocean-atmosphere general circulation model,
Paleoceanography, 23, PA3223, doi:10.1029/2008PA001596
69
7
APPENDICES
Appendix 1
Box photos of the studied interval, photos aretaken in GEUS photo laboratory. Photos has
been edited in Adobe Lightroom in order to enhance contrast.
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Appendix 2
The sedimentary log and legend created in Adobe Illustrator.
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Appendix 3
The core report (in Danish) and the results of the Natural gamma ray wireline log executed in
December 2013 Wireline log displays the entire Dalbyover-1 core interval.
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