Integration of Seismic Interpretation with Remote Sensing Techniques to Study the Neotectonics of the Fold-And-Thrust Belts of Northwestern Pakistan

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INTEGRATION OF SEISMIC INTERPRETATION WITH REMOTE SENSING TECHNIQUES TO STUDY THE NEOTECTONICS OF THE FOLD-AND-THRUST BELTS OF NORTHWESTERN PAKISTAN

------

A Dissertation Presented to

the Faculty of the Department of Earth and Atmospheric Sciences

University of Houston

------

In Partial Fulfillment

of the Requirements for the Degree

Doctor of Philosophy

------

Ismail Ahmad Abir

May 2016

INTEGRATION OF SEISMIC INTERPRETATION WITH REMOTE SENSING TECHNIQUES TO STUDY THE NEOTECTONICS OF THE FOLD-AND-THRUST BELTS OF NORTHWESTERN PAKISTAN

Ismail Ahmad Abir

APPROVED:

Dr. Shuhab D. Khan, Professor (Committee Chair) Department of Earth and Atmospheric Sciences, University of Houston

Dr. Paul Mann, Professor Department of Earth and Atmospheric Sciences, University of Houston

Dr. Gulzar M. Aziz ION Geophysical

Dr. Aibing Li, Professor Department of Earth and Atmospheric Sciences, University of Houston

Dr. Dan Wells, Dean, College of Natural Sciences and Mathematics

DEDICATION

To Mak and Ayah

Ilyas, Aisyah and Ishak.

To my favorite poet,

Yesterday I was clever,

So I wanted to change the world.

Today I am wise, so I am changing myself

-Rumi

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ACKNOWLEDGEMENTS This work, which took about 4 years to be completed, would not have been possible without the tremendous help and support from my colleagues in the GeoRS lab. The important guidance from my committee members and the advice and encouragement from my advisor and my mentor, Dr. Shuhab Khan was invaluable.

I would like to thank the GeoRS students who made my working environment exciting and who motivated me to improve my work. Firstly, I would like to thank Daisy

(Jingqiu Huang) for valuable discussions on the processing of InSAR and for teaching me how to update SEGY header files in VISTA so that they could be loaded into Petrel. I would also like to acknowledge Unal Okyay, Kivanc Biber, Sun Lei, Diana Krupnik,

Virginia Alonso de Linaje, Casey Snyder, Proma Bhattacharya, Macey Crockett, and

Wanda Crupa for their help and support during my graduate career. They will surely be missed.

I would like to thank Dr. Wasit (Abuduwasiti Wulamu) from Saint Louis

University for taking time to teach Daisy and I in InSAR processing during his visit to

Houston and countless other times through Skype and meeting at the AGU conference.

Without his help, I would not have processed my data.

I would like to thank my committee members: Dr. Paul Mann for his tremendous help in reading my papers and giving valuable suggestions on improving this work; Dr.

Gulzar Aziz for inviting me to present my research at ION Geophysical and giving me valuable input for seismic interpretation. He also assisted in reviewing and editing my

iv chapter in Bannu Basin; Dr. Aibing Li for her assistance in reviewing and editing of my dissertation.

Most importantly, I would like to thank Dr. Shuhab Khan for his kindness and patience in guiding me ever since I started my graduate studies in the fall of 2010. His encouragement and advice has led me to become a better researcher and more importantly, a better person. His work ethics and teaching philosophy have inspired me to pursue a career in teaching.

I would also like to thank Kevin Foto and Ben Browning who kept me company through many nights in the geoscience computer lab while I mapped faults. Additionally,

I would like to thank the University of Houston and the Department of Earth &

Atmospheric Sciences for funding my graduate studies and for giving me an opportunity to teach as a teaching assistant. I’m also very grateful for the help and discussions with

Dr. Kevin Burke, Dr. Jolante van Wijk, Dr. Pete Emmet, Dr. Shahina Tariq, and Ms.

Rosemary Mullin.

This work is funded by the National Science Foundation, the USAID, the

National Academy of Sciences, and the Higher Education Commission of Pakistan with

InSAR data provided by the European Space Agency.

Lastly, I would like to extend my deepest gratitude to my parents, family, and friends for their untiring support and help.

This dissertation contains the following three manuscripts that are either published, in review stages, or in preparations for different journals; v

1. Abir, I. A., Khan, S. D., Ghulam, A., Tariq, S., and Shah, M. T. (2015). Active

tectonics of western Potwar Plateau–Salt Range, northern Pakistan from InSAR

observations and seismic imaging. Remote Sensing of Environment, 168, 265-

275.

2. Abir, I. A., Khan, S. D., Aziz, G. M., and Tariq, S. Bannu Basin, fold-and-thrust

belt of northern Pakistan: subsurface imaging and its implications for hydrocarbon

exploration (in review, 2016).

3. Abir, I. A., Khan, S. D., Mann, P., Ghulam, A., and Li., A. Western Himalayan

front geometry and relation to earthquake occurrences revealed by InSAR and

satellite mapping . Nature Geoscience (in prep, 2016).

INTEGRATION OF SEISMIC INTERPRETATION WITH REMOTE SENSING TECHNIQUES TO STUDY THE NEOTECTONICS OF THE FOLD-AND-THRUST BELTS OF NORTHWESTERN PAKISTAN

------

An Abstract of a Dissertation

Presented to

the Faculty of the Department of Earth and Atmospheric Sciences

University of Houston

------

In Partial Fulfillment

of the Requirements for the Degree

Doctor of Philosophy

------

Ismail Ahmad Abir

May 2016

vii

ABSTRACT The fold-and-thrust belts of Pakistan are actively deforming and consequently produced devastating earthquakes which destroyed many lives, infrastructures, and properties over the last century. This work focuses on three fold-and-thrust belts, located along the Main

Frontal Thrust; from east to west, the Potwar Plateau, the Bannu Basin, and the Sulaiman

Fold Belt. Coupled with these fold belts are curved structures referred to as re-entrants.

The Sibi Re-entrant, located adjacent to the Sulaiman Fold Belt, has experienced many earthquakes in comparison to the Tank and Kalabagh Re-entrants.

In order to understand the factors that control the formation of these re-entrants and fold belts, radar satellite image processing technique, InSAR (Interferometric Synthetic

Aperture Radar), was utilized and integrated with other available data, such as seismic profiles, well logs, gravity, and multi-spectral satellite imagery mapping.

The integration of InSAR using ten PALSAR images and seismic data shows that the

Potwar Plateau is still tectonically active with areas uplifting up to 15 mm/yr. Based on seismic and well data, salt acts as the main detachment layer displaying thin-skinned deformation. In addition, salt tectonics is observed to be concentrated near the Main

Frontal Thrust, where the overlying rocks are the weakest. The Tank and Kalabagh Re- entrants were interpreted as ‘basin-controlled’ curves with the presence and the extent of salt controlling the shape of re-entrants. Differential movement between areas containing salt and areas with no/lack of salt resulted in the formation of right-lateral strike slip faults (Pezu-Bhittani and Kalabagh faults) and in consequence their respective re- entrants.

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In contrast, there is no clear indication of a major right-lateral strike-slip fault forming the

Sibi Re-entrant. InSAR processing of 34 Envisat satellite images showed that the western

Sulaiman belt experienced a complex deformation with a mixture of different lateral motions. Satellite mapping of active structures in this region using Landsat 8 and Sentinel

2 images suggested a right-lateral shear zone with evidence of ‘bookshelf faulting’, indicating a distribution of deformation across the zone rather than along a strike-slip fault. The difference is attributed to the shape of the Katawaz basin and the weak detachment sliding over thick sediments.

TABLE OF CONTENTS

DEDICATION ...... iii ACKNOWLEDGEMENTS ...... iv ABSTRACT ...... viii TABLE OF CONTENTS ...... x LIST OF FIGURES ...... xiii LIST OF TABLES ...... xvii CHAPTER 1: Introduction ...... 1 1.1 The fold-and-thrust belts of Pakistan ...... 1 1.2 InSAR, seismic and satellite imagery observations ...... 2 1.3 Thesis outline ...... 3 CHAPTER 2: Active tectonics of western Potwar Plateau-Salt Range, northern Pakistan from InSAR observations and seismic imaging ...... 7 2.1. Abstract ...... 7 2.2. Introduction and tectonic setting ...... 8 2.3. Methodology ...... 13 2.3.1. SBAS (Small Baseline Subset) InSAR data processing ...... 13 2.3.2. 2D-seismic ...... 18 2.4. Results and analysis ...... 19 2.4.1. SBAS surface displacement map ...... 19 2.4.2. Structural styles from seismic interpretation...... 23 2.4.2.1. Western Potwar Plateau-Salt Range (Figures 2.4 A, B, C and D) ...... 24 2.4.3. Tectonic interpretation ...... 36 2.4.3.1. Role of Salt Range formation (SRF) ...... 37 2.4.3.2. The movement rate of the dextral Kalabagh fault ...... 41 2.4.3.3. Comparison with Kuqa fold-and-thrust belt, China (Across-strike structural variations) ...... 43 2.4.3.4. Comparison with structural style of central and eastern Potwar Plateau-Salt Range (Along-strike structural variations) ...... 44

2.5. Conclusions ...... 47 CHAPTER 3: Bannu Basin, fold-and-thrust belt of northern Pakistan: subsurface imaging and its implications for hydrocarbon exploration ...... 49 3.1 Abstract ...... 49 3.2 Introduction ...... 50 3.3 Geological background ...... 59 3.3.1. Stratigraphy ...... 59 3.3.1.1. Infra-Cambrian Salt Range formation ...... 60 3.3.1.2. Cambrian to Eocene sedimentary units ...... 60 3.3.1.3. Miocene to Pleistocene molasse sedimentary units ...... 62 3.3.2 Regional tectonics ...... 63 3.3.2.1. Pre-Cambrian to Cambrian ...... 64 3.3.2.2. Permian to Eocene ...... 64 3.3.2.3. Miocene to present ...... 64 3.3.2.4. Petroleum system ...... 65 3.4 Data and seismic observation ...... 67 3.4.1 Northeastern Bannu Basin (Seismic Lines 1-4) ...... 67 3.4.2. Southwestern Bannu Basin (Seismic Lines 5-7) ...... 75 3.4.3 Marwat and Khisor Ranges ...... 88 3.5 Interpretation ...... 89 3.5.1. Structural style of the Bannu Basin ...... 89 3.5.2. Salt diapirism and transpression zones ...... 98 3.6 Discussions ...... 100 3.6.1. Comparison with structural style of the Potwar Plateau-Salt Range ...... 100 3.6.2. Implications for hydrocarbon exploration ...... 103 3.7 Conclusions ...... 106 CHAPTER 4: Western Himalayan front geometry and relation to earthquake occurrences revealed by InSAR and satellite mapping ...... 108 4.1 Abstract ...... 108 4.2 Introduction and tectonic setting ...... 109 4.3 Methodology ...... 113 xi

4.3.1 InSAR (Interferometric Synthetic Aperture Radar) ...... 113 4.3.2 Satellite data processing ...... 118 4.4 Results and analysis ...... 120 4.4.1 SBAS surface displacement map ...... 120 4.4.2 Active geomorphic features from remote sensing ...... 124 4.4.2.1 Western Sulaiman belt (Figures 4.5A and 4.5B) ...... 124 4.4.2.2 Southern Sulaiman belt (Figures 4.6 and 4.7) ...... 129 4.4.3 Tectonic interpretation ...... 129 4.4.3.1 Shear zone along western boundary of the Sulaiman fold belt ...... 132 4.4.3.2 The southwestward escapement of the Sulaiman fold belt ...... 140 4.4.3.3 Comparison of the Sibi Re-entrant to the Tank and Kalabagh Re-entrants ...... 142 4.4.3.4 Potential earthquake around the Sibi Re-entrant ...... 144 4.5 Conclusions ...... 146 CHAPTER 5: Summary and conclusions ...... 147 5.1 The role of salt in fold-and-thrust belts of northern Pakistan ...... 147 5.2 Right lateral shear zone: A model for the western Sulaiman fold belt ...... 148 Bibliography ...... 150

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LIST OF FIGURES Figure 2.1: Map of the study area in northern Pakistan. ……………..……………...……9

Figure 2.2: Normal baselines used for SBAS processing at western Potwar Plateau and Salt Range. ……………………………………………….….….………...……16 Figure 2.3: A map showing the locations of interpreted seismic lines and the displacement map……………………………………………...... …………...20

Figure 2.4A: Interpreted Line 3………………….…………….……...……….………...25

Figure 2.4B: Interpreted Line 4………………………………………………….………27

Figure 2.4C: Interpreted Line 2……………………………..……………..………...…..29

Figure 2.4D: Interpreted Line 1…………………………………………...…….….……31

Figure 2.5: A detailed stratigraphic column of Potwar Plateau-Salt Range (Modified from Faisal and Dixon, 2014; Jadoon et al., 2014)……..……..…….…….…………33

Figure 2.6: A simple drawing of the interpreted structures from the InSAR displacement map……………………………………………………………………...….…..38

Figure 2.7a: Cross-section of western Potwar Plateau-Salt Range (Modified from Jaume and Lillie, 1988)………………………………………………………...……...45

Figure 2.7b: Cross-section crossing Zones A and B……….……..………….…………..45

Figure 3.1: A hillshade map (using the Shuttle Radar Topography Mission Digital Elevation Model) of the Trans-Indus-Salt Range fold-thrust belt, located in northern Pakistan (Kazmi and Rana, 1982; Alam, 2008; Ali, 2010; Khan, 2013) ……………………………………………………………….………….……...51

Figure 3.2: Tectonic setting and generalized map of Bannu Basin-Khisor Range in northern Pakistan (Kazmi and Rana, 1982; Alam, 2008; Ali, 2010; Khan, 2013). ………………………………………………………………………...………..54

Figure 3.3: Regional stratigraphy and hydrocarbon potential of the Fold-thrust Belt of Northern Pakistan (from Wandrey et al., 2004; Qayyum et al., 2014)………....57

Figure 3.4: Bannu Basin North-South Stratigraphic Well Correlation (from Ali, 2010)……………………………………………………………………………66

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Figure 3.5: Bannu Basin West-East Stratigraphic Well Correlation (from Ali, 2010)……………………………………………………………………………68

Figure 3.6: (A) Uninterpreted seismic line 1 in the northeastern Bannu basin (Figure 3.2). (B) Interpretation of Line 1 is assisted by Kundi-X1 well……………………..70

Figure 3.7: (A) Uninterpreted seismic line 2 in the northeastern Bannu basin (Figure 3.2). (B) Interpretation of Line 2………………………...……...…….……………..72

Figure 3.8: (A) Uninterpreted seismic line 3 in the northeastern Bannu basin, located to the south of Lines 1 and 2 (Figure 3.2). (B) Interpretation of the southern section of line 3……………..……………………………………….………………….76

Figure 3.9: (A) Uninterpreted seismic line 4 in the northeastern Bannu basin, intersecting Line 1 (Figure 3.2). (B) Interpretation of line 4………………………………..78

Figure 3.10: (A) Uninterpreted seismic line 5 in southwestern Bannu basin, intersecting Line 6 (Figure 3.2). (B) Interpretation of line 5…………………………….....80

Figure 3.11(A): Uninterpreted seismic line 6a (the northern half of the line) in southwestern Bannu Basin……………….…….…………………..…………..82

Figure 3.11(B): Interpreted seismic line 6a.………………….…………………...……..83

Figure 3.12(A): Uninterpreted seismic line 6b (the southern half of the line) in southwestern Bannu basin…………………………………………………...…85

Figure 3.12(B) Interpreted seismic line 6b………….…………………………………...86

Figure 3.13: (A) Uninterpreted seismic line 7 in western Bannu basin (Figure 3.2). (B) Interpreted seismic line 7……………………….…….……………………...…87

Figure 3.14: Map showing locations of 5 cross-sections used for the fence diagram (Figures 3.15, 3.16)…………………………..…………….…………………..90

Figure 3.15: Fence diagram showing regional structure of the eastern Bannu basin. ……………………………………………………………………………….....91

Figure 3.16: Fence diagram showing regional structure of the western Bannu basin……………………………………………………………...... 92

Figure 3.17: Top: Structural cross-section of the Bannu basin (A). Bottom: Structural cross-section of the Potwar Plateau-Salt Range (B) (Modified from Jaume and Lillie, 1988)…………………………………………..……..……………….....93 xiv

Figure 3.18: Top: Generalized burial history chart for the Kundi-X1 well. Bottom: A critical moment history …………………………………………………….…104

Figure 4.1: A 1-arcsecond SRTM Digital Elevation Model (DEM) map showing the northwest region of Pakistan, where the Sulaiman fold belt is located. ………………………………………………………….…………………..…111

Figure 4.2: A close-up hillshade map of the Sulaiman fold belt and the Sibi Re-entrant showing the main structural features………….………………………..…….114

Figure 4.3: Spatial-temporal baseline for Envisat ASAR images used in this study. ………………………………………………………………………………..116

Figure 4.4: The mean displacement velocity (mm/yr) map of the Sibi Re-entrant and the western portion of the Sulaiman fold belt for a period of 7 years from May 5th 2003 to May 3rd 2010…………………………………………………….…..121

Figure 4.5A: Geologic map of western Sulaiman fold belt. Modified from Jones et al., 1960 and Landsat 8 images. …………………………..……………….……..125

Figure 4.5B: Landsat 8 view of the Dungan and Miri anticlines (Figure 4.5A for location)……………………………………..………………...………………127

Figure 4.6: Sentinel-2 view of the southeastern Sulaiman fold belt (Figure 4.2 for location). …………………………………………...... …………………....130

Figure 4.7: Sentinel-2 view of the southern Sulaiman fold belt (Figure 4.2 for location). …………………………………………………………….……………..……131

Figure 4.8: Map of angle of relative plate motion (α = 52°), instantaneous strain features (θp), and the Harnai fault…………………….………………………….….…133

Figure 4.9: A simple diagram showing the mechanism for the right lateral shear zone (modified from Teyssier et al., 1995)………………………….…….………..135

Figure 4.10: Elevation profiles (A-B and C-D) across the shear zone…………………………………………………………………………....137

Figure 4.11: Simple diagram showing the idealized right-lateral shear geometry with left lateral ‘bookshelf faulting’ (Adapted from Sigmundsson et al., 1995)…………………………………………………………………………..138

Figure 4.12: Focal mechanisms for the Sulaiman fold belt and the Sibi Re-entrant (Dziewonski et al., 1981; Ekstrom et al., 2012; Ekstrom and Nettles, 1997)……………………………………………………………………….....139

Figure 4.13: Simple line drawing of the main faults of the Sulaiman fold belt (after Bannert, 1992) including newly mapped faults (Figures 4.5A, 4.5B, 4.6 and 4.7)…………………………………………………………………………….141

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LIST OF TABLES Table 2.1: A list of the PALSAR data used in SBAS approach. ……………………………………………...…………………………………..15

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CHAPTER 1: Introduction

1.1 The fold-and-thrust belts of Pakistan The active fold-and-thrust belts of Pakistan are one of the most interesting places on

Earth to study compressional tectonic features. They were formed along the Main Frontal

Thrust due to the continental-continental collision between the Indian and Eurasian plates. This work focuses on three fold-and-thrust belts; the Potwar Plateau, the Bannu

Basin, and the Sulaiman Fold Belt. Many models and theories have been discussed on the mechanics of fold-and-thrust belts (Davis et al., 1983). One of the most accepted models is the wedge model based on the critical taper theory (Davis et al., 1983; Dahlen et al.,

1984; Platt, 1986; Dahlen and Suppe, 1988). This model focuses on the cross-sectional view of the deformation.

Another perspective that is often overlooked is the deformation in plan-view. Looking at the three fold belts in plan-view, it is hard not to notice the bending of the thrust front that accompanies each of the fold belts. These bends or curves are called re-entrants; the

Kalabagh Re-entrant (Potwar Plateau), the Tank Re-entrant (Bannu Basin), and the Sibi

Re-entrant (Sulaiman Fold Belt). Many theories have also been proposed to explain the formation of re-entrants (Carey, 1955; Ries and Shackleton, 1976; Marshak, 2004; Weil and Sussman, 2004; Soto et al., 2006). Basically, there are two main ideas on how these bends formed: 1) it was formed due to the irregular shape of the collision boundary or 2) it was formed after the collision due to strain (Carey, 1955; Marshak, 2004).

It is important to understand how these fold-and-thrust belts and re-entrants formed.

Firstly, it will give a valuable insight into how mountain building process works (Carey,

1955). As each fold belt and re-entrant is unique, the mechanism in which these structures deformed are different which is why each of them should be carefully studied.

Secondly, the fold-and-thrust belts along the Main Frontal Thrust is swarming with earthquakes, some of them have resulted in loss of lives, infrastructures, and properties.

One of these earthquakes is the 1935 Quetta earthquake which resulted in the death of up to 60,000 lives (Cox et al., 1936; Skrine, 1936; Armbruster et al., 1980; Avouac et al.,

2014). In comparison to the Potwar Plateau and the Bannu Basin, the Sulaiman Fold Belt and the Sibi Re-entrant are earthquake prone regions. The mechanisms of how these fold belts and re-entrants deform may give us valuable insight on potential future earthquakes.

Finally, these fold belts are important areas for oil and gas production and exploration for

Pakistan. One of the first wells drilled is near Kundal (southwest of Bannu Basin) in

1866, which is one of the first wells drilled in south Asia (Khan et al., 1986; Wandrey et al., 2004). Since then, many oil fields have been discovered in the Potwar Plateau and major gas fields have been discovered around the Sulaiman Fold Belt (Khan et al., 1986;

Jadoon et al., 1994).

1.2 InSAR, seismic, and satellite imagery observations In order to study these active features, we have integrated multiple datasets. Two types of datasets were utilized; satellite remote sensing for surface information and subsurface information from seismic and well data. Both of these datasets give us different perspectives on the fold-and-thrust belts which can give a more complete picture of the deformations that have occurred. 2

The satellite remote sensing techniques that were used can be separated into active- and passive-remote sensing. InSAR (Interferometric Synthetic Aperture Radar) is a powerful active-remote sensing technique that measures surface deformation up to one mm in accuracy over a time interval. This method gives us the current deformation pattern.

Active-remote sensing is a type of satellite sensor that emits its own electromagnetic signal and records the reflected or diffracted signal from the surface. On the other hand, passive remote sensing uses the electromagnetic energy from the sun as the source. In this work, multi-spectral imagery from Landsat-8 and Sentinel-2 were used for active fault mapping.

2D seismic profiles and well logs were interpreted which give us a cross-sectional view of the fold-and-thrust belts. The data was provided by the Oil and Gas Development

Corporation of Pakistan (OGDC) with collaboration with the COMSATS Institute of

Information Technology, Pakistan. In addition, Bouguer anomaly maps were also used to interpret subsurface structures of Bannu Basin (Din, 2007).

1.3 Thesis outline

In Chapter 2, I begin by analyzing the eastern most fold belt, the Potwar Plateau. The integration of InSAR technique and subsurface data (2D seismic and well) were utilized to understand the active tectonics of the Potwar Plateau, with a focus of western Potwar

Plateau (Abir et al., 2015). For the InSAR technique, PALSAR (Phased Array type L- band Synthetic Aperture Radar) images from 2007 to 2010 were processed. In addition, four seismic profiles overlapping the InSAR scenes were interpreted. The surface

3 deformation trends from InSAR were analyzed with the support of the seismic interpretation and published geological maps. Finally, I summarized my findings in a simple figure showing the main deformation zones of western Potwar Plateau, which agrees with previous studies that salt plays a major role in the thin-skinned deformation of this fold belt. In Chapter 2, I also discussed the role of salt, the movement of the dextral Kalabagh fault and compared the Potwar Plateau to the Kuqa fold-and-thrust belt in China.

Chapter 2 has been published in the journal Remote Sensing of Environment (Abir et al.,

2015). We had two reviewers; the first is anonymous and the second is Guido Ventura.

Based on their reviews, we have improved on the writing of the paper which includes grammar and the structuring of the paper. We also improved the figures and clarified the

InSAR processing section as well as the discussion section.

In Chapter 3, I analyzed the Bannu Basin using mainly 2D seismic and well data. Using

Petrel, seven seismic profiles were interpreted with the assistance of published wells and seismic profiles (Ali, 2010). As there are not many published studies on the Bannu Basin, this chapter helps introduce the main geological features of this area. Simple cross- sections were drawn based on the seismic lines and published well data. They were presented in a fence diagram format to show the 3D relationship between these profiles.

This chapter shows clear evidence for the presence of salt in the Bannu Basin. I compared the cross-section of Potwar Plateau to the Bannu Basin showing similarities in their structure and stratigraphy. A case was made for the high potential for a large hydrocarbon accumulation around Bannu Basin. The timing of the petroleum elements were also 4 discussed with the help of burial history and critical moment charts generated in

PetroMod.

Chapter 3 has been submitted to the journal AAPG Bulletin. The paper has been accepted and is awaiting further review. Three reviewers reviewed this paper; the first is anonymous, the second is Thomas E. Hearon and the third is Sandro Serra. Based on their reviews, we have clarified the motivation of our paper which is focused on the structural interpretation of the Bannu Basin using available seismic and well data. Furthermore, we have reinterpreted our seismic lines conservatively and removed the vertical exaggeration of the seismic lines. Finally, we have improved the figures and the organization of the paper.

In Chapter 4, I analyzed the western most Sulaiman Fold Belt. InSAR technique is integrated with multi-spectral remote-sensing mapping of the fold belt. For InSAR processing, 34 Envisat images from 2003 to 2010 covering the western boundary of the

Sulaiman belt were used. I analyzed the surface deformation pattern from InSAR with the help of published geological maps. New faults were mapped for the western and southern parts of the Sulaiman Belt using Landsat-8 and Sentinel-2 images. I summarized my findings into a simple figure showing the shear zone of western Sulaiman Belt and the southwestward escapement of southern Sulaiman Belt. The right-lateral shear zone of

Western Sulaiman Belt is characterized by bookshelf faulting with the identification of parallel left-lateral faults. In Chapter 4, I discussed the importance of studying the mechanism that formed the Sulaiman belt and the Sibi Re-entrant. I also compared the possible mechanisms explaining the difference between the Potwar Plateau-Bannu Basin 5 and the Sulaiman Fold Belt. As salt plays an important role in deforming the Potwar

Plateau and Bannu Basin, the formation of the Sulaiman Fold Belt is more complicated and may involve many factors. I discussed these possible factors in this chapter. Finally, the potential for earthquakes was discussed.

In summary, Chapters 2 and 3 looked mostly at the deformation in the cross-sectional view, while Chapter 4 focuses on plan view deformation. Each chapter focused on a specific fold belt with Chapter 4 discussing the different mechanisms that control the deformation of each re-entrant and fold belt.

CHAPTER 2: Active tectonics of western Potwar Plateau-Salt Range, northern Pakistan from InSAR observations and seismic imaging

2.1. Abstract The foreland fold-and-thrust belt of northern Pakistan is located at the western end of the

Himalayan arc, where salt tectonics is responsible for structural styles, hydrocarbon source areas, and seismicity. Three sub-regions of fold-and-thrust belt are the Potwar

Plateau–Salt Range, Kohat Plateau–Surghar Range, and the Bannu Basin–Khisor Range.

The difference in deformation intensity between these regions is mainly attributed to the presence, or absence, of an Infra-Cambrian salt layer. This study investigates the active tectonics of the Potwar Plateau and Salt Range region, emphasizing the role of salt, using the Small Baseline Subset Interferometry (SBAS) technique and 2-D seismic interpretations. Ten PALSAR images and four seismic profiles from western Potwar

Plateau–Salt Range region were used. SBAS results, derived from PALSAR images spanning from 2007 to 2010, suggest that the Potwar Plateau–Salt Range is active with the western portion of the region experiencing an uplift at an average rate of around 10 mm/year. Two uplift anomalies were observed, which were interpreted as zones of transpression and salt diapirism. Time-migrated seismic profiles showed that the salt layer acted as a detachment. Our results showed that salt has different roles in different regions of the fold-and-thrust belt; in the Potwar Plateau region the salt layer acts as a detachment, while in Salt Range salt flow-induced structures are prominent. The integration of SBAS and 2D seismic interpretation revealed that the deformation of western Potwar Plateau–Salt Range is influenced by two main faults, the dextral

Kalabagh fault and the Main Frontal Thrust. Finally, this work was compared to the Kuqa fold-and-thrust belt in western China due to their structural similarities.

2.2. Introduction and tectonic setting The collision of India with Eurasia resulted in crustal deformation along an arc-shaped convergence zone: the Himalayan–Tibetan orogeny (Hodges, 2000; Molnar, 1984; Yin and Harrison, 2000). Currently, the Indian plate slides northward into the Eurasian plate at an estimated rate of 45 mm/year and this leads to a tectonically active region, which has suffered several devastating earthquakes (Bilham, 2006) (Figure 2.1). An earthquake

(7.9 magnitude) occurred in the northwestern Himalayas near Muzafarabad, Pakistan on

October 8, 2005 claiming the lives of around 86,000 people (Peiris et al., 2006; USGS)

(Figure 2.1). Furthermore, this convergence generated a southward progression of large north-dipping thrusts to accommodate crustal thickening/shortening; from north to south, the Main Karakorum Thrust (MKT), Main Mantle Thrust (MMT), Main Boundary Thrust

(MBT), and Main Frontal Thrust (MFT) (Banerjee and Bürgmann, 2002; Butler et al.,

1989; Sella et al., 2002) (Figure 2.1).These thrust faults separate the Himalayan orogeny into structurally and geologically distinct blocks (Hodges, 2000; Molnar, 1984; Moores and Twiss, 1995; Yin and Harrison, 2000). Located between the Main Boundary Thrust and the Main Frontal thrust is the foreland fold-and-thrust belt, which is a common feature of orogenic belts (Figure 2.1). Since fold-and-thrust belts are located far from the center of orogenic belts, they tend to experience most of the current deformation (Dahlen and Suppe, 1988; Dahlen et al., 1984; Moores and Twiss, 1995). Focal mechanisms along the Main

4 are in shown are 4

Sargodha High is is High a Sargodha

ines 1 ines

Nettles, 1997). Nettles,

3 is indicated by the red box. the is 3 red by indicated

f the ALOS PALSAR scenes that were used scenes were that PALSAR ALOS the f

Bhittani Fault, MMT: Main Mantle Thrust, MKT: MKT: Thrust, Mantle Main MMT: Fault, Bhittani

ic lines that were interpreted interpreted ( were that lines ic

thrust belt. The arrow (inset) The shows estimated current the thrust belt.

and

Ekstrom et al., 2012; Ekstrom 2012; al., and et Ekstrom

of the fold the of

ham, 2006). The location of Figure Theof location 2006). ham,

ult, JF: Jhelum Fault, PBF: Pezu PBF: JF: ult, Jhelum Fault,

. The map map The shows also distribution the . circles) of (red earthquakes area. in Focal study the

Hadi et al., 2012). The yellow rectangle is the location the is o rectangle The yellow al., et Hadi 2012).

Map of the study area in northern Pakistan. The Chaman Fault marks the western boundary of the the of western boundary the marks Fault Chaman The northern in Mapstudy Pakistan. area the of

. .

ure

Himalayas. KF: Kalabagh Fa Kalabagh KF: Himalayas. Fig from (Modified Pivnik,Thrust. 1992; Frontal Main Thrust,MFT: Boundary Main Thrust,MBT: Karakorum Main 2010; Ali, Ul 2D are lines white seism and processing. Black in InSAR 4A Figures compressional with oblique a the slight show and deformation active region Kashmir MFT the along mechanisms 1981; al., et (Dziewonski slipcomponent to uplift located south the basement (Bil plate the of movement Indian

Frontal Thrust show that active compressions are occurring along this fault (Figure 2.1).

Some focal mechanisms also show a minor oblique slip component.

Located at the western edge of the Himalayan arc is the foreland fold-and-thrust belt of northern Pakistan (Figure 2.1). They have unique landforms where regions of relatively flat topography, referred to basins or plateaus, are followed by relatively elevated regions to the south, referred to as ranges. The basins are filled with Miocene to recent molasse sediments originating from the Himalayan orogeny, while the ranges expose older sedimentary layers that have been thrusted over younger layers. The fold-and-thrust belt of northern Pakistan consists of three main regions: the Potwar Plateau–Salt Range,

Kohat Plateau–Surghar Range and Bannu Basin–Khisor Range (Figure 2.1). The study area covers western Potwar Plateau–Salt Range, which is an area that is experiencing transpressional deformation due to the relative motion of dextral Kalabagh fault and the

Main Frontal Thrust. The Kalabagh fault delineates the western limit of the Potwar

Plateau and is an important aspect to active tectonics in this region (Figure 2.1). Recent geodetic studies have suggested that the Kalabagh fault is still active, with an average slip rate of around 5.3 mm/year (Chen and Khan, 2010; Jouanne et al., 2014). Moreover, a

GPS study indicated that the Potwar Plateau is moving southward at rate of 5 mm/year

(Jouanne et al., 2014).

The fold-and-thrust belt of Potwar Plateau–Salt Range is underlain by thick salt and is bounded to the east by the sinistral Jhelum fault (Butler et al., 1987; Jaume and Lillie,

1988). The Kalabagh and Jhelum faults are believed to be related to the fact that thick salt 11 is present in the Potwar Plateau–Salt Range and absent or thinning to the east of the

Jhelum fault and west of the Kalabagh fault (Davis and Engelder, 1985; Sarwar and De

Jong, 1979; Seeber et al., 1981) (Figure 2.1). Figure 2.1 shows that the Potwar Plateau was translated more southwardly than the adjacent Kohat Plateau, with the Kohat Plateau experienced relatively higher deformation. The difference in structural styles and deformation intensities between them are mainly attributed to the nature of their respective detachment layers (Cotton and Koyi, 2000; Jaume and Lillie, 1988; Khan et al., 2012; Yeats et al., 1984). The detachment layer for the Potwar Plateau is at the level of a weak Infra-Cambrian salt layer, the Salt Range formation. Due to the weak nature of the detachment's lithology, which resulted in its low shear stress, the overburden slides effectively along the sole thrust without significant resistance (Davis and Engelder,

1985). Another important feature of salt is the presence of salt mines along the southern boundary of the Salt Range, delineated by the Main Frontal Thrust, which may be related to salt tectonics.

This observation shows the importance of the salt layer in studying the complex, thin- skinned deformation of this region (Chapple, 1978; Jaume and Lillie, 1988). In order to fully understand how the fold-and thrust belt of northern Pakistan deforms, the regional faults and the local lithological variability, such as salt and overburden thickness, must be taken into account. Previous models explaining the deformation of this region have been mainly based on geological field works, seismic profiles and well data (Cotton and Koyi,

2000; Jadoon et al., 2014; Jaume and Lillie, 1988; Khan et al., 2012; Yeats et al., 1984).

A recent approach in studying the Kohat Plateau by Satyabala, Yang, and Bilham (2012) 12 using Interferometric Synthetic Aperture Radar (InSAR) gives new insight into how fold- and-thrust belts currently deform. Similarly, this work utilizes InSAR in order to better understand the current deformation pattern of western Potwar Plateau–Salt Range and the

Kalabagh fault.

This work focuses on the active tectonics of western Potwar Plateau and Salt Range, with emphasis on the identification of actively deforming structures. Two methods were used in this study: SBAS (Small BAseline Subset), an InSAR processing technique and 2D seismic interpretation. SBAS was used to map the surface deformation of the southwestern region of the Potwar Plateau–Salt Range from 2007 to 2010. Results showed that the Salt Range underwent uplift up to 15 mm/year. 2D seismic sections and published well data give a clear picture of the subsurface structures of the Salt Range formation. This work provides a clear evidence for active transpressional deformation and salt diapirism at the western Salt Range. Furthermore, the presence of salt in this region affects the deformation of Potwar Plateau and the Salt Range differently. In the

Potwar Plateau, the salt acts as the detachment layer, while salt diapirism is prominent in the Salt Range.

2.3. Methodology

2.3.1. SBAS (Small Baseline Subset) InSAR data processing InSAR is a powerful tool in detecting crustal deformation and movements of salt structures over a large spatial area with centimeters to millimeters accuracy (Berardino et al., 2002; Lanari et al., 2007;Massonnet et al., 1993). In contrast to point-based GPS

13 studies, InSAR provides spatial and temporal deformation patterns, which can be used to identify large-scale active features. For example, it has been used to map and model a salt dome in Iran (Aftabi et al., 2010), and the displacement of the Kalabagh fault between the

Potwar Plateau–Salt Range and the Kohat Plateau–Surghar Range systems (Chen and

Khan, 2010). One of the common approaches in detecting slow deformation is the Small

Baseline Subset Interferometry (SBAS) (Berardino et al., 2002; Lanari et al., 2007), which derives incremental displacements by inversion of temporal phase profiles effectively reducing atmospheric effects, topographic uncertainties, and/or orbital errors.

SBAS technique has been successfully used to study deformation trends of calderas and major cities, such as Phoenix, Arizona, USA, Houston, Texas, USA and Nanjing, China

(Berardino et al., 2002; Casu et al., 2005; Huang and He, 2008). Ten ascending SAR images from the Phased Array type L-band Synthetic Aperture Radar (PALSAR) sensor onboard the Advanced Land Observing Satellite (ALOS) over a period of 3 years between January 2007 and March 2010, were used in this study (Table 2.1). The SAR images cover the western Salt Range (Figure 2.1).

A total of 32 InSAR pairs were generated using normal baseline thresholds of 50% of the critical baseline for the spatial baseline and 600 days for the temporal baseline. Figure 2.2 shows the time-baseline plot for the PALSAR images that were used for SBAS processing. The interferograms were processed using the SARscape modules of ENVI software from EXELIS VIS Information Solutions. The processing steps include the co-

Final displacement Final was

lected in Fine Beam Single lectedFine in mode Beam

to which a null displacement was null displacement a which to

, 2007), ,

nadir angle on path/row of 533/640. The image image The path/row on 533/640. of angle nadir

the first acquisition date (January 7 (January acquisition date first the

1 1

list of the PALSAR data used in SBAS approach. The images were were col images The approach. SBAS in used data listPALSAR the of

Table Table A degrees 34.3 with off Dual (FBD) mode and (FBS) for interferograms. master the 2008 27th, all image as used May on was collected to respect with estimated assigned.

, 2007), to to 2007), ,

ow diamonds refer to the SBAS master image (May (May image SBAS the to master refer diamonds ow

. .

Normal baselines used for SBAS processing at western Potwar Plateau and Salt Range. Green western Potwar at Salt SBAS Range. Normal and baselines Green processing for Plateau used

, 2008). Final displacement was estimated with respect to the first acquisition date (January 7 (January first date acquisition the to with respect estimated was displacement Final 2008). ,

27 Figure while pairs, the interferogram valid represent diamonds yell assigned null was displacement a which

registration of the image pairs, interferogram generation, inteferogram flattening using

Shuttle Radar Topography Mission (SRTM) version 4 (http://srtm.csi.cgiar.org/) digital elevation model (DEM), Goldstein filtering (Goldstein and Werner, 1998), and coherence generation. A complex multi-look operation taking one look in range and five looks in azimuth was performed to produce ground resolution of about 15 m.

Phase contributions due to the earth's topography from the interferograms were removed during the flattening step using the simulated phase corresponding to the reference DEM at the SAR imaging geometry. Residual phase ramps due to imprecise orbit knowledge was estimated and removed using a best fitting linear phase ramp of reference points determined along orbital fringes. A combination of minimum cost flow (MCF) network

(Costantini, 1998) and Delauney 3D method (Hooper and Zebker, 2007) was employed for phase unwrapping. The phase errors, caused by the atmospheric signal, were correlated in space and were removed. Atmospheric phase screening was conducted to estimate and remove atmospheric effects before the final displacement velocities were calculated. The spatial variation of the atmospheric phase in the same acquisitions was typically small over the spatial scale and much stronger over time. A low pass spatial filter (at 1.2 km × 1.2 km window) on each single acquisition, followed by a high-pass filter on the time series images, was used to screen the atmospheric phase component of the signal.

It is worth noting that the displacement from InSAR is a relative measure in the line of sight (LOS) direction. Ground control points with assumed zero deformation (motionless) were selected as reference points for SBAS processing chain. The criteria for identifying such pixels may include a temporal coherence value of 0.75 or greater, unwrapped phase value close to zero and flat areas identified from a topographic map projected at LOS direction. The mean displacement value calculated over the ground control points was subtracted from the displacement image, as it is supposed to be “zero” over these motionless points. Therefore, it is likely that the absolute values of cumulative displacements were affected by the selection of the ground control points.

2.3.2. 2D-seismic The seismic data were provided by the Directorate General of Petroleum Concessions

(DGPC) of Pakistan. The seismic lines were acquired during 1978 to 1981 by the Oil and

Gas Development Company Limited (Pakistan) using dynamite as source, with the length of the profiles ranges from 25 to 45 km. Four seismic reflection profiles were interpreted for structural and stratigraphic information (Figure 2.3). The details of the interpreted seismic lines are presented and discussed in Section 3.2. All of the seismic lines (Lines

1–4) overlap the PALSAR images. The overlapping lines were utilized in the interpretations of the InSAR surface displacement result. Line 3 (A–A′), line 4 (B–B′) and line 2 (C–C′) are oriented north–south, while line 1 (D–D′) is oriented east–west

(Figure 2.3). Information from well Karang-01 (TD: 1091 m) from Leathers (1987) was used to interpret the seismic lines (Figure 2.3). The interpretations of the seismic lines reveal the subsurface structures, which include strike-slip faults, variable thicknesses of

18 the Salt Range Formation, the basement ramping to the south and the southward tapering of the overburden. Petrel Schlumberger software was used for interpretation with the assistance of published well data and published velocity models (Chen, 2009; Pennock,

1988). Seismic attributes, such as instantaneous phase, were used to easily detect horizons and faults.

2.4. Results and analysis

2.4.1. SBAS surface displacement map Figure 2.3 shows the accumulated total displacement in mm along the Line of Sight

(LOS) averaged for the duration of approximately 3 years (January 7th, 2007 to March

2nd, 2010). Overall, the western Potwar Plateau–Salt Range has moved toward the satellite as indicated by a decrease of the sensor-to-target slant range distance. On ascending path, the ALOS satellite was moving north with its antenna pointed to the right. Therefore, a decrease in the slant-range distance can be regarded as a westward shift, uplift or both. We attributed this movement primarily to an uplift for the following reasons: 1) from the general tectonics of the area, we know that the plateau is on the hanging wall side of the Main Frontal Thrust system, where uplift is expected; 2) A GPS observation deployed in central Potwar plateau, which indicated that there was a south- southeast (SSE) motion of about 3 mm/year rate relative to the Indian plate (Khan et al.,

2008) (Figure 2.1). The GPS observation is consistent with the InSAR displacement map that shows a very low displacement rate at around 4 to 5 mm/year in the same region

(Figure 2.1). This suggests that the observed deformation is predominantly caused by surface uplift. However, the rate of uplift is not consistent over the whole map, with uplift

ne A, A, ne

Potwar Plateau region region Plateau Potwar

01 well (Leathers, 1987). The The 1987). (Leathers, well 01

d seismic lines and the displacement map. The map. the seismic d and lines displacement

ta for a period of 3 years spanning from Jan 7, 2007 to March 2, 2010. The from 2010. 2, 3 Jan of spanning March to 2007 7, period for ta a years

A map locations the showing interprete of A

band PALSAR da PALSAR band

slip fault is also interpreted from the map (located at western side of western side at map the map). (located from interpreted also is slipfault

Figure 2.3 Figure assistance the Karang with interpreted the of seismicwere lines SBAS Salt western Range obtained technique for by was map displacement using L the the signify towards which movement from mm/yr, 15 to 0 displacement rates ranges averaged seen denoted be by Zo can anomalies uplift Two the of (Line LOS Sight). along satellite a dextral interpreted diapirism. salt transpression as B, a Moreover, as Zone zone interpreted and strike

21 rates that generally range from 4–11 mm/year. Moreover, two uplift anomalies were observed (denoted by Zone A and Zone B in Figure 2.3). Both zones experienced an uplift rate of around 15 mm/year. With the assistance of detailed geological maps and cross sections of the Salt Range by Gee (1980) and Gee and Gee (1989), we interpreted

Zone A (Sakesar) as a transpression zone and Zone B (Warcha Salt Mine) as a salt tectonic zone. This showed that deformation was strongly affected by localized geological events. In the case of Zone A, the combination of the interpreted strike-slip fault and the Main Frontal Thrust created a dextral transpression zone, where significant uplift may occur. The interpreted strike-slip fault was clearly observed as a linear feature on the InSAR displacement map, located to the northwest of Zone A. This dextral strike- slip fault is believed to be related to the Kalabagh fault. The eastern fault block has a displacement rate in LOS of approximately 7.5 mm/year and the western fault block has around 0–2 mm/year displacement rate. Although Zone A coincides with the region of highest topography in Salt Range, with the Sakesar Mountain peaking at 1522 m, we believe that due to the active Kalabagh fault, it is very probable that uplift did occur. In addition, mapped faults coincide very well with the southern limits of the uplifted Zone

A. This strongly shows that tectonic has a role in the deformation of this region.

By contrast, Zone B is surrounded by exposed salt, where an active salt mine (Warcha

Salt Mine) is located. The Warcha Salt Mine is administered by the Pakistan Mineral

Development Corporation (PMDC), where dome-like salt structures are mined. The anomalous surface deformation of Zone B suggests that salt diapirism may be the cause of the uplift, which is controlled by active transpressions and compressions in this region. 22

This is a further confirmation that internal deformation of Potwar Plateau and Salt Range is not consistent along the strike of the Main Frontal Thrust, which may be attributed to local factors such as faulting, salt tectonics, basement geometry, overburden geometry or all of them combined.

In addition, the eastern part of the displacement map was not interpreted due to unwrapping errors in InSAR processing. The identification and interpretation of active structures were only performed for the western half of the displacement map. This error could be attributed to the lack of reliable interferograms due to insufficient number of

SAR images for SBAS processing. Areas of low coherence are shown as regions of no data, which is mainly due to highly vegetated areas.

2.4.2. Structural styles from seismic interpretation Four time-migrated seismic reflection profiles were interpreted (Figures 2.4A–D) along with available well and velocity model information. Four seismic lines (Lines 1–4), overlapping InSAR displacement map, are located in western Potwar Plateau–Salt Range

(Figure 2.3). Four main stratigraphic layers were distinguishable, which are from the top, the molasses section (Siwalik and Rawalpindi from Pleistocene to Miocene), the carbonate platform (Eocene to Cambrian), the Infra-Cambrian Salt Range Formation

(SRF), and the Pre-Cambrian basement. Figure 2.5 shows a more detailed stratigraphy of the Potwar Plateau–Salt Range region. The most distinguishable layer in the seismic profiles is the carbonate platform. This layer is characterized by very strong reflectors in the seismic profiles. Below the platform, the SRF is characterized by a seismically

23 transparent layer. The boundary between the SRF and the basement rock is also a strong reflector, which is mainly due to the high acoustic impedance difference. The Siwalik and

Rawalpindi groups are identified as moderate parallel reflectors. In all of the seismic profiles, the boundary between the Siwalik and the Rawalpindi is inferred. Generally, the carbonate platform thickness is consistent throughout all the profiles. The SRF has the most variation in thickness, which is due to its ductile nature. The descriptions of the interpreted seismic lines are as follows.

2.4.2.1. Western Potwar Plateau-Salt Range (Figures 2.4 A, B, C and D) In general, the seismic profiles show that the thickness of the Salt Range Formation is directly related to overburden thickness. Also, it is clear from the seismic interpretation that the detachment layer is located in the Salt Range formation. For instance, Line 3 showed an area of salt weld or thinning of salt on the north side of the line (Figure 2.4A).

Faults were interpreted above this area, which suggested that the salt evacuation, most probably to the south, disturbed the overlying sedimentary layers (Figure 2.4A). This observation also correlates well with the thickness of the overburden, especially the

Rawalpindi and Siwalik molasse section. Due to differential loading, salt escapes from the higher load (thick overburden) to a region of lower load to the south. Due to the relatively rigid nature of the Cambrian–Eocene platform ‘floating’ above the ductile salt layer, it tends to break apart, resulting in faults. Another important observation was that there is no presence of a basement normal fault, which can be seen in central Potwar

Plateau (Faisal and Dixon, 2014; Jaume and Lillie, 1988). Instead, the Pre-Cambrian basement appears to flex upwards toward Salt Range.

is line to the south. The Salt The line is south. the to

01 well intersects th intersects well 01

, which may be due to salt flow. Also, reflectors strong at may due be which , to flow. salt

on were interpreted as a layer of interpreted or anhydrite layer as gypsum. a were on

Interpreted Line 3. The Karang The 3. Line Interpreted

of the Salt Range Formati Salt Range the of

(as indicated the (as arrow) by

Figure Range Salt the occurs above Faulting generally as layer. detachment Formationacts a Range Formation bottom the

cated to the north of the line. of the north the to cated

Interpreted Line 4. The structural style is similar to the previous line. The Salt Range Salt Range The line. style structural previous similar is the to The 4. Line Interpreted

basement normal fault, with a relatively small throw, lo throw, small relatively fault, a with normal basement Figure the occurs above Formation, SaltRange Faulting generally detachment a acts as layer. Formation Formationwere Salt bottom the Range the of reflectorsstrong Also, at salt to due be flow. may which a of observation Anotherimportant presence the is or anhydrite layer gypsum. of a as interpreted

t under synclinal structures. Also, strong reflectors at the bottom of the Salt bottom the the of reflectors strong Also, at structures. synclinal under t

Interpreted Line 2. The Salt Range Formation acts as a detachment layer. A basement basement A detachment a as Salt layer. Range Formationacts The 2. Line Interpreted

Figure anticlinal thicker with SRF the of under salt thickness varies, The interpreted. is fault normal sal thinner and structures or layer interpreted of a anhydrite as gypsum. Formationwere Range

slip fault was interpreted, which interpreted, was slipfault

map. map.

Interpreted Line 1. Most of the line is located west of the Kalabagh fault and has and a the of is fault line the of Most 1. Kalabagh west located Line Interpreted

t stratigraphy. The layers are mainly parallel and undisturbed. However, they are they are mainly parallel However, Theundisturbed. and are layers stratigraphy. t

Figure differen strike dextral a Also, Thrust. Main the by Frontal truncated the with well displacement InSAR correlates

Figure 2.5: A detailed stratigraphic column of Potwar Plateau-Salt Range (Modified from Faisal and Dixon, 2014; Jadoon et al., 2014).

Although to a lesser extent, Line 4 also shows similar structures; a faulted zone of

Cambrian to Eocene platform is interpreted above a thinning salt zone (Figure 2.4B). In addition, the molasse sections, the Rawalpindi and Siwalik formations, are relatively undisturbed, except for some minor faults. Another important observation is the north- dipping normal fault of the Pre-Cambrian basement rock. However, the throw of the normal fault is relatively less than those in central Potwar Plateau (Faisal and Dixon,

2014; Jaume and Lillie, 1988). This suggests that the basement normal fault does not play a major role in the ramping of the western Salt Range. Line 2 shows a basement normal fault with a small throw (Figure 2.4C). This indicates that the basement normal fault is mainly prominent in central Potwar Plateau. The southern portion of the line shows a gentle syncline followed by a gentle anticline to the north. Thicker molasse was deposited in the syncline, which increased the load and pushed the salt to the north, into the anticline. Moreover, it is clear that the salt detached the overlying Cambrian to Eocene platform and the Rawalpindi/ Siwalik layers from the Pre-Cambrian basement. The north- dipping detachment surface, which is also the thrust surface, is likely to be in the Salt

Range Formation.

Line 1 runs through the Kalabagh fault (Figure 2.4D). Most of the line is located to the west of the Kalabagh fault and has a different stratigraphy (Figure 2.3). The formations that were interpreted are, from the oldest layer, the Pre-Cambrian basement, Cambrian strata, Permian strata, Mesozoic strata, Lower Tertiary strata, Chinji, and Nagri formations. These layers are mainly parallel and undisturbed. However, two faults were interpreted to the east of the line. A thrust fault separates the parallel strata to the west 34 from the over-thrusted Salt Range strata. A possible right-lateral strike-slip fault was also interpreted and this is consistent with the SBAS displacement map (Figure 2.3). In general, the seismic interpretation of western Potwar Plateau–Salt Range can be summarized as the following:

1. Most of the structural deformation, such as thrust faults and folds are striking east– west. This shows that most of the compressional forces are oriented north–south. The general folding that occurs is gentle, symmetrical and can be characterized as low– frequency folds. Most of the structures are south-verging.

2. The basement normal fault is absent or has relatively small throw. However, the Pre-

Cambrian basement shows an upward flexing toward the south. This may explain the translation of the hanging wall without much internal deformation.

3. The Salt Range Formation (SRF) varies in thickness from 900 m to 3500 m, which is a direct consequence of the variability in overburden thickness. Salt tends to escape higher load area (synclines) into lower load area (anticlines).

4. Other than some thrust faults cutting across the overburden layers (molasses section and carbonate platform), the suprasalt layers are relatively undeformed. The carbonate platform, which is the most distinguishable layer in the seismic section, has a constant thickness of roughly 600 m. The faulted rigid Cambrian–Eocene carbonate platform can be described as ‘floating’ on the ductile salt layer.

5. A southern portion of the dextral Kalabagh fault was interpreted, with the help of

SBAS displacement map (Figure 2.3).

2.4.3. Tectonic interpretation By integrating the InSAR results and seismic interpretation, this work focuses on the tectonic and structural framework of western Potwar Plateau–Salt Range region. Previous studies have shown that the Potwar Plateau–Salt Range is a thin-skinned foreland fold- and thrust riding on thick Infra-Cambrian salt (Faisal and Dixon, 2014; Jaume and Lillie,

1988). Studies have also been done comparing the structural styles of the Potwar Plateau and the adjacent Kohat Plateau. Essentially, the salt layer in this region affects the advance of both the Potwar Plateau as well as the Kohat Plateau. It is suggested that the

Potwar Plateau advanced more southward because the Salt Range formation acts as a detachment layer (Cotton and Koyi, 2000; Jaume and Lillie, 1988). This is evident in the fact that the Kohat Plateau has more internal deformation than the Potwar Plateau. The key is the basal shear stress between the overburden and the basement rock. In the Potwar

Plateau, the salt layer acts as a lubricant and decreases the shear stress and cohesion significantly. This is supported that more internal deformation is seen in the Kohat

Plateau than the Potwar Plateau.

The deformation mechanics of this region is proposed to be analogous to a bulldozed wedge of snow (bulldozer model) that is moving on a ductile substrate (Cotton and Koyi,

2000; Lillie et al., 1987). The wedge is essential for the generation of a thin-skinned fold- and-thrust belt, such as the Potwar Plateau–Salt Range (Chapple, 1978; Davis et al.,

1983). The wedge is thickest at the back part near the Main Boundary Thrust and thins out in the direction of the Main Frontal Thrust.

2.4.3.1. Role of Salt Range formation (SRF) The Salt Range Formation was interpreted as the layer between the strong reflectors of the carbonate platform and the basement rock. From the folding of the overburden and the relatively unchanged basement floor, the detachment is located in the SRF which acts as a lubricant between them. As a result of only the overburden advancing southward on the mechanically weak salt layer, this region is categorized as a thin-skinned fold-and- thrust system. Furthermore, it is clear from geological maps and the seismic data that the salt layer did not reach the surface in the Potwar Plateau region (Gee, 1980; Gee and Gee,

1989). This indicates that the SRF is mainly acting as a detachment layer. However, exposed salt and salt mining are prominent in the Salt Range and these salt structures are mainly concentrated near the Main Frontal Thrust, suggesting that salt flow may play a significant role toward the south. Evidence from the InSAR map supports this idea (Zone

B) (Figures 2.3 and 2. 6).

The seismic interpretations showed that the salt thickness varies from 900 m to 3500 m.

These variations were mostly due to the folding of the overburden. The salt in synform areas tend to move to antiform structures, creating salt-cored anticlines. However, the scale of overburden deformation for the Potwar Plateau is very broad and the folding occurs over long distances (around 5–10 km). Therefore, looking through a broader scale, the SRF has a relatively consistent thickness throughout the Potwar Plateau. Seismic Line

3 showed the collapse of the faulted Cambrian–Eocene platform, which may be due to salt evacuation to the south (Figure 2.4A).

istinct the regions: from

Salt Range can be divided into three d be into divided three can SaltRange

A simple drawing of the interpreted structures from the simple structures the of drawing displacement InSAR interpreted A

ctions were shown drawn, Figure in were ctions

Figure Plateau Potwar The map. and Syncline Soan Salt the the Deformation Potwar Zone), (Northern NPDZ the north, cross Two these regions. boundaries between black dashed represent lines The Range. se

Our results suggest that the Salt Range formation has two main roles in this fold-and thrust belt: the salt layer acts as a decollement for the Potwar Plateau region and salt flow becomes prominent in the Salt Range. Salt is mechanically weak and is less dense than the surrounding rocks (Hudec and Jackson, 2007). Therefore, the buoyancy force tend to push the salt upwards through the overburden. However, if the overburden is too hard or too thick for the buoyancy force to overcome, the salt will stay in place or move laterally.

This is the case for Potwar Plateau, where the overburden is around 3–5 km in thickness, which is further strengthen by folding and thrusting due to compressional forces.

Furthermore, as the fold-and-thrust belt is further compressed, the salt is further pressurized tectonically to move southward toward Salt Range. This movement is due to differential loading, where salt flows from higher pressure (back of wedge) to lower pressure (front of wedge) region (Hudec and Jackson, 2007).

Zone B, located near the Warcha Salt Mine, shows a significant uplift from 2007 to 2010

(Figure 2.3). This may be due to salt diapirism. In order for salt diapir to move into its overburden, the rocks of the overburden, occupying that space, must be removed or displaced (Hudec and Jackson, 2007). This removal of the overburden may be due to uplift and erosion of the hanging wall (overburden), which is widespread along the Main

Frontal Thrust. This may explain the prominence of salt mines and salt diapirism along the Main Frontal thrust. Furthermore, since Zone B experienced an anomalous uplift, this suggests that it may be a teardrop diapir. Teardrop diapirs are common in compressional salt basins and are mainly controlled by regional tectonics (Hudec and Jackson, 2007). As compression continues, teardrop salt diapirs will rise due to tectonic pressurization. 40

2.4.3.2. The movement rate of the dextral Kalabagh fault Zone A is interpreted as an oblique compression zone (Figure 2.3). Transpressional zones are strike-slip structures that are undergoing an oblique shortening deformation due to compressional forces (Dewey et al., 1998). These zones are usually regions of uplift. A similar uplifted structure can be seen to the south of Bannu Basin, where the dextral

Pezu–Bhittani fault intersects the Main Frontal Thrust (Figure 2.1). Zone A is located at the point where strike-slip deformation transition into mainly compressional deformation.

The uplifted Zone A is directly related to the movement of the Kalabagh fault.

Using InSAR, the slip rate of the fault was calculated in a study by Chen and Khan

(2010). According to their study, the internal deformation of the Potwar Plateau is greater than the deformation at the front of the MFT. However, our results suggest that most of the deformation is concentrated near the MFT. Figures 2.3 and 2.6 show the interpreted dextral fault intersecting Zone A. It is likely to be a right-lateral strike-slip fault due to the different rate of displacement for western (0–2 mm/year) and eastern (7.5 mm/year) fault blocks. This suggests that the western boundary of the Potwar Plateau transitions from a purely right-lateral transform fault (Kalabagh fault) to the north into a transpressional deformation region near the Main Frontal Thrust. This is consistent with a study by McDougall and Khan (1990). According to their work, the minimum average displacement rate near the Indus River is around 7–10 mm/year. Additionally, Chen and

Khan (2010) calculated an average rate of displacement of 5–6 mm/year for the Kalabagh fault. Their results show that different parts of the Kalabagh fault move at different rates.

These movements may be due to the distribution and thickness of salt.

The different rates of movement of different regions of the Kalabagh fault and the Salt

Range seems to support the Caterpillar model by Oldham (1921). According to an InSAR study by Satyabala et al. (2012), the movement of the Kohat Plateau can be equated to a caterpillar. In this model, the plateau moves in blocks of rock, where a block above a weak layer (salt) moves forward and a block that lacks salt is locked due to friction. The block of rock that is locked could accumulate energy and be released as a big earthquake, such as the magnitude 6 earthquake that occurred in 1992 (Satyabala et al., 2012). In order for that to occur, the salt layer underneath the Kohat Plateau must have thickness variations, where some blocks are locked whereas some move aseismically (Satyabala et al., 2012). This model may better explain the current deformation of the Kalabagh fault and the western Potwar Plateau–Salt Range.

Moreover, a recent GPS study (data from 2006–2012) by Jouanne et al. (2014), suggests that the western portion of the Potwar Plateau–Salt Range is not active, which is contradictory to our findings. This may be explained by the lack of GPS stations in western Salt Range. Only one of their GPS station overlaps with our InSAR displacement map and is located to the east of the InSAR map.

Overall, our InSAR results showed that western Potwar Plateau–Salt Range region and the Kalabagh fault may still be tectonically active, especially in the western region of the

Salt Range (Figures 2.3 and 2.6). The InSAR displacement map showed that the region was mostly uplifted from 2007 to 2010 with two main uplift anomalies, which may be 42 due to zones of transpression and salt diapirism. Figure 2.6 shows our interpretations based on the InSAR results.

2.4.3.3. Comparison with Kuqa fold-and-thrust belt, China (Across-strike structural variations) The Kuqa foreland fold-and-thrust belt is located in Xinjiang Uyghur Autonomous

Region, China (Lat: 41° 53′ 20.28″ N, Long: 81° 50′ 03.38″ E), where it is underlain by

Palaeogene evaporite layer. Similar to the Potwar Plateau–Salt Range, the Kuqa belt has three main regions (Refer to figs. 2 and 5 from Chen et al., 2004). Northward, closer to the mountain belt is the highly deformed zone, the Trailing Edge (equivalent to the North

Potwar Deformation Zone in Potwar Plateau) (Figures 2.6 and 2.7a). This is followed southward by the Transitional Belt, where a broad syncline is located (equivalent to the

Soan syncline of the Potwar Plateau), and finally the Leading Edge (equivalent to the Salt

Range) (Figure 2.7a). Modeling studies have successfully emulated these different regions of the Potwar Plateau–Salt Range (Cotton and Koyi, 2000; Faisal and Dixon,

2014). These distinct features of the foreland fold-and-thrust belt are mainly influenced by the presence of a weak lithological layer, Salt Range formation in this case, which acts as a detachment for the overriding layers.

Another important observation from the Kuqa belt is that exposed salt structures are also seen near the Leading Edge, which may be due to the thrusting of the salt. This uplifted region was eroded after some time, leading to the exposure of the salt at the surface

(Chen et al., 2004). Furthermore, the thickest salt is located under anticlinal structure, where the overburden is thinnest.

Figure 2.7b shows a cross-section that goes through both Zone A and Zone B (Figures

2.6 and 2.7b). The transpression zone is dominated by thrust faults, which may be the main cause of the anomalous uplift of Zone A. This uplift increases the overburden load in Zone A and in turn pushes the salt to the south toward Zone B, where salt diapirism is believed to be active (Figure 2.7b).

2.4.3.4. Comparison with structural style of central and eastern Potwar Plateau-Salt Range (Along-strike structural variations) The deformation in eastern Salt Range is very different than its western counterpart, which can be seen in the different structural styles between them (Refer to Figs. 2, 6, 10 and 12 from Jaume and Lillie, 1988). Jaume and Lillie (1988) argued that this difference is mainly due to the thinning of salt to the east. According to a recent study by Qayyum,

Spratt, Dixon, and Lawrence (2014), this is unlikely as they pointed out the generally similar stratigraphy along-strike. The Main Frontal thrust sheet is internally undeformed in western Salt Range, while it is internally folded and faulted in eastern Salt Range

(Qayyum et al., 2014). This is clearly shown in Line 3 (Figure 2.4A) showing relatively undeformed thrust sheet for western Salt Range. Furthermore, Qayyum et al. (2014), suggested that the variations in their structural styles are due to different ramping mechanism: translation versus telescoping. Central Salt Range underwent translation,

. The The .

ical maps by ical by maps

e and Lillie, 1988). and e Lillie,

in turn creates uplift in Zone uplift Zone in B turn in creates

al faults were also added. These faults may may Thesefaults added. also faults al were

Salt Range (Modified from Jaum (Modified from SaltRange

Eocene platform due to salt escaping. NPDZ: Northern NPDZ: Potwar platform escaping. salt to due Eocene

nto Zone B, where salt diapirsm is active. This where diapirsm salt B, Zone nto is active.

ection of western Potwar Plateau ectionwestern of

6 for location of profiles. The dashed yellow line along the bottom of the Salt Range Salt Range bottom the Thethe of along line dashed yellow profiles. of for 6 location

This profile crosses Zones A and B. The faults were drawn were according faults The to the and geologB. A Thisprofile crosses Zones

Cross

7a 7b

2. 2.

Gee (1980). The yellow arrows show the possible movement of salt from Zone A (transpression zone) to Zone B B to Zone zone) (transpression A from Zone salt of possible movement the show arrows The yellow (1980). Gee Figure to Figure Refer Addition interpreted the signifies anhydrite/gypsumlayer. Formation of collapse the to due Cambrian the be Zone. Deformation Figure it thrusting to southward increase load the may due pushing salt, the on A uplift The Zone in diapirism). (salt more i salt feeding and uplift profile the rates (mm/yr). above are labeled respective

2.7b

2.7a

46 with relatively low internal deformation for the allochthon. Basically, translation ramping mechanism works by sliding of overburden subhorizontally over basement normal fault, which resulted in a repetition of strata (Qayyum et al., 2014). This is very similar to western Salt Range, with a minor difference in that a normal fault basement ramp is absent in the western Salt Range (Jaume and Lillie, 1988). This is also evident in our seismic interpretations (Figures 2.4A–D). In contrast, the eastern portion of Salt Range underwent telescoping, with high internal deformation including thrust faults, anticlines and pop-up structures. The normal fault basement ramp is also not present in the eastern

Salt Range, with no repetition of sedimentary layers (Qayyum et al., 2014).

Our seismic interpretation agrees with the translation mechanism, which is similar to the central Salt Range. The lack of internal deformation in the hanging wall of the thrust sheet suggests that the overburden slides smoothly over a flexed upward basement. This basement flexure may be related the Sargodha High, located south of western Salt Range, where it is believed to be the forebulge of the Punjab foreland basin. This suggests that the main control on the deformation of western Potwar Plateau–Salt Range is the movement along Kalabagh fault and the Main Frontal Thrust.

2.5. Conclusions This work has provided clear evidence that the western Potwar Plateau–Salt Range is still tectonically active. The InSAR results showed that most of western Salt Range underwent uplift, from 2007 to 2010, at an average rate of 10 mm/year. Two uplift anomalies, with an uplift rate of 15 mm/year, were interpreted as related to zone of

47 transpression and salt diapirism. However, the results also suggest that most of the deformation was tectonically induced by compression and transform zones. Similar to the

Kuqa fold-and-thrust belt, the Potwar Plateau has three main equivalent regions, with the salt playing two roles in their deformation: salt acted as a detachment in the Transitional

Belt and salt diapirsim occurred in the Leading Edge.

Seismic interpretation showed that western Potwar Plateau and Salt Range have different structural styles than eastern Potwar Plateau–Salt Range. This was mainly due to ramping mechanism, where western and central Salt Range underwent translation while eastern

Salt Range underwent telescoping (Qayyum et al., 2014). However, the hanging wall of western Salt Range has been translated over a flexed Pre- Cambrian basement. InSAR and seismic data, two very different datasets, were utilized in this study. Both data provided different views of this region. While InSAR showed the vertical movements in the region, the seismic data showed how those movements deformed the subsurface. The lack of internal deformation in this region can be related to salt due to its weak nature.

This work supports the idea that the Potwar Plateau may be deforming similar to the

Caterpillar model by Oldham (1921). This is mainly due to the varying rates of movement along the Kalabagh fault. Our study showed that the salt layer acted as a decollement in the Potwar Plateau region, while salt flows are prominent in the Salt

Range. Finally, this work showed how powerful InSAR can be in the study of active tectonics.

CHAPTER 3: Bannu Basin, fold-and-thrust belt of northern Pakistan: subsurface imaging and its implications for hydrocarbon exploration

3.1 Abstract The Trans Indus-Salt Range, located in northern Pakistan, is one of the most tectonically active fold-and-thrust belts and comprises three main regions: the Potwar-Salt Range, the

Kohat-Surghar Range and the Bannu Basin-Khisor Range. Of these, the Bannu Basin is the least studied and only a handful of publically accessible datasets and publications are available. Recently made public 2D seismic profiles and well data from the Bannu Basin indicate the presence of salt as well as evidence for two detachment surfaces: Eocene-

Paleocene and Cambrian/Infra-Cambrian in age. Our findings suggest that the salt could be the main detachment for the basin.

Interpretation also showed a Miocene-Eocene basin-wide unconformity that marks the

Himalayan orogenic event which separates the pre-Himalayan from the syn-Himalayan sedimentary units. On the basis of seismic reflection data, we concluded that the basin experienced three main tectonic settings. An early stage of pre-Himalayan passive tectonic environment was followed by the compressional Himalayan tectonics which resulted in uplifted areas sourcing the fluviatile fill of the subsided basin. This was followed by a more recent stage of thrusting that produced folds and thrusts which deformed all of the sedimentary units.

Structural geometries suggest that prospective traps were developed mainly in the anticlines outlining the eastern and western boundaries of the Bannu Basin, as well as the southern zone of the basin. Furthermore, the presence of salt diapirism and transpression

49 zones together with numerous oil seeps in and around the basin increased the probability of hydrocarbon accumulation and indicated great potential for future exploration.

3.2 Introduction The fold-and-thrust belt of northern Pakistan is situated at the western end of the

Himalayan orogenic belt and is bounded between two north-dipping thrust systems: the

Main Boundary Thrust (MBT) to the north and the Main Frontal Thrust (MFT) to the south (Figure 3.1). These thrust systems accommodated crustal shortening due to the convergence between the Indian and Eurasian plates (Molnar, 1984; Hodges, 2000; Yin and Harrison, 2000). The MFT, which is the youngest and the most active of the thrust systems, delineates the southern boundary of the Himalayan orogeny. Due to structural differences along-strike, the thrust fault bends to form re-entrants (Kalabagh and Tank re- entrants) and is offset laterally to form strike-slip faults (Kalabagh and Pezu-Bhittani faults) (Figure 3.1). According to previous studies, three general factors that control the movement of the fold-and-thrust belt of northern Pakistan are: the thickness and the extent (depositional limit) of the underlying Infra-Cambrian salt (Salt Range Formation), as well as the geometry of the Pre-Cambrian basement shield (Lillie et al., 1987; Jaume and Lillie, 1988; Cotton and Koyi, 2000; Qayyum et al., 2014).

Indus

del)Trans the of

Salt Range, the Plateau SaltKohat Range,

Khisor Range. The thin dashed lines represent fold axes. KF = Kalabagh MR fold = Fault; represent lines Kalabagh axes.KF thin dashed Range. Khisor The

thrust belt, located in northern Pakistan, depicting the main structural features (Kazmi and Rana, 1982; 1982; (Kazmi Rana, features thrustmain the and Pakistan, structural belt, depicting northern in located

A hillshade map (using the Shuttle Radar Topography Mission Digital Elevation Mo Elevation Mission Digital Topography Shuttle the Radar hillshade A (using map

Figure 3.1: Figure fold SaltRange Plateau the Potwar the and regions: main three 2013) 2008; 2010; Ali, Alam, Khan, Basin Bannu the and Range Surghar Development Corporation PMDC KR = Mineral Pakistan = Range; Range; Khisor Marwat =

The thrust belt can be divided into three main regions: the Potwar Plateau-Salt Range, the

Kohat Plateau-Surghar Range, and the Bannu Basin-Khisor Range (Figure 3.1).

Hydrocarbon exploration in the fold-and-thrust belt of northern Pakistan has been ongoing since the 1800s with mixed results (Khan et al., 1986: Parvez, 1992; Wandrey et al., 2004; Ali, 2010). One of the first exploration wells in the world was drilled in this region in 1886 near the Kundal oil seep (Figure 3.2). Since then, approximately 340 wells have been drilled, mainly in the Potwar and Kohat plateaus (Wandrey et al., 2004). Many of the successful discoveries are faulted anticlinal traps located in the Potwar Plateau

(Khan et al., 1986; Wandrey et al., 2004). Other traps include wrench structures, such as drag folds and fault-bounded traps, and structures related to thrust faults (Moody, 1973;

Parvez, 1992; Sercombe et al., 1998). More recent discoveries have been made in the

Kohat Plateau while relatively little hydrocarbon exploration activity has targeted the

Bannu Basin (Paracha, 2004). A paucity of seismic and well data has been an obstacle to further understand the structural geology and stratigraphy of the basin. Hence, a reduced focus on hydrocarbon exploration in this basin. However, the presence of similar structures to the hydrocarbon-rich Potwar Plateau and the presence of oil seeps indicate that the Bannu Basin contains mature source rocks and thus, a high potential for a working petroleum system (Figure 3.2).

The Bannu Basin is a foreland basin filled with thick (~ 4-5 km [2.5-3 mi]) Miocene-

Pleistocene Siwalik and Rawalpindi molasse sedimentary sections underlain by the

Cambrian to Eocene platform, the Infra-Cambrian Salt Range Formation and the Pre- 53

X1 well X1 shown. are

Khisor Range in northern Pakistan (Kazmi and Rana, Pakistan Rana, northern in and (Kazmi Range Khisor

u u Basin

Tectonic setting and Bann setting and of map generalized Tectonic

Figure Kundi location and lines 2D seven the The of 2013). Ali, 2008; Alam, 1982; Khan, 2010;

Cambrian basement (Blisniuk et al., 1998; Wandrey et al., 2004; Shah, 2009; Ali, 2010)

(Figure 3.3). Similar to the Potwar Plateau, the Bannu Basin consists of a wedge of sediments that experienced periods of northwest-southeast directed compression while sliding on a weak salt detachment (Chapple, 1978; Davis and Engelder, 1985). The basin is surrounded by topographically high structures. These include the Marwat and Khisor

Ranges to the south, the Kohat Plateau to the north, the Surghar Range to the east and the

Pezu-Bhittani Range to the west (Figure 3.2). Based on classification of conglomerate composition and paleocurrent directions , the Bannu Basin experienced two major deformation phases: 1) normal faulting event (Miocene to Pliocene) and 2) southward thrusting event (Pliocene to present day) (Blisniuk et al., 1998). The Miocene normal faulting event resulted in normal faults in the Pre-Cambrian basement rocks in the Potwar

Plateau.

Previous studies have suggested thin-skinned deformation for the Bannu Basin (Parvez,

1992; Ali, 2010). The close similarity in their stratigraphy and general structural geology suggests that the Bannu Basin may be the western extension of the Potwar Plateau (Ali,

2010). Both the Bannu Basin and the Potwar Plateau have wider deformational belts than the Kohat Plateau which is ascribed to the difference in the nature of the detachment layer (ductile vs. brittle) (Lillie et al., 1987; Jaume and Lillie, 1988; Cotton and Koyi,

2000) (Figure 3.1). In the case of the Bannu Basin and Potwar Plateau, the overlying sedimentary wedge glides effectively along a weak detachment layer of salt, resulting in little internal deformation of the wedge (Davis and Engelder, 1985). In contrast, the 56

Figure 3.3: Regional stratigraphy and hydrocarbon potential of the Fold- thrust Belt of Northern Pakistan (from Wandrey et al., 2004; Qayyum et al., 2014). Stratigraphic formations that are potential source rocks are denoted by black diamonds, while formations that are potential reservoir rocks are denoted by the circled ‘R’.

Kohat Plateau is complexly folded and faulted due to its mechanically stronger detachment, which provides more resistance to movement (Davis and Engelder, 1985;

Parvez, 1992).

The main objective of this work is to describe and understand the deformation style and the tectonics of the Bannu Basin in relation to the entire fold-and-thrust belt of northern

Pakistan. Since salt has been suggested to be a fundamental element in the deformation of this region, this work focuses on the extent and the role of salt during shortening. In order to accomplish this, we present 2D seismic interpretations of the Bannu Basin which includes the Bannu depression, the Marwat and Khisor Ranges, the Surghar Range and the Pezu-Bhittani Range using recently released seismic and well data (Figure 3.2). We also used the Kundi-X1 well (drilled in 1995) in order to further constrain our seismic interpretation (Figure 3.2). Combining our work with previous studies (Parvez, 1992; Ali,

2010) in the Bannu Basin region, we presented a more complete structural interpretation of the basin. Finally, by comparing Bannu’s structural and stratigraphic similarities with the proven hydrocarbon play of the Potwar Plateau, we discussed some implications for the hydrocarbon exploration of the Bannu Basin. A burial history chart and a critical moment chart were generated to discuss the timing of the petroleum elements of the basin. A structural cross-section and two fence-diagrams were generated showing the general structure style of the Bannu Basin. Through these analyses, we made several insights regarding the function of salt in the deformation of the fold-and-thrust belts. A key point was that the thickness and strength of the overlying molasse sedimentary 58 sections are important factors in the generation of salt-related structures in the southern part of the Bannu Basin, which are potential hydrocarbon traps.

3.3 Geological background

3.3.1. Stratigraphy Sediment deposition in the fold-and-thrust belt of northern Pakistan started during the

Pre-Cambrian and continued until the Pleistocene (Figure 3.3). The stratigraphy of the

Bannu Basin can be divided into three main groups overlying the Pre-Cambrian basement: the Infra-Cambrian Salt Range Formation, the Cambrian to Eocene sedimentary units (also called the Cambrian to Eocene platform), and the Miocene to

Pleistocene fluviatile sedimentary units (Figure 3.3). Two major unconformities during

Cambrian-Permian and Eocene-Miocene represent two episodes of major uplift and erosion related to orogenic processes (Drewes, 1995; Shah, 2009; Ali, 2010). The orogenic processes of the Himalayan-arc, which started during Eocene, initiated the deposition of the thick fluviatile Mio-Pleistocene sedimentary units overlying the

Cambrian-Eocene platform.

The surface geology of the Bannu Basin is entirely covered by Quaternary alluvial sediments and most rock outcrops are located along the Khisor, Surghar and Pezu-

Bhittani Ranges (Khan et al., 1986). Brief descriptions of the three stratigraphic groups are as follows.

3.3.1.1. Infra-Cambrian Salt Range formation The Salt Range Formation is the oldest sedimentary formation in this region and is categorized as infra-Cambrian due to its location below the Cambrian sedimentary units

(Khan et al., 1986). This is further complicated as no biostratigraphic information records exist for absolute age determination (Gee, 1945, 1947; Khan et al., 1986; Shah, 2009).

The formation is dominantly composed of red gypseous marl with halite which includes dolomite and is similar to the Hormuz Salt Formation of Iran (Shah and Quennell, 1980;

Gee and Gee, 1989). Salt thickness varies from 50 m (164 ft) to 1000 m (3281 ft) owing to salt diapirism and tectonics (Parvez, 1992; Wandrey et al., 2004). The Salt Range

Formation is exposed in southern Potwar Plateau-Salt Range along the Main Frontal

Thrust but is not exposed in the Bannu Basin (Shah, 2009). However, the Marwat-01 well, drilled along the Marwat anticlinal structure, penetrated the Salt Range Formation at the depth of 2013 m (6604 ft) (Ali, 2010).

3.3.1.2. Cambrian to Eocene sedimentary units The Jhelum Group comprises Cambrian-aged sedimentary units including the Khewra-,

Kussak-Jutana sandstones and the Khisor evaporite, which are uncomformably overlain by Permian to Paleogene sedimentary units (Gee, 1980) (Figure 3.3). The Khewra sandstone has a porosity that ranges from 7-27 % and is a proven reservoir in the Potwar

Plateau (Shah, 2009; Ali, 2010). The overlying Kussak Formation is composed of glauconitic sandstone overlain by the Jutana Formation composing of mainly sandstone with sandy dolomite (Wandrey et al., 2004; Shah, 2009). The Jutana Formation is

60 followed by the Khisor dolomite which marks the top of the Cambrian units (Figure 3.3)

(Shah, 2009; Ali, 2010).

The Permian to Paleogene sedimentary units include the Permian Nilawahan-Zaluch

Groups, the Triassic Musa Khel Group, the Jurassic Baroch Group, the Cretaceous

Surghar Group, and the Paleocene-Eocene Makarwal-Chharat Group (Wandrey et al.,

2004; Shah, 2009) (Figure 3.3). These sedimentary units were deposited before the

Himalayan-arc orogenic events and include carbonates, sandstone, and shale.

The contact between the Khisor Formation and the Permian Nilawahan Group is identified as an unconformity (Shah, 2009). The Nilawahan Group includes the Tobra glacial tillites, the Dandot sandstone, the arkosic Warcha sandstone, and the Sardhai shale

(Shah, 2009; Wandrey et al., 2004).

The overlying Permian Zaluch Group is divided into the Amb Formation, which is composed of limestone, sandstone and shale, overlain by the Wargal limestone, and topped by the Chhidru Formation composed of calcareous sandstone with sandy limestone (Shah, 2009). The Triassic Musa Khel Group, overlying the Chhidru

Formation, is around 120 m (394 ft) thick in the Khisor Range and is composed of the

Mianwali Formation (mudstone and fine grained sandstone with shales and carbonates),

Tredian Formation (sandstone with intervals of mudstone), and the Kingriali Formation

(carbonates) (Wandrey et al., 2004; Ali, 2010).

The Musa Khel Group is overlain by the Jurassic Baroch Group, which is composed of the thick-bedded Datta sandstone, followed by the sandy Shinawari limestone and topped by the thick-bedded Samana Suk limestone (Ali, 2010). The Cretaceous Surghar Group, overlying the Samana Suk limestone, is divided into the muddy Chichali sandstone followed by the Lumshiwal sandstone (Ali, 2010).

The Paleocene Makarwal Group, which overlies the Surghar Group, consists of three formations: the Hangu sandstone with interbedded shale units, the Lockhart marly limestone, and the organic-rich Patala shales (Shah, 2009; Ali, 2010). Overlying the

Makarwal Group is the Eocene Chharat Group consists of the organic-rich Panoba shales, the Nammal Formation (shale, marl and limestones), the Sakesar Limestone, the Chorgali

Formation (shale and limestone), the Kuldana shales, and the Kohat Formation

(interbedded limestone and shale) (Wandrey et al., 2004; Shah, 2009).

3.3.1.3. Miocene to Pleistocene molasse sedimentary units The orogenic events of the Himalayan arc started during late Eocene and this initiated the deposition of Miocene to Pleistocene molasse sediments. These sediments were transported southward through the paleo Himalayan river systems (Wandrey et al., 2004). 62

Two main stratigraphic groups constitute the molasse sedimentary units: Rawalpindi and

Siwalik. These fluviatile and terrestrial sediments were eroded from the uplifted area to the north of the Bannu Basin. The Miocene Rawalpindi Group contains the Murree and

Kamlial formations, which is primarily composed of massive sandstone with interbedded shale units and basal conglomerate (Meissner et al., 1974; Johnson et al., 1985; Khan et al., 1986; Gee and Gee, 1989; Shah, 2009). The Pliocene-Pleistocene Siwalik Group mainly contains sandstone and shale, consisting of the Chinji, Nagri, Dhok Pathan, and

Soan Formations (Fatmi, 1973; Johnson et al., 1985; Shah, 2009) (Figure 3.3). The

Siwalik and Rawalpindi Group sections unconformably overlie the Cambrian to Eocene platform (Wells, 1984; Pivnik and Wells, 1996).

3.3.2 Regional tectonics The tectonics of northern Pakistan is dominated by contractional structures due to continent-continent collision that resulted in the Himalayan orogenic belt. The crustal shortening was accommodated by north-dipping thrust systems including the the Main

Boundary thrust and the Main Frontal Thrust (Figure 3.1).The internal folds and faults in this region trends in a general east-west direction (Figure 3.1). The three regions (the

Potwar Plateau-Salt Range, Kohat Plateau-Surghar Range, and the Bannu Basin-Khisor

Range) are separated by strike slip faults, which are the Jhelum, Kalabagh, Southern

Surghar, and Pezu faults (Figures 3.1 and 3.2). The regional tectonics of the fold-and- thrust belt of northern Pakistan is explained as follows:

3.3.2.1. Pre-Cambrian to Cambrian A shallow marine transgression followed by rapid evaporation during this time led to the deposition of the Salt Range Formation (Gee and Gee, 1989). The Salt Range Formation was deposited unconformably on the Pre-Cambrian basement rock and was followed by the unconformable deposition of the Cambrian sediments (Shah, 2009). A major regional unconformity marks a tectonic uplift event or sea regression between Cambrian and

Permian (Shah, 2009; Ali, 2010).

3.3.2.2. Permian to Eocene During this period, the Indian plate started to move northward: colliding with the

Kohistan-Ladakh island arc during the early Paleocene and then colliding with the

Eurasian plate in the late Eocene (Garzanti et al., 1996; Pivnik and Wells, 1996; Khan et al., 2009). A major regional unconformity separates the Eocene from the overlying

Miocene sediments relating to the Himalayan orogenic processes (Wandrey et al., 2004;

Ali, 2010). The rapid uplift of the Himalayan orogeny deflected the Indian plate resulting in a foreland basin (Pivnik and Wells, 1996).

3.3.2.3. Miocene to present Rapid erosion of the uplifted structures into the foreland basin of northern Pakistan is recorded by the Rawalpindi and Siwalik sedimentary units. Throughout the Miocene to

Pliocene sedimentation, localized normal faulting events to the south of the Bannu Basin and the Potwar Plateau created normal fault basement ramps (Blisniuk et al., 1998). It is

64 suggested that the normal faulting event is linked to the lithospheric flexure of the Indian plate due to the loading of the Eurasian plate (Lillie et al., 1987; Baker et al., 1988;

Duroy et al., 1989). This was followed by ramping and thrusting of the sediments which started in Pliocene and continues presently (Blisniuk et al., 1998).

3.3.2.4. Petroleum system Most of the information regarding the petroleum system in this region originated from the hydrocarbon exploration of the Potwar Plateau and the Kohat Plateau (Figure 3.1). The petroleum systems in this region are complex as they include multiple source rocks and reservoir rocks (Wandrey et al., 2004). Due to the similarities in the stratigraphy and subsurface structure of the Bannu Basin with the Potwar Plateau, potential source rocks, reservoir rocks, seal and traps can be inferred.

Major potential source rocks in this area include the Panoba (Eocene) and Patala

(Paleocene) marine shales. The Kundi-X1 well was drilled to the Eocene Panoba shales at a depth of around 6300 m (20669 ft) (Figure 3.4). Other potential source rocks are the shale intervals in the Lower Cretaceous, Jurassic, and Triassic ages (Ali, 2010).

Hydrocarbon from these source rocks migrates either sub-vertically through thrust faults or laterally into traps, such as anticlinal traps or stratigraphic pinch-outs (Wandrey et al.,

2004; Ali, 2010). 65

2010

South Stratigraphic Well Correlation (from Ali, Ali, (from Correlation Well SouthStratigraphic

nu Basin North Basin nu

Ban

Figure

Possible reservoir rocks include the Murree sandstone (Rawalpindi), the Chorgali limestone, the Sakesar limestone, and the Lockhart formation (Paleocene) (Ali, 2010)

(Figure 3.3). Furthermore, multiple interbedded shale units in the reservoir formations as well as regional unconformities and faults could act as likely seals (Ali, 2010).

3.4 Data and seismic observation Poor to fair quality 2D seismic profiles used in this paper are located in and around the

Bannu Basin (Figure 3.2). These were acquired between 1978-1979 by the Oil and Gas

Development Company Limited (Pakistan) and were interpreted using geological maps

(Ali, 2010) and well data. The Kundi-X1 Chonai-01, Marwat-01, Isa Khel-01, and the

Pezu-01 wells provided stratigraphic constraints for seismic interpretation (Figures 3.2,

3.4 and 3.5). With the exception of Kundi-X1, stratigraphic well data was from Ali

(2010). Following are the data observations for the three Bannu Basin regions:

3.4.1 Northeastern Bannu Basin (Seismic Lines 1-4) The Bannu Basin is bounded on the east by the north-south trending transpressive left- lateral Southern Surghar Fault (Pivnik and Sercombe, 1993; Ahmad et al., 2003) (Figure

3.2). Parallel to the fault is the Southern Surghar anticline where Eocene to Late Triassic formations are exposed at its core (Ali, 2010). Four seismic lines (Lines 1-4) and one well are located in this region (Kundi-X1 well) (Figure 3.2). Within the Northeastern

East Stratigraphic Well Correlation (from Ali,2010). (from Correlation Well Stratigraphic East

Bannu Basin West Basin Bannu

Figure

Bannu Basin, two distinct seismic packages have been identified: a package of moderate, parallel and continuous reflectors (X) overlying a package of strong, continuous, and parallel reflectors (Y) (Figure 3.6). Line 1 is interpreted using the Kundi-X1 well

(Figures 3.4, 3.6). Kundi-X1, one of the deepest in the region with a true vertical depth of

6400 m (20,997 ft), was drilled on an anticlinal seismic anomaly through thick molasse comprising of ~3800 m [12,467 ft] of Siwalik and ~2200 m [7218 ft] of Rawalpindi

Groups, terminating in the Eocene Panoba shales (Figure 3.4).

Line 1 shows two major thrust faults displacing seismic package X, which is interpreted as thick molasse sediments of the Siwalik and Rawalpindi Groups and terminating at the

Miocene-Eocene unconformity (Figure 3.6). The thrust faults are dipping northward at approximately 45-50 degrees with an offset of around 120 m (394 ft). These are buried faults with no surface exposure. Another observation was that seismic reflectors mimicking an anticlinal structure are located near the Kundi-X1 well. The interpreted

Rawalpindi Group sedimentary units were observed as onlapping the underlying seismic package Y, interpreted as Cambrian to Eocene platform, marking an unconformity surface (Miocene-Eocene unconformity) (Figure 3.6).

Deformation above and below the Miocene-Eocene unconformity is different in the northern part of the basin (Figures 3.6, 3.7). The overlying molasse sedimentary units were shortened, forming a wedge-shaped basin with thicker Siwalik Group (~3800 m

2).

= =

Eocene Eocene

Cambrian and older sedimentary units; older and sedimentary Cambrian

X1 well. Three thrust faults were faults thrust Three were well. X1

Є = = Є

Permian; Permian;

Eocene unconformity unconformity Eocene

P = Cretaceous = P

(A) Uninterpreted seismic line 1 in the northeastern Bannu basin (Figure basin Bannu (Figure northeastern the in 1 line seismic Uninterpreted (A)

pretation of Line 1 is assisted by Kundi pretation of assisted is 1 by Line

Paleocene; K Paleocene;

Figure (B) Inter Miocene the at thick and displacing sediments molasse terminating interpreted P dotted Group; Siwalik Group; Rawalpindi = NR NS line). (black = unconformity Eocene line dotted Miocene = Black

)

Figure 3.6 (A) 3.6 Figure

Figure 3.6 Figure

(seconds) Time way - Two (seconds) Time way - Two

2).

3. e e

Cambrian and older older Cambrian and Є = = Є

Permian; Permian;

Eocene unconformity Eocene -

P = Cretaceous = P

Paleocene; K Paleocene;

(A) Uninterpreted seismic line 2 in the northeastern Bannu basin Bannu (Figur northeastern the in 2 line seismic Uninterpreted (A)

Eocene =

Figure 1 to Rawalpindi faults thrust Similar NR interpreted. = were Group; Siwalik = NS (B) Line P Group; Miocene = units; line dotted Black sedimentary

)

(A)

Figure 3. Figure

(seconds) Time way - Two (seconds) Time way - Two

[12,467 ft]) in the north and thinning towards the south. The well correlation in Figure

3.4 also shows the thinning of the molasse section towards the south. A key observation was that the base of the folded and faulted molasse section is marked by the Miocene-

Eocene unconformity (Figure 3.6). This unconformity could also act as a detachment surface, separating the Cambrian to Eocene platform from the overlain molasse section.

On the contrary to the folded and faulted Siwalik and Rawalpindi sections, the underlying

Cambrian to Eocene platform (thickness is ~ 2200 m [7218 ft]) is relatively undeformed with a constant thickness throughout the profile. The platform dips to the north at around

6 degrees (south of the profile) to around 1 degree (north of the profile).

Line 2, which is parallel to Line 1, shows similar structures. Thrust faults displace the

Miocene to Pliocene molasse sediments and terminate at the unconformity (Figure 3.7).

The orientation of these north-dipping thrust faults is consistent with the general compression direction of the basin (Figures 3.6 and 3.7). Although to a lesser extent, the wedge-shaped molasse sediments deform differently than the underlying north-dipping platform (Figure 3.7).

Figure 3.8 shows the interpreted seismic profile Line 3, located to the southeast of Lines

1 and 2. In the northern part of this section, the Rawalpindi Group layer pinches out from north to south. The Siwalik Group is unconformably atop the Cambrian to Eocene platform along the rest of the seismic profile. The southern end of the section shows a

74 positive flower structure displacing upwards both the molasse and the underlying platform (Figure 3.8). Another observation is an anticlinal structure above the positive flower structure at around 1 second (Figure 3.8). The flower structure is located at the southern termination of the left lateral Southern Surghar Fault (Figure 3.2).

Line 4 is oriented east-west and provided an along-strike profile of the subsurface (Figure

3.9). One key observation is that the reflectors are dipping west at around 2 degrees. We interpreted this as the result of the eastern flank of the Bannu Basin being thrusted onto the Punjab foreland basin in the area of the Kalabagh Re-entrant (Figure 3.2). Another observation was the tapering geometry of the Miocene Rawalpindi Group to the east, which indicates that the Rawalpindi layer is mainly concentrated to the northern and central parts of the basin.

3.4.2. Southwestern Bannu Basin (Seismic Lines 5-7) The southwestern Bannu Basin includes the Pezu-Bhittani Range and the western end of

Marwat Range (Figure 3.2). The Pezu-Bhittani Range is defined by a right-lateral transpressive fault system which separates the Bannu Basin from the Tank Re-entrant to the west (Figure 3.2). Siwalik Group strata (Chinji, Nagri and Dhok Pathan Formations) are exposed along the core of the Pezu Anticline that parallels the Pezu-Bhittani Range

(Ali, 2010; Khan, 2013). Quaternary alluvium covers most of the basin in this region.

The Pezu-01 and Chonai-01 wells were used in the interpretation of the three seismic

Eocene Eocene -

ying platform. NS = = NS platform. ying

P = Cretaceous = P

Paleocene; K Paleocene;

molasseunderl the and

2). line section (B) the of southern Interpretationthe of

Uninterpreted seismic line 3 in the northeastern Bannu basin, the to Bannu located northeastern the in 3 line seismic Uninterpreted

Cambrian and older sedimentary units; Black dotted line = Miocene = units; line dotted sedimentary and Black older Cambrian

(A)

Є = = Є

Figure 1 (Figure 2 and south of Lines the displacing structure positive flower a shows Eocene PƐ Group; = Rawalpindi NR = SiwalikGroup; Permian; unconformity

)

8 (B 8

(A)

Figure 3. Figure Figure 3. Figure

(seconds) Time way - Two (seconds) Time way - Two

)

way (seconds Time

Two

way Time (seconds) way Time

- Two

Figure 3.9: (A) Uninterpreted seismic line 4 in the northeastern Bannu basin, intersecting Line 1 (Figure 3.2). (B) Interpretation demonstrates that layers are dipping to the west at around 2.2 degrees with the Miocene Rawalpindi layer tapering out to the east. NS = Siwalik Group; NR = Rawalpindi Group; PƐ = Eocene-Paleocene; K-P = Cretaceous-Permian; Є = Cambrian and older sedimentary units; Black dotted line = Miocene-Eocene unconformity

78 profiles in this part of the basin (Figure 3.2). Within the southwestern part of the basin, we also observed two distinct seismic packages: a package of moderate, parallel, and continuous reflectors (X) overlying a package of strong, continuous, and parallel reflectors (Y) (Figure 3.10). Package X is interpreted as the molasse sedimentary section composed of the Siwalik and the Rawalpindi Groups and package Y is interpreted as the

Cambrian to Eocene platform.

Line 5 is oriented east-west and intersects Line 6 (Figure 3.2). At the western end of the seismic profile, the Rawalpindi section was observed to be the thickest (Figure 3.10). The

Rawalpindi Group tapers out eastward, and the entire molasse sequence is relatively undeformed in this profile view. The underlying Cambrian to Eocene platform sequence appeared to be affected by broad wavelength folds. The platform thickness remains constant throughout the entire profile at around 2000 m (6562 ft) (Figure 3.10). Another important observation was the onlapping of the molasse section onto the Cambrian to

Eocene platform which marks the Miocene-Eocene unconformity.

Figure 3.11 and Figure 3.12 show the interpreted seismic profile of Line 6, which is the longest profile of the seismic lines used in this study (Figure 3.2). Similar to previous profiles, the molasse sedimentary units unconformably overlie the Cambrian to Eocene platform. The molasse thins to the south, which can also be seen in the north-south stratigraphic well correlation (Figure 3.4). Well correlation shows that the Kundi-X1

e 6 (Figure 3.2). (Figure 6 3.2). e

Cambrian and Cambrianand

Є = = Є

Permian; Permian;

P = Cretaceous = P

Eocene unconformity Eocene

Paleocene; K Paleocene;

ne ne Miocene =

Uninterpreted seismic line 5 in southwestern Bannu basin, basin, southwestern in 5 line seismic Uninterpreted Lin intersecting Bannu

(A)

(B) The Siwalik and Rawalpindi Groups are observed to onlap the sedimentary units below. NS = Siwalik = NS units below. observed sedimentary the onlap to Rawalpindi are Siwalik Groups and The (B) Rawalpindi Eocene PƐ NR = = Group; Group; units; li dotted sedimentary Black older Figure 3.10: Figure

10 (A) 10

10 (B) 10

Figure 3. Figure

)

(A)

(

(seconds) Time way - Two (seconds) Time way - Two

Uninterpreted seismic line 6a (the northern half of the line) in southwestern Bannu Basin, line) the half of Basin, southwestern in northern Bannu 6a line seismic (the Uninterpreted

(A)

Figure 3.11 Figure (Figure 5 3.2). Line intersecting

(seconds) Time way - Two

Group; PƐ =

Gal) for the corresponding seismic 6a. line for corresponding the Gal)

Cambrian and older sedimentary units; dotted Black older line and sedimentary Cambrian

dipping reflectors are observed with the thinning of of the thinning the observed with are reflectors dipping

Є = = Є

malymilli (in profile

Permian; Permian;

Northward

P = Cretaceous = P

Top: A Bouguer ano gravity Bouguer A Top:

(B)

Eocene unconformity Eocene

Paleocene; K Paleocene;

Bottom: Interpreted seismic line 6a. 6a. seismic line Bottom: Interpreted Figure 3.11 Figure south. the Rawalpindi NR towards = Groups Group; Siwalik = NS Rawalpindi Siwalikand Eocene Miocene =

11 (B) 11

Figure 3. Figure

Distance (km) Distance

(seconds)

Gal) - (milli

Time way - Two Anomaly Gravity 84

ern ern Bannubasin (Figure

Uninterpretedseismic 6b line (the of half southern in line) southwest the

(A)

Figure 3.12 Figure 3.2

(seconds) Time way - Two

he corresponding seismic corresponding he line

Permian; Є = Cambrian and older Permian;and Cambrian = Є

Gal) for for t Gal)

P = Cretaceous P=

lateral transpressive transpressive profile gravity fault.Bouguer A lateral

Eocene unconformity Eocene

At the southern end of the interpreted the At the of southern end seismic salt 6b, line a diapir

Paleocene; K

Top: A Bouguer gravity anomaly profile (in milli (in anomaly gravity profile Bouguer A Top:

(B)

Bottom: Interpreted seismic Bottom:6b. line Interpreted interpreted was cture with the Pezu along right

Figure 3.12 Figure 6b stru 2007) Din, to diapir salt over from the shows anomaly density low Siwalik = NS south. the Group; (taken a Group; Rawalpindi Eocene PƐ = NR = Miocene = units; line dotted Black sedimentary

(seconds) Time way - Two

Gal) - Gravity Anomaly (milli Anomaly Gravity 86

way Time (seconds) way Time

- Two

Figure 3.13 (A)

way Time (seconds) way Time

- Two

Figure 3.13 (B)

Figure 3.13: (A) Uninterpreted seismic line 7 in western Bannu basin (Figure 3.2). (B) Cambrian to Eocene platform dips to the west as the profile covers the western limb of the Pezu anticline. NS = Siwalik Group; NR = Rawalpindi Group; PƐ = Eocene-Paleocene; K-P = Cretaceous- Permian; Є = Cambrian and older sedimentary units; Black dotted line = Miocene-Eocene unconformity

(north) well penetrated 6000 m (19,685 ft) of molasse, while the Chonai-01 and Marwat-

01 wells penetrated 2500 m (8202 ft) and 400 m (1312 ft) of molasse, respectively

(Figure 3.4). In this profile, the platform also has a constant thickness of around 2000 m

(6562 ft). The anticlinal feature at the southern end of the section is interpreted as a salt diapir structure. This structure is located where the line crosses the Pezu right-lateral transpressive fault along the Pezu-Bhittani Range (Figure 3.2). We interpret the structure as a salt diapir because of the dipping reflectors on the flank of the structure, the vertical zone of incoherent seismic signal in the core of the feature, and because of the close proximity of the structure to the salt-cored Marwat Range. A Bouguer gravity profile

(taken from Din, 2007) shows a low density anomaly to the south of the seismic section, which correlates with the structure (Figure 3.12B).

Line 7 is located to the west of the Pezu-Bhittani Range and extends across the western limb of the Pezu Anticline (Figures 3.2, 3.13). The Cambrian to Eocene platform dips to the west and the molasse section unconformably rests on the platform (Figure 3.13).

3.4.3 Marwat and Khisor Ranges The Marwat and Khisor Ranges separate the Bannu Basin from the Punjab foreland basin to the south (Figures 3.1 and 3.2). The Marwat Range is an anticline formed by the northwest-southeast contraction. The Marwat-01 well was drilled at the core of the range and penetrated the Salt Range Formation at around 2000 m (6562 ft) (Figure 3.4). Khisor

Range is also an anticline. Cambrian to Triassic units are exposed in the core of the structure, and the southern limb is cut by a thrust that forms the southeastern boundary of the Bannu Basin (Ali, 2010; Alam et al., 2014). A cross-section of the Marwat and

Khisor Ranges modified from Ali (2010) is shown in Figures 3.15, 3.16 and 3.17.

3.5 Interpretation Seismic and well data provide an insight into the subsurface structures of the Bannu

Basin. Cross section A-A’ across strike was constructed to illustrate overall structural elements of the Bannu Basin using seismic Line-1, Kundi-X1 well, Marwat-01 well and the cross-section of the Marwat-Khisor ranges from Ali (2010) (Figure 3.14). Figure

3.15 and 3.16 show fence diagrams of Eastern and Western Bannu basins, respectively.

The cross sections for the fence diagram were created from seismic profiles. Based on the newly released well and seismic data, the general structural style of the Bannu Basin was interpreted, which showed two unique structures; salt diapir and tranpressional structure.

Finally, the hydrocarbon potential of the Bannu Basin and its comparison with the eastern equivalent, the Potwar Plateau-Salt Range, are discussed.

3.5.1. Structural style of the Bannu Basin The Bannu Basin can be divided into three main regions: the thrusted region to the north, the central Bannu syncline, and the thrust front to the south (Figure 3.17). At the northern end of the section, thrust faults have been identified to have displaced Siwalik and

Rawalpindi Group (Figures 3.6, 3.7). Ali (2010) suggested that the Miocene normal faulting event resulted in the Pre-Cambrian basement ramps. In consequence, these

sections 3.15, (Figures fence the for used diagram 3.16).

Map showing locations showing Map cross 5 of

Figure 3.14: Figure

A’ was created using was created using A’

north.

to the to

01 wells. The southern part of the profile was modified from modified was the part wells. 01 of southern Ali profile The

E’ were created using seismic Line 4 and Line 3 respectively. White 3 respectively. and 4 seismic were E’ createdLine using Line

nd Marwat nd

D’ and E and D’

X1a

sections D sections

Fence diagram showing regional structure of the the of regional diagram structure Bannu eastern A showing basin. Fence

Figure 3.15: Figure Kundi 1, seismic Line Cross (2010). point arrow surfaces. Green detachment interpreted the represent arrows

A’ was created using was A’

respectively. White respectively.

and Line and Line

re created using seismic Line seismic re createdLine using

01 wells. The southern part of the profile was modified from Ali Ali from modified was the part of southern profile The wells. 01

C’ we C’

B’ and C and B’

X1 and Marwat and X1

sections B sections

Fence diagram showing regional structure of the western Bannu basin. A the of regional diagram basin. structure Bannu western showing Fence

Figure 3.16: Figure Kundi 1, seismic Line Cross (2010). points north. the to arrow surfaces. Green detachment interpreted the represent arrows

s s

01 well 01

X1 and Marwat and X1

Lillie, 1988). White arrows Whitearrows 1988). Lillie,

e e and

faces.

Salt Range (B). (Modified from Jaum from (Modified (B). SaltRange

section of the Bannu basin 1, basin the Kundi of (A). Line Bannu section

section. The southern section was modified from Ali (2010). Bottom: Structural Structural Bottom: (2010). Ali from modified was southern section The section.

Top: Structural cross Structural Top:

17:

section of the Potwar Plateau Potwar the of section

were used to create the the cross used create to were Figure cross sur interpreted the detachment represent

South

17 (A) 17

17 (B) 17

Figure3. Figure3.

94 normal fault ramps contributed in the formation of the Marwat Anticline during the southern progression of the Bannu Basin. A summary of our observations is given below:

1) Most of the structures were formed as a result of northwest-southeast contraction.

This is seen in the orientation of the Marwat Anticline, the Khisor thrust, and the interpreted thrust faults in northern Bannu Basin (Figures 3.2, 3.6 and 3.7). In general, the

Bannu syncline displayed no extensive deformation. This is seen clearly in the Cambrian to Eocene sedimentary units across the basin, which seems to be consistent in thickness

(2000-2200 m [6562-7218 ft]) with no sign of significant deformation. However, contractional structures appeared to be concentrated in the south of the basin, in the form of anticlines and thrust faults (Marwat and Khisor Ranges), and in the north, in the form of thrusts (Figures 3.6 and 3.7). The thrusts in the north of basin were observed to be terminated along a detachment surface (around 6400 m in depth) located in the Eocene-

Paleocene section (Figure 3.6), while the main thrust of the basin appeared to terminate at the Cambrian/Infra-Cambrian section (Parvez, 1992; Ali, 2010)

2) Transpression zones and positive flower structures near both ends of the Marwat

Range were linked with the intersection between transpressional faults and the Marwat anticline. These structures have been interpreted in Lines 3 and 6 (Figures 3.8, 3.11).

Discussions on the transpression zones and salt are explained in the section below.

3) Cambrian to Eocene platform has a constant thickness of around 2000-2200 m

(6562-7218 ft). It is generally undeformed and dips to the north. Cambrian to Triassic layers are exposed along the Khisor thrust (Ali, 2010).

4) Seismic interpretations suggest that the Bannu Basin contains two detachment horizons. The evidence of salt and salt-related structures suggests that the main sole detachment may be the Salt Range Formation. The conformity of deformation in the

Cambrian-Eocene platform suggests that the sole detachment is located below the

Cambrian strata (Figures 3.6-3.13). The confirmation of the presence of the Salt Range

Formation by the Marwat-01 well and the interpretation of a salt structure (Figure 3.12B), which is further supported by the lower gravity anomaly, implies that the salt could act as a major detachment. It detaches the entire stratigraphic section from the Pre-Cambrian basement rock (Figure 3.17).

The other detachment was seen in northern Bannu Basin, where it separates the deformed molasse section (Siwaliks and Rawalpindi Groups) from the underlying

Cambrian to Eocene platform (Figures 3.6, 3.7). Figure 3.6 shows two packages of strata

(Siwalik/Rawalpindi and the Cambrian-Eocene platform) that display different deformation suggesting a detachment layer between the two packages. The Eocene-

Paleocene shale units are possible detachment surfaces.

5) A Miocene-Eocene unconformity was observed in all of the interpreted seismic lines (Figures 3.6-3.13). The unconformity surface was interpreted along the contact of the Cambrian-Eocene platform and the overlain Siwalik and Rawalpindi Groups. Onlaps of the Rawalpindi units on the Eocene-Paleocene units can be seen clearly in Figure 6. In addition, this basin-wide unconformity was interpreted to relate to the Himalayan orogenic processes, which caused uplifts and erosion (Wandrey et al., 2004).

6) Furthermore, the Miocene-Eocene unconformity separates two distinct tectonic settings of the basin. In the earlier periods (Infra-Cambrian to early Eocene), the undeformed Cambrian to Eocene platform implied a tectonically passive environment, where the deposition of marine sediments were mainly controlled by paleoclimate and events of transgression/regression. On the contrary, the fluviatile sedimentary deposition, which started in early Miocene, is more tectonically-driven. Uplifted regions due to the compressional events influenced the source of the sediments deposited. In addition, contractional structures observed in the Bannu Basin, specifically the positive flower structure and salt diapir structure (Figures 3.8 and 3.12), disrupted the Cambrian to

Pliocene stratigraphic layers. This implies a recent transpressional and compressional tectonic event which may have started during Pliocene and could be continuing today.

3.5.2. Salt diapirism and transpression zones Seismic line 6 (Figure 3.12) and well tops from Marwat-01 well indicate the presence of the Salt Range Formation in the Bannu Basin. A relatively low gravity anomaly above the anticlinal structure at the southern end of Line 6 (Section B-B') suggests that the structure may be cored by salt (Figure 3.12B). Our work also suggests the possibility of the Salt Range Formation acting as the main detachment in the Bannu Basin and is continued to the west of Kalabagh fault, where it apparently terminates. Structural cross section B-B’ shows a salt diapir located at the southern section of the profile (Figure

3.16). As seismic and well data do not provide information below the Cambrian sedimentary units, the exact location of the main detachment of the Bannu Basin is still in debate. However, we can infer that the location of the detachment is below the Cambrian units and above the Pre-Cambrian basement. With the presence of the Salt Range

Formation confirmed by the Marwat-01 well, it is very likely that the salt could act as the main detachment surface. It is also important to note that the structural trend and the low internal deformation of the Bannu Basin is similar to the thin-skinned deformed Potwar

Plateau.

Seismic profiles showed that salt-structure and transpressional zone may have formed simultaneously (Figure3.12). Figure 3.12 shows the transpressional Pezu fault located above the salt structure, which is similar to the Kalabagh fault in the Potwar Plateau

(Figure 3.1) (Abir et al., 2015). Areas of uplift along and near transpressional faults are usually related to positive flower structures, which is seen in Figure 3.8. These

98 transpressional structures created vertical space where ductile rocks, such as salt, flow and invade. However, these structures could also strengthen the overlying sedimentary units, making it hard for salt to push upwards. A key factor in the upward movement of salt is the strength of the overlying layers (Hudec and Jackson, 2007). Regions to the south of the Bannu Basin have the weakest overburden due to the thin molasse section.

Therefore, salt structures tend to be prominent in this region (Abir et al., 2015).

Moreover, the formation of the transpressional and salt structures seems to be initiated by the recent transpressional and compressional tectonic event which relates to the southward progression of the Bannu Basin started during Pliocene (Blisniuk et al., 1998).

The southward movement of the basin depends heavily on the extent of the salt with the transpressional Pezu and Southern Surghar faults as the western and eastern depositional limit of the salt.

This interpretation implies that the dextral Pezu fault and the sinistral Southern Surghar fault may still be active today. These transpressional zones are located at the intersections of the Marwat Anticline with the Southern Surghar Fault to the east and the Pezu-Bhittani

Range to the west (Figure 3.2). A similar transpressional uplift has been interpreted in western Potwar Plateau along the right-lateral Kalabagh fault (Abir et al., 2015).

3.6 Discussions

3.6.1. Comparison with structural style of the Potwar Plateau-Salt Range The structural style of the Potwar Plateau-Salt Range has been well studied when compared to the Bannu Basin (Leathers, 1987; Lillie et al., 1987; Jaume and Lille, 1988;

Cotton and Koyi, 2000; Grelaud et al., 2002; Chen and Khan, 2010; Faisal and Dixon,

2014; Ghazi et al., 2014; Jouanne et al., 2014; Qayyum et al., 2014). Both fold-and-thrust belts are described as undergoing thin-skinned deformation. The difference in the structural style between the Kohat Plateau and the Potwar Plateau is mainly attributed to the nature of the detachment (Jaume and Lillie, 1988; Cotton and Koyi, 2000). Salt

Range Formation is the main detachment in the Potwar Plateau (Lillie et al., 1987; Baker et al., 1988; Jaume and Lillie, 1988; Faisal and Dixon, 2014; Ghazi et al., 2014). Salt acts as a detachment layer upon which the overburden slides relatively effortless during episodes of compression. In map view, the width and the surface topography of the

Bannu Basin is very similar to the Potwar Plateau (Figure 3.1). In contrast, the main detachment in the Kohat Plateau is a higher frictional surface (McDougal and Hussain,

1991; Ahmad, 2003). Geologic mapping by Ahmad (2003) suggests that Kohat’s main detachment surface is in the Paleozoic units. Moreover, the structural trend of the Kohat

Plateau is closely spaced in comparison to the Potwar Plateau or the Bannu Basin (Figure

3.1).

This work suggests that the Salt Range Formation is also a possible detachment in the

Bannu Basin. Therefore, we describe the Bannu Basin as the western extension of the

100

Potwar Plateau and that the Salt Range Formation extends westward of the Kalabagh fault. Moreover, similar to the Potwar Plateau, salt act as a detachment in the north of the

Bannu Basin where overburden is thick, while close to the southern edge of the basin where overburden is thinned due to thrusting and transpression, salt-related structures are prominent (Figures 3.15, 3.16, 3.17) (Abir et al., 2015). This is the direct effect of the strength and thickness of the overlying sedimentary units. The northern part of the basin is where the overlying rocks are the thickest and strongest impeding the salt from flowing upwards. This is totally different for the southern part of the basin, where the overlying rocks are thinner and contractional structures create spaces for salt to flow. In some cases, such as in the Potwar Plateau, the overburden is thrusted and eroded exposing the salt to the surface (Lillie et al., 1987).

The Bannu Basin can also be divided into three distinct regions similar to other thin- skinned fold-and-thrust belts, such as the Potwar Plateau and the Kuqa basin in China

(Chen et al., 2004). The northern part of the basin, where most of the deformation occurs, is called the Trailing Edge (Chen et al., 2004). This is equivalent to the Northern Potwar

Deformation Zone and the western Kohat Plateau for the Potwar Plateau and Bannu

Basin respectively (Jaswal et al., 1997) (Figure 3.17B). Southward of the Trailing Edge is the Transitional Belt, where a synclinal structure is filled with thick fluviatile sediments.

The Soan syncline and the Bannu syncline are recognized as the Transitional Belt of the

Potwar and Bannu basins respectively. It must be stressed that the Bannu syncline is the subsided central part of the Bannu Basin and must not be confused with the term ‘Bannu 101

Basin’, which refers to the name of the region. Finally, the frontal thrusts of the basins

(the Khisor and Salt Range thrusts) are labeled as the Leading Edge (Figure 3.17).

The structural style difference between the Bannu Basin and the Potwar Plateau is prominent along the strike, where the Bannu Basin forms a homogeneous wedge of sediments and Potwar Plateau displays assorted structural deformation styles along the

Salt Range thrust (Faisal and Dixon, 2014; Qayyum et al., 2014) (Figures 3.15 and 3.16).

This can be attributed to salt distribution and Pre-Cambrian basement rock geometry

(Lillie et al., 1987). The Potwar Plateau displays different deformation styles along strike and can be separated into western, central and eastern Potwar (Lillie et al., 1987). Seismic observation, well interpretation and geological mapping show that the structural styles depends on the thickness of the salt and the location of Pre-Cambrian basement ramps

(Lillie et al., 1987; Qayyum et al., 2014). The stratigraphy and structure of the Bannu

Basin, on the other hand, appears to be consistent along strike (Figure 3.7).

The western and eastern boundaries of the Bannu Basin are transpressive fault systems

(Figure 3.2). In summary, current data suggests that the extent and thickness of the Salt

Range Formation is an essential factor in generating different structural styles in this region. The location of salt deposition plays a major role in determining the boundaries of the Bannu Basin, as well as the Potwar Plateau.

102

3.6.2. Implications for hydrocarbon exploration The Bannu Basin has been relatively unexplored when compared to the Potwar Plateau.

Many oil fields that have been discovered in the Potwar region include the Dhurnal,

Dakhni, Toot, Baikassar and Adhi fields (Sercombe et al., 1998; Wandrey et al., 2004).

Both basins have similar stratigraphy in terms of source and reservoir rocks. The three main groups of stratigraphic sections can be found in both regions: the Salt Range

Formation followed by the Cambrian to Eocene Platform overlain by the

Siwalik/Rawalpindi molasses (Figure 3.17). Furthermore, multiple oil seeps have been located along the Southern Surghar Fault, the Khisor Range and the Pezu-Bhittani Range indicating the presence of mature source rock in the Bannu Basin (Figure 3.2). These oil seeps have been identified to originate from various source rocks that include the

Miocene-Eocene unconformity, Siwaliks-Kingriali formations and Cambrian gypsum beds (Ali, 2010). Other major source rocks from the Potwar and Kohat basins are the

Panoba-Patala formations (shales) and shale formations that are from the lower

Cretaceous, Jurassic, Triassic, Permian and Infra-Cambrian ages (Wandrey et al., 2004;

Ali, 2010).

Seismic and well data shows that the most promising source rock, the Panoba shales

(Miocene-Eocene unconformity), are present in the Bannu Basin and it may be mature owing to deep burial under the thick Siwalik and Rawalpindi layers. The Kundi-X1 penetrated the Panoba shales at the depth of the 6400 m (20997 ft) (Figures 3.2 and 3.4).

Possible hydrocarbon traps in the Bannu Basin are anticlinal structures, transpressional

103

Depth (Km) Depth

Time (million years) 40 30 20 10 0

50 40 30 20 10 0 Time (million years)

Figure 3.18: Top: Generalized burial history chart for the Kundi- X1 well. A geothermal gradient of 1.2C/100 m was used (Ali, 2010). Bottom: A critical moment history chart showing the critical moment at around Pliocene in age when all the most recent compression event took place.

104 zones (positive flower structures) and thrust-related traps, many of which are localized in the ranges that surround the basin. The Southern Surghar and the Pezu-Bhittani Ranges display transpressive structures and are characterized as wrench-fault zones (Pivnik and

Sercombe, 1993; Ahmad et al., 2003; Khan, 2013). In general, wrench-fault zones deform continuously over a long period of geologic time (Moody, 1973). Due to their continuous deformation, these zones tend to develop localized structural highs concurrently or shortly after the deposition of potential source rock (Moody, 1973). Line 3 and line 6 show transpressional structural highs, which could be the result of wrench-fault tectonics in the Southern Surghar and Pezu-Bhittani Ranges respectively (Figures 3.8 and 3.12).

Oil migration to traps located at the frontal structures (Marwat and Khisor Ranges) of fold thrust belts (Marwat and Khisor ranges) may be responsible for late-stage accumulation of hydrocarbons (Roure and Sassi, 1995). Figure 3.18 shows a generalized burial history chart with a critical moment chart for the Kundi-X1 well. The burial history chart shows that the main potential source rock, the Panoba shale, was buried by thick fluviatile sediments of the Siwalik and Rawalpindi formations initially around early

Miocene and entered the oil window by early Pliocene. The most recent thrusting and folding event occurred during late Pliocene after the deposition of the source rock, the reservoir rock and seal. We suggest that the generation of hydrocarbons started in early

Pliocene and continues through the last phase of thrusting in late Pliocene, when the potential traps were formed (Figure 3.18).

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In summary, the similarities in structure and stratigraphy makes it is highly possible for working petroleum systems that produced the oil fields in the Potwar Plateau to also be present in the Bannu Basin (Wandrey et al., 2004). Salt structures are usually associated with stratigraphic traps, such as pinch-outs, and structural traps. Based on our results, salt and transpressional structures located at the eastern and western ends of the Marwat

Anticline are possible areas for hydrocarbon exploration, although more seismic and well data are needed to further access the potentiality of this region.

3.7 Conclusions This work clearly demonstrates that the Salt Range Formation is present under the Bannu

Basin, west of the Potwar Plateau. The Marwat-01 well penetrated to the Salt Range

Formation and seismic profiles show structures related to salt diapirism and transpressional deformation. Structural geology of the Bannu Basin is similar to the

Potwar Plateau and can be divided into three distinct regions: the Trailing Edge, the

Transitional Belt and the Leading Edge.

Wells and interpreted seismic profiles suggest that the Bannu Basin contains two detachment layers. The Eocene-Paleocene shales detach the molasses section from the underlying Cambrian to Eocene platform, while the Infra-Cambrian salt separates the

Pre-Cambrian basement from the overlying sedimentary units.

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The ranges surrounding the basin are high potential areas for hydrocarbon exploration based on the presence of oil seeps that have been identified along the Southern Surghar,

Pezu-Bhittani and Khisor Ranges which indicate the presence of mature source rocks in the Bannu Basin. We recommend focusing data acquisition efforts along the southern structures of the basin, especially the Marwat and Khisor Ranges. Although there is high potential in the hydrocarbon exploration of the Bannu Basin, more data is required to fill in the gaps in the understanding of the possible petroleum systems in the basin.

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CHAPTER 4: Western Himalayan front geometry and relation to earthquake occurrences revealed by InSAR and satellite mapping

4.1 Abstract The Sulaiman fold belt has been a locus of earthquakes in comparison to the eastern fold belts of western Himalayas which is related to how they deform. Competing hypotheses suggest that the geometry and curvature of fold belts are controlled by along strike changes in detachment, or they were formed due to irregularities of the collision margin.

Here we use InSAR measurements of surface displacement to show that the western boundary of the Sulaiman fold belt is a right-lateral shear zone. The deformation of the shear zone is controlled by two parallel transpressive faults that bounds the zone with a net right lateral shear of 3 mm/yr. We use the InSAR data combined with multi-spectral satellite imagery to map active faults in the shear zone and the southern Sulaiman areas.

Left lateral faults related to ‘bookshelf faulting’ are observed along the right-lateral shear zone. Structural analyses are best explained by a southwestward escapement of the

Sulaiman fold belt with right-lateral shear and left-lateral shear bounding the belt to the west and east respectively. We suggest that the formation of the Sulaiman fold belt is controlled by both the irregularities of the collision boundary and the difference in sedimentary thickness along strike. In the eastern fold belts, right-lateral shear zones are not observed, but clear right-lateral faults displaces the fold belts sharply which is due to across strike changes in salt thickness. Furthermore, given that there are no surface faults to explain the right-lateral slip of the 2008 Ziarat earthquake (Mag: 6.4), we proposed that our interpretation of a right-lateral shear zone may be a possible explanation.

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4.2 Introduction and tectonic setting The curvature of orogens can give us insights into the process of mountain building

(Marshak, 2004). Two types of curvature are important: 1) the gently curved large mountain belts, such as the Himalayas and 2) the smaller scale syntaxes and re-entrants, such as the Sulaiman fold belt and the Sibi Re-entrant (Lu and Malavieille, 1994). Even though the causes of these curves have been studied since the 1800s, there are still many unanswered questions. One important observation is that each curve is unique and can’t be related to a single cause (Marshak, 2004). An important region for the study of orogenic curves is located in Pakistan, especially western Pakistan, where syntaxes and re-entrants are actively deforming.

Western Pakistan is an active region which has produced devastating earthquakes due to its complex transpressional tectonics, such as the Mw 7.8 Quetta earthquake in

1935 during which around 35,000 people lost their lives (Mahmood et al., 2015).

Evidences of transpressional deformation are observed all along the main transform fault in this region, the left-lateral Chaman fault, which is identified as the boundary between the Afghan block and the Indian plate (Ul-Hadi et al., 2013) (Figure 4.1). Recent GPS and geomorphologic studies show that the slip rate of the Chaman fault ranges from 18-

33 mm/yr depending on the sections of the fault (Ul-Hadi et al., 2013; Mohadjer et al.,

2010). The complex transpressional tectonics due to the oblique collision between the

Indian plate and the Afghan block also resulted in fold belts, mainly the Kirthar and

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Sulaiman fold belts (Figure 4.1). Earthquake occurrences are localized to certain regions along the transpressional zone, in particular the Sulaiman fold belt (Figure 4.1).

The Sulaiman fold belt is easily recognized in map-view due to its conspicuous festoon- shape and its location adjacent to a structural bend, the Sibi Re-entrant (Figure 4.1). Two other structural bends are observed to the northeast of the Sulaiman belt, namely the Tank

Re-entrant and the Kalabagh Re-entrant (Figure 4.1). In comparison to the well-studied fold belts of northern Pakistan (Bannu Basin and Potwar Plateau), there are still many unanswered questions regarding the still debated deformation mechanics of the Sulaiman fold belt (Copley, 2012; Bernard et al., 2000; Haq and Davis, 1997; Jadoon et al., 1994;

Humayon et al., 1991). Overall, little work has been done in Sulaiman belt due to political reason and lack of resources (Waheed and Wells, 1990).

Many of the previous studies have focused on the central and eastern regions of the

Sulaiman fold belt (Jones et al., 1960; Abdel-Gawad, 1971; Rowlands, 1978; Armbruster et al., 1980; Verma et al., 1980; Klootwijk et al., 1981; Waheed and Wells, 1990; Asim et al., 2015; Humayon et al., 1991; Jadoon et al., 1994; Jadoon and Khurshid, 1996). In this paper, we used InSAR and other remote sensing techniques to study the slow surface deformation of the western boundary of the Sulaiman belt (Figure 4.2). InSAR

(Interferometric Synthetic Aperture Radar) can be effectively used to study the active deformation of remote regions, such as the Sulaiman belt. Recent InSAR studies have

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2. 2. 4.

Hadi et al., al., et Hadi

ion of earthquakes (yellow earthquakes of ion

e e 2006). Bilham, (after

(Modified from Pivnik, 1992; Yin, 2006; Ul Yin, Pivnik, (Modifiedfrom 1992;

approximate location of the Main Frontal Thrustapproximate(MFT) Main Frontal is the of location which boundary southern the

arcsecond SRTM Digital Elevation Model (DEM) map showing the northwest region northwest the showing map of (DEM) Model Elevation Digital SRTM arcsecond

thrust belts of northern Pakistan belts thrust northern of

A 1 A

and

The arrow shows the plat the of shows velocity arrow estimated The Indian

Figure 4 Figure distribut the shows map The Sulaiman the is belt located. fold where Pakistan, boxes solid black The Program. from Hazards 5 Earthquake magnitude with USGS the above or circles) of location the Figure black datasets box acquired of dashed location the and represents InSAR represent fault the is red The fold the of 2012)

111

112 utilized the 2008 Ziarat earthquake and demonstrated a right-lateral movement along the

Sibi Re-entrant, which has no surface expression (Figure 4.2) (Pezzo et al., 2014; Pinel-

Puyssegur et al., 2014). As future earthquakes will have significant impact on the population centers (Quetta) of this region, it is imperative to further study the tectonics and map hidden faults which could pose a potential threat to this region. Our InSAR results suggest an actively deforming shear zone along the western boundary of the

Sulaiman belt, where geomorphic evidences of clockwise rotations can be observed in active structures along this zone resulting in bookshelf faulting. In addition, geomorphic mapping of active structures of Southern Sulaiman belt seems to suggest a southwestern movement.

4.3 Methodology

4.3.1 InSAR (Interferometric Synthetic Aperture Radar) InSAR is a radar satellite processing technique that measures accurately the deformation, from centimeters up to millimeters, of the Earth’s surface (Berardino et al.,

2002; Lanari et al., 2007; Massonnet et al., 1993). It has been used to study earthquakes, volcanoes, landslides, fault slip rates, and urban subsidence rates (Chen and Khan, 2010;

Abir et al., 2015; Hooper et al., 2004; He et al., 2015; Amelung et al., 1999; Guzzetti et al., 2009; Pezzo et al., 2014; Pinel-Puyssegur et al., 2014). In comparison to GPS (Global

Positioning System) measurements, InSAR gives a continuous measurement over a large spatial region. With new radar satellites being launched, such as the ALOS (Advanced

Land Observation Satellite) PALSAR-2 (Phased Array type L-band Synthetic Aperture

Radar 2) by the Japanese Aerospace Exploration Agency (JAXA), more data are

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Figure 4.2: A close-up hillshade map of the Sulaiman fold belt and the Sibi Re- entrant showing the main structural features. The yellow box represents the descending Envisat ASAR footprint used in this study and the white-black boxes represents study areas where detailed satellite image mapping have been done. Modified from Bannert, 1992; Jadoon et al., 1994; Pinel-Puyssegur et al., 2014.

114 available for monitoring the Earth. This technique utilizes the phase information of SAR

(Synthetic Aperture Radar) image pairs by calculating the phase difference or interferograms of each image pair. The pairs were chosen from the same satellite platform and covers a similar region over a time range. However, included in the interferograms are phase noises derived from the topography, the orbital errors and the atmosphere. Therefore, an important part of InSAR processing is the removal or filtering out of unwanted phase noises so that the desired phase signal from slow surface deformation can be extracted and measured.

In order to minimize phase noises, especially noises due to the atmosphere, an advanced InSAR processing technique, the SBAS (Small Baseline Subset), was used

(Berardino et al., 2002; Lanari et al., 2007). Basically, the SBAS time-series processing technique exploits large number of interferogram pairs, up to hundreds of pairs, and averages them in order to increase signal-to-noise ratio (Zebker et al., 1997). In this study, 34 descending Envisat ASAR (Advanced Synthetic Aperture Radar) images were acquired from the European Space Agency (ESA) between May 5th 2003 and May 3rd

2010 (Figure 4.3). The SAR scenes cover the Sibi Re-entrant, the western portion of the

Sulaiman fold belt and eastern Kirthar Range (Figure 4.1). ASAR radar sensor emits C- band (5.6 cm wavelength) microwave energy and has a shorter wavelength that the L- band PALSAR sensor (23.6 cm) (Rosenqvist et al., 2007).

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temporal baseline for Envisat ASAR images used in this in used ASARimages for Envisat baseline temporal

Spatial

en diamonds represent the interferogram pairs that were used in the in used were that pairs interferogram the represent diamonds en

(December 25th 2006) 25th (December

study. Gre study. Figure 4 Figure master super SBAS the diamond represents while the processing, SBAS yellow image

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SARscape modules of ENVI software from EXELIS VIS Information Solutions were used for the generation of the interferograms. In order to improve the coherence of the interferograms, the image pairs were selected based on the maximum temporal baseline of 5 years and perpendicular baseline threshold of 50% (466 meters) (Figure 4.3).

Interferograms processing consists of image pair coregistration, interferogram generation, interferogram flattening using 1-arcsecond Shuttle Radar Topography Mission (SRTM) digital elevation model, Goldstein filtering (Goldstein and Werner, 1998), coherence generation and interferogram unwrapping.

The topography phase signal was removed using the SRTM digital elevation model during the flattening step. A complex multi-look with 4 in range and 20 in azimuth was applied to ensure a high signal-to-noise ratio during the filtering step which further reduces phase noise (He et al., 2015; Guzzetti et al., 2009). The minimum cost flow

(MCF) (Costantini, 1998) and the 3D Delauney methods were combined for phase unwrapping (Hooper and Zebker, 2007). 272 unwrapped interferograms were generated and each of them was analyzed for quality check. After the removal of ‘bad’ interferograms, 145 interferograms were used for the remaining processing steps. The basis for the selection of ‘bad’ interferograms include very low coherence and extensive unwrapping errors.

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Atmospheric effects in the phase signal represent the spatial and time variability of water vapor over the study area, which affect displacement calculations significantly due to phase time delay (Zebker et al., 1997). Two filters were used to effectively estimate the atmospheric effects and remove them from the final displacement measurements. A square low pass filter (1.2 km x 1.2 km) was used to take into account the spatial variations of the atmospheric effects, while a high pass filter (365 days) was performed to take into account the time variations of the atmospheric effects (Berardino et al., 2002).

It is important to note that the final displacement velocity map (Figure 4.4) is the surface displacement velocity projected in the direction of LOS (line of sight) of the radar sensor. It is a relative displacement measurement with reference to selected ground control points where deformation is assumed to be zero. These ground control points have been selected based on certain criteria which include (1) high coherence pixels

(above 0.6); (2) flat regions based on the DEM; and (3) the well distributions of points on the image. As a result, the final cumulative displacement values may be affected by the selection of ground control points.

4.3.2 Satellite data processing Multi-spectral Landsat-8 satellite images (downloaded at http://glovis.usgs.gov) were used for identifying and mapping active geomorphic features in the study area.

Landsat-8 is the most recent NASA satellite launched in a series of continuous Landsat satellites since 1972 (Roy et al., 2014). In contrast to radar sensors, such as Envisat

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ASAR, Landsat-8 is a passive remote sensing system relying on electromagnetic energy from a natural source, the sun. A total of 11 spectral bands were recorded by two sensors, the Operational Land Images (OLI) and the Thermal Infrared Sensors (TIRS) (Roy et al.,

2014). These spectral bands were composed of reflected energy recorded at specific ranges of wavelength: 0.43-0.68 μm, 0.85-0.88 μm, 1.57-2.29 μm, and 10.6-12.51 μm

(Roy et al., 2014). The multispectral bands (Bands 1-7 and band 9) with the spatial resolution of 30 m were analyzed using the software ENVI version 5.3 after employing band ratio and false composite color techniques. These techniques have been successfully applied to multi-spectral satellite data for studying geomorphic responses of tectonically active areas, such as the Lesvos island in Greece (Novak and Soulakellis, 2000) and the

Chaman fault in Pakistan (Ul-Hadi et al., 2012).

Four Landsat-8 images were selected for this study due to absence of cloud cover. After investigating with different band combinations, it was found that the red-green-blue

(RGB) combination of Band 5 (NIR), Band 6 (SWIR 1) and Band 2 (Blue) gave the best results in helping to identify surface features. Band ratio is a simple and effective technique that enhances surface features and minimizes shadow and topographic effects

(Ul-Hadi, 2013). Basically, band ratio divides the pixel values of one band to another band and displays the relative spectral difference. Furthermore, composite color combinations of band ratios were highly effective in enhancing different lithology and other features in the Landsat scenes. Many composite color combinations were employed and the best combination in assisting to identify geomorphic features is combination 7/5- 119

6/3-4/3. In addition to Landsat 8, high spatial resolution multi-spectral images from the

Sentinel-2 satellite were also utilized. The European Space Agency Sentinel-2 satellite consists of 13 spectral bands with 4 bands at 10 m resolution, 6 bands at 20 m resolution and 3 bands at 60 m resolution (Drusch et al., 2012).

Geomorphic features were identified and mapped by integrating the processed satellite images (Landsat-8 and Sentinel-2) with hillshade maps (using SRTM Digital

Elevation Model) and published geologic maps (Jones et al., 1960). The results (Figures

4.5, 4.6 and 4.7) of the mapped areas are discussed in the next section. This study focuses on the identification of folds, thrust faults and strike-slip faults. These are important features for understanding the active tectonics of fold-and-thrust belts (Keller and Pinter,

1996).

4.4 Results and analysis

4.4.1 SBAS surface displacement map Figure 4.4 displays the averaged accumulated displacement rate of the study area for an interval of 7 years from May 5th, 2003 to May 3rd, 2010. This map shows the rate of surface displacement that is projected in the direction of Line of Sight (LOS), which is at an angle from the surface towards the satellite. As the Envisat ASAR scenes used were on a descending track, the right-looking sensor pointed westward in the direction of LOS

(Figure 4.4). Positive values signify the moving of the surface towards the satellite and can be interpreted as uplift, eastward movement or both. On the other hand, negative

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entrant entrant

The mean displacement velocity (mm/yr) map Sibi (mm/yr) the of Re velocity displacement mean The

the western portion of the Sulaiman fold belt for a period of of for belt period from 7 Sulaiman fold the of a portion western the years

Figure 4 Figure and 3rd to 2003 5th May 2010. May

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122 values represent the moving of the surface away from the satellite and can be interpreted as subsidence, westward movement or both. Overall, the trend of deformation varies greatly which is expected for this highly faulted region dominated with thrust and strike- slip faults. Tectonically, this area can be separated into three main regions; the Sulaiman

Fold Belt, the Sibi Re-entrant, and the Kirthar Range to the west (Figure 4.4).

With the assistance of published geological maps and remote sensing techniques, major faults in the region were mapped (Jones et al., 1960; Bannert, 1992). The displacement map covers the western portion of the Sulaiman Fold Belt (Figure 4.4). The

Karahi fault and the Harnai fault are two main parallel faults located in this area which is striking NW-SE. In the north, the area that lies in between these faults shows a majority of positive values up to 11.8 mm/yr. We interpreted this as mainly eastward movement due to 1) previous studies showing the right-lateral movement of the Harnai fault based on geological mapping and focal mechanisms (Bannert, 1992; Pinel-Puyssegur, 2014) and 2) GPS interseimic velocities showing a southeastern movement relative to stable

Indian plate, with station SHRG moving at a rate of ~20 mm/yr and station HRNI at a rate of ~10 mm/yr (Szeliga, 2010) (Figure 4.4). Parallel to the Harnai fault is the Karahi fault which has been interpreted as a thrust fault (Bannert, 1992). However, our InSAR results showed a slight left lateral movement of the Karahi fault at a rate of about 3 mm/yr as can be seen of the Dabbar anticline (Figure 4.4). Other important observations were the right-lateral movement of Fault 1 (F1) and the thrusting movement of Fault 2

(F2) (Figure 4.4). We interpreted F1 and F2 as transpressional faults were due to 123 geomorphic evidence of rotational tectonics which is discussed in subsequent sections. In addition, a possible fault (F3) were also interpreted which is located to the south of Fault

2 (F2) (Figure 4.4).

According to our displacement map, the Sibi Re-entrant was uplifted during the 7 years at a rate of up to 7 mm/yr with the rate of uplift decreasing southward. This highly folded area consists of massive synform structures (Bannert, 1992). Separating the Sibi

Re-entrant from the Kirthar Range to the west is the Bolan thrust fault (Figure 4.4). The sharp difference in the rate of surface uplift between the western (up to 8 mm/yr) and eastern blocks (up to 2 mm/yr) of the Bolan fault seems to support the thrusting motion

(Figure 4.4). In addition, the areas of no data represent low coherence which are mainly due to 1) highly vegetated areas or 2) areas of agriculture activities.

4.4.2 Active geomorphic features from remote sensing

4.4.2.1 Western Sulaiman belt (Figures 4.5A and 4.5B) The western Sulaiman fold belt is characterized by a highly deformed elongated shear zone which is controlled by two main faults: the Karahi fault to the north and the Harnai fault to the south (Figure 4.5A). The Karahi fault is interpreted as a thrust fault with a small left-lateral component based on our InSAR results and published GPS velocities

(Figure 4.4) (Szeliga, 2010). The fault can be traced easily on the Landsat 8 image along a distinct ridge which separates the Dabbar anticline and the shear zone to the south

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f Figure Figure f

Dziewonski et al., 1981; al., Dziewonskiet

Nettles, 1997 Nettles,

Geologic map of western Sulaiman fold belt. Modified from Modified belt. Sulaiman western Jones fold Geologic of map

5A:

Figure 4 Figure o area box The black study the shows images. 8 and 1960 al., et Landsat in two showing 1998 mechanisms earthquakes and 1997 from Focal 4.5B. movement possible a with ( thrusting lateral left small Ekstrom 2012; al., and et Ekstrom

125

126

iri anticlines (Figure 4.5A location). for (Figure anticlines iri

Landsat 8 8 Dungan and the of Landsat M view

5B:

. Figure 4 Figure

127

(Figure 4.5A). Similarly, the Harnai fault was traced along a linear ridge separating the

Cretaceous Belemnite shales to the south from the Eocene Ghazij shale formation to the north (Figure 4.5A). The Harnai fault is interpreted as a thrust fault with right lateral component which is based on our InSAR results and GPS velocities from Szeliga (2010).

The thrust Fault 2 (F2) is interpreted as the continuation of the Harnai fault to the south.

This different sense of motion along the northern and southern sections of the Harnai fault may have resulted in a local uplift where these faults meet (Figure 4.5A).

The shear zone is illustrated by complex interaction of thrust, strike-slip and transpressional faults (Figures 4.5A and 4.5B). The Dungan and Miri anticlines were mapped to better understand the deformation of the shear zone (Figure 4.5B). The anticlines are composed of Paleocene Dungan formation with exposed cores that are made of Jurassic Chiltan limestone. One important observation is the left lateral faults that cover both anticlines. It is evident from the sets of parallel left lateral faults and lineaments that these anticlines have undergone shearing and clockwise rotation (Figure

4.5B). A local uplift has been identified to the south of the Miri anticline which has been interpreted as being due to left-lateral transpressional deformation. Another interesting observation was the normal faults identified from Landsat 8 images and SRTM digital elevation models (Figure 4.5B). These normal faults may be related to the rotation of the

Miri anticline.

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4.4.2.2 Southern Sulaiman belt (Figures 4.6 and 4.7) Southern Sulaiman fold belt is composed of east-west trending anticlines which bend northward towards both ends resulting in a spectacular map-view curve (Figures 4.1 and

4.2). The southeastern Sulaiman fold belt is composed of Eocene to Paleocene formations. Based on Sentinel-2 imagery (10 meters resolution), we interpreted a set of parallel left lateral faults, which displaces the western fault blocks towards the southwest

(Figure 4.6). Similar left lateral faults were also identified in the southwestern Sulaiman fold belt (Figure 4.7). Many SW-NE trending lineaments and faults were observed for the

Loti and Pirkoh anticlines (Figure 4.7). One important observation is the shear structure that connects the Bambor anticline to the Pirkoh anticline which suggests a left lateral motion.

4.4.3 Tectonic interpretation We have integrated our InSAR results with geomorphic mapping of active features to better understand the complex active tectonics of the Sulaiman fold belt and the Sibi Re-entrant. Many of the earlier studies of the Sulaiman fold belt, through satellite

(Landsat), focal mechanisms and aircraft photography of western Pakistan, show that the

Sibi bend is highly affected by differential lateral movement surrounding the Sulaiman fold belt (Jones et al., 1960; Abdel-Gawad, 1971; Rowlands, 1978; Armbruster et al.,

1980). Focal mechanisms have shown an east-west left lateral transverse motion along the Loralai Ranges, which is one of the most tectonically active regions of the fold belt

(Figure 4.2) (Armbruster et al., 1980; Verma et al., 1980). This has been further supported by a paleomagnetic study by Klootwijk et al. (1981) that suggested a clockwise rotation of the Loralai Ranges during post-Eocene. Furthermore, evidences of very recent

129

2 view of the southeastern Sulaiman southeastern the of (Figure belt view 2 for 4.2 fold

Sentinel

Figure 4 Figure faults left of is set observed. lateral A location).

130

for location). Recent left Recent location). for

2 view of the southern Sulaiman fold belt (Figure 4.2 southern (Figure belt fold the of Sulaiman view 2

Sentinel

. lateral faults are also observed in this region. this in observed also faults are lateral 4 Figure

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(Quaternary) deformation is represented by the Zinda Pir anticline, which was suggested as the most recent structure (Figure 4.2) (Waheed and Wells, 1990; Asim et al., 2015).

Seismic, well and gravity studies have shown that the subsurface structure of the eastern

Sulaiman belt, also called the Sulaiman Range, is different from the central portion of the belt which acts as a thin-skinned system (Humayon et al., 1991; Jadoon et al., 1994;

Jadoon and Khurshid, 1996). In contrary to the thin-skin model, recent studies have suggested new tectonic models to explain the formation of the Sibi Re-entrant and the

Sulaiman Belt (Haq and Davis, 1997; Bernard et al., 2000; Reynolds et al., 2015; Reiter et al., 2011; Copley et al., 2012). Moreover, the question of how orogenic curves were formed has been studied extensively (Marshak, 1988; Macedo and Marshak, 1999; Davis and Lillie, 1994).

4.4.3.1 Shear zone along western boundary of the Sulaiman fold belt Our InSAR results and geomorphic mapping of the western Sulaiman fold belt suggest that shearing had played a major role in its deformation (Figures 4.4, 4.5A and 4.5B). The shear zone was strongly affected by the movements along the Karahi fault and the Harnai fault (Figure 4.8). Both faults display a sense of strike-slip and thrust motions. However, the compressional forces perpendicular to the Harnai and Karahi faults seem to dominate when compared to lateral motions along these faults (Figure 4.8). As a result of the shearing of this zone, possible right-lateral strike-slip faults, such as Fault 1 (F1), compartmentalized this zone into distinct blocks. At the same time, sets of parallel left- lateral strike-slip faults perpendicular to the Harnai fault were observed displacing anticlines in this region (Figure 4.5B). These parallel faults seem to support

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Figure 4.8: Map of angle of relative plate motion (α = 52°), instantaneous strain features (θp), and the Harnai fault. S3 is the maximum instantaneous shortening direction. The shear zone is located between the northern block and the southern block.

133 our interpretation of shearing in this region with a sense of clockwise rotation (Figure

4.8).

The culmination of our interpretation is that the shear zone has undergone both simple shear and pure shear deformation (Figure 4.9). This may be related to the oblique convergence of the Indian plate moving at a direction of N05E at a rate of around 10 mm/yr in relative to the Eurasian plate (Figure 4.8) (Abdel-Gawad, 1971; Haq and Davis,

1997). Oblique convergent boundaries have resulted in a 3D distribution of deformation

(simultaneous interaction between contractional and strike-slip motions), which was observed in the shear zone of western Sulaiman fold belt (Teyssier et al., 1995; Fossen and Tikoff, 1993). Our results agree with Teyssier’s strike-slip partitioned transpression model shown in Figure 4.9 (Teyssier et al., 1995). The model is effective in understanding the relationship between plate motion, instantaneous strain axes and degree of strike-slip partitioning. In conforming to the model, the northern block of the

Karahi fault was assumed to be fixed and rigid. Our InSAR results and published GPS data support this assumption (Figure 4.4). The left lateral movement of the Karahi fault is at a rate of around 3 mm/yr, while the right lateral Harnai fault slips at around 6 mm/yr.

Since the Harnai fault moves at a faster rate than the Karahi fault, the net movement should result in a fixed northern block (Figure 4.8). In contrast to the northern block, the southern block of the Harnai fault is assumed to be rigid and moving at a net rate of around 3 mm/yr (Figures 4.8 and 4.9).

134

ation. The Karahi fault fault fixed, be to Karahi assumed is block The ation.

A simple diagram showing the mechanism for the right lateral lateral the mechanism showing diagram simple A shear right the for

Figure 4 Figure simple shear shear and pure 1995). al., Teyssier Both et from zone(modified deform the in role a played left the to block faultsfault lateral Due shearing, Harnai moving. is the while the on anticlines surface. displace

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The mapping of active structures in the shear zone suggests no strike slip partitioning which implies that the deformation is predominantly due to pure shear. According to

Teyssier et al. (1995), non-strike slip partitioned model should have the angle of plate convergence (α) of more than 20°, which agrees with the convergence at 52° along the

Harnai fault (Figure 4.8). In addition, the orientation of the maximum instantaneous shortening (S3) should be at θp = 70°, where θp is the angle between the plate margin and

S3 (Figure 4.8) (Teyssier et al., 1995). The calculated θp ranges from 61° -72°. We also observed that the elevation across the shear zone is predominantly higher than the elevation for the northern and southern blocks (Figure 4.10). This also supports the idea that pure shear is dominant where both blocks compresses the shear zone.

Our interpretation is similar to the rotational block model suggested by Szeliga (2010).

According to this model, the shear zone of western Sulaiman belt is compartmentalized into blocks that have rotated in a clockwise rotation due to right-lateral shear (Szeliga,

2010). One distinct characteristic of this model is the presence of parallel strike-slip faults which resembles a horizontal stack of books being displaced and hence the name

‘bookshelf faulting’ (Figure 4.11) (Wetzel et al., 1993; Zuza and Yin, 2013). We observe similar faulting with the faults having a left lateral sense of motion (Figures 4.5A and

4.5B). A plot of focal mechanisms of the Sulaiman fold belt and Sibi Re-entrant seems to support the left lateral movement along the shear zone of western Sulaiman belt (Figures

4.5A and 4.12). Beach ball A (1998) is consistent with the orientation of the left-lateral faults (N75E) found along the shear zone with a slight left-lateral component (Figure

4.12).

136

D) across the shear zone. across D) shear the

B and C and B

Elevation profiles (A Elevation

10:

. Figure 4 Figure

137

Figure 4.11: Simple diagram showing the idealized right-lateral shear geometry with left lateral ‘bookshelf faulting’ (Adapted from Sigmundsson et al., 1995).

138

Figure 4.12: Focal mechanisms for the Sulaiman fold belt and the Sibi Re- entrant (Dziewonski et al., 1981; Ekstrom et al., 2012; Ekstrom and Nettles, 1997).

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Other studies have also investigated the shearing and rotation of structures, such as anticlines, in active transform zones such as the San Andreas fault in California (Miller,

1998), the Omar fault in Iran (Freund, 1970), the Dead Sea fault system in Israel (Ron et al., 1984) and the Alpine fault in New Zealand (Berryman, 1979; Norris et al., 1990;

Teyssier et al., 1995). Similar to the western Sulaiman shear zone is the Alpine fault shear in New Zealand. The deformation for both zones is distributed across the region with no evidence of strike slip partitioning (Teyssier et al., 1995).

4.4.3.2 The southwestward escapement of the Sulaiman fold belt The geomorphic mapping of the western and southern Sulaiman fold belt suggests a southwestward movement (Figure 4.13). This escapement appears to be a recent stage of deformation for the fold belt. The main supporting observations are:

1) The western shear zone (Figure 4.5A) impedes the westward movement of the

Sulaiman lobe, while the Sulaiman range impedes the eastward movement of the lobe.

The southwestern section of the Sulaiman fold belt is the only region without a major structure obstructing its movement (Figure 4.13).

2) In southern Sulaiman belt, the Loti and Pirkoh anticlines have been displaced by left-lateral faults striking NE (Figures 4.6 and 4.7). These southwestward displacements may have induced the formations of the Sui and Uch anticlines (Figure 4.13).

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Figure 4.13: Simple line drawing of the main faults of the Sulaiman fold belt (after Bannert, 1992) including newly mapped faults (Figures 4.5A, 4.5B, 4.6 and 4.7).

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3) The focal mechanisms (beach balls B and C) show a left lateral fault movement with a N30E orientation which is consistent with the faults mapped in the southern

Sulaiman belt (Figure 4.12).

This important observation indicates that the shape of the Sulaiman fold belt is highly affected by preexisting structures which could be related to sediment load or basement highs.

4.4.3.3 Comparison of the Sibi Re-entrant to the Tank and Kalabagh Re-entrants The study of curved orogens started since the 1800s (Marshak, 2004). Since then, many models have been produced in order to explain the cause for these fascinating structures. An important finding is that each curve is unique which could not be explained by a single model (Marshak, 2004). Many of the orogenic curves are mainly caused by structural or stratigraphic differences along strike which are called ‘basin- controlled’ curves (Marshak, 2004). The Kalabagh and Tank Re-entrants, located to the northeast of the Sulaiman belt, are excellent examples of ‘basin-controlled’ curves

(Marshak, 2004; Abir et al., 2015). Another important type of curve is called the

‘indenter-controlled’ curve where the shape of the hinterland, or in our case the irregularities of the southern boundary of the Eurasian plate, produce curved fold belts

(Marshak, 2004). Other types of curves include ‘margin-controlled’ and ‘obstacle- controlled’ curves.

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Two main models have been proposed to explain the formation of the Sulaiman fold belt and the coupled Sibi Re-entrant (Haq and Davis, 1997; Jadoon et al., 1994). One perspective is interpreting the Sulaiman belt as a ‘basin-controlled’ fold belt similar to the

Potwar Plateau and the Bannu Basin (Jadoon et al., 1994). According to this model, the

Sulaiman fold belt experienced thin-skinned deformation and slides southward along a weak detachment layer. This idea is supported by the presence of thicker predeformational sediment for southern Sulaiman belt based on seismic and well data

(Marshak, 2004; Jadoon et al., 1994). Another perspective is more focused on the shape of the colliding margin (Haq and Davis, 1997). Sandbox modelling by Haq and Davis

(1997) demonstrated that the movement and the shape of the Katawaz basin, located to the north of Sulaiman belt, can produce a curve and other important features similar to the Sulaiman belt (Figure 4.12). From their experiment, they were able to produce curved folds, a left lateral fault similar to the Kingri faults, and a re-entrant similar to the Sibi

Re-entrant (Haq and Davis, 1997).

Our results suggest that both the shape of the rigid Katawaz basin and the sediment thickness are important factors in producing the Sulaiman fold belt and in consequence the Sibi Re-entrant. Firstly, the sandbox model by Haq and Davis (1997) also produced a similar fault to the west of the Sulaiman belt which agrees with our observation of the Karahi fault. Although this fault was not highlighted in the paper by

Haq and Davis (1997), this model supports our interpretation of the Karahi fault which has a slight left-lateral component. Secondly, the southward movement of the Sulaiman fold belt is agreeable with our observations. The region of the thickest preexisting

143 sediments appears to be located at the apex of the Sulaiman fold curve (Marshak, 2004).

The presence of a weak detachment can explain the southwestward escapement of the

Sulaiman belt which still continues. In summary, the deformation due to the Katawaz basin represent the early stage of deformation due to the collision between the Indian and

Eurasian plates, while the southward movement of the Sulaiman belt represent the later stage of development.

Comparing the Sibi Re-entrant to the ‘basin-controlled’ Tank and Kalabagh re- entrants, we observe a huge distinction. The shape of the Tank and Kalabagh re-entrants is predominantly controlled by the movement along right-lateral strike slip faults which are the Pezu-Bhittani and Kalabagh faults, respectively. These strike-slip faults are linear features which can be traced clearly on surface maps. Studies have shown that these strike-slip faults are due to the lateral variations in the strength of the detachment layer with thick salt as the main detachment for this region (Abir et al., 2015). In contrast, no clear right-lateral strike slip fault can be mapped for the Sibi Re-entrant. As mentioned before, this increases the importance of the Katawaz basin for the formation of the Sibi

Re-entrant and the Sulaiman fold belt which is significantly larger than the fold belts of northern Pakistan.

4.4.3.4 Potential earthquake around the Sibi Re-entrant In comparison to the Kalabagh or the Tank Re-entrant, the Sibi Re-entrant experiences an anomalously high number of earthquakes (Figure 4.1). One of the main reason for the lack of earthquakes in the active fold belts of northern Pakistan is the

144 presence of thick Infra-Cambrian salt that act as the main detachment for the overlying rocks (Abir et al., 2015). Currently, there is no evidence for the presence of salt in the

Sulaiman fold belt. An important observation is that the earthquake is concentrated along the Kingri fault, the western boundary of the Sulaiman belt and the Loralai Ranges

(Figure 4.2). The fact that the central Sulaiman belt is experiencing a lower number of earthquakes is probably due to the weak detachment sliding.

Recently, InSAR techniques have been utilized to study earthquakes near the Sibi

Re-entrant (Pezzo et al., 2014; Pinel-Puyssegur et al., 2014). The 2008 Baluchistan earthquake occurred near the study area close to the Ziarat anticline. InSAR results and modelling showed that right-lateral shear was the main culprit for the source of the 2008 earthquake (Pezzo et al., 2014; Pinel-Puyssegur et al., 2014). However, there is no clear indication of a surface fault. This may be due to the diffused nature of deformation for this region as suggested by our results. According to Stein and Yeats (1989), other than surface ruptures, huge earthquakes could also occur along blind faults located under actively deforming folds. The shear zone located in western Sulaiman belt is composed of many actively deforming anticlines, such as the Dungan anticline, the Tor Khan anticline and the Miri anticline (Figure 4.5A).

145

4.5 Conclusions This work has provided clear evidence that the Sulaiman fold belt is actively deforming based on InSAR processing and mapping of active structures. This work is important to better understand how mountain fronts deform. We have interpreted the Sulaiman fold belt as a combination of ‘basin-controlled’ and ‘indenter-controlled’ curve. We suggest that the ‘indenter-controlled’ factor, related to the shape of the Katawaz basin, controls formation of the Sulaiman belt in its early stage. This is followed by southward movement (‘basin-controlled’) due to weak detachment sliding in a later stage.

Geomorphic mapping of actively deforming anticlines suggests that pure shear deformation is the main cause for the formation of the shear zone in western Sulaiman belt. The degree of strike slip partitioning is zero for the shear zone which means that deformation is distributed across the entire zone instead of concentrated along a fault.

This could explain the reason for no clear indication of surface rupture for the 2008

Ziarat earthquake. Blind faults located beneath folds could be areas of potential earthquakes in the future.

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CHAPTER 5: Summary and conclusions

This dissertation consists of two main projects to study the deformation mechanics of the fold-and-thrust belts of Pakistan. These fold belts are located along the actively deforming Main Frontal Thrust. Other than contributing to the understanding of tectonics in this region, this work also added to the earthquake studies and hydrocarbon exploration of this fascinating region. The first project is focused on the tectonics of fold-and-thrust belts of northern Pakistan, the Potwar Plateau (Chapter 2) and the Bannu Basin (Chapter

3). Even though the Potwar Plateau has been studied extensively, due to oil and gas exploration, this work is the first to fully integrate InSAR technique with seismic and well data. In comparison to the Potwar Plateau, the Bannu Basin is under-studied. This work utilized seismic and well data of the Bannu Basin to show its structural similarities with the Potwar Plateau. Salt played an important role in the deformation of both fold belts.

The second project focuses on the tectonics of the Sulaiman fold belt (Chapter 4), located to the west of the Bannu Basin. For this project, InSAR technique and satellite mapping were integrated. This work compares the mechanisms for the formation of re-entrants related to each fold belt; the Sibi Re-entrant, the Tank Re-entrant and the Kalabagh Re- entrant.

5.1 The role of salt in fold-and-thrust belts of northern Pakistan According to our InSAR results, the Potwar Plateau is still active tectonically with the uplift rate up to 15 mm/yr. However, this area is quiet with respect to earthquakes which is in contrast to the earthquake prone Sulaiman fold belt. This may be due to the presence 147 of thick salt in the Potwar Plateau, which is absent in the Sulaiman fold belt. In addition, an anomalous uplifted zone is observed from the InSAR results of the western Potwar which has been interpreted due to salt diapirism. This implies the southward flow of the salt layer.

Seismic and well data showed clear similarities in structure and stratigraphy between the

Potwar Plateau and the Bannu Basin. Three distinct zones of deformation are observed across both fold belts. They are the ‘Trailing edge’, the ‘Transitional Belt’ and the

‘Leading Edge’ which is related to the role of salt. Areas where the overburden (Trailing

Edge and Transitional Belt) is strong and thick, salt act as the main detachment layer. On the other hand, salt tectonics is prominent in the Leading Edge, located at the southern section of the fold belt.

Furthermore, an important observation is the map-view curves or re-entrants located next to each fold belt. Right lateral faults are observed bounding the Potwar Plateau (Kalabagh fault) and Bannu Basin (Pezu-Bhittani fault) to the west. The lateral faulting is mainly due to the across-strike variation in salt thickness.

5.2 Right lateral shear zone: A model for the western Sulaiman fold belt InSAR results show the complicated surface displacement of the western Sulaiman fold belt. This is further supported by the GPS velocities from Szeliga (2010). Satellite mapping using Landsat-8 and Sentinel-2 images show sets of recent left lateral faults displacing geologic structures. These faults are striking NE-SW. This has been interpreted as the southwestward movement of the Sulaiman fold belt.

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The integration of InSAR and satellite image mapping suggests that the western Sulaiman fold belt is a right lateral shear zone. This differs from the right lateral faults of the

Potwar Plateau and the Bannu Basin. In the shear zone, the deformation is distributed across the zone instead of along a fault. This is a likely explanation for the lack of a surface fault for the right lateral 2008 Ziarat anticline earthquake. An important implication is that there is a high potential for future earthquakes along these hidden faults located near the numerous anticlines of this active region.

149

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