microfacies analysis and sequence stratigraphy of eocene
TRANSCRIPT
MINISTRY OF HIGHER EDUCATION
AND SCIENTIFIC RESEARCH
UNIVERSITY OF BAGHDAD
COLLEGE OF SCIENCE
MICROFACIES ANALYSIS AND
SEQUENCE STRATIGRAPHY OF
EOCENE -MIOCENE SUCCESSTION AT
KARBALA – NAJAF – SAMAWA AREA
SOUTH WEST IRAQ
A THESIS SUBMITTED TO THE COLLEGE OF SCIENCE
UNIVERSITY OF BAGHDAD IN PARTIAL FULFILLMENT
OF THE REQUIREMENT FOR THE DEGREE OF
MASTER OF SCIENCE IN GEOLOGY
BY
DHIYA KHURBAT SHATHER B.Sc. IN GEOLOGY (1994)
SUPERVISED BY
Asst. Prof. LAMEES SADIQ HASSOUN
2011
1
The Supervisor Certification
I certify that this thesis (Microfacies Analysis and Sequence Stratigraphy of
Eocene –Miocene succession at Karbala-Najaf-Samawa area south west
Iraq),was prepared under my supervision at the Department of Geology, College
of Science , University of Baghdad, in partial fulfillment of the requirements for
the Degree of Master of Science in Geology (Stratigraphy and Paleontology).
Signature:
Name: Lamees Sadiq Taha
Scientific Degree: Assistant Professor
Address: Department of Geology
College of Science University of Baghdad
Date: / /2011
Recommendation of the Head of Committee of Postgraduate Studies in the
Department of Geology
In view of the available recommendations I forward this thesis for debate by the
examining committee.
Signature:
Name: Dr. Ahmad Shehab Al - Banna
Title: Professor
Address: University of Baghdad (Head of the Department of Geology)
Date: / /2011
2
Committee Certification
We certify that we have read this thesis entitled (Microfacies Analysis
and Sequence Stratigraphy of Eocene –Miocene succession at Karbala-Najaf-
Samawa area south west Iraq), and as the examination committee examined the
student in its content and in our opinion it is adequate for award of the degree of
Master Geology Master of Science in Geology (Stratigraphy and Paleontology).
Chief Signature:
Name: Saad S. Al- Sheikhly
Title: Professor
Address: Department of Geology
College of Science University of Baghdad
Date: / 11 / 2011
Member
Member Signature: Signature:
Name: Rafah Tariq Ismail Name: Saad S. Al- Jumaily
Title: Assistant Professor Title: Assistant Professor
Address: Department of Geology Address: Department of
Geology College
College of Science University of Baghdad of Science University of Baghdad
Date: / 11 / 2011 Date: / 11 / 2011
Approved by the Deanery of the College of Science.
Signature:
Name:
Title:
Address:
Date:
3
بسم الله الرحمن الرحيم
ق ل سيروا في الأرض ف انظروا
عى ثم الله ينشى النشأة الآخرة أن الله قكيف بدأ الخل كل شيء قدير
دق الله اللظيم
/20)سورة اللنكبوت(
4
Acknowledgements
I am gratefully indebted to my supervisor Asst. Prof Lamees
Sadiq Hassoun for her supervision , guidance , help and reading
the manuscript.
Thanks are also due to the Department of Geology , College of
Science , Baghdad University for providing the opportunity and
facilities for the present study.
Im greatly indebted to the State Company of Geological Survey
and Mining for offering me the opportunity to study for the master
level with special thanks to the D.G.Dr.Khaldoun S. Al-Bassam .
I extend my sincere thanks and appreciation to Prof . Dr.Ali ,
D.Gayara
I also owe many thanks to Dr.Buthaina Salman (senior chief
geologist) for her help in this thesis , Mr.Dhiya Aldeen Kadhim ,Mr.
Mohamed Karim and Mr. Ahmed khalil for their help during The
field work.
Thanks and appreciation to all my family who expressed
supports , love and care .
DHIYA
5
ABSTRACT
The Eocene – Miocene succession in the southwest desert of Iraq revealed the
presence of the Dammam , Euphrates and Nfayil Formations . Two hundred and
thirty nine of thin sections from three boreholes and two outcrops have undergone
detailed petrographic identification and used to build both stratigraphic and
diagenetic models .
Microfacies characteristics of the whole successions showed the presence of
skeletal and non-skeletal grains within the Nfayil and Euphrates Formations.
Only skeletal grains are observed in the Dammam formation .
Details gained from textural and faunal properties helped in the designation of
microfacies zones leading to environmental subdivisions for a suggested ramp .For
the Nfayil formation : peritidal , shoal , restricted , and deep marine environments .
For the Euphrates formation : restricted , shoal , open marine , and deep marine
environments .For the Dammam formation : peritidal , restricted , shoal , and open
marine environments.
Generally the diagenetic model of the three sections showed two dolomitization
episodes . The first dolomitized the lower part of the Dammam Formation , by a
subtidal model , considering the crystal sizes and the maintenance of the original
textures of deposition . The top of the Dammam Formation probably persisted
longer in the mixing zone due to high stand conditions at the end of the Eocene
until the second episode of dolomitization . For the Euphrates and Nfayil
Formations . The absence of dolomite is due to the fast rising sea – level after the
Oligocene break ( above basal conglomerate) . Silicification sometimes
accompanied the dolomitization .
Neomorphism in addition to different types of cement , in the Dammam
Formation occurred at Karbala and Samawa sections , suggesting an active
freshwater zone of diagenesis due to the rising sea level . For the Euphrates and
Nfayil Formations , neomorphism and cement occurred too.
Dedolomitization may be due to the presence of many aquifers known in the
Dammam Formation at Najaf and Samawa sections.
6
Five 3rd
order cycles were designed for the Dammam succession at Samawa
section, minor fluctuations during the four cycle divided it into two 4th order ones .
At Najaf section another cycle was recognized . At Karbala section , the first two
cycles may not be encountered . Cycles represented episodes of sea-level rises(
represented by shallow open marine and deep marine facies) followed still stand
represented by shoal facies .
An (SB1) boundary occurs between the Euphrates Formation and the Dammam
Formation . It is a basal conglomerate , with different thicknesses : 0.8 meter at
Karbala section , 4.0 meter at Najaf and Samawa sections.
During sea-level rise after the Oligocene , three 3rd
order cycles were designed
for the three sections .These cycle are different in their symmetry , thickness and
stacking pattern from one section to the other . This may be attributed to local
changes in tectonic subsidence which have affected the velocity of relative sea-
level rise .
In the current study the Miogypsina sp.(index fossil of the Euphrates Formation)
is found above the olive green marl unite of the lower part of the Nfayil Formation.
7
1.1 preface ………………………………………………………………………. …. 1
1.2 Location of study area ……………………………………………………….1
1.3 Aim of the study ………………………………………………………............1
1.4 Methodology …………………………………………………………..………4
1.4.1 Field work ……………………………………………….…..……….4
1.4.1.1. Samawa composite section …………………….....…..4
1.4.1.2 Najaf composite section ……………………………..…..…..……4
1.4.1.3 Karbala borehole section ……………………………………….……..5
1.4.2 Workshop ……………………………………. …………….……..…….5
1.4.2.1 Thin section preparing …………………………….………….…….5
1.4.2.2 Staining……………………………………………………….…..……..5
1.5 Previous study …………………………………………………….……..……….5
1.5.1 Nfayil Formation ………………………………………….………....5
1.5.2 Euphrates Formation ………………………………………..……….. .7
1.5.3 Dammam Formation …………………………………………..………..8
1.6 Geological setting ………………………………………………………….…..……13
Chapter One : INTRODUCTION
Contents
8
2.1 Petrography………………………………………………………………………………..14
2.1.1 preface…………………………………………………………………………………14
2.1.2 Nfayil Formation………………………………………………………………..14
2.1.2.1 Skeletal grains …………………………………………………….15
2.1.2.2 Non- Skeletal grains …………………….………………………………...16
2.1.3 Euphrates Formation ………………………………………………….……….17
2.1.3.1 Skeletal grains……………………………………………………………. 18
2.1.3.2 Non-skeletal grains ………………………………………………..……..19
2.1.4 Dammam Formation ……………………………………………………………19
2.1.4.1 Skeletal grains ……………………………………………………………..20
2.2 Diagenetic Processess ………………………………………………………………….27
2.2.1 Cementation ……………………………………………………………………….27
2.2. 1.1 Syntaxial rim overgrowth ………………………………………..…..……28
2.2.1.2 Geopetal cement ………………………………………….……..…………..28
2.2.1.3 Intraparticle cement ……………………………………..…….…………28
2.2.1.4 Interparticle cement ……………………………………..………………29
2.2.2 Silicification ……………………………………………………………………….29
2.2.3 Dolomitization ……………………………………………………………………30
2.2.4 Dedolomitization …………………………………………………………….31
Chapter Two : PETROGRAPHY AND DIAGENESIS
9
2.2.5 Neomorphism …………………………………………………………..……..32
2.2.6 Dissolution…………………………………………………………………..……32
2.2.6.1 Intraparticle porosity …………………………………………..……….33
2.2.6.2 Moldic porosity ………………………………………………….………33
2.2.6.3 Vugy porosity …………………………………………………….………34
2.2.6.4 Channel porosity …………………………………………………….……34
3.1 Preface ……………………………………………………………………………….43
3.2 Nfayil Formation ……………………………………………………………………..43
3.2.1 Peritidal Environment ……………………………………………..……43
3.2.2 Shoal Environment ………………………………………………………44
3.2.3 Restricted Environment …………………………………………...……45
4.2.4 Deep Environment ……………………………………………….…..…..45
3.3 Euphrates Formation ………………………………………………………...…...46
3.3.1 Restricted Environment ……………………………………….……….46
3.3.2 Shoal Environment ……………………………………………….…….46
3.3.3 Open marine Environment ……………………………………….….……46
3.3.4 Deep Environment ………………………………………………..…….47
3.4 Dammam Formation ……………………………………………………….….…….48
3.4.1 Shoal Environment ……………………………………………….…..…..48
3.4.2 Restricted Environment ……………………………………….……..…..49
3.4.3 Open marine Environment …………………………………………………49
Chapter Three : MICROFACIES AND ENVIRONMENTS
10
3.4.4 Peritidal Environment ………………………………………..…….………50
4.1 Contacts…………………………………………………………………….…….56
4.1.1 Lower contact of the Dammam Formation ………………………….…….56
4.1.2 Lower contact of the Euphrates Formation……………..…………….……56
4.1.3 Nfayil Formation contacts ………………..……………………………….…56
4..1.3.1 Lower contact of the Nfayil Formation……………...…… ….….56
4.1.3.2 Upper contact of the Nfayil Formation ……………...……….57
4.2 Sequence Stratigraphy ……………………………………………………………..58
4.2.1 preface ………………………………………………………………………58
4.2.2 Concept and Definition………………………………………………………..58 4.2.2.1 Parasequence ……………………………………………………….……59
4.2.2.2 Key Surfaces ……………………………………………………..……60
4.2.2.2.A Sequence Boundaries ………………………………….……60
4.2.2.2.B Transgressive Surface (TS) …………………………………61
4.2.2.2.C Marine flooding surface……………………………………..61
4.2.2.2.D Maximum Flooding Surface (MFS)………………………....61
4.2.3 Sequence Development ………………………………………………….……62
4.2.3.1 Dammam Cycles ………………………………………………..………62
4.2.3.2 Euphrates-Nfayil cycles…………………..………………………….………63
Chapter Four: Sequence Stratigraphy
11
4.2.4 Basin development in the Miocene …………………….………………..…..64
4.3 Diagenetic Model ………..…………………….…………………………….…66
Summary and Conclusions ………………………………………………………………..69
References …………………………………………………………………………………73
1.1 Location map of the study area …………………………………………………….…3
1.2 Stratigraphic correlation Eocene Formations …………………………………………11
1.3 Stratigraphic correlation Miocene Formations………………………………………12
2.1 Legend for figures 2.2 , 2.3 and 2.4 …………………………………………………...38
2.2 Distribution of Microfacies, Environments, Diagenetic processes and Sequence
stratigraphic subdivisions at Karbala section ………………………………………39
2.3 Distribution of Microfacies, Environments, Diagenetic processes and Sequence
stratigraphic subdivisions at Najaf section……………………………………...……40
2.4 Distribution of Microfacies, Environments, Diagenetic processes and Sequence
stratigraphic subdivisions at Samawa section……………………………………..…41
2.5 Chert layer and Alveolina sp. in the field………………………………………….…42
4.1 Sequence Stratigraphic subdivision of the Eocene –Miocene succession……. ……65
4.2 Diagenetic Model of Eocene –Miocene succession at Karbala-Najaf –Samawa sections..69
Chapter Five: SUMMARY AND CONCLUSIONS
Figures
12
1.1 Geographic coordinates thickness and total samples of the selected sections
at the study area ……………………………………………………………………..…..2
Plate (1) Non-Skeletal grains……………………………………………………………22
Plate (2) Non –Skeletal grains…………………………………………………………..23
Plate (3) Skeletal grains……………………………………………………………………24
Plate (4) Skeletal grains…………………………………………………………………25
Plate (5) Skeletal grains………………………………………………………………..…..26
Plate (6) Diagenetic processess………………………………………………………....35
Plate (7) Diagenetic processess…………………………………………………………36
Plate (8) Diagenetic processes ………………………………………………….....37
Plate (9) Nfayil microfacies ………………………………………………………...51
Plate (10) Nfayil and Euphrates microfacies ……………………………………...52
Plate (11) Euphrates microfacies…………………………………………………….53
Plate (12) Dammam microfacies……………………………………………………....54
Plate (13) Dammam microfacies………………………………………………….55
Table
Plates
Chapter Two
Chapter Three
13
CHAPTER ONE
INTRODUCTION
14
CHAPTER ONE INTRODUCTION
1.1 Preface:
The Eocene-Miocene succession in Karbala- Najaf- Samawa area south west
Iraq is represented by Dammam, Euphrates, and Nfayil Formations. Some of these
are regarded as a source of limestone for cement factory, such as Euphrates
Formation, and a good water aquifer such as the Dammam Formation .
1.2. Location of study area
The study area is located within the Karbala , Najaf and Samawa Governorates
in South west Iraq ( Table 1.1 , Fig.1.1)
1.3. Aim of the study:
The aim of the study is to investigate the Eocene-Miocene succession in
Karbala-Najaf-Samawa area from the following aspects:
1- Detailed microfacies analysis and depositional environment interpretation aimed
to better understanding of the formations.
2-Fossil identification to assist age determination and environment
characterization.
3- Designing depositional and diagenetic models .
4- Sequence stratigraphic interpretation and basin analysis.
15
Table (1.1) Geographic coordinates , thicknesses and total samples of selected
Karbala –Najaf-Samawa at the study area
Section Name
Geographic Coordinate
Total Samples
Latitude Longitude Thickness
Karbala borehole
Section
32° 34′ 05″
43° 29′ 21″
Nafyil Fn. 26.5m 11
75 Euphrates Fn. 22.4m 17
Dammam Fn. 51.5m 47
Najaf composite
Section
31° 27′ 26″
44° 28′ 48″
Nafyil Fn. 15.0m 11
87
Euphrates Fn. 7.5m 5
Dammam Fn. 97.5m 70
Rus Fn. 4.0 1
Samawa
composite Section
31° 14′ 53″
45° 04′ 52″
Nafyil Fn. 10.5 6
77 Euphrates Fn. 7.0m 3
Dammam Fn. 115.5m 67
Rus Fn. 3.5m 1
16
17
1.4. Methodology and Study Area:
This study deals with three formations. Detailed description and sample
collection was carried on every noticeable change for the three studied formations ,
Dammam, Euphrates and Nfayil.
To achieve the goals of this study, two stages of work were performed. They
are :
1.4.1. Field work:
The field work included sampling of two composite sections (Najaf section
and Samawa section) , the third is Karbala borehole section (Fig 1.1).Selection of
samples from these sections was based on facies change , colour change ,hardness
of the beds and difference in other factors.
The studied composite sections and borehole sections were as follows
1.4.1.1. Samawa composite section
Samawa section is a composite section showing borehole (Euphrates and
Dammam Formations) located at (31° 14’ 53˝N) (45° 04’ 52˝ E) and an outcrop
showing Nfayil and Euphrates Formations . Total thickness is 137.0 meters .
Samples were selected from this composite section mostly of limestone ,marl
beds, in addition to some gypsum beds. Six samples are taken from the Nfayil
Formation, three samples from the Euphrates Formation, sixty seven samples from
the Dammam Formation and one sample from the Rus Formation .( Table 1-1).
1.4.1.2. Najaf composite section
Najaf section is a composite section showing borehole (Euphrates and Dammam
Formations) located at (31° 27’ 26˝ N) , (44° 28’ 48˝ E) and an outcrop
showing Nfayil and Euphrates Formations. Total thickness is 124.0 meters.
Samples selected from this composite section were mostly of limestone and marl
beds, in addition to samples from Rus Formation. Eleven samples are taken from
18
the Nfayil Formation, five samples from the Euphrates Formation , seventy
samples from the Dammam Formation and one sample from the Rus Formation.
1.4.1.3. Karbala borehole section
Karbala borehole section is located (32° 34’ 05˝ N) , (43° 29’ 21˝ E) . Its
elevation is 56.5 meters with a total thickness of 100 meter.
Samples selected from borehole were mostly of limestone , clastic rocks and
marl beds. Eleven samples were taken from the Nfayil Formation , seventeen
samples from the Euphrates Formation, forty seven samples from the Dammam
Formation .
1.4.2. Workshop
The workshop included two stages .These are :
1.4.2.1 Thin section preparation
Two hundred and thirty nine thin sections were prepared at the state company
of Geological Survey and Mining . The thin sections were done for the Samawa
composite section and Najaf composite section. While the Karbala borehole thin
sections were previously prepared .
1.4.2.2 Staining
Distinction between calcite and dolomite minerals required staining process to
239 thin sections , for clear identification of diagenetic features specially
dedolomitization . The staining effects calcite (red colour) and dose not effect
dolomite.
1-5 Previous study
1-5-1 Nfayil Formation
The Formation type locality lies near the (Qariat Al-Nfayil) (Al-Nfayil village )
which is 23km , west of Haditha town.
This Formation was divided into two members (Sissakian,1999) .
1- The lower member consists of three cycles , each cycle consists of marl and
limestone. The marl is olive green, soft, papery or massive ,concoidally fractured,
19
fractures are filled with secondary gypsum. The thickness of marl beds range from
(0.5- 5.0)m . The limestone is yellowish white to greenish grey, fractured, jointed,
locally undulated and deformed slightly oolitic, partly recrystallized and shelly
,shells are mainly pelecypods, gastropods, and Oysters . Oysters found only in the
second cycle and considered as good markers over the whole exposed area of the
Nfayil Formation.
2- The upper member is exposed in the extreme west part of the exposed area in
Al-Kherish vicinity along the Iraq-Syrian border. It consists of claystone and
limestone. The claystone is reddish ,bedded, and calcareous ,whereas the limestone
is pinkish with quartz grains , bedded and hard.
The top of the upper member is always capped by splintery limestone and very
hard in the type locality and ranges in thickness from (10.0-50.0)m.
The Nfayil Formation is deposited in shallow to very shallow marine
environment with normal to high saline water ,with clear oscillation in the sea
level. The upper part of the upper member may indicate near shore environment
,with some deltaic influences, as indicated by the type of the clastics, fining
upward of the uppermost part of the Nfayil Formation ,(Sissakian,1999).
Other author’s opinion about the Nfayil Formation position are as follows:-
1-Al-Mubarak,(1972) named the sequence (unit c) of the Euphrates Formation in
Al-Qaim vicinity.
2- Al-Jumaily,(1974) named the sequence as (the unit B) of the second Miocene
sedimentary cycle .
3- Tyracek and Youbert ,(1975) adopted the same terminology in Haditha, as that
of Al- Jumaily .
4- Hamza ,( 1975 ) named the sequence as (unit of alternating limestone and green
marl ).
5- Al-Mubark and Amin,(1983) named the sequence as (unit C) of the Euphrates
Formation in west of Najaf and Karbala vicinities.
20
6- Jassim et .al.,(1981) named the sequence with the overlying sediments as
(Kherish Beds) and (Najaf and Habbanya Beds).
7- Mahdi et .al .(1986) named the sequence as (Nfayil unit ) in Haditha .
8- Sissakian and Salih ,(1994) named the upper member as (Nfayil member ) of the
Fatha Formation in Haditha vicinity .
The age of the Nfyail Formation according to the fossil assemblage is Middle
Miocene ,(Sissakian,1999).
The lower contact between the Nfayil Formation and the underlying Euphrates
Formation is conformable .
1.5.2. Euphrates Formation
The original description was given by Boeck (1929). It was later amended by
Bellen in 1957. The Formation 's type locality lies near wadi Fuhaimi Anah trough
on the stable shelf.
The Formation is composed at the type locality , of shelly , chalky , well-
bedded , recrystallized limestone ,(Van Bellen et . al ., in 1959) .
The thickness in the surrounding areas , as well as in the boreholes is usually
many times more , reaching to a maximum of 100.0 meters , with an average
thickness of around ( 60.0-70.0 ) meters , ( Buday,1980).
Ctyrocy and Karim ,(1971) , Al-Greri , (1985) made a very detailed evaluation
of the fauna and determined its age to be lower Miocene and early Middle
Miocene.
The Euphrates Formation was deposited under shallow marine –reef and
lagoonal conditions , with local coral and lithophyllid reef and with intermittently
occurring fore-reef condition , on the one side , and lagoonal condition on other
side , ( Buday,1980) .
21
Al-Mubarak (1971) divided the formation into four units named A ,B ,C and
D, whereas Al-Mehaidi (1975), described this formation from outcrops between
Al-Razaza – Habanyia area and divided the formation into three member :-
A- Basal braccia member consist of fragmented Nummulitic limestone and chert .
B- Om Sufaya chalky limestone .
C- Limestone marl member.
Euphrates Formation overlies various formations all unconformably and with
thick conglomerate , near Anah and Haditha area the formation overlies Upper
Oligocene Anah Formation , in Khan Al-Baghdadi Area it overlies Lower
Oligocene Sheikh Alas Formation. In the southern desert , the Euphrates
Formation overlies various units of Dammam Formation ,(Buday,1980).
Near wadi Hauran , the Euphrates formation overlies Eocene , Oligocene ,
Lower Cretaceous and Jurassic sequence all with basal conglomerate
(Buday,1980).
The formation in Iraq is a facies equivalent to the Ghar ,Serikagni and Dhiban
Formations and has no other age and /or facies equivalents ,(Buday,1980),(Fig 1-
2).
1.5.3 Dammam Formation
The Dammam Formation in its type locality in Saudi Arabia was described by
Bramkamp (1931) in (Van Bellen et a., 1959) as a sequence of partly chalky and
organodetrital or dolomitic limestones , marl and shales , representing the Eocene
with no recorded intra formational break.
A supplementary type section from Zubair 3 oil well was chosen by Owen and
Nasr (1958) in (Van Bellen et al,. 1959) for the same formation represented by “
whitish grey ,porous dolomitized limestone ; limestones are sometimes chalky and
near the base a persistent grey green waxy shale body is encountered” .
Huber and Ramsdon (1945) in Van Bellen et al., (1959) divided the formation
into 10 informal unites for the convenience of field mapping ; their stratigraphical
22
value as such , is limited . However later devision by Ramsdon and Andre in
(1953)Van Bellen et al ., (1959) introduced four unites as combinations of
previous ones these are from top :
1- Tiqiaiyid –Ghanimi – Barbak – Radhuma unit which is mainly characterized by
bryozoans and peneroplid limestones and shoal limestones.
2- Chabd – Shawiya –Huweimi ( a shoal Nummulites units) .
3- Huweimi ( chalk ) ,Shbicha and sharaf units .
4- Wagsa units.
Further work by Al- Hashimi(1972) led to the a assignment of the formation to
whole Eocene (lower Ypresian –Upper Eocene ) and subdivision of the formation
into four faunal benthonic foraminiferal zones and three planktonic zones in the
southern and western desert of Iraq . The same zonation was followed by the
paleontologists of GEOSURV during the evaluation of the Dammam Formation .
These zones from bottom to top are:
1-Nummulites desert - N. frassi zone .
Recorded from Akashat and Ratga sections,Wagsa unit.
2-Nummulites planulates - N. lacsanus zone .
Recorded in Akashat and Ratga section .
3-Nummulites discorpinus - N gizehensis zone .
4-Nummulites baullei – N.icrassatus zones .
Three planktonic zones were recognized from the western desert at these area
only:-
1- Globorotalia lehneri zone equivalent to N.discorbinus .
2-Truncorotaloides rohri zone .
3- Globorotalia cerroazulensis zone
So the Dammam Formation is restricted to Middle –Upper Eocene . The
formation has two close correlatives in Iraq : the Avanah Formation and the Pilaspi
Formation ,the first is almost of the same facies , and includes proved Upper
23
Eocene beds too, the second correlative of the Dammam , is the Pilaspi Formation,
it differs from the Dammam by its facies, however it probably represents the
equivalent of the upper parts of the Dammam Formation only. The lower parts of
the Dammam Formation is contemporaneous with the Gercus Formation ,Buday
(1980). Figure (1.3)
24
Figure (1.2) Stratigraphic correlation Miocene Formations (compiled according
Jassim and Goff , 2006)
25
Figure (1.3) stratigraphic correlation Eocene Formations (compiled according to
Jassim and Goff , 2006 )
26
1.6 Geological Setting
The studied area is located within the Southwest Desert .Tectonically , the
Southern Desert is a part the stable shelf of the Arabian platform , which is
characterized by the presence of block tectonics and the absence of tectonic folds (
Buday and Jassim , 1987 ). It is characterized by flat nature , due to almost
horizontal beds , with regional dip towards east and northeast . The Euphrates
Fault Zone with NW-SE trend is the main outstanding feature along the exterior
(northeastern ) part of the Southern Desert (Al-Amiri ,1979; Al-Ani and Ma'ala
,1983;Al-Hadithi and Al-Mehaidi,1983 ; Al-Mubarak and Amin,1983;Buday and
Jassim,1987) .
Straigraphically , the denudation processes have exposed a sequence of
marine and continental sediments , which range in age from Paleocene to
Pleistocene . The Paleogene rock units are shallow marine sediments ,which cover
most of the Southern Desert .The oldest formation , which is exposed along the
Iraqi- Saudi Arabian border , is Umm Erdhuma Formation .The carbonate facies of
this formation passes laterally to anhydrite facies of the Rus Formation .The
Dammam Formation of carbonate facies overly conformably forenamed two
formations .A gap exists between Eocene and Early Miocene rock units due to
missing of the Oligocene rock units (Al-Hashmi,1972 ;Al-Ani and Ma'ala ,1983 ,
Al-Hadithi and Al-Mehaidi,1983).
The Neogene rock units are expressed by shallow marine and continental
sediments . The former is represented by Euphrates, Ghar and Nfayil formations ,
whereas the Zahra and Dibdibba formations represent the latter.
27
CHAPTER TWO
Petrography and
Diagenesis
28
Petrography and Diagenesis Chapter Two
2.1 Petrography
2.1.1 Preface
The aim of this chapter is to diagnose the petrography characteristic of 239 thin
sections in order to delineate the depositional environment of the Eocene-Miocene
studied sections. Thin sections were classified on the bases of Dunham’s
classifications (1962) .Study reveals that the carbonate grains represented within
the Eocene-Miocene successions are both skeletal and non-skeletal grains. The
main components of the skeletal grains are benthonic foraminifera, Molluscs
(pelecypoda and gastropoda) ,algae,ostrcoda,while non-skeletal grains are
represented by peloids,Ooids , grapstone , and lithoclastes. The Eocene-Miocene
succession is represented in this study by the Nfayil Formation, Euphrates
Formation and Dammam Formation , each will be described separately .
2.1.2 Nfayil formation
Rhythmic cyclicity characterizes the Nfayil Formation in the field . At Karbala ,
two cycles are recorded for the lower Nfayil Formation ,each comprises green marl
and grey fossiliferous limestone . Three cycles were recognized at Najaf outcrop ,
they are from the bottom to the top : The first ( 4.0 meters thick ) consisted of
green marl alternating with thin beds of recrystallized limestone followed by grey
,tough, and fossiliferous limestone. The second (1.5 meters thick ) yellow -green
marl ,fissile , followed by (1.5 meters ) grey oyster bearing limestone , the oyster
bearing bed is a marker to the second cycle of the Nfayil Formation (previous
studies) . The third (3.0 meters) green marl , is followed by grey, tough , well –
bedded , fossiliferous limestone with yellow stains .At Samawa outcrop two cycles
are recognized from the bottom to the top . The first (1.0 meter thick) olive green
marl followed by 0.75 meter pink to creamy , soft limestone with rusty patches
29
,also viens filled with secondary calcite .This is followed by 2.25 meters of
fossiliferous white , steep –forming cliff limestone , thinly bedded at its upper parts
. The second cycle is represented by marl followed by ( 4.0 meters thick ) , light
grey , fossiliferous limestone with secondary calcite filling , followed by 1.0 meter
yellow brown limestone , fossiliferous ,containing calcite viens . Limestone
interbedded with marly limestone is the capping unit of the lower Nfayil
Formation .
2.1.2.1 Skeletal grains
Benthonic foraminifera are found as whole tests in most of the studied thin
sections . Fragmented test are found at depth 10.0 meters at Najaf outcrop and at
depth 21.0 meters at Karbala section .
Benthonic foraminifera within the Nfayil Formation are : miliolid ,Dendiritina
sp. , rotalid , Ammonia beccarii (Plt 3.F) . At Samawa composite section miliolid
was profound from 1.5 – 2.5 meter .
Miogypsina sp.( Middle Oligocene- Early Miocene ) was recorded for the first
time within the lower part of the Nfayil Formation. at Karbala borehole section at
depth 25.0 meters , and at Samawa composite section at 9.0 meters below the top
of the outcrop.
Generally the last appearance of Miogypsina sp. is used to delineate the top of
the Euphrates Formation , but in the current study , the occurrence of Miogypsina
sp. is recorded at the lower part of the Nfayil Formation (Plt.3-C ) exactly above
the green marl unit both at Karbala and Samawa Sections , whereas no occurrence
recorded at Najaf section which may be due to neomorphism of the unit above the
green marl . It is important to denote that the green marl unit forms the contact
between Nfayil and Euphrates formation ( Sissakian,1999).
Molluscs represent the most dominant skeletal component within the Nfayil
Fomation , and found generally as shell fragments which resulted from the effect
of tides or currents activation or high energy environment .This occurs at 4.5-6.5
30
meters from the outcrop at Najaf composite section and at 9.0 meters below the top
of the outcrop at Samawa section .Molluscs are recognized as whole shells at 8.75-
9.5 meters at Samawa composite section (Plt 3.B) , and at depth 20.5, 25.5 meters
at Karbala borehole section . At Karbala section , however , and because of
diagenetic processes the molluscans (Mainly pelecypods) are vanished and only
its moldic pore spaces at 25.0 meters are left . Oysters at the field are recognizable
by the naked eyes . There width reaches (3) centimeter differentiating the
limestone of the second cycles within the lower part of Nfayil formation . It may
also be as coquina , rare occurrence of algae (Dasycladacea ), Ostracoda , and
bioclasts (echinodermata fragments and shell fragments) are found in the Nfayil
Formation .
2.1.2.2 Non-skeletal grains
Non-skeletal grains within the Nfayil formation are peloids , lithoclasts and
ooids . Peloids are sand-sized grains with an average size of 100-200 micron,
composed of microcrystalline carbonate .They are generally rounded or
subrounded ,spherical, ellipsoidal to irregular in shape and are internally
structureless (Mckee and Gutshick,1969). Peloids were observed at depth 24.8
meter at Karbala section. while in the Samawa composite section, peloids are
found in the uppermost part of the formation at 2.0 meters from top of the outcrop,
whereas no occurrence recorded at Najaf section (Plt.2.C) . Lithoclasts are
millimeter-to centimeter-sized redoposited grains , intraclasts and extraclasts
(Folk,1959).
An intraclast is a carbonate fragment of lithified or partly lithified sediment,
derived form erosion of nearby penecontemporaneous sediment, from within the
basin and redepositied within the same area. An extraclast is a fragment of
carbonate rock derived from the erosion of an exposed ancient limestone on land
outside the depositional basin in which it is found (Flugel,2004).
31
Lithoclasts are found as intraclast in intraclastic packstone-grainstone in
Najaf composite section at 4.5-5.5 meters from top of the outcrop(plt.1.C) .
Lithoclasts found as extraclast in extraclastic wackestone-packstone from top of
the outcrop down to 1.5 meters in Samawa composite section (plt.1.B) . This unit
is characterized by extraclasts of two types ,one is a silt-sized bearing quartz, the
other is diagenetically different , also with appreciable quantity of sand grains . Its
margins are oxidized (plt.1-F) .whereas, lithoclasts are found as intraclast in
intraclastic mudstone (plt.1.A) and as intraclast in intraclastic mudstone-
wackestone in Karbala borehole section .
Ooids are spherical or ovoid grains, consisting of smooth and regular lamina
formed as successive concentric coatings around anucles. Lamina may exhibit
tangential or radial microfabrics-size between 0.20 and about 2mm,commonly
between 0.5 and 1mm (Flugel,2004).
Ooids were diagnosed, in Karbala borehole section at depth 25.5 meters (Plt.2.A
and B) . in Najaf composite section, Ooids are found at top of the outcrop down to
1.5 meters and from 5.5-6.5 meters in the same section. (Plt.2.D), whereas no
occurrence recorded at Samawa section . Ooids are small and of superfacial
type(Plt.2.A ), also with grapstone (Plt.2.E )
Ooids are generally limited to the shoal facies , which indicate tropical and sub
tropical , normal marine or hypersaline in the area and generally high-energy
shallow water ( tides and wave action) usually at depths 25 (about to 15 m)
(Fugel,1984).
2.1.3 Euphrates Formation
The Oligocene break at the western part of Iraq , has left a recognizable basal
conglomerate . At Karbala section it is represented by 0.8 meter thick layer ,
increasing to 4.0 meters thick at Najaf and Samawa sections . Its pebbles are sub –
angular to subrounded in shape . Its length ranges from 1 to 4 centimeters . These
32
pebbles were cemented by carbonate material . Under the microscope , the pebbles
are made of dolomite rock fragments . The basal conglomerate is overlain by
recrystallized limestone at Samawa , become intraclastic , peloidal packstone to
grainstone with moldic porosity and vugs at Najaf section .
As mentioned before , the basal conglomerate at Karbala is thin , but the
overlying succession of Euphrates is thicker than they are at Najaf and Samawa .It
is rich in fossils , shows deep facies as marl units , restricted facies bearing peloids
, Miogypsina , Dendiritina , miliolid , Peneroplis , and open marine facies bearing
Miogypsina associated with pelecypods and bioclasts.
The main microfacies characters of the Euphrates Formation were obtained
from the Karbala borehole section , while in both Samawa and Najaf composite
sections carbonate grains were not recognized because the limestones were highly
recrystallized . Peloids were the major component of the non–skeletal grains.
2.1.3.1 Skeletal grains
Miogypsina sp. :It is an excellent index fossil for the middle Oligocene-early
Miocene time interval . It occurs both in lagoon and shallow subtidal environments
of open platform (Flugel,2004). Sartorio and Ventarini (1988) indicated a fore
barrier environment for these .
The first appearance of Miogypsina sp. In Karbala section is at 38.8 meters (Plt
4.B) and last appearance at 26.5 meters (Plt 4.A) . It is accompanied with many
other foraminifera such as , Dendiritina , miliolid , Peneroplis , rotalid , Elphidium
,also with pelecypods , and gastropods . Miogypsina is abundant at the first 4.5
meters of Euphrates Formation within a Miogypsina packstone facies (Plt 4.F) .
Dendiritina : restricted or lagoonal environment (Flugel,2004)) .In this study,
Dendiritina is observed abundant at Karbala borehole section with its last
appearance occurring at 34.4 meters (Plt 4.C) and its first appearance is at 45.5
meters (Plt 4.E) . It is abundant enough to classify the rock as Dendiritina
33
packstone . Peneroplis : Peneroplis and Dendiritina both are Peneroplidae .
Peneroplis is recognized at 29.3 meters (pl.4.D) , 42.1 meters and 45.5 meters at
Karbala section . The latter two depths may be Peneroplis Planatas .Other
foraminifera such as miliolids, rotalids are recognized within formation , (pl.4.F)
.Molluscs : mainly pelecypods,whole shells are abundant at 26.5 m with many
Miogypsina sp. , and shell fragments . At depth 40.1 m pelecypods are also
abundant , some of them are recognized as thin small shell fragments . It becomes
rare at 41.6 m . Pelecypods are sometimes affected by diagenesis (Plt 3.A) Shell
fragments leached by meteoric water and left its molds . Bioclasts are shell
fragments and echinodermata fragments are found in Karbala section and never in
Samawa and Najaf sections . And microtube occurs only at the base of the
formation. (Plt11.D ) .
2.1.3.2 Non-skeletal grains
Non-skeletal grains within the Euphrates Formation are represented by peloids
only . Peloids are well sorted at depth 44.6 m ,with Dendiritina sp. at depth from
34.1-35.5 meters at Karbala section , it occurred at Najaf section (Plt 10.E).
2.1.4 Dammam Formation
The Dammam Formation consists mainly of light grey to white , hard and
Nummulitic limestone , alternating with white massive recrystallized sugary and
chalky limestone followed by whitish grey , hard ,fossiliferous and dolomitic
limestone ,chert layers are recorded at the lower part of the formation , sometime
silicified , locally with chert nodules , grey – green marl (2.0-3.0) meters
alternating with thin dolomite at or near the base of the formation .The lowermost
of the upper part of the Dammam Formation consists of grey, thick bedded , very
hard , recrystallized and dolomitic limestone , whereas the uppermost of the upper
Dammam formation consists of grey massive , fossiliferous , dolomitic limestone ,
with silicified bands.
34
The Dammam Formation is rich in skeletal grains only . At Karbala section
there is Nummulites sp. with Lindrina sp. , Alveolina sp. and Discocyclina sp. at
Samawa section , Bryozoa and shell fragments were also present . At Najaf section
, Dammam Formation was highly and intensively affected by diagenesis leaving
molds of Nummulites sp. and other fossils .
2.1.4.1 Skeletal grains
Nummulites sp. It characterizes shallow waters both inner and outer platform or
ramp, (Flugel,2004). Sartorio and Ventarini (1988) suggested a platform edge
environment.
Nummulies sp. is the index fauna of the Dammam Formation .It is found both
as whole tests and broken ones. Nummulites sp. is found within different
assemblages of fossils :
1- Nummulites sp., with shell fragments and echinodermata fragments . This
assemblage is repeated many times at both Karbala and Samawa sections (Plt 5.B).
2- Nummulites sp. with Alveolina sp. .This assemblage Is repeated two times in
Samawa section and one time in Karbala section (Plt 5.E) (Fig 2.2,2.4).
3- Nummulites sp., Linderina sp. with Bryozoa occur in Karbala section only .(Plt
5.A) .
4- Nummulites sp, with miliolids occur only in Samawa section .
5- Nummulites sp. with Assilina sp. occur in Samawa section only , (Plt 5.D) .It is
also associated with shell fragments and echinodermata fragments .
At Najaf , most of the Nummulites sp. have left its molds in the rock , in
response to meteoric water diagenesis. At Samawa it never appeared at the upper
most part of the Dammam Formation because of the diagenetic process ; the
dolomatization at the top of Dammam , Figure (2.4 ) shows the microfacies and
environments for Samawa section.
Nummulites sp. The last appearance in Samawa section is at depth 61.0 meters
and its first appearance is at depth 126.0 meter . At Karbala section , its first
35
appearance as broken fragments is at depth 100.0 meters , and its last appearance
was at depth 49.7 meter .
Nummulites sp. and Alveolina sp. are index fossils for the biozonation of
early Tertiary shallow inner platform and shelf edge carbonate , ( Flugel ,2004 ) .
At Samawa section , the Alveolina sp. first appearance at depth 103.0 meters
. It appeares twice only . Its last appearance is at depth 70.0 meters .It always
appears as Alveolina , Nummulites sp. packstone .
Miliolids occurred at Samawa section and at Karbala section only .
Dammam bioclasts are : echinodermata fragments , Nummulites sp. fragments
and shell fragments.
Three main groups of benthic biota according to light dependence are :Euphotic
biota need relatively high light conditions , live in shallow – water environments ,
oligophotic biota inhibits environments with low light level , and photo –
independent biota ( Pomer,2001). In the current study fossils like Nummulites sp.,
Alveolina sp. , Miogypsina sp., and others are oligophotic biota which are common
in the Eocene – Miocene marginal shelves bordering Tethys , they seen to here
mainly accumulated in situ through winnowings events and have formed extensive
lithosomes (Pomer,2001) within ramp.
36
A- Intraclasts in intraclastic mudstone (Karbala section) ,sample no.1
B- Extraclasts with sand grains in extraclastic wackestone-packstone (Samawa section)
,sample no.1
C- Intraclasts in intraclastic packstone-grainstone (Najaf section),sample no.1/14
D-Marl with fine silt size (Najaf section), sample no.1/12
E- marl with rotalid ( Najaf section), sample no.1/9
F- Oxized extraclasts in extraclastic wackstone -packstone (Samawa section) ,sample no.1
37
A- Superficial ooids with vugs in ooids pelecypod packstone(Karbala section) , sample
no.10
B- Ooids in ooids pelecypod packstone (Karbala section) , sample no.10
C- Peliods in peliodal packstone (Samawa section) , sample no.2
D- Ooids constrict in ooid packstone (Najaf section) ,sample no.1/16
E- grapstone ooid in ooid packstone (Najaf section), sample no.1/13
38
A- Effect of diagenesis (pelecypod mold) (Karbala section) ,sample no.13
B- whole pelecypods (Samawa section) ,sample no.5
C- Miogypsina sp. Above green marl in miogypsina packstone (Samawa section) at Nfayil
Formation ,sample no.5
D- Pebble from the basal conglomerate showing shelly pelecypods (Najaf section) sample
no.2
E- Miogypsina sp. with miliolid , Ammonia beccarii in Miogypsina packstone (Samawa
section) ,sample no.5
F-Ammonia beccarii in intraclastic bioclastic packstone-grainstone(Karbala section),sample
no.8
39
A- Last appearance of Miogypsina sp.in the Euphrates Formation (Karbala section) sample
no.12
B- First appearance Miogypsina sp.in Miogypsina packstone in the Euphrates Formation
(Karbala section) ,sample no.18
C- Last appearance of Dendiritina sp.in peloidal packstone in the Euphrates Formation
(Karbala section),sample no.15
D-Dendiritina with Peneroplis in Dendritina packstone(Karbala section)sample no.12
E- First appearance of Dendiritina in Dendiritina packstone(Karbala section) sample no.24
F-Miogypsina sp.with miliolid in Miogypsina packstone(Karbala section) sample 12
40
A- Lindrina sp. with Bryozoa in lindrina packstone (Karbala section) Dammam Fn.,
sample no.29d
B- Last appearance of Nummulites sp. in (Karbala section) , sample no.29
C- Whole pelecypoda in (Karbala section) , sample no.13
D- Nummulites sp. with Assilina sp. (Dammam Fn.) at Samawa section, sample no.61
E- Alveolina sp. with Nummulites sp. in Nummulitic Alveolinid packstone (Dammam Fn.)
at Samawa section ,sample no.44
41
2.2 Diagenetic processess
Rhymond ( 1995 ) defined diagenesis as all physical ,chemical and biological
processes that collectively result in transformation of sediment into sedimentary
rocks . Diagenetic processes continue to operate after the sediment has become
rock ,altering the rock texture and mineralogy . Diagenetic processes give the
sedimentary rocks many characteristics observed in outcrop , hand specimen , and
thin section .
Diagenesis refers primarily to the reactions which take place within the
sediment between one or several minerals and the interstitial fluid ( Selly ,2000 ) .
Diagenesis is a term used somehow to define all the changes that occur in
sediments during the interval between deposition and before the transition to
metamorphism . These diagenetic changes may take place in submarine , subarial –
fresh water and subsurface environments ( Larson and Chilingar ,1979 )
The studied samples of Nfayil , Euphrates and Dammam Formations have
undergone some diagenetic processes through their geologic history . The
following diagenetic processes are thought to be the main ones that observed in the
studied samples .
2.2.1 Cementation :
Cementation is the diagenetic process by which voids and porosities are filled
with newly precipitated materials during the deposition by filling the interpartical
porosity or after deposition by filling dissolution porosity such as fractures and
joints resulting from compaction .
Cementation has affected most of the Eocene-Miocene formations with
different types of cement :
42
2.2.1.1 Syntaxial rim overgrowth
Syntaxial rim cement (overgrowth) found as syntaxial growth of calcite
particles on echinoderms fragments indicating an early fresh water phreatic cement
( Koch and Schorr ,1986 ) .
Syntaxial rim cement has affected the Dammam Formation only in Karbala
section at depths 92.2 m , 78.0 m , 73.0 m , 70.0 m , 68.0 m , and at 56.5 m .
At Samawa section ,this type of cement appears in the Dammam Formation too , at
depths 89.0 m, 80.5 m , and at 69.0 m . (Plt 7.B)
Syntaxial rim overgrowth is associated with or without neomorphism Figures
(2.2 ,2.4). The former indicates active fresh water phreatic zone the latter indicates
stagnant fresh water phreatic zone .
2.2.1.2 Geopetal cement :
Sander, (1936) in Flugel ,(2004) indicated the relationship between top and
bottom at the time the rock was formed recognizing that geopetal cement in
limestones is crucial for understanding the depositional post –depositional history
of carbonate rocks ( Flugel,2004) .
Geopetal cement occurs at Karbala section only within Dammam Formation at
depths 94.8 , 89.5 , 83 .0 , and at 65.5 meter.
Geopetal cement indicates active fresh water phreatic zone.
2.2.1.3 Intraparticle cement :
This type shows an early stage of diagenesis within the marine phreatic zone .
This type of cement is the only cement within Nfayil formation occurring at 1.0 ,
5.0 meters in Najaf section , at depth 9.0 meters in Samawa section and at 21.0
meters in Karbala section .(Plt 7.A)
43
Euphrates Formation never showed any cement type both at Najaf and
Samawa sections . At Karbala section , the intraparticle cement occurred at depths
42.5, 36.0 -40.5 meters , and at depth 30.0 meters .
No cement occurred within the Dammam Formation at Najaf section , while at
Karbala section , the intraparticle cement is profound nearly throughout the
Dammam succession, clogged the intraparticle vugs of the main skeletal grains the
Nummulites sp. . Middle part of the Dammam Formation at Samawa section shows
also intraparticle cement .
2.2.1.4 Interparticle cement :
Interparticle cement occurred only within Dammam Formation in Karbala
section at depths 59.0 – 61.0 meters and at 62.5-64.0 meters , and was associated
with both neomorphism and intraparticle cement . (Plt 7.D)
2.2.2 Silicification :
The appropriate chemical conditions to dissolve calcite and precipitation of silica
include supersaturation of pores solutions by silica and decrease of pH and
temperature (Blatt et al., 1972). The source of silica probably is from siliceous
skelton debris including sponge spicules and radiolarian or the corrosion of quartz
and clay minerals at high pH; when pH decreases, precipitation of dissolved silica
occurs. Moreover, the silica precipitation is produced by the decreases of
temperature (Engelhardt, 1977). Silicification are recognized within the Dammam
Formation in the study area , at Karbala , Samawa , and Najaf sections . Fig .(2.2,
2.3 ,and 2.4).(Plt 7.E) .
In marine setting cherts occur as nodules varying in size from a few
millimeters to about 2 cm , or in layer often interbedded with shale or limestone .
44
Most chert nodules are formed early during diagenesis . They are common in
pelagic chalks . In shallow – marine area , (ramp, Platforms ) the input of silica
from land is an important source , Laschet ,(1984) in Flugel (2004) . In shallow –
marine setting chert nodules are sometimes related to mixing zones .
Field observations has confirmed the silicification within the Dammam
Formation in Samawa section , as chert nodules within the Nummulitic packstone
at depth from 91.5-94.0 meters , as chert layer about 10cm .occurring at depth
125.0 meters , (Fig .2.5.A) .
2.2.3 Dolomitization :
Amthor and Friedman (1992) style of dolomitization as a subtidal one is
acceptable in the current study on the basis that rising of sea level had led to the
deposition of the Dammam formation (chapter four) giving subtidal conditions for
semi evaporative dolomitizing fluids showed by the fine crystals of dolomite and
the maintance of textural characters . This may explain the dolomitization of the
lower parts of the Dammam formation . Evidence for the mixing model of
dolomitization also present in the thick dolomite beneath the unconformity , the
euhedral coarse size , and the associated silicification sometimes (at the top of the
Dammam formation. Mixing model may be suggested for the upper part of the
formation .
Dolomitization had a major impact on the sediments of the Dammam
formation . It affected Najaf and Samawa sections . The upper part of Dammam
Formation at Samawa section begins with thick microcrystalline dolomite,
subhedral – anheadral ,about 41.5 meters . This interval shows medium – coarse
euhedral crystals also , at depth 123m ,euhedral cloudy center clear rim is seen
dolomitizing Nummalitic wackestone microfacies . Fig.(2.2 , 2.3 , and 2.4 ) .
All the Dammam Formation at Najaf section was dolomitized with the same
above characteristics with fine – medium , subheadral –anheadral crystals . The
dolomitization was fast enough , dolomitizing the fossils (Nummulites ) and others
45
like echinoderm fragments and the matrix maintaining their original structure and
texture .
Cloudy center- clear rim are found at 123.0 meter in Samawa section and at
28.0 meter in Najaf section . No dolomitization is recorded at Karbala section .
According to (Amthor and Friedman ,1992) ,two stages of late – diagenetic
replacement dolomites are observed for the dolomitization. This is adapted for the
dolomitization of the Dammam Formation on the bases of crystal size and shape of
crystal boundary
The method concluded is that of syn depositional subtidal dolomitization . Two
types of texture are recognized ; the fine , subhedral to anhedral , unimodel which
indicate shallow burial dolomitization , and the coarse , euhedral indicating
intermediate burial .
Amthor and Friedman suggested that the coarser –grained and more porous
lithofacies remained undolomitized during early diagenesis and could have served
as permeable horizons for late dolomitizing fluids .(Plt 6.A , 6.B and 6.E) .
2.2.4 Dedolomitization :
The alteration of dolomite to calcite take place in several diagenetic settings ,
but is a common feature of near-surface vadose zone , Kenny,(1992) in Flugel
(2004) .
Different dedolomitization textures are recognized within the Dammam
Formation , at Samawa and Najaf sections .
At Najaf section , dedolomitization is more effective .Textures recognizable
are :
1- Blocky calcite , cleaveged or non- cleaveged with fine relict rhombs of dolomite
even where the blocky calcite is filling Nummulite molds .(Plt 7.F), (Plt8.D).
46
2-Calcite spar ,coarse crystals fused with each other by serrated boundaries
(Plt8.C)
3- Dolomite rhombs with calcite cores .
4- Cleaveged rhombs of dolomite (Plt 6 .D and 6.F) .
2.2.5 Neomorphism :
The term neomorphism involved three processes, the first by which aragonite
was altered to calcite by inversion, while the second where the calcite become new
calcite particles by recrytallization, or forming new calcite by crystal growth (Folk
1965).
Neomorphism dominates the Eocene-Miocene succession at Karbala section
except the marl lithofacies in Nfayil Formation , but it occur at Najaf section at
Nfayil and Dammam Formations, whereas this type of diagenetic process occur at
Samawa section in Nfayial Formation especially in its lower parts , and it
dominates the Dammam Formation , Fig (2.2, 2.3 and 2.4).
Neomorphism in this study included the transformation of micrite into microspraite
and sometimes to sparite , for the matrix and / or the grains.
2.2.6 Dissolution :
Dissolution is the most important diagenetic process affecting the Eocene –
Miocene succession because it is responsible of forming the vugy, channel and
moldic porosities , these porosity types are described and classified according to
Chaquitte and Pray (1970 ) where porosity types are divided into fabric selective
and non-selective .
Four types of porosity are recognized in the study area through thin sections
examination of the Eocene – Miocene succession in Dammam, Euphrates , and
Nfayil Formations ,they are :
47
1-Intraparticle porosity
2- Moldic porosity
3- Vugy porosity
4-channal porosity
2.2.6.1 Intraparticle porosity :
This type of porosity is noticed within individual particles or grain particles
within skeletal grains ( internal chambers and other openings ) such as Nummulites
sp.(Plt 8.B) , pelecypods , and other fossils . Intraparticle porosity may also be
developed within peloids or intraclasts . Sometimes ,the intraparticle pores are
clogged by calcite cement .
2.2.6.2 Moldic porosity :
Moldic porosity usually forms by the selective removal normally by solution of
former individual constituent of the sediment or rock such as shell or Ooids
especially common in limestone where molds are of primary aragonite constituents
( Nummulites sp. , gastropods , pelecepod shells ), molds in dolomite are usually
formed by selective solution of either aragonite or calcite primary constituents may
also result in the formation of molds .
This type of porosity occurs in the Nfayil Formation at Karbala section only at
depth 25.0 m (Plt8.A). And at depth from`15.0- 18.2 meters ,at Najaf section in
the Euphrates Formation , while it occurs in the Dammam Formation at Samawa
section at depth from 72.0-74.0 m . No moldic porosity is recorded in the
Dammam Formation at Karbala section , moldic porosity occur throughout the
Dammam Formation at Najaf section except in some place. Fig.( 2.2 , 2.3 and 2.4 )
Moldic porosity typically indicates differential solubility between more and
less soluble carbonate constituents in the rock fabric. In some cases , the more
soluble constituents may be metastable mineral such as Mg-calcite or aragonite (
Ahr, 2008).
48
2.2.6.3 Vugy porosity : Vugs are pores nearly equant large enough to be visible
with unaided eye . The dominant type is (usually larger than 1/16 mm and
generally not dependent on fabric .They represent solution enlargement of fabric
selective,( Tuker ,1990) . Vugs are found mainly at Najaf section , Figure ( 2.3 )
Fig.2.5.B
2.2.6.4 Channel Porosity :
Limestone is prone to dissolution in undersaturated water and a common
product is channel pores , developed along fractures .Near-surface karstic solution
pipes are a common example in the geological record .
Intraparticle pores are fabric-selective indicating depositional textures , while
vugs and moldic pores might be of intermediate diagenetic stage . The channel
indicates stress or tectonic forces or may be solution effect , then it might be of
later stages of diagenesis .Tuker(1990).
49
A- Medium to coarse dolomite crystals , cloudy center - clear rim (CCCR) sample no.68
B- Coarse crystalline dolomite in the Dammam Formation (Samawa section),sample no.17
C- Fine crystalline dolomite in the Dammam Formation (Samawa section),sample no.13
D- Dedolomitization in Dammam Fn.(Najaf section) sample no.62
E- Coarse crystalline dolomite in the Dammam Formation (Najaf section),sample no.36
F- Dedolomitization in the Dammam Fn.(Najaf section) sample no.63
50
A- Intraparticle cement (Karbala section) sample no.8
B- Syntaxial rim cement in the Dammam Fn.(Karbala section) sample no.48
C- Vugs within Nummulites sp. (Karbala section) sample no. 51
D- Interparticle cement (Karbala section), sample no.55
E-Silicification in the Dammam Fn.(Samawa section) sample no.46
F-Dedolomitization,blocky calcite filled Nummulites sp. mold (Najaf section) sample no.33
51
A-Moldic porosity ,Nfayil Formation (Karbala section ),sample no.10
B-Intraparticle porosity ,Dammam Formation (Samawa section), sample no.43
C-Dedolomitization ,calcite spare, coarse crystals,Dammam Formation(Najaf
section),sample no.33
D- Dedolomitization,blocky calcite ,Dammam Formation((Najaf section),sample no.26
Plate 8
52
Figure(2.1) Legend of figures (2.2 , 2.3 and 2.4 ).
53
54
55
56
Figure 2.5A Chert layer(10 centimeter) in the Dammam Formation at Samawa
section sample no.70
Figure 2.5 B Vugs in the Dammam Formation at Najaf section , sample no. 51
57
CHAPTER THREE
MICROFACIES AND
DEPOSITIONAL
ENVIRONMENTS
58
Microfacies And Depositional Environment chapter three
3.1 Preface
Detailed examination of Eocene-Miocene thin sections carried on the
bases of Dunham’s classification, (1962) and using the Ramp Microfacis
(RMF) in Flugel (2004) and Standard Microfacies (SMF) assigned by Wilson
(1975), a range of environments are designated for each rock based on its
depositional texture and its fossil content.
3.2 Nfayil Formation
The Nfayil microfacies reveal four types of environments using the ramp
standard microfacies of (Flugel ,2004).
3.2.1 Peritidal Environment
Peritidal carbonates are shallow-subtidal, intertidal and supratidal sediments
found in marginal-marine and shoreline depositional environments. These facies
are vertically arranged (regressive) shallowing upward succession consisting of
shallow-marine sediment overlain by intertidal and supratidal carbonates that are
subject to periods of subaerial exposure (Flugel,2004) .Facies responsible for the
designation of this environment is the intraclastic mudstone -wackestone at
Karbala with quartz (sand – silt size) clastic influx , and extraclastic wackstone -
packstone at Samawa section at depth 0.0-1.5 meter and intraclastic wackstone -
packstone at depth 8.0 meter in same section .Both are matching ramp standard
microfacies number 24 (Flugel ,2004) which is intraclast mudstone /wackestone.
Microfacies responsible for this environment is not found at Najaf section .
Fig.(2.2 and 2.4) ( Plt.9A , D)
.
59
3.2.2 Shoal Environment
Carbonate sand shoal sediments are composed of sand to granule –sized loose
carbonate material occurs in shallow, high energy areas, these shoal carbonate may
be made up of ooids, mixture of broken shelly debris or may be an accumulation of
benthonic foraminifera reworked by wave and tidal currents which results in a
deposit made up of well-sorted, well rounded material: when lithified these form
beds of grainstone or sometimes packstone , (Gary,2009)
Two types of microfacies were recognized for this environment:
A- An Ooid wackestone-packstone, at 0.0-1.5 meter at Najaf section another
occurrence is at 5.5-6.5meters in the same section (Plt10.F), with the presence of
Dendiritina , peloids, grapstones , pelecypods, gastropods, and shell fragments.
whereas at Karbala section ,this facies occur at depth 25.5 meter as Ooid
pelecypod packstone. Ooids are small and of superfacial , concentric types , also
with grapstones, peloids, and shell fragments (Plt10.B). Corresponds to ramp
microfacies 29 (Flugel,2004),ooid grainstone with concentric ooids.
B- Intraclastic packstone- grainstone with Miogypsina sp. ,others are Elphidium
, Ammonia beccarii , miliolid , rotalid , pelecypods , and shell fragments (Plt10.A).
At Karbala and Najaf sections this diversified assemblage of fauna similar to ramp
microfacies 26 (Flugel,2004) bioclastic packstone-grainstone with divers skeletal
grains. Both microfacies never recognized at Samawa section ,Fig.(2.2 and 2.3) .
3.2.3 Restricted Environment
Four types of microfacies characterize this environment .
A-Bituminous siltstone (1.4 meters thick) at depth 14.5 meter at Karbala section ,
followed by silty lime mudstone (7.1 meters thick) interbedded with bituminous
siltstone. ( Plt 9.B )
B-Recrystallized lime mudstone at Najaf and Karbala sections , similar to
standard microfacies number 23 which is homogeneous , non-fossiliferous micrite.
60
C- Peloidal intraclastic packstone at the top of Samawa outcrop . Associated
fossils are: miliolid , Dendiritina matching ramp microfacies number16 (Flugel
,2004) which is mudstone /wackestone with miliolids . ( Plt 9.C )
The dominance of family miliolidea as Dendiritina , Articulina ,and others
unidentified miliolds is due to restricted water conditions .
D- Miogypsina packstone with miliolid , pelecypods and shell fragments, more
restricted conditions are reflected at 8.75 -9.5 meters at Samawa section similar to
ramp microfacies number (13) (Flugel,2004) wackestone -packstone with larger
foraminifera . C and D microfacies present only at Samawa section. ( Plt 9.E)
Miogypsina packstone with miliolid at depth 9.5 meters is designated as
restricted at the Samawa section and intraclastic, bioclastic packstone to
grainstone with presence of Miogypsina sp. at depth 25.0 meters in Karbala
section as shoal environment , both are located above the olive green marl (the
index unit of the Nfayil Formation ). Then if the Miogypsina is the index of the
Euphrates formation both above mentioned microfacies might be within the
Euphrates Formation.
3.2.4 Deep Environment
Deep sediments are medium-bedded, fine grained bioclastic limestone and
marls ,often burrowed . Skeletal grains are often worn, echinodermata, mudstone ,
wackestone , packstone and some grainstone. (Flugel ,2004)
Many layers of marl are found in the succession of the Nfayil Formation .Some
are bearing echinodermata fragments ,rotalids , and unidentified fauna, such that at
depth 11.0 meters below the top of Najaf outcrop (Plt1.E ) , and at Karbala at depth
24.0 meters . Some layers of marl are olive green color which may indicate deep
marine environment .It is present in all three sections. This unit is a characteristic
one defining the contact between the Nfayil and the Euphrates Formation
(Sissakian,1999) . Other marl unites with fine clastic influx are also present .
Fig.(2.2, 2.3,and 2.4)
61
3.3 Euphrates Formation
Four types of environments involved in the formation of the Euphrates
sediments .They are:
3.3.1 Restricted Environment:
This was reflected by:
A- Recrystallized limestone unit at Karbala and Samawa sections only. It is
similar to microfacies (I9) , which is finely laminated dolomitic or lime
mudstone microfacies, facies zone number 8 .
B- peloidal packstone at Karbala section depth 35.0 meters . Associated fossils
are : Dendritina, Miogypsina and other unidentified. (Plt 10.D ) .
C- Dendritina packstone with Peneroplis and gastropods at depths 45.5 , 42.5
meters at Karbala section (Plt 10.C ), similar to microfacies no. 18 , which is
packstone with abundant foraminifera or algae . (Flugel,2004) .
3.3.2 Shoal Environment
Shoal is represented by peloidal grainstone microfacies ,consisting mainly of
abundant peloids , Dendritina ,bioclasts ,and intraclasts . Peloids are well sorted
and rounded at depth 44.5 meters at Karbala section (Plt 10.E ) . It appeared as
intraclastic peloidal packstone–grainstone at depth from 15.0-18.0 meters at
Najaf section , similar to ramp microfacies no. 27 , which is bioclastic grainstone
and packstone composed of few dominant skeletal grains, this facie is not found at
Samawa section .
3.3.3 Open marine Environment
Three types of microfacies are recognized indicating this environment at
Karbala section only :
62
A- Miogypsina packstone at depths 26.5-31.0 meters and at 36.0 -39.0 meters .
Associated fauna : pelecypods, gastropods, rotalid , echinoderm fragments, shell
fragments similar to ramp microfacies (13) (Flugel,2004), which is bioclastic
wackestone with abundant larger foraminifera (Plt11.A). .
B- Fossiliferous packstone at depth 39.0-40.5 meters. Associated fauna
are pelecypoda , gastropods , ostracoda , and shell fragments similar to ramp
microfacies (13) which is wackestone /packstone with larger foraminifera
.(Plt11.B)
C- Bioclastic wackstone –packstone at depth 40.5 and 41.8 meters . Associated
fauna are pelecypoda ,rotalids whole tests accompanied with abundant shell
fragments and echinodermata fragments similar to microfacies no.10
(Flugel,2004), which is bioclastic wackestone- packstone with skeletal
grains.(Plt11.C)
3.3.4 Deep Environment
Two microfacies possibly fit in this environment at Karbala section only , they
are:
A-marls :
Marl thin sections show few silt size quartz grains, echinodermata fragments and
rotalids. It is similar to ramp microfacies 11 (Flugel,2004) ,which is marl with
intraclasts and limestone pebbles ,referring to distally steepened ramps (Flugel,
2004).
B-Microbioclastic packstone
Characterized by the presence of microtubes , shell fragments, echinodermata
fragments , rotalids, and others, at Karbala section only depth , 46.2 -48.0 meters ,
similar to ramp microfacies (7) (Flugel,2004) which is bioclastic packstone with
abundant echinodermata .(Plt11.D).
63
3.4 Dammam Formation
This formation is widely distributed in southwest Iraq . It was characterized
by vertical changes in lithology and faunal assemblages . Therefore different
environments and microfacies are recognized throughout the succession of the
formation. They are :
3.4.1 Shoal Environment
The domination of Nummulites sp. in the Dammam Formation came in
different styles , as mentioned in chapter two. Although the Nummulites sp. is the
main constituent of these microfacies, texture is different grainstone, packstone ,
and wackestone .The important bases for the designation of this environment are:
either the larger size of the Nummulites sp. , (Fig.2.2, 2.3,and 2.4) such as : the
larger Nummulitic packstone at depth 65.0 meters, Karbala section(Plt12.A,C )
.Matching ramp microfacies 27 , bioclastic grainstone / packstone with few
dominant skeletal grains. Reekman and Friedman (1982) suggested that the larger
size of the grain (Nummulites sp. in the current study ) would be a perfect
indicator of shoal or barrier, or concentration of one type of fossils or bioclasts
(Flugel,2004).This is also found at Karbala section , sample no. 67 the Nummulites
packstone / grainstone (Plt12.B). Algae ( indicate of shallow water conditions)
were also found nearly at the base of the same section.
At Samawa section the shoal microfacies showed large sized Nummulites sp,
echinodermata fragments , Nummulites sp. fragments ,shell fragments , rotalid and
algae. At the base of Samawa section ,the Dammam Formation shows the presence
of Assilina sp. (Plt12.C), Fig.2.4
Even though the Nummulites sp. were ghosts nearly all over the Dammam
Formation at Najaf but the detection of larger sized Nummulites sp. was easy at
depth 61.0-63.5 meters indicate shoal environment .
64
3.4.2 Restricted Environment
Characteristic microfacies for restricted environment are :
A- Alveolina sp. and miliolids thrive in restricted conditions . In this study they
are the main key to distinguish this environment ,with or without the presence of
Nummulites sp. The bearing microfacies for this assemblage is at Karbala section
at depth 80.0 -82.0 meters with Nummulites sp. , Alveolina sp. , Dasycladacea
packstone. At Samawa section at depth 70.0-72.0 meters Nummulites sp.,
Alveolina wackestone with miliolid , echinodermata fragments(Plt12.D) .And at
depth 97.0- 103.0 meters Nummulites sp. , Alveolina sp. , with Lindrina sp.
packstone, it is similar to ramp microfacies (13) , wackestone- packstone with
larger foraminifera ,and ramp microfacies (17) ,bioclastic wack estone with
dasycladacea.
The presence of miliolid ,rotalid ,ostracode or may be pelecypods, and quartz
grains within the fossiliferous packstone at depth 57.25 meters in Karbala ,similar
to ramp microfacies (16) which is mudstone -packstone with miliolid also
characterizes restricted environment. At Samawa section miliolid appeared with
Nummulite sp. within Nummulitic wackestone or packstone at depth 85.5-91.2
meters , the presence of miliolids also characterized restricted environment ,
similar to ramp microfacies (13) and (16) (Flugel ,2004 ).
B-Recrystalized limestone unit within the Dammam Formation at Najaf section
only at depth 53.5 -57.0 and at 59.0-61.0 meters , It is similar to microfacies (19)
which is non- burrowed lime mudstone .
( Fig 2.3 ) .
3.4.3 Open marine Environment
Earlier consideration for the larger Nummulites sp. was to be on the edge of the
ramp giving shoal environment , wherever the Nummulites sp. are smaller in size ,
65
it means imperfect conditions for building a shoal . It is considered to show an
open marine conditions especially with the presence of bioclasts (Nummulites sp.
fragments ,echinodermata fragments, and shell fragments, Lindrina sp., Asslina sp.
,bryozoa and other small foraminifera. ) , (Plt13. A , B, D)
The texture is packstone ,sometimes wackestone (Fig 2.2, 2.3, 2.4 ) ,the
matching microfacies are ramp microfacies (7) and (13) at open marine
environments, which is wackestone / packestone with larger foraminifera
(Flugel,2004).
3.4.4 Peritidal Environment
The dolostone showen in ( Fig 2.3 , 2.4 ), indicates the presence of this
environment .It is similar to ramp microfacies 22 dolomite being fine crystalline
subhedral, euhedral dolomite . (Plt13.C,E)
66
A- Intraclastic mudstone-wackestone , Nfayil Formation ( Karbala section) ,sample no.2
B- Bituminous siltstone , Nfayil Formation ( Karbala section) ,sample no.5
C- Peloidal packstone , Nfayil Formation ( Samawa section) ,sample no.2
D- Extraclastic wackestone – packstone ,Nfayil Formation ( Samawa section) ,sample no.1
E- Miogypsina packstone , Nfayil Formation ( Samawa section) ,sample no.5
Plate 9
67
A- Intraclastic packstone- grainstone ,Nfayil Formation(Najaf section),sample no.1/14
B- Ooids packstone ,Nfayil Formation ( Karbala section ) , sample no.8
C- Dendritina packstone,Euphrates Formation (Karbala section) ,sample no.12
D- Dendritina packstone,Euphrates Formation (Karbala section) ,sample no.24
E- Intraclastic peloidal packstone-grainstone,Euphrates Formation(Najaf section)
sample no.1/5
F- Ooid wackstone – packstone , Nfayil Formation (Najaf section ), sample 1/13
Plate 10
68
A- Miogypsina packstone , Euphrates Formation (Karbala section), sample no.12
B- Fossiliferous packstone , Euphrates Formation (Karbala section), sample no.19
C- Bioclastic wackestone-packstone , Euphrates Formation (Karbala section), sample
no. 20
D- Microbioclastic packstone , Euphrates Formation (Karbala section), sample no. 26
Plate 11
69
A-Larger Nummulitic packstone, Dammam Formation(Karbala section),sample no.65
B-Nummulitic packstone-grainstone, Dammam Formation(Karbala section),sample no.67
C- Larger Nummulitic packstone, Dammam Formation(Samawa section),sample no.62
D-Nummulitic-Alveolinid-wackestone, Dammam Formation(Karbala section),sample no.44
Plate 12
70
A-Lindrina packstone , Dammam Formation (Karbala section),sample no.29c
B-Nummulitic packstone , Dammam Formation (Karbala section),sample no.29
C-Dolomite , , Dammam Formation (Samawa section),sample no.51
D-Nummulitic packstone, Dammam Formation (Karbala section),sample no.31
E- Dolomite , , Dammam Formation (Najaf section),sample no.49
Plate 13
71
CHAPTER FOUR
SEQUENCE
STRATIGRAPHY
72
Sequence Stratigraphy chapter four
4.1 Contacts
4.1.1 Lower contact of the Dammam Formation
In the study area , the contact is conformable with the Rus underlying
Formation which is encountered at Najaf and Samawa boreholes . It is the first
appearance of anhydrite that underlies the grey –green marl , papery with rusty
stains. This contact is not encountered at Karbala borehole .
4.1. 2 Lower contact of the Euphrates Formation
The contact is between the Euphrates Formation and the underlying Dammam
Formation . It is unconformable , sharp contact , represented by the basal
conglomerate indicating the Oligocene absence . Thickness of basal conglomerate
is 0.8 meter at Karbala borehole above Nummulitic packstone , 4.0 meters at
Najaf borehole above whitish grey dolomite with secondary calcite filling
fractures , and 4.0 meters at Samawa borehole above 42.0 meters whitish grey ,
tough ,fractures filled with secondary calcite . The conglomerate consisted of 1-4
centimeter long pebbles of dolomite bearing recrystallized pelecypod shells .
4.1.3 Nfayil Formation contacts
The Nfayil Formation consists of two member according to previous studies
(Sissakian,1999),the upper and lower Nfayil Formation
At Karbala both upper and lower members are encountered . At Najaf and
Samawa , the upper member of the formation is absent .
4.1.3.1 Lower contact of the Nfayil Formation
In the study area, the lower contact of the Nfayil Formation is conformable
with the underlying Euphrates Formation , it is assumed to be above the olive
green marls . This is acceptable at the field . The current study reveals different
73
contact using the Miogypsina sp. which is an index fossil for the Euphrates
Formation and it is present within the limestone unit overlying the olive green marl
marker . This marl marker is 4.0 meters thick at the Najaf outcrop , interbedded
with thinly – bedded marly limestone .The latter is seen recrystallized under the
microscop , (Miogypsina sp. is not detected at the Najaf outcrop) . At Samawa
outcrop the olive green marl is 1.0 meter thick , limestone unit overlying the olive
green marl bearing Miogypsina sp, whereas at Karbala borehole the olive green
marl is 0.75 meter thick , Miogypsina sp. is present within the limestone unit
overlying the olive green marl. The contact between the Nfayil and Euphrates
formations must be constructed on the bases of Miogypsina (index fossil for the
Euphrates Formation ) then the contact will be based on the Miogypsina
disappearance which occurs above the olive green marl unit in the current study .
4.1.3.2 Upper contact of the Nfayil Formation
The upper contact of the Nfayil Formation is not seen in the field of the study
area. At Karbala borehole section (0.3) meter of soil , pale brown ,friable with rock
fragments capping the formation .
At Najaf borehole , the Nfayil Formation is not encountered . The studied
section is a composite section of both Najaf borehole and Najaf outcrop (distance
between outcrop and borehole is 3 km). At Najaf outcrop the Nfayil is capped by
tough , well- bedded ,fossiliferous limestone with black stains , represented by
sample number 1/16 which is ooid wackestone-packstone .
At Samawa the studied section is a composite one , both outcrop and borehole
,distance between them is 7 km . The Nfayil Formation is not encountered at
Samawa borehole , at the outcrop a cap of marly limestone represented by (sample
no. 1) which is an extraclastic wackestone – packstone.
74
4.2 Sequence Stratigraphy
4.2.1 Preface
Sequence stratigraphy is the study of rock relationship within a
chronostratigraphic framework (Van Wagoner et al ., 1990).
The fundamental unit of sequence stratigraphy is the sequence . A sequence
is a relatively conformable succession of genetically related strata bounded by
unconformities and their correlative conformities .(Mitchum ,1977; Posaentier et al
., 1988).
4.2.2 Concept and Definition
The individual sequence generally consists of three genetically related facies
packages known as “ systems tract” that are deposited during a single cycle of sea
level rise , stillstand , and eventual fall .
These system tracts are the fundamental architectural components carbonate
platform , they are referred as lowstand systems tract (LST) ,transgressive systems
tract (TST), and high stand systems tract (HST) ,(Sarg ,1988; Van Wagoner et
al.,1988, Postamentire et al ., 1988) .
The lowstand systems tract is deposited during an interval of relative sea level
fall at the offlap break , and subsequent slow relative sea level , (Emery , and
Myers ,1966 ). The base of the lowstand systems tract is represented by type -1
Sequence boundary .The transgressive systems tract is deposited during that part
of a relative sea level rise cycle when top set accommodation volume is increasing
faster than the rate of sediment supply ,(Emery and Myers,1996).
75
The transgressive systems tract may exhibit catch up or keep up sedimentation
depending on the wetter conditions and rate of rise of sea level .
The high stand systems tract represents progradational top set clinoform
system deposited after maximum transgression and before a sequence boundary ,
when the rate of creation of accommodation is less than the rate of sediment supply
(Emery and Myers ,1996).
The top of the transgressive systems tract a down lap surface bound below the
high stand systems tract are genetically characterized by a relatively thick
aggradational to progradational geometry . Deposition of high stand systems tract
are generally characterized by early and late stages that reflect different rate of
accommodation and associated water mass condition during early and late high
stand.
4.2.2.1 Parasequence
The fundamental building blocks of a sequence are parasequences and
parasequence sets . Parasequence is defined as a relatively conformable succession
of genetically related beds bounded by marine flooding surfaces or their correlative
surfaces. A marine flooding surface is a surface separating younger from older
strata across which there is evidence of an abrupt increase in water depth . While
the parasequence set is a succession of genetically related parasequences which
from a distinctive stacking pattern bounded by marine flooding surface ,( Van
Wagoner et al., 1990 ). Stacking patterns of parasequences may be :
A- progradational stacking that result when the long term rate of a accommodation
exceeded by rate of sedimentation .
B-Aggradation stacking pattern results when the long- term rate of
accommodation closely matches the long term rate of sedimentation .
76
C- Retrogradational stacking results when the long term rate of accommodation
exceeds the long term of sedimentation .
Accommodation space is defined as the space available for sediment to
accumulate at any point in time (Jervey,1988) .This space is controlled by the rate
of subsidence , rate of eustatic sea level change ,and sedimentation rates (Hanford
and Loucks , 1993) .
4.2.2.2 Key Surfaces
4.2.2.2.A Sequence Boundaries
Two types of sequence boundaries can be recognized in the rock record , they
are defined and identified on the basis of arrangement of strata into systems tracts
between the sequence boundaries and types of bounding unconformities (Van
Wagoner et al., 1990).
Type -1 sequence boundary is characterized by subaerial exposure and
concurrent subaerial erosion associated with stream rejuvenation , a basin ward
shift in facies , a downward shift in coastal onlap , and onlap of the overlying
strata.
As a result of the basin ward shift in facies , non-marine facies such braided
stream or estuarine sandstone or very shallow marine facies above a sequence
boundary may directly overlain deeper water marine rocks.
A type-1 sequence boundary is interpreted to from when the rate of eustatic fall
exceeds the rate of basin subsidence at the depositional shore line
break,(Posamentier et . al., 1988 ;Van Wagoner et. al., 1990 ).
A type -2 sequence boundary marked by subaerial exposure and down ward
shift in coastal on lap landward of the depositional shoreline break .However it
lacks both subareial erosion associated with stream rejuvenation and basin ward
77
Shift in facies . A type -2 sequence boundary is interpreted to form when the rate
of eustatic fall is less than the rate of basin subsidence at the deposition shoreline
break,(Van Wagoner et .al.,1990).
4.2.2.2.B Transgressive Surface (TS)
This surface is the first significant marine flooding surface on top of the low
stand systems tract (Einsele,2000) , and it is the limit between lowstand systems
tract and transgressive systems tract (Loutit ,et .al.,1988) .
This surface considers the first indication of marine flooding on the shelf
within a succession (Van Wagoner et .al., 1988).
4.2.2.2.C Marine flooding surface
Diachronons surface indicating minor submarine erosion (nosubaerial erosion )
and separating strata of shallower environment (bottom) from deposits deeper
environment (top) ,(Einsele,2000).
This surface correspond with stratigraphic relationship like (onlap) than it is
considered a sequence boundary (Van Wagoner et . al.,1988).
4.2.2.2.D Maximum Flooding Surface (MFS).
This surface is represented as the boundary between a transgressive unit , or
retrogradational parasequence sets , and an overlying regressive unit, or
progradational parasequence sets , (Emery and Myers ,1996).
At this surface the stacking patterns change from retrogradational to
progradational (Van Wagoner et. al.,1988).
78
4.2.3 Sequence development
4.2.3.1 Dammam cycles
Five third order cycles (A,B,C,D,E ) can be recognized within the Dammam
succession , minor fluctuation within the third order cycle D can be recognized and
divided into two fourth order cycles represented by D1 and D2 at Samawa section
At Najaf section , six third order cycles (A,B,C,D,E,F) are recognized , cycle D is
divided into two fourth order cycles D1 ,D2 , Cycle E is also divided into three
fourth cycles (E1,E2,E3).
At Karbala section , only four third order cycles (C,D,E,F) can be recognized
within the Dammam succession .
The asymmetry of cyclicity was due to the changing magnitude of eustatic sea-
level (Van Wagoner et al ., 1990).These cycles represent successive episodes of the
sea-level rises and still stands. Cycle A at Samawa section is symmetrical where
the shallow open and deep facies represented by the transgressive systems tract
(TST) and separated from the underlying conformable contact with the Rus
Formation by a transgressive surface (TS). It was overlain by the shoal facies of
the high stand systems tract .
Cycle A at the Najaf section on the other hand is asymmetrical where the thick
transgressive systems tract (TST) consists of deep facies followed by thin peritidal
facies of the high stand systems tracts (HST).
Cycle B shows a marked difference at the Najaf section in terms of being thick
(thicker than the section at Samawa specially the transgressive systems tract (TST)
and the nature of its symmetry where the thick transgressive systems tract (TST) at
Najaf may reflect a keep up situation due to the balance between carbonate
production and relative sea –level rise , in this case the major controlling factor is
the tectonic subsidence . .
79
The nature of cycle C is similar at Samawa and Najaf sections , although cycle
C is not complete at the Karbala section .The nature of succession may suggest its
similarity with the Najaf section .
Cycle D shows an almost equal thickness in all studied sections but can be
divided into two fourth order cycles D1 and D2 at Najaf and Samawa sections due
to minor fluctuation of the relative sea –level .These minor fluctuations may be
due to lower rates of subsidence at these sections.
Cycle E shows a similar behavior and can be divided into three fourth order
cycles at Najaf section , cycle F is incomplete due to the truncation by the upper
unconformable surface (SB1) of the Dammam Formation . The massive
dolomitized interval at the top of Dammam at the Samawa section masked the
original depositional texture and facies and consequencetly the nature of cycles E
and F.
4.2.3.2 Euphrates –Nfayil cycles
Deposition of the Euphrates and the Nfayil was due to a major sea-level rise
and three third order cycles were recognized in the studied sections . These cycles
are different in all aspect (symmetry , thickness and stacking pattern ) from one
section to another . This may be attributed to local changes in tectonic subsidence
which have affected the velocity of relative sea –level rise and the nature and
subdivision of these cycles.
Cycle G is bounded below by a transgressive surface (TS) which coincides
with the lower unconformable contact with the underlying Dammam Formation .
This cycle is underlain by SB1surface .Cycle G at Samawa and Najaf sections are
nearly of the same thickness and represented by transgressive systems tract.This
parasequence at these sections consists of restricted facies in Samawa and shoal
80
facies at the Najaf section .This cycle can be divided into four fourth order cycles
(G1,G2,G3 and G4) at Karbala section, this together with its high stand systems
tract being thicker at Karbala section may suggest the almost equal effect of
eustatic and tectonic component . This is contrary to the case at the Samawa and
Najaf where eustacity was the major controlling factor . This may explain the
difference in thickness of the basal conglomerate .
Cycle H is thin and shows the change into lower accommodation in all sections
and can be divided at the Najaf section into two fourth order cycles in that area of
relatively low rate of subsidence .
Cycle I is incomplete and truncated by (SB1) and shows the maximum
thickness at Karbala section where the transgressive systems tract is represented by
deep facies followed by a thick high stand systems tract (HST) of the shoal ,
restricted and peritidal facies . This cycle was divided into a number of fourth
order cycles at the Najaf section .It may also be due to the major control of the
eustatic component in this area of low rate of subsidence .Fig 4.1
4.2.4 Basin development in the Miocene
The Miocene succession in the study area was developed in an area of low
subsidence which reflects the major effect of eustacy as the main controlling factor
in sequence development . .
The Euphrates-Nfayil succession was deposited on a slowly subsiding carbonate
platform as a result of a major transgression where successive episode of sea level
rise and still stand , were responsible for the formation of three third order cycles
and a number of fourth order cycles within third order cycles . A block movement
may explain the variation in potential accommodation from one section to another
.This may result of the tectonic component being the major controlling factors
during the deposition of the Miocene succession at Karbala area.
81
82
4-2-4 Diagenetic Model
For simplicity ,the diagenetic characters for the three formations, will be
discussed separately .
The Nfayil Formation was diagenetically less affected. On the basis of former
studies , Nfayil can be divided into upper and lower members ,both are present at
Karbala section only. The upper Nfayil (mostly cycle I) was affected by
neomorphism . The lower (interbedded marls and limestones ) , limestone units
also gained neomorphism . Intraparticle cement is found at its upper limestone
unit. Vugs and moldic pores is found at its lower limestone unit. The presence of
intraparticle cement indicates passing through marine phreatic zone ,while
neomorphism is gained by passing through fresh water phreatic zone. Reaching the
vadose zone , dissolution has affected the rocks creating vugs porosity .
At Najaf and Samawa sections , only the lower member of Nfayil Formation is
encountered . It shows the same diagenetic imprints , neomorphism is less
effective, cement nearly rare at Samawa , vugs also present .
The succession of these processes may indicate a state of fast rising of the sea-
level. Tuker , (2005) suggested the rates of sea level change are too rapid , then
there may not be sufficient time for dolomitization to take place. This fact will
clarify absence of dolomite in the Nfayil Formation.
The Euphrates Formation at Samawa shows neomorphism and vugs for the
crystalline limestone while at Najaf only vugs and moldic pores. At Karbala
section the same features are present but with different pattern i.e. cementation is
on and off, vugs also . Current study suggest that the lower part stayed at the
stagnant fresh water phreatic while the upper part when cement and neomorphism
appeared together in the same rock meaning its presence within the active fresh
water phreatic zone ( Longman,1980).
83
The basal conglomerates are dolomite pebbles with cementing material .
Dolomite pebbles may be the result of the exposure of the Dammam Formation .
The Dammam Formation is affected by diagenesis differently in the studied
sections .The rising sea-level at Karbala section gave the rocks ,neomorphism with
cementation types like syntaxial rim overgrowth , geopetal and interparticle
cements ,also intraparticle cement (an early diagenetic cement type) . The
association of neomorphism with syntaxial rim overgrowth indicates passing
through the active fresh water phreatic zone ( Longman ,1980) .Tuker , (2005)
suggested that during relative sea-level rise , ground water zones move landward
through carbonate platform , so the transgressive system tracts sediment will be
subject to marine diagenetic processes and sediments could well have abundant
marine cements, but if they move into the shallow –burial , a stagnant marine
diagenetic environment relatively rapidly then they will not suffer any further
cementation. Cycle B,C, D, E and parts of A at Samawa also shows the same
features .
The dolomite at Samawa section is thick and beneath an unconformity (both
features are indicative of mixing zone dolomitization ). Tuker (2005) suggested
that during the high stand , the main diagenetic pattern will be an initial marine
diagenesis replaced in time either by supratidal diagenesis and evaporative
dolomitization or meteoric dissolution , cementation and mixing zone related
dolomitization depending on climate( Tuker ,2005 ). This study adapted the above
explanation for the Dammam Formation . .
The Dammam Formation at Najaf section undergone dolomitization and leaching
of Nummulite fauna (cycle A-D2 ) (only D1 showed some neomorphism )After
that cycles E1-F show dolomitization and vugs .
84
Diagenetic model for the studied Eocene-Miocene succession suggests : after
the deposition of the Dammam Formation by rising sea-level a subtidal model of
dolomitization at Najaf section affected the succession while neomorphism
associated with different cements took place at Karbala and Samawa. Reaching D
cycle , a high stand condition might begin causing another episode of
dolomitization by mixing conditions which was associated with silicification .
Dedolomites are caused by aquifers . After the Oligocene break , fast rising sea-
level put the Euphrates and Nfayil formation in the fresh water phreatic zone of
diagenesis (both stagnant and active ) showing neomorphism with or without
cementation . No dolomitization occurred .(Fig.4-2)
85
86
CHAPTER FIVE
Summary and
Conclusions
87
Summary and Conclusion chapter five
Summary and Conclusions
1. On the west of the Euphrates river ,south west of Iraq , three boreholes and
two outcrops were fully investigated for the study of the Eocene- Miocene
succession. It revealed three formations : the Dammam Formation , the
Euphrates Formation, and the Nfayil Formation .
2. Thin sections were petrographically studied . Two types of grains ; skeletal
and non-skeletal were found within the Nfayil formation ; they are miliolid ,
Dendritina , rotalid , and Elphidium , mollusks as skeletal ones . Non-skeletal are
Peloids , Ooids, intraclasts , and extraclasts .
Moulluscs , a most dominant skeletal component , are found as whole shells
and fragmented . Molluscs molds are found at Karbala section due to the effect
of diagenesis . Oysters at the field were recognizable with unaided eyes
differentiating limestone of the second cycle within the lower part of the Nfayil
formation , may be as coqina .
3. Miogypsina SP.( an index fossil for the Euphrates formation) is recorded for
the first time , included in the limestone unit directly above the olive green marl
index unit of the Nfayil Formation .
4. The Euphrates Formation consists of the lower part ( basal conglomerate) and
the upper (limestone ) . Basal conglomerate consisted of (1-4 cm ) pebbles of
dolomite imbracing recrystallized mollusks .
Limestone under the microscope reveals : Miogypsina sp. ( an index fossil )
Peneroplis , Dendritina , Ammonia beccarii , rotalid , mollusks , echinodermata
fragments , and microtubes .
88
Peloids are the major non- skeletal elements.
5. The current study suggests that if the Nfayil Formation is a different formation
than the Euphrates Formation , the boundary between them must be shifted to a
new position . This will be taken above the Miogypsina sp. index fossil
disappearance. The latter includes the limestone unit directly above the olive
green marl .
6. The Dammam Formation is rich in skeletal grains only . The index fossil is
the Nummulites sp. others are Lindrina sp ; Alveolina sp ., Discocyclina ; also
bryozoa and shell fragments .
Tremindes diagenetic effect left Nummulitic moldic pores and other fossils at
Najaf section .
The Nummlites sp. is associated with different groups of fauna ; a. Nummulites
sp. with shell fragments and echinodermata fragments.
b. Nummulites sp. with Alveolina sp. , c- Nummulites sp. with bryozoa , d.
Nummulites sp. with miliolid .
Large size Nummulites sp. is a fundamental concept in differentiation shoal
environment.
7. Four environments are distinguished in the Nfayil Formation. These include
:A) Peritidal environment which is characterized by intraclastic mud-
wackestone , extraclastic wackestone –packstone and intraclastic wackestone
–packstone. B) Restricted environment is represented by Bituminous siltstone ,
Silty lime mudstone , recrystallized lime mudstone , peloidal intraclastic
packstone and more restricted environment which include Miogypsina sp. with
miliolid. C) shoal environment is characterized by the Ooid wackestone –
packstone and intraclastic bioclastic packstone-grainstone . D) deep marine
environment represented by many layers of green marl.
89
8. Facies analysis shows four environments for the Euphrates Formation ; A)
restricted environment represented by recrystallized limestone , peloidal
packstone , Dendritina packstone facies . B) shoal environment which is
characterized by peloidal grainstone , intraclastic peloidal packstone-
grainstone microfacies . C) open marine environment represented by
Miogypsina sp. packstone , fossiliferous packstone , bioclastic wackestone-
packstone microfacies . D) deep marine environment ,two facies possibly fit in
this environment were : marl beds and microbioclastic packstone .
9. Four environments are recognized within the Dammam succession , these are
: A) peritidal environment represented by the dolomite , B) restricted
environment characterized by the presence of Alveolina sp. , miliolid with or
without the presence of Nummulites sp. and represented by recrystallized
limestone. C) open marine environment represented by Nummulites sp. were
small size with presence of bioclastics , Nummulites fragments , echinodermata
fragments as packstone or wackestone microfacies . D) shoal environment
characterized by either larger size of Nummulites sp. or texture is grainstone like
Nummulitic packstone – grainstone .
10. Several diagenetic processes affected the Eocene – Miocene succession ,
they include : neomorphism , dissolution ( mold porosity , vugs ) ,
dolomitization , cementation , silicification , and dedolomitization , these
processes are related to three main diagenetic environments ; marine phreatic ,
mixing , meteoric phreatic .
Cementation processes is recognized within the succession resulting in the
formation of many types of cement such as syntaxial rim cement , intraparticle
cement , interparticle cement , geopetal cement . Neomorphism which has
resulted in microsparite , dissolution (moldic porosity and vugs ) highly affected
the Dammam Formation and formed many types of porosity making the
90
Dammam Formation a good water aquifer . Four types of porosity are
recognized throughout the succession , they are : intraparticle porosity , moldic
porosity , vugy porosity and channel pores . Silicification process is limited but
the cementation , neomorphism and dolomatization are common .
11. Five third order cycles ( A, B,C, D and E) are designed for the Dammam
formation . Cycle D is divided into two 4th
order cycles due to minor fluctuations
at Samawa and Najaf . Another cycle( F ) is designed at the top of Najaf and
Karbala sections, cycle E is divided into three 4th order cycles only at Najaf
section . Cycles A and B is not detected at Karbala section .The asymmetry of
cyclicity is due to changing of eustatic sea-level magnitude .
Cycle A is symmetrical at Samawa but asymmetrical at Najaf section .
Cycle B gives opposite situation as being thick and asymmetrical at Najaf
than at Samawa .Thickening may be related a keep up situation due to the
balance between carbonate production and relative sea-level rise .
Euphrates and Nfayil deposition is due to major sea-level rise .Three third
order cycles are designed for this reason , cycles are different in symmetry ,
thickness , and stacking pattern due to local tectonic changes .
Cycle G is underlain by SB1 surface due to the presence of the basal
conglomerate which indicates Oligocene absence from the study sections , and is
divided into four 4th order cycles at Karbala section . Cycle H is divided into two
4th
order cycles at Najaf , Cycle I is incomplete and truncated by an SB1 surface
also it is divided into three 4th order cycles at Najaf section .
12. The current study suggests analyzing the microfossils of the basal
conglomerate between Euphrates and Dammam formations to determine its
origin and age of deposition and comparing it with the basal conglomerate of the
upper Euphrates area .
91
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97
المستخلص
يبس ف انصذشاء انجثخ انغشثخ ي انعشاق كشف ع -رزبثع عصشالاس
ششذخ صخشخ ي ثلاثخ أثبس يبئزب رسع ثلاث ,انفشاد، انفبم,جد ركب انذيبو
انطجبل اندم يكشف صخش خضعذ نزذذذ انصخبسخ انفصهخ انز اسزخذيذ نجبء
.نزذش ا
ف كم انمبطع إن جد انذججبد انجشخ انكهخ أشبسد انسذبد انجشخ نهززبثع
غش انكهخ ض ركب انفشاد ،انفبم، انذججبد انجشخ انكهخ فمظ ض رك
.انذيبو
عذد ف رصى اطمخ انصفبد انسجخ انزذجشاد سب انبرجخ ي دساسخ أ انزفبصم
ثئخ ، انمشجخ ي انذ ثئخال رشمانز انسذبد انجشخ انز أدد إن انزمسبد انجئخ
انذبجض انزضذم ، انجئخ انجذشخ انضذهخ انذصسح ثئخ انجذش انعك ثبنسجخ نزك
ح انجذشخ انضذهخ ، انجئانزضذم انفبم رشم انجئخ انجذشخ انذصسح ، ثئخ انذبجض
انفزدخ ثئخ انجذش انعك ثبنسجخ إن رك انفشاد أيب رك انذيبو فأ رشست ض
، انجئخ انجذشخ انذصسح ، ثئخ انذبجض انزضذم ثئخ انجذش انمشجخ ي انذ ثئبدال
. انفزح
الأن ، ي انذنزخ يشدهزإن ف كم انمبطع اشبس نهززبثع انرج انزذش عيب ،
أنذ انذسح انثبخ انزثهخ ثبنجضء ثبندمف انجضء الأسفم ي رك انذيبو انزثهخ
ثجبد ثمبء فزشح أطل ف طبق انخهظ ثسجت ظشف انز أشبسد إن الأعه نهزك فس
انفشاد انفبم ثسجت الاسرفبع لادع غبة انذنزخ نزكبانعبن ، يسز سطخ انجذش
نسهكزخ أدبب كبذ الامطبع انذبصم ف صي الانغس ، ا دانسشع نسز سطخ انجذش ثع
. يصبدجخ إن عهخ انذنزخ
افخ إن أاع يخزهفخ ي انزسذ ف رك انذيبو ضراجذ عهخ انزشكم انجذذ ثبلإ إ
طبق انب انعزثخ ) ثأ انزك رشست ض انجئخ انزذشخ سجخدنمبطع كشثلاء انسب
إعبدح .أضب خلال ركب انفشاد انفبم دذثذ عهخ انزشكم انجذذ انسزخ .(انفعبل
. دذثذ ثست جد انكثش ي انخضابد انبئخ انعشفخ ف انطمخ اوةانذنزخ س
ح ي انذسجخ انثبنثخ رى رشخصب ض رك انذيبو ف يمطع خسخ دساد سسث
انسبح ثسجت انزمهجبد انثبخ نسز سطخ انجذش ف انذسح انشاثعخ فأب لسذ إن
، ف يمطع انجف فمذ رى رض دسح سسثخ أخش، دسر سسثز ي انذسجخ انشاثعخ
98
انذساد انشسثخ رثم فزشاد ي ، ر نى رخزشق ف يمطع كشثلاء فب أل دسر سسث
رزجعب ( رزثم ثسذبد انب انجذشخ انضذهخ انفزدخ انعمخ ) اسرفبع يسز سطخ انجذش
. فزشاد ثجبد نسز سطخ انجذش انزثهخ ثسذبد انذبجض انضذم
ثبنذيهكبد انمبعذخ انزثم SB1انذذ انفبصم ث رك انفشاد انذيبو ي ع
يزش ف يمطع كشثلاء ثسك لذس أسثعخ أيزبس ف كم ي يمطع 0.8ثسبكبد يخزهفخ ،
.انسبح انجف
خلال اسرفبع يسز سطخ انجذش ثعذ عصش الانغس أد إن راجذ ثلاثخ دساد
رهف ثزبثهب ثسبكبرب أبط ز انذساد رخ، سسثخ ي انذسجخ انثبنثخ نهمبطع انثلاثخ
انزكذس انسذ نب ي يمطع لأخش زا ادزبل ست إن انزغشاد انذهخ ف انزجهس
. انزكز انز اثش ف سشعخ اسرفبع يسز سطخ انجذش انسج
انفشاد فأ راجذ فق دذح نزك( انبججسب) ف انذساسخ انذبنخ ، انزذجش انذال
. انبسل الأخضش ي انجضء الأسفم نزك انفبم
99
وزارة التعليم العالي والبحث العلمي جامعة بغداد
العراق ـ بغداد
مايوسين في –تتابع الايوسين تحليل السحنات المجهرية وطباقية ، جنوب غرب العراق ( السماوة-النجف-كربلاء)
رسالة مقدمة إلى كلية العلوم ـ جامعة بغداد
وهي جزء من متطلبات نيل درجة الماجستير في علم الأرض
من قبل
ضياء خرباط شذر
بأشراف الأستاذ المساعد لميس صادق حسون
2011
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