University of Baghdad

MINISTRY OF HIGHER EDUCATION AND SCIENTIFIC RESEARCH UNIVERSITY OF BAGHDAD COLLEGE OF SCIENCE DEPARTMENT OF GEOLOGY

STRUCTURAL ANALYSIS OF KOSRAT ANTICLINE AND ITS TECTONIC IMPLICATIONS, NORTHEASTERN IRAQ A thesis Submitted to the College of Science University of Baghdad In partial fulfillment of the requirements for the degree of Doctor of Philosophy In Geology (Structural Geology) By

Janan Mansour Gorael Barno M.Sc. 2001

Supervised By Dr. Manal Shakir Alkubaisi Asst. Professor

Dr. Nabeel Kadir Alazawi Professor

2014

Supervisor’s Certification We certify that this thesis in titled (Structural Analysis of Kosrat Anticline and Its Tectonic Implications, Northeastern Iraq) was prepared under our supervision at the Department of Geology, college of Science, University of Baghdad in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Structural Geology.

Signature: Supervisor: Asst. Professor Dr. Manal Shakir Ali Alkubaisi Address: College of Science – Baghdad University Date:

Signature: Co-supervisor: Professor Dr. Nabeel Kadir Bakir Alazawi Address: College of Science – Mosul University Date:

Certification of the Department In view of the available recommendations, I forward this thesis for debate by the examining committee.

Signature: Name: Chairman of Geology Department Date:

Declaration This is to certify that the dissertation / thesis titled

Structural Analysis of Kosrat Anticline and Its Tectonic Implications, Northeastern Iraq

Submitted by: Janan Mansour Gorael Barno Department of Geology College of Science – Baghdad University

Has been written under my linguistic supervision and its language, in its present form, is quite acceptable.

Name: Dr. Ameen I. Al-Yasi Address: College of Science – Baghdad University Signature:

Examining Committee Approval We, the Examining committee, here by certify that we have read this Thesis and examined the student in its contents and whatever relevant to it and, in our opinion; it is adequate for the Degree of Doctor of philosophy in Structural Geology. Signature: Name: Dr. Dhiaa Y. Alrawi Title: Professor Address: Baghdad University Date: / / 2014 (Chairman)

Signature: Name: Dr. Ayser M. Alshamaa Title: Professor Address: Baghdad University Date: / / 2014 (Member)

Signature: Name: Dr. Thamer A. Alshammary Title: Professor Address: Baghdad University Date: / / 2014 (Member)

Signature: Name: Dr. Munther A. Taha Title: Professor Address: Diyala University Date: / / 2014 (Member)

Signature: Name: Dr. Mohamed R. Abod Title: Assistant Professor Address: Tikret University Date: / / 2014 (Member)

Signature: Name: Dr. Manal Sh. Alkubaisi Title: Assistant Professor Address: Baghdad University Date: / / 2014 (Supervisor & Member)

Signature: Name: Dr. Nabeel K. Alazawi Title: Professor Address: Mosul University Date: / / 2014 (Co-Supervisor & Member)

Approved by the Council of the College of Science Signature: Name: Title: Address: Date: /

/ 2014

Acknowledgments I wish to express my great gratitude and appreciation to my supervisors, Assistant Professor Dr. Manal Shakir Ali Alkubaisi (University of Baghdad) & Professor Dr. Nabeel Kadir Bakir Alazawi (University of Mosul) for their continuous supervisions, encouragement, kindness, friendliness & valuable help during my study. I am thankful to the college of Science and Department of Geology, University of Baghdad for providing available facilities and administrative supports. I am also thankful to the State Company for Geological Survey and Mining of Iraq and to the General Commission of Survey in Iraq for their kind and considerable assistance. My thanks also to administration of Dokan district in Province of Sulaymania for their kind cooperation and facilities during my field study. Thanks are also to the committee of the field course for undergraduates in Geology Dept. at University of Baghdad especially Dr. Saad Alsheikhly, Dr. Mazin Tamragha, Dr. Thamer Alshammary, Dr. Medhet Elewi and Dr. Salman Zain Alabdin for their valuable advice, effective help and supports during the stages of my study, and I am thankful to Dr. Saad Zeki who helped me in thin sections interpretations. My thanks to my colleague Mr. Atheer Edan for his cooperation in the field and to Dr. Arsalan Aljaf (Geosurve) and Dr. Rabeea Khalaf (University of Mosul) for their encouragement and supports. Thanks are also due to all my colleagues in the Department of Geology, for their assistance and continuous encouragement during my study and to those that helped me in one way or another.

I

Abstract Kosrat Anticline structure in northeastern part of Iraq has been studied from structural and tectonic points of view. The study area is located within the high folded zone of the Zagros Fold Thrust Belt in northeast of Iraq, between (E 44o 48' 36" – 44o 58' 12") latitude and (N 35o 54' 36" – 36o 01' 48") longitude. The 15 Km. tracing length of the fold and the strike of the strata are of NW-SE direction in accordance with the main trend of Zagros folds. The exposed rocks of the studied region range in age from Lower Cretaceous up to the Middle Pliocene, comprising by Qamchuqa, Dokan, Gulneri, Kometan, Shiranish, Tanjero, Kolosh, Sinjar, Khurmala, Gercus, Pila Spi, Fatha, Injana, Mukdadiya and Bai Hassan formations. The anticline was described and classified according to the field measurements. The relation between the axial plane and the two limbs was determined to find the symmetry of the anticline. The southwestern limb is steeper and shorter than the northeastern one which makes it asymmetrical anticline verging towards southwest. As the northeastern limb dips 21o and the southwestern one dips 30o. The fold is double plunged anticline. A geometrical classification was carried out using the interlimb angle and according to Fleuty, 1964 the fold is classified to be a gentle fold. Folding Kinematics model was based on the changing of the competency of the formations to have a flexural slip fold that controlled by the compositions of the layers and the primary response of each rock unit to deformation. Many types of fractures were observed in the field, such as Veins, Fissures, Joints, Faults, Striations and stylolites. The analysis was carried out only to Joints, Faults, Striations and stylolites. The Joints were classified and analyzed according to the relation between the Joint surface and the principal tectonic axis of the Anticline. It showed abundant distribution of the systems (in downward order according to their II

percentages) ab, hko>a, hkl as first order. ac, bc, hko>b, hol>c, okl>c in the second order and in the third order are okl>b and hol>a which is form in the inner arc of the fold that make it unobservable in spite of being the maximum stress direction coincides with major compressive stress that formed the anticline. The analysis revealed that the joints might be due to the influence of the main horizontal compression stress that is responsible of folding, or it might be caused by the stretching of the outer arc for the folded layers. Faults in the study area have been identified. Dynamic analysis of the faults revealed that thrust faults are predominating over the Normal and StrikeSlip faults, which confirms the prevalence of thrusting due to Arabian Plate collision especially in the southwestern limb of the anticline. Strike – slip faults were observed in the southwestern limb which might be sharing the same main stress direction of the thrust faults. Normal faults could be resulted from the extension caused by the folding especially in the outer arcs of the folded layers. The observed striations reflect the sense of slip orientation by fault movement on a fault surface, the obtained field data were analyzed by using P&T method which is designed for a single fault plane data to find the direction for the compressional and extensional axis that is near to σ1 and σ3 respectively. The Stylolites were analyzed and classified geometrically and according to the relation of the host rock bedding planes. Two sets of stylolite surfaces were recorded; one parallel to bedding planes which might cause due to of the overburden load "non-tectonic origin" and the other perpendicular to the bedding planes as a result of tectonic activity, the direction of the stylolite teeth in the perpendicular one is a good indicator for the main compressional stress direction which is towards northeast in the case of the study area.

III

Structural and tectonic history of Kosrat Anticline was phrased according to the study of faults that have been reactivated. The deduction of the reactivation was through the comparison between the thicknesses of the geologic formations in both limbs of the anticline as thickness of Kometan Formation in the northeastern limb is approximately double than on the southwestern limb, which gives a clue to the presence of inverted listric fault that is parallel to the fold axis and the lithological units sequence indicates for a positive inversion tectonic. Thin sections analysis for rock samples in an extension fractures showed the evidence of a faulting mechanism representing by the deformed crystals to give a clue of being an inverted faults in Kosrat Anticline.

IV

LIST OF CONTENTS

No. 1.1 1.2 1.3 1.3.1 1.4 1.4.1 1.4.2 1.5 1.6

2.1 2.2 2.3 2.3.1 2.3.2 2.3.3 2.3.4 2.4 2.4.1 2.4.2 2.5 2.6 2.7 2.8 2.8.1 2.8.2 2.8.3 2.9 2.9.1 2.9.2 2.9.3 2.10

Subject

Page

CHAPTER ONE Location of the Study Area Aim of the Study Data Acquisition Software that used for data analysis Literature Review Regional Tectonics and Structural Studies Geological Researches Stratigraphy of the Study Area Tectonic Settings CHAPTER TWO General Description of Folds Fold in three dimensions Classification Criteria for Folds in Rocks Classification of Folds According To Their Symmetry Geometrical Classification of Folds Morphological Classification of Folds Fold tightness Causes of folding Layer-parallel shortening Fault-related folding General Field Description of Kosrat Anticline Geometric Analysis Geometrical Description Folding Mechanism Active Folding or Buckling Passive Folding Bending Folds Folding Kinematics Models Flexural Slip/Flow Folding Neutral Surface Folding Shear Folding Multilayered Fold Controlling Factors

1 1 2 3 5 5 7 7 27

30 32 34 34 36 38 39 40 40 40 47 49 55 63 63 65 66 67 67 68 69 70

CHAPTER THREE 3.1 3.1.1

Joints Geometric Analysis of Joints V

76 77

3.1.2 3.1.3 3.1.4 3.1.5 3.1.6 3.2 3.2.1 3.2.2 3.2.2.1 3.2.2.2 3.2.2.3 3.2.3 3.2.4 3.2.4.1 3.2.4.2 3.2.4.3 3.2.4.4 3.2.5 3.3 3.3.1 3.4 3.4.1 3.4.2 3.4.3 3.5

4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8

Joint Systems in the Study Area Joint Analysis in the Study Area Fracture Frequency and Spacing Fracture Development Data Analysis Faults Faults and Forces Types of Faults Normal faults strike – slip faults Thrust Faults Thrust trajectory Types of Duplex Structures Hinterland-dipping duplex Antiformal Stack Foreland-dipping duple Out of Sequence Faulting In Kosrat Anticline Slickensides Slickensides of Kosrat Anticline Stylolites Stylolite Classification Pressure Solution Process The Use of Stylolites for Structural Analysis Stylolites in the study area CHAPTER FOUR Structural Inversion Positive Inversion of Extensional Fault Systems Negative Inversion of Contractional Fault Systems Controls on the Geometry of Tectonic Inversion Economic Importance Models of Inversion Tectonics Stratigraphic Separation as Criteria for Fault Reactivation Inversion Tectonics in the Study Area

78 90 90 92 93 104 104 105 106 108 110 111 113 114 115 115 116 118 133 134 147 149 152 155 156

160 161 163 166 167 167 173 174

CHAPTER FIVE 5.1 5.2

Conclusions Recommendations

185 188

References

189 VI

LIST OF FIGURES

No.

Figure Name

Page

1-1 1-2 1-3 1-4 1-5 1-6 1-7 1-8 1-9 1-10 1-11 1-12 1-13 1-14 1-15

CHAPTER ONE Location of the Study Area Geological Software used in the study Geological Map of the Study Area Qamchuqa limestone Formation Dokan Limestone Formation Gulneri Shale Formation Kometan Formation Shiranish Formation Tanjero Formation Sinjar Formation Kolosh and Khurmala Formations Gercus Formation Pela Spi Formation Arabian Plate Boundaries Tectonic zones and structural elements

3 4 8 9 11 13 14 16 18 21 22 23 24 27 29

2-1 2-2 2-3 2-4 2-5 2-6 2-7 2-8 2-9 2-10 2-11 2-12 2-13 2-14 2-15 2-16 2-17 2-18 2-19 2-20 2-21

CHAPTER TWO the important features of the fold The Enveloping Surface Axial surface and hinge line of a fold trend and plunge of fold hinge line Axial surface orientation in a fold Classification of folds Symmetric and asymmetric Schematic diagrams Types of folding according to their geometry Anticlinorium and Synclinorium Progressive developments of a fault-bend fold Formation of a rollover anticline fault-propagation fold the evolution of a symmetric detachment Topographic Map of the study area Study area in relation to surrounded structures Synoptic pi-diagram of the study area stereographic projection for each limb Qamchuqa Formation bedding planes attitude Kometan Formation bedding planes attitude Shiranish Formation bedding planes attitude

30 31 32 33 33 34 35 36 37 38 41 42 43 45 47 48 49 50 51 52 53

VII

2-22 2-23 2-34 2-25 2-26 2-27 2-28 2-29 2-30 2-31 2-32 2-33 2-34 2-35 2-36 2-37 2-38 2-39 2-40 2-41

Tanjero Formation bedding planes attitude Synoptic Pi-diagram of Kosrat Anticline Synoptic Pi-diagram of Kosrat Anticline Traverse 1 Synoptic Pi-diagram of Kosrat Anticline Traverse 2 Pi-diagram of Qamchuqa and Kometan – T1 Pi-diagram of Shiranish and Tanjero – T1 Pi-diagram of Kometan and Shiranish – T2 Pi-diagram of Tanjero – T2 The interlimb angle and wave length Small-scale disharmonic folds Buckling of a single layer Strain distribution of a folded layer Passive folding Bending in various settings and scales Flexural slip The strain pattern of neutral-surface folding strain pattern of shear folding The competency for some formations Suggested fold models resulted from listric faults Geological Map of the study area

54 55 56 57 58 59 69 61 62 62 64 65 65 66 67 68 69 72 73 75

3-1 3-2 3-3 3-4 3-5 3-6 3-7 3-8 3-9 3-10 3-11 3-12 3-13 3-14 3-15 3-16 3-17 3-18 3-19 3-20

CHAPTER THREE Geometrical classification of the joints ab fracture system ac fracture system Calcite veins in Shiranish Formation Tectonic Stylolite and bc joint hko acute about (a) fracture subsystem Movement on hol faults hol acute about (a) fracture subsystem hol acute about (c) fracture subsystem okl acute about (b) fracture subsystem okl acute about (c) fracture subsystem hkl fracture system and hko acute about (b) sys. Joint analysis of the study area Principal stresses and an extension fracture Joints ratio in Kosrat Anticline Synoptic Joint planes of Kosrat Anticline Synoptic Joint planes of Qamchuqa – T1 Synoptic Joint planes of Kometan – T1 Synoptic Joint planes of Shiranish – T1 Synoptic Joint planes of Tanjero– T1

78 79 80 81 82 83 84 85 86 87 88 89 91 93 94 95 96 97 98 99

VIII

3-21 3-22 3-23 3-24 3-25 3-26 3-27 3-28 3-29 3-30 3-31 3-32 3-33 3-34 3-35 3-36 3-37 3-38 3-39 3-40 3-41 3-42 3-43 3-44 4-45 3-46 3-47 3-48 3-49 3-50 3-51 3-52 3-53 3-54 3-55 3-56 3-57 3-58 3-59 3-60 3-61 3-62

Synoptic Joint planes of Kometan – T2 Synoptic Joint planes of Shiranish – T2 Synoptic Joint planes of Tanjero– T2 relationship between stresses and ideal faults Normal Faults formed due to radial stretching Listric and Domino Faults Geometries associated with strike-slip faults Tear Fault Flower Structures in Strike – Slip fault zone Flat and Ramp in Duplex Thrust System Ramps in thrust system Horses in a Duplex system The propagation of thrust system Hinterland – dipping Duplex Antiformal Stack Foreland – dipping duplex Out of Sequence Thrusting Normal Fault in Qamchuqa Formation Normal Fault in Dokan Formation Normal Fault in Kometan Formation Normal Fault in Shiranish Formation Vertical Fault in Tanjero Formation Normal Faults in Kometan Formation Strike – Slip Faults in Kometan Formation Positive Flower Structure in Tanjero Formation Thrust Faults in Kometan Formation Thrust Faults in Kometan Formation Thrust Faults in Kometan Formation Thrust Faults in Tanjero Formation Thrust Faults in Shiranish Formation Duplex Thrust System in Kometan Formation Duplex Thrust System in Kosrat Anticline Thrust Fault in SW Limb of Kosrat Anticline Pop-Up Structure Stress directions in thrust fault Pop – Up structure in the study area Slickenside on a fault plane in Kosrat Anticline Fault plane with two slickensides layers Scatter Plots of P and T axis for Slickenlines Slickensides in Kosrat Anticline Stylolite Stylolites in relation to compression IX

100 101 102 105 106 107 108 109 110 111 112 113 114 115 115 116 117 118 119 120 121 122 122 123 124 125 126 126 127 128 129 130 130 131 131 132 133 143 145 146 147 148

3-63 3-64 3-65 3-66 3-67 3-68 3-69 3-70 3-71

Stylolite classification according to their geometry classification of the stylolites in relation to the bedding plane Schematic diagram of pressure solution Stylolite in Kometan Formation Stylolite surface affected by two sets of veins Sketch showing typical stylolite teeth Stylolites in Kometan Formation in the study area Sketch showing the bedding parallel stylolites Vertical stylolites in the study area

4-13

CHAPTER FOUR classical positive inversion structure contractional inversion Negative Inversion Model for the development of a footwall Shortcut thrust system Domino Extensional Fault Systems Inversion of Simple Listric Fault Systems Inversion of Ramp/Flat Listric Fault Geometry normal fault reactivations Inverted fault in NE Limb of Kosrat Anticline Inverted fault Diagram in NE Limb Sketch section showing the footwall shortcut Dolomitic Limestone within Kometan Footwall Shortcuts in SW Limb of Kosrat Anticline

4-14 4-15 4-16

Thrust Fault in Southwestern limb Inverted faults in Kosrat Anticline Geological cross section of the study area

4-1 4-2 4-3 4-4 4-5 4-6 4-7 4-8 4-9 4-10 4-11 4-12

149 151 152 153 154 156 157 158 159

162 163 164 165 170 171 172 173 175 176 177 177 179 180 182 184

LIST OF TABLES

No. 2-1 2-2 3-1

Table Name Terms used to describe the tightness of a fold Kosrat Anticline Formations competency slickensides stations analysis in Kosrat anticline

X

Page 39 72 135

Chapter One

Introduction

CHAPTER ONE INTRODUCTION 1.1: Geographical Location of the Study Area: Kosrat Anticline is a part of the high folded zone of the Zagros simply folded belt in north Iraq, it lies between longitudes (E 44o 48' 36") and (E 44o 58' 12") East and latitudes ( N 35o 54' 36") and (N 36o 01' 48") North in the Iraqi Kurdistan Region in Sulaimaniyah Province on the western side of Dokan lake (Figure 1 – 1). The area covers about (200) square Kilometers It is surrounded by distinguished structures such as Surdash (Sara) Anticline in the Southeast side, Khalakan Anticline in the Northeast side, Dokan Lake to the East and Northeast side. The study area extended to the Southwest to include Haibat Sultan Mountain.

1.2: Aim of the Study: The study focuses on a general and detailed structural study by: 1- Finding the relation of structural and tectonic analysis with the surrounding structures to the anticline. 2- Studying the type of folding mechanism that is related to the stress acting on layered rocks. 3- Studying the models of folding kinematics which is associated with the strain pattern and the factors that control the folding. 4- Fracture analysis (Joints, Faults, Striation and Stylolites) are within the study aim as well to be classified and analyzed to find geometrical and genetic

1

Chapter One

Introduction

relationship with the principal tectonic axes of the anticline that acts on the study area for paleostress analysis. 5- Reconstructing the structure and tectonic history of the studied anticline.

1.3: Data Acquisition: The data in this study were acquired mainly from field measurements and observations through field work which was carried out in the studied area and satellite imagery. The first reconnaissance field trip was started at August 2011 and the field work continued to the end of November 2011. The other periods of field work were lasted three months between April and June and in September 2012, June 2013 after that other short trips were carried out for checking some measurements during analysis of data and drawing the geological map. The tools used in the field are: Silva Ranger Compass type 15, Hammer, digital camera, notebooks, measuring tape and GPS type Garmin - eTrex vista hiking companion were used in the field to mark the locations, elevations and the attitude of the geological features on the topographic maps. Topographic maps of scales 1:20000 which were printed in April 1956 were used as base maps. In spite of many demographic changes that have been occurred since then (change and removing locations) the aid of remote sensing images from Google Earth was used to appoint roads and shortcuts before trips, Checking latitudes and longitudes with the GPS reading and maps; and Interpret structural relationships some times were performed.

2

Chapter One

Introduction

1.3.1: Software that used for data analysis: Many of the geological software were used for analyzing the data of the bedding planes, joint planes, and striations of fault planes and graphic software for drawing the geological map, diagrams, cross sections and interpreting pictures that were taken for different structures in the field.

(Figure 1 – 1) Location map of the Study Area

3

Chapter One

Introduction

The geological software's (Figure 1 – 2) that were used are: 1- GEOrient ver.9.5.0 2- GeoCalculator 4.9.7 3- Global Mapper ver 11.02 4- Stereo 32 These software used for determining attitudes of the bedding planes for each limb of the anticline, fold axis, axial plane, joint analysis as a pole plots and Striations or slickensides orientation to find P&T by stereographic projections and Interlimb angles.

(Figure 1 – 2) Geological Software used in the study

4

Chapter One

Introduction

1.4: Literature Review: Many geological, tectonic and structural researches were carried out in the north and northeastern of Iraq (in the high folded zone) some of them included parts of the study area. These researches were divided into two parts. The first part was concerned with the structural and tectonical aspects and the other part was related to the geological researches in the study area, which were summarized as in the following: 1.4.1: Regional Tectonics and Structural Studies:

1-

Numan

and

Al-Azzawi,

1993.

Structural

and

geotectonic

interpretation of vergence directions of anticlines in the Foreland folds in Iraq, they pointed to the influence of the extensional and wrench tectonics for opposing the vergence direction of anticline.

2-

Taha, et al., 1995. A microtectonics study was carried out for Dokan area NE Iraq and came up with the conclusion that the area was subjected to two major compressive tectonic phases which are NNE-SSW and E-W.

3-

Marouf, 1999. Studied the Thrust, Folded and Unfolded Zones in tectonic points of view in his study on the dynamic evolution of the sedimentary basins in northern Iraq and hydrocarbon formation, migration and entrapment. He pointed to shortening ranging between 2% to 27%.

4-

Al-kubaisi, 2000. A morphotectonic analysis was carried out on the Tigris River and its tributaries basins, within the folded zone of Iraq

5

Chapter One

Introduction

A relationship between structural factors and lithology that affecting the type of drainage pattern was determined by the assist of longitudinal cross section analysis of the basin. It was deducted from linear structures analysis that the general trend direction of the tributaries coincide with the general direction of the transversal faults.

5-

Al-Jumaily, 2004, gave a tectonic interpretation of the brittle failure structures of the Foreland Folds in Iraq.

6-

Omar, 2005. Draws a detailed structural map for the Bina BawiSafin-Bradost anticlines using Panchromatic Aerial-photo, Landsat images at different bands and its combinations incomposite color, as well as Thermal band of Landsat TM. And he proposed that most of the folds in the high fold zone are Fault-Propagation folds and/or Fault-bend Folds.

7-

Karim et al., 2009. The study dealt with the location, types and historical development of the lineaments in western Zagros Mountain Belt that is located parallel to Iranian –Iraqi border.

8-

Al-Hakari, 2011. Azmar, Surdash, Piramagroon, Sulaimani, Miran and Darbandi Bazian-Sagrma-Qaradagh structures which located within the high folded and imbricated zones of the northwestern segment of the Zagros Foreland Fold Thrust Belt in northeast of Iraq, have been studied from structural and tectonic points of view.

6

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Introduction

1.4.2: Geological Researches: 1- Karim, 2005. Ball and Pillow-like Structures were studied in Tanjero and Kolosh Formations in Sulaimaniya area, NE-Iraq in several localities and he concluded that they were formed during burial after deposition by differential load pressure and tectonic stresses. No evidence is found to relate the recorded ball-and- pillow to the deposition or early digenetic process. 2- Al-Barzinjy, 2008. Studied the origin Chert nodules in Kometan Formation - Dokan Area which are widespread and associated with well-developed and high amplitude stylolites. The growth of the nodules and stylolites are attributed to deep burial diagenesis of the rocks of the formation under vertical lithostatic pressure and not due to tectonic stress.

3-

Karim et al., 2008. Studied the contact between Kometan and Shiranish Formations (Cretaceous) in Sulaymania governorate, Kurdistan region, NE Iraq. It is described and analyzed in eight different sections and grouped into three types.

4-

Taha and Karim, 2009. New ideas about Gulneri Formation (Early Turonian) In Dokan Area, Kurdistan Region, NE Iraq were studied about the consistence and depositional environment.

1.5: Stratigraphy of the Study Area: The exposed rocks, in the studied region range in age from Early Cretaceous up to the Middle Pliocene (Figure 1 – 3). They are represented

7

Chapter One

Introduction

by fourteen Formations, which are briefly explained from older to younger according to field observations.

(Figure 1 – 3) Geological Map of the Study Area (Sissakian, 2000)

8

Chapter One

Introduction

1- Qamchuqa Limestone Formation: Cretaceous (Hauterivian – Albian) Qamchuqa limestone Formation is the important, massive, feature-forming limestone unit of the Middle-Lower Cretaceous succession in Kurdistan – Iraq. It forms the carapace of some of the more impressive anticlinal

(Figure 1 – 4) Qamchuqa limestone Formation in the core of Kosrat Anticline

9

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Introduction

mountains in the folded belt, (Bellen et al., 1959). It forms the core of Kosrat Anticline (Figure 1 – 4). The section is 799 meters thick, the upper part of it comprising generally coarsely crystalline, granular, rhombic and mosaic dolomites replacing neritic, organic limestone with molluscan detritus. The lower part comprises of very coarsely crystalline dolomite without significant vestiges of original fauna (Bellen et al., 1959). The formation was deposited in neritic, sometimes shoal environment (Buday, 1980). The upper contact is marked by a break and is either non-sequential or unconformable; it is an unconformity in N Central, N and NE part of Iraq (Jassim and Goff, 2006). The competent beds consist of massive dolomite (Ameen, 2008). Calcite veins and irregular erosional face are well obvious on the outcrop.

2- Dokan Limestone Formation: Cretaceous (Cenomanian) Dokan Limestone was formerly included in the Kometan Formation. It was first described as a separate formation by Lancaster and Jones in 1957 (Bellen et al., 1959). The type locality is on the site of the Dokan Dam in the high folded zone of northeastern Iraq. It comprises 5 meters of light colored grey and white oligosteginal limestone, locally rubbly, with glauconitic coatings of the pebble-like masses (Bellen et al., 1959). The environment of the deposition is an open marine, evidenced by the abundant pelagic faunal elements, including Ammonite, it corresponds to the maximum extent of the Cenomanian transgression (Buday, 1980).

10

Chapter One

Introduction

Both the lower and upper contacts of the formation in the type area are unconformable. The overlying formations are of Turonian age, mostly represented by the Kometan Formation. Dokan Formation occurs in a restricted area in the High Folded and Foothill zones, (Jassim and Goff, 2006). Figure (1 – 5) shows Dokan Limestone Formation near Dokan dam site in Kosrat Anticline. The formation is well bedded and a massive competent unit rich with calcite crystals and veins.

(Figure 1 – 5) Dokan Limestone Formation in Kosrat Anticline

11

Chapter One

Introduction

3- Gulneri Shale Formation: Cretaceous (Turonian) Gulneri shale Formation was first described by Lancaster Jones (1957) in (Bellen et al., 1959) from the Dokan Dam site, in the High Folded Zone to the North of Sulaymania city in Iraq (Jassim and Goff, 2006). Where it consists mainly of about 1.2 – 2 meters thickness of marl and marly limestone with no more than 20% of laminated shale (Taha and Karim, 2009). The formation occupies a peculiar position within the Turonian – Lower Campanian subcycle (Buday, 1980). The Formation is separated by unconformities of both the underlying "Dokan Formation" and overlying "Kometan Formation" (Buday, 1980). Both unconformities are erosional one (Bellen et al., 1959). The high bitumen content and fossils indicate the formation was deposited in an euxinic environment (Bellen et al., 1959) and small relic (recession of water from the land) basin (Taha and Karim, 2009). The shale is highly deformed, which has foliation-like texture. Therefore, the previously described shale is originally marl, which is changed to laminated shale-like rock, by pressure that released insoluble residue and bitumen materials from surrounding rocks, by filtering of these materials, the marl was changed to black shale-like rock (Taha and Karim, 2009). Figure (1 – 6) shows Gulneri Shale Formation in Kosrat Anticline Northeastern limb.

12

Chapter One

Introduction

(Figure 1 – 6) Gulneri Shale Formation in Kosrat Anticline

4- Kometan Formation: Late Cretaceous (Turonian) Kometan Formation was defined by Dunnington, in 1953 from the Kometan village near Endezah in NE Iraq (Jassim and Goff, 2006). The type section is located at 400 meters to the West of Kometan village in the Naudasht valley in the foothills of Qandil Mountain about 20 km to the north of Ranyia town in the Imbricated Zone (Karim et al., 2008). The formation comprises 260 meters of light grey, thin bedded, globigerinal oligosteginal limestone, locally silicified "with Chert nodules in some beds" with a glauconitic bed at the base, it is differential by color and by weathering characteristics from the adjacent formation (Bellen et al., 1959).

13

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Introduction

(Figure 1 – 7) Kometan Formation in Kosrat Anticline

14

Chapter One

Introduction

Chert nodules become widespread and associated with well-developed and high amplitude stylolites, they are mainly distributed along or around the bedding planes, the long axes of nodules and stylolite surfaces are aligned parallel to the bedding plane, the growth of the nodules and stylolites are attributed to deep burial diagenesis of the rocks of the formation under vertical litho-static pressure and not due to tectonic stress (Al-Barzinjy, 2008). The age of the formation is ascertained, the typical Kometan facies is Lower (but not basal) Turonian at the base, and Santonian at the top (Buday, 1980). The lower contact of the formation with Albian-Cenomanian formations is an unconformity and the upper boundary is a disconformity (Bellen et al, 1959, Buday, 1980 and Jassim and Goff, 2006). Sediments of the Kometan Formation were deposited in different environments ranging from shallow shelf to open marine (Jassim and Goff 2006). Figure (1 – 7) shows Kometan Formation in the study area.

5- Shiranish Formation: Late Cretaceous Shiranish Formation was defined by Henson (1940) from the High Folded Zone of Northern Iraq near the village of Shiranish Islam, NE of Zakho. (Bellen et al., 1959 and Buday, 1980). The formation in its type area is composed of blue marl in its upper parts and of thin bedded marly limestone in the lower part. The sediments are

15

Chapter One

Introduction

(Figure 1 – 8) Shiranish Formation in Kosrat Anticline

16

Chapter One

Introduction

pelagic marls, sometimes dolomitic and marly limestone beds (Buday, 1980). In the study area, Shiranish Formation is 378 meters thick. In other outcrop areas it varies in thickness from 100 to 400 m. Fossils are very abundant in Shiranish Formation; they confirm that the formation is of Late Campanian-Maastrichtian age. (Kassab, 1972 and 1973 in Jassim and Goff, 2006). The lower contact of the formation with the underlying Kometan Formation is disconformable, and it is gradational with overlaying Tanjero Formation (Bellen et al, 1959, Jassim and Goff, 2006). Shiranish formation in its type development is a typical deeper open sea sediments (outer shelf - basinal) environment (Buday, 1980 & Jassim and Goff, 2006). Figure (1 – 8) shows Shiranish Formation in the study area.

6- Tanjero Clastic Formation: Late Cretaceous Tanjero Clastic Formation belongs to the typical formations of the miogeosynclinal area of Iraq (Buday, 1980). The formation was first defined by Dunnington, in 1952. The type locality of the formation lies in the Sirwan valley, southeast of Sulaymania city and belongs structurally to the imbricated zone (Buday, 1980). The thickness of the formation is variable; the maximum thickness of the formation is about 2000 m between Rowanduz and Chuwarta (Jassim and Goff, 2006). But in the study area is 870 meters.

17

Chapter One

Introduction

(Figure 1 – 9) Tanjero Formation in Kosrat Anticline

18

Chapter One

Introduction

The age of the formation is Upper Cretaceous; the upper part is Maastrichtian whereas the lower part is Maastrichtian at top and late upper Campanian at base (Bellen et al., 1959). The formation is composed mainly of alternation of sandstones, claystones, shale, and beds of conglomerates that have dark yellowish green and olive green colors with common lateral and vertical variation. The formation was deposited as flysch in a rapidly subsiding fore deep basin immediately in front of the thrust sheets of the obducted margin of the Southern Neo-Tethys. The onset of flysch deposition occurred when these thrust sheets were elevated above sea level and rapidly eroded (Jassim and Goff 2006). The formation usually conformably and gradationally overlies the Shiranish Formation. This contact is recognizable in the field by the first appearance of the interbedded sandstones and marls, as well as the change in color between Shiranish and Tanjero formations is very clear in the field. The upper contact commonly unconformable with the overlying Kolosh Formation (Bellen et al., 1959). It is distinguished in the field by the change of colors from olive green for Tanjero Formation to the dark gray for Kolosh formation. Figure (1 – 9) shows Tanjero Clastic Formation in the study area. 7- Kolosh Formation: Paleocene – lower Eocene Kolosh Formation was first described by Dunnington in 1952 from Kolosh village, North of Koi Sanjak, in the High Folded Zone Northeast of Iraq (Jassim and Goff, 2006).

19

Chapter One

Introduction

Kolosh Formation is about 400 meters thickness in the type area and it was deposited in a marginal marine depositional environment in a narrow rapidly subsiding trough (Jassim and Goff, 2006). The basic sediments of the formation lithology are shale and fine grained sandstone, composed of fragments of various grain sizes of green-rock, Chert and radiolarite (Bellen et al., 1959). The formation unconformably overlies Upper Cretaceous beds. In the type area it overlies the Tanjero Clastic Formation; the clastics of the Kolosh were derived from erosion of the Tanjero, Qulqula and other CretaceousJurassic formations. Bellen et al. (1959) suggested that the upper boundary of the Kolosh Formation was unconformable. However, where the Kolosh is overlain by Palaeocene - Lower Eocene limestones (as in the type section) the upper boundary is conformable and gradational (Jassim and Goff 2006).

8-

Sinjar Limestone Formation: Paleocene – Lower Eocene

Sinjar formation was first described from the Jebal Sinjar area near Mamissia village by Killer (1941) in (Bellen et al., 1959). The formation deposited in reef, fore reef and lagoonal environments. The lithology of the formation is reefal limestone, fore reef limestone, and lagoonal dolomitic limestone. The thickness of the formation is about 170 meters in the type section. In the study area the thickness is around 150 meters. The age of the formation is Late Paleocene - Early Eocene. In the study area Sinjar Formation inter-fingering with Khurmala Formation unconformably (Figure 1 – 10) (Jassim and Goff 2006).

20

Chapter One

Introduction

(Figure 1 – 10) Sinjar Formation in the study area

9- Khurmala Formation: Paleocene – Lower Eocene Khurmala Formation was described by Bellen in 1953 in the Kirkuk-114 well (Bellen et al., 1959) thickness of the formation is around 200 meters in the study area, lithology comprises of argillaceous limestone and marls. The calcareous beds inter-fingering strongly with material from Kolosh Formation. The environment of deposition is a restricted lagoon environment. The lower contact of the formation is usually gradational with Kolosh Formation which inter-fingers with (Figure 1 – 11) and the upper contact is probably erosional surface (Jassim and Goff 2006).

21

Chapter One

Introduction

(Figure 1 – 11) Kolosh and Khurmala Formations in Kosrat Anticline

10- Gercus Formation: Middle Eocene The formation was first described by Maxon in 1936 in the Gercus region SE Turkey, which extends into the Iraqi High Folded Zone (Bellen et al., 1959). A supplementary type section for Iraq was described by Wetzel from the Dohuk area North Iraq (originally referred to as the Dohuk Red Beds). It comprises 850 meters of red and purple shales, mudstones, sandy and gritty marls, pebbly sandstones and conglomerates. Gypsum lenses and halite occur near the top of the formation (Jassim and Goff, 2006). The thickness of the formation in the study area (Figure 1 – 12) is around few meters. The formation was deposited in a relatively broad trough

22

Chapter One

Introduction

(foredeep) along the NE margin of the Middle Eocene basin. The age of the formation considered of Middle Eocene. Gercus Formation overlies the Lower Eocene Khurmala Formation and interfingers with the Avanah Formation. In both these localities the Gercus is overlain by the Pila Spi Formation. These stratigraphic relationships indicate that the Gercus Formation is of late Early Eocene to Middle Eocene age (Bellen et al., 1959).

(Figure 1 – 12) Gercus Formation in the study area

23

Chapter One

Introduction

11- Pila Spi Formation: Middle – Late Eocene Pila Spi Formation was described for the first time by Less (1930) in (Buday, 1980) in its type locality near Pila Spi village at the southern part of high folded zone. The age is Late Eocene (Bellen et al, 1959). The thickness is about 40 meters (Figure 1 – 13). The formation overlaying Gercus Formation conformably and overlain by Fatha Formation unconformably, in the supplementary type section it consists of dolomitic and chalky limestone with Chert nodules (Bellen et al., 1959). The formation was deposited in a shallow lagoon. Fossils are abundant and indicate a Late Eocene age. In North Iraq the formation may be partly of Middle Eocene age (Jassim and Goff, 2006).

(Figure 1 – 13) Pela Spi Formation in the study area

24

Chapter One

Introduction

12- Fatha (Lower Fars) Formation: Middle Miocene Fatha Formation is one of the most aerially widespread in Iraq. It comprises anhydrite, gypsum and salt, interbedded with limestone and marl. The formation is deposited in Middle Miocene evaporitic lagoon and has wide spread outcrops in the northeastern Iraq (Bellen et al, 1959). The formation overlay Pila Spi Formation unconformably and overlain by Injana Formation conformably. The thickness of the formation is very variable; it ranged between 100 to 900 meters. In the High Folded Zone a limestone, sandstone and mudstone succession (equivalent to the Fatha Formation) is occasionally preserved in synclines (Jassim and Goff, 2006). 13 – Injana (Upper Fars) Formation: Late Miocene: The formation comprises from cycles of sandstone, siltstone, and red mudstone the thickness of the sandstone beds are increased upward. The age of the formation is usually accepted as Late Miocene (Jassim& Goff.2006). The formation comprises fine grained pre-molasse sediments deposited initially in coastal areas and later in the fluviolacustrine system (Jassim and Goff, 2006). The formation overlaid Fatha Formation conformably; the contact is detected by the first appearing of the sandstone beds of Injana Formation.

The

formation

overlain

by

Mukdadiyah

Formation

gradationally, the contact is marked by appearance of pebbly sandstone. The average thickness is about 700 meters (Jassim and Goff, 2006). No fossil evidence has been found, it is probable that the age is high Miocene (Bellen et al, 1959).

25

Chapter One

Introduction

14 - Mukdadiya and Bai Hassan (Lower and Upper Bakhtiari) formations: The two formations are strongly diachronous but can be recognized throughout the Foothill and High Folded zones. The names Mukdadiya and Bai Hassan Formations were used by Jassim et al. (1984) to replace the Lower and Upper Bakhtiari formations respectively (Jassim and Goff, 2006). Mukdadiya (Lower Bakhtiari) Formation comprises up to 2000 meters of fining upwards cycles of gravely sandstone, sandstone and red mudstone. The Formation was deposited in fluvial environment in a rapidly subsiding foredeep basin. The age based on the vertebrate fauna is Late Miocene (Bellen et al., 1959). The lower contact is recognized lithologically by the first occurrence of the pebbly sands. It is distributed mostly in the Foothill Zone. It is replaced almost totally by 3000 meters of conglomerates of the Bai Hassan (Upper Bakhtiari) conglomeratic facies in the High Folded Zone of Northeastern Iraq which is the youngest formation in the stratigraphic column of the study area. It is of Middle Pliocene age (Jassim and Goff, 2006). The lower contact of the formation with underlying Mukdadiya Formation is diachronous (Buday, 1980); it is recognized lithologically by the appearance of the first thick (more than 1meter) conglomerate horizon (Sissakian & Youkhanna, 1978 in Omar, 2005). The formation was deposited in alluvial fans originated from the erosion of the rising mountains in the High Folded Zone and the Zagros Suture into sinking basins (Bellen et al., 1959) and hinterland of orogenic morphology.

26

Chapter One

Introduction

1.6: Tectonic Settings: Zagros fold and thrust belt in Iraq are parts of the main Zagros folds and thrust belt that extends form south-west Iran to south-east Turkey (Figure 1 – 14) between Oman right lateral strike slip fault in the extreme south east to the junction of the left lateral levant with South Anatolian strike slip faults just north of north west Syria in the north west, Along its whole length, Zagros fold and thrust belt can be divided in Iraq to foothill zone, high folded zone, imbricated zone and thrust zone (Marouf, 1999).

(Figure 1 – 14) Arabian Plate Boundaries (Saudi Arabian Geological Survey)

27

Chapter One

Introduction

Kosrat Anticline is located in the High Folded Zone (Figure 1 – 15), which covers most of the Iraqi Kurdistan region, which are areas where the platform cover had been folded and orogenically uplifted during Alpine orogeny, it comprises harmonic folds with Mesozoic limestone in their cores and Palaeogene and Neogene limestone and clastics on their limbs (Buday, 1980, Jassim and Goff, 2006). The cretaceous period in Iraq witnessed a geodynamic inversion of the regional tectonic regime from extensional to compressional tectonism, as the subduction of the Neo – Tethyan oceanic crust gave rise to a compressive tectonic environment in which the normal displacement on the listric normal faults of the passive continental margins were thwarted; compression led to renewed strike-slip and dip-slip reverse displacement along these faults giving rise to a phase of "block folding" in the foreland folds belt (Numan, 2000). The high folds, often with a broad box like geometry, are separated by narrow deep synclines as the structures are mostly asymmetrical, with steep SW or S limbs with reverse faults. Along the NE boundary of the zone the synclines are over-ridden by reverse faults (Jassim and Goff, 2006). The sedimentary cover of the High Folded zone comprises: a possible InfraCambrian section, Paleozoic, Triassic, Jurassic, Lower Cretaceous, Upper Cretaceous and Palaeogene sediments. Neogene sediments occur only locally in some synclines (Jassim and Goff, 2006). Mesozoic units are widely exposed throughout the fold-mountain zone of northern and northeastern Iraq (Bellen et al., 1959).

28

Chapter One

Introduction

Figure (1 – 15) Tectonic zones and structural elements of the Unstable Shelf units (Jassim and Goff, 2006)

29

Chapter Two

Fold Description and Analysis

CHAPTER TWO FOLD DISCRIPTION AND ANALYSIS

2.1: General Description of Folds: A fundamental understanding of the folds is important in the evaluation of the structural and tectonic features. A geological fold occurs when one or a stack of originally flat and planar surfaces, such as sedimentary strata, are bent or curved as a result of permanent deformation. Folds in rocks vary in size from microscopic scale to mountain-sized folds in orogenic belts. They occur singly as isolated folds and in extensive fold trains of different sizes, on a variety of scales. A set of folds distributed on a regional scale constitutes a fold belt. Folds are commonly formed by shortening of existing layers, but may also be formed as a result of displacement on a non-planar fault (fault bend fold), at the tip of a propagating fault (fault propagation fold), (Ramsay and Huber, 1987).

(Figure 2 – 1) The important features of the fold (Senanayake, 2013)

30

Chapter Two


When describing folds in rocks there are terminologies are generally used as shown in (Figure 2 – 1). The angle between fold limbs as measured in the profile plane is called the interlimb angle which offers a qualitative estimate of the intensity of folding; the smaller the interlimb angle, the greater the intensity of folding (Lisle, et al; 2010). Another used terminology is the Enveloping surface is an imaginary plane that is tangential to the hinge zones of a series of small folds in a layer; it contains all the antiformal or synformal hinges (Figure 2 – 2). The enveloping surface for the largest folds is called the first-order enveloping surface, which is typically of regional scale. The enveloping surfaces of successively smaller structures have a higher order (secondorder enveloping surface, third order enveloping surface, and so on) (Pluijm and Marshak, 2004).

(Figure 2 – 2) The Enveloping Surface connects the Antiform or Synform Hinges of consecutive folds (Pluijm and Marshak, 2004)

31

Chapter Two


2.2: Fold in three dimensions: The hinge points along an entire folded surface form a hinge line, which can be either a crest line or a trough line. The trend and plunge of a linear hinge line give information about the orientation of the fold. Connecting all the hinge lines of stacked folding surfaces gives the axial surface (Figure 2 – 3).

(Figure 2 – 3) Axial surface and hinge line of a fold (Pluijm and Marshak, 2004)

If the axial surface is a planar surface then it is called the axial plane and can be described by the strike and dip of the plane. An axial trace is the line of intersection of the axial surface with any other surface. Knowing the orientation of the hinge line of a fold does not uniquely establish the orientation, or the attitude of the fold. Folds having the same hinge line orientation can have strikingly different configuration (Figure 2 – 4). To describe unambiguously the attitude of a fold, it is necessary to measure another structural element, a geometric element which is the axial surface (Figure 2 – 5). Because axial surface of folds are planar or curviplanar surfaces, their orientations are described in terms of strike and dip (Davis, et. al., 2012; Ramsay 1967). 32

Chapter Two


(Figure 2 – 4) trend and plunge of fold hinge line (Davis, et. al., 2012)

(Figure 2 – 5) Axial surface orientation in a fold (Davis, et. al., 2012)

Fleuty (1964) created a useful classification scheme, which is based on both the relative orientations and the absolute inclinations of hinge lines and axial surfaces. The classification scheme (Figure 2 – 6) which is presented in the form of diagram permits fold to be named according to fold configuration. Along the x – axis of Fleuty's diagram is plotted the dip of the axial surface and along the y – axis is plotted the plunge of the hinge line to come out with the following fold types: subhorizontal upright, moderate plunging, steeply inclined, gently plunging, gently inclined and 33

Chapter Two


reclined fold which is a fold whose hinge line plunges directly down the dip of the fold's axial surface (Davis, et. al., 2012).

Figure (2 – 6) Classification of folds based on the orientation of the hinge line and the axial surface (after Fleuty, 1964)

2.3: Classification Criteria for Folds in Rocks It is possible to classify one specific fold in more than one category, which is made to easily distinguish between various kinds of folds (Billings, 1972, Pluijm and Marshak, 2004; Plummer, et al. 2007; Ramsay and Huber, 1987; Suppe, 1985; Wicander, et al., 2006). 2.3.1: Classification of Folds According To Their Symmetry It is a descriptive classification of folds in rocks is based on

appearance of axial plane and limb, which is classified to be: 34

Chapter Two


1- Symmetrical and Asymmetrical Folds: To determine if a fold is symmetric or asymmetric a median surface is used, which is the surface that passes through the inflection points of opposing limbs. If the axial surface is perpendicular to the median surface, then the fold is symmetric; otherwise the fold is asymmetric; in which the limb dip and the length of the limbs are different (Figure 2 – 7).

(Figure 2 - 7) Symmetric (a) and asymmetric folds (b) are defined by the angular relationship between the axial surface and the enveloping surface (Pluijm and Marshak, 2004)

2- Overturned Folds. 3- Recumbent Folds. 4- Isoclinal Fold: Depending upon the appearance of axial plane, it is further categorized as: • Vertical Isoclinal. Vertical axial plane. • Inclined Isoclinal. Inclined axial plane. • Horizontal/Recumbent Isoclinal. Horizontal axial plane. Descriptive classification of folds are shown in (Figure 2 – 8)

35

Chapter Two


(Figure 2 – 8) Schematic diagrams of symmetrical, asymmetrical, overturned and recumbent anticlines and synclines (Haywick, 2011)

2.3.2: Geometrical Classification of Folds These are the folds which are primarily classified depending on their geometry and named after the shape they resemble (Figure 2 – 9). In these folds, neither the axial plane nor the angle and direction of dip are considered. They are: 1- Box Fold: A fold in which the broad, flat top of an anticline or the broad, flat bottom of a syncline is bordered by steeply dipping limbs. 2- Chevron Fold: A type of fold which shows characteristically long, planar limbs with a short, angular hinge zone. Ideal chevron folds have interlimb angles of 60°. Chevron folds occur in sequences of regularly bedded layers of alternating competent and incompetent material which deform by flexural slip and ductile flow respectively. 3- Fan Fold: is one in which both limbs are overturned, Crest and trough are sufficiently rounded, when the two limbs dip toward each other it called Anticlinal Fan Fold and when the two limbs dip away from each other it called Synclinal Fan Fold.

36

Chapter Two


4- Open Fold: In open fold the interlimb angle ranged between 70o – 120o. 5- Closed Fold: the interlimb angle ranged between 30o – 70o. 6- Monocline Fold: They are anticline – syncline pairs in which the beds are horizontal but at different elevations on opposite sides of the fold. 7- Drag Fold: when a competent bed slides past an incompetent bed, such minor folds may form on the limbs of larger folds because of the slipping of beds past each other. The definition of drag folding focuses on the mechanism of formation, rather than the shape of the folds. For this reason drag folds may be difficult to identify unambiguously in some cases. The prime necessary property for a fold to be a drag fold is that it be closely localized near the fault surface. A second necessary property of drag fold is that they show orientations and asymmetries appropriate to the orientation and sense of slip on the fault.

(Figure 2 – 9) Types of folding according to their geometry (Fossen, 2010)

37

Chapter Two


2.3.3: Morphological Classification of Folds This classification of folds is based on the mode of occurrence. Unlike descriptive

and

geometric

classification,

in

morphological

classification of structures made of folds and introduce broader terminologies. Consequently folds can be classified as: 1- Anticlinorium: A series of anticlines and synclines so arranged structurally that together they form a general arch or anticline (Figure 2 – 10). 2- Synclinorium: it called for the fold in which a number of small synclines are on the limb of a large syncline.

(Figure 2 – 10) Anticlinorium and Synclinorium

3- Holomorphic Folding: in which a regular sequence of anticlines and synclines that are stretched to sufficiently long areas, it happens in areas where stresses are comparatively stronger and cause more deformation. This extensive deformation develops regular sequence of folds; Areas in which are found holomorphic folding are also called as “Orthotectonic area” or “Intense Deformation area”. 4- Idiomorphic Folding: in which anticline and syncline are disconnected, anticlines are visible on the surface and synclines are 38

Chapter Two


not visible on the surface. Synclines are present but they are below the surface. It happens because stresses were less and deformation was not sufficient. 5- Disharmonic Folding: A fold in which changes in form or magnitude occur with depth. It is not uniform through out the stratigraphic column. 6- Supratenous Folding: A pattern of fold in which there is thickening at the synclinal troughs and thinning at the anticlinal crests. It is formed by differential compaction (plastic materials flow) on an uneven basement surface. As there are more stresses below the surface causing more folding and it decrease upward which results into less folding. 2.3.4: Fold tightness: Fold tightness is defined by the angle between the fold's limbs, called the interlimb angle, Fleuty (1964) has suggested classifying the folds on their tightness by using the measured interlimb angle as shown in table (2 – 1):

(Table 2 -1) Terms used to describe the tightness of a fold (After Fleuty, 1964) Description of fold

Angle between surface inclinations measured at the two inflection points

Gentle

180 – 120

Open

120 – 70

Close

70 – 30

Tight

30 – 0

Isoclinal

0

Elasticas

Negative value

39

Chapter Two


2.4: Causes of folding: Folds appear on all scales, in all rock types, at all levels in the crust and arise from variety of causes.

2.4.1: Layer-parallel shortening: When a sequence of layered rocks is shortened parallel to its layering, this deformation may be accommodated in a number of ways, homogeneous shortening, reverse faulting or folding. The response depends on the thickness of the mechanical layering and the contrast in properties between the layers. If the layering does begin to fold, the fold style is also dependent on these properties. Isolated thick competent layers in a less competent matrix control the folding and typically generate classic rounded buckle folds accommodated by deformation in the matrix. In the case of regular alternations of layers of contrasting properties, such as sandstone-shale sequences, kink-bands, box-folds and chevron folds are normally produced (Ramsay and Huber, 1987).

2.4.2: Fault-related folding: Many folds are directly related to faults, associate with their propagation, displacement and the accommodation of strains between neighboring faults. 1- Fault bend folding: Fault-bend folds occur where a thrust fault steps up from a structurally lower flat to a higher flat. Figure (2 – 11) shows the evolution of a faultbend fold. Initially, two kink bands form in the hanging wall, one above the base of the ramp, and the other above the top of the ramp, with continued slip on the fault, these two kink bands grow in width. As the truncated hanging wall moves up the ramp, and the two kink bands widen, an anticline forms at the top of the ramp. This anticline terminates downward into the upper flat. The ramp anticline grows in amplitude as the kink bands 40

Chapter Two


grow in width. Meanwhile, one syncline develops at the base of the ramp, and another develops on the foreland-side of the anticline. Taking in consideration that that the ramp height determines the amplitude of the fold, which, in turn, determines the structural relief (Suppe, 1983).

(Figure 2 – 11) Progressive developments of a fault-bend fold (Suppe, 1983)

Fault bend folds occur in both extensional and thrust faulting. In extension, listric faults (Figure 2 – 12) form rollover anticlines in their hanging walls, 41

Chapter Two


they form when the hanging wall slumps into the low pressure extensional zone, the amount of tilting proportional to the amount of displacement on the fault. Because, of the curvature of listric faults. If the hanging-wall block moves to the right, without bending over, a gap develops, but when gravity pulls the lip of the hanging-wall block down, to maintain contact with the footwall, a rollover anticline is formed (Pluijm and Marshak, 2004).

(Figure 2 – 12) Formation of a rollover anticline above a listric normal fault (Pluijm and Marshak, 2004)

2- Fault propagation folding: Fault – propagation folding, a common folding mechanism in fold and thrust belts, occurs when a propagating thrust fault loses slip and terminates up-section by transferring its shortening to a fold developing at its tip. Considering that the fault tip coincides with the hinge of an asymmetric syncline. The mechanism of fault propagation folding requires the continuous folding of beds at the tip of the fault (Figure 2 – 13). Because of the variation in mechanical properties of layered sedimentary units, this mechanism may operate only within some units of a multilayered sequence. A fault may initiate within a fault Propagation fold and subsequently propagate through additional units, branch in to a number of imbricates splays, or flatten in to a detachment within an incompetent unit. In all of these cases, the geometry of the earlier formed fault-propagation fold may be modified during subsequent translation through fault bends. Conversely 42

Chapter Two


a fault may initially propagate as a simple fracture through a number of brittle units and terminates within a fault-propagation fold (Mitra, 1990).

(Figure 2 – 13) Progressive development of a fault-propagation fold at the tip of a thrust (Mitra, 1990)

3- Detachment folding: Detachment folds form in sedimentary units with significant thickness and competency contrasts. The basal layer is usually an incompetent unit, such as shale or salt, and is overlain by thick competent units such as carbonates or sandstones. The fold geometry and evolution are strongly dependent on the mechanical stratigraphy, including the thickness, ductility, and stratigraphic sequence of the units. Detachment folds are generally more 43

Chapter Two


symmetric than other fold forms in fold belts, particularly in the early stages of evolution. Unlike fault-bend and fault propagation folds, they commonly display opposite vergence both across and along fold trends. Detachment folds can be classified into two main geometric types: disharmonic detachment folds, and lift-off folds. Disharmonic detachment folds are characterized by parallel geometries in the outer layers, and disharmonic and non-parallel geometries in the lower units, with the folds terminating in a detachment. Lift-off structures are characterized by tight isoclinal geometries of the upper units, and a weak lower unit, which is isoclinally folded in the core of the anticline. Disharmonic detachment folds initiate as high wavelength structures, or rapidly acquire this geometry in the early stages of fold growth. These folds are then are progressively tightened by limb rotation, and also undergo additional increase in the fold wavelength by hinge migration. Disharmonic detachment folds and lift-off folds represent different stages of the same evolutionary process. Continued growth of the fold occurs by limb lengthening, involving the migration of hinges through beds, and limb rotation. Both of these mechanisms may operate simultaneously and in different proportions at different stages of fold growth. Rotation of bed segments to steeper dips may occur in two ways: 1-

Rotation of a segment of the limb to a steeper dip without any internal deformation of the beds.

2-

Rotation of a limb segment to a steeper dip by internal shear, between fixed hinges, which may not involve the migration of the outer hinges.

In the early stages of fold tightening, the upper competent units are deformed primarily by hinge migration without appreciable internal deformation (Figure 2 – 14). Continued deformation results in progressive reduction of the synclinal area through hinge migration, Variations in the

44

Chapter Two


geometry of detachment fold geometry, are related to variations in the initial mechanical stratigraphy and preexisting structure (Mitra, 2003).

(Figure 2 – 14) The evolution of asymmetric detachment fold involving a competency contrast between the basal and cover units (Mitra, 2003)

4- Fault-Propagation Folding on Planar Faults: During extension, a broad fault-propagation (or drape) fold develops above the master fault, with the fault subsequently breaking through the fold. Synextensional growth units deposited in the hanging wall typically thicken into the basin. Compressional reactivation results in slip reversal on the master and secondary faults, their rotation to shallower dips, and the

45

Chapter Two


development of a compressional fault- propagation fold; Inversion structures formed (Mitra, 1993).

5- Fault-Bend Folding on Listric Faults: Also called positively inverted fault bend folds. As rollover folding in the hanging wall occurs during extension, possibly accompanied by a small component of fault-propagation folding in the vicinity of the fault tip. Deformation is primarily localized along a system of antithetic faults. Synextensional growth sediments typically thicken into the fault, but also show thinning in the immediate vicinity of the fault. During compression, the extensional fold is first unfolded and then folded into a compressional fault-bend fold (Mitra, 1993).

46

Chapter Two


2.5: General Field Description of Kosrat Anticline: Kosrat Anticline is asymmetrical fold as the southwestern limb (30o) is steeper and shorter than the northeastern limb (21o). The axial length of the structure approaches 15 km and the width is about 14.5 km and the maximum topography from the profile section is about 960 meters for Kosrat Anticline and 1230 meters for Haibat Sultan Mountain (Figure 2 – 15) as extracted from the DEM from Global Mapper v11.02 software.

(Figure 2 – 15) Topographic Map and Topographic Profile of the study area

47

Chapter Two


The fold plunged southeasterly near Dukan Dam site and the northwestern plunge is enechelon with the southeastern plunge of Khalakan anticline which is represented by the hanging syncline as shown in (Figure 2 – 16).

(Figure 2 – 16) Kosrat Anticline in relation to surrounded structures

48

Chapter Two


The attitude of the fold is composed mostly of Kometan, Shiranish and Tanjero Formations. Whereas Qamchuqa and Dokan Formations exposed only in the center of the structure, which are obvious along the cutting road that’s connect both sides of the anticline. Gulneri Formation as incompetent rock unit is crushed between Dokan and Kometan Formations during the deformation or slightly eroded, that’s why the exposed locations are not widespread, so that these locations are difficult to be mapped due to their small scale appearance.

2.6: Geometric Analysis: Number of measurements of bedding planes was taken from Kometan, Shiranish and Tanjero formations in the southwestern and northeastern limbs of the anticline. This is because the Tertiary Formations were not found in the Northeastern limb. Geometrical analysis of these measurements using GEOrient, ver 9.5.0 and GeoCalculator 4.9.7 software revealed the geometrical attitude of this fold. Figure (2 - 17) shows a synoptic stereographic pi-diagram of Kosrat Anticline.

(Figure 2 – 17) Synoptic stereographic pi-diagram of the study area

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It can be seen from the stereogram that the anticline has a southwestward vergence, fold axis attitude in terms of trend and plunge is 147°/3°, axial plane attitude is 057°/85° as dip direction and dip amount, interlimb angle is 129° and the fold is classified as Gentle fold according to Fleuty, 1964 classification, the average attitude of the northeastern limb is 064°/21° in form of dip direction and dip amount, whereas the southwestern one is 232°/30°. Bedding plane attitudes that were measured and taken from different formations in both limbs of Kosrat Anticline along the traverses were plotted in Stereographic Projection to get the mean attitude of the bedding planes of the anticline in order to find the limbs dips, axial surface, and axis attitude in addition to interlimb angle for each formation. Figure (2 – 18) shows the attitudes of the formations bedding planes for both limbs of the anticline.

(Figure 2 – 18) Synoptic stereographic projection for each limb of the study area 50

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Figure (2 – 19) to Figure (2 – 22) illustrate the stereographic projections for the attitudes of the formations bedding planes of the anticline displaying each formation separately.

(Figure 2 – 19) Qamchuqa Formation bedding planes attitude in Kosrat Anticline

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(Figure 2 – 20) Kometan Formation bedding planes attitude in Kosrat Anticline 52

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(Figure 2 – 21) Shiranish Formation bedding planes attitude in Kosrat Anticline 53

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(Figure 2 – 22) Tanjero Formation bedding planes attitude in Kosrat Anticline 54

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2.7: Geometrical Description: The geometric description of the anticline was carried out for each traverse by the revealing results that obtained from the field measured data and process results that came out with the values of the Interlimb angle, Fold axis and Axial plane attitudes for each traverse and each formation (representing same age) of Kosrat Anticline. Figure (2 – 23) is a synoptic pi-diagram for Kosrat Anticline showing the fold axis and axial plane.

(Figure 2 – 23) Synoptic Pi-diagram of Kosrat Anticline

Interlimb Angle = 129o Fold Axis = 147 o / 03o Axial Plane = 057 o / 85o SW Limb (mean) = 232 o / 30 o NE Limb (mean) = 064 o / 21 o Therefore according to Fleuty, 1964 fold classification the fold could be classified as Gentle fold. 55

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Geometric descriptions of Kosrat Anticline were illustrated in synoptic pidiagram for each formation on each traverse of the study area that are shown in (Figure 2 – 24) to (Figure 2 – 29).

(Figure 2 – 24) Synoptic Pi-diagram of Kosrat Anticline – Traverse 1

Interlimb Angle = 135o Fold Axis = 149 o / 02o Axial Plane = 059 o / 86o SW Limb (mean) = 234 o / 26 o NE Limb (mean) = 065 o / 19 o Fleuty, 1964 fold classification = Gentle fold

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(Figure 2 – 25) Synoptic Pi-diagram of Kosrat Anticline – Traverse 2

Interlimb Angle = 123o Fold Axis = 147 o / 04o Axial Plane = 057 o / 86o SW Limb (mean) = 231 o / 32 o NE Limb (mean) = 064 o / 25 o Fleuty, 1964 fold classification = Gentle fold

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Qamchuqa Fn. Traverse No. 1 Fold axis: 129 / 01 Axial plane: 90 NE limb: 041 / 08 SW limb: 218 / 08 Interlimb angle: 164ᵒ Fleuty classification: Gentle fold

Kometan Fn. Traverse No. 1 Fold axis: 150 / 06 Axial plane: 060 / 88 NE limb: 077 / 20 SW limb: 226 / 23 Interlimb angle: 137ᵒ Fleuty classification: Gentle fold

(Figure 2 – 26) Synoptic Pi-diagram of Qamchuqa and Kometan Formations Kosrat Anticline – Traverse 1

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Shiranish Fn. Traverse No. 1 Fold axis: 149 / 01 Axial plane: 059 / 88 NE limb: 060 / 31 SW limb: 238 / 34 Interlimb angle: 115ᵒ Fleuty classification: Open fold

Tanjero Fn. Traverse No. 1 Fold axis: 154 / 03 Axial plane: 065 / 86 NE limb: 069 / 31 SW limb: 241 / 39 Interlimb angle: 110ᵒ Fleuty classification: Open fold

(Figure 2 – 27) Synoptic Pi-diagram of Shiranish and Tanjero Formations Kosrat Anticline – Traverse 1

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Kometan Fn. Traverse No. 2 Fold axis: 150 / 06 Axial plane: 060 / 89 NE limb: 077 / 19 SW limb: 224 / 21 Interlimb angle: 140ᵒ Fleuty classification: Gentle fold

Shiranish Fn. Traverse No. 2 Fold axis: 144 / 03 Axial plane: 054 / 87 NE limb: 059 / 30 SW limb: 229 / 35 Interlimb angle: 115ᵒ Fleuty classification: Open fold

(Figure 2 – 28) Synoptic Pi-diagram of Kometan and Shiranish Formations Kosrat Anticline – Traverse 2

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Tanjero Fn. Traverse No. 2 Fold axis: 145 / 02 Axial plane: 056 / 81 NE limb: 058 / 31 SW limb: 234 / 48 Interlimb angle: 101ᵒ Fleuty classification: Open fold

(Figure 2 – 29) Synoptic Pi-diagram of Tanjero Formation Kosrat Anticline – Traverse 2

According to the stereographic projections to the bedding planes values a significant difference is obvious in decreasing the interlimb angle from 164o in Qamchuqa Formation to 137o in Kometan Formation to 115° for Shiranish Formation and to be 110° for Tanjero Formation in the first traverse and the decreasing of the interlimb angle from 140o in Kometan Formation and in Shiranish Formation 115o to be 101o for Tanjero Formation for the second traverse indicate that the fold acted as a disharmonic fold. As If some layers have different wavelengths and/or amplitudes (Figure 2 – 30), the folds are disharmonic (Figure 2 - 31) (Fitzgerald and Braun, 1965).

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The interlimb angle offers a qualitative estimate of the intensity of folding; the smaller the interlimb angle, the greater the intensity of folding is (Pluijm and Marshak, 2004).

(Figure 2 – 30) The interlimb angle (ρ), the wavelength (Lw), the amplitude (a), and the arc length (La) of a fold system (Pluijm and Marshak, 2004)

(Figure 2 – 31) Small-scale disharmonic folds (Pluijm and Marshak, 2004) 62

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It is recognizable from the changing or decreasing of Interlimb values for the folded layers of Kosrat Anticline versus time that the wave length is decreasing as well for each formation which reveals that the intensity of folding is increasing. This estimation can not be accepted in the field because the folded layers for each formation were not outcropped along the entire anticline which made the data acquiring for the attitudes of the bedding planes not adequate to have a complete measurements for the folded layer to get the accurate interlimb angle. The dip of the axial plane ranged from (81o to 90o) and the fold axis plunging of the anticline is swinging within two degrees in the direction of Southeast. By plotting these values on the classification of folds based on the orientation of the hinge line and the axial surface (after Fleuty, 1964; Ramsay, 1967) puts the anticline as upright subhorizontal fold.

2.8: Folding Mechanism: There are different approaches and process-related terms about how did the fold structures actually form? One approach is to consider the way that force or stress acts on a layered rock, other terms are related to how the layers react to force and stress. For this reason, several different fold mechanisms are defined, and many of them overlap in definition. The most important distinction between the ways in which folds form probably lies in whether the layering responds actively or passively to the imposed strain field (Fossen, 2010), (Ramsay and Huber, 1987). 2.8.1: Active Folding or Buckling (Stress parallel to bedding): Is a fold process that can initiate when a competent layer in a less competent matrix is shortened parallel to the length of the layer the result of buckling is rounded folds, typically (Figure 2 – 32). The resistance to the formation of the folds can be divided into two parts: one depends upon the resistance offered within the competent layer itself, the other relates to the 63

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resistance offered by the incompetent matrix as is pushed aside by the developing buckle fold (Ramsay and Huber, 1987). Single-layer folds formed by buckling have the following characteristics: • The fold wavelength–thickness ratio is constant for each folded layer if the material is mechanically homogeneous and if they were deformed under the same physical conditions. • The outer arc of the competent layer is stretched while the inner arc is shortened. The two parts are typically separated by a neutral surface (Figure 2 – 33).

(Figure 2 – 32) Buckling of a single layer (Fossen, 2010)

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(Figure 2 – 33) Strain distribution of a folded layer (Ramsay and Huber, 1987)

2.8.2: Passive Folding: Produced by simple shear, it can be formed in response to any kind of ductile strain. Passive folds geometry can easily be generated by differentially shearing a card deck. Drawing lines perpendicular to the cards prior to shearing helps visualize the fold. Passive folding produces harmonic folds where the layering plays no mechanical role and therefore no influence on the fold shape (Figure 2 – 34) (Donath and Parker, 1964), (Ragan, 2009).

(Figure 2 – 34) Passive folding (Donath and Parker, 1964) 65

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2.8.3: Bending Folds: Occurs when forces act across layers at a high angle, unlike buckle folds where the main force acts parallel to a layer. This is also the case for passive folding, and the two are closely related. Bending occurs when forces act across layers (Figure 2 – 35), and may involve more than one mechanism. Bending as such is a boundary condition- or external loadrelated model, not a strain model (Ramsay and Huber, 1987), (Ragan, 2009).

(Figure 2 – 35) Bending in various settings and scales (Fossen, 2010)

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2.9: Folding Kinematics Models Three fundamental models, Flexural folding, Neutral surface folding, and Shear folding can explain the inner workings of the folded layer and the associated strain pattern. 2.9.1: Flexural Slip/Flow Folding: Where layering exerts a strong influence in the folding of a rock sequence, flexing of layers is accomplished by slipping of one layer past another, by flow within the layers, or by a combination of the two. In each case the layering controls the mechanism of folding and, hence, the geometry and internal features of the resultant fold. The development of a flexural – slip fold is illustrated in (Figure 2 – 36). In the ideal flexural – slip fold zero displacement occurs at the hinge line, but the displacement increase progressively away from the hinge line. The amount of displacement parallel to layering is proportional to the degree of folding and distance from the hinge line. The cohesion between layers is commonly less than that within layers, and slip occurs if the shear stress on the surface of the layers exceeds the cohesion and frictional resistance to slip between these layers (Donath and Parker, 1964).

(Figure 2 – 36) Flexural slip, showing opposite sense of slip on each limb (Butler, et al., 2009) 67

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2.9.2: Neutral Surface Folding: Neutral surface is a theoretical surface in a fold hinge zone or in the middle of the layer separating layer-parallel extension in the outer arcs from layerparallel shortening in the inner arcs of the hinge. It's a surface where there is no strain (Groshong and Richard, 2006). (Figure 2 – 37) it can be seen that on the top folded surface, the long axis of each ellipse is perpendicular to the hinge line, but on the bottom the long axis is parallel to the hinge line. In the profile plane the long axis is parallel or perpendicular to the top and bottom surfaces of the folded layer, depending on where we are in that plane? Therefore there must be a surface in the fold where there is no strain. This zero-strain surface gives the model its name, Neutral-Surface Fold. The fold shape from neutral-surface folding is parallel and cylindrical (Van der Pluijm and Marshak, 2004), (Donath and Parker, 1964).

(Figure 2 – 37) The strain pattern of neutral-surface folding (Van der Pluijm and Marshak, 2004)

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2.9.3: Shear Folding: The prime mechanism or motion is one of shearing or slipping along closely spaced fractures not parallel to the original bedding (Badgley, 1965). Axial plane cleavages may act as shear planes, Shear folds can be formed in regions where the flow field is heterogeneous. A deck of cards is a good example to illustrate the shear folding process, as a layer was drawn on the sides of the deck. When the cards are differentially moves relative to one another, they produce a fold by a mechanism called Shear Folding (Van der Pluijm and Marshak, 2004) as illustrated in (Figure 2 – 38).

(Figure 2 – 38) The strain pattern of shear folding (Van der Pluijm and Marshak, 2004)

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2.10: Multilayered Fold Controlling Factors: The wide range of fold style and size arises because of the mechanical instabilities in a multilayered sequence depending upon a number of factors that controls the fold geometry which are: (Ramsay and Huber, 1987), (Treagus and Fletcher, 2009). 1- The composition of the layers and the primary rheological properties of each rock type, as each one have its own characteristics depending upon its mineralogical composition and mineral grain size. Strain rates are not simply proportional to the values of the applied stresses. In basically simple mineralogical assemblages (e.g. calcite and clay) different proportions of the end members can produce a range of rock types showing a whole spectrum of varying rheology (e.g. coarse grained limestone, fine grained limestone, marly limestone, marl, calcareous shale and shale). 2- Changing the pressure and temperature conditions as a reason for changing in rheological properties of the layers during the period of fold formation which probably takes a million years duration that leads to modify the grain sizes or species due to the change in environmental conditions. 3- The development of orientation of mineral grains during deformation as a result of mechanical rotation or recrystallization processes. 4- The thickness of each of the stock layers in the rock packet, and whether or not the different rock layers are grouped into units. 5- The scale of the folding is an important factor which decides whether or not gravitational force exerts an influence on the fold geometry. 70

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Folds with small wavelength, gravity plays only a minor roll in the controlling of fold shape, whereas folds with greater wavelength can't be formed by sideways compression of the layers alone because the buckling forces are too small to uplift the antiforms or depress the synforms against the gravity forces. 6- The nature of the boundary constrains on the rock units undergoing folding, as some groups of layers in a multilayered rock complex may undergo free buckling into an incompetent host material without external lateral constrains apart from the resistance offered by the host material. 7- The mechanical properties of the interfaces between layers which control strongly the development of a fold. As the nature of the contacts between adjacent individual layers might be effectively welded together or the layers are mechanically detached and, in doing so, allow the individual layers to glide past another. In the study area of Kosrat Anticline this factor might control the forming of the fold which consists of layers that are different in mechanical properties, as there are competent and incompetent layers that make the slipping or gliding between adjacent individual layers possible during the folding. Gulneri Shale Formation which is the incompetent rock layer that is relatively weak (Figure 2 – 39) let Kometan Limestone Formation which can withstand an applied load without collapsing and is relatively strong to slip above it as a flexural

slip anticline in an active buckling mechanism. In (Table 2 – 2) can be found the formations of Kosrat Anticline and their competency.

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(Figure 2 – 39) The competency for some formations in Kosrat Anticline

(Table 2 – 2) Kosrat Anticline Formations competency

No.

Formation

Competency

1

Qamchuqa Fn.

Competent (Dolomitic Limestone)

2

Dokan Fn.

Competent (Dolomitic Limestone)

3

Gulneri Fn.

Incompetent (Shale)

4

Kometan Fn.

Competent (Limestone)

5

Shiranish Fn.

Competent (Limestone) Incompetent(Marl) Competent (Sandstone)

6

Tanjero Fn.

Incompetent (Siltstone, Claystone and Shale)

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The study area is affected by a wide spectrum fault system, the study of (Numan and Al-Azzawi, 1993) was the first attempt about the relation between the folds and listric faults in the foreland fold belt in the northern Iraq. They suggested tectonic models for the attitudes of these listric faults depending on the geometry of folds which were affected by these listric faults (Figure 2 – 40).

(Figure 2 – 40) Suggested fold models which resulted from listric faults (After Numan and Al-Azzawi, 1993)

These faults play an important role in the shaping of the folds during the formation of the folds by the main horizontal stresses which push the sedimentary strata parallel to dip of the listric faults, this movement is responsible about the vergence and symmetry of the folds, propagation of the synthetic increase the asymmetry of the fold while the antithetic 73

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increase the symmetry, by progressive movement the forelimb overturned and/or fracture occurred and the fault exposed to the surface (Al-Azzawi, 2003). Geologically the synthetic are formed during the extension phase therefore their ages are Triassic and the antithetic may formed as a conjugate with the synthetic or during the compression phase in the Cretaceous or collision phase during the Eocene (Numan, 1997). Therefore Kosrat Anticline might be acted upon the above idea of being going through extensional and compressional phases because of its location, vergence direction and fold shape which might be affected by fault systems that are widespread in the study area. The decreasing in the values of the interlimb angles for the geological formations from the older one to the younger of Kosrat Anticline is due to the station locations for each formation along the folded layer which were not covering the entire folded rock unit. Therefore the measurements were according to the outcrops of the formations on a limited area along the limbs, for example Qamchuqa Formation was exposed only in the core of the anticline for a very limited area and the same is for Dokan Formation, they didn't cover the entire limbs of the anticline. Which made the data acquiring doesn't cover the entire formation along the limbs. A geological map was drawn for the study area (Figure 2 – 41) and the values of the dip amount and directions, formation contacts, the anticline and syncline axes, faults location and the plunge area were plotted on the map as obtained from the field measurements on both traverses and from scattered stations in the study area. For the data of the formation outcrops which are located to the west side of Haibat Sultan Mountain and the structures to the North and Northeast side of the study area were obtained from the geological map of Geosurv (1989) with a scale of 1:100.000 for Koisanjaq region.

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(Figure 2 – 41) Geological Map of the study area compiled from the field measurements data and Geosurve geological map, 1989

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CHAPTER THREE FRACTURES & FEATURES ASSOCIATED 3.1: Joints The most common geological structures that are created in the upper crust are joints (Weinberger, et al; 2010). Joints are surfaces, simple fractures which there have been no displacement (Bates and Jackson, 1987) or partings in a rock across that do not show any evidence of shear movement and that typically occur perpendicular to bedding of sedimentary rocks (Hodgson, 1961; Price, 1966; Hancock, 1985; Pollard and Aydin, 1988). They profoundly control the shape of many spectacular landforms, and play an important role in the sub-surface transport of fluids such as water and hydrocarbons (Pollard and Aydin, 1988; Gross and Eyal, 2007). Establishment of reliable relationships between joints and their cause provides important tools for inferring the loading conditions and mechanical behavior of rocks. It is widely agreed that tension joints form as mode of fractures parallel to the maximum compressive principal stress, and perpendicular to the minimum principal stress (the direction in which the rock is being stretched) (Engelder and Geiser, 1980) and shear joints are generated by shear stresses on their boundaries. They occur as two nonorthogonal sets, and intersecting each other forming an acute angle to the σ1 axis of the stress field (Mandl, 2005). The main jointing mechanisms (Engelder, 1985; Bahat et al., 2005) are responses of the host rock to a regional or local stress field, effect of pore pressure and hydro-fracturing, stress relaxation due to rock uplift, and/or jointing due to material shrinking (columnar joints in basalts). Hence they can be classified according to the basis of origin into: 1- Shear Joints: Joints which resulted from shear stresses. 2- Tension Joints: Joints which resulted from extensional stresses.

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3- Columnar Joints. These joints are formed in igneous rocks which are formed during cooling of lava, when it comes out of earth in molten state. Joints may have any attitude; some joints are vertical, others are horizontal, and many are inclined at various angles. The strike and dip of joints are measured in the same way as for bedding. 3.1.1: Geometric Analysis of Joints The orthogonal tectonic axes (a), (b), and (c) are used for the classification of different fracture types, detected of the studied structure. These axes are geometrically related to the hinge line of the anticline and bedding planes. The axis (a) is perpendicular to the fold hinge line (in the case that the hinge line is horizontal), (b) is parallel to the hinge line and (a) + (b) lies within the plane parallel to the bedding plane, (c) axis is perpendicular to (a-b) plane so it's perpendicular to the bedding plane (Turnner and Wiess, 1963). Fractures are two dimensional surfaces, they are either parallel to two tectonic axes, or one tectonic axes or cut the three ones. As the tectonic axes are related to the fold geometry, the above method of defining the fracture systems is in fact relates the geometry of fractures to the geometry of their hosting major folds (figure 3 – 1). The distribution and spacing of joint planes can be described by (Ladeira & Price, 1981): 1- Joint set: is a series of parallel joints, they are commonly observed to have relatively constant spacing.

2- Joint system: Two or more of joint sets intersecting each other and related to a specified stress field. 3- Conjugate system: Two sets of joints nearly 60o angle to one another, produced by the same stress system.

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(Figure 3 – 1) Geometrical classification of the joints with respect to three orthogonal geometrical axes after (Hancock, 1985)

3.1.2: Joint Systems in the Study Area: More than (510) readings of joint planes were collected from Kosrat Anticline through the distributed stations in the study area. Strike and dip were measured for the joint planes as well as the attitude of the bedding plane which contain the joints. Software (GEOrient, ver 9.5.0) was used for classifying the joints. Joint planes data in Kosrat Anticline were collected from Qamchuqa, Dokan, 78

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Kometan, Shiranish and Tanjero formations through many stations distributed in the study area mostly along the two traverses. The fractures are described and classified geometrically in proportion to the orthogonal tectonic axes, into the following sets and systems: 1- ab set fractures: The planes of these fractures are perpendicular to (c) axis and parallel to both (a) and (b) axes. This set comprise all the planes parallel to bedding plane. The bedding planes are rough and less regular in Qamchuqa Formation and Stylolites that developed on the bedding plane or within beds are also rough surfaces as in Kometan Formation on other hand they are generally regular and smooth planes in Gulneri, in the marly limestone beds of Shiranish and Tanjero Formations (Figure 3 – 2).

(Figure 3 – 2) ab fracture system in the study area

The set (ab) commonly appear in surfaces parallel to bedding plane and usually intersected by other sets. Possibly they could be release fractures resulted from recent unloading or due to weathering process (Hancock, 1969; Hancock and Atiya, 1979). 79

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2- ac set fractures: The planes of this set of fractures are parallel to tectonic axes (a) and (c), whereas a tectonic axis (b) is perpendicular to them. In other word (ac) sets are perpendicular to the hinge line of the fold. The general trend of this set is Northeast – Southwest within different geological formations of the anticline such as Kometan, Shiranish and Tanjero Formations (Figure 3 – 3).

(Figure 3 – 3) ac fracture system in the study area

Fractures of this set comprise joints and veins. The joints form the majority of fractures of this set and these joints are either closed or opened. Blocky and fibrous crystals of calcite are developed on the wall of these opened joints to form veins, as in the marly limestone beds of Shiranish Formation (Figure 3 – 4). These veins developed to reach 30 centimeters thick.

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(Figure 3 – 4) Calcite veins in Shiranish Formation in NE limb of Kosrat Anticline

3- bc set fractures: The planes of this set of fractures are parallel to tectonic axes (b) and (c) and perpendicular on the (a) axis. They are normal to subnormal to the bedding planes. The majority of fractures of this set that observed in the study area (in Qamchuqa, Kometan, Shiranish and Tanjero Formations are joints and the rest are veins and tectonic stylolites (Figure 3 – 5).

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(Figure 3 – 5) Tectonic Stylolite and bc joint in Kometan Formation SW Limb of Kosrat Anticline

Tectonic stylolites can be used to determine the maximum compressive stress direction; they are younger than the horizontal stylolites which are parallel to bedding as a result of the overburden pressure as in Kometan Formation. 82

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4- hko system: Planes of this system are parallel or subparallel to the (c) tectonic axis and intersect both (a) and (b) tectonic axes. The planes of this system makes approximately orthogonal angle with the bedding planes. This system subdivided into the following groups of conjugate subsystems. 4.1- hko acute about (a) subsystem: This subsystem consists of intersecting two sets; the tectonic axis (a) bisects the acute angle between these two sets. Whereas, the tectonic axis (b) bisects the obtuse angle. These fractures occur and observed through the exposed geological formations of the anticline (Qamchuqa, Dokan, Kometan, Shiranish and Tanjero formations) as conjugate sets (Figure 3 – 6) or single set that form less than 45o with tectonic axis (a). The sets of this subsystem comprise; joints, mesoscopic faults and veins. To slickensides part, striations also noticed on some of the fault surfaces of this subsystem in Kometan Formation.

(Figure 3 – 6) hko acute about (a) fracture subsystem in the study area 83

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4.2 – hko acute about (b) subsystem: The intersected two sets of this subsystem are bisected by the tectonic axes (b) and (a). The axes (a) and (b) bisect the obtuse and acute angle respectively. The sets of this subsystem were observed within Qamchuqa, Shiranish and Tanjero formations in the studied area. The fractures of this subsystem exists as conjugate sets or as an individual set, they are in the form of joints and veins (Figure 3 – 12). 4.3 – hol system: The orientation of the planes for this system is parallel to tectonic axis (b) and intersects both (a) and (c) axis. These planes form an acute angle with bedding plane. The direction of movement on the synthetic fault is in good comparison with flexural sense of movement, whereas the sense of the comparative movement on the antithetic faults is reversed (Figure 3 – 7).

(Figure 3 – 7) Movement on hol faults (modified from Marouf, 1983 in Balaki, 2004)

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4.3.1 – hol acute about (a) subsystem: The two sets of this subsystem are bisected by the tectonic axes (a) and (c) and make an acute and obtuse angle around each of them respectively. This subsystem of fractures recorded in Qamchuqa and Kometan formations in the study area, and was exists in the form of a fault in Tanjero formation (Figure 3 – 8) it exists in the inner arcs of the fold more than the outer arcs (Fouad, 1983).

(Figure 3 – 8) hol acute about (a) fracture subsystem in the study area

4.3.2 - hol acute about (c) subsystem: This subsystem is also consisting of two conjugate shears trending parallel to the (b) axis. The tectonic axis (c) bisects the acute angle between the two sets of this subsystem, whereas the tectonic axis (a) bisects the obtuse angle. The fractures of this subsystem were documented in Kometan, Shiranish and Tanjero formations in the study

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area. They are existing in the form of single set or conjugate sets. These joints form the majority of fractures are shown in (Figure 3 – 9).

(Figure 3 – 9) hol acute about (c) fracture subsystem in the study area

4.4 – okl system: The planes of this fracture system are parallel to the tectonic axis (a) and intersect the tectonic axes (b) and (c). This system consists of two conjugate subsystems: 4.4.1 – okl acute about (b) subsystem: The tectonic axis (b) bisects the acute angle between the two set of this subsystem. They are existing as conjugate sets or individual set. These fractures observed in Kometan and Tanjero formations in the study area (Figure 3 - 10).

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(Figure 3 – 10) okl acute about (b) fracture subsystem in the study area

4.4.2 - okl acute about (c) subsystem: The two planes of this subsystem intersect forming an acute and obtuse angle. Tectonic axis (c) bisects the acute angle between the two sets and the tectonic axis (b) bisects the obtuse angle. These fractures exists in the form of conjugate sets or individual set and their planes make angles range between 50o to 70o with bedding plane. The fractures of subsystem distributed mainly in the northeastern limb of Kosrat Anticline in Kometan Formation and they are recorded in Shiranish and Tanjero formations as well (Figure 3 – 11).

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(Figure 3 – 11) okl acute about (c) fracture subsystem in the study area 88

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4.5 – hkl system The fracture planes of this system intersect the entire tectonic axes so there is no geometrical relationship between the system and the fold. These fracture planes usually appear on the fold as single group or conjugate groups was observed and recorded in Qamchuqa, Kometan, Shiranish and Tanjero formations of Kosrat Anticline (Figure 3 – 12).

(Figure 3 – 12) hkl fracture system and hko acute about (b) subsystem in the study area

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3.1.3: Joint Analysis in the Study Area: Joints are among the most common of all geological features , hardly any outcrop of rock exist that does not have some types of joints through it. They are significant both for information they provide regarding the sequence of tectonic event during which the joints formed and the physical characteristics they impart to the rock in which they occur (Twiss and Moores, 2007). Fractures were studied in stations (Figure 3 – 13); each station was normally distributed in the areas where different sets of fractures together with the bedding appear clearly in three dimensions (i.e. in cross section and plan view) the dimension of each station is different from place to place but they range from 10 x 10 x 10 to 50 x 50 x 50 meters. The location of each station is defined on the geologic map. In each station the lithology is defined, the orientation of the bedding, each set of joints and other fractures are measured and the frequency of each set is also measured. The types of fractures of each set are defined and photographed. The relation between the different sets themselves and the beddings and other fractures are also discussed. 3.1.4: Fracture Frequency and Spacing Joint spacing is the orthogonal distance between adjacent parallel joints of particular set; hence bed thickness is a primary factor to determine joint spacing in well-bedded sedimentary rocks (Gross, et al., 1995). Taking in consideration that the development of fractures in the competent beds is also related to the thickness of the adjacent layers of incompetent one. As when the adjacent layers are "relatively thick" the fractures in the competent layers are little and more widely spaced than when the adjoining incompetent layers are thin (Ladeira and Price, 1981). Fracture frequency refers to the number of fractures of a particular fracture set in a unit length (fractures / meter) and it is the reciprocal of the fracture 90

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(Figure 3 – 13) Joint Analysis of the study area

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spacing (e.g. if the fracture spacing is 0.3 meter, the frequency is 1/0.3 = 3.3 fractures / meter). Fracture spacing is low (frequency is high) in the thinly bedded competent rocks. In contrast the fracture frequency in the massive thick competent beds is low. In the studied area fracture frequency in Qamchuqa thick massive beds is around 3 fractures / meter, whereas it is around 5 fractures in Kometan Formation and up to 10 fractures in Shiranish Formation. More clayey competent rocks suffer from high frequency of fractures. In the studied area the very thin bedded upper clayey sequence of Shiranish Formation exhibit fracture frequencies range from 50 to 100 fractures / meter. 3.1.5: Fracture Development It was found through laboratory experiments (Brace 1964, Price 1966, Hobbs et al. 1976, Jaeger & Cook 1976, Paterson 1978) that when a brittle rock is loaded to failure under "tri-axial" compression test (Figure 3 – 14) the resulting fractures are symmetrically orientated with respect to the three effective principal stresses (σ1 > σ2 > σ3). The class of developed fracture is related to the value of σ3 and the stress difference (σ1 - σ3) compared with the tensile strength (T) of the rock. The orientations of the principal stresses can be determined knowing that at the time of failure an extension fracture is initiated perpendicular to σ3 and in the principal stress plane containing σ1 and σ2, and that shear fractures enclose an acute bisector parallel to σ1 (Hancock, 1985).

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(Figure 3 – 14) Block diagram showing relationships between effective principal stresses and an extension fracture (Hancock, 1985)

Price (1966) and Nickelsen (1976) concluded from field observations that: "it is unlikely.., all joints are the result of a single mechanism". They commented, "Fracture patterns are cumulative and persistent. These statements say that in sedimentary rocks joints may propagate at several different times during a tectonic cycle which includes burial, diagenesis, tectonic compression, uplift, and erosion. Joint propagation occurs when failure criteria are met (Engelder, 1985). 3.1.6: Data Analysis: The measured data for joints of the study area were analyzed by using stereographic techniques for each formation of the anticline. Joint planes data were collected along the backlimb and forelimb traverses from Qamchuqa, Dokan, Kometan, Shiranish and Tanjero formations. The two orthogonal tension sets (ac) and (bc) recognized in the study area outcrops at the rate of (10%) from the total distributed joint types. The (ac) tension sets might be resulted from the influence of the main horizontal compression stress, which is responsible for forming folds. They are possibly caused by water pore pressure or natural hydraulic fracturing that accompanying tectonic events; the existence of crystalline minerals 93

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like calcites in such joint sets supports to this idea. While the (bc) tension sets that are parallel to the anticline axis could be caused by the local extensional stress due to folding in the outer arcs of the folded layers. The shear fracture systems appear either as individual set or conjugate systems; the data showed that there are at least four regional sets of conjugate shear joints exist. But the hko>a subsystem is the wide spreading one as σ1 is parallel to tectonic axis (a) and bisecting the acute angle which is indicating to the main stress field that is perpendicularly to the fold axis, σ2 is parallel to tectonic axis (c) and σ3 is parallel to tectonic axis (b). Figure (3 – 15) illustrates the rate of each set and subsystem in the study area.

(Figure 3 – 15) Joints ratio in Kosrat Anticline

The Joint planes data in Kosrat Anticline illustrated stereographically for each formation in both limbs separately in the figures (3 – 16) to (3 – 23) as following:

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(Figure 3 – 16) Synoptic Joint planes of Kosrat Anticline

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(Figure 3 – 17) Synoptic Joint planes of Qamchuqa Formation in Kosrat Anticline Traverse – 1

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(Figure 3 – 18) Synoptic Joint planes of Kometan Formation in Kosrat Anticline Traverse – 1 97

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(Figure 3 – 19) Synoptic Joint planes of Shiranish Formation in Kosrat Anticline Traverse – 1 98

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(Figure 3 – 20) Synoptic Joint planes of Tanjero Formation in Kosrat Anticline Traverse – 1 99

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(Figure 3 – 21) Synoptic Joint planes of Kometan Formation in Kosrat Anticline Traverse – 2 100

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(Figure 3 – 22) Synoptic Joint planes of Shiranish Formation in Kosrat Anticline Traverse – 2 101

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(Figure 3 – 23) Synoptic Joint planes of Tanjero Formation in Kosrat Anticline Traverse – 2 102

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Through the distribution of the joints in the study area and the ratio of each fracture system or subsystem, it can be seen that the main compression stress was representative in the form of shear joint system hko acute about (a) which is in the direction of NE – SW and hol acute about (a) that is form in the inner arcs of the anticline which is not observable in the field as wide as hko acute about (a). While the extension stress was recorded in the form of hol acute about (c) fracture subsystem and bc fracture system that their plane or joint surface strikes are parallel to the fold axis or tectonic axis (b). The (ab) fracture system was recorded in all the formations of the study area because their surfaces are parallel to the bedding planes. They could be release fractures resulted from recent unloading or due to weathering process. The (hkl) fracture system cuts the entire tectonic axis, and it could be related to fracturing and faulting in different direction. This system could be resulted due to local stresses in the area that might be resulted from the fracturing and collapses of rock units during the folding. Same as other fracture systems in the study area which might be related to tectonic phases in more than one direction such as the opening of the red sea and the anticlockwise rotation of the Arabian plate.

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3.2: Faults Fault is a fracture or zone of fractures between two blocks of rocks. Faults allow the blocks to move relative to each other. This movement may occur rapidly, in the form of an earthquake - or may occur slowly, in the form of creep. Faults may range in length from a few millimeters to thousands of kilometers. Most faults produce repeated displacements over geologic time. The fault surface can be horizontal or vertical or some arbitrary angle in between (Press and Siever, 1986). The attitude of a fault is measured in the same way as the bedding. Thus the dip of the fault is the angle between the horizontal and the plane of the fault, measured in a vertical plane perpendicular to the strike of the fault. The fault trace is the intersection of the fault plane with the ground surface. The movement on a fault plane is translation either straight-line movement without rotation; or rotational movement (Badgley, 1965). Surface breaks along faults can generally be recognized on the ground or from the air on the basis of topographic features or differences in vegetation that reflect varying groundwater depths or soil differences across the fault. Perhaps the most marked sedimentary effects of faulting are the conglomerates (imbricated structure) and sedimentary breccias in narrow zones along many active fault scarps (Suppe, 1985). Deformation patterns are described by the style, intensity and distribution of structures throughout a volume of rock. In fault-related folds, presently observed deformation patterns are controlled by structural factors like kinematics history, environmental factors like burial history and stratigraphic factors like layer thickness and competence (Fischer and Jackson, 1999). 3.2.1: Faults and Forces The geometry of a fault system is a clue to the regional stress conditions that caused the faulting. A thrust system reflects conditions where regional 104

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σ1 is horizontal and at a high angle to the trace of the system and σ3 is vertical. A normal fault system reflects extension conditions where regional σ3 is horizontal and σ1 is vertical. A Strike - Slip fault system indicates neither extension nor compression, but identifies regions where rocks are sliding past each other, this system reflects Wrench tectonics where regional σ1 and σ3 are horizontal (Ramsay and Huber, 1987) and (Van der Pluijm and Marshak, 2004), as shown in (Figure 3 – 24).

(Figure 3 – 24) relationship between stresses and ideal faults (Burg, 2013)

3.2.2: Types of Faults Earth scientists use the fault dip angle and the direction of slip along the fault to classify faults. Faults which move along the direction of the dip plane are dip-slip faults and described as either normal or reverse (thrust), depending on their motion. Faults which move horizontally are known as 105

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strike-slip faults and are classified as either right-lateral or left-lateral. Faults which show both dip-slip and strike-slip motion are known as oblique-slip faults (Press and Siever, 1986). 3.2.2.1: Normal faults: These are faults in which the hanging wall has moved down relative to the footwall. Their movement is thus of normal dip – slip nature. The major maximum stress (σ1) is essentially vertical, and the direction of the minimum stress (σ3) is essentially horizontal. Such faults maybe related to an actual lengthening of the earth crust, or maybe related to radial stretching (outward) over the crest of an anticline (Figure 3 – 25). In the latter case the normal faulting is really a secondary effect of folding, so it cannot be said that crustal lengthening is predominant in such cases. It will be noted that faulting is the result of an outward – directed tensional stress and is not actually caused by the downward – directed maximum principal inward stress (σ1). These faults on anticlines are probably the most common type of normal fault. The collapse toward the center of the uplift is generally characteristic of such features. This inward direction of collapse is not always predominant (Badgley, 1965), (Ramsay and Huber, 1987).

(Figure 3 – 25) Normal Faults formed due to radial stretching over the crest of an anticline (Ramsay and Huber, 1987) 106

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Normal faults generally occur in places where the lithosphere is being stretched. Consequently they are the chief structural components of many sedimentary rift basins. Normal faults can show different geometries (Figure 3 – 26). In some situations the faults can become gently dipping at depth so that they have a spoon (or listric) shape. Other normal faults are found in batches, dipping in the same direction, with rotated fault blocks between. These are termed domino model faults. Although most active normal faults can be shown to dip at angles steeper than 50 degrees. These faults are sometimes termed "detachments" – different from the common normal faults, detachments show gentle dips and often expose high grade metamorphic rocks in their footwalls. Normal faulting is now thought to be an important way in which metamorphic rocks come to be at the earth's surface today (Fossen, 2010), (Butler et al; 2009).

(Figure 3 – 26) Listric and Domino Faults (Butler et al., 2009) 107

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3.2.2.2: strike – slip faults Strike-slip faults are those where the main relative displacement is parallel to the strike of the fault. Strike-slip fault zones are commonly, but by no means exclusively, steep and can be rather difficult to recognize on cross-sections. However, active strike-slip faults are sometimes associated with spectacular tectonic landforms, such as pull – apart basins (Figure 3 – 27) (Butler et al; 2009).

(Figure 3 – 27) Geometries associated with strike-slip faults (Ramsay and Huber, 1987)

The faulting occurs in a triaxial stress field in which the maximum and minimum principal stresses σ1 and σ3 lay in the horizontal plane and the intermediate principal stress σ2 is vertical. Strike-slip faults are typically steeper than other faults. It can be a right-lateral (dextral) strike-slip fault, in which the rocks on one fault block appear to have moved to the right when viewed from the other fault block. Or a left-lateral (sinistral) strike slip fault, which displays the opposite sense of displacement (Billings, 1972; Lisle, 2004 and Rowland, et al, 2007).

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Strike – slip faults occur frequently in fold – thrust belts. They may cut across the fold axes diagonally, or they may cut across the fold axis and thrust traces almost at right angles. Those strike – slip faults which cut across the regional strike perpendicularly are frequently referred to as tear faults (Figure 3 – 28), which are parallel to the movement direction of thrusts or normal faults; they are usually common in hanging walls of low-angle faults. as they generally occur at one end of large thrust sheets. While strike – slip faults which have a diagonal relationship to the regional trend of an area are believed to be simply part of conjugated shear system (Badgley, 1965), (Ramsay and Huber, 1987).

(Figure 3 – 28) Tear Fault (Burg, 2013)

Flower structure (Figure 3 – 29) is an array of splay faults in a strike – slip fault zone that merges at depth into a near-vertical fault plane, but near the ground surface diverges so as to have shallower dips. In a positive flower structure, there is a component of thrusting on the faults, and in a negative flower structure, the vertical component is normal, faults tend to be listric and to form a depressed area (Van der Pluijm and Marshak, 2004). 109

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(Figure 3 – 29) Flower Structures in Strike – Slip fault zone (Burg, 2013)

3.2.2.3: Thrust Faults These Faults in which the hanging wall has moved up relative to the footwall. They are characterized by reverse dip – slip movement. The structural settings in which thrust faults develop may be divided into two major classes (Suppe, 1985): (1) Compressive plate boundaries in both continental and oceanic setting. (2) Secondary faulting developing in response to folding, flexure, igneous or sedimentary intrusion or large – scale land sliding. Thrust faults are common in mountain belts. They move older rocks over younger ones and accommodate crustal shortening. Horizontal shortening of crustal elements is mainly achieved by faulting and compression folding as the orientation of the external stresses responsible for that are the same. To understand how thrust systems form, it is important to know the sequence of development of the faults in duplexes. The structure of duplexes consists of a 110

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series of sub-parallel, S-shaped ramps that branch off a relatively flat, lower floor thrust and merge upward into the upper roof thrust. It can give clues as to the order of thrusting and folding in a given situation. (Suppe, 1983), (Allmendinger, 1998) and (Koyi and Maillot, 2007). 3.2.3: Thrust trajectory The thrust trajectory is the path that a thrust surface takes across the stratigraphic units. They generally follow a staircase trajectory made up of alternating flats and ramps (Ragan, 2009), (Van der Pluijm and Marshak, 2004) as shown in ( (Figure 3 – 30):

(Figure 3 – 30) Flat and Ramp in Duplex Thrust System (Ragan, 2009)

Flats: are parts of the fault that run parallel to a specific, typically incompetent stratigraphic horizon for a large distance. Flats are where the hanging-wall slides along a relatively weak bedding plane are also called décollement plane. Two parallel flats are distinguished as floor (bottom, sole) and roof (top) thrusts (Van der Pluijm and Marshak, 2004) and (Ragan, 2009).

Ramps: Thrust-ramps occur where a fault cross the bedding and climbs through a competent stratigraphic sequence, usually over short distances and typically at angles of 30-45° to the bedding. Most 111

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commonly thrust faults ramp up section in the direction of tectonic transport. Frontal ramps approximately strike perpendicular to the transport direction. Ramps are also found oblique ramp or parallel to the transport direction (lateral ramp, transfer and tear faults) as in (Figure 3 – 31) (Van der Pluijm and Marshak, 2004), (Ragan, 2009) and (Fossen, 2010).

(Figure 3 – 31) Ramps in thrust system (Burg, 2013)

In structural geology, a duplex is a system of imbricate (overlapping) thrusts that branch off from a single floor fault below and merge with at thrust fault stratigraphically higher roof. Duplexes form stacks of thrust-bounded rock bodies, which are bounded by roof and floor thrusts (Figure 3 – 32). The rock body that is bounded by faults above and below is called a horse. Horses can be folded, faulted and rotated during the thrusting history so that their primary geometries and orientations become modified. (Dennis, 1967), (Boyer & Elliott, 1982), (Laney and Gates, 1996) and (Fossen, 2010).

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(Figure 3 – 32) Horses in a Duplex system (Wikipedia)

Thrusts commonly propagate and cut up-section in the direction of slip. The major thrust is first initiated and climbs over a ramp from a lower to an upper flat, thus bringing older rocks over younger rocks. The first ramp is deactivated when the movement on it becomes impossible. The thrust movement continued on the lower flat and then transferred over a second ramp in front of the system. A third and additional ramps can form successively as long as shortening must be absorbed. Accordingly, younger, normal sequence thrusts form progressively forward from the first thrust in hinterland, toward the foreland while older ones are abandoned (Figure 3 – 33). In this way, the thrust system grows toward the foreland (Mitra, 1986). 3.2.4: Types of Duplex Structures Five possible models for the formation of duplexes have been advanced. The first three involve progressive faulting into the footwall with different amounts of displacement of older horses relative to newly formed horses (hinterland, antiformal, and foreland). The fourth involves different ordering of thrust fault formation, with faulting into the hanging wall (outof-sequence thrust). The fifth involves cross cutting of older faults by younger faults in the hanging wall (Boyer& Elliott, 1982), (Mitra, 1986) and (Suppe, 1983). 113

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(Figure 3 –33) The propagation of thrust system (Burg, 2013)

3.2.4.1: Hinterland-dipping duplex In most duplexes the ramps bounding the horses have only small displacements; new horses are formed at the front (in the slip direction) and the older horses are tilted to the back. The ramps and the horses dip away from the foreland. The final geometry is a hinterland-dipping duplex. This is the most common type of duplexes (Figure 3 – 34) (Boyer& Elliott, 1982), (Van der Pluijm and Marshak, 2004) and (Fossen, 2010).

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(Figure 3 – 34) Hinterland – dipping Duplex (Burg, 2013)

3.2.4.2: Antiformal Stack The displacement on the individual older ramps can be greater, such that horses are piled on top of each other and form an antiformal stack (Figure 3 – 35), which appears as eyelid window when the hanging wall is eroded (Mitra, 1986).

(Figure 3 – 35) Antiformal Stack (Mitra, 1986)

3.2.4.3: Foreland-dipping duplex In this type the ramp displacement is still greater for higher, older horses, they may have moved over and beyond the antiformal stack 115

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of younger horses. The geometry is a foreland-dipping duplex. It include the portion of an orogenic belt closer to the undeformed continental interior (Figure 3 – 36) (Mitra, 1986), (Van der Pluijm and Marshak, 2004), (Fossen, 2010) and (Burg, 2013).

(Figure: 3 – 36) Foreland – dipping duplex (Burg, 2013)

3.2.4.4: Out of Sequence New thrusts may develop in the already thrust-faulted and folded hinterland back from the frontal thrust or in a random succession. Or ramps should cut upsection, not down-section. Younger thrusts that develop behind early-formed thrusts are termed “out-of-sequence faults” they can influence the overall geometry of a duplex (Figure 3 – 37), (Van der Pluijm and Marshak, 2004), (Fossen, 2010) and (Burg, 2013).

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(Figure 3 – 37) Out of Sequence Thrusting (Burg, 2013)

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3.2.5: Faulting In Kosrat Anticline Different types of faults were observed and recorded during the field work at Kosrat Anticline which were resulted by the applied regional stresses to the area and the associated local stresses. A normal fault was observed in Qamchuqa Formation in the Northeastern limb within the hinge zone of the anticline, which might be resulted from the radial stretching (outward) over the crest of the anticline (Figure 3 – 38). According to the relation between the fracture surface and tectonic axis, the fault could be classified as hol>c fracture subsystem. The direction of the maximum stress σ1 that caused the faulting is vertical and the direction of the minimum stress σ3 to be northeast - southwest.

(Figure 3 – 38) Normal Fault in Qamchuqa Formation – Kosrat Anticline

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In Dokan Formation near Dokan dam site on the Southwestern limb of Kosrat Anticline, another normal fault was recorded (Figure 3 – 39) with a high dip angle. The fault is classified as okl>c fracture subsystem.

(Figure 3 – 39) Normal Fault in Dokan Formation – Kosrat Anticline

A normal fault was recorded in Kometan Formation in the Southwestern limb of Kosrat Anticline (Figure 3 – 40). It's classified as okl>c fracture subsystem, as the fault plane cuts the tectonic axis's (b) and (c) and parallel to tectonic axis (a) indicating vertical local stress.

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(Figure 3 – 40) Normal Fault in Kometan Formation – Kosrat Anticline

Also a normal fault that was observed in Shiranish Formation in the back slop of the Southwestern limb of Kosrat Anticline (Figure 3 – 41) is classified as okl>c where the direction of the maximum stress σ1 is vertical and the minimum stress direction σ3 is northwest - southeast.

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(Figure 3 – 41) Normal Fault in Shiranish Formation – Kosrat Anticline

Vertical fault is a Fault that have a dip of about 90°; if the fault dip is close to 90° (is between about 80° and 90°), the fault can be called sub-vertical fault (Van der Pluijm and Marshak, 2004). In Tanjero Formation in the SW Limb of Kosrat Anticline a small vertical fault was recorded (Figure 3 – 42). The fault plane is parallel to the tectonic axes (b) and (c) and perpendicular to the

tectonic axis (a); therefore the fault is related to the (bc) fracture set. It is normal to subnormal to the bedding planes and indicates local stress.

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(Figure 3 – 42) Vertical Fault in Tanjero Formation – Kosrat Anticline

The most obvious manifestation of active extension is normal faulting which was recorded in Kometan Formation in the SW limb of Kosrat Anticline (Figure 3 – 43). Set of parallel normal fault that belong to the (hol>c) fracture subsystem.

(Figure 3 – 43) Normal Faults in Kometan Formation – Kosrat Anticline

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Two strike – slip faults were observed in the study area during the field work of Kosrat Anticline. They were recorded in the Southwestern limb in Kometan within Shiranish Formation; the northwestern one is sinistral whereas the southeastern is dextral making the area between them displaced toward the fold axis (Figure 3 – 44). It means of part of Shiranish Formation was moved to be settled within Kometan Formation. According to the relation of the fault surface and tectonic axis it could be classified as hko>a fracture subsystem as the maximum stress direction σ1 is perpendicular to the fold axis and σ3 is horizontal.

(Figure 3 – 44) Strike – Slip Faults in Kometan Formation – Kosrat Anticline

A positive flower structure was recorded in Tanjero Formation in the Southwestern limb of Kosrat Anticline (Figure 3 – 45), which is a strike – slip fault bifurcate and widen toward the surface due to the changes in the mechanical properties near the surfaces of increasing the un-consolidation of sedimentary rocks that make it easier to form multiple faults (Fossen, 2010). The direction of maximum stress σ1 and minimum stress σ3 are horizontal and σ2 is vertical. The faults are classified as a plane of hko>b fracture subsystem according to the relation with the tectonic axis, as the direction of σ1 is running parallel to the fold axis of the anticline 123

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(northwest – southeast). No field evidence was available to determine if the fault is dextral or sinistral one.

(Figure 3 – 45) Positive Flower Structure in Tanjero Formation SW Limb of Kosrat Anticline

Many thrust faults were observed and recorded in Kosrat Anticline during the field work. Thrust faults are not necessarily to be a planar surface; they are often listric faults (concave upward) and antilistric faults (concave downward) (Fischer and Jackson, 1999). In Kometan and Tanjero Formations in the SW Limb of the anticline, Thrust faults were observed and recorded in different locations; they are all 124

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sharing to be in the same fracture classification according to the relation with the tectonic axis. They belong to hol>a fracture subsystem in which the maximum stress direction σ1 is perpendicular to the fold axis and the fault surface strike is parallel to tectonic axis (b) which is the fold axis as shown in Figures (3 – 46) to (3 – 49).

(Figure 3 – 46) Thrust Faults in Kometan Formation SW limb of Kosrat Anticline

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(Figure 3 – 47) Thrust Faults in Kometan Formation - Kosrat Anticline

(Figure 3 – 48) Thrust Faults in Kometan Formation - Kosrat Anticline

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(Figure 3 – 49) Thrust Faults in Tanjero Formation - Kosrat Anticline

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In Shiranish Formation in the SW limb of Kosrat Anticline a thrust fault was observed and classified to be hol>a as the maximum stress direction is perpendicular to the anticline fold axis (Figure 3 – 50).

(Figure 3 – 50) Thrust Faults in Shiranish Formation - Kosrat Anticline

In the valley between the Southwestern limb of Kosrat Anticline and the Ridge of Haibat Sultan Mountain a duplex thrust structure was observed which consists of a series of sub-parallel, S-shaped ramps that branch off a relatively flat, lower floor thrust. Duplex thrust system in the study area (Figure 3 - 51) was classified to be hol>a fracture subsystem in which the maximum stress direction σ1 is perpendicular to the fold axis and Tectonic axis (b) is parallel to the strike of the thrust fault surface.

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(Figure 3 – 51) Duplex Thrust System in Kometan Formation - Kosrat Anticline

Near the core of Kosrat Anticline on the SW limb, Duplex thrust system was also observed. Affecting three lithological formations which are Dokan, Gulneri and Kometan formations. The duplex structure comprises three horses which are a tectonic sheets bounded by thrust faults on each side and occurring in trains having S-shaped geometry (Figure 3 – 52). The fault system is hol>a fracture subsystem, as the maximum stress direction σ1 is perpendicular to the fold axis. The direction of the maximum stress σ1 for thrust faults on the SW limb of Kosrat Anticline may give a clue that it's related to the alpine type style, so its fitting in the general tectonic frame of the Arabian plate.

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(Figure 3 – 52) Duplex Thrust structure on SW limb of Kosrat Anticline

Another thrust fault was observed in the southwestern limb of the anticline, it belong to okl>b fracture subsystem in which the maximum stress direction σ1 is perpendicular to tectonic axis (a) and parallel to the fold axis (Figure 3 – 53). The fault might be resulted due to the relaxing stage after the folding.

(Figure 3 – 53) Thrust Fault in SW Limb of Kosrat Anticline

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A pop-up structure was observed in the back slop of Haibat Sultan Mountain within the study area, which is a section of hanging wall strata that has been uplifted by the combination of a foreland verging thrust and a hinterland verging thrust (McClay, 1981). The uplifted hanging-wall block between a thrust and its conjugate backthrust (Figure 3 – 54) form to compensate for strain within thrust sheets. Therefore a backthrust has a dip and movement direction opposite to that of the main thrust (dip towards the foreland, transport towards the hinterland).

(Figure 3 – 54) Pop-Up Structure (McClay, 1981)

The pop-up structure is classified according to the stress direction relationship with the fault plane (Figure 3 – 55). The structure is classified to be okl>b fracture system as the direction of the maximum stress σ1 is horizontal and parallel to the fold axis (Figure 3 – 56).

(Figure 3 – 55) Stress directions in thrust fault (Butler, et al., 2009) 131

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(Figure 3 – 56) Pop – Up structure in the study area

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3.3: Slickensides Is a smoothly polished surface caused by frictional movement between rocks on the two sides of a fault, it is a very common and diagnostic feature of fault planes (Figure 3 – 57). They display a prominent parallel scratches or striation, are believed to be parallel to the direction of relative movement during their formation (Ramsay and Huber, 1987). Slickensides with striation usually contain small steps facing in one direction and oriented more or less normal to the striation. They have a stepped appearance that can be used to determine the sense of movement across the fault plane. The surface seems smoother when the hand is moved in the same direction that the eroded side of the fault moved, as the surface steps down in that direction. Nevertheless any details about irregularities and structures on and around the slip surface must be checked. As two or more sets of linear structures are common to be found on a single slip surface that reveals different movements at different times, when the stress field changed between different slip events (Billings, 1972) and (Fossen, 2010).

(Figure 3 – 57) Slickenside on a fault plane in Kosrat Anticline 133

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3.3.1: Slickensides of Kosrat Anticline Faults are observed on various scales at outcrops in the study area. The slip orientation of a fault is recognized by the scratches or grooves produced by fault movement on a fault surface that have been measured. Several criteria such as the influence of lithology and the size of the fault plane exist to distinguish the different fault rock types in the field. The goal is to use these measurements to calculate the paleostress regime or direction.

The systematic relationship that exists between brittle structures and principal stress directions provides a basis for interpreting paleostresses directions. In particular, it is important to separate, in the field, the different compression directions that may correspond to separate paleostresses tensors responsible for successive deformation event (Doblas, 1998). Fry (1999) assumed that each striation on a fault surface indicates the direction of the normal projection of the traction vector on that surface.

For the analysis of paleostress directions, the parameters of fault attitudes, slip sense and pitch angle (or rake angle) of slickenlines are required. The data that measured in the field were used to calculate the compression (Paxis) and an extension axis (T-axis) direction by P&T axes graphical method. It is a common, simple, direct representation of fault geometry and the sense of slip method for a single rock fault. The P & T directions may, but do not have to coincide with the principal stresses σ1 and σ3. As the axes would coincide with the principal stress directions only if the fault plane and its conjugate were planes of maximum shear stress (Allmendinger et al., 1989). The software program (Stereo 32) was used to plot the fault plane and slickenlines attitudes stereographically in form of strike-dip and dip sense for fault planes and bearing and plunge for the values of P & T as shown in table (3 - 1): 134

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(Table: 3 – 1) slickensides stations analysis in Kosrat Anticline

Fault Plane: 050\86 NW Fault Type: Strike-Slip Rake:232o \ 17o P: 184o \ 15o T: 276o \ 7o

Fault Plane: 350\60 SW Fault Type: Strike-Slip Rake: 332o \ 26o P: 116o \ 4o T: 025o \ 42o

Fault Plane: 352\87 Fault Type: Normal Rake: 349 o \ 40o P: 043 o \ 30 o T: 298 o \ 24 o

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Fault Plane: 026\88 NW Fault Type: Strike-Slip Rake: 025 o \ 15o P: 070 o \ 11 o T: 340 o \ 10 o

Fault Plane: 353\86 Fault Type: Normal Rake: 175 o \ 24o P: 126 o \ 21 o T: 222 o \ 13 o

Fault Plane: 312\88 SW Fault Type: Normal Rake: 311 o \ 20o P: 264 o \ 14 o T: 357 o \ 14 o

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Fault Plane: 276\58 SW Fault Type: Strike-Slip Rake: 268 o \ 12o P: 312 o \ 30 o T: 050 o \ 15 o

Fault Plane: 036\85 Fault Type: Strike-Slip Rake: 037 o \ 20 o P: 349 o \ 17 o T: 083 o \ 10 o

Fault Plane: 014\50 NW Fault Type: Normal Rake: 345 o \ 30 o P: 038 o \ 53 o T: 135 o \ 8 o

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Fault Plane: 027\85 SE Fault Type: Strike-Slip Rake: 205 o \ 15 o P: 252 o \ 13 o T: 161 o \ 7 o

Fault Plane: 340\74 NE Fault Type: Strike-Slip Rake: 341 o \ 6 o P: 296 o \ 15 o T: 207 o \ 8 o

Fault Plane: 345\83 NE Fault Type: Normal Rake: 161 o \ 20 o P: 211 o \ 20 o T: 118 o \ 10 o

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Fault Plane: 088\85 NW Fault Type: Thrust Rake: 270 o \ 18 o P: 316 o \ 10 o T: 223 o \ 18 o

Fault Plane: 346\83 SW Fault Type: Normal Rake: 343 o \ 10 o P: 030 o \ 12 o T: 300 o \ 2 o

Fault Plane: 200\70 SE Fault Type: Normal Rake: 192 o \ 18 o P: 242 o \ 28 o T: 330 o \ 2 o

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Fault Plane: 340\82 SW Fault Type: Strike-Slip Rake: 160 o \ 5 o P: 027 o \ 2 o T: 116 o \ 10 o

Fault Plane: 058\78 NW Fault Type: Thrust Rake: 242 o \ 18 o P: 286 o \ 4 o T: 195 o \ 22 o


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Fault Plane: 342\75 NE Fault Type: Strike-Slip Rake: 159 o \ 8 o P: 205 o \ 18 o T: 295 o \ 5 o


Fault Plane: 006\70 NW Fault Type: Strike-Slip Rake: 002 o \ 10 o P: 137 o \ 8 o T: 047 o \ 22 o

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Fault Plane: 317\88 SW Fault Type: Strike-Slip Rake: 315 o \ 20 o P: 003 o \ 14 o T: 270 o \ 12 o

Dip slip slickensides on the competent bedding surfaces could be indicating for the prevalence of flexural slip mechanism of folding for the study area (Ramsay and Huber, 1987). Some faults show many slickenside layers, in each of which the striation have different orientation as shown in (Figure 3 – 58). Only the last movement along the fault may record as slickenside layer and the earlier displacement may have been in some other direction because the latest predominate ones scratches the first one.

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Fault Plane: 340\88 SW Fault Type: Strike-Slip o

Rake1 : 160 \ 10 o

o

o

o

P1: 115 \ 9 T1: 206 \ 6

o

Rake2 : 339 \ 26 o

o

o

o

P2: 028 \ 20 T2: 292 \ 16

o

o

(Figure 3 – 58) Fault plane with two slickensides layers in the study area

Traditional theory assumes that each set of slickenlines in a single fault plane represents a distinct tectonic phase. According to this theory, more than one tectonic phase could be obtained from the measured data in the study area. Hence it might be considered that these multiple sets of slickenlines could have been produced in part by block rotation. The rotation is attributable to two factors. One is folding and another is by the movement of major faults. Large faults can rotate during their activity. In 143

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addition, small faults can also rotate due to block rotation near larger faults. During the rotation, the apparent fault type can change. Moreover, block rotation can reactivate preexisting planes of weakness due to changes of stress in a fault plane. In this way, new sets of slickenlines in rotated faults can be produced. The effects of block rotation can lead to a series of superimposed slickenlines in a fault during a single tectonic event (Shunshan et. al., 2011). The Striated meso-faults in Kosrat Anticline have different orientations with respect to the axis of their enclosing fold. Their surface striations trend in various directions which categorized them kinematically into normal and thrust faults according to the sense of movement along the fault plane. The compressional P-axis direction (near σ1) that lies in NE – SW for the striated faults which represent 39% for the normal faults measured data which might be resulted due to the extension during folding, and 8.6% for the thrust fault data, might be resulted from the major compressive stress that affected the area and caused the folding due to the Arabian Plate collision, as they might be sharing the same surfaces of hko>a and hol>a fracture subsystem which the movement occurred along it. And 52% for the strike-slip faults which might be resulted due to local stresses. The compressional P-axis direction NNW – SSE that obtained from the field and according to the scattered plots of P-axis (Figure 3 – 59) was obvious that they coincides the major direction of the compressional stress direction and the other direction might be due to sharing the same surfaces of okl>b and hko>b fracture subsystem during the releasing phase after the tectonic events of the Arabian Plate collision. Figure (3 – 60) shows some striated fault planes that were recorded in the study area of Kosrat Anticline.

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(Figure 3 – 59) Scatter Plots of P and T axis for Slickenlines in Kosrat Anticline

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(Figure 3 – 60) Slickensides in Kosrat Anticline 146

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3.4: Stylolites Stylolites (Greek: stylos, pillar; lithos, stone) are rough paired surfaces (Fig. 3 – 61), mainly observed in monomineralic sedimentary rocks. They form by localized stress induced dissolution. They reflect important digenetic processes in sedimentary basins like compaction, local mass transfer, and porosity reduction. They are often used to estimate the amount of dissolved material in the rock, and therefore the total amount of deformation. The long axis of stylolite teeth-like patterns is also commonly used to determine the largest principal compressive stress direction based on field observations (Ebner et al., 2009).

(Fig. 3 – 61) The Stylolite Pattern (Bauerle, et al., 2000)

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Stylolites are very common in a variety of mono-mineralic rock types and have several distinct characteristics: Stylolite seams result from the accumulation of insoluble materials during the dissolution of the rock (Park and Schot, 1968). The stylolite surface has a pronounced roughness of

peaks or spikes with parallel or inward sloping sides, such that they can be pulled apart without breaking the rock; and this roughness occurs on a range of scales (Koehn et al., 2012). Stylolites are commonly present in limestone and dolomite, usually form parallel to bedding, because of overburden load "non-tectonic origin", but they can be oblique or even perpendicular to bedding, as a resulted from tectonic activity (Fig. 3 – 62), (Hassan, 2007).

(Fig. 3 – 62) Stylolites in relation to compression (Rey, 2002)

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3.4.1: Stylolite Classification Classification of stylolites is approached in two ways (Park and Schot, 1968):

A. By means of the geometry of the stylolite seams themselves. B. By means of the congruency of the stylolites in relation to the bedding plane of the host rock. A- According to the pure geometry of the stylolites: Six basic geometric (two-dimensional) types of stylolites have been differentiated as shown on (Fig. 3 – 63). This classification was originally based on many years of observations in various stratigraphic horizons in carbonate rocks. These basic configurations are shown together with a simplified terminology. 1. Simple or primitive wave-like: it is also called a high amplitude type of residual clay parting, seam or groove. 2. Sutured type: it has a thick, insoluble seam in the crests or valleys. 3. Up-peak type (Rectangular type). 4. Down-peak type (Rectangular type). 5. Sharp-peak type (tapered and pointed): it has the lowest amplitude with thin accumulation of insoluble residue. Most of inclined stylolites are of this type. 6. Seismogram type: is found in oolitic limestones and novaculites.

(Fig. 3 – 63) Stylolite classification according to their geometry (Park and Schot, 1968) 149

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B- In relation to the bedding plane of the host rock (Park and Schot, 1968), (Figure 3 – 64): 1. Horizontal stylolites - This is the most commonly observed stylolite type. They occur parallel or nearly parallel to the bedding of rocks. This type is most frequently found in layered sedimentary rocks, mostly in carbonate rocks, which have not been effected by intensive tectonic structural activity.

2. Inclined stylolites - or slickolites: This type occur oblique to bedding. It appears in rock which affected by tectonic activity.

3. Horizontal-inclined (vertical)-crosscutting stylolites - This type is a combination of horizontal and inclined types of stylolites. Horizontal stylolites usually have higher amplitude than inclined stylolites. Types 3A and 3B in (Figure 3 – 64) represent inclined stylolites displaced by horizontal stylolites and could therefore be called "Horizontal – Inclined (Vertical) – crosscutting stylolites". In this case, the horizontal stylolites usually represent the major stylolite seams and have a higher amplitude and greater regional extent than the inclined stylolites. This combination was apparently formed by two, successive stress systems. The inclined stylolites must have been formed prior to the horizontal stylolites.

4. Vertical stylolites - This type of stylolite is at right angle related to the bedding. It is associated with tectonic activity.

5. Interconnecting network stylolites - This type is a network of stylolites, which intersect each other with relatively small angle. This type can divided on two subtypes. Stylolites of subtype A are characterized higher amplitudes. They related to the bedding 150

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horizontally, or small angle. Stylolites of subtype B usually appear in rocks which have been affected tectonic activity. These stylolites have low amplitude with undulations. Their relation to the bedding can vary from horizontal to vertical.

6. Vertical-inclined (horizontal)-crosscutting stylolites - This type is a combination of horizontal or inclined and vertical stylolites types. Type 6A and 6B in (Figure 3 – 64) represent inclined stylolites that have been displaced by vertical stylolites; here the inclined or horizontal stylolites were formed first and the vertical ones later. In type 6A the displacements could have resulted from vertical stylolization, whereas in type 6B the displacement could only be accounted for by a process prior to the vertical stylolization.

(Fig. 3 – 64) classification of the stylolites in relation to the bedding plane (Park and Schot, 1968)

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3.4.2: Pressure Solution Process When Clastic sediment initially settles, it is a mixture primarily of grains and water. The proportion of solid to fluid varies depending on the type of sediment. Progressive burial of sediment squeezes the water out, and the sediment compacts. Compaction results in a decrease in porosity that results in an increase in the bulk density of the sediment. Deeper burial resulted in more and more compaction, when mechanical compaction becomes impossible, stylolites start to form and grains start to dissolve at point of maximum normal stress, a process by which soluble grains or parts of grains preferentially dissolve along the faces at which the normal stress is the greatest (Figure 3 – 65) (Van der Pluijm and Marshak, 2004).

(Figure 3 – 65) Schematic diagram of pressure solution accommodating compression/compaction in a clastic rock (Wikipedia)

Compaction here is not only used for a reduction in porosity of a rock but also for a vertical shortening of the rock due to the weight of the overlying sediments (Koehn et al., 2007). In pure limestone or sandstones, this process causes grains to suture together, meaning that grain surfaces interlock with one another like jigsaw puzzle pieces. In limestone and Sandstones that contain some clay, the clay 152

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enhances the pressure solution process. Specifically, pressure solution occurs faster where the initial clay concentration is higher. As a result, distinct seams of clay and insoluble residue develop in the rock. These seams are called stylolites (Figure 3 – 66). In rocks with little clay ( a fracture subsystem. In which tectonic axis (a) that indicates to σ1 direction bisect the acute angle between the two sets, and the tectonic axis (c) bisect the obtuse angle. The observed section of the inverted fault in the field may give the sense of being the fault plane trend is inclined to the fold axis as the section direction is NW-SE. Figure (4 – 10) explain the relation between the fold axis of Kosrat Anticline and the Inverted fault plane section in the field which is inclined and not vertical to the fault plane strike.

(Figure 4 – 10) Inverted fault Diagram in NE Limb of Kosrat Anticline

Another structural feature was observed in the southwestern limb of Kosrat Anticline during the field work that may indicate to an inversion tectonics. As within Kometan Formation there were observed parts that differ in lithology and showing a deformation or crushing zones in different levels. These parts might be a footwall shortcut as mentioned by (Hayward and Graham, 1989) as it was suggested that a pre-existing extensional faults are rotated too steeply to be reactivated themselves as reverse faults. In nature

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footwall shortcut thrusts produce isolated wedges of footwall rocks which may be translated in a thrust hanging wall (Figure 4 – 11).

(Figure 4 – 11) Sketch section showing the footwall shortcut in the external Alpine zones of Southeastern France (Hayward and Graham, 1989)

According to the suggestion of (Hayward and Graham, 1989) the observed deformed or crushed parts might be belong to Qamchuqa Fn. or Dokan Fn. as the lithology of these parts is dolomitic limestone (Figure 4 – 12) which may give the idea of being isolated lenses of dolomitic limestone were emplaced or moved high within Kometan Formation as a footwall shortcut as identified in the field.

(Figure 4 – 12) Dolomitic Limestone within Kometan Fn. SW Limb of Kosrat Anticline 177

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On the SW Limb of Kosrat Anticline footwall shortcuts of Qamchuqa Formation were identified within Kometan Formation which might be moved up to be exposed on the surface of the limb during the positive inversion in the area (Figure 4 – 13). In other hand these dolomitic limestone might be the crushed or damaged zone that result along of a major thrust fault in the southwestern limb of Kosrat Anticline. The hanging wall is pushed up over the footwall and produce a crushed or damaged area in between as shown in (Figure 4 – 14). However during the field investigation it was found that some of these zones are spatially related to each other in location of existence along the road that crosses over the anticline. Samples of some crushed zone were taken and studied in thin sections under microscope and found that it is dolomite which can be derived from the zoning property that could be resulted from the late digenetic possibly due to faulting (Tamragha – personal communications). The thrust fault plane is classified to be hol>a fracture subsystem in which the tectonic axis (a) bisect the acute angle between the two sets of this subsystem indicate compressive stress (σ1) direction for faulting.

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(Figure 4 – 13) Footwall Shortcuts "Qamchuqa Formation" in SW Limb of Kosrat Anticline

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(Figure 4 – 14) Thrust Fault in Southwestern limb of Kosrat Anticline

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Another case is in Kometan Formation near Dokan dam in the southwestern limb of Kosrat Anticline vertical or steeply dipping faults were observed, which are possibly inverted faults because of their highly dipping planes. Rock samples of the observed structure were taken and studied under microscope as thin sections which gave a clear picture of the deformation that occurred for the calcite crystals along the fault plane in Kometan Formation. It is obvious from (Figure 4 – 15) that calcite crystals undergo a "smashing mechanism" along the fault plane which results crystal that has a curved shape and broken ones. Besides, the changing of the optical axes of the crystals by faulting was visible by the dark tone of color (black color) in thin sections (Tamragha – personal communications). The faults were classified to be ac set fracture system which is perpendicular to the hinge line of the fold and are parallel to tectonic axis (a) and (c), whereas a tectonic axis (b) is perpendicular to them. These faults are exist as sets to be parallel to each other which may indicate that they have same age of occurrence due to a tectonic event by which a vertical movement took place along their planes. Being these faults belong to ac fractures system which is an extensional one, with thin sections details may give a clue of a thrust movement occurred along their planes. That means these faults are inverted ones.

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Inversion Tectonics (Figure 4 – 15) Inverted faults in Kosrat Anticline – SW limb

A geological cross section (Figure 4 – 16) was draw for the study area along the traverse (A – 'A) in the geological map in chapter two (Figure 2 – 41). It shows the attitudes of the bedding planes for the formations and the inverted faults and their traces on the surface represented by the pictures that explain the effect of the faults on the surface. The compressional phase of fault movement starts in early Tertiary with Kolosh Formation deposition to have a positive inversion in which Haibat Sultan Mountain formed by the rising up of the hanging wall and became topographically higher than Kosrat Anticline.

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(Figure 4 – 16) Geological cross section of the study area along (A – 'A) in the Geological Map (Figure 2 – 41)

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Chapter Five

Conclusions & Recommendations

CHAPTER FIVE CONCLUSIONS & RECOMMENDATIONS 5.1: Conclusions The main conclusions of present work can be summarized as follows: 1- Kosrat Anticline is a part of the high folded zone of the Zagros simply folded belt in northeastern Iraq. 2- The southwestern limb is steeper and shorter than the northeastern limb which make it asymmetrical fold with SW vergence. As the northeastern limb dips 21o and the southwestern one dips 30o. 3- The southeastern plunge of the anticline is near Dokan dam site and the northwestern plunge is represented by the hanging syncline with Khalakan Anticline. The fold axis of the anticline plunge is 3O in trend of 147O and the axial plane dips 85O in the direction of 057O. 4- The exposed rocks in the studied region range in age from Early Cretaceous up to the Middle Pliocene represented by fifteen formations which are: Qamchuqa, Dokan, Gulneri, Kometan, Shiranish, Tanjero, Kolosh, Sinjar, Khurmala, Gercus, Pila Spi, Fatha, Injana, Mukdadiya and Bai Hassan formations. 5- Kosrat Anticline is a gentle fold according to the interlimb angle classification by Fleuty, 1964 which is 129o. 6- The model of folding kinematics is a flexural slip folding that based on the changing of the lithological units or formations that differs from each other in competency and their response to compressional forces, such as Gulneri Formation is incompetent rock unit in the folded layers of the anticline which help to let the competent unit of Kometan Formation to slip easily during folding. The same is for the marly part of Shiranish Formation and the sandy part of Tanjero Formation as incompetent units.

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The studied anticline is a fault propagation fold uplifted through the reverse slipping of the hanging wall of the listric thrust fault. The trend of the fold is of NW-SE direction in accordance with the main trend of Zagros folds.

8- The fold tightening increased form Qamchuqa Formation up to Tanjero formation according to the stereographic projections for the attitudes of the formation bedding planes as the interlimb angle decreased with time. This made the anticline to act as a disharmonic one because of the changing in wavelength for each formation. 9-

Joint analysis revealed the geometrical and genetic relationship with the principal tectonic axes of the anticline as the main compression stress was representative in the form of shear joint system hko acute about (a) which is in the direction of NE – SW and hol acute about (a) that is form in the inner arcs of the anticline which is not observable in the field as wide as hko acute about (a).

10- Extension stress was represented in the form of hol acute about (c) fracture subsystem and (bc) fracture system. 11- The (ab) fracture system could be release fractures resulted from recent unloading or due to weathering process, their surfaces are parallel to the bedding planes. 12- The (hkl) fracture system could be caused by local stresses. 13- Normal, Thrust and Strike-slip faults were identified and analyzed in the study area with a distinguished distribution of thrust faults in the southwestern limb of Kosrat Anticline. 14- Thrust faults and Strike-slip faults could be related with the Arabian plate collision and normal faults might be resulted by the stretching of the outer arcs of the anticline during the folding or as a result of local stresses.

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15- The analysis of fault plane striation showed that the plotted faults have a direction of NE-SW for the compressional stress axis which is conformable with major stress that acted on the study area. 16- Two types of stylolites were identified in the field within Kometan Formation. The first type have a horizontal surface parallel to the bedding plane which is resulted from the overburden load "nontectonic origin" and the other one have a perpendicular surface to the bedding planes which results from tectonic activity as the teeth direction for the second type is towards NE direction between (44o to 46o) as a direction for the tectonic forces that made them. 17- Paleostress analysis for fracture structures (Joints, Faults, Striations and Stylolite Seams) indicated that the studied area was subjected throughout its geological history to a compression stresses which was perpendicular to sub perpendicular in direction to the fold axis (NE – SW) and the other stress was parallel to sub parallel to the fold axis (NW – SE). 18- Faults were identified and analyzed in the study area by using a stratigraphic separation as criteria for fault reactivation and their locations according to the folded layers of the anticline that is showing a positive inversion from extension fault to thrust one. 19- Formation thickness comparison in both limbs of the anticline gave a clue that between the deposition of Kometan and Shiranish formations in the northeastern limb the inversion had started because Kometan Formation thickness is almost double than the one in the southwestern limb. 20- Within Kometan Formation in the Southwestern limb of Kosrat Anticline, crushing zones were found on the road that crosses over the anticline. these zones might be a result of a thrust fault that crushed the rocks or could be parts of dolomitic limestone belong to

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Qamchuqa or Dokan Formations that were separated from the footwall as a short cut. 21- Foot wall shortcuts were identified in the field as a clue for a positive inversion tectonics as parts or lenses of Qamchuqa or Dokan formations that were emplaced high within Kometan Formation in the southwestern limb of Kosrat Anticline. 22- Thin section analysis for rock samples in the (ac) set fracture gave a clear view of faulting along the fracture plane because calcite crystals were smashed and have a curved elongation with dark tone color in some spots in the section due to changing the position of the optical axis that resulted from the deformation of the inverted movement along the fault plane from extension to compression to give a positive inverted fault near Dokan dam site. 23- It was found that Haibat Sultan Mountain is a part of the southwestern limb of Kosrat Anticline and was uplifted due to a thrusting to the area that made it to move on the fault plane and to rise up as a result of a compressional phase of the inversion that occurred in early Tertiary during Kolosh Formation deposition.

5.2: Recommendations 1- Reflection seismic sections studies for the study area to understand

the subsurface structure image of the basement-cover relationship and the detachments. 2- Bio-stratigraphic and petrographic study to understand the normal

sequence and contacts of the geological formations in the study area. 3- Mapping and analysis of more major structures around the study area

together with cross section balancing. 4- Using modern techniques of remote sensing imagery which may

reveal local and regional features. 188

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191

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References Arabian Journal for Science and Engineering, Volume 32, Number 2A, pp. 139 – 148. • Hayward, A. B. and Graham, R. H. 1989. Some Geometrical Characteristics of Inversion. Inversion Tectonics Geological Society Special Publication; No. 44, edited by: Cooper, M. A. and Williams, G. D. pp. 17 – 39. • Haywick, D. W. 2011. Lecture notes in structural geology, Associate Professor of Geology, Department of Earth Sciences , University of South Alabama, www.usouthal.edu/geology/haywick/GY111/folds.pdf • Hobbs, B. E., Means, W. D. and Williams, P.F., 1976. An outline of structural geology. John Wiley and sons, USA, 571p. • Hodgson, R.A., 1961. Classification of structures on joint surfaces. American Journal of Science, Vol. 259, 493 - 502. • Hudleston, P. J. and Stephansson. O. 1973. Layer shortening and fold shape development in the buckling of single layers. Tectonophysics, Vol. 17, pp. 299 – 321. • Jaeger, J. C. & Cook, N. G. W. 1976. Fundamentals of Rock Mechanics. (2nd ed.). Chapman & Hall, London. • Jassim, S. Z. and Buday,T., 2006, Units of the unstable Shelf and the Zagros Suture, chapter 6, pp. 71-90, in Jassim, S. Z. and Goff, J. C., 2006, Geology of Iraq, Published by Dolin, Prague and Moravian Museum, Brno, Czech Republic, 341 P. • Jassim S.Z. and Goff J.C., 2006. Geology of Iraq. Dolin, Prague and Moravian Museum Brno, Czech republic, P.352. • Johnson, P. R. 1998. Tectonic Map Of Saudi Arabia And Adjacent Areas, Ministry of Petroleum and Mineral Resources, Deputy Ministry for Mineral Resource, P. 2. • Karim, K. H., 2005. Origin of Ball and Pillow-like Structures in Tanjero and Kolosh Formations in Sulaymania area, NE-Iraq. (KAJ) Kurdistan Academicians Journal, Vol. 4 (1) part A. • Karim, K. H., Fatagh, A. I., Ibrahim, A. and Koyi, H. 2009. Historical Development of the Present Day Lineaments of the Western Zagros Fold-Thrust Belt: A Case Study from Northeastern Iraq, Kurdistan Region. Iraqi journal of Earth Sciences, Vol.9, No.1, pp.55-70. 193

References • Karim, K. H., Ismail, K. M. and Ameen, B. M. 2008. Litho stratigraphic study of the contact between Kometan and Shiranish formations (cretaceous) from Sulaymania governorate, Kurdistan region, NE Iraq. Iraqi Bulletin of Geology and Mining Vol.4, No.2, p.16 -27. • Karim, K. H. and Taha, Z. A. 2009. Tectonical history of Arabian platform during Late Cretaceous An example from Kurdistan region, NE Iraq. Iranian Journal of Earth Sciences 1, p 1-14. • Knipe, R. J., 1989. Deformation Mechanism – Recognition from natural tectonites, Journal of structural geology, Vol. 11, No. 1/2, pp. 127 – 146. Printed in Great Britain. • Koehn, D., Ebner, M., Renard, F., Toussaint, R., and Passchier, C.W. 2012. Modelling of stylolite geometries and stress scaling, Earth and Planetary Science Letters 341–344, pp. 104 – 113. • Koehn, D., Renard, F., Toussaint, R., and Passchier, C.W., 2007. Growth of stylolite teeth patterns depending on normal stress and finite compaction. Earth and Planetary Science Letters 257, 582–595 • Koyi, H. A. and Maillot, B. 2007. Tectonic thickening of hangingwall units over a ramp, Journal of Structural Geology, Vol. 29, PP 924 – 932. • Ladeira, F.L. & Price, N.J. 1981. Relationship between Fracture Spacing and Bed Thickness. Journal of Structural Geology, Vol. 3, pp. 179-183. • Laney, S.E. & Gates, A.E. 1996. Three-dimensional shuffling of horses in a strike-slip duplex: an example from the Lambertville sill, New Jersey, Tectonophysics, Vol. 258, pp. 53-70. • Lisle, R. J., 2004. Geological Structures and Maps: A Practical Guide, third edition, Elsevier Butterworth-Heinemann, 106 P. • Lisle, R.J., Toimil, N., Aller, J., Bobillo-Ares, N., and Bastida, F., 2010. The hinge lines of non-cylindrical folds, Journal of Structural Geology 32, 166–171. • Mandl, G. 2005. Rock Joints The Mechanical Genesis, Springer, 222P. • Marouf, N. Z. 1983. structural Geology Of Aqra Area, M.Sc. thesis (Unpub), University of Baghdad, 162 p. (Arabic). 194

References • Marouf, N. Z., 1999. Dynamic evolution of the sedimentary basins in Northern Iraq and Hydrocarbon formation, Migration and entrapment. Unpub. Ph.D. thesis, Baghdad University, 245 p. • McClay, K. R. 1981. Glossary of Thrust Tectonics Terms, Department of Geology, Royal Holloway and Bedford New College, University of London, 15 P. • McClay, K. R. 1989. Analogue Models of Inversion Tectonics, Inversion Tectonics Geological Society Special Publication; No. 44, edited by: Cooper, M. A. and Williams, G. D. pp. 41 – 59. • Mitra, S. 1986. Duplex Structures and Imbricate Thrust System: Geometry, Structural Position and Hydrocarbon Potential. AAPG Bulletin, Vol. 70, No. 9, PP. 1087 – 1112. • Mitra, S. 1990. Fault – Propagation folds: Geometry, Kinematics Evolution, and Hydrocarbon Traps. American Association of Petroleum Geologists Bulletin, Vol. 74, No. 6, PP. 921 – 945. • Mitra, S. 1993. Geometry and Kinematic Evolution of Inversion Structures, AAPG Bulletin, Vol. 77, Issue: 7, PP. 1159 – 1191. • Mitra, S. 2003. A Unified Kinematic Model for the Evolution of Detachment Folds, Journal of Structural Geology, Vol. 25, PP. 1659 – 1673. • Mitra, S. and Namson, J. 1989. Equal – Area Balancing, American Journal of Science, Vol. 289, pp. 563 – 599. • Nickelsen, R. P. 1976. Early jointing and cumulative fracture patterns: 1974. New Basement Tectonics contribution n. 23. Utah Geol. Ass. Vol. 5, pp. 193-199. • Numan, N. M. and Al – Azzawi, N. K. 1993. Structural and geotectonic interpretation of vergence directions of anticlines in the Foreland Folds of Iraq, Abhath Al – Yarmouk, 2 (2), pp. 57 – 73. • Numan, N. M. S., 1997. A Plate Tectonic Scenario For The Phanerozoic Succession In Iraq. Jour. Geol. Soc. of Iraq, 30 (2), pp. 85-110. • Numan, N. M. S., 2000. Major Cretaceous Tectonic Events in Iraq, Raf. Jour. Sci. Vol. No. 3, pp.32-52.

195

References • Omar, A. A., 2005. An Integrated Structural and Tectonic Study of the BinaBawi-Safin-Bradost Region in Iraqi Kurdistan. Unpub. PhD thesis, Salahaddin University, 314 p. • Park, W.C., and Schot, E.K., 1968. Stylolites: Their nature and origin. Journal of Sedimentary Petrology, 38: 175-191. • Park, W.C., Schot, E.K., 1968. Stylolites: Their nature and origin. Journal of Sedimentary Petrology, Vol. 38 No. 1. (March), Pages 175-191 • Paterson, M. S. 1978. Experimental Rock Deformation--The Brittle Field. Springer, Heidelberg. • Plummer, C. C., Carlson, D.H. and McGeary, D. 2007. Physical Geology – Text books, Eleventh Edition, McGraw Hill Higher Education Publications, 617 P. • Pollard, D.D., and Aydin, A., 1988. Progress in understanding jointing over the past century. Geological Society of America Bulletin, Vol. 100, 1181 – 1204. • Press, F. and Siever, R. 1986. The Earth. Fourth Edition, W.H. Freeman, P. 656. • Price, N.J., 1966. Fault and Joint Development in Brittle and SemiBrittle Rock. Pergamon Press, New York, 568 pp. • Ragan, D. M., 2009, Structural Geology: An Introduction to Geometrical Techniques, Fourth edition, Published in the United States of America by Cambridge University Press, New York, 602 P. • Ramberg, H. 1971, Folding of laterally compressed multilayers in the field of gravity, II numerical examples, Vol. 4, PP. 83–120. • Ramsay, J. G., 1967. Folding and fracturing of rocks. McGraw-Hill book Co., New York, 568p. • Ramsay, J. G and Huber, M. I., 1987. The techniques of modern structural geology. V.2, Folds and Fractures. Academic press, London, 700p. • Rey,P, 2002. Third year notes, University of Sydney, web address: http://www.geosci.usyd.edu.au/users/prey/Teaching/Geol3101/Paleostress02/rellations.html

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References • Rispoli, R., 1981. Stress fields about strike-slip faults inferred from stylolites and tension gashes. Tectonophysics 75, 29–36. • Butler, R., Casey, M., Lloyd, G. and McCaig, A. 2009. web-based teaching resources in structural geology in the School of Earth Sciences of the University of Leeds, web address: http://www.see.leeds.ac.uk/structure/folds/mechanisms/how/flexsl.htm • Roberts, D. G., Thompson, M., Mitchener, B., Hossack, J., Carmichael, S. and Bjornseth, H. M. 1999. Palaeozoic to Tertiary Rift and Basin Dynamics: Mid-Norway to the Bay of Biscay – a new context for Hydrocarbon Prospectivity in the Deep Water Frontier, Geological Society, London, Petroleum Geology Conference series, vol. 5, pp. 7 – 40. • Rowland, S. M., Duebendorfer, E. M. and Schiefelbein, I. M. 2007. Structural Analysis and Synthesis: A Laboratory Course in Structural Geology. Third Edition, Blackwell Publishing Ltd, 301p. • Rutter, E. H. 1983. Pressure solution in nature, theory and experiment, J. geol. Soc. London, Vol. 140, pp. 725-740, 11 figs. Printed in Northern Ireland. • Saudi Arabian Geological Survey, website address: http://www.sgs.org.sa/english/Pages/default.aspx • Senanayake, S. 2013. Geometry of Folds, website address: http://sanuja.com/blog/geometry-of-folds • Shunshan S. X., Angel F. N., Susana A. A. and Luis G. V. M. 2011. Effect of block rotation on the pitch of slickenlines, Central European Journal of Geosciences, vol. 3(1) pp. 29-36. • Sissakian, V. K. and Youkhana, R., 1978. Report on regional geologic mapping of ErbilShaqlawa- Koisanjaq- Raider area. D.G. Geol. Surv. Min. Invest., Baghdad, Iraq, Unpub. Report, No. 975. SOM Library. • Sissakian, V. K., 2000. Geological map of Iraq. Sheets No.1, Scale 1:1000000, 3rd edit. GEOSURV, Baghdad, Iraq. • Suppe, J. 1983. Geometry and Kinematics of fault – bend folding, American Journal of Science, Vol. 283, pp. 684 – 721.

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199

‫المستخلص‬ ‫ت م دراس ة طي ة كوس رت المحدب ة م ن الناحي ة التركيبي ة والتكتوني ة والواقع ة ض من نط اق‬ ‫الطيات العالية لحزام زاكروس ش مال ش رق الع راق ب ين خط ي ط ول '‪(N 35 54' 36" – 36 01‬‬ ‫)"‪ 48‬و دائرت ي ع رض )"‪ (E 44 48' 36" – 44 58' 12‬والممت د محورھ ا باتج اه ‪.NW-SE‬‬ ‫التتابع الطبقي الرئيسي لمنطقة الدراسة يقع ضمن فت رة الكريتاس ي االس فل ال ى الباليوس ين االوس ط‬ ‫والمتمث ل بمكاش ف التكوين ات م ن االق دم ال ى االح دث وھ ي تك اوين قمجوق ة‪ ،‬دوك ان‪ ،‬كلني ري‪،‬‬ ‫كوميت ان‪ ،‬ش رانش‪ ،‬ت انجيرو‪ ،‬كول وش‪ ،‬س نجار‪ ،‬خورمال ة‪ ،‬ج ركس‪ ،‬بيالس بي‪ ،‬الفتح ة‪ ،‬انجان ة‪،‬‬ ‫المقدادية وباي حسن‪.‬‬ ‫تم وصف وت صنيف الطي ة اعتم اداً عل ى الق راءات المستح صلة م ن العم ل الحقل ي لمنطق ة الدراس ة‪.‬‬ ‫طية كوسرت المحدبة من النوع الغير متناظر حي ث الجن اح الجن وبي الغرب ي اكث ر م يالً م ن الجن اح‬ ‫ال شمالي ال شرقي م ع اتك اء باتج اه الجن وب الغرب ي‪ .‬يبل غ مي ل الجن اح ال شمالي ال شرقي ‪ 21‬درج ة‬ ‫والجناح الجنوب الغربي ‪ 30‬درجة‪ .‬من خالل دراسة الزاوية الداخلية صنفت الطية ح سب ت صنيف‬ ‫فلوتي ‪ 1964‬من النوع ‪.Gentle Fold‬‬ ‫عملي ة الط ي للوح دات ال صخرية ف ي منطق ة الدراس ة ك ان مت أثراً بالتغ اير ف ي ال صفات ال صخرية‬ ‫ومدى استجابتھا لالجھادات المؤثرة عليھا‪.‬‬ ‫ت م تحلي ل البيان ات والقياس ات المت وفرة م ن العم ل الحقل ي ف ي منطق ة الدراس ة والخاص ة بالك سور‬ ‫بانواعھ ا )الفاص ل‪ ،‬ال صدوع‪ ،‬ح زوز الفوال ق واس طح االذاب ة ال ضغطية – ال ستايلواليت(‪ .‬ج رى‬ ‫تصنيف الفواصل من الناحيتين الھندسية والمنشأية الى مجاميع وانظمة متعددة اعتماداً على عالقتھ ا‬ ‫بالمحاور التكتونية وجناح الطية المحدبة‪.‬‬ ‫ص نفت الفوال ق الظ اھرة ف ي مواق ع الدراس ة اعتم ادا عل ى اتج اه الحرك ة عل ى ج انبي س طح الف الق‬ ‫كفالق اعتيادي‪ ،‬مضربي و عكسي مع مالحظة االشكال التي تنتج عن ھذه الفوال ق ح سب امت داداتھا‬ ‫ومقدار االزاحة التي احدثتھا‪.‬‬ ‫اتجاھات االجھاد القديم استنبطت من تحلي ل ح زوز اس طح الفواص ل ف ي منطق ة الدراس ة واظھ رت‬ ‫ان االتجاه الرئيسي لالجھاد ھو عمودي على محور طية كوسرت المحدبة‪.‬‬ ‫مالحظ ة وج ود مجموعت ان م ن اس طح االذاب ة ال ضغطية )ال ستايلواليت( اح داھما موازي ة ألس طح‬ ‫التطب ق وذات الت سننات ال شاقولية‪ ،‬مم ا ت شير ال ى احتم ال تكونھ ا بع د الترس يب نتيج ة الثق ل الھائ ل‬ ‫للطبق ات ال صخرية الت ي تعلوھ ا‪ .‬واالخ رى عمودي ة عل ى اس طح التطب ق والمتكون ة نتيج ة ن شاط‬ ‫تكتوني والتي تؤشر الى االتجاه العام لألجھادات او القوى المسببة لعملية الطي‪.‬‬

‫‪I‬‬

‫من خالل مقارن ة ال سماكات للتك اوين الجيولوجي ة عل ى ج انبي الطي ة ودراس ة موق ع واتج اه الفوال ق‬ ‫تبين وجود فالق ليستيري على الجناح ال شمالي ال شرقي وم وازي لمح ور الطي ة المحدب ة ف ي منطق ة‬ ‫الدراسة من النوع المعكوس ايجابيا‪ .‬كذلك من خالل دراسة الشرائح المجھري ة لنم اذج ص خرية م ن‬ ‫مواقع الفوالق اظھر وجود فوالق عكسية مما يؤيد تعرض المنطقة لعملي ة ‪Inversion Tectonics‬‬ ‫‪.Positive‬‬

‫‪II‬‬

‫وزارة التعليم العالي والبحث العلمي‬ ‫جـامـعـة بـغـداد‬ ‫كـلـيـة الـعـلـوم‬ ‫قـسـم عـلـوم األرض‬

‫التحليل التركيبي لطية كوسرت المحدبة‬ ‫ومدلوالته التكتونية شمال شرق العراق‬ ‫اطروحة مقدمة الى مجلس‬ ‫كلية العلوم – جامعة بغداد‬ ‫وھي جزء من متطلبات نيل شھادة الدكتوراه فلسفة‬ ‫في الجيولوجيا التركيبية‬

‫من قبل‬

‫جنـان منصـور كورئيـل برنـو‬ ‫باشراف‬

‫أ‪.‬م‪.‬د‪ .‬منال شاكر علي الكبيسي‬

‫‪ 2014‬م‬

‫أ‪.‬د‪ .‬نبيل قادر بكر العزاوي‬

‫‪ 1436‬ھـ‬

University of Baghdad

University of Baghdad

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