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FACIES DISTRIBUTION, DEPOSITIONAL ENVIRONMENTS, PROVENANCE AND RESERVOIR CHARACTERS OF UPPER CRETACEOUS SUCCESSION KIRTHAR FOLD BELT PAKISTAN BY MUHAMMAD UMAR THESIS PRESENTED TO THE CENTRE OF EXCELLENCE IN MINERALOGY UNIVERSITY OF BALOCHISTAN QUETTA FOR THE DEGREE OF DOCTOR OF PHILOSOPHY NOVEMBER 2007.
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Page 1: Cretaceous of Kirthar

FACIES DISTRIBUTION, DEPOSITIONAL ENVIRONMENTS, PROVENANCE AND RESERVOIR CHARACTERS OF UPPER

CRETACEOUS SUCCESSION KIRTHAR FOLD BELT PAKISTAN

BY

MUHAMMAD UMAR

THESIS PRESENTED TO THE

CENTRE OF EXCELLENCE IN MINERALOGY

UNIVERSITY OF BALOCHISTAN QUETTA

FOR THE DEGREE OF

DOCTOR OF PHILOSOPHY

NOVEMBER 2007.

Page 2: Cretaceous of Kirthar

CERTIFICATE

This is to certify that this thesis titled “Facies Distribution, Depositional

Environments, Provenance and Reservoir Characters of Upper Cretaceous

succession Kirthar Fold Belt Pakistan” presented for the degree of Doctor of

Philosophy in the Centre of Excellence of Mineralogy, University of Balochistan,

Quetta, is based on the original research work carried out by me. The thesis has

been prepared and written by me. This research work has not been submitted for

higher degree in any other institution.

Muhammad Umar Student of Ph.D. Centre of Excellence in Mineralogy University of Balochistan Quetta

Page 3: Cretaceous of Kirthar

CERTIFICATE

This is to certify that Mr. Muhammad Umar has been engaged in Ph.D. research

in the Centre of Excellence in Mineralogy, University of Balochistan Quetta,

under the supervision of undersigned. He has fulfilled all the requirements

regarding his registration and examination for the degree of Doctor of Philosophy

in accordance with the rules and regulations of the University of Balochistan.

Dr. Abdul Salam Khan Research Supervisor

Dr. AKhtar Muhammad Kassi Co- Supervisor Director Centre of Excellence in Minerology University of Balochistan, Quetta. Dean Faculty of Physical Science University of Balochistan Quetta

Page 4: Cretaceous of Kirthar

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CONTENTS Page No.

LIST OF CONTENTS LIST OF FIGURES LIST OF TABLES LIST OF APPENDICES ACKNOWLEDGEMENT ABSTRACT CHAPTER 1- INTRODUCTION

1.1 AIMS AND OBJECTIVES OF THE STUDY 1.2 LOCATION AND ACCESSIBILITY 1.3 PREVIOUS WORK 1.4 METHODS OF STUDY

CHAPTER 2- GEOLOGIC SETTING AND STRATIGRAPHY

2.1 GEOLOGIC SETTING 2.2 STRATIGRAPHY OF THE KIRTHAR FOLD BELT

2.2.1 Ferozabad Group 2.2.1.1 Kharrari Formation 2.2.1.2 Malikhore Formation 2.2.1.3 Anjira Formation

2.2.2 Parh Group 2.2.2.1 Sembar Formation 2.2.2.2 Goru Formation 2.2.2.3 Parh Limestone

2.2.3 Mughal Kot Formation 2.2.4 Pab Formation 2.2.5 Rani Kot Group

2.2.5.1 Khadro Formation 2.2.5.2 Bara Formation 2.2.5.3 Lakhra Formation

2.2.6 Ghazij Formation 2.2.7 Kirthar Formation 2.2.8 Nari Formation 2.2.9 Gaj Formation 2.2.10 Manchar Formation 2.2.11 Dada Conglomerate

CHAPTER 3 - FACIES DESCRIPTION, INTERPRETATION AND

DISTRIBUTION 3.1 INTRODUCTION 3.2 FACIES DESCRIPTION AND INTERPRETATION

3.2.1 Trough Cross-bedded Sandstone Facies (F1) 3.2.1.1 Description

I V XIV XIV XV XVI 1 1 3 4 5 6 6 12 12 14 15 15 16 16 18 19 22 23 25 25 26 27 29 30 30 31 32 33 34 34 36 36 36

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3.2.1.2 Interpretation 3.2.2 Parallel-to Cross–laminated Sandstone Facies(F2)

3.2.2.1 Description 3.2.2.2 Interpretation

3.2.3 Massive Sandstone Facies (F3) 3.2.3.1 Description 3.2.3.2 Interpretation

3.2.4 Bioturbated sandstone Facies (F4) 3.2.4.1 Description 3.2.4.2 Interpretation

3.2.5 Hummocky Sandstone Facies (F5) 3.2.5.1 Description

3.2.5.1y Small-Scale hummocky cross-stratified sandstone Facies (F5y)

3.2.5.1y.1 Description 3.2.5.1b Sandstones with hummocky-type

bedforms (F5z) 3.2.5.1b.1 Description

3.2.5.2 Interpretation 3.2.6 Mudstones, Marls with Sandstones interbeds (F6)

3.2.6.1 Description 3.2.6.2 Interpretation

3.2.7 Laterally Continuous graded Sandstone Facies (F7)

3.2.7.1 Description 3.2.7.2 Interpretation

3.2.8 Lenticular Graded Sandstone Facies (F8) 3.2.8.1 Description 3.2.8.2 Interpretation

3.2.9 Mudstones interbedded with thin lenticular sandstones, associated with submarine fan turbidites (F9)

3.2.9.1 Description 3.2.9.2 Interpretation

3.2.10 Mudstones with occasional sandstones and marls (F10)

3.2.10.1 Description 3.2.10.2 Interpretation

3.2.11 Large scale Planner cross-bedded sandstones (F11)

3.2.11.1 Description 3.2.11.2 Interpretation

3.2.12 Chaotic Units (F12) 3.2.12.1 Description 3.2.12.2 Interpretation

36 36 36 37 38 38 38 41 41 42 42 42 42 42 44 44 44 46 46 46 47 47 49 49 49 50 50 50 50 51 51 51 52 52 52 52 52 55

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3.3 FACIES ASSOCIATIONS: THEIR NATURE AND DESCRIPTION

3.3.1 Shoreface facies Association 3.3.2 Shelfal Delta lobe Association 3.3.3 Deeper Shelf or Ramp Association 3.3.4 Submarine channels facies Association 3.3.5 Levee facies Association 3.3.6 Submarine fan lobe facies Association 3.3.7 Submarine base of slope mud lobe facies

Association 3.3.8 Submarine slope sandstones facies Association 3.3.9 Fluviodeltaic to shoreface facies association

3.4 FACIES VARIATIONS 3.4.1 Facies variations in the northern sequences 3.4.2 Facies Variations in the southern sequences

CHAPTER 4 –PETROGRAPHY, GEOCHEMISTRY AND

PROVENANCE 4.1 INTRODUCTION

4.1.1 Methods Used 4.2 SANDSTONE PETROLOGY

4.2.1 Texture 4.2.2 Characters of framework grains

4.2.2.1 Quartz 4.2.2.2 Feldspar 4.2.2.3 Lithic fragments

4.2.3 Cement/matrix 4.2.4 Modal Analysis

4.3 COMPARISON BETWEEN NORTHERN AND SOUTHERN DEPOSITIONAL SYSTEMS 4.3.1 Lower Unit 4.3.2 Upper Unit

4.4 GEOCHEMISTRY OF MUDSTONE AND SANDSTONE

4.5 DEFICIENCY OF FELDSPAR 4.6 PROVENANCE 4.7 SUMMARY

CHAPTER 5 –DIAGENESIS OF SANDSTONE

5.1 INTRODUCTION 5.2 METHODS 5.3 BURRIAL HISTORY 5.4 DIAGENESIS OF SANDSTONE

5.4.1 Compaction 5.4.2 Authigenic components 5.4.3 Microfractures

55 55 59 59 68 78 78 81 81 82 82 82 84 86 86 87 88 88 89 89 89 92 92 96 98 98 101 101 108 109 115 117 117 117 120 122 122 122 143

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5.4.4 Paragenetic sequence 5.5 RESERVOIR CHARACTERISTICS 5.6 SUMMARY

CHAPTER 6 –DEPOSITIONAL MODEL

6.1 INTRODUCTION 6.2 NORTHERN DEPOSITIONAL SYSTEM 6.3 SOUTHERN DEPOSITIONAL SYSTEM 6.3.1 Mughal Kot Turbidites 6.3.2 Pab Turbidites 6.4 SUMMARY

CHAPTER 7 –CONCLUSIONS REFERENCES

146 151 159 160 160 160 164 166 168 173 174 176

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Figure No.

LIST OF FIGURES Page No.

1.1

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

2.10

2.11

2.12

Map showing location of the study area in Kirthar Fold Belt. Map showing generalized major tectonic zones of Pakistan and location of Kirthar Fold Belt (modified after Kazmi and Snee, 1989). The map showing major tectonic features of Kirthar Fold Belt Pakistan and location of the study area (modified after Bannert et al., 1992). Geological map of the study area showing important tectonic location of measured stratigraphic sections (modified after Bakr and Jackson, 1964). Disconformable contact between the Sembar Formation (arrow) and Anjira Formation (dip direction is shown by symbols) of the Ferozabad Group section-5. Bioturbation (arrow) in shale of Sembar Formation section 16. Parallel-lamination (arrows) in limestone of Goru Formation section-9. Contacts between the Goru Formation, Parh Limestone, Mughal Kot Formation and Pab Formation section-9. Parallel-lamination (arrows) in limestone of the Parh Limestone section-16. Gradational and conformable contact between the Mughal Kot Formation and Pab Formation section-9, two persons in the circle are shown for scale. Pelecypods (arrow) on top of limestone bed of the Mughal Kot Formation section-1. Close up view of nautilus (arrow) at the top most limestone bed of the Mughal Kot Formation section-1. Far view of the contacts between Lakhra Formation of Rani Kot Group, Ghazij Formation and Kirthar Formation section- 1.

2 7 8 9

17

17

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21

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24

28

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3.1

3.2

3.3

3.4

3.5

3.6

3.7

3.8

3.9

3.10

3.11

3.12

3.13

3.14

Field Photograph of parallel lamination (arrow) in sandstone (F 2), section-7; after Khan et al., 2002). Field Photograph showing amalgamated, thick, massive (arrow) sandstone bed (F 3), section-5 (after Khan et al., 2002). Field Photograph of mottled (Bioturbated) sandstone bed (F 4), section-6 (after Khan et al., 2002). Field Photograph of small scale hummocky cross stratified (arrow) sandstone subfacies (F5a), section-9 (after Khan et al., 2002). Field Photograph of sandstone with hummock-type bed forms subfacies (F5b), section-15. Field Photograph of Mudstones, Marls (arrows) with Sandstone interbeds facies (F6), section-7 (after Khan et al., 2002). Field Photograph of normally graded (arrow) sandstone (F8), section-17. Field Photograph of large scale planar cross-bedding (arrows) in sandstone of fluviodeltaic facies (F11), section-11. Field Photograph showing sandstone dikes and sills (F 12), section-8 (after Khan et al., 2002) Field Photograph showing rounded slumped bodies (F 12), section-15 (after Khan et al., 2002). Field Photograph of cross bedded sandstone in shoreface facies association, section-1. Field Photograph showing vertical cross cut burrows within cross bedded sandstone of shoreface facies association, section-1. Sedimentary log of section-1 measured at Langerchi, grid ref. 710190, showing shoreface facies association (see Fig. 2.3 for location). Sedimentary log of section-2 measured at Karkh nala, grid ref. 596185, showing shoreface facies association (see Fig.

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3.15

3.16

3.17

3.18

3.19

3.20

3.21

3.22

3.23

3.24

2.3 for location and 3.13 for legends; modified after Khan et al., 2002). Sedimentary log of section-3 measured at Bhalok, grid ref. 584205, showing shelfal delta lobe facies association (see Fig. 2.3 for location and 3.13 for legends). Sedimentary log of section-4 measured near Khori village, grid ref. 553228, showing shelfal delta lobe facies association (see Fig. 2.3 for location and 3.13 for legends). Sedimentary log of section-5 measured at Siman Jhal, grid ref. 059163, showing shelfal delta lobe facies association (see Fig. 2.3 for location and 3.13 for legends; modified after Khan et al., 2002). Sedimentary log of section-6 measured near Pirmal village, grid ref. 984070, showing shelfal delta lobe facies association (see Fig. 2.3 for location and 3.13 for legends; modified after Khan et al., 2002). Sedimentary log of section-8 measured near Ferozabad village, grid ref. 050321, showing dominantly shelfal delta lobe facies association (see Fig. 2.3 for location and 3.13 for legends; modified after Khan et al., 2002). Sedimentary log of section-7, measured at Tibbi Jhal, grid ref. 860350, showing deeper shelf or ramp facies association (see Fig. 2.3 for location and 3.13 for legends; modified after Khan et al., 2002). Sedimentary log of section-9 measured at Chashma Murrad Khan, grid ref. 978137, showing deeper shelf or ramp facies association (see Fig. 2.3 for location and 3.13 for legends). Sedimentary log of section-10 measured near Nal village, grid ref. 541443, showing deeper shelf or ramp facies association (see Fig. 2.3 for location and 3.13 for legends). Field Photograph showing flute marks at the base of sandstone bed, section-9, current direction towards west (after Khan et al., 2002). Sedimentary log of section-12, measured at Naka Pabni, grid ref. 290545, showing thin channelized succession of Pab Turbidite System in most proximal setting (see Fig. 2.3 for location and 3.13 for legends).

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3.25

3.26

3.27

3.28

3.29

3.30

3.31

3.32

3.33

3.34

Sedimentary log of section-13 measured at Akri Dhora, grid ref. 58590, showing proximal channelized succession of Pab Turbidites (see Fig. 2.3 for location and 3.13 for legends). Sedimentary log of section-14 measured at Korara Lak, grid ref. 366611, showing submarine channels with slope-fan lobes of Pab Turbidites (see Fig. 2.3 for location and 3.13 for legends). Sedimentary log of section-15 measured at Jakker Lak grid ref. 69780, showing both Mughal Kot and Pab Turbidites (see Fig. 2.3 for location and 3.13 for legends). Sedimentary log of section-16 measured at Sandh Dhora, grid ref. 401078, showing both Mughal Kot and Pab Turbidites (see Fig. 2.3 for location and 3.13 for legends). Sedimentary log of section-17, measured at Zarro Range, grid ref. 388780, showing both Mughal Kot and Pab Turbidites (see Fig. 2.3 for location and 3.13 for legends). Sedimentary log of section-18, measured at Khude Range, grid ref. 547729, showing both Mughal Kot and Pab Turbidites (see Fig. 2.3 for location and 3.13 for legends). Field Photograph showing fluid escape structures (arrows) in sandstone, section-16. Sedimentary log of section-19 measured at Kalghalo Jhal, grid ref. 051263, showing basin floor-fan lobes of Mughal Kot Turbidites and submarine slope-fan lobes of Pab Turbidites in distal settings (see Fig. 2.3 for location and 3.13 for legends). Sedimentary log of Mughal Kot Turbidite System measured at section-20 Pundu Pash Jhal, grid ref. 101255, showing basin-floor and fan-lobe facies in most distal setting (see Fig. 2.3 for location and 3.13 for legends). Sedimentary log of section-11 measured at Bur Nai, grid ref. 336353, showing fluviodeltaic facies association, proximal component of Southern Depositional System (see Fig. 2.3 for location and 3.13 for legends).

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4.1

4.2

4.3

4.4

4.5

4.6

4.7

4.8

4.9

Photomicrographs showing texture of sandstone: A) Very coarse grained; B) Very fine to fine grained; C) Well sorted; D) Poorly sorted; E) Well rounded F) Grain supported. Photomicrographs showing varieties of framework grains: A) Undulose monocrystalline quartz; B); Polycrystalline quartz consists of two sub grains; C) Polycrystalline quartz consists of more than two sub grains; D) K-feldspar; E) Plagioclase showing albite type twinning in central part; F) Microcline showing cross hatched twinning all indicated by circles. Photomicrographs showing varieties of framework grains: A) Sedimentary fragment (siltstone); B to E); Various forms of fossil fragments; F) Chert; all shown by arrows. Photomicrographs showing: A) Volcanic lithic fragment; B) Mica grain (lower central part: arrow); C) Micritic calcite (arrow): D) Sparry calcite (arrow); E) Iron oxide/hydroxide cement (arrow); F) Well rounded quartz grain with overgrowth (arrow) showing reworking. Classification of sandstone samples of Upper Cretaceous succession (after Folk, 1974), open circles indicate lower unit of both the Northern and Southern Depositional Systems. Closed circles indicate Upper unit of Southern Depositional System. Comparison in concentration of Q-F-L and Qm-F-Lt in sandstones of Upper Cretaceous succession; A and C lower unit (in both Northern and Southern depositional Systems); and B and D upper unit (only in Southern Depositional System). SiO2-Al2O3+K2O+Na2O diagram for the sandstone (after Suttner and Dutta, 1986); open circles indicate Northern and closed circles show Southern Depositional system. The A-CN-K diagram of mudstone samples, showing high CIA values (after Nesbitt and Young, 1984); open circles indicate Northern and closed circles show Southern Depositional system. QFL plot for detrital modes of sandstone showing Craton Interior and Recycled Orogen provenance (after Dickinson et al., 1983 and Dickonson, 1985), Open circles indicate lower

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4.10

4.11

4.12

5.1

5.2

5.3

5.4

5.5

5.6

5.7

5.8

5.9

unit of both the Northern and Southern Depositional system, closed circles show upper unit of Southern Depositional System. Qm-F-Lt plot for detrital modes of sandstone showing Craton Interior and Recycled Orogen provenance (after Dickinson et al., 1983 and Dickonson, 1985), Open circles indicate lower unit of both the Northern and Southern Depositional system, closed circles show upper unit of Southern Depositional System. Qp-Lv-Ls triangle for detrital modes of upper unit of Southern Depositional System (after Dickinson et al., 1983 and Dickonson, 1985). Map showing paleocurrent directions in study area. Microphotograph of Straight contact (arrows) between neighboring framework grains. Microphotograph of concavo-convex contacts (arrows) between neighboring framework grains. Microphotograph of sutured contacts (arrow) between neighboring framework grains. Microphotograph of Quartz overgrowth (arrows). SEM image quartz overgrowth along C-axis (arrows). SEM photograph of Quartz overgrowth obstructed by early formed clay minerals (arrows). X-ray Diffractogram showing peak positions of feldspar, mixed clay layers, goethite and plagioclase (albite) in untreated, ethylene glycol treated and heated to 500 0C samples in clay separates. X-ray Diffractogram showing peak positions of illite, plagioclase (albite) in untreated, ethylene glycol treated and heated at 500 0C sample in clay separates. X-ray Diffractogram showing peak positions of chlorite and plagioclase (albite) in untreated, ethylene glycol treated and heated to 500 0C samples in clay separates.

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5.10

5.11

5.12

5.13

5.14

5.15

5.16

5.17

5.18

5.19

5.20

5.21

5.22

5.23

5.24

5.25

5.26

SEM image of albite showing plagioclase laths (arrows) within volcanic fragments. X-ray Diffractogram showing peak positions of kaolinite, goethite, dolomite, calcite and hematite in untreated, ethylene glycol treated and heated to 500 0C samples in clay separated. Photomicrograph of calcite replaced framework grain at margins (arrows). Photomicrograph of calcite replaced framework grain in core (arrows). SEM of calcite replaced framework grain in core (encircled). SEM photograph showing dolomite rim around volcanic fragment. SEM photograph showing kaolinite booklets (arrows). SEM photograph showing alteration and dissolution of feldspar grain (arrows). SEM photograph showing chlorite (arrows) in BSC mode. SEM photograph showing illite-smectite mixed layer in SEI mode. SEM photograph showing brush and hairy illite (arrows). SEM photograph showing anatase (arrows) well developed crystals. SEM photograph showing hematite (arrows). SEM photograph showing pyrite (arrows) within a shell. SEM photograph showing iron oxide/hydroxide with rosette structures (arrows). SEM photograph showing randomly oriented (arrows) iron oxide/hydroxide. SEM photograph of iron oxide laths showing little dissolution (arrows).

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5.27

5.28

5.29

5.30

5.31

5.32

5.33

5.34

5.35

6.1

6.2

6.3

6.4

6.5

6.6

SEM photograph of later stage iron oxide/ hydroxide (arrows) into early calcite cement. Photomicrograph of microfractures (arrows) in framework grains. A sketch of microfractures in framework grains perpendicular to maximum stress axis (same thin section as in Fig. 5.28). SEM photograph showing dissolution (arrows) of calcite along microfractures. SEM photograph of physically fractured feldspar grain (within ellipse). SEM photograph showing calcite penetration within early formed kaolinite booklets (arrows). SEM photograph of massive calcite cementation (arrows) which reduced porosity of sandstone. SEM photograph of dissolution (arrows) of unstable framework grains enhanced porosity of sandstone. Photomicrograph of late stage dissolution (arrows). Depositional model of Upper Cretaceous succession showing two contrasting, coeval depositional Systems. Field photograph showing synsedimentary normal fault (ellipse), section-9. Field Photograph showing basin-floor lobes of Mughal Kot Turbidites, section-20 (line across strike). Field Photograph showing laterally continuous beds (line), section-16, person encircle for scale. Field Photograph showing view of thinning upward (arrow) trend in Mughal Kot Turbidites, section-15. Field Photograph of channels (arrows) within mud rich lobes of Mughal Kot Turbidites, section-16.

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6.7

6.8

6.9

6.10

6.11

Field Photograph showing mud rich lobes and channels (C)-levee (L) in Mughal Kot Turbidites, section-16. Field Photograph showing individual channel (arrow) within mud rich lobes of Mughal Kot Turbidites, section-16. Field Photograph of thickening upward cycle (arrow) of slope fan lobes of Pab Turbidites, section-15. Field Photograph showing laterally continuous beds of submarine slope fan lobes of Pab Turbidites, section-15. Field Photograph showing view of thinning upward cycle (arrows) of Pab Turbidites, section-15, man encircled for scale.

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Table No.

List of Tables Page No.

2.1

3.1

4.1

4.2

4.3

4.4

4.5

5.1

5.2

5.3

Generalized Stratigraphic succession of the Kirthar Fold Belt showing the stratigraphic position of Upper Cretaceous succession. Location of measured sections and logged through Upper Cretaceous succession in Central and Southern Kirthar Fold Belt (see Fig. 2.3). Average of point counting results in percentages (Fig. 4.6) of measured sections in lower units of both Northern and Southern Depositional Systems. Note that Upper unit is observed only in Southern Depositional System Major element concentrations and other geochemical parameters for mudstone samples of Upper Cretaceous succession. Major element concentrations for sandstones. Average major element concentrations for mudstone and sandstone samples. Point counting results of sandstone samples in percentages (Qp-Lv-Ls diagram) of measured sections. Conditions for identification of bulk mineralogical composition of sandstones and clay separates. Showing burial depths (B. Depth), mean porosity (n), Intergranular Volume (IGV) and depositional settings of Upper Cretaceous succession. Paragenetic sequence of sandstones of Upper Cretaceous succession.

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Appendix No.

LIST OF APPENDICES

Page No.

4.1

4.2

Results of point counting of sandstone of the Upper Cretaceous succession, Central and Southern Kirthar Fold Belt. Results of point counting in percentages (for Figs. 4.5, 4.9, 4.10) of sandstone.

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ACKNOWLEDGEMENT

I am indebted to my research supervisor, Dr. Abdul Salam Khan,

Professor and Director Centre of Excellence in Mineralogy, for proposing

research project, his guidance, valuable suggestions, discussions and cooperation

during fieldwork, laboratory work and writing up of this thesis. I am grateful to

my Co-Supervisor, Prof. Dr. Akhtar Muhammad Kassi, who equally contributed

and guided me in the field, laboratory and during writing up of the thesis. The

guidance of Professor Henrik Friis is specially acknowledged during my six

month research visit to Aarhus University, Denmark. I really appreciate the

cooperation of Professor Rasmussen, Anne Thoisen, Charlotte Rasmussen, Lab

Staff for their assistance in XRD analyses. The cooperation of Lab staff of Keele

University U.K., and Geoscience Laboratory Pakistan are appreciated for making

good thin sections and polished thin sections.

The research carried out for this thesis was partly funded by Pakistan

Science Foundation under a Project awarded to Dr. Abdul Salam Khan, Professor,

Centre of Excellence in Mineralogy. I acknowledge the financial assistance of the

Pakistan Science Foundation. I acknowledge the University of Balochistan for

granting funds for six months split PhD. The cooperation of Mr. Jiand Khan

Jamaldini, Treasurer University of Balochistan and Mr. Ghulam Nabi Chairman

Geology Department, during split Ph.D. case is highly appreciated. I would like to

thank Mr. Aimal kassi Assistance Professor Centre of Excellence for guidance in

computer softwares used to prepare this dissertation. I acknowledge the

cooperation of Mr. Alam Baloch, Registrar, Balochistan University of

Engineering and Technology, Khuzdar, for providing accommodation during

fieldwork. Ali Muhammad Driver is acknowledged here for safe driving and

making food during field.

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ABSTRACT Excellent exposures of Upper Cretaceous succession (Campanian-Maastrichtian;

Mughal Kot and Pab formations) in the north-south trending Kirthar Fold Belt, Pakistan

are studied in detail. The succession is 7 m to 467 m thick in the study area and is

comprised of fine to coarse, thin to thick-bedded sandstone with subordinate mudstones

and marls. The succession was deposited on west (northwest)-facing passive margin of

the Indian Plate. Twelve facies are identified and grouped into nine facies associations,

which exhibit that they were formed in two partly coeval depositional systems: the

Northern Depositional System and Southern Depositional System.

The Northern Depositional System consists of shoreface (upper shelf), shelfal

delta lobes (middle shelf) and outer shelf ramp (lower shelf) facies association, formed on

a storm and flood dominated, low gradient clastic shelf of Mutti type shelf delta lobes.

The Southern Depositional System is characterized by fluviodeltaic deposits in the

southeast (proximal) and deep water turbidite sandstones in the northwest, formed in

channel-levee and lobes complex within deep slope and basin floor settings. In the

Southern system, the Mughal Kot Formation is comprised of basin floor lobes, channel

filled sand bodies and base of slope mud rich lobes, whereas, the Pab Formation is

comprised of submarine slope fan, channels and levee deposits. The succession was

deposited during regression phase as indicated by shallowing upward trend which is

evidenced from thickening upward cycles, grain size, bed thickness increase and shallow

marine Ranikot Group deposited over the succession. Physiography and tectonic

character of Indian Passive margin during its drifting towards north deduce its regional

distribution, vertical & lateral sequences and style of sandstone bodies both in northern

and southern depositional systems.

Sandstones composition and petrography of these two systems are also

significantly different. The sediments were supplied to the shallow marine deposits in

Northern Depositional System from thermally uplifted Indian shield in the east as

evidenced from persistent westward paleocurrent directions. Deep marine turbidite sands

were sourced by north-northwest directed density currents. Uppermost parts of the Upper

Cretaceous succession in Southern Depositional System contain an appreciable amount of

Page 20: Cretaceous of Kirthar

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volcanic fragments, which were most probably caused by Deccan Trap volcanism in

south-southeast to the studied area.

Low K2O/Al2O3 ratio in mudstones, high values of CIA (Chemical Index of

Alteration) and SiO2 – Al2O3+K2O+Na2O diagram suggest the initial feldspar deficiency

was caused by intense chemical weathering due to warm humid paleoclimatic conditions

in source area. Further reduction of feldspar was caused by long transport distance and

most effectively by diagenetic dissolution, alteration and replacement.

The sandstones have undergone intense and complex diagenetic changes due to

framework composition of sandstones, burial depth and thrusting of Bela Ophiolites. The

unstable grains like feldspar and lithic volcanic fragments were dissolved considerably

and altered to a variety of clay minerals. Compaction, authigenic cementation, dissolution

and grain fracturing are important diagenetic events identified. Calcite, quartz, clay

minerals and iron oxide are the common authigenic cements. Dissolution and alteration

of feldspar and volcanic lithic fragments and pressure solution were the main sources of

quartz cements. Mechanical compaction, authigenic cements like calcite and quartz

reduced the primary porosity of the sandstones, whereas, dissolution of feldspar and

volcanic grains have enhanced and produced secondary porosity up to 15.53% (average

2.77 to 10.61%). Chlorite coating has prevented the quartz cementation, so some

microporosity was preserved. Some microporosity in interbooklets of kaolinite is

observed.

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1

CHAPTER - 1

INTRODUCTION

1.1 AIMS AND OBJECTIVES OF THE STUDY

The major aims of this research work are to provide a detailed account of

the facies and facies associations, distribution of facies, depositional model,

petrography and provenance and diagenesis of sandstone of the Upper Cretaceous

succession (Pab and Mughal Kot formations) in central and southern Kirthar Fold

Belt Pakistan. Description, interpretation and distribution of each facies are

described in terms of processes and paleoenvironments. This study shows that the

sand-rich Upper Cretaceous succession was formed in diverse marine conditions,

ranging from shoreface to deep marine conditions. Based on facies variations,

petrography and paleocurrent data, rocks in the study area have been grouped into

the Northern and Southern Depositional systems (Fig. 1.1). The Northern

Depositional System was formed in transition from shoreface to deeper shelf

settings with westward paleoflow, whereas, the Southern Depositional System is

characterized by deep marine turbidites with north-northwest paleocurrent

directions.

Detailed petrography of sandstone has been carried out in order to

understand its composition, classification and provenance. Major element

geochemistry of the sandstone and mudstone was carried out and plotted in

different models to know their influence on sandstone composition, chemical

weathering and paleoclimatic conditions of the source area.

Diagenesis is an important parameter for the evaluation of reservoir

Page 22: Cretaceous of Kirthar

2

Page 23: Cretaceous of Kirthar

3

characters of sandstone. This thesis aims also to provide a general account of the

diagenetic composition of sandstones, effects of diagenesis on the composition

and reservoir quality of sandstones, diagenetic sequence with respect to time,

burial history and grain fracturing due to tectonism and emplacement of

ophiolites.

The Upper Cretaceous succession has attracted attention of local and

foreign geologists during recent years, because of its hydrocarbon potential in gas

and oil fields of the Lower Indus basin (Zaigham and Mallick, 2000; Hadley et

al., 2001). Pab Formation is one of the major reservoir in southwest Pakistan

(Hedley et al., 2001; Beswetherick and Bukhari 2000; Kadri, 1995; Sultan and

Gipson, 1995 and Dolan, 1990), whereas, Mughal Kot Formation is an important

source potential (Kadri, 1995) for hydrocarbons in Sulaiman and Kirthar Fold

belts. The primary reservoir targets for hydrocarbon exploration in Pakistan are

the Sui Main Limestone (Eocene) and the Pab Formation (Masstrichtian) of

Upper Cretaceous succession, e.g., in Sui, Pirkoh, Loti, Dhodak, Jandran and Savi

Ragha fields (Beswetherick and Bokhari 2000; Dolan 1990; Kadri 1995; Sultan

and Gipson 1995; Hedley et al. 2001; Fitzsimmons et al., 2005). The present

study is an effort to enhance the knowledge of the depositional architecture,

composition, provenance and reservoir characteristics of sediments of the Upper

Cretaceous succession for future hydrocarbon exploration.

1.2 LOCATION AND ACCESSIBILITY

The study area comprises parts of Khuzdar, Lasbella and Dadu districts in

central and southern Kirthar Fold Belt, southern Pakistan (Fig. 1.1). Due to arid –

Page 24: Cretaceous of Kirthar

4

semi arid climatic conditions the excellent exposures provide a good opportunity

to measure sections at outcrop scale. The succession is exposed in 350 km long

and 225 km wide. Twenty continuous stratigraphic sections having well defined

with upper and lower boundaries have been measured. The sections studied are

located on toposheets, 35I/1, 35 I/6, 35 I/9, 35 J/5, 35J/14, 35J/15, 35 K/15, 35

M/2, 35N/3 and 35N/16 of the Survey of Pakistan. The area is accessible partly by

metalled and partly by unmetalled roads and lies between 250 16/ E and 270 47/ E,

latitudes and 660 08/ N and 670 54/ N longitudes.

1.3 PREVIOUS WORK

The Hunting Survey Corporation (1960) during their reconnaissance

survey provided a very general description of rock types and interpreted them as

fluviatile and marine/deltaic. Sultan and Gipson (1995) assigned the sediments of

Pab Formation in the eastern Sulaiman Fold Belt to dominantly upper shoreface

environments, with subordinate fluvial, lagoonal, estuarine and lower shoreface

facies in the eastern Sulaiman Fold Belt, some 500 km to the northeast of the

study area. They also carried out brief petrography and diagenesis of the

sandstone of Pab Formation in the eastern Sulaiman Fold Belt. Recently Eschard

et al., (2003 and 2004), Smewing et al., (2002), , Khan et al., (2002), Umar (2002)

and Hedley et al., (2001) have studied sequence stratigraphy, tectonics and

sedimentology in some selected parts of the Kirthar Fold Belt. A preliminary

account of petrography of few sections in Kirthar and Sulaiman Fold belts was

carried out by Kassi et al., (1991).

Page 25: Cretaceous of Kirthar

5

1.4 METHODS OF STUDY

A total of three months field work was carried out in the study area for

reconnaissance and detailed study of the Upper Cretaceous succession. Twenty

eight localities were studied during reconnaissance trips. Twenty well-exposed

stratigraphic sections were selected and studied in detail. Extensive sampling was

carried out and rock (sandstone, mudstone and marl) samples, representing

various facies, were collected for laboratory analyses. Description of the primary

and authigenic mineralogy of the sandstone is based on study of 65 thin sections.

Scanning Electron Microscope (SEM), X-ray diffraction (XRD) and X-ray

Florescence (XRF) techniques were used for geochemical analyses, diagenesis

and identification of clay minerals. Detailed methodology used in this study is

described in relevant chapters.

Page 26: Cretaceous of Kirthar

6

CHAPTER – 2

GEOLOGIC SETTING AND STRATIGRAPHY

2.1 GEOLOGIC SETTING

The study area is located (Figs. 2.1, 2.2 and 2.3) within the central and

southern Kirthar Fold Belt (Bender and Raza 1995, Bennert et al. 1992, Jadoon

1991) south of the Quetta Syntaxis (Wadia 1953, Powell 1979, Sarwar & DeJong

1979). Upper Cretaceous succession (Pab and Mughal Kot formations) has

achieved great thickness (White, 1981) in Kirthar Fold Belt (Figs. 2.1, 2.2 and

2.3) within West Pakistan Fold Belt (Bannert et al., 1992). The succession was

deposited on northwestern passive margin of the Indian Plate, which has been

subdivided into the Sulaiman and Kirther blocks based on their structural style

observed on satellite images (Bender and Raza, 1995; Bennert et al., 1992). The

West Pakistan Fold Belt (comprising the Sulaiman and Kirther Fold belts), Bela-

Zhob-Waziristan Ophiolite Belt, Markran-Khojak-Pishin Flysch belt and Indus

Basin are important tectono-stratigraphic belts of the region. The West Pakistan

Fold Belt and the associated syntaxial belts (Powell 1979, Jadoon 1991, Bender

and Raza 1995), including the Kirthar Fold Belt, comprises the sedimentary cover

of the Indian Plate, which deformed during the collision process when the Indian

Plate collided with the Eurasian Plate. It consists of continuous range of fold-

thrust belts (Bender and Raza, 1995). The Kirthar Fold Belt forms the southern N-

S trending part of the West Pakistan Fold Belt (Bannert et al., 1992), which is

located adjacent to the present day western strike slip margin of the Indian Plate

(Figs. 2.2 and 2.3). The belt is 350 kilometers long and generally north–south

Page 27: Cretaceous of Kirthar

7

Page 28: Cretaceous of Kirthar

8

K E Y

Fig. 2.2 The map showing major tectonic features of Kirthar Fold Belt, and ocation of the study area (Modified Bannert et al., 1992)

: Pakistan l after .

Page 29: Cretaceous of Kirthar

9

670660

O

NL

UL

BL

KHI

Uthal

Bela

Karachi

Sehwan

28o

27o

26o

66o

68o

67o

25o

ARABIAN SEA

50 Km0

Fig.2.3:.Geological Map of the study area showing important tectonic features andlocation of measured stratigraphic sections (modified after Bakr and Jackson, 1964).

12

14

Location of stratigraphic sections measuredCities and Towns

Northern Depositional System

Southern Depositional System

1

Page 30: Cretaceous of Kirthar

10

trending (Kazmi and Jan, 1997). Based on tectonic style and stratigraphic

variations, this belt may be divided into a number of smaller structural units.

Khuzdar Knot is a syntaxial bend of complex nature, where fold axes are

zigzag, arcuate and convex northward (Niamatullah, 1998). It is a deformed zone

which formed under the influence of sinistral northeast–southwest trending

Diwani fault, 45 kilometers northwest of Khuzdar (Bannert et al. 1992). It is about

50 kilometers wide and 70 kilometers long structural complex, where anticlinal

axes trend in various directions from northeast to northwest. Folds are large,

broad and dome shaped with a northwest to northeast axial trends, a feature

attributed to the left-lateral Ornach–Nal fault.

Ornach-Nal Fault marks the northwestern boundary of the Indian Plate in

the region. It separates the Kirthar Fold Belt to the east from the Makran Flysch

zone to the west (Niamatullah, 1998). It offsets the youngest (Neogene) sediments

of the Makran Flysch zone against the Khuzdar Block (Bannert et al., 1992). The

fault can be traced from the shores of Arabian Sea for 250 kilometers to the north

towards Khuzdar. It is a sinistral fault as indicated by the structural style of the

Miocene sediments.

Kirthar Thrust Sheet (KTS) is an east dipping thrust zone. At its northern

extremity, it becomes vertical and then dips westward with a slight swing to the

east (HSC, 1960). It develops within the east-dipping Eocene Kirthar Formation.

Traces of Kirthar Thrust Sheet recede eastward into an apparent imbricate zone

within the Kirthar Formation.

Page 31: Cretaceous of Kirthar

11

Khude Range is situated southeast of Khuzdar Knot. It is 200 kilometers

long and 30 kilometers wide, north-south oriented tectonic belt, consisting of

Upper Cretaceous succession. It is separated by Pab Fault and Kirthar Thrust

Sheet on its western and eastern margins respectively (Fig. 2.2). Mor Range is

made up of Jurassic–Cretaceous Ferozabad and Parh groups, which are followed

by ophiolite nappe. Pab and Zarro Ranges are N-S and NW-SE oriented ranges

which are mainly composed of Upper Cretaceous succession. Laki Range

comprises north-south oriented ridges and consists of Cretaceous–Pleistocene

rock units.

The Bela Ophiolite complex is a southern segment of the N-S trending

Bela-Zhob-Waziristan Ophiolite Belt, which extends from the coast of Arabian

Sea to the Khuzdar Knot, covering a 320 kilometers long stretch. The Bela

Ophiolite complex is bounded by the Pab and Ornach–Nal faults to east and west,

respectively. The Bela-Waziristan Ophiolite Belt shows fragments of oceanic

crust obducted on to the Indian Plate during the Late Cretaceous just before the

Paleocene (Asrarullah et al. 1979, Gansser 1979, Allemann 1979, Abbas and

Ahmad 1979).

The Makran-Khojak-Pishin Flysch Zone is an accretionary belt situated to

the south and east of the Eurasian Plate. In the Makran area, an E-W trending belt

of flysch sediments makes a very wide accretionary zone, which formed in

response to the collision and subduction of the Arabian Plate beneath the Afghan

Block of the Eurasian Plate (Jacob and Quittmeyer 1979, Powell 1979, Farhoudi

and Kerig 1977). The Khojak-Pishin flysch segment (Katawaz in Afghanistan)

Page 32: Cretaceous of Kirthar

12

comprises the deltaic and flysch succession (Qayyum et al. 1996) associated with

the Makran Belt, however, compressed and stretched in response to the collision

of Indian Plate along its northwestern margin with the Eurasian Plate and the

succession dragged anticlockwise (northwards) along the Ornach-Nal and the

Chaman fault zones of the Chaman Transform Boundary (Wittekindt & Weippert

1973, Tapponnier et al. 1981, Lawrance and Yeats 1979, Stocklin 1977). The

Makran arc-trench system developed over a long period, possibly throughout

Cenozoic (Jacob and Quittmeyer 1979).

2.2 STRATIGRAPHY OF THE KIRTHAR FOLD BELT

The study area is composed of sedimentary rocks which range in age from

Triassic to Holocene (Fig. 2.3; Table 2.1). Detailed stratigraphy of the area is

behind the scope of the present study. Lithological characters of various rock

units were noted briefly, however, the Upper Cretaceous succession was studied

in detail. Early researchers have used various stratigraphic nomenclatures for the

rock succession, but in this thesis nomenclature of the Hunting Survey

Corporation (1960), Shah (1977), Fatmi et al. (1986, 1990), Anwar et al. (1991)

and Smewing et al., (2002), pertaining to different localities of the study area has

been used. Details of the various groups and formations of the study area are as

under:

2.2.1 Ferozabad Group

The earlier names of the Zidi Formation and Windar Group of the Hunting

Survey Corporation (1960) was later on replaced by Fatmi et al. (1986, 1990) as

Ferozabad Group, which was approved by Stratigraphic Committee of Pakistan

Page 33: Cretaceous of Kirthar

13

Table 2.1: Generalized stratigraphic succession of the Kirthar Fold Belt showing the stratigraphic position of Upper Cretaceous succession. Age Group Formation Lithology Holocene Recent-Subrecent Mixture of clay, sand and gravel

Unconformity Pleistocene Dada Formation Boulders and pebble

conglomerates with subordinate coarse grained sandstone

Pliocene Manchar Formation

Sandstone and shale interbedded with subordinate conglomerate

Unconformity Miocene Gaj Formation Shale, sandstone with

subordinate limestone and conglomerate

Oligocene Nari Formation Sandstone interbedded with shale Kirthar Formation Fossilifereous limestone

interbedded with shale and marl Eocene Ghazij Formation Dominantly shale with minor

sandstone Lakhra Formation Intraclastic limestone and shale Bara Formation Sandstone and shale

Paleocene

Rani Kot Group

Khadro Formation Sandstone, shale and marl Pab Formation Sandstone intercalated with

marl and mudstone Maastrichtian-Campanian

Upper Cretaceous succession Mughal Kot

Formation Marl, arenaceous limestone, mudstone and sandstone

Parh Limestone Biomicritc limestone Goru Formation Micritic limestone with shale,

siltstone and sandstone

Early – Late Cretaceous

Parh Group

Sembar Formation Shale, siltstone and marl Disconformity

Anjira Formation Limestone interbedded with shale and marl

Malikhore Formation

Oolitic limestone with subordinate shale and marl

Early-Late Jurassic

Ferozabad Group

Kharrari Formation

Limestone, shale, marl and minor sandstone

Base not exposed

Page 34: Cretaceous of Kirthar

14

(Farhat, 1988). In the Sulaiman Fold Belt (Bender & Raza, 1995; Kazmi & Jan

1997) Shirinab Formation and Chiltan Limestone are the lateral equivalents of the

Ferozabad Group. The name is derived from Ferozabad Village (lat.27o 48/ N;

long. 66o 30/ E), 13 kilometers west of Khuzdar.

The Ferozabad Group consists of cyclic succession of pisolitic and oolitic

limestone, shale and marl. Shale is dominant in lower part. It is olive grey,

greenish grey and green in color. Base of the Ferozabad Group is not exposed,

whereas, upper contact with the Sembar Formation of the Parh Group is sharp and

disconformable (Fatmi et al., 1986; 1990; Anwar et al., 1991). The Ferozabad

Group has been subdivided by Fatmi (1990) into the following three formations:

2.2.1.1 Kharrari Formation

The name Kharrari Formation was proposed by Fatmi et al. (1990) for the

mixed carbonate facies of Windar Group and Zidi Formation of the Hunting

Survey Corporation (1960), after Kharrari Nai, Mor Range (lat. 25o 55/ N; long.

66o 47/ E) in Windar area. The Stratigraphic Committee of Pakistan (Farhat,

1988) has approved the name Kharrari Formation.

The formation is composed of limestone, siltstone, shale and sandstone.

The limestone is brownish gray, thin bedded and biomicritic. The shale and

siltstone are dark gray, greenish gray, brownish gray, arenaceous and fissile.

Sandstone is light gray, purple, brownish gray, fine to coarse grained and gritty.

The base of the formation is not exposed, whereas the upper contact is transitional

and conformable with Malikhore Formation (Fatmi et al. 1990; Anwar et al.,

1991). The formation is not fossilifereous, so on the basis of the stratigraphic

Page 35: Cretaceous of Kirthar

15

position, an Early Jurassic age has been assigned (Fatmi et al. 1990 and Anwar et

al., 1991).

2.2.1.2 Malikhore Formation

The name Malikhore Formation was introduced by Fatmi et al. (1990) for

the massive, thick bedded, carbonate unit within the middle part of the Windar

Group (and Zidi Formation) of Hunting Survey Corporation (1960). The

Stratigraphic Committee of Pakistan (Farhat, 1988) has approved the name

Malikhore Formation. It is derived from the Malikhore Village (lat. 27o 50/ N;

long. 66o 29/ E), 27 kilometers west-northwest of Khuzdar.

The formation is composed of brownish gray, thick bedded, biomicritic,

oolitic, bioturbated and hard limestone with subordinate dark gray and greenish

gray calcareous shale and marl. The formation conformably underlies the Anjira

Formation (Anwar et al., 1991). Gastropods, bivalves (Pecten, Weyla, Gervillea),

crinoids (Isocrinus), brachiopods (Spiriferina sp.) and corals have been reported

from the formation (Fatmi et al. 1990; Anwar et al., 1991), on the basis of which

Early Jurassic age has been assigned to the formation.

2.2.1.3 Anjira Formation

The uppermost unit of the Ferozabad Group has been named as Anjira

Formation (Williams, 1959). Its type section is 12 kilometers east of the Anjira

Village (lat. 28o 20/ N; long. 66o 28/E) of Kalat.

The formation comprises thin to thick-bedded limestone with minor shale

and marl. Limestone is dark gray and fossilifereous. Shale and marl are cream,

greenish gray, soft and nodular. Its lower contact with Malikhore Formation is

Page 36: Cretaceous of Kirthar

16

transitional, whereas upper contact with the Sembar Formation of the Parh Group

is disconformable (Fig. 2.4) and is marked by presence of laterite (Anwar et al.,

1991). Gastropods (Polyplectus sp., Tachylytoceras sp., nanolytoceras),

brachiopods (Spiriferina, Terebratula, Trigonia) and corals are present within the

formation, on the basis of which its age is considered to be Toarcian to Middle

Bajocian (Early-Late Cretaceous) (Fatmi et al., 1990; Anwar et al., 1991).

2.2.2 Parh Group

The name Parh Group of the Hunting Survey Corporation (1960) is named

after Parh Range (lat. 26o 54/ 45// N; 67o 05/ 45// E). The group has been further

subdivided into the following three formations:

2.2.2.1 Sembar Formation

Williams (1959) introduced the name Sembar Formation for the rock

succession exposed two kilometers southeast of the Sembar Pass (lat. 290 55/ 05//

N: long. 68034/ 48// E) in the Marri-Bugti hills.

The formation mainly consists of shale with interbeds of siltstone, fine

sandstone and arenaceous limestone. Shale is greenish grey, green, olive grey,

maroon, purple in lower part and grades upward to dark grey and black. It is

highly cleaved, fissile and bioturbated (Fig. 2.5). The light grey shale

gradationally changes to black shale upward. Shale is calcareous, soft, flaky

bioturbated and laminated. Siltstone is olive grey, dark greenish grey and greyish

olive green, parallel and cross-laminated. Sandstone and arenaceous limestone

beds are parallel and cross-laminated showing Bouma Tbc sequences with their

tops horizontally bioturbated. Flute marks at their base show northwest

Page 37: Cretaceous of Kirthar

17

Fig. 2.5: Bioturbation (arrows) in shale of Sembar Formation, section-16.

Fig. 2.4: Disconformable contact between the Sebmar Formation (arrow) and Anjira Formation (dip direction is shown by symbols) of the Ferozabad Group, section-5.

Page 38: Cretaceous of Kirthar

18

paleocurrent direction. The sandstone and arenaceous limestone beds are present

in packets as well as individually. Packets are 1-10 meters thick, whereas,

individual beds are 1-70 centimeters in thickness. Thickness and frequency of the

sandstone and arenaceous limestone beds increases upward.

Upper contact of the formation is conformable with the Goru Formation.

Various belemnites species such as Belemnopsis, and Hibolithus and small size

Phylloceras sp., Pochianites sp., Olcostephanus sp. and Neohoploceras sp. have

been reported (Fatmi et al., 1986, Anwar et al., 1991) from the formation. Age of

the Sembar Formation is considered to be Late Jurassic to Early Cretaceous

(Fatmi et al., 1990).

2.2.2.2 Goru Formation

The name Goru Formation was proposed by Williams (1959) for the rocks

exposed near Goru village (lat. 27o 50/ N; long. 66o 54/ E) along the Nar River in

southern Kirthar Fold Belt. The formation consists of shale interbedded with marl,

limestone and siltstone. Shale is interbedded with marl and limestone in regular

alternations. Shale and siltstone are dark greenish grey, brownish grey, dark

brown, dark maroon and greenish grey. Proportion of shale decreases upward.

Shale is calcareous, soft, flaky, pelagic and fissile. Marl is medium brown,

brownish grey and greyish red purple. Limestone is greenish red purple, light

olive grey, greenish orange, pinkish grey and medium grey. The limestone is

micritic, porcellaneous and breaks with conchoidal fracture. Frequency and

thickness of limestone increase upward. Horizontal burrows at top surface of

limestone beds are present. Some limestone horizons of the formation posseses

Page 39: Cretaceous of Kirthar

19

the characters of turbidites such as grading, parallel (Fig. 2.6) and cross–

lamination. Thin bedded limestones seem like distal turbidites. Massive and

bioturbated limestone are also present in the formation. Chert nodules and bands

are common in the limestone beds.

Upper contact of the Goru Formation with the Parh Limestone is

transitional and conformable (Fig. 2.7). The formation contains globotruncana

and Belemnites (Fritz & Khan, 1967) and has been assigned Early-Middle

Cretaceous age (Shah, 1977).

2.2.2.3 Parh Limestone

The name Parh Limestone was introduced by Williams (1959). Its type

section is in the upper reaches of Gaj River (lat. 26o 54/ 45// N; 67o 05/ 45// E) in

Parh Range.

It comprises white, cream, bluish white, medium light grey, medium grey,

greenish grey and dark grey limestone, which is biomicritic, porcellaneous and

breaks with conchoidal fracture. Some of the limestone beds are parallel

laminated (Fig. 2.8). Limestone is micritic and contains pelagic foraminifers.

Commonly the limestone beds are thin but some beds are up to 50 centimeters

thick. The limestone in lower part of the formation is highly bioturbated with

chondrites type bioturbation. The limestone gradually changes to marl and

calcareous shale upward. Upper contact of the Parh Limestone with the Mughal

Kot Formation is conformable and transitional (Fig. 2.9). The limestone contains

micro foraminifera of the globotruncana sp. (Gigon, 1962; Fatmi et al., 1986).

Page 40: Cretaceous of Kirthar

20

Fig. 2.7: Contacts between the Goru Formation, Parh Limestone, Mughal Kot Formation and Pab Formation, section-9.

Fig. 2.6: Parallel-lamination (arrows) in limestone of Goru Formation, section-9.

Page 41: Cretaceous of Kirthar

21

Fig. 2.9: Gradational and conformable contact between the Mughal Kot and Pab formations, section-9, two persons in circle are shown for scale.

Fig. 2.8 Parallel-lamination (arrows) in limestone of the Parh Limestone, section-16.

Page 42: Cretaceous of Kirthar

22

The formation has been assigned Barremian to Campanian age by Kazmi (1955 &

979) in the Kach-Ziarat area of the Sulaiman Fold Belt and Senonian by

illiams (1959).

.2.3 Mughal Kot Formation

Williams (1959) proposed the name Mughal Kot Formation for the rocks

xposed between 2 to 5 kilometers west of Mughal Kot Fort along Zhob–Dera

mail Khan road (lat. 31o 26/ 52// N; long. 70o 02/ 58// E).

The formation within the study area comprises marl, mudstone and

ccasional limestone. Marl is white (N9), bluish white (5B 9/1), light brownish

rey (5YR 6/1), greyish orange (10Y 7/4), greenish grey (5GY 4/1) and dark

ellowish orange (10YR 6/6). Marl is massive, parallel and cross-laminated. The

eds of marl are lenticular, thin bedded, ranging from 5 to 50 centimeters in

ickness. The frequency and thickness of marl beds decreases upward and

radually changes to mudstone completely. Marl is highly cleaved, homogeneous

nd partly laminated. Upper 30-35 meters part of the formation is composed of

in to thick bedded arenaceous limestone, which is graded, parallel-cross and

ummocky cross-laminated. Occasional sandstone beds are also present in the

rmation. Mudstone is olive grey (5Y 4/1), dark greenish grey (5GY 4/1), olive

Mughal Kot Formation is conformable and

transitional with the Pab Formation (Fig. 2.9). About 50 meters thick transitional

1

W

2

e

Is

o

g

y

b

th

g

a

th

h

fo

green (5GY 3/2), calcareous and flaky. Limestone is brownish grey (5YR 4/1),

light brownish grey (5YR 6/1), medium light grey (N6), medium grey (N5) and

biomicritic.

Upper contact of the

Page 43: Cretaceous of Kirthar

23

zone be

pelecypods (Fig. 2.11)

and bi

and pale yellowish brown (10YR 6/2). It is thin bedded, finely

d r

tween the underlying Parh Limestone and Mughal Kot Formation can be

seen in places. Vertical, horizontal and inclined burrows of up to 6 centimeters in

diameter are present. Brachiopods, Nautiliods (Fig. 2.10),

valves are present in the formation. On the basis of various types of

foraminifera a Campanian to Maastrichtian age has been assigned to the Mughal

Kot Formation (Williams, 1959; Fatmi, 1977).

2.2.4 Pab Formation

The name Pab Sandstone was introduced by Vredenburg (1907) and is

derived from the Pab Range in Kirthar Fold Belt. Williams (1959) designated its

type locality as a section along the route to Somalji Trail west of Wirhab Nai (lat.

25o 31/ 12// N; long. 67o 00/ 19// E). Later the name Pab Formation was introduced

as it comprises various lithologies like sandstone, mudstone and marl.

The sandstone is light brownish grey (5YR 6/1), very light grey (N8),

medium grey (N5), moderate yellowish brown (10YR 5/4) and pale red purple

(5PR 6/2). It is very fine to very coarse-grained and in places pebbly. Marl is

brownish grey (5YR 4/1), greyish orange (10YR 7/4), moderate yellowish brown

(10YR 5/4)

laminated, massive and cleave . Mudstone is mottled ed, massive, fissile,

bioturbated and thin bedded. The Pab Formation was depicted within Moro

Formation and Ranikot Group on the Hunting Survey Corporation (1960) maps,

where (mostly in northern Kirthar Fold Belt) it is present as thin member and

difficult to map.

Page 44: Cretaceous of Kirthar

24

Fig. 2.10: Pelecypod (arrow) on top of limestone bed of the Mughal Kot Formation, section-1.

Fig. 2.11: Close up view of Nautilus (arrow) at the top most limestone bed of the Mughal Kot Formation, section-1.

Page 45: Cretaceous of Kirthar

25

Its upp ntact is conformable and sharp with the Khadro Formation of Ranikot

Group. On t

Pab Form

& Raza, 199

er co

he basis of faunal record a Maastrichtian age has been assigned to the

ation (Vredenburg, 1909; HSC, 1960; Shah, 1977; Shuaib, 1982; Bender

5; Kazmi and Jan, 1997).

2.2.5 Ranikot Group

Various names for Paleocene rock units were used by Hunting Survey

Corporation (1960), such as Thar Formation, Wad Limestone, Jakker Group,

Karkh Group, Khude Limestone, Rattaro Formation and Bad Kachu Formation in

Kirthar old Belt. These local names were complied in to the Ranikot Group

(Khadr , Bara and Lakhra formations) by Shah (1977) and are used in this thesis.

The Ranikot Group of Blandford (1876, 1879) and Vredenberg (1909b) is named

after the Ranikot Fortress in Laki Range (lat. 25o 53/ N: long. 67o 56/ E).

he group comprises olive, yellowish brown sandstone and shale

interbedded with limestone. Basaltic lava flows are also a minor component of the

group. The upper contact of the group with Ghazij Formation and lower contact

with Pab Formation are conformable. The group contains fossils such as

Globogerina pseudobulloides, Venericardia vredenburgi, assilina ranikoti,

Ostraea talpur, N. thalicus. A Paleocene age has been assigned to the group

(Shah, 1977). The group comprises three formations which are described below:

2.2.5.1 hadro Formation

The name Khadro Formation was introduced by Williams (1959). Khadro nala

at. 26o 07/ 06// N: long. 67o 53/ 12// E) near Bara Nai in Laki Range is the type

ction of the formation.

F

o

T

K

(l

se

Page 46: Cretaceous of Kirthar

26

The formation consists of shale, marl and sandstone with occasional

limestone. Sandstone is yellowish brown, olive, grey, greenish grey and green in

color. It is fine to coarse grained, graded, parallel and cross-laminated and

contains groove casts at the base. At places it is also massive, load casted and

clasts. Shale is pale green, olive, greenish grey, grey,

browni

d 1878,

Nagapp

.

cross-laminated. Shale is bluish grey, greenish grey

contains rip-up mud

sh grey, reddish brown and pale bluish grey. Marl is cream, purple, pale

green, maroon and dark green in color. It is silty and parallel laminated.

Upper contact of the formation with Bara Formation is conformable.

Common fauna found in the formation include Venericardia vredenburgi,

leionucula rakhiensis, corbula harpa, Tibba rakhiensis, Globogerina

pseudobulloides, G. triloculinoides, Cardieta beaumonti, Paracypris rectoventra,

H. micromma and Howecythereis multispinosa (Eames 1952, Blandfor

a 1959 and Sohn 1959). The formation has been given an Early Paleocene

(Danian) age based on the above mentioned fauna.

2.2.5.2 Bara Formation

Bara Formation (Shah, 1977) is well exposed in the type section located at

Bara Nai (lat. 26o 07/ 06// N: long. 67o 53/ 12// E) in Laki Range.

The formation is composed of sandstone, shale and minor volcanic rocks.

Varicolored sandstone is fine to coarse grained, massive and thin to thick bedded

In places it is calcareous and

and green in color. It is bioturbated and mottled at places. Upper contact of the

formation is conformable with Lakhra Formation. Oyester shells and Ostraea

Page 47: Cretaceous of Kirthar

27

talpur

rownish

gray, i

edded and cross-bedded.

sharp and conformable with the Ghazij Formation (Fig.

2.12).

880, Vredenburg

1909b,

(Vredenburg, 1928) are found in the formation, who assigned Middle

Paleocene (Thanetian) age to the formation.

2.2.5.3 Lakhra Formation

Lakhra Formation of (Shah, 1977) is exposed at Lakhra anticline ((lat. 26o

11/ N: long. 67o 53/ E), at Laki Range.

The formation is composed of limestone, marl, shale with minor

proportion of sandstone. Limestone is light gray, olive gray and dark b

ntraclastic, arenaceous, parallel-laminated, cross-laminated, convolute

laminated and hummocky cross-stratified. Chert nodules and bands of secondary

origin are also present within the intraclastic limestone. Nodules and bands do not

show any relationship with the clasts. Ghosts of the unaltered limestone may be

seen within the chert nodules and bands. Marl is light gray, cream, maroon and

red, whereas shale is red, maroon, creamy and light gray. Sandstone is grey to

chocolate color, fine to coarse grained, thin to thick b

Its upper contact is

The formation is highly fossilifereous and contains foraminifera, corals,

molluscs and echinoids (Davies 1927, Nuttall 1931, Duncan 1

1928 and Duncan & Sladen 1882). Important foraminfers of the formation

are M. stampi, Discocyclina ranikotensis, Miscellanea miscella, N. globulus,

Assilina ranikoti, Lochartiahaimei, Lepidocyclina punjanensis and N. thalicus

(HCS, 1960). Based on fossil assemblage Late Paleocene age is assigned to the

formation (Iqbal, 1972).

Page 48: Cretaceous of Kirthar

28

Fig. 2.12: Far view of the contacts between the Lakhra Formation of Rani KotGroup, Ghazij Formation and Kirthar Formation, section-1.

Page 49: Cretaceous of Kirthar

29

2.2.6 G

cks exposed at Ghazij Rud, a stream to the southeast of Spintangi Railway

ation (lat. 29o 57/ N; long. 68o 05/ E). It is equivalent of the Gidar Dhor Group

SC, 1960), Ghazij Group (Oldhalm, 1890; Shah, 1990; Bendar & Raza, 1995;

azmi & Jan, 1997) and Laki Formation (Hunting Survey Corporation, 1960;

oetling, 1903; Shah, 1977).

The formation is composed of shale, sandstone, conglomerate and coal

ams. Shale is grey and greenish yellow, pale greenish grey, brown and olive

rey, calcareous, flaky, ferruginous and gypsifereous. Sandstones are greenish

rey, yellowish brown, pale brown, light olive brown, fine to very coarse grained,

arallel-laminated, and cross-laminated and possess sole marks. Some other

ndstones are white, cream and calcareous. Conglomerate is composed of

agments of limestone, sandstone and chert of older formations. It is moderately

rted, well rounded to subrounded and clast supported.

Its upper contact with the Kirthar Formation is conformable (Fig. 2.12).

oraminifera, gastropods, bivalves, algae, echinoids, vertebrate bones and plant

mains have been reported from the formation (Eames, 1952; HSC, 1960; Latif,

964; Iqbal, 1969; Kakar, 1995; Kakar & Kassi, 1997 and Ginsberg et al., 1999).

he fossil assemblage mostly include: assilina granulose, A. postulosa,

chartiahunti, flosculina globosa, fasciolites oblonga, gisortia murchisoni,

elates perversus and amblypygus subrotundus and echinolampus nummulitica

hazij Formation

The name Ghazij Formation was proposed by Williams (1959) for the

ro

st

(H

K

N

se

g

g

p

sa

fr

so

F

re

1

T

lo

v

Page 50: Cretaceous of Kirthar

30

(HSC 1960; Iqbal 1973; Nuttall 1925; Noetling 1905; Davies 1926; Haque 1962).

ggests an Early Eocene age for the Ghazij Formation.

2.2.7 K

brown, orange, yellow, grey, gypsifereous and

calcare

/ 10// E) in the Kirthar

Range.

This assemblage clearly su

irthar Formation

The name Kirthar Formation was proposed by Blandford (1876) and

derived from the Kirthar Range (lat. 26o 56/ 10// N; 67o 09/ 06// E).

The formation is composed of fossilifereous limestone, interbedded with

subordinate shale and marl. Limestone is white, cream, light grey, massive and

thick bedded. Shale is olive

ous. Marl is light brown, gray, thinly laminated and in places massive.

The formation conformably and transitionally underlies the Nari

Formation. It is rich in foraminifers, gastropods, bivalves and echinoids (Oldhalm,

1890; Vredenburg, 1906 & 1909; Pilgrim, 1940; Eames, 1952; HSC, 1960), on

the basis of which a Middle Eocene to Early Oligocene age has been assigned.

2.2.8 Nari Formation

The name Nari Formation was introduced by Williams (1959) for the

rocks exposed at Nari River (lat. 26o 56/ 12// N; long. 67o 10

The formation is composed of sandstone rhythmically interbedded with

shale. Sandstone is pale brown, moderate brown, greenish brown and greyish

orange. Sandstone is generally fine to coarse grained and thin bedded. Shale is

brown, yellow, green, reddish brown, purple, flaky and arenaceous. Within the

lower part minor amount of conglomerate is found. Pebbles of the conglomerates

are composed of limestone and chert. Minor proportion of maroon to reddish

Page 51: Cretaceous of Kirthar

31

brown marl is also present in the formation. Shale is highly bioturbated containing

horizontal burrows. The formation is characterized by grading, parallel-

n and sole marks. It is generally a flysch succession

showin

able with the

Gaj Fo

2.2.9 G

ainly consists of shale, sandstone with subordinate

limesto

grey, yellowish brown and ferruginous. It is very coarse grained to

pebbly

lamination, cross-laminatio

g the characters of turbidites.

Upper contact of the formation is transitional and conform

rmation. The formation contains foraminifers, algae, corals, molluscs and

echinoids (Khan 1968; Iqbal 1969), on the basis of which an Oligocene to Early

Miocene (Rupelian to Early Aquitanian) age has assigned (Latif, 1964; Khan,

1968).

aj Formation

The term Gaj series of Blandford (1876) was revised as Gaj Formation by

the Hunting Survey Corporation (1960) for the rocks exposed near Gaj River (lat.

26o 51/ 40// N and long. 67o 17/ 18// E).

The formation m

ne and conglomerate. Shale is purple, dark grey, pale brown and greenish

grey in color. It is soft, partly gypsifereous and sandy. Sandstone is dark brown,

greenish

, hard, very thick bedded and cross-bedded. Limestone is brown, pale

yellow and arenaceous at places. In the southern part of the study area, the

formation dominantly consists of yellowish brown sandstone and cream and

pinkish white argillaceous limestone.

The formation is overlain unconformably by the Manchar Formation. It is

rich in fossils and contains varieties of gastropods, pelecypods, bryozoans, corals,

Page 52: Cretaceous of Kirthar

32

echinoderms and foraminifers (Duncan and Sladen 1885; Nuttall 1926;

Vredenberg 1928; HSC 1960 and Khan 1968). Some important fossils of the

formation are: Lepidocyclina marginata, L Blanfordi, Miogypsina globulina, M.

cushmani, Ostrea vestita, Glycimeris sindensis, Caleloplearus frobesi, Breynia

carinat

landford (1876) proposed the name Manchar Formation for rocks

ake (lat. 26o 23/ N and long. 67o 38/ E).

Sandstone is grey, greenish grey, coarse

grained

e basis of which a Pliocene age is given to

the form

a and Clypeaster depressus. The age of the formation is Early Miocene

(Late Aquitanian to Burdigalian) up to Middle Miocene (Vredenberg 1906b;

Pascoe 1963; Khan 1968).

2.2.10 Manchar Formation

B

exposed near Manchar L

The formation is composed of interbedded sandstone, shale with

subordinate conglomerate. Shale dominates the lower part, whereas, the sandstone

is rich in upper part of the formation.

to pebbly, soft and cross-bedded. Shale is soft, yellow, brown and brick

colored. Conglomerate contains pebbles of sandstone and arenaceous and

fossilifereous limestone fragments, which resembles with the Nari, Gaj, and

Kirthar formations. Pebbles of the conglomerates are subangular to subrounded.

The formation transitionally underlies the Dada Conglomerate and unconformably

overlies various older rock units such as the Gaj Formation, Laki Formation,

Kirthar Formation and Pab Formation. Mammal bones and silicified wood fossils

are reported from the formation, on th

ation (Pilgrim 1908b).

Page 53: Cretaceous of Kirthar

33

2.2.11 Dada Conglomerate

The name Dada Conglomerate was introduced by the HSC (1960) for the

rocks exposed at Dada River, south of the Spintagi Railway Station (lat. 29o 56/ N

and long. 68o 06/ E).

The formation comprises boulder and pebble conglomerates interbedded

with coarse grained sandstone. Pebbles of conglomerates were derived from

limestone and marl of the old rock units exposed. The corglomerate is thick

mposed mostly of calcareous material with sandy

matrix.

rey and brown,

coarse

bedded, poorly sorted and co

Pebbles and cobbles are subangular to well rounded. Maximum clast size

reaches up to 0.5 meters in diameter. Sandstone is greenish g

granied, pebbly and cross-bedded. Lower contact of the Dada

Conglomerate is conformable with Manchar Formation and unconformable with

the Gaj Formation. There are no fossils in the formation and based on

stratigraphic position a Pleistocene age is given to the formation by the HSC

(1960).

Page 54: Cretaceous of Kirthar

34

CHAPTER-3

FACIES DESCRIPTION, INTERPRETATION AND DISTRIBUTION

3.1 INTRODUCTION

The Upper Cretaceous Succession of the Kirthar Fold Belt that ranges in

age from Early Campanian to Maastrichtian includes Mughal Kot and Pab

formations. The excellent exposures provided a good opportunity to study the

rocks in detail, describing lithology, grain properties, bed thickness, lateral

continuity of beds, sedimentary and biogenic structures, nature of contacts and

paleocurrent directions. Twenty continuous stratigraphic sections (Table 3.1)

have been measured in a 350 km long and 280 km wide study area, (Figs.2.1 and

2.3). Some part of this chapter includes (also partly modified and improved) our

published paper (Khan et al., 2002).

Twelve facies are recognized. These are: Facies 1 (Trough Cross-Bedded

Sandstones), Facies 2 (Parallel to Cross-laminated sandstones), Facies 3 (Massive

Sandstones), Facies 4 (Burrowed Sandstones), Facies 5 (Hummocky Sandstones),

Facies 6 (Mudstones, Marls with Sandstone interbeds), Facies 7 (Laterally

Continuous Graded Sandstones), Facies 8 (Lenticular Graded Sandstones) Facies

9 (Mudstones interbedded with thin lenticular sandstones, associated with

submarine fan turbidites), Facies 10 (Mudstone with occasional sandstones and

marls), Facies 11 (Large scale planar cross bedded sandstones) and facies 12

(Chaotic Units).

Page 55: Cretaceous of Kirthar

35

Table 3.1: Location of measured sections logged through the Upper Cretaceous succession in Central and Southern Kirthar Fold Belt (see Fig. 2.3). No. of section

Name Latitude Longitude

1 Langerchi section 270 41/ 670 10/

2 Karkh Nala section 270 41/ 670 05/

3 Bhalok section 270 39/ 670 03/

4 Khori section 270 44/ 670 01/

5 Siman Jhal section 270 37/ 660 31/

6 Pirmal village section 270 35/ 660 31/

7 Tibbi Jhal section 270 03/ 660 22/

8 Ferozabad section 270 45/ 660 31/

9 Chashma Murrad Khan section

270 38/ 660 28/

10 Nal section 270 47/ 660 08/

11 Bur Nai section 260 04/ 670 54/

12 Naka Pabni section 250 16/ 660 56/

13 Akri Dhora section 250 19/ 660 58/

14 Korara Lak section 250 20/ 660 58/

15 Jakker Lak section 250 31/ 670 00/

16 Sandh Dhora section 250 46/ 670 00/

17 Zarro Range section 260 24/ 660 55/

18 Khude Range section 260 26/ 670 04/

19 Kalghalo Jhal section 260 38/ 660 46/

20 Pundu Pash Jhal section

260 41/ 660 44/

Page 56: Cretaceous of Kirthar

36

3.2 FACIES DESCRIPTION AND INTERPRETATION

3.2.1 Trough cross-bedded sandstone Facies (F1)

3.2.1.1 Description

Trough cross bedded sandstone facies occur only in eastern part of the

Northern Depositional System (see Chapter-6; sections 1 and 2). This facies is

characterized by fine to coarse grained (pebbly) trough cross-bedded, thin to thick

bedded sandstones. Lower part of the sections is thin bedded and fine grained

sandstones with trough cross sets, which grades into low angle cross lamination in

some places. Very coarse grained (pebbly), thick beds of sandstones are common

in upper part. They are moderately bioturbated and have large trough sets. Lower

surfaces of these beds are undulatory, irregular with moderate scouring into

underlying beds of sandstone.

3.2.1.2 Interpretation

Deposition of trough cross bedded sandstone facies was caused by high-

energy conditions by river induced flows or storm rip currents. Such currents

develop virtually channeled paths through the shoreline area to deliver sediments

offshore and are well established on many modern wave or storm dominated

shorefaces (Komar, 1976).

3.2.2 Parallel- to cross- laminated Sandstone Facies (F2)

3.2.2.1 Description

The facies is the most common in the eastern part of the Northern

Depositional System, but is locally present in the middle part of the Northern

Depositional System (sections 1, 2, 6 and 7). The sandstone of this facies is fine to

Page 57: Cretaceous of Kirthar

37

medium grained, thin bedded showing parallel lamination (Fig. 3.1) and very low

angle wedge-shaped cross-bedding with rare bioturbation (Khan et al., 2002).

Fine grained sandstones of this facies meets gradationally with lower F3 (massive

sandstones) in the western part. On contrary the sandstones of the facies are

medium to coarse grained with sharp erosive bases with underlying beds in

eastern part. The facies is gradually change to low angle cross laminated upward.

3.2.2.2 Interpretation

Similar horizontal to gently undulatory laminated sandstones have been

attributed to upper flow regime deposition under oscillatory, unidirectional and/

or combined-flow currents (Swift et al., 1983; Arnott and Southard, 1990). There

was no wave action involved in the formation of this facies as evidenced from the

lack of wave ripples and other wave related features in the sandstones of Upper

Cretaceous succession. The parallel laminated sandstone intervals are

gradationally associated with the massive sandstones, which were deposited under

the influence of strong traction flows following rapid dumping of sediment to

form the massive interval (Khan et al., 2002). Combined flows are probably

responsible for most plane-bed lamination on the storm dominated shoreface

(Swift and Niedoroda, 1985). It is interpreted that the parallel to small scale low

angle cross laminated sandstone was deposited under unidirectional/combined-

flows on the shoreface to lower delta slope. This interpretation is also based on

the association of parallel laminated sandstone facies with F5 (hummocky

sandstone facies), which indicate storm activities.

Page 58: Cretaceous of Kirthar

38

3.2.3 Massive Sandstone Facies (F3)

3.2.3.1 Description

The sandstones of this facies is medium to coarse grained, medium to

thick bedded and commonly amalgamated (Fig. 3.2) with sole marks (grooves and

flutes) at the base and is more common in the Northern Depositional System.

Some beds show trails and horizontal burrows at their bases, indicating they

existed as depressions in the underlying marl/mudstone before the overlying

sandstone was emplaced. Tops of few beds show slight normal grading with

indistinct parallel to small scale cross and slumped laminations. Few beds show

Current ripples are found on upper surfaces of some beds but others beds are

capped by hummocky bedforms (Khan et al., 2002). Beds are very thick I some

cases as their thickness range 50 cm to 8 m thick, they are commonly

amalgamated, lenticular and rarely parallel-sided on outcrops. Some of the beds

consist of angular clasts of marl up to 8 cm. This facies transitionally meets

upward with bioturbated sandstones (F4)/ hummocky sandstones (F5).

3.2.3.2 Interpretation

The deposition of sandstones of this facies was caused by freezing of

concentrated traction currents or by rapid dumping from high-density gravity

currents in deeper shelf setting (Khan et al., 2002). Presence of abundant sole

marks such as, groove and a few flute marks at the base of the massive sandstones

(F3)

Page 59: Cretaceous of Kirthar

39

Fig. 3.1: Field photograph showing parallel lamination (arrow) in sandstone (F 2 section-7 (after Khan et al 2002).

Fig. 3.2: Field Photograph of amalgamated, thick, massive (arrow) sandstone bed (F 3), section-5 (Khan et al., 2002).

Page 60: Cretaceous of Kirthar

40

indicate the high erosive power of strong unidirectional flows. The prominent

westward orientations of these flows show that the paleocurrent directions were

consistently towards west which were mainly controlled by paleoslope. The

narrow spread of the paleocurrents further confirms the operation of slope

controlled density flows (Khan et al., 2002).

Accumulation of massive sandstones in the deep marine realm is believed

to result from any of the following four depositional mechanisms (Stow et al.,

1999; Stow and Johansson, 2000): (1) freezing of a sandy debris flow, (2)

collapse fall-out from the turbulent stage of a high density turbidity current, (3)

continuous aggradation beneath a sustained high density turbidity flow or (4)

continuous traction beneath a sustained high density flow. Thus turbidity currents

are the most plausible offshore transport mechanism for thick massive sands

(Allen, 1982; Walker, 1984). Can sandstones of this type be deposited from such

currents in deeper shelf areas? Recently Mutti et al. (1996; 2000) have interpreted

sand-rich shelfal sandstone lobes in the Tertiary of the central Pyrenees as the

result of river-fed hyperpycnal flows. The characteristics of the massive

sandstones of the Upper Cretaceous succession and their intimate association with

thick burrowed sandstones (F4) suggest that deposition took place by gradual

aggradation of sediment which was continuously supplied to maintain the quasi-

steady state of the flow (Kneller and Branney, 1995). As deposition continues at

the base of the flow, it is continuously replenished with grains from above (Khan

et al., 2002). In the basal part of the flow the temporal variations and fluctuations

in the concentration of sediments were caused the subtle grading as well as

Page 61: Cretaceous of Kirthar

41

indistinct lamination in some massive beds. These variations permit traction to

intervene and prevented settling. The deposition of Facies 6 (mudstone, marl with

sandstones interbeds) was occurred during period of slow sedimentation as shown

by the presence of feeding trails and horizontal burrows on the top of few

sandstone beds. The rare rippled surfaces are due to current reworking when the

cascading of the grains ceased, followed by hemipelagic settling of the carbonate

mud. Similar massive sandstones from ancient successions have been reported

from a variety of depositional settings. These include: (1) Slope apron gully-lobe

systems (Surlyk, 1987), (2) Delta-fed turbidite ramp systems (Heller and

Dickinson, 1985) and, (3) Sand-rich submarine fan systems (Armstrong et al.,

1987; Busby-Spera, 1985; Cardman and Young, 1981; Link and Nelson, 1980).

In the absence of slope facies and component facies of the submarine fan system,

it is considered that the massive sandstones of the Upper Cretaceous succession

represent shelfal delta lobe (deeper shelf) depositional settings.

3.2.4 Bioturbated Sandstone Facies (F4)

3.2.4.1 Description

Bioturbated sandstones commonly occur in middle (western) part of

Northern Depositional System (section 8, 9 and 10). The sandstone of this facies

is fine to medium grained, medium to thick bedded and intensely bioturbated and

mottled (Fig. 3.3). Beds are commonly laterally continuous, regular and bearing

same thickness. Skolithos/Ophiomorpha are vertical and inclined burrows (upto

20 cm long and 5 cm diameter), penetrated downward from the upper surface, and

contain hard, brown meniscoid sandy walls filled with pure sandstone. Intense

Page 62: Cretaceous of Kirthar

42

bioturbation and mottling destroyed most primary sedimentary structures at

palces.

3.2.4.2 Interpretation

Bioturbated sandstones are believed to have been deposited in both inner

shoreface (sections 1 and 2) and middle to deeper shelf settings below the fair

weather wave base by slow and continuous suspension fall-out from storm-

generated suspension clouds, enabling infaunal reworking to keep pace with

sediment accumulation (Khan et al., 2002). Continuous wave and strong

reworking were responsible for the supply of sediments from the upper shoreface.

The alternation of bioturbated sandstones with parallel laminated sandstones (F2)

and trough cross bedded sandstones (F1) in the most proximal eastern sections

may be the result of alternate periods of intermittent slow deposition during calm

conditions and by high energy events (Khan et al., 2002). The organisms were

able to rework sediments severely and destroying the primary sedimentary

structures during slow sedimentation periods.

3.2.5 Hummocky Sandstone Facies (F5)

3.2.5.1 Description

On the basis of internal features F5 can be subdivided into two subfacies

(F5y and F5z):

3.2.5.1y Small scale hummocky cross stratified sandstone Facies (F5y)

3.2.5.1y.1 Description

This subfacies very commonly occurs on the upper surfaces of thicker

massive sandstones but in some cases is embedded in pelagic marl (Fig. 3.4).

Page 63: Cretaceous of Kirthar

43

Fig. 3.4: Field Photograph of small scale hummocky cross stratified (arrow) sandstone subfacies, (F 5y), section-9 (after Khan et al., 2002).

Fig. 3.3: Field Photograph of mottled (Burrowed; arrows) sandstone bed (F 4), section-6 (after Khan et al., 2002).

Page 64: Cretaceous of Kirthar

44

The sandstone of this facies is fine to medium grained and thin to medium

bedded. A package of 1 to 5 amalgamated beds showing low angle to hummocky

cross stratification with internal truncation/laminations. Asymmetric hummocks

show bedform movement to the offshore (westward; 2700) direction (Fig. 3.4).

3.2.5.1z Sandstones with hummock-type bedforms (5z)

3.2.5.1z.1 Description

The sandstones of this subfacies indicate hummocky bedform surfaces

without any internal cross stratification (Fig. 3.5). Such beds commonly occur in

the stratigraphically higher parts of sandstones of shelfal delta lobe in outcrops of

Northern Depositional System of the central Kirthar Fold Belt and cap many of

the thickening-upwards cycles in the turbidite sequences located Southern

Depositional System (see in Chapter-6). This facies is characterized by fine to

medium grained sandstones which is thin to thick bedded (20cm to 1m thick),

amalgamated, with or rare bioturbation. The sandstones are low angle cross

laminated. Beds are very lenticular and pinch and swell over very short lateral

distances. Few beds show large-scale current ripples, which are generally

asymmetrical and there are no intervening mudstones.

3.2.5.2 Interpretation

Sandstone beds containing hummocky cross stratification have been

widely recorded and are considered to represent shallow marine storm deposits

(Harms et al., 1975; Dott and Bourgeois, 1982; Swift et al., 1983; Brenchley,

1985). However, the reliability of this structure as an unequivocal criterion for

such an environment is now less certain because of its highly variable form and

Page 65: Cretaceous of Kirthar

45

possibly different mode of formation (Cheel and Leckie, 1993). Hummocky cross

stratified type structures have also been reported from deep marine turbidites

(Prave and Duke, 1990) and shelfal deltaic sandstone lobes (Mutti et al., 1996;

2000), and these have been attributed to formation by slope controlled density

currents and flood related hyperpycnal flows respectively.

Based on the external morphology and internal cross strata of the

hummocky cross stratification, it is proposed that subfacies 5y was deposited

from rapid suspension under waning energy conditions and influenced by frequent

high-energy storm episodes but occasionally by oscillatory waves with

superimposed unidirectional flows (Kreisa, 1981; Craft and Bridge, 1987; Duke,

1990). The amalgamation of hummocky sandstone beds exhibits the frequent

high-energy episodes, restricting the settling of fine-grained sediments.

Alternatively, intervening fine-grained sediments may have been removed by

scouring and erosion by the following high-energy storm waves (Dott and

Bourgeois, 1982). The capping of massive sandstones (F3) and bioturbated

sandstones (F4) by hummocky bedforms (F5b), probably were resulted from

shoaling and progradation, producing increased ambient energy conditions (Khan

et al., 2002). Subfacies 5z (Hummocky type bedforms), that are associated with

both the massive sandstones of the shelf delta lobes and the graded sandstones of

submarine fan lobes, are believed to be the result of high energy, high density

purely unidirectional flows (Prave and Duke, 1990).

Page 66: Cretaceous of Kirthar

46

3.2.6 Mudstones, Marls with Sandstones interbeds (F6)

3.2.6.1 Description

This facies is best developed in the distal part of the Northern Depositional

System (section 7). It is dominantly composed of mudstone, marl with

subordinate very fine grained, thin-bedded (mostly upto 5cm thick) sandstone

interbeds (Fig. 3.6). Bioturbation is moderate to severe in mudstone and due to

variations and animal activity the intensity of bioturbation varies vertically.

Specific identification of trace fossils is difficult and beyond the scope of this

study, but those recognizable are chondrites and planolites (Khan et al., 2002).

Body fossils are absent and are not found during extensive field work. Thin beds

are very fine grained showing parallel and cross lamination, whereas, thicker beds

are fine grained, graded with highly erosive bases. Graded beds are parallel and

cross-laminated and in places convolute laminated. Flutes, grooves, prod marks

and load casts can be seen on the bases of these sandstone beds.

3.2.6.2 Interpretation

Mudstone, marl and fine sandstones in rhythmic alternation are quite

common in marine environments, either in storm influenced shelves or deep-

water turbidites. The common occurrence of trace fossils and bioturbation in the

mudstones, intercalation of pelagic marl and presence of hummocky bedforms in

sandstones in the stratigraphically upper part of the section suggest a relatively

shallow environment with well oxygenated bottom water conditions, supporting

the infauna responsible for homogenizing the sediments (Khan et al., 2002).

Fluctuations in the rates of sedimentation were caused different zones of strong

Page 67: Cretaceous of Kirthar

47

and weak bioturbation. Waning currents, storm-generated suspension currents and

low-density turbidity currents were responsible for the deposition of fine, thinner

beds of sandstones. Because these sandstone beds are associated with shelf facies,

so can easily be distinguished from deep marine turbidites. Similar normally

graded, thin sandstone beds from the Mesozoic sequences of Canada and the

Southwest USA have been interpreted as storm generated deposits, formed in

middle to outer shelf settings (Hamblin and Walker, 1979; Walker, 1984; Swift,

1987). Based on the present data, absolute water depth of deposition is difficult to

determine but comparison with the modern facies analogs (Nelson, 1982)

suggests that facies 6 was deposited below fair-weather storm-base at water

depths greater than 50 m, probably in deeper shelf or ramp setting (Khan et al.,

2002).

3.2.7 Laterally Continuous Graded Sandstone Facies (F7)

3.2.7.1 Description

Laterally Continuous Graded Sandstone facies is more common in

southern and partly in northwestern parts of the study area and is characterized by

normal grading with or without Bouma sequence, containing flutes and grooves at

the base. Sandstones occur in packets with a high sand percentage (upto 95%),

that commonly form thickening upward cycles (upto 10m thick) or interbedded

with marl and mudstone. Bed thickness ranges between 10 cm and 1 m, which are

laterally continuous. Thin beds are well graded, parallel and cross-laminated

showing Tabc (most common) Bouma sequences, whereas, thicker beds show

subtle grading and ripple cross lamination at the top in some cases. Thick

Page 68: Cretaceous of Kirthar

48

Fig. 3.5: Field Photograph of sandstone with hummock-type bed forms (arrows) subfacies, (F 5z), section-15.

Fig. 3.6: Field Photograph of mudstones, marls (arrows) and Sandstone interbed facies (F 6), section-7 (after Khan et al., 2002).

Page 69: Cretaceous of Kirthar

49

sandstones display hummocky bedforms on upper surfaces of some sections (14

and 15) in the upper part. Amalgamation is common but fine sediments

(mudstones or marls) can also be interbedded with thin bedded sandstones.

3.2.7.2 Interpretation

The sandstones of this facies exhibit deposition from high density turbidity

currents as suggested by the characteristics of the thick beds. Sheet flows were

prograding progressively towards the basin as indicated by upward thickening

cycles. The scour structures at the base of thick sandstone beds represent high

erosive power of thick and successive flows. The thin beds interbedded with

mudstones and/or marls, were deposited from more evolved, low density turbidity

currents.

3.2.8 Lenticular Graded Sandstone Facies (F8)

3.2.8.1 Description

This facies also occurs in the southern part of the study area. It is

composed of fine to coarse grained, medium to thick bedded sandstones.

Individual beds of the sandstones range from 15 cm to 4 m, but generally are less

than 1m in thickness. Most of the beds are well graded (Fig. 3.7) showing Bouma

Ta and Tb divisions. Sandstone beds are lenticular which pinch out laterally

within small distances with erosive base truncating underlying sediments.

Amalgamation is very common in this facies however; isolated lenticular beds are

also present. Sandstone beds contain mud-clasts at different levels. Some of the

beds are bioturbated. Both thickening-upward and thinning-upward cycles are

Page 70: Cretaceous of Kirthar

50

present. The flute marks at the base of the beds show north-northwest

paleocurrent trend.

3.2.8.2 Interpretation

This facies was deposited from dense, sand-rich, high energy turbidity

flows followed by another flows without allowing the suspended sediments of the

previous flows and the flows were erosive enough to remove the tops of the

preceding deposits. The lenticular nature of the beds indicates deposition in

channel setting.

3.2.9 Mudstones interbedded with thin lenticular sandstones, associated with

submarine fan turbidites (F9)

3.2.9.1 Description

This facies occurs in the southern part of the study area. It is composed of

mudstones interbedded with thin beds (5 to 25 cm in thickness) of fine grained

sandstones. The mudstone is grey, dark grey, laminated, fissile and at places

highly bioturbated. The sandstone is lenticular, parallel and cross laminated

showing Bouma Tbc, Tbcd, Tbcde and Tcde divisions.

3.2.9.2 Interpretation

The mudstones of this facies which show no bioturbation were deposited

by low density turbidity currents and those which are highly bioturbated were

formed by hemipelagic processes. The very fine grained, thin bedded (average

5cm thick) sandstones showing Bouma Tbc, Tbcd, Tcd divisions were formed by

low energy turbidity currents.

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51

3.2.10 Mudstone with occasional sandstones and marls (F10)

3.2.10.1 Description

This facies is present in the southern part of the study area. It is composed

of mudstones with occasional thin marl and fine grained sandstone beds. This

facies overlies both facies 7 (laterally continuous graded sandstones, section-16)

and facies 8 (lenticular graded sandstones, section-15). It is 150m thick at Sandh

Dhora (section-16) and 90 m thick at Jakker Lak (section-15). The mudstone is

green, greenish, red, brown, cleaved, unconsolidated to semi consolidated, fissile

and bioturbated. The marl is creamy and maroon, thin bedded and bioturbated.

Beds of the marls vary from 1cm to 5cm in thickness. The sandstone is fine

grained, thin bedded (1-10cm), well graded, parallel and cross-laminated showing

Bouma Tcde divisions.

3.2.10.2 Interpretation

This facies was deposited from low density and low velocity turbidity

currents. In a turbidite system, deposition of coarse sediments may leave a

residual suspension of fine grained sediments. These residual flows may range

from low density to high density and can move down slope as discrete turbidity

flows (Ricci Lucchi and Valmori, 1980). The interbedded fine sandstones

showing features of turbidites indicate that this facies was deposited from

turbidity currents. The interbedded marls and red clay were deposited from

pelagic and hemipelagic settling. This indicates abandonment of turbidity flows

allowing deposition of background sediment in form of marl and red clays.

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52

3.2.11 Large scale planar cross bedded sandstones (F11)

3.2.11.1 Description

This facies is present in the southeastern part of the study area (section-

11). It is composed of coarse to pebbly, thick to very thick (1.2 to 3 m),

amalgamated sandstones with large scale planar cross-bedding (Fig. 3.8). Some of

the sandstone beds are highly lenticular showing channel morphology. The

presence of hummocky cross stratification at places is a clear indication of some

storm influence.

3.2.11.2 Interpretation

Highly amalgamated, large scale planar cross bedded nature of this facies

suggests deposition from strong and high energy flows. The deposition took place

in fluvial deltaic setting.

3.2.12 Chaotic Units (F12)

3.2.12.1 Description

This facies is more common in the southern part (sections-15 and 16) of

the study area; however it is also present in the northern part (sections-6 and 8) of

the study area. Packages of this facies range in thickness from less than 1 to 14 m

and comprise strata characterized by internally contorted beds that include both

sandstones and interbedded mudstones and marls. The sandstones are thin to thick

(40cm to 7 m), medium to coarse grained. In some cases, the chaotic units show

minor synsedimentary folds, faults, intrusion of sandstone dykes, sills (Fig. 3.9)

and irregular rounded sandstone balls (Fig. 3.10).

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Fig. 3.7: Field Photograph of normally graded (arrow) sandstone (F8), section-17.

Fig.3.8: Field Photograph of large scale planar cross-bedding (arrows) in sandston of fluviodeltaic facies (F11), section-11.

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54

Fig. 3.9: Field Photograph showing sandstone dikes and sills (arrows) (F 12), section-(after Khan et al., 2002).

Fig. 3.10: Field Photograph showing rounded slumped bodies (arrows) (F 12), section-15.

Page 75: Cretaceous of Kirthar

55

3.2.12.2 Interpretation

Various processes (both sedimentary and structural) can cause slumping

(Lewis, 1971; Clari and Ghibadudo, 1979). Important triggering mechanisms for

slumping related to sedimentary processes include: deposition on steep slope and

rapid deposition on slopes and liquification of the under lying porous material.

The abundance chaotic units in the southern part of the study area indicate rapid

deposition on a relatively steep slope. Some of the localized chaotic units seem to

have been cause by slumping of the sediment along the channel margins. The

chaotic units associated with sandstone dykes and sills indicate post-depositional

remobilization and liquefaction of the thick massive sandstones.

3.3 FACIES ASSOCIATIONS: THEIR NATURE AND DISTRIBUTION

Nine facies associations can be defined in the Upper Cretaceous

succession of the study area. These are:

3.3.1 Shoreface facies association

Shoreface facies association occurs in the eastern part of the Northern

Depositional System (partly in proximal settings of Southern Depositional

System) and is characterized by trough cross bedded sandstone facies (F1),

parallel and low angle cross laminated sandstones (F2), hummocky sandstones

(F5) and bioturbated sandstone facies (F3) (Fig. 3.11, 3.12, 3.13 and 3.14). The

above facies and their combination give an ample evidence of consistent to

episodic strong tractional energy conditions, which are common in the shoreface

to inner shelf setting (khan et al., 2002). This facies association represents by the

most proximal environmental setting (section 1 and 2) of the Northern

Page 76: Cretaceous of Kirthar

56

Fig. 3.11: Field Photograph showing cross bedded (arrows) sandstone in shorefac facies association, section-1.

Fig. 3.12: Field Photograph showing vertical cross cut burrows (arrows) within cross bedded sandstone of shoreface facies association, section-1.

Page 77: Cretaceous of Kirthar

57

216 m

121 m

0 m

S 1-19

F 3.11 &3.12

Page 78: Cretaceous of Kirthar

58

sh m c vc

S 2-2

S 2-3

S 2-4 & 2-5

S 2-6

S 2-7

S 2-8

S 2-9

S 2-10

S 2-1

Page 79: Cretaceous of Kirthar

59

depositional System.

3.3.2 Shelfal delta lobe facies association

Shelfal delta lobe facies association is common in middle part of the

Northern Depositional System of the study area (Figs. 3.15, 3.16, 3.17, 3.18 and

3.19). This facies association is characterized dominantly by thick massive

sandstone facies (F3), with bioturbated sandstone facies (F4), hummocky

sandstones (F5), mudstones, marls with sandstones interbeds (F6) and chaotic

units (F12). Deposition of these facies occurred below the fair weather wave base

and some below storm wave base in the outer shelf, probably fed by a major,

sand-rich delta (Khan et al., 2002). This facies association displays many of the

features of the “shelfal delta lobes” and “flood generated delta-front sandstone

lobes” of Mutti et al., (1996; 2000). For instance, the association is dominated by

thick packets (upto 25 m thick) of sharp-based and regular sandstone beds with

massive and hummocky cross bedded alternating with bioturbated and

fossilifereous mudstones and marls. Paleoflows dominantly toward west

(dominantly 2700) as measured from flutes and grooves at the base of the

sandstone beds which indicate that the sediments were transported from land

located in the east.

3.3.3 Deeper shelf or ramp facies association

Deeper shelf facies association occurs in the distal part of the central

Kirthar Fold Belt, in Northern Depositional Systems. It consists of massive

sandstone facies (F3), mudstones, marls with sandstones interbeds (F6),

bioturbated sandstone facies (F4) with subordinate sandstones with hummock-

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60

Fig. 3.15: Sedimentological log of section-3 measured at Bhalok, grid ref 584205-35M/2, showing shelfal delta lobe faies association (see Fig. 2.3 for location and 3.13 for legends).

S 10-5

S 10-4

S 10-3

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Fig. 3.16: Sedimentary log of section -4 measured near Khori village, grid ref. 553228, showing shelfal delta lobe facies association (see Fig. 2.3 for location and 3.13 for legends).

82 m

S 11-1

0 m

24 m48 m

72 m

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141 m94 m47 m

0 m

S 5-1

F 3.2

S 5-3

S 5-2

S 5-4

S 5-5

S 5-6

S 5-7

S 5-8

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63

132 m

S 6-2

S 6-3

S 6-4

S 6-8

S 6-5

S 6-6

S 6-7

44 m 88 m

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64

Fig. 3.19: Sedimentary log of section-8 measured near Ferozabad village, grid ref 050321, showing shelfal delta lobe association (see Fig. 2.3 for location and 3.13 for legends; modified from Khan et al., 2002))

119 m

S 8-1

F 3.9

S 8-2

S 8-3

S 8-4

S 8-5

S 8-6

S 8-7

S 8-8

S 8-9

S 8-10

S 8-11

42 m 85 m

0 m

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65

Fig 3.20: Sedimentary log of section-7 measured at Tibbi Jhal, grid ref. 860350, showing deeper shelf or ramp facies association, (see Fig. 2.3 for location and 3.13 for legends; modified from Khan et al., 2002).

225 mRanikotGroup56 m 112 m 168 m

S 7-1

S 7-2, 3

S 7-4

F 3.6

S 7-5

S 7-6

S 7-7

S 7-8

S 7-9, 10

F 3.1

S 7-11

S 7-12

S 7-13

0 m

Page 86: Cretaceous of Kirthar

66

S 9-1

F 3.4

S 9-2

F 3.23

0 m

75 m 150 m 225 m Ranikot Group

Page 87: Cretaceous of Kirthar

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245 m

S 10-1

S 10-2

S 10-3

97 m 194 m

Ranikot Group

Page 88: Cretaceous of Kirthar

68

- type bedforms (F5z) (Figs. 3.20, 3.21 and 3.22) (Khan et al., 2002). Sandstones

with hummock type bedforms are common in the upper parts and usually caps

thick massive sandstones. This facies association was deposited below storm

wave base in a deeper shelf (ramp environment) and the massive sandstones are

distal equivalents of the shelf-lobe units, probably supplied by flooding events

from nearby delta-front (Khan et al., 2002). Sole marks such as grooves and flutes

at the base of different beds of the massive sandstones show westward

paleocurrent direction (2550; Fig. 3.23), and also slightly northwest in places.

3.3.4 Submarine channels facies association

This facies association is common in the southern most part of the study

area and consists of facies 8 (lenticular graded sandstones) and facies 12 (chaotic

units) (Fig. 3.24, 3.25, 3.26, 3.27, 3.28, 3.29 and 3.30). It is characterized by

coarse to pebbly, thick to very thick sandstone beds. Sandstone beds are highly

lenticular with erosive bases displaying channel morphology. Most of the

sandstone beds pinch out laterally at outcrop scale. Sole marks like grooves, flutes

and load casts are common at the base of the sandstone beds showing NNW

paleoflow. Sandstone is graded, showing Bouma Ta and Tab divisions.

Sandstone beds are thick and amalgamated at channel axis and become thinner

and separated by intervening mudstone at channel margins. Intraclasts of mud are

quite common in these sandstones. Fluid escape structures (Fig. 3.31) are also

common in these sandstones indicating rapid deposition. In places the sandstone

beds are highly distorted and slumped which indicate collapse of the channel

margin (Fig. 3.10). All this indicates deposition in submarine channels by high

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69

Fig. 3.23: Field Photograph showing flute marks (arrows) at the base of sandston bed, section-9, current direction toward west (after Khan et al., 2002).

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70

Fig. 3.24: Sedimentary log of section-12 measured at Naka Pabni, grid ref. 290545, showing thin channelized succession of Pab Turbidites in most proximal setting (see Fig. 2.3 for location and 3.13 for legends).

7 m

7 m

Ranikot Group

Page 91: Cretaceous of Kirthar

71

S 13-3 S 13-2

Ranikot Group

Page 92: Cretaceous of Kirthar

72

Ranikot Group

S 14-4

S 14-5

S 14-10

S 14-9

S 14-8

S 14-7

S 14-6

Page 93: Cretaceous of Kirthar

73

Ranikot Group

F 3.5

S 15-1-3

S 15-5

S 15-6

S 15-7

S 15-4

F 3.10

F 6.10

F 6.5

F 6.11

F 6.9

Page 94: Cretaceous of Kirthar

74

S 16-1

F 6

.4

S 16-2,3

F 6.8

RanikotGroup

S 16-17

S 16-16

S 16-15

S 16-14

S 16-13

S 16-12

F 6.6S 16-11

S 16-8S 16-9

S 16-10

S 16-7

S 16-5

F 3.31

S 16-6

S 16-4

F 6.7

0 m

Page 95: Cretaceous of Kirthar

75

Ranikot Group

S 17-5

F 3.7

S 17-4

S 17-3

S 17-2

S 17-1

0 m

62 m 124 m 186 m 248 m

Page 96: Cretaceous of Kirthar

76

203 mRanikot Group

0 m

48 m 96 m 144 m 192 m

S 18-5

S 18-4

S 18-3

S 18-2

S 18-1

Page 97: Cretaceous of Kirthar

77

Fig. 3.31: Field photograph showing fluid escape structures (arrows) in sandstone section-16

Page 98: Cretaceous of Kirthar

78

density turbidity currents.

3.3.5 Levee facies association

This facies association occurs in the southern part of the study area and

consists of facies 9 (mudstones interbedded with thin lenticular sandstones

associated with submarine fan turbidites) and facies 12 (chaotic units). The

sandstones are medium to thin bedded (2cm-20cm), well graded with Bouma Tc,

Tcd and Tcde division. Sandstone beds are commonly lenticular and show either

rapid or gradual transition in the overlying mudstones. This facies association

occurs with channel fill deposits and affected by varying degree of slumping.

Mudstones were formed from the settling of the suspension cloud of the turbidity

currents and hemipelagic processes. Flute marks at the base of some of the

sandstone beds indicate NNW paleocurrent direction.

3.3.6 Submarine fan lobe facies association

This facies association occurs in the north (distal) of the southern part of

the study area (section-16, 19 and 20) and comprises dominantly facies 7

(laterally continuous graded sandstones) with subordinate facies 9 (mudstones

interbedded with thin lenticular sandstones associated with submarine fan

turbidites) and facies 8 (lenticular graded sandstones) (Figs. 3.27, 3.28, 3.29, 2.32

and 3.33). Sandstones are coarse to very fine grained, well graded and typically

displaying Bouma Ta, Tab, Tac and Tabc. Most of the sandstone beds are

medium to thick bedded, parallel sided and laterally continuous at outcrop scale

with no obvious erosion at the bases (Figs. 3.32 and 3.33). Sandstone beds are

either separated by thin mudstones units or amalgamated. However, few beds are

Page 99: Cretaceous of Kirthar

79

N ari Formation200 m

S 19-1

S 19-2

104 m

0 m

Page 100: Cretaceous of Kirthar

80

N ari Formation103 m

F 6.3

S18-2

S18-1

Page 101: Cretaceous of Kirthar

81

lenticular with shallow scouring at the base. Sandstones of this facies association

are segregated into packets ranging from 3 m to 23 m in thickness. This facies

association shows Tabc, Tbcde, Tcde, Tcd, Tde Bouma divisions. These

sandstone sequences are characterized commonly by thickening upward cycles.

3.3.7 Submarine base of slope mud lobes facies association

This facies association occurs in the southern part of the study area

(section 15 and 16) and is composed of facies 10 (mudstone with occasional marl

and very fine grained sandstone) and facies 8 (lenticular graded sandstones) (Fig.

3.27 and 3.28). The thickness of the mudstones ranges from 4m to 20m and are

interbedded with channel fill sandstones. Mudstone is unconsolidated to

consolidated, purple, red, brown, maroon, greenish grey and grey in color.

Bioturbation can be seen in mudstone at places. Marl is greenish grey, brown and

red. Marl is parallel and cross laminated showing Bouma divisions Tb, Tbc. The

interbedded sandstones are very fine and fine grained, very thin bedded (2cm- 10

cm) and laterally continuous at outcrop scale. Sandstones are well graded

displaying Bouma Tbc, Tc divisions. This was deposited at the base of the slope

as a result of the back-stepping of the turbidite system.

3.3.8 Submarine slope sandstones facies association

This facies association occurs in the southern part of the study area and

consists of facies 7 (laterally continuous graded sandstones) facies 8 (lenticular

graded sandstones), facies 5 (hummocky sandstones) facies 12 (chaotic units).

Sandstones are commonly thick to medium bedded, well graded, fine to coarse

grained, displaying Bouma Tabc, Tab, Tac divisions. Sole marks such as flutes

Page 102: Cretaceous of Kirthar

82

and grooves are common at the base of the sandstone beds, indicating

paleocurrent directions towards NNW (3100-3500). Packets of laterally continuous

sandstones and lenticular sandstones occur alternating with one another. Laterally

continuous sandstone packets are common in the basal part of the sequences while

packets of the lenticular sandstones are common toward the top of the sequence

(Figs. 3.27, 3.28, 3.29, 3.30 and 3.32). Hummocky sandstones occur at the upper

most part of the sequence. Several chaotic units are present in the sequence.

3.3.9 Fluviodeltaic to shoreface facies association

This facies association occurs in the east of the Southern Depositional

System and comprises of large scale planar cross bedded sandstone facies (F11),

massive sandstone facies (F3), bioturbated sandstone facies (F4) and hummocky

sandstones (F5; Fig. 3.34). All these indicate that the deposition took place in

fluvial dominated deltaic setting under high energy flow conditions. The presence

of hummocky sandstones is a clear indication of storm effects.

3.4 FACIES VARIATION

Two distinct facies variations can be observed within the Upper

Cretaceous succession of the Kirthar Fold Belt.

3.4.1 Facies variations in the northern sequences

Sandstone rich Upper Cretaceous succession display evidence of shallow

marine deposits and show a progressive transition from shoreface facies

associations in the east (proximal) to shelfal lobe sandstones and prodelta-like

facies associations of the deeper shelf setting in the west (distal) in the northern

part of the study area Khan et al., 2002). The hummocky cross stratified

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83

Fig. 3.34: Sedimentary log of section-11 measured at Bur Nai, grid ref.336353 showing fluviodeltaic facies association, proximal component of Southern Depositional System (see Fig. 2.3 for location and 3.13 for legends).

F 3.17

145 m

S 11-5

S 11-4

S 11-3

S 11-2

S 11-1

F 3.8

78 m

Page 104: Cretaceous of Kirthar

84

sandstones are internally cross laminated and bioturbated on their tops and are

associated with parallel-to low angle cross-lamination in proximal parts, but in

comparison these beds are generally massive in distal settings. Thick massive

sandstone facies (F3) pass down gradient (westward) into mudstones, marls

interbedded with well graded sandstones (F7 and F8). There is a clear and broad

increase in grain size, bed thickness and an increase in proportion of hummocky

beds upward in the vertical section in Northern Depositional System. The

underlying Mughal Kot Formation was formed in a mud rich shelf grades upward

into the storm-influenced shoreface Pab sediments (Khan et al., 2002). Upper

Cretaceous succession is overlain by mudstone-carbonate mixed succession (shelf

deposits) of Rani Kot Group (Paleocene).

Bed and set thicknesses of the trough cross-strata also increase upwards in

these deposits. The distal sequences show a transition upwards from pelagic, thin–

bedded marls and carbonate turbidites (prodelta deposits) of the underlying

Mughal Kot Formation to shelfal delta sandstones of the Pab Formation, which

are capped by distal storm carbonates of the Rani Kot Group (Khan et al., 2002).

All these features suggest an overall upwards shoaling and progradational trend.

3.4.2 Facies variations in southern sequences

In the southern part of the study area, the Upper Cretaceous deposits are

composed dominantly of deep marine turbidite, characterized by basin floor sand-

rich lobes, channel fill sandstones, mud-rich base of slope lobes, sand-rich slope

lobes and channels-levee and fluvio-deltaic sequences. The basin floor sand-rich

lobes which grade northward into mudstone dominated sequences and change into

Page 105: Cretaceous of Kirthar

85

channel fill sandstone sequences represent the lower most part of the Upper

Cretaceous succession. This is overlain by mud-rich lobes and associated

channelized sandstones and levee deposits of base of slope setting which in turn

are overlain by a slope fan turbidite system. This slope fan turbidite deposits are

characterized by fan lobes in the distal part of the system (towards north) and

slope channels in the proximal part of the system (towards south). In the upper

part of the sequence, these sandstones change into hummocky type sandstone

beds. All these sequences are overlain by greenish grey hemipelagic shales of

Paleocene Ranikot Group.

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86

CHAPTER-4

PETROGRAPHY, GEOCHEMISTRY AND PROVENANCE

4.1 INTRODUCTION

The composition of source rocks has a great influence on the ultimate

composition of sandstone. So, provenance studies are mainly based on modal

analysis of detrital framework grains (Dickinson and Suczek, 1979; Dickinson et

al., 1983) and bulk rock geochemistry (Bhatia; 1983, 1985; Bhatia and Crook,

1986; Roser and Korsch, 1986). Detrital modes of sandstone also provide

informations about the tectonic settings of basins of deposition (Dickinson et al.,

1983). The relationship between sandstone petrography and tectonic setting has

been studied by many authors (Dickinson et al., 1983; Dickinson and Suczek,

1979; Ingersoll and Suczek, 1979). The composition (both mineralogical &

chemical) of fine grained sedimentary rocks (mudstone and shale) are generally

used as sensitive indicators of provenance, weathering conditions and tectonic

settings (Cullers, 2000; Cullers and Brendensen, 1998; Nesbitt et al., 1996; Cox et

al., 1995; Cox and Lowe, 1995; Ronov et al, 1990; Taylor and McLennan, 1985

& 1991). Geochemistry of mudstone and sandstone is useful to understand

provenance characterization, paleoclimatic conditions and intensity of chemical

weathering (Baulaz et al., 2000; Joo et al., 2005; Maslov et al., 2003). Major

elements of sediments are helpful for determination of their original detrital

mineralogy. The K2O/Al2O3 ratio, Index of Compositional Variability (ICV),

Chemical Index of Alteration (CIA), SiO2-Al2O3+K2O+Na2O diagram and Al2O3 -

CaO+Na2O - K2O (A-CN-K) plot are useful geochemical parameters for the study

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of provenance, paleoclimate conditions, maturity and intensity of weathering

(Cox et al., 1995; Weaver, 1989; Barshad, 1966; Nesbitt and Young, 1984).

Sandstone petrology and geochemistry of mudstones and sandstones of the

Upper Cretaceous succession Kirthar Fold Belt Pakistan have not been studied

previously in detail to determine their provenance and geochemical parameters.

This chapter deals with petrology of sandstone, geochemistry of sandstone and

mudstone in order to understand provenance and chemical weathering due to

paleoclimatic conditions in source area. Furthermore, relationship of paleoclimate

conditions with intensity of chemical weathering in source area also has been

interpreted using geochemical Modals of mudstone and sandstone.

4.1.1 Methods Used

Sandstone samples were collected from 20 localities, where the

stratigraphic succession of the Upper Cretaceous is well exposed. Sixty five thin

sections were prepared and studied under Olympus BH-2 Modal research

microscope. Thin sections of sandstone were selected to cover textural, lateral and

vertical variations. Five hundred (500) points were counted in each thin section

(Appendix 4.1) using the Gazzi Dickinson method, which manages to minimize

the effect of grain size (Ingersoll et al., 1984; Zuffa, 1985). Constituent minerals

of the sandstone were classified into monocrystalline quartz, polycrystalline

quartz, K-feldspar, plagioclase, volcanic lithic fragments, sedimentary lithic

fragments, chert and minor heavy minerals. Compositional fields are shown in

triangular plots of Q-F-L (quartz-feldspar-lithic fragments), Qm-F-Lt

(monocrystalline quartz-feldspar-total lithic fragments), and Qp-Lv-Ls (quartz

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polycrystalline- volcanic lithic fragments- sedimentary lithic fragments) which are

useful to determine the maturity and provenance (Dickinson, 1985; Dickinson et

al., 1983; Dickinson and Suczek, 1979).

The poles of the above mentioned figures are given in the following table:

Poles Description

Q Total stable quartz grains (both monocrystalline and polycrystalline

quartz) including chert

F Feldspar grains including both plagioclase and K-feldspar

L Unstable lithic fragments of volcanic, sedimentary and metamorphic

origin.

Qm Monocrystalline Quartz

Lt Total lithic fragments including chert fragments

Qp Polycrystalline quartzose grains

Lv Total volcanic lithic fragments

Ls Unstable sedimentary lithic fragments

For the purpose of geochemical analyses, the mudstone and sandstone

samples were analyzed to determine major element oxides using Shimadzu Rayny

EDX-700 HS X-Ray fluorescence spectrometer at High Tech Central Resource

Laboratory, Institute of Biochemistry University of Balochistan, Quetta.

4.2 SANDSTONE PETROLOGY

4.2.1 Texture

Studied thin sections of sandstone were prepared from fine to coarse

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grained samples. Some are very coarse to pebbly (Fig. 4.1A), whereas, others are

fine to very fine grained (Fig. 4.1B). Samples are moderate to well sorted (Fig.

4.1C), poor to moderate sorted (Fig. 4.1D) and subrounded to well rounded (Fig.

4.1E). Most sandstone samples are cemented with calcite mud matrix, whereas,

some are grain supported (Fig. 4.1F). The nature of sorting, roundness and low

clay content suggests that the sandstone is texturally submature to supermature.

4.2.2 Characters of framework grains

4.2.2.1 Quartz

Quartz, feldspar and lithic fragments in sandstones were observed and

studied. Most abundant framework grains are quartz in the sandstone. Both

monocrystalline and polycrystalline quartz types are present. The monocrystalline

quartz is clean and shows nonundulose extinction, although in thin sections

undulose (more than 50) extinction is also noted (Fig. 4.2A). The undulose quartz

grains do not show common orientation, thus indicating that strain was acquired

in the source area. Polycrystalline quartz is comparatively less common. Both two

(Fig. 4.2B) or more than two crystals (Fig. 4.2C) per grain varieties of

polycrystalline quartz are present in thin sections. But polycrystalline quartz (Qp)

with more than two crystals are more frequent. The subgrain size is variable, even

within a single composite grain of polycrystalline quartz. Most subgrains are as

fine to very fine sand size.

4.2.2.2 Feldspar

Feldspar is an important mineral group present in sandstone in minor

amount. K-feldspar (Fig. 4.2D) including microcline (Fig. 4.2E), and plagioclase

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Fig. 4.1: Photomicrographs showing texture of sandstone: A) Verycoarse grained; B) Very fine to fine grained; C) Well sorted; D) Poorly sorted; E) Well rounded; and F) grained supported.

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Fig. 4.2: Photomicrographs showing varieties of framework grains: A) Undulosemonocrystalline quartz; B) Polycrystalline quartz consists of two sub grains;C) Polycrystalline quartz consists of more than two sub grains; D) K-feldspar; E) Plagioclase showing albite type twinning in central part; and F. Microclineshowing cross hatched twinning; all indicated by circles.

Page 112: Cretaceous of Kirthar

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(Fig. 4.2F) were observed. K-feldspar is more abundant than plagioclase.

Feldspars were intensively altered to clay minerals and replaced by calcite as

well. Plagioclase is Na-rich (albite).

4.2.2.3 Lithic Fragments

Igneous and sedimentary (including fossil lithic and chert fragments are

present in specified horizons and sections. In few thin sections the sedimentary

fragments (Fig. 4.3 A) are noted and they are composed of cemented very fine

grained quartz clasts (siltstone). A variety of fossil fragments (Fig. 4.3B to E)

were seen in sandstone in few thin sections. They are mainly composed of calcite

composition with no alteration of their margins, which show that these fossil

fragments are not reworked. Chert is also recognized and counted in thin sections.

It has been distinguished during petrograohic study by its finer internal grain size

from polycrystalline quartz grains (Fig. 4.3 F). The volcanic fragments are

common in upper part of Southern Depostional System (defined in section 4.3) of

the study area. They are mafic in origin (Fig. 4.4A) and are composed of basalt.

Some traces of mica (Fig. 4.4B) are present in sandstone of Upper Cretaceous

succession.

4.2.3 Cement / matrix

The framework grains are bounded by cement and matrix, however, in

some cases sandstone is partly grain supported. Matrix and cement collectively

comprises an average of 21.45 % of the rock volume. The most common cement

is calcite with some iron oxide, quartz overgrowth and clay matrix. Calcite

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Fig. 4.3: Photomicrographs showing varieties of framework grains: A) Sedimentary fragment (siltstone); B to E) Various forms of shells fragments and F) Chert; all shown by arrows.

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Fig. 4.4: Photomicrograph showing: A) Volcanic lithic fragment; B) Mica grain (lower cental part: arrow); C) Micritic calcite (arrow); D) Sparry calcite (arrow); E) Iron oxide/hydroxide cement (arrow); F)Well rounded quartz grain with overgrowth (arrow) showing reworking.

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cement is present in most samples. Both micritc calcite matrix (Fig. 4.4 C) and

Sparry calcite cement (Fig. 4.4D) were observed. The sections exposed to the

eastern parts of the study area such as Karkh nala, Langerchi, Bhalok and Khori

village (sections 1, 2, 3 and 4), have rare calcite cement and show partly grain

supported texture or/and contain iron oxide cement (Fig. 4.4E). Calcite cement

ranges from 1.4 to 31.4 % of total. Calcite has been altered to siderite in some

cases.

Quartz overgrowths are best developed in rocks located stratigraphically

in upper part of the succession. Quartz cement in the form of quartz overgrowth is

present in most of the samples and range from 0.8 to 12.4 %. In thin sections

quartz overgrowth can only be distinguished from the detrital grains by rims of

authigenic clay and penetrative nature of the cement which occupy the interstices.

Euehedral crystals of quartz overgrowth in void spaces are commonly present.

Clay minerals include kaolinite, chlorite and illite, which were identified

with the help of scanning electron microscopy (Figs. 5.15 to 5.20 and 5.32) and

XRD (Figs. 5.7 to 5.9 and 5.11). They collectively range from 0.2 to 6.6 % of the

total composition. Kaolinite is the most abundant clay mineral followed by

chlorite and illite present in comparatively low amount. Clay minerals were

mostly formed as a result of alteration of feldspar grains during diagenesis.

Iron oxide cement is also present in most thin sections. It ranges from 0.2

to 25.2 %. Iron oxide cement is predominant in thin sections of Bur Nai and

Bhalok (sections-11 and 3) and also present in appreciable amounts in samples of

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Karkh nala and Langerchi (sections-1 and 2). All these sections are located in

eastern most part (proximal) of the study area.

Minor accessory (heavy) minerals were observed in most thin sections. These

constitute trace to 2% and include glauconite, apatite, zircon and tourmaline.

Tourmaline is mostly composed of its pink variety.

4.2.4 Modal Analysis

Results of point counting of sandstone are shown in appendix 4.1. Point

counts of the detrital grains like quartz, feldspar and lithic fragments were

recalculated into 100 and then plotted into a triangular diagram (Fig. 4.5) for

classification (Folk, 1974). The sandstone is mainly quartz arenites (contain more

than 95% detrital quartz) and sublithic arenites. The framework components

percentages of sandstone are shown in appendix 4.2.

Quartz is most dominent within all sandstone samples, and it ranges from

45.6 to 91.4% of the whole composition. Monocrystalline quartz is more abundant

than polycrystalline quartz ranging from 42.2 to 89.4 % (average is 72.88%) of

the whole composition, whereas, the polycrystalline quartz ranges from 0.2 to

20.2 % (average is 1.85 %).

The sandstone contains very low quantity of feldspar in all sections.

Plagioclase is much less abundant and is present in trace amount (0.2 – 0.6 %) in

few thin sections, whereas, the K-feldspar is more abundant ranging from 0.2 to

2.8 % (average is 0.64 %) of the whole rock composition.

The sedimentary fragments are noted in few thin sections in Northern

Depositional System (defined in section 4.3), comprising 0.2 to 8.6 % (including

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fossil fragments) of the whole rock composition. The volcanic fragments are rich

in upper part of Southern Depositional System of the study area. Volcanic

fragments range from 0.6 to 27.6 % of the whole rock composition. The

concentration of volcanic fragments is slightly increasing toward the proximal

depositional setting. The chert ranges from 0.2 to 4.2 % of the whole rock

composition.

4.3 COMPARISON BETWEEN NORTHERN AND SOUTHERN

DEPOSITIONAL SYSTEMS

On the basis of facies associations, paleoflow and presence of petrology

the Upper Cretaceous succession is grouped into Northern and Southern

Depositional Systems. The most striking difference between the petrology of the

Northern and Southern Depositional Systems is the presence of volcanic lithic

fragments in the upper part of the Southern Depositional System, and thus the

successions are grouped into two petrographic units, namely Upper and Lower

units.

4.3.1 Lower Unit

Lower unit is most common throughout the study area both in Northern

and Southern Depositional Systems. Samples of Northern Depositional System

show Upper Cretaceous succession sandstones fall into lower unit as these have

no volcanic lithic fragment. Staratigraphically lower portion of the Upper

Cretaceous succession in Southern Depositional System is also grouped as lower

unit. This unit can be distinguished by abundant quartz (average, 98.89 to 99.58

%), minor feldspar and no volcanic fragments (Table 4.1; Fig. 4.6A & C).

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Table 4.1: Average of point counting results in percentages (Figs. 4.6) of measured sections in lower and upper units of both Northern and Southern Depositional Systems. Note that Upper unit is observed only in Southern Depositional System. Sections

No Q F L Qm F Lt

Lower unit of Northern Depositional System 1 99.74 0.25 0 98.93 0.26 0.8 2 98.53 1.45 0 95.7 1.5 2.78 3 98.86 0.94 0.18 98.74 0.95 0.29 4 98.16 1.83 0 98.15 1.84 0 5 97.71 2.27 0 97.57 1.86 0.54 6 99.25 0.73 0 98.99 0.74 0.23 7 98.9 0.94 0.14 98.72 0.95 0.3 8 99.23 0.75 0 98.37 0.66 0.95 9 99.41 0.57 0 98.41 0.61 0.96 10 98.97 1.02 0 96.56 1.37 2.06

Lower unit of Southern Depositional System 11 99.08 0.91 00 98.43 0.96 0.58 15 99.54 0.45 00 99.52 0.47 00 16 98.89 0.67 0.41 98.86 0.7 0.42 17 99.55 0.44 0 98.10 0.47 1.41 18 99.58 0.40 00 98.95 0.41 0.61

Upper unit of Southern Depositional System 11 78.63 0.7 20.65 78.43 0.71 20.85 13 88.73 0.24 11.01 88.48 0.24 11.27 14 87.74 0.49 11.75 87.04 0.51 12.42 15 78.94 1.19 19.8 78.79 1.19 19.99 16 87.41 1.59 10.97 87.36 1.59 11.02 17 95.78 0.91 3.3 95.47 0.87 3.64 18 96.74 0.82 2.42 96.71 0.83 2.44

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Conc

entra

tion

in p

erce

ntag

e

Fig. 4.6: Comparison in concentrations of Q-F-L and Qm-F-Lt Upper Cretaceous succession; A and C lower unit

; and B and D upper unit.

in sandstones of (in both Northern and Southern depositional Systems) (only in Southern Depositional System)

A

0

20

40

60

80

100

1 2 3 4 5 6 7 8 9 10 15 16 17 18

QFL

Q

F L

B

QmFLt

0

20

40

60

80

100

13 1411 15 16 17 18

Qm

F

Lt

QFL

C

0

20

40

60

80

100

1 2 3 4 5 6 7 8 9 10 11 15 16 17 18

Q

F L

D

QmFLt

0

20

40

60

80

100

13 1411 15 16 17 18

Qm

F

Lt

Section No.

Section No.

Section No.

Section No.

Page 121: Cretaceous of Kirthar

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4.3.2 Upper Unit

The Upper Unit comprises sandstone rich intervals of the stratigraphically

upper of the Southern Depositional System. Sandstones of this unit contain

dominantly quartz but in lower proportions (minimum 68.96 %) than the lower

unit, and low proportion of feldspar. This unit contains abundant volcanic

fragments (Table 4.1; Fig. 4.6 B & D). The comparison of both systems are given

in Table 4.1 and plotted in Figs. 4.6.

Calcite is the most dominant cement in sandstones of both Northern and

Southern Depositional Systems. Other cements are iron oxide and quartz

overgrowth in sandstone. The iron oxide cement is dominant in eastern sections in

both systems. Sandstone is partly grain supported with little iron oxide cement

and quartz overgrowth in sections exposed on easternmost side of the Northern

Depositional System. The sandstone of Northern Depositional System contains

fossil fragments and sedimentary lithic fragments in few thin sections, whereas,

such fragments are lacking in thin sections of Southern Depositional System.

4.4 GEOCHEMISTRY OF MUDSTONE AND SANDSTONE

The composition of the studied samples depend upon the distribution

pattern of major element. In Table 4.2 major element data is shown. Major oxides

of mudstone in the descending order are; Al2O3, SiO2, Fe2O3, K2O, CaO with

minor oxides of TiO2, MnO, V2O5, SrO, ZrO, Rb2O, ZnO and Nb2O. The average

values of major oxides are as: Al2O3 (45.74 %); SiO2 (42.38 %); Fe2O3 (5.05 %); K2O

(3.71 %); CaO (2.22 %).

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Table 4.2: Major element concentrations and other geochemical parameters for mudstone samples of Upper Cretaceous succession.

Oxides/ Parameters

1-7 2-11 3-5 12-1 14-2 15-2 15-3 16-4 16-6 16-9

SiO2 43.45 40.22 48.45 42.88 32.91 42.25 40.23 44.07 43.84 43.37 Al2O3 41.96 45.90 39.44 44.82 46.05 49.23 47.8 44.65 49.46 49.32 CaO 5.314 4.92 2.858 1.975 2.013 0.803 4.768 2.288 0.252 0.458 Fe2O3 3.068 2.956 3.818 4.528 14.611 4.647 3.841 3.55 2.086 3.398 K2O 4.972 5.414 4.528 4.638 2.941 2.372 2.619 4.994 3.856 2.901 TiO2 0.409 0.496 0.712 1.053 0.895 0.642 0.471 0.397 0.459 0.398 MnO 0.034 0.037 0.121 0 0.517 0 0.229 0 0 0.106 V2O5 0.027 0.026 0.036 0.043 0.038 0.038 0.034 0.023 0.022 0.031 SrO 0.01 0.009 0.007 0.004 0.007 0.003 0.008 0.003 0.003 0.002 ZrO2 0.008 0.007 0.007 0.008 0 0.004 0.005 0.004 0.005 0.003 Rb2O 0.002 0.002 0.005 0.002 0.008 0 0.002 0.003 0.002 0.001 ZnO 0 0.005 0.007 0.006 0 0.005 0.005 0.002 0.003 0.004 NbO 0.001 0.001 0.001 0.002 0 0 0 0 0 0 CIA 80.31 81.62 84.22 87.14 96.16 93.94 86.61 85.97 92.33 93.62 ICV 0.327 0.075 0.302 0.22 0.44 0.17 0.24 0.25 0.13 0.14 CIW 88.76 90.32 93.24 95.78 95.81 98.39 90.93 95.12 99.49 99.08 K2O/Al2O3 0.118 0.117 0.114 0.1 0.063 0.04 0.05 0.11 0.07 0.05

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Table 4.3: Major element concentrations for sandstones.

Oxides 6-7 7-10 9-5 10-3 15-4 16-5 17-1 17-4 18-1 19-2 20-1 SiO2 95.138 96.815 92.032 96.71 97.351 98.065 96.645 97.433 92.024 96.936 94.756 Fe2O3 0.691 0.361 2.871 1.257 0.306 0.650 1.343 0.316 2.983 0.397 0.753 CaO 3.169 0.497 2.219 0.54 1.352 0.518 0.522 1.480 2.224 0.547 3.266 K2O 0.479 1.698 1.37 1.008 0.56 0.510 1.018 0.552 1.5 1.716 0.528 TiO2 0.097 0.352 0.693 0.351 0.096 0.122 0.387 0.098 0.712 0.347 0.165 NiO 0 0 0 0 0 0.031 0 0 0 0 0 CuO 0 0.20 0 0 0.004 0.012 0 0.005 0 0.18 0 MnO 0 0 0.046 0 0 0 0 0 0.050 0 0 V2O5 0 0.031 0 0.006 0 0 0.007 0 0 0.029 0 SO3 0 0.003 0.067 0.069 0.039 0.089 0.073 0.046 0.074 0.003 0 ZrO2 0.004 0 0.296 0.005 0.004 0.002 0.005 0.004 0.311 0 0.005 Cr2O3 0 0 0.137 0 0.063 0 0 0.060 0.122 0 0 ZnO 0 0.006 0 0 0.004 0 0 0.005 0 0.007 0 SrO 0.002 0 0 0 0 0 0 0 0 0 0.002 Sm2O3 0.497 0 0 0 0 0 0 0 0 0 0.524

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The sandstones are mainly composed of SiO2, which ranges from 92.02 to

98.06 % (average = 95.99 %) (Table: 4.3, 4.4). CaO, Fe2O3 and K2O also present

with averages of 1.40 %, 1.04 % and 0.94 %, respectively (Table. 4.4). ZrO2,

V2O5, MnO, NiO, Cr2O3, ZnO, SrO and Sm2O3 are also present in traces. Such

geochemical data indicates that the sandstone is silica (Quartz) rich. The

distribution data points characterized the sandstone on SiO2 versus

Al2O3+K2O+Na2O diagram (Fig. 4.7), proposed by Suttner and Dutta (1986),

suggest that sediments were derived from humid environment. An approach

toward assessing original detrital mineralogy is to use the Index of Compositional

Variability (ICV) and ratio of K2O/Al2O3 (Cox et al., 1995). ICV is defined as:

ICV (Index of Compositional Variability) = (Fe2O3 + Na2O+CaO+ MgO +Ti O2)/ Al2O3

More mature mudstone with mostly clay minerals ought to display lower

ICV values that are <1.0 (Cox et al., 1995). Such mudstone are derived from

craton environments (Weaver, 1989), where recycling and weathering processes

predominate. In addition, mudstone displaying ICV values less than 1 have also

been found in some intensively weathered first cycle sediments (Barshad, 1966).

The ICV values of the mudstones of Upper Cretaceous succession range from

0.075 to 0.44 with an average of 0.23 (Table 4.2 and 4.4).

K2O/Al2O3 ratio indicates relative abundance of alkali feldspar versus

plagioclase and clays in mudstone. K2O/Al2O3 ratios of the alkali feldspar ranges

from 0.4 – 1, illite approximately 0.3 and other clay minerals nearly zero (Cox et

al., 1995). K2O/Al2O3 ratio greater than 0.5, suggests dominance of alkali feldspar

as compared to other minerals in the original mudstone. In contrast those having

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Table 4.4: Average major element concentrations for mudstone and sandstone samples. Oxides/Parameters Mudstone Oxides/Parameters Sandstone

SiO2 42.38 SiO2 95.99 Al2O3 45.74 CaO 1.40 CaO 2.22 Fe2O3 1.04

Fe2O3 5.05 K2O 0.94 K2O 3.71 TiO2 0.29 TiO2 0.58 MnO 0.008 MnO 0.17 V2O5 0.006 V2O5 0.033 SrO 0.003 SrO 0.005 ZrO2 0.053 ZrO2 0.005 ZnO 0.002 Rb2O 0.002 NiO 0.005 ZnO 0.005 CuO 0.032 NbO 0.001 SO3 0.047 CIA 89.05 Cr2O 0.03 IVC 0.23 Sm2O3 0.08 CIW 95.39 --- ---

K2O/Al2O3 0.079 --- ---

Page 126: Cretaceous of Kirthar

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A

CN K

CIA

Original CIASmectite Illite

Muscovite

Biotite

K-FeldsparPlagioclase50

60

70

80

90

100

Fig. 4.8: The A-CN-K diagram of mudstone samples, showing high CIA values (after Nesbitt and Young, 1984); open circles indicate Northern and Closed circles show Southern Depositional System.

Al O + K O+Na O2 3 2 2

20

40

60

80

100

10 20 30

SiO2

Fig. 4.7: SiO -Al O + K O+Na O diagram for the sandstone (after, Suttner and Dutta, 1986)2 2 3 2 2 open circles indicate Northern and Closed circles show Southern Depositional System.

Page 127: Cretaceous of Kirthar

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K2O/Al2O3 ratios of less than 0.4 suggest minimal alkali feldspar in the original

mudstone (Cox et al., 1995). The K2O/Al2O3 ratio in mudstone of the Upper

Cretaceous succession of study area ranges from 0.04 to 0.118 (average = 0.079).

It suggests that mudstone have minimal K-feldspar (Table 4.2). This result is

consistent with petrographic results of sandstone.

Another approach to asses the composition of the original source rock is to

plot A-CN-K (after Nesbitt and Young, 1984). Such a plot is useful for

identifying compositional changes of mudstones and sandstones that are related to

chemical weathering, transport, diagenesis, metamorphism and source rock

composition (Fedo et al., 1995; 1997a, b). The average source rock composition

of mudstone can be deduce from A-CN-K diagram. Data of mudstone samples of

the Upper Cretaceous succession were plotted in A-CN-K diagram (Fig. 4.8),

which indicates that all samples plot near the A end member, which suggests

intense chemical weathering and transportation of the mudstones.

The Chemical Index of Alteration (CIA) is used to infer the degree of

weathering of source rocks and is calculated by using following formula (Nesbitt

and Young, 1982):

Chemical Index of Alteration (CIA) = (Al2O3/ Al2O3+CaO+K2O+Na2O) x 100

The CIA values of mudstone of the Upper Cretaceous succession range from

80.31 to 96.16 (average = 89.05) (Table 4.2; Fig. 4.8), which indicate intense

chemical weathering of mudstone and presence of minerals rich in

compositionally mature alumina. Low K2O/Al2O3 ratios and average CIA values

(89.05) of the mudstone samples suggest some reduction of feldspar in source

area. Such interpretations and petrographic data, both are quite consistent with

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each other. CIA also shows that mudstones passed through intense chemical

weathering and transportation.

4.5 DEFICIENCY OF FELDSPAR

Sandstone of Upper Cretaceous succession is characterized by very low

proportion of feldspars. This deficiency of feldspars has been caused by

combination of factors such as chemical weathering, transportation and

diagenesis. The quartz-rich composition of sandstone and presence of glauconite

indicate that the source rocks/ sediments were passed through intense chemical

weathering in warm, tropical climatic conditions as proposed by Maslow et al.,

(2003). Warm and humid climatic conditions at source area indicated by values of

CIA, ICV, A-CN-K diagram, K2O /Al2O3 (Fig. 4.8 and Tables 4.2 and 4.4).

Sediments of Upper Cretaceous succession have traveled long distance and so

intensive abrasion was occurred as also indicated by high mature nature of

sandstone. Most important factor responsible for the reduction of feldspar is

diagenesis. During diagenesis of sandstone appreciable amounts of feldspar were

lost by its alteration to kaolinite. Replacement of feldspars by clay minerals and

calcite (Morad and Aldahan, 1987) were partial or complete. Feldspar deficiency

is, therefore was caused by diagenesis, distant transportation and chemical

weathering in source area. In contrast to feldspar, volcanic lithic fragments are

present in some samples comparatively in higher amount in Upper Unit of

Southern Depositional System. Why volcanic fragments were not much reduced

as feldspar was? It is because of two reasons; firstly, it could be due to rapid

erosion of volcanic source rocks, which were introduced very late and also

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syndepositional in terms of time with Upper Cretaceous succession, and;

secondly, the volcanic source is near as basaltic beds are present within the Upper

Cretaceous succession in Bur Nai section (section-11). The near source was due

to wide spread volcanisim in the source area, which covers the Indian Craton and

its surrounding areas. Diagenetic alteration of volcanic fragments into chlorite

was common. The above facts clearly indicate that chemical weathering in source

area with combination of long transport and diagenesis were important factors in

reducing feldspar.

4.6 PROVENANCE

Dickinson et al. (1983) demonstrate that provenance and tectonic settings

of sandstones can be deciphered by considering their Q-F-L, Qm-F-Lt and Qp-Lv-

Ls compositional diagrams. Q-F-L plot (Fig. 4.9) indicates that the sandstone

formed within the Craton Interior and Recycled Orogen. The Qm-F-Lt plot (Fig.

4.10) shows that the sandstones plot within the Craton Interior and Quartzose

Recycled fields; Qp-Lv-Ls plot (Fig. 4.11; Table 4.5) indicates that the

sandstones of upper unit of the Southern Depositional System fall within the

fields of Arc Orogen and Mixed Recycled Orogen. Q-F-L and Qm-F-Lt plots

indicate that sandstone of the lower unit, which is common throughout the study

area (both in Northern and Southern Depositional Systems), were derived mostly

from the Craton Interior setting. Whereas sandstone of the upper unit, which

makes upper part of the succession in Southern Depositional System were derived

mostly from Recycled and Quartzose Recycled and partly from Arc and Mixed

Recycled Orogen (Fig. 4.9, 4.10 and 4.11). Well rounded quartz overgrowth (Fig.

Page 130: Cretaceous of Kirthar

110

Page 131: Cretaceous of Kirthar

111

Craton interior

TransitionalContinental

Basement Uplift

Mixed

Dissected arc

Transitionalarc

Undissected arc

Recycled

QuartzoseRecycled

TransitionalRecycled

LithicRecycled

Qm

F Lt23 13

29

42

20

43

20

Craton interior

QuartzoseRecycled

Qm

LtF

Page 132: Cretaceous of Kirthar

112

Table 4.5: Point counting results of sandstone samples in percentages (Qp-Lv-Ls diagram) of measured sections.

Sample No Qp Lv Ls 11-5 4.34 95.65 0 13-2 11.66 88.33 0 13-3 2.7 97.29 0 14-7 16.72 83.72 0 14-9 16.25 83.75 0 14-10 5.0 95.0 0 15-5 0.71 99.28 0 15-6 2.17 97.82 0 16-7 11.11 88.88 0 16-8 1.88 98.11 0 6-11 3.44 96.55 0 17-4 66.66 33.33 0 17-5 10.0 90.0 0 18-1 61.9 38.89 0 18-3 10.0 90.0 0

Fig. 4.11: Qp-Lv-Ls triangle for detrital modes of upper unit of Southern Depositional System (after, Dickinson et al., 1983 and Dickinson 1985

Page 133: Cretaceous of Kirthar

113

4.4F) is also an evidence of reworking of sediments. Predominance of quartz

(Anani, 1999) in sandstones, high degree of sorting, roundness, texturally and

compositionally mature nature of sandstone indicate, long distance of transport.

Predominance of the nonundulose monocrystalline quartz over polycrystalline

quartz suggests that the sandstone was derived from plutonic igneous source

(Blatt, 1967). The presence of tourmaline and zircon support the notion that

sediments were derived from acidic igneous source (Feo-Codicido, 1956).

During the latest Maastrichtian, the Indian Plate passed over a hot spot

(Gombbos et al., 1995). This caused thermal doming of the Indian Plate and

induced erosion of the Indian Craton to the southeast of present Pab Range

(Hedley et al., 2001). Volcanic activity also increased in relation with the thermal

doming (Eschard et al., 2004), and both fine and coarse material was reworked

and transported to Southern Depositional System. It may be noted that some

samples of sandstone from the upper unit of Southern Depositional System

contain upto 27.6 % volcanic fragments. Therefore, presence of mafic volcanic

fragments in sandstone of the upper unit of Southern Depositional System is

related to this volcanic activity and thermal doming of the Indian Craton.

Flute marks, grooves marks, elongated ridges and furrows at the base of

sandstone beds and cross-bedding are useful directional sedimentary structures,

which are commonly used for paleocurrent data. During fieldwork, paleocurrent

directions were measured from such structures, which show that sediments

deposited in Southern System were transported from south-southeast to north-

northwest (Fig. 4.12). The Indian Craton was located to the east and south-

Page 134: Cretaceous of Kirthar

114

Paleocurrent direction

Uthal

Bela

Karachi

Nal

Sehwan

KhuzdarKarkh

Cha

man

Fau

lt-O

rnac

h N

al F

ault

Lak

i Ran

ge

K i

r t h

a r

R a

n g

e

Zar

ro R

ange

M o

r R

a n

g e

KK

Khude

Ran

geP

a b

R a

n g

e

28o

27o

26o

66o

68o

67o

25o

ARABIAN SEA

N

Location of measured stratigraphic sectionCities and Towns

50 Km

Key

B e

l a

O p

h i

o l i

t e

s

KK Khuzdar Knot

Pab / Mughal Kot formations(Upper Cretcaceous succession)

Fig. 4.12: Map showing paleocurrent directions in the study area.

Page 135: Cretaceous of Kirthar

115

southeast of the study area. Based on paleocurrent, geochemical and petrographic

data it is suggested that the sediments of the Upper Cretaceous succession were

derived from the Indian Craton, which was exposed to south, southeast and east of

the study area Sediments of the Northern Depositional System of the studied area

were derived from east. The southern Depositional System was fed from part of

Indian Craton exposed to the SSE. Where sediments were derived from Craton

Interior and no volcanic activity was going on during the deposition of lower unit.

During second phase (i.e., time of deposition of upper unit) volcanic activity

(Deccan Volcanism) had been started and Indian Plate was passing over a hot spot

and mafic fragments incorporated in the upper unit of Southern Depositional

System. On the contrary Northern Depositional System was supplied from the

eastern part of the Indian Craton, where no volcanic activity was occurred at that

time; hence this unit is lacking volcanic fragments. So, different source areas are

suggested for Southern and Northern Depositional systems on the basis of

petrographic variations and paleoflow.

4.7 SUMMARY

Sandstone petrography and detrital modes on discrimination diagrams

indicate that Upper Cretaceous succession was derived from Craton Interior and

Recycled Orogen. Sandstones of the Northern Depositional System are classified

as quartz arenites and derived from Indian Craton located to east of study area,

whereas, sandstones in Southern Depositional System are quartz arenite and

sublithic arenite (one sample is litharenite) and were derived from Craton Interior,

Recycled, Quartz Recycled, Arc, and Mixed Recycled Orogens and were derived

Page 136: Cretaceous of Kirthar

116

from Indian Craton located to SSE. Overall the sandstone composition is quartz

rich with increased lithic fragments in the upper unit of the Southern Depositional

System. The difference was caused by Deccan Volcanism in Indian Shield located

towards SSE.

The geochemical data of major elements show that sandstone and

mudstone have the same source. High content of Quartz, low primary clay, high

degree of sorting and roundness of framework grains in sandstone and low ICV

values (<1) of mudstone show, high maturity of sediments of Upper Cretaceous

succession. High CIA, low K2O/Al2O3 ratios of mudstone and petrographic data

show that feldspar present in sediments in low percentage. Geochemical

parameters such as CIA, K2O/Al2O3 ratio in mudstone, SiO2–Al2O3+K2O+Na2O

diagram of the sandstone show that paleoclimate of the source area was warm and

humid, which caused chemical weathering of source rocks reducing some initial

feldspar in source rocks. Long distance of transport, (i.e., perhaps hundreds of

kilometers) is also an important process responsible for further reduction of

feldspars. Diagenetic alteration of feldspar was the most important factor reducing

feldspar in the sandstone.

Page 137: Cretaceous of Kirthar

117

CHAPTER-5

DIAGENESIS OF SANDSTONE

5.1 INTRODUCTION

The primary reservoir targets for hydrocarbon exploration in Pakistan are

the Sui Main Limestone (Eocene) and the Pab Formation of Upper Cretaceous

succession, e.g., in Sui, Pirkoh, Loti, Dhodak, Jandran and Savi Ragha fields

(Beswetherick and Bokhari 2000; Dolan 1990; Kadri 1995; Sultan and Gipson

1995; Hedley et al. 2001; Fitzsimmons et al., 2005). Upper Cretaceous succession

has source rocks as Sembar Formation (Early Cretaceous) and cap rocks as shale

of Rani Kot Group (Paleocene) in the study area. Thus sandstones of the

succession provide an opportunity to evaluate the effects of important variables

such as framework composition, burial depth and ophiolite thrusting on diagenetic

modifications. This chapter aims to provide a general account of the diagenesis of

sandstones to concentrate on the following objectives:

1. describe the diagenetic composition of sandstones,

2. assess the effects of diagenesis on the composition and reservoir quality of

sandstones,

3. describe the diagenetic sequence with respect to time, burial and history,

and

4. grain fracturing due to ophiolite thrusting and uplifting.

5.2 METHODS

Twenty stratigraphic sections with continuous exposures were measured

and sampled. The description of primary and authigenic mineralogy of the

Page 138: Cretaceous of Kirthar

118

sandstones is based on study of 65 thin sections, including point counting and

SEM and X-ray diffraction (XRD) analyses. Polished thin sections were coated

with carbon using Leica Emitech K950 Evaporator. Sandstone chips for SEI study

were coated with gold. Scanning electron microscopy (SEM) has done by using

Jeol JSM 6400, equipped with a link system Energy Dispersive X-ray

microanalyser (EDAX). XRD of sandstones and their clay separates were carried

by PANanalytical X’pert PRO MPD. SEM, XRD and petrography were done in

Aarhus University Denmark. The samples were examined in secondary electron

(SEI) and backscattered electron (BSC) modes of imaging. The Adobe Photoshop

of SEM micrographs and point counting of stained thin sections were used to

assess the sandstones porosity. (following methods are taken by a printed

document of Geologisk Institut Aarhus University Denmark)

The sandstones samples are prepared for bulk mineralogical composition

and clay separates for XRD analyses. For bulk mineralogical composition of

sandstones, a couple of grams of sample are dried and grinded in a wolfram

carbide mortar. The powder is pressed into a steel sample holder. Bulk

mineralogical composition is thus performed on un oriented and un fractionated

preparations under conditions given in Table 1. Minerals are identified based on

their X-ray reflections (crystal lattice distances) which, by JCPDS-ICDD index-

card are related to minerals. The quantification is based on the height of the

selected reflections which are measured or read on the datasheet and corrected

with empirical calculated correction factors and then calculated to %-values,

assuming that the sum of identified minerals are 100%. For clay composition, few

Page 139: Cretaceous of Kirthar

119

Table 5.1: Conditions for identification of bulk mineralogical composition of sandstones and clay separates.

Clay Mineralogy Conditions/Parameters Bulk Mineralogy Untreated

(ubh) Ethylene Glycol treated (eth)

Heated to 5000 C

Interval 2O 20-650 20-650 20-260 20-260 Goniometer Speed 1.80-2O/min 1.80-2O/min 1.80-

2O/min 1.80-2O/min

The speed corresponds to length of 0.020 2O with a counting time of 1 second/step. Voltage 45kV 45kV 45kV 45kV Current 40mA 40mA 40mA 40mA Program Long Long Long Long

Page 140: Cretaceous of Kirthar

120

millilitres of the established 2 micrometers-fraction is smeared onto a glass plate and

dried at room temperature. The plate shaped clay minerals will thus be oriented (with

001) parallel to the glass plate. These preparations are X-rayed as:

a. As it is (untreated “ubh”),

b. After treatment with ethylene glycol vapours in a desiccator for 24 hours at 600 C

(eth), and

c. After heating to 5000 C for one hour (opv).

5.3 BURIAL HISTORY

The burial history of Upper Cretaceous succession is difficult to establish

due to the complex tectonic history of the study area. Before collision of the

Indian and Eurasian Plates the Kirthar Fold Belt acted as passive margin till Late

Eocene. Major continental collision was initiated in Early Eocene and was

completed by Pliocene to Early Pleistocene times (Waheed and Wells 1990). In

Early-Late Cretaceous the western margin of the Indian Plate was separated from

Madagascar Plate and the Indian Plate started a rapid movement towards north

(Scotese et al. 1988, Gnos et al. 1997) with anticlockwise rotation towards

northwest. During this time the Indian passive margin was greatly affected by

active normal faults and fragmentation into basins of different bathymetry.

When the Indian Plate was passing over the Reunion Hot Spot during Late

Cretaceous, the Indian shield area to the east was thermally uplifted and huge

amount of sand-rich sediments were supplied to the margin and deposited as

Upper Cretaceous succession in a variety of tectonically controlled intra-slope

basins. During Paleocene a widespread transgression resulted in a reduction of the

supply of coarse terrigeneous clastics to the basin, and pelagic and hemipelagic

Page 141: Cretaceous of Kirthar

121

shale was deposited in the slope settings and the shallow marine Rani Kot Group

was deposited on the shelf. Emplacement of the Bela and Muslimbagh ophiolites

occurred on the western continental margin of the Indian Plate during Paleocene

(Alleman et al. 1979, Tapponier et at. 1981; Gnos et al. 1998). This affected the

margin and a flexural foreland basin started developing in the west while passive

margin sedimentation continued on the eastern margin in the form of Ghazij

shales and the shallow marine limestones of the Kirthar Formation. The studied

area was subsided and deep marine clastic sedimentation of the Nari Formation

took place in the Oligocene and piled up additional overburden. Final collision

between the Indian and Eurasian plates resulted in the uplift of the Himalayan

mountain belt on the northern margin and Sulaiman and Kirthar mountain belts on

the western margin. Compressional deformation continued till Pliocene -

Pleistocene and is recorded in imbricated thrust sheets in the Kirthar Fold Belt

(Niamatullah et al., 1986).

Then a major uplift caused exposure of the whole succession and much

erosion occurred, resulting in an unconformity between Gaj and the fluvial

Manchhar Formation (Pliocene). Manchhar Formation and Dada Conglomerate

were deposited in Pliocene-Pleistocene in estuarine and fluvial environments

respectively.

Exact rate and amount of erosion and deposition above Upper Cretaceous

succession is difficult to estimate on outcrops because of complex tectonics,

thrusting of ophiolites and variations in paleotopography of depositional basin

with time and space. Keeping in view the above facts, minimum burial depths are

Page 142: Cretaceous of Kirthar

122

estimated by present day overburden above Upper Cretaceous succession at

various locations in the study area based on Hunting Survey Corporation, (1960)

and Shah (1970) data and maps. Thus minimum burial depths range from 2710m

to 2916m and 2704m to 3252m in Northern and Southern Depositional Systems

respectively. Proximal depositional settings of both systems have slightly greater

burial depths.

5.4 DIAGENESIS OF SANDSTONE

5.4.1 Compaction

The sandstones of Upper Cretaceous succession were subjected to intense

mechanical and chemical compaction during its continuous burial as evidenced

from much loss in primary porosity and Intergranular Volume (IGV) of the

sandstones. The compaction effect in the sandstones is also evidenced by straight,

concavo-convex and sutured contacts (Fig. 5.1, 5.2 and 5.3) of neighbouring

framework grains. During compaction framework grains are sliding past each

other and packed into a tighter configuration. The grains were penetrated into one

another with increased force of overburden and chemical compaction. Initially all

sandstones were subjected to mechanical compaction till calcite cementation

occurred. Massive calcite cementation ceased the effect of mechanical

compaction. But the mechanical compaction continued in sandstones with little or

rare calcite as indicated by their lower IGV (Table 5.2).

5.4.2 Authigenic components

A variety of authigenic minerals are observed in thin section and SEM

microscopy including quartz, feldspar, calcite, dolomite, kaolinite, chlorite, illite,

Page 143: Cretaceous of Kirthar

123

Fig. 5.1: traight contact between neighbouringframework grains.Microphotograph of s (arrows)

Fig. 5.2: oncavo-convex contacts betweenneighbouring framework grains. Microphotograph of c (arrows)

Page 144: Cretaceous of Kirthar

124

Fig. 5.3: utured contacts between neighbouringframework grains.Microphotograph of s (arrow)

Fig. 5.4: Microphotograph of quartz overgrowth (arrows).

Page 145: Cretaceous of Kirthar

125

iron hydroxide, anatase, hematite and pyrite. Calcite, clay minerals, quartz and

iron hydroxide are the main cement types identified in sandstones with only minor

dolomite in few samples. The sandstones are mainly composed of

monocrystalline quartz, which shows excellent quartz overgrowths (Fig. 5.4).

Quartz is common cement in the sandstones and constitutes up to 12.4% of the

whole rock volume as shown by the point counting results (Appendix 4.1). The

amount of quartz overgrowth may be under estimated because of the small size of

some overgrowths and because of unrecognizable boundaries between some

overgrowths and their detrital core in thin section. In porous sandstones quartz

overgrowths are generally euhedral and tend to be elongated in the direction of C-

axis (Fig. 5.5).

Quartz overgrowths are common throughout the formation, laterally and

vertically. The excellent overgrowth crystals were developed preferentially in

sandstones of shoreface facies depositional setting, where calcite is poorly

precipitated. Large euhedral quartz overgrowths were formed in clean sands with

detrital cores sometime outlined by dust rings (Fig. 5.4). Authigenic quartz

formed overgrowths on detrital grains, where surfaces of quartz grains were free

or only partially coated by clay. The presence of clays, such as kaolinite, illite and

chlorite modified overgrowth habit of quartz. Quartz commonly nucleates on

clean, clay free parts of the detrital grain surface and then grows outward and

laterally to form overgrowth. Thus, irregular quartz cementation (Fig. 5.6) has

resulted where the presence of clay obstructed the complete quartz overgrowth.

Early calcite matrix (micritic calcite) reduced the primary porosity and prevented

Page 146: Cretaceous of Kirthar

126

Fig. 5.5: SEM image of quartz overgrowth along C-axis (arrows).

Fig. 5.6: SEM Photograph of quartz overgrowth obstructed by early forme clay minerals (arrows).

Page 147: Cretaceous of Kirthar

127

quartz cementation. During diagenesis sediments were subjected to different

conditions which might activate sources of silica for quartz cementation, such as

dissolution of feldspar (Hawkins 1978), pressure solution (Bjørlykke et al. 1986;

Houseknecht 1988; Dutton and Diggs 1990; Bjørlykke and Egeberg 1993; Dutton

1993; Walderhaug 1994), replacement of quartz and feldspar by calcite (Burley

and Kantorowicz 1986) and transformation of clay (Hower et al. 1976; Boles and

Franks 1979). For every mole of K-feldspar altered to kaolinite, two moles of

silica are released and made available for cement (Siever, 1957). The extensive

dissolution of feldspar and volcanic lithic fragments and kaolinitization were the

potential sources of the silica for quartz cementation especially in early diagenetic

stages.

Feldspar is determined in some samples on XRD by 3.24Å peak (Fig. 5.7).

Albite showing 3.18Å reflection (Figs. 5.7, 5.8 and 5.9) and is thought to be

formed by albitization of Ca-Na plagioclase or/and Ca-plagioclase within

volcanic fragments. Albite is found in the interior of volcanic fragments as

plagioclase laths (Fig. 5.10), as determined by SEM-BSC and EDAX. No such

type albite was observed in those samples which are lacking volcanic fragments.

Calcite is the most dominant cement in the sandstone and it ranges from

traces to 31.4 % (Appendix 4.1). It is found in sandstones as both primary

(micrite) and authigenic (sparry). The micritic calcite is yellowish brown in colour

under cross polarized light. Calcite is detected by presence of strong 3.03Å

reflection on X-ray diffractogram (Fig. 5.11) in all samples (except sandstones of

shoreface facies), covering all depths. Calcite occurs as intergranular cement and

Page 148: Cretaceous of Kirthar

128

Plag

iocl

ase

6.56

12.2

5

4.18

3.34

13.0

3.24

3.18

4.25

Qua

rtzFe

ldsp

ar

Goe

thite

Qua

rtz

Mix

ed il

lite-

smec

tite

Mix

ed il

lite-

smec

tite

Mix

ed il

lite-

smec

tite

c = samples heated at 500 C0

b = samples treated with ethylene glycol

a = untreated samples

a

b

c

D-spacing (A)Fig. 5.7: X-ray Diffractogram showing peak positions of feldspar, mixed clay layers, goethite and plagioclase (albite) in untreated, ethylene glycol treated and heated to 500 C samples in clay separates.0

Page 149: Cretaceous of Kirthar

129

Illite

Illite Qua

rtz

Illite

Plag

iocl

ase

c = samples heated at 500 C0

b = samples treated with ethylene glycol

a = untreated samples

D-spacing (A)

a

bc

10.0

5.0 3.3

Fig. 5.8: X-ray Diffractogram showing peak positions of illite, plagioclase (albite), in untreated, ethylene glycol treated and heated to 500 C samples in clay separates.0

4.25

Page 150: Cretaceous of Kirthar

130

Quar t

z

Chlo

rite

Plag

ioclas

e

Chlor

ite

Chl

orite

Chl

orite

Qua

rtz

Chl

orite

D-spacing (A)

c = samples heated at 500 C0

b = samples treated with ethylene glycol

a = untreated samples

a

b

c

14.0 7.0

3.34 3.18

3.524.

7

4.25

Fig. 5.9: X-ray Diffractogram showing peak positions of chlorite and plagioclase (albite) in untreated, ethylene glycol treated and heated to 500 C samples in clay separates.0

Page 151: Cretaceous of Kirthar

131

Fig. 5.10: SEM image of albite showing plagioclase laths (arrows) within volcanic fragments.

Fig. 5.12: Photomicrograph of calcite replaced framework grains at margins (arrows).

Page 152: Cretaceous of Kirthar

132

Kao

linite

Goet

hite

Kaol

inite

Calc

ite

Dol

omite

Hem

atite

Qua

rtz

3.587.

1

4.18

3.34

3.03

2.89 2.

7

3.52

D-spacing (A)

Chlo

rite

a

b

c

c = samples heated at 500 C0

b = samples treated with ethylene glycol

a = untreated samples

Fig. 5.11: X-ray Diffractogram showing peak positions of kaolinite, goethite, dolomite, calcite and hematite in untreated, ethylene glycol treated and heated to 500 C samples in clay separates.0

Page 153: Cretaceous of Kirthar

133

as complete or partial replacement of detrital components. The etching, formation

of embayments and partial replacement of quartz during carbonate precipitation is

well known (Friedman et al 1976). Calcite replaced feldspar and quartz grains

partly or completely, mostly at their margins (Fig. 5.12). Locally these grains

were severely attacked and replaced by calcite, and replacement even penetrated

into the cores of grains (Fig. 5.13 and 5.14). Authigenic calcite has filled most

pores which were formed by dissolution of feldspar in many sandstone samples.

Minor dolomite rims (Fig. 5.15) were formed around altered volcanic

fragments in sandstones. It consists of rhombic shape crystals. During the

alteration and dissolution of volcanic fragments, Mg ions were liberated and

reacted to precipitate dolomite overgrowth on calcite cement into the dissolved

grain void. XRD shows 2.8Å peak confirming the presence of dolomite (Fig.

5.11). Little siderite in few samples are identified on X-ray diffractogram at 2.8Å

reflection (Fig. 5.8).

Authigenic clay minerals identified in sandstones are kaolinite, chlorite,

minor illite and mixed illite-smectite. Diagenetic clay minerals found in a wide

variety of morphologies in SEM. The presence of such clay minerals is confirmed

by SEM, BSC, EDAX and XRD.

Authigenic kaolinite is present in most studied sandstone samples. It

occurs as booklets and vermicular aggregates of stacked platelets as indicated by

SEM (Fig. 5.16). Kaolinite is the most frequent clay mineral, which is identified

at 7.1 Å, 3.58Å peaks (Fig. 5.11) on XRD. Both these peaks are strong and 3.58 Å

is the strongest (Fig. 5.11). These peaks were reduced on heating at 5000C

Page 154: Cretaceous of Kirthar

134

Fig. 5.13: Photomicrograph of calcite replaced the framework grains in core (arrows).

Fig. 5.14: SEM Photograph of calcite replaced framework grains in core (encircled).

Page 155: Cretaceous of Kirthar

135

Fig. 5.15: SEM photographs showing dolomite rim around volcanic fragmen

Fig. 5.16: SEM photograph showing kaolinite booklets (arrows).

Page 156: Cretaceous of Kirthar

136

confirming the presence of kaolinite. But it does not show variation when treated

with ethylene glycol and also not completely disappeared on heating at 5000C

(Fig. 5.11). Kaolinitized perthite shows its formation along cleavage planes (Fig.

5.17). It was formed after feldspar dissolution and occupies oversized, irregular or

elongated pores. Kaolinite is found within secondary pore spaces, which were

most probably formed by dissolution of feldspar, because some partially dissolved

fragments of feldspar still present in such pores. K-feldspar and plagioclase both

were altered to kaolinite in sandstone samples. Delicate euhedral booklets,

vermicular texture, high intercrystalline microporosity within patches of pore

filling kaolinite indicate an in situ diagenetic origin of the kaolinite (Hurst and

Nadeau 1995).

Chlorite occurs as grain-coating rims, rosette aggregates and in secondary

pores left by the dissolution of unstable grains like volcanic fragments and

feldspar (Fig. 5.18 and 5.19). It also partly replaces authigenic kaolinite. It is also

observed that complete chlorite coatings on quartz grains show rare quartz

overgrowths. Chlorite precipitated through the alteration (Anjos et al., 2003) and

dissolution of volcanic fragments (Klass et al., 1981) and alteration of a kaolinite

(Burton et al., 1987). Volcanic fragments may have contributed Mg, Fe and Si to

the precipitation of chlorite. Chlorite may be totally engulfed within later quartz

overgrowth. Presence of chlorite is confirmed by 14Å, 7Å, 4.7Å, 3.5Å and 2.83Å

reflections (Fig. 5.9). The 7Å and 3.5Å are strong peaks and 3.5Å being the

strongest. Chlorite is distinctly separated from kaolinite peaks. Heating at 5000C

and ethylene glycol treatments caused depression of 7Å and 3.5Å peaks, may

Page 157: Cretaceous of Kirthar

137

Fig. 5.18: SEM photograph showing chlorite (arrows) in BSC mode.

Fig. 5.17: SEM photograph showing alteration and and dissolution of feldspar grains (arrows).

Page 158: Cretaceous of Kirthar

138

Fig. 5.19: SEM photograph showing illite-smectite mixed layer in SEI mode

Fig. 5.20: SEM photograph showing brush and hairy illite (arrows).

Page 159: Cretaceous of Kirthar

139

suggesting some mixed clay layer. An important authigenic clay mineral illite is

found in clay separates of sandstones of Upper Cretaceous succession as

identified by SEM, BSC, EDAX and XRD. X-ray Diffractogram shows 10Å, 5Å

and 3.3 Å and 3.3 Å reflections (Fig. 5.8) indicating the presence of illite. Illite

shows hair like radially disposed crystals, fibrous and membraneous (Fig. 5.20)

types textures, which occur as pore filling and pore lining cement as proposed by

(Cocker et al., 2003). Illite occurred as pore filling among framework grains and

with quartz overgrowth. Illite may be formed diagenetically by a number of

processes. Among these the important ones are replacement of feldspar and

volcanic fragments particularly along thin cleavage planes and illitization of

kaolinite. These mentioned two causes were responsible in the formation of illite.

Mixed clay fractions with smectite are also observed in few samples in deeper

shelf facies associations. These mixed clays are identified with XRD by 12.25 Å,

13 Å, 6.56 Å and 3.8 Å peaks (Fig. 5.7). These may be illite-smectite and/or

chlorite-smectite fractions.

Rhombohedral crystals of anatase (Fig. 5.21) are observed in sandstones

of Upper Cretaceous succession. Anatase is found as trace amount and present in

the pore spaces among the framework grains. The titanium oxide in pure quartz

arenite is present in a small amount. It is suggested that the titanium ions needed

for the formation of the authigenic titanium oxides are mainly derived from in-situ

alteration of detrital Fe-Ti oxide grains. Biotite was also a possible source of Ti

ions (Mader 1980; 1981; Turner 1980), for the formation of anatase in sandstones.

The presence of anatase within pores slightly reduced the porosity of sandstones.

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Fig. 5.21: SEM photograph showing anatase (arrows) well developed crystals

Fig. 5.22: SEM photograph showing hematite (arrows).

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Minor hematite occurs in the sandstones as small ball like clusters (Fig. 5.22) and

in the intergranular space among framework grains. Hematite is identified by 2.7Å

reflection, which is not much effected by either by glycol treatment or heating on

5000C. The iron released from the alteration of Fe-Ti oxide grains may have

crystallized as hematite in the sandstones. Pyrite is less commonly present in

sandstones as framboidal and cubic crystals (Fig. 5.23). Scattered distribution of

pyrite cubes in calcite cement within a shell indicates the formation of pyrite prior

to the precipitation of calcite cement. Pyrite probably was an early diagenetic

product and probably formed during the sulphate reduction phase. Hematite and

pyrite have no significant influence on reservoir characters of sandstone of Upper

Cretaceous succession.

The iron oxide and iron hydroxide cements vary from trace to 27.2% in

sandstones of Upper Cretaceous succession (Appendix 4.1), although most of

sandstones are not rich in these cements as observed in thin sections and SEM

studies. It occurs as interstitial pore filling which completely filled most pores

reducing sandstone porosity. It also occurs as rosette forms (Fig. 5.24) and are

distributed randomly (Fig.5.25) or concentrated in clusters. Goethite is common

iron mineral in clay fraction of sandstones as determined by 4.18Å reflection

(Figs. 5.7 and 5.11). Goethite is differentiated from hematite by a 4.18Å or/and

4.19Å peak, which disappeared on heating at 5000C (Figs. 5.7 and 5.11). Pre-

existing unstable iron bearing materials were altered and caused the precipitation

of iron cement. These cements are quite rich in proximal depositional setting of

Southern depositional System which shows fluvio-deltaic environments. It can be

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Fig. 5.23: SEM photograph showing pyrite (arrow) within a shell.

Fig. 5.24: SEM photograph showing iron oxide/hydroxide with rosette structures (arrows).

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concluded that iron oxide and hydroxide were formed in oxidizing environmental

conditions as primary constituents of sandstones. During Eocene-Pleistocene

time, the area was strongly affected by uplift, folding and faulting. Such uplift

caused migration of water to iron rich zones originating iron oxide/hydroxide

cements in later stages. A minor origin of iron oxide/hydroxide cements might be

the liberation of iron ion by alteration of some Ti-Fe oxides rich minerals and

volcanic fragments. Some iron rich lath types crystals were also seen in SEM

(Fig. 5.26) which might be later dissolved, may probably due to containing

unstable impurities. Iron oxide replaced nearly all older cements in sandstones, so

is later stage cement (Fig. 5.27).

5.4.3 Microfractures

Sandstone grains were intensely fractured in some sections. Such a grain

fracturing reveal a large stress, and it could be caused by uplift and were thrusting

of Bela Ophiolites. The grain fracturing was not a result of burial compaction as

indicated by least grain fractures in sandstones with great burial depths 2916 and

3252 m, farthest away from the ophiolite thrust (sections 1,2,3 and 11; Fig 2.3).

The Bela Ophiolites obduction were responsible for various thrust faults present

in the study area. The Bela ophiolites were thrusted over the Paleocene Rani Kot

Group and Maastrichtian Pab Formation (Upper Cretaceous succession) in

westernmost (distal) part of the study area and buried all the younger rock units

under thrust. This controls the intense fracturing of framework grains in

sandstones. As the distance from the ophiolites increases, the intensity of grain

fracturing reduces, which indicate the tectonic origin of grain fracturing in

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Table 5.2: Showing burial depths (B. Depth), mean porosity (n), Intergranular Volume (IGV) and depositional settings of Upper Cretaceous succession. S. NO B. Depth Mean

n.% IGV Depositional setting

Northern Depositional System 1-19 2893m 7.42 20.2 Shoreface facies association 2-2 2916 m 8.70 17.0 Shoreface facies association 5-2 2792 m 9.96 24.0 Shelfal delta lobe facies

association 5-8 2710 m 9.25 19.6 Shelfal delta lobe facies

association 6-2 2812 m 8.04 34.0 Shelfal delta lobe facies

association 6-5 2747 m 8.59 29.0 Shelfal delta lobe facies

association 7-1 2825 m 7.63 34.2 Deeper shelf facies association 7-7 2757 m 9.51 23.0 Deeper shelf facies association 8-1 2835 m 7.84 33.8 Shelfal delta lobe facies

association 8-5 2790 m 10.61 34.6 Shelfal delta lobe facies

association 9-2 2743 m 2.77 25.2 Deeper shelf facies association 10-1 2824 m 10.11 20.2 Deeper shelf facies association

Southern Depositional System 11-3 3252 m 8.52 22.2 Fluvio-deltaic facies association 11-5 3185 m 10.30 14.8 Fluvio-deltaic facies association 13-3 2754 m 9.47 6.2 Submarine slope channels-fan lobe

facies association 14-7 2704 m 6.98 24.2 Submarine slope channels-fan lobe

facies association 16-5 2765 m 6.74 33.0 Submarine basin floor and slope

fan lobes and channels turbidites. 18-1 2777 m 8.83 15.2 Submarine basin floor and slope

fan lobes and channels, turbidites. 19-2 2760 m 3.29 10.2 Submarine basin floor and slope

fan lobes and channels, turbidites. 20-1 2780 m 6.65 26.2 Basin floor fan lobe facies

association

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Fig. 5.25: SEM photograph showing randomly oriented (arrows) iron oxide/hydroxide.

Fig. 5.26: SEM photograph of iron oxide laths showing little dissolution (arrows)

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sandstones. Sandstones located away from the ophiolite thrust are unfractured,

even some with rare/little calcite, high remnant porosity and buried at great depths

(3166m) (Table 5.2). On the other hand the samples with less burial depth

(2743m) and high calcite cement located near the ophiolites were severely

fractured. The major fractures were perpendicular to stress axis with some

diagonal, irregular microfractures were also resulted due to brittle behaviour of

quartz (Fig. 5.28 and 5.29). Minor later stage dissolution of framework grains and

calcite cement (particularly along some fractures) (Fig. 5.30) occurred due to

uplift and flushing of meteoric waters.

5.4.4 Paragenetic sequence

The inferred paragenetic sequence of sandstones of Upper Cretaceous

succession is indicated in Table-5.3. The sandstone has undergone intense and

complex episodes of diagenesis, including eogenesis, mesogenesis and telogenesis

due to influence of depositional environment, deep burial and uplift. The

paragenetic sequence is inferred with respect to time by SEM, XRD and thin

section studies. The major diagenetic events include early mechanical

compaction, dissolution of unstable framework grains like feldspar and volcanic

fragments, kaolinitization, chloritization, quartz, carbonate and iron oxide /

hydroxide cementation, chemical compaction, illitization, pyrite, hematite and

anatase formation.

Earliest diagenetic event was formation of pyrite followed by early

mechanical compaction. Compaction can be shown by tight grain supported fabric

of sandstones. The compaction continued in all sandstones till the precipitation of

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Table 5.3: Paragenetic sequence of sandstones of Upper Cretaceous succession.

Relative Timing Event Early Late

Mechanical Compaction Dissolution of feldspar and volcanic fragments Kaolinite Chlorite Chemical compaction Quartz cement Illite Calcite Dolomite Grain fracturing Iron Oxide Dissolution

––––––––––----------––––––––––– –––––––––––––------ ---––––––––––––––– -----––––––––––––––– ––––––––––––––------- ––––––––––––––––––––– ----––––––––––------------- --------––––––––––––––––– ----––––– –––––------ ––––––––– ----––––---

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Fig. 5.27: SEM photograph of late stage iron oxide/hydroxide (arrows) into early formed calcite cement.

Fig. 5.28: Photomicrograph of microfractures (arrows) in framework grain

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M a x i m u m S t r e s s

M a x i m u m S t r e s sFig. 5.29: A sketch of microstructures in framework grains perpendicular to maximum stress axis (same thin section as in Fig. 5.28).

Fig. 5.30: SEM photograph showing dissolution (arrows) of calcite along microfractures.

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massive calcite in some sandstones prevented further compaction and continued

upto late stages in those sandstones with little/rare calcite cement. Mechanical

compaction continued from early to late diagenetic stages particularly in

sandstones showing shoreface facies depositional environment. Mechanical

compaction can be observed by physical breakdown of feldspar grains (Fig. 5.31).

The dissolution and alteration of unstable grains like feldspar and volcanic

fragments to kaolinite was the second important diagenetic event in terms of

relative timings. Partial to complete kaolinitization of feldspar took place. The

kaolinite is not replacing any other authigenic product and is absent in secondary

microfractures in framework grains indicating its in situ origin at the former

position of feldspar grains in most cases, but some exceptions of non

kaolinitization can be observed even in cracked feldspars, which show partial

dissolution. The chlorite was formed in next stage of diagenesis. Chlorite is found

in samples rich in volcanic fragments, which indicate that it is an alteration

product of such fragments. This is an earlier diagenetic product than quartz

cementation because it obstructed the quartz overgrowth.

Then quartz cement started to precipitate in the available pore space

provided by the dissolution or kaolinitization and chloritization of feldspar and

volcanic fragments. It is indicated by infiltration and penetration of quartz cement

in pores and its growth effected by presence of some earlier formed kaolinite and

chlorite (Fig. 5.6). Because chemical compaction was active at that time, pressure

solution may have provided the silica for quartz cementation. The presence and

growing of illite on kaolinite shows its later origin. The growth of illite over

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kaolinite indicates its later origin than kaolinite. Another major and important

episode of diagenesis of sandstones was the precipitation of most abundant calcite

cement. The calcite post dates of all the above mentioned diagenetic events and

products. The calcite cements penetrated in all available pores among framework

and earlier authigenic components. The calcite infiltered into kaolinite booklets

(Fig. 5.32) and stopped further quartz cementation are the evidences of its later

origin. It also filled microfractures redistributed to ophiolite thrusting (Fig. 5.28).

Minor and less common dolomite was formed after calcite, however it is found in

a minor amount in some sections.

The iron oxide and hydroxide were precipitated in the last stages of

diagenesis. These replaced and engulfed earlier diagenetic products particularly

calcite cement. The iron oxide cement observed in deep seated (approximately

3252m) samples is suggested to be the product of telogenesis. Some dissolution of

calcite along fractures (Fig. 5.30) and impurities in iron rich laths (Fig. 5.26)

caused in later stages have created some secondary porosity in sandstones but it is

not common.

5.5 RESERVOIR CHARACTERISTICS

Reservoir characters of the sandstones were most likely to be affected by

burial diagenesis. Sandstone reservoir quality is largely determined by diagenetic

processes that either reduce or enhance porosity. For instance mechanical

compaction and authigenic cements reduced the porosity and permeability,

whereas, dissolution of unstable framework grains and soluble cements (Burley

and Kanotorowicz 1986) increased porosity in sandstone. Although the latter

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Fig. 5.31: SEM photograph of physically fractured feldspar grains (within ellipse

Fig. 5.32: SEM photograph showing calcite penetration within early formed kaolinite booklets (arrows).

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process is not much common but it is important process active laterally especially

where early calcite cement was not formed. The porosity was influenced by

Mesogenetic calcite cementation, compaction and dissolution. Sultan & Gipson

(1995), in their petrographic study of broadly coeval succession in the Sulaiman

Fold Belt, obtained slightly higher estimates (0 – 16 %, mean approximately 9 %).

They pointed out that primary porosity was originally much higher but has been

greatly reduced by successive phases of cementation, mechanical compaction

during diagenesis.

Two dimensional estimation of porosity in sandstones is carried out by

using Adobe Photoshop to SEM images and point counting of few thin sections

stained with blue epoxy. The porosity in sandstones is up to 15.53 %. The present

porosity of the sandstones varies from 3.50 to 15.53 %, averaging 8.06 %. The

primary porosity of the sandstones is reduced appreciably due to intense

mechanical compaction and due to filling of early authigenic cements such as

calcite, clay minerals, quartz and iron oxides.

The initial porosity was reduced by mechanical compaction. Porosity

reduction was continued due to mechanical compaction in sandstones with little

or rare calcite. The mechanical compaction and intergranular pressure solution

decreased intergranular volume (IGV) of sandstones, which ranges from 7.88% to

21.53% (Table 5.2). The intergranular pressure solution is a well known

phenomenon of reducing porosity in sandstones by compaction. Grain supported

fabric, long and sutured contacts between neighbouring framework grains of the

sandstones were resulted due to intense mechanical compaction and is more

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intense in sandstones with rare or poor calcite cement. The rapid burial was

responsible for reduction in porosity due to compaction. Calcite matrix (micrite)

has reduced the compaction effect and prevented the close packing of framework

grains in some samples. The mesogenetic calcite cement reduced and ceased the

mechanical effect in porosity reduction but its massive precipitation decreased

porosity in sandstones (Fig. 5.33) appreciably.

Kaolinitization and chloritization also played an important role in either

deteriorating or preservation of porosity in sandstones. Large amount of

authigenic kaolinite and chlorite have reduced the permeability but preserve the

intercrystalline porosity and formed rims around to prevent the inclusion of quartz

and calcite cements. Micropores in interbooklets of kaolinite are common in

sandstones.

An appreciable amount of dissolution of unstable grains occurred during

diagenesis of sandstones. The dissolution of feldspar and volcanic fragments in

early and late diagenetic stages created of secondary porosity in sandstones (Figs.

5.34, 5.35). The early secondary porosity was partly filled by later authigenic

cements most commonly calcite, quartz and clay minerals. It is thought that the

sandstones with comparatively little calcite cement retained secondary porosity in

sandstones. The late stage episode of dissolution of grain, calcite cement and to

little extent iron oxide laths, have created little secondary porosity.

Dissolution can occur at shallow depths by meteoric groundwater

(Bjørlykke 1984; Mathisen 1984) or at greater depths by fluids produced during

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Fig. 5.33: SEM photograph of massive calcite cementation (arrows) which reduced porosity of sandstone.

Fig. 5.34: SEM photograph of dissolution (arrows) of unstable framework grains enhanced porosity in sandstone.

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Fig. 5.35: Photomicrograph of late stage dissolution (arrows).

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diagenesis of organic matter or clay minerals (Seibert et al. 1984; Surdam et al.

1984). The dissolution of unstable framework grains was started in early stages of

diagenesis which produced an empty pore volume for secondary cementation and

some pore were still existed and prevented by clay coats. Another episode of

dissolution occurred at greater depths in late stages and dissolved authigenic

minerals and caused secondary porosity.

Reservoir characters are largely concerned with the regional distribution

of attributes, like total thickness and percentage of sandstones together with the

internal architecture, heterogeneity and geometries of major sand bodies and their

constituent facies (Khan et al., 2002). Thick sandstones packages showing

massive, trough cross bedded, hummocky cross stratified, submarine channels and

slope fan lobe facies bear higher porosity values. The sandstones packages attains

great thicknesses in the submarine slope channels-fan lobe complexes (sections

13, 14, 15,16,17 and 18; Fig. 2.3 ) and in the shelfal delta lobe facies association

(Sections 5, 6 and 8) of the Southern and Northern Depositional systems

respectively. The sandstone percentage is the highest in shoreface facies

association (sections 1 and 2) followed by shelfal delta lobe facies association

(sections 5,6 and 8) and submarine slope channels-fan lobe succession (sections

13, 14, 15, 16, 17, and 18). Deeper shelf facies association bears the lowest sand

percentages (estimated 35%; section-7) and basin-floor fan lobe facies

associations (section-20). The nature and geometry of the sandstone bodies show

great variations in such facies associations. Sandstones are thick & cross-bedded,

lenticular to slightly tabular in section1 & 2 (shoreface facies association).

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Whereas, the sandstones in mid shelf and submarine slope channels-fan lobes

complexes (sections 5, 6, 8, 13, 14, 15, 16, 17 and 18) are arranged in a stacked

pattern and laterallt continuous for hundreds of meters. The vertical and lateral

connectively of these sandstone packages is favourable and convincing. But

intense bioturbation (burrows), has obscured texture, structures and original

boundaries of some of these compound bodies particularly in sections 5, 8, 9 and

10. The deep marine channels and slope fan lobe complexes in Southern

Depositional System (sections 13, 14, 15, 16, 17, and 18) are laterally continuous

for hundreds of meters on the outcrops. Strongly amalgamated and thickening

upward packages exhibit good vertical connectivity. Thick, massive and

hummocky cross stratified sandstone of the shelfal delta lobe successions in the

Northern Depositional System show the most convincing internal architecture,

external geometries and lateral/vertical connectivity. Lateral and vertical

interleaving of these bodies with finer grained shelf sediments also offers

additional potential for fluid trapping and sealing, augmented in the basal parts of

these sequences by local channelling into the fine grained substrate (Khan et al.,

2002).

It is concluded that coarse grained, well sorted, amalgamated and thick

packages of sandstones are more porous and have a good lateral and vertical

connectivity. The submarine channels and slope fan lobes and shelfal delta lobe

facies associations are thought to be better resources in future, whereas, mud-marl

dominated and bioturbated sandstone facies have poor reservoir characters. The

sandstone rich, amalgamated, laterally extensive packages of the succession with

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better vertical connectivity are thought to be the good future prospective for

hydrocarbon exploration.

5.6 SUMMARY

Diagenetic signatures observed in sandstones of Upper Cretaceous

succession include compaction, cementation, grain fracturing and dissolution.

Sandstones composition, burial depth and uplifting were the factors which

influenced the diagenetic modifications. Major authigenic cements are calcite,

quartz, iron oxide/hydroxide and clay minerals. The paragenetic sequence is

identified with relative diagenetic timings. The feldspar and volcanic fragments

were severely affected during diagenesis as shown by their intense dissolution and

alteration to clay minerals. Early-Late dissolution of framework and authigenic

minerals/cements has created secondary porosity in sandstones. Compaction and

calcite cementation were the main causes of deterioration of porosity in

sandstones. The Bela Opiolite thrusting was responsible for grain fracturing.

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CHAPTER-6

DEPOSITIONAL MODEL

6.1 INTRODUCTION

The characteristics of sandstones such as composition, facies associations

and distribution and clearly indicate that the sediments of the Upper Cretaceous

succession (Maastrichtian-Late Campanian) in Kirthar Fold Belt Pakistan were

deposited in deltaic shelf in north and deep marine turbidites in south (Fig. 6.1).

Basin floor topography controlled the deposition in two coeval depositional

systems. The paleoflow directions show that the sediments were supplied through

different routes but from the same source rocks (Indian Craton). Prior to the

deposition of the Upper Cretaceous sediments the upper shelf area of the western

passive margin of the Indian Plate was covered by shallow marine mudstone and

marl, while the lower shelf (and part of the slope?) was blanketed by pelagic marl

of relatively deep marine characters (Khan et al., 2002). This indicates that the

sediments of the Upper Cretaceous succession were formed during a regressive

and upwards shallowing episode. This regression appears to have commenced

with the deposition of the Upper Cretaceous succession and extended up to the

end of the Eocene, followed by transgression in the east that allowed deposition of

the sandy turbidites of the Nari Formation (Khan et al., 2002).

6.2 NORTHERN DEPOSITIONAL SYSTEM

The rocks in the north show a lateral transition from shoreface through

shelfal delta lobe sandstones to outer shelf sandstones. This shows that sediments

of Upper Cretaceous succession were deposition on a low angle shelf (Fig. 6.1).

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Southern Depositional SystemNorthern Depositional System Fluviodeltaic facies association

F

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Deep marine sediments (such as lope or basin plain) are absent in Northern

Depsositional System. Deeper slope deposits may be disguise in the western part

by overlying thrusted Bela Ophiolites, which were emplaced from the west

following the deposition of Upper Cretaceous succession and the overlying Late

Paleocene sediments.

What was the mechanism by which the sand was carried offshore down a

relatively low gradient shelf? It is widely agreed that sand may be transported

across the shelf in density currents and that these currents can be generated by

storm ebb flows (Goldring and Bridges, 1973; Brenchley et al., 1979; Hamblin

and Walker, 1979; Dott and Bourgeois, 1982; Rice, 1984), or off river mouths at

times of catastrophic flooding (Swift, 1976; Sparks et al., 1993; Mulder and

Syvitski, 1995; Mutti et al., 1996; 2000), or they may be generated by slumping

on high internal slopes (Walker, 1984; 1985).

The common characters of the sandstones of Upper Cretaceous succession

in the north (dominance of trough cross bedding, parallel lamination, bioturbation

and some hummocky cross stratification in the east, and abundance of coarse,

rarely pebbly, massive sandstone with scoured bases and hummocky tops, graded

sandstone and rare bioturbated sandstone in the west) all indicate deposition from

energetic, very high density unidirectional currents, episodically influenced by

storm reworking and suspension (Khan et al., 2002).

The storm processes were played an important role in the deposition of

sediments of Upper Cretaceous succession. The association of bioturbated

sandstone facies and hummocky sandstones with parallel lamination was formed

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by storm reworking and suspension. The thin, lenticular, graded sandstones with

parallel and cross lamination and sole marks may also have resulted from storm

reworking followed by suspension and traction from the sediment clouds

(Reineck and Singh, 1972; Nelson, 1982). Very thick, massive sandstones (F3)

have been generated solely by storm reworking. An alternative sediment supply

mechanism seems to be necessary for the deposition of such units and the most

plausible mechanism is river-fed hyperpycnal flow, which can transport sediment

directly from the coastline into the offshore region (Mulder and Alexander, 2001;

Kassem and Imran, 2001).

Turning to ancient sequences, Mutti et al., (1996; 2000) have interpreted

the sand-rich shallow marine Eocene strata of the south-central Pyrenean foreland

basin as “flood generated delta-front sandstone lobes” and invoked hyperpycnal

flows rather than storm reworking, as the transport mechanism for such

sequences. It is considered that such flows, operating on the shelf of the

northwestern margin of the Indian Plate in Late Cretaceous time, offer the most

plausible mechanism for most of the thick massive sandstones in Upper

Cretaceous succession. Some of these hyperpycnal flows were relatively of high

density and initially capable of localized erosion as confirmed by the presence of

large grooves and some flutes at the base of some massive sandstone beds.

Moreover, it has been argued that such flows are capable of transporting sands

even on relatively gentle slopes (Kneller and Branney, 1995; Mulder and

Alexander, 2001). Density flows were non-erosive and traveled offshore at low

speeds due to the gentle slope of the shelf as evidenced from the absence of large

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channels (except from small chutes in lower portion of the succession). The

variations in bed thickness of these massive sandstones may indicate fluctuations

in the intensity of the floods that supplied sediment to the sea. Deposition of very

thick beds was probably caused during catastrophic flood events resulting in high

sediment discharge at sufficient velocities to generate hyperpycnal flow and

related self-sustained turbidity currents (Khan et al., 2002). Normal marine

conditions were prevailed as indicated by the presence of the mudstone and marl

interbeds after the discontinuance of the flood/storm conditions. Rare presence of

graded sandstones (F7 and F8) interbeds is an evidence of low-density

hyperpycnal flows/storm-generated turbidity flows were responsible for

deposition. River flooding apparently was often accompanied by storm waves,

which produced hummocky bedforms at the top of the massive sandstone and

graded sandstone beds (Mutti et al., 1996; 2000).

6.3 SOUTHERN DEPOSITIONAL SYSTEM

The sandstones of Upper Cretaceous in Southern Depositional System

consist of different Bouma divisions and showing thickening and thinning upward

cycles various parts through vertical sections. These clearly indicate deeper-water

turbidity current deposition and can best be assigned to a sand-rich submarine fan

turbidite system (Khan et al, 2002; Eschard et al, 2004) formed in tectonically

influenced closed basin (Figs. 6.1,6.2).

Based on composition of sandstones and contrasting depositional style, the sand-

rich turbidite system can be divided into two systems termed as Mughal Kot

Turbidites and Pab turbidites.

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Fig. 6.2: Field photograph showing synsedimentary normal fault (ellipse), section-9

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6.3.1 Mughal Kot Turbidites

Following depositional components of submarine fan system can be

recognized within the Mughal Kot Turbidites:

(1) Sand rich basin floor lobes and their bypass surfaces

(2) sandy channel-levee complexes

(3) Mud-rich lobes

The sand-rich basin floor lobes (Fig. 6.3) were formed in the distal part of the

system (north), lapping directly on Parh Limestone of slope origin. These lobes

are 5m to 12m thick in the proximal part and grades into mudstones in the distal

part. The sand-rich material was delivered through high efficient submarine

canyon, incised in the Parh slope limestone bypassing the slope (Eschard et al.,

2003). Sandstones are medium to coarse grained, thin to medium bedded, laterally

continuous (Fig. 6.4), well graded, occasional parallel laminated showing Ta, Tab

Bouma sequences. These sandy lobes are well developed in distal most part

(section-20) and extend proximally to section-16. Incised channel deposits are

most proximal equivalents of these basin floor lobes and are pinch out just south

of section-15. Sandy channels overly the basin floor lobes. Deeply incised

channels were filled with coarse to pebbly sandstones. Channels show thinning

upward (Fig. 6.5) trend in vertical section. Hemipelagites are present between the

submarine channelized packages. The channels in lower part have well developed

fan lobes in distal settings, whereas, in upper part they are lacking well developed

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Fig. 6.3: Field Photograph showing basin floor-lobes of Mughal Kot Turbidites, section-20 (line across strike).

Fig. 6.4: Field photograph showing laterally continuous beds (line), section-16, person encircle for scale

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lobes. Channels are highly erosive, amalgamated and aggradational showing high

energy flow conditions, which evidenced bypass processes.

Then backstepping of basin was occurred as indicated by the deposition of

thick mud rich lobes (Figs. 6.6, 6.7 and 6.8) over sandy channels. Thick

mudstones with subordinate marls show that the sand deposition ceased and finer

sediments were deposited mostly by low energy flows. These mud rich lobes are

well developed in the Sandh Dhora and Jakker Lak (section-15 and 16), where

they are upto 150 m thick. This changed the morphology of the slope from steep

slope to gentle.

6.3.2 Pab Turbidites

Due to thermal uplifting of the source area (Indian shield) caused by

passage of Indian Plate across major “hot spot” (Smewing et al., 2002; Gnos et

al., 1998), sufficient sands were supplied to basin and deposited in submarine

slope fan, characterized by slope channels with associated lobes and overall

shallowing up trend. Well developed fan lobes show tabular, laterally continuous

beds with thickening upward trend (Figs. 6.9 and 6.10). The sandstones are fine to

coarse grained, thin to thick bedded, graded, parallel to cross laminated showing

Tabc, Tab Bouma sequences. The channel sandstones are coarse to pebbly, thick

bedded, highly amalgamated, lenticular, highly erosive and very rich in mud

clasts. Erosive surfaces of these sandstones suggest high energy conditions of

turbidity. Slumping are common phenomena in these successions which indicate

collapse of the channel margin. These channels show thinning upward trend (Fig.

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Fig. 6.5: Field photograph showing view of thinning upward (arrow) trend, in Mughal Kot Turbidites, section-15.

Fig. 6.6: Field photograph of channels (arrows) within mud rich lobes of Mughal Ko Turbidites, section-16.

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Fig. 6.7: Field Photograph showing mud rich lobes and channels (C)-levee (L) in Mughal Kot Turbidites, section-16.

Fig. 6.8: Field photograph showing individual channel (arrow) within mud rich lobe of Mughal Kot Turbidites, section-16.

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Fig. 6.9: Field Photograph of thickening upward cycle (arrow) of slope-fan lobes o Pab Turbidites, section-15.

Fig. 6.10: Field Photograph showing laterally continuous beds of Submarine slope fan lobes of Pab Turbidites, section-15.

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Fig. 6.11: Field Photograph showing view of thinning upward cycles (arrows) of Pab Turbidites, section-15, man encircled for scale.

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6.11). Hummocky type beds are common in the upper part of the sections which

is attributed to remolding by high energy, high density unidirectional currents

(Pave and Duke, 1990). In proximal setting feeder channels are composed of

pebbly to very coarse grained sandstone and marked by any well developed lobes

(section-13).

6.4 Summary

Distribution of the facies and facies associations and paleocurrent

directions indicate that the deposits of the Upper Cretaceous Kirthar Fold Belt

were formed in two different, partly coeval depositional systems. The sediments

of the Northern Depositional System were deposited in shallow marine conditions

on a broad, delta fed clastic ramp dominated by Mutti-Type deeper shelf lobes. It

shows transitional variations from shoreface to outer shelf settings from east to

west with prominent westward paleoflow. The sediments of the Southern

Depositional System were deposited into submarine fan system. The lower part of

the system (Mughal Kot Formation) represents basin floor lobes, channel filled

sand-bodies and base of slope mud-rich lobes while the upper part is comprised of

sand-bodies showing characters of slope channels and associated lobes. Sandstone

composition and paleocurrent directions show that the material of the Upper

Cretaceous succession was supplied from the Indian Craton (east-southeast)

through different courses.

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CHAPTER 7

CONCLUSIONS

This study led to following conclusions:

1. Two different depositional systems occur within the Upper Cretaceous

succession of the Kirthar Fold Belt Pakistan. The Northern Depositional

System consists of shallow marine deposits ranging from shoreface facies

(proximal, east) to outer shelf facies (distal, west). These deposits were the

product of episodic storm waves and high density, westward flowing

hyperpycnal flows, which were produced at the mouth of rivers during

intense catastrophic flooding conditions. Material was supplied to the

basin from the uplifting Indian Craton to the east. Deep marine turbidites

are found in the Southern Depositional System. This sandstone rich

succession was formed as a result of high density currents towards north,

and/or slightly northwest. The lower part (Mughal Kot Formation) of the

Southern Depositional System was deposited in channel-levee and basin

floor lobes complex. The upper part (Pab Formation) of the system was

deposited in slope fan lobes and associated channels.

2. The existence of two contrasting depositional systems indicate complex

physiography with at least two different basins separated by structural

high and this complex sea floor morphology is the consequence of tectonic

activity that has affected the western margin of Indian Plate during its

northwards drift in Cretaceous times.

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175

3. The Upper Cretaceous succession was formed during regression as

marked by an overall shoaling trend. This is evidenced by overall

thickening upwards trend, increase of grain size, frequency of hummocky

bed-forms and vertical facies variations. The abrupt influx of these sands

was caused by uplifting of the Indian Craton when it was passing across a

major ‘hot spot’.

4. Compaction and complex cementation have occluded much of the primary

porosity in these Upper Cretaceous sandstones. However, the reservoir

potential of these rocks is also related to original depositional

environment. For example, the coarse grained, well sorted, amalgamated

and thick packages of sandstones of submarine channels and slope fan

lobes and shelfal delta lobe facies are more porous and have a good lateral

and vertical connectivity. Secondary porosity created by dissolution of

unstable minerals and primary cements (most commonly; feldspar and

volcanic fragments).

5. The scarcity of feldspar was caused by intense chemical weathering due to

warm and humid paleoclimatic conditions in source area and followed by

long distance transportation and diagenesis.

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