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.
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
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
I
CONTENTS Page No.
LIST OF CONTENTS I LIST OF FIGURES V LIST OF TABLES XIV LIST OF APPENDICES XIV ACKNOWLEDGEMENT XV ABSTRACT XVI
CHAPTER 1- INTRODUCTION 1 1.1 AIMS AND OBJECTIVES OF THE STUDY 1 1.2 LOCATION AND ACCESSIBILITY 3 1.3 PREVIOUS WORK 4 1.4 METHODS OF STUDY 5
CHAPTER 2- GEOLOGIC SETTING AND STRATIGRAPHY 6 2.1 GEOLOGIC SETTING 6 2.2 STRATIGRAPHY OF THE KIRTHAR FOLD BELT 12 2.2.1 Ferozabad Group 12 2.2.1.1 Kharrari Formation 14 2.2.1.2 Malikhore Formation 15 2.2.1.3 Anjira Formation 15 2.2.2 Parh Group 16 2.2.2.1 Sembar Formation 16 2.2.2.2 Goru Formation 18 2.2.2.3 Parh Limestone 19 2.2.3 Mughal Kot Formation 22 2.2.4 Pab Formation 23 2.2.5 Rani Kot Group 25 2.2.5.1 Khadro Formation 25 2.2.5.2 Bara Formation 26 2.2.5.3 Lakhra Formation 27 2.2.6 Ghazij Formation 29 2.2.7 Kirthar Formation 30 2.2.8 Nari Formation 30 2.2.9 Gaj Formation 31 2.2.10 Manchar Formation 32 2.2.11 Dada Conglomerate 33
CHAPTER 3 - FACIES DESCRIPTION, INTERPRETATION AND 34 DISTRIBUTION 3.1 INTRODUCTION 34 3.2 FACIES DESCRIPTION AND INTERPRETATION 36 3.2.1 Trough Cross-bedded Sandstone Facies (F1) 36 3.2.1.1 Description 36 II
3.2.1.2 Interpretation 36 3.2.2 Parallel-to Cross–laminated Sandstone Facies(F2) 36 3.2.2.1 Description 36 3.2.2.2 Interpretation 37 3.2.3 Massive Sandstone Facies (F3) 38 3.2.3.1 Description 38 3.2.3.2 Interpretation 38 3.2.4 Bioturbated sandstone Facies (F4) 41 3.2.4.1 Description 41 3.2.4.2 Interpretation 42 3.2.5 Hummocky Sandstone Facies (F5) 42 3.2.5.1 Description 42 3.2.5.1y Small-Scale hummocky cross- 42 stratified sandstone Facies (F5y) 3.2.5.1y.1 Description 42 3.2.5.1b Sandstones with hummocky-type 44 bedforms (F5z) 3.2.5.1b.1 Description 44 3.2.5.2 Interpretation 44 3.2.6 Mudstones, Marls with Sandstones interbeds (F6) 46 3.2.6.1 Description 46 3.2.6.2 Interpretation 46 3.2.7 Laterally Continuous graded Sandstone Facies 47 (F7) 3.2.7.1 Description 47 3.2.7.2 Interpretation 49 3.2.8 Lenticular Graded Sandstone Facies (F8) 49 3.2.8.1 Description 49 3.2.8.2 Interpretation 50 3.2.9 Mudstones interbedded with thin lenticular 50 sandstones, associated with submarine fan turbidites (F9) 3.2.9.1 Description 50 3.2.9.2 Interpretation 50 3.2.10 Mudstones with occasional sandstones and marls 51 (F10) 3.2.10.1 Description 51 3.2.10.2 Interpretation 51 3.2.11 Large scale Planner cross-bedded sandstones 52 (F11) 3.2.11.1 Description 52 3.2.11.2 Interpretation 52 3.2.12 Chaotic Units (F12) 52 3.2.12.1 Description 52 3.2.12.2 Interpretation 55
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3.3 FACIES ASSOCIATIONS: THEIR NATURE AND 55 DESCRIPTION 3.3.1 Shoreface facies Association 55 3.3.2 Shelfal Delta lobe Association 59 3.3.3 Deeper Shelf or Ramp Association 59 3.3.4 Submarine channels facies Association 68 3.3.5 Levee facies Association 78 3.3.6 Submarine fan lobe facies Association 78 3.3.7 Submarine base of slope mud lobe facies 81 Association 3.3.8 Submarine slope sandstones facies Association 81 3.3.9 Fluviodeltaic to shoreface facies association 82 3.4 FACIES VARIATIONS 82 3.4.1 Facies variations in the northern sequences 82 3.4.2 Facies Variations in the southern sequences 84
CHAPTER 4 –PETROGRAPHY, GEOCHEMISTRY AND 86 PROVENANCE 4.1 INTRODUCTION 86 4.1.1 Methods Used 87 4.2 SANDSTONE PETROLOGY 88 4.2.1 Texture 88 4.2.2 Characters of framework grains 89 4.2.2.1 Quartz 89 4.2.2.2 Feldspar 89 4.2.2.3 Lithic fragments 92 4.2.3 Cement/matrix 92 4.2.4 Modal Analysis 96 4.3 COMPARISON BETWEEN NORTHERN AND 98 SOUTHERN DEPOSITIONAL SYSTEMS 4.3.1 Lower Unit 98 4.3.2 Upper Unit 101 4.4 GEOCHEMISTRY OF MUDSTONE AND 101 SANDSTONE 4.5 DEFICIENCY OF FELDSPAR 108 4.6 PROVENANCE 109 4.7 SUMMARY 115
CHAPTER 5 –DIAGENESIS OF SANDSTONE 117 5.1 INTRODUCTION 117 5.2 METHODS 117 5.3 BURRIAL HISTORY 120 5.4 DIAGENESIS OF SANDSTONE 122 5.4.1 Compaction 122 5.4.2 Authigenic components 122 5.4.3 Microfractures 143 IV
5.4.4 Paragenetic sequence 146 5.5 RESERVOIR CHARACTERISTICS 151 5.6 SUMMARY 159
CHAPTER 6 –DEPOSITIONAL MODEL 160 6.1 INTRODUCTION 160 6.2 NORTHERN DEPOSITIONAL SYSTEM 160 6.3 SOUTHERN DEPOSITIONAL SYSTEM 164 6.3.1 Mughal Kot Turbidites 166 6.3.2 Pab Turbidites 168 6.4 SUMMARY 173
CHAPTER 7 –CONCLUSIONS 174
REFERENCES 176
V
Figure LIST OF FIGURES Page No. No. 1.1 Map showing location of the study area in Kirthar Fold Belt. 2
2.1 Map showing generalized major tectonic zones of Pakistan 7 and location of Kirthar Fold Belt (modified after Kazmi and Snee, 1989).
2.2 The map showing major tectonic features of Kirthar Fold 8 Belt Pakistan and location of the study area (modified after Bannert et al., 1992).
2.3 Geological map of the study area showing important tectonic 9 location of measured stratigraphic sections (modified after Bakr and Jackson, 1964).
2.4 Disconformable contact between the Sembar Formation 17 (arrow) and Anjira Formation (dip direction is shown by symbols) of the Ferozabad Group section-5.
2.5 Bioturbation (arrow) in shale of Sembar Formation section 17 16.
2.6 Parallel-lamination (arrows) in limestone of Goru Formation 20 section-9.
2.7 Contacts between the Goru Formation, Parh Limestone, 20 Mughal Kot Formation and Pab Formation section-9.
2.8 Parallel-lamination (arrows) in limestone of the Parh 21 Limestone section-16.
2.9 Gradational and conformable contact between the Mughal 21 Kot Formation and Pab Formation section-9, two persons in the circle are shown for scale.
2.10 Pelecypods (arrow) on top of limestone bed of the Mughal 24 Kot Formation section-1.
2.11 Close up view of nautilus (arrow) at the top most limestone 24 bed of the Mughal Kot Formation section-1.
2.12 Far view of the contacts between Lakhra Formation of Rani 28 Kot Group, Ghazij Formation and Kirthar Formation section- 1.
VI
3.1 Field Photograph of parallel lamination (arrow) in sandstone 39 (F 2), section-7; after Khan et al., 2002).
3.2 Field Photograph showing amalgamated, thick, massive 39 (arrow) sandstone bed (F 3), section-5 (after Khan et al., 2002).
3.3 Field Photograph of mottled (Bioturbated) sandstone bed 43 (F 4), section-6 (after Khan et al., 2002).
3.4 Field Photograph of small scale hummocky cross stratified 43 (arrow) sandstone subfacies (F5a), section-9 (after Khan et al., 2002).
3.5 Field Photograph of sandstone with hummock-type bed 48 forms subfacies (F5b), section-15.
3.6 Field Photograph of Mudstones, Marls (arrows) with 48 Sandstone interbeds facies (F6), section-7 (after Khan et al., 2002).
3.7 Field Photograph of normally graded (arrow) sandstone (F8), 53 section-17.
3.8 Field Photograph of large scale planar cross-bedding (arrows) 53 in sandstone of fluviodeltaic facies (F11), section-11.
3.9 Field Photograph showing sandstone dikes and sills (F 12), 54 section-8 (after Khan et al., 2002)
3.10 Field Photograph showing rounded slumped bodies (F 12), 54 section-15 (after Khan et al., 2002).
3.11 Field Photograph of cross bedded sandstone in shoreface 56 facies association, section-1.
3.12 Field Photograph showing vertical cross cut burrows within 56 cross bedded sandstone of shoreface facies association, section-1.
3.13 Sedimentary log of section-1 measured at Langerchi, grid ref. 57 710190, showing shoreface facies association (see Fig. 2.3 for location).
3.14 Sedimentary log of section-2 measured at Karkh nala, grid 58 ref. 596185, showing shoreface facies association (see Fig. VII
2.3 for location and 3.13 for legends; modified after Khan et al., 2002).
3.15 Sedimentary log of section-3 measured at Bhalok, grid ref. 584205, 60 showing shelfal delta lobe facies association (see Fig. 2.3 for location and 3.13 for legends). 3.16 Sedimentary log of section-4 measured near Khori village, 61 grid ref. 553228, showing shelfal delta lobe facies association (see Fig. 2.3 for location and 3.13 for legends).
3.17 Sedimentary log of section-5 measured at Siman Jhal, grid 62 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).
3.18 Sedimentary log of section-6 measured near Pirmal village, 63 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).
3.19 Sedimentary log of section-8 measured near Ferozabad 64 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).
3.20 Sedimentary log of section-7, measured at Tibbi Jhal, grid 65 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).
3.21 Sedimentary log of section-9 measured at Chashma Murrad 66 Khan, grid ref. 978137, showing deeper shelf or ramp facies association (see Fig. 2.3 for location and 3.13 for legends).
3.22 Sedimentary log of section-10 measured near Nal village, 67 grid ref. 541443, showing deeper shelf or ramp facies association (see Fig. 2.3 for location and 3.13 for legends).
3.23 Field Photograph showing flute marks at the base of 69 sandstone bed, section-9, current direction towards west (after Khan et al., 2002). 70 3.24 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). VIII
3.25 Sedimentary log of section-13 measured at Akri Dhora, grid 71 ref. 58590, showing proximal channelized succession of Pab Turbidites (see Fig. 2.3 for location and 3.13 for legends).
3.26 Sedimentary log of section-14 measured at Korara Lak, grid 72 ref. 366611, showing submarine channels with slope-fan lobes of Pab Turbidites (see Fig. 2.3 for location and 3.13 for legends). 3.27 Sedimentary log of section-15 measured at Jakker Lak grid 73 ref. 69780, showing both Mughal Kot and Pab Turbidites (see Fig. 2.3 for location and 3.13 for legends).
3.28 Sedimentary log of section-16 measured at Sandh Dhora, grid 74 ref. 401078, showing both Mughal Kot and Pab Turbidites (see Fig. 2.3 for location and 3.13 for legends).
3.29 Sedimentary log of section-17, measured at Zarro Range, 75 grid ref. 388780, showing both Mughal Kot and Pab Turbidites (see Fig. 2.3 for location and 3.13 for legends).
3.30 Sedimentary log of section-18, measured at Khude Range, 76 grid ref. 547729, showing both Mughal Kot and Pab Turbidites (see Fig. 2.3 for location and 3.13 for legends).
3.31 Field Photograph showing fluid escape structures (arrows) in 77 sandstone, section-16.
3.32 Sedimentary log of section-19 measured at Kalghalo Jhal, 79 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).
3.33 Sedimentary log of Mughal Kot Turbidite System measured 80 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).
3.34 Sedimentary log of section-11 measured at Bur Nai, grid ref. 83 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 Photomicrographs showing texture of sandstone: A) Very 90 coarse grained; B) Very fine to fine grained; C) Well sorted; D) Poorly sorted; E) Well rounded F) Grain supported.
4.2 Photomicrographs showing varieties of framework grains: A) 91 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.
4.3 Photomicrographs showing varieties of framework grains: A) 93 Sedimentary fragment (siltstone); B to E); Various forms of fossil fragments; F) Chert; all shown by arrows.
4.4 Photomicrographs showing: A) Volcanic lithic fragment; B) 94 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.
4.5 Classification of sandstone samples of Upper Cretaceous 97 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.
4.6 Comparison in concentration of Q-F-L and Qm-F-Lt in 100 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).
4.7 SiO2-Al2O3+K2O+Na2O diagram for the sandstone (after 106 Suttner and Dutta, 1986); open circles indicate Northern and closed circles show Southern Depositional system.
4.8 The A-CN-K diagram of mudstone samples, showing high 106 CIA values (after Nesbitt and Young, 1984); open circles indicate Northern and closed circles show Southern Depositional system.
4.9 QFL plot for detrital modes of sandstone showing Craton 110 Interior and Recycled Orogen provenance (after Dickinson et al., 1983 and Dickonson, 1985), Open circles indicate lower X
unit of both the Northern and Southern Depositional system, closed circles show upper unit of Southern Depositional System.
4.10 Qm-F-Lt plot for detrital modes of sandstone showing Craton 111 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.
4.11 Qp-Lv-Ls triangle for detrital modes of upper unit of 112 Southern Depositional System (after Dickinson et al., 1983 and Dickonson, 1985).
4.12 Map showing paleocurrent directions in study area. 114
5.1 Microphotograph of Straight contact (arrows) between 123 neighboring framework grains.
5.2 Microphotograph of concavo-convex contacts (arrows) 123 between neighboring framework grains.
5.3 Microphotograph of sutured contacts (arrow) between 124 neighboring framework grains.
5.4 Microphotograph of Quartz overgrowth (arrows). 124
5.5 SEM image quartz overgrowth along C-axis (arrows). 126
5.6 SEM photograph of Quartz overgrowth obstructed by early 126 formed clay minerals (arrows).
5.7 X-ray Diffractogram showing peak positions of feldspar, 128 mixed clay layers, goethite and plagioclase (albite) in untreated, ethylene glycol treated and heated to 500 0C samples in clay separates.
5.8 X-ray Diffractogram showing peak positions of illite, 129 plagioclase (albite) in untreated, ethylene glycol treated and heated at 500 0C sample in clay separates.
5.9 X-ray Diffractogram showing peak positions of chlorite and 130 plagioclase (albite) in untreated, ethylene glycol treated and heated to 500 0C samples in clay separates.
XI
5.10 SEM image of albite showing plagioclase laths (arrows) 131 within volcanic fragments.
5.11 X-ray Diffractogram showing peak positions of kaolinite, 132 goethite, dolomite, calcite and hematite in untreated, ethylene glycol treated and heated to 500 0C samples in clay separated.
5.12 Photomicrograph of calcite replaced framework grain at margins 131 (arrows).
5.13 Photomicrograph of calcite replaced framework grain in core 134 (arrows).
5.14 SEM of calcite replaced framework grain in core (encircled). 134
5.15 SEM photograph showing dolomite rim around volcanic 135 fragment.
5.16 SEM photograph showing kaolinite booklets (arrows). 135
5.17 SEM photograph showing alteration and dissolution of 137 feldspar grain (arrows).
5.18 SEM photograph showing chlorite (arrows) in BSC mode. 137
5.19 SEM photograph showing illite-smectite mixed layer in SEI 138 mode.
5.20 SEM photograph showing brush and hairy illite (arrows). 138
5.21 SEM photograph showing anatase (arrows) well developed 140 crystals.
5.22 SEM photograph showing hematite (arrows). 140
5.23 SEM photograph showing pyrite (arrows) within a shell. 142
5.24 SEM photograph showing iron oxide/hydroxide with rosette 142 structures (arrows).
5.25 SEM photograph showing randomly oriented (arrows) iron 145 oxide/hydroxide.
5.26 SEM photograph of iron oxide laths showing little 145 dissolution (arrows).
XII
5.27 SEM photograph of later stage iron oxide/ hydroxide 148 (arrows) into early calcite cement.
5.28 Photomicrograph of microfractures (arrows) in framework 148 grains.
5.29 A sketch of microfractures in framework grains 149 perpendicular to maximum stress axis (same thin section as in Fig. 5.28).
5.30 SEM photograph showing dissolution (arrows) of calcite 149 along microfractures.
5.31 SEM photograph of physically fractured feldspar grain 152 (within ellipse).
5.32 SEM photograph showing calcite penetration within early 152 formed kaolinite booklets (arrows).
5.33 SEM photograph of massive calcite cementation (arrows) 155 which reduced porosity of sandstone.
5.34 SEM photograph of dissolution (arrows) of unstable 155 framework grains enhanced porosity of sandstone.
5.35 Photomicrograph of late stage dissolution (arrows). 156
6.1 Depositional model of Upper Cretaceous succession showing 161 two contrasting, coeval depositional Systems.
6.2 Field photograph showing synsedimentary normal fault 165 (ellipse), section-9.
6.3 Field Photograph showing basin-floor lobes of Mughal Kot 167 Turbidites, section-20 (line across strike).
6.4 Field Photograph showing laterally continuous beds (line), 167 section-16, person encircle for scale.
6.5 Field Photograph showing view of thinning upward (arrow) 169 trend in Mughal Kot Turbidites, section-15.
6.6 Field Photograph of channels (arrows) within mud rich lobes 169 of Mughal Kot Turbidites, section-16.
XIII
6.7 Field Photograph showing mud rich lobes and channels (C)- 170 levee (L) in Mughal Kot Turbidites, section-16.
6.8 Field Photograph showing individual channel (arrow) within 170 mud rich lobes of Mughal Kot Turbidites, section-16.
6.9 Field Photograph of thickening upward cycle (arrow) of 171 slope fan lobes of Pab Turbidites, section-15.
6.10 Field Photograph showing laterally continuous beds of 171 submarine slope fan lobes of Pab Turbidites, section-15.
6.11 Field Photograph showing view of thinning upward cycle 172 (arrows) of Pab Turbidites, section-15, man encircled for scale.
XIV
Table List of Tables Page No. No. 2.1 Generalized Stratigraphic succession of the Kirthar Fold 13 Belt showing the stratigraphic position of Upper Cretaceous succession.
3.1 Location of measured sections and logged through Upper 35 Cretaceous succession in Central and Southern Kirthar Fold Belt (see Fig. 2.3).
4.1 Average of point counting results in percentages (Fig. 4.6) of 99 measured sections in lower units of both Northern and Southern Depositional Systems. Note that Upper unit is observed only in Southern Depositional System
4.2 Major element concentrations and other geochemical parameters 102 for mudstone samples of Upper Cretaceous succession.
4.3 Major element concentrations for sandstones. 103
4.4 Average major element concentrations for mudstone and 105 sandstone samples.
4.5 Point counting results of sandstone samples in percentages (Qp- 112 Lv-Ls diagram) of measured sections.
5.1 Conditions for identification of bulk mineralogical composition 119 of sandstones and clay separates.
5.2 Showing burial depths (B. Depth), mean porosity (n), 144 Intergranular Volume (IGV) and depositional settings of Upper Cretaceous succession.
5.3 Paragenetic sequence of sandstones of Upper Cretaceous 147 succession.
Appendix LIST OF APPENDICES Page No. No. 4.1 Results of point counting of sandstone of the Upper i Cretaceous succession, Central and Southern Kirthar Fold Belt.
4.2 Results of point counting in percentages (for Figs. 4.5, iv 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. XVI
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 XVII
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.
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 2
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 – 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).
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. 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
7
8
K E Y
Fig. 2.2: The map showing major tectonic features of Kirthar Fold Belt, Pakistan and location of the study area (Modified after Bannert et al., 1992).
9
0o 0o 28o 66 67 O
NL
27o
68o
Sehwan
Bela BL
26o
Uthal UL
14
12 Northern Depositional System ARABIAN SEA Southern Depositional System Cities and Towns 25o 0 50 Km Karachi 1 Location of stratigraphic sections measured KHI Fig.2.3:.Geological Map of the study area showing important tectonic features and location of measured stratigraphic sections (modified after Bakr and Jackson, 1964).
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.
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)
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
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 Sandstone and shale interbedded Formation 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 Eocene interbedded with shale and marl Ghazij Formation Dominantly shale with minor sandstone Rani Kot Lakhra Formation Intraclastic limestone and shale Paleocene Group Bara Formation Sandstone and shale Khadro Formation Sandstone, shale and marl Maastrichtian- Upper Pab Formation Sandstone intercalated with Campanian Cretaceous marl and mudstone succession Mughal Kot Marl, arenaceous limestone, Formation mudstone and sandstone Early – Late Parh Limestone Biomicritc limestone Cretaceous Parh Group Goru Formation Micritic limestone with shale, siltstone and sandstone Sembar Formation Shale, siltstone and marl Disconformity Anjira Formation Limestone interbedded with shale and marl Early-Late Ferozabad Malikhore Oolitic limestone with Jurassic Group Formation subordinate shale and marl Kharrari Limestone, shale, marl and minor Formation sandstone Base not exposed
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
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
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
17
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.
Fig. 2.5: Bioturbation (arrows) in shale of Sembar Formation, section-16.
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
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).
20
Fig. 2.6: Parallel-lamination (arrows) in limestone of Goru Formation, section-9.
Fig. 2.7: Contacts between the Goru Formation, Parh Limestone, Mughal Kot Formation and Pab Formation, section-9.
21
Fig. 2.8 Parallel-lamination (arrows) in limestone of the Parh Limestone, section-16.
Fig. 2.9: Gradational and conformable contact between the Mughal Kot and Pab formations, section-9, two persons in circle are shown for scale.
22
The formation has been assigned Barremian to Campanian age by Kazmi (1955 &
1979) in the Kach-Ziarat area of the Sulaiman Fold Belt and Senonian by
Williams (1959).
2.2.3 Mughal Kot Formation
Williams (1959) proposed the name Mughal Kot Formation for the rocks
exposed between 2 to 5 kilometers west of Mughal Kot Fort along Zhob–Dera
Ismail Khan road (lat. 31o 26/ 52// N; long. 70o 02/ 58// E).
The formation within the study area comprises marl, mudstone and occasional limestone. Marl is white (N9), bluish white (5B 9/1), light brownish grey (5YR 6/1), greyish orange (10Y 7/4), greenish grey (5GY 4/1) and dark yellowish orange (10YR 6/6). Marl is massive, parallel and cross-laminated. The beds of marl are lenticular, thin bedded, ranging from 5 to 50 centimeters in
thickness. The frequency and thickness of marl beds decreases upward and
gradually changes to mudstone completely. Marl is highly cleaved, homogeneous
and partly laminated. Upper 30-35 meters part of the formation is composed of
thin to thick bedded arenaceous limestone, which is graded, parallel-cross and
hummocky cross-laminated. Occasional sandstone beds are also present in the
formation. Mudstone is olive grey (5Y 4/1), dark greenish grey (5GY 4/1), olive
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 Mughal Kot Formation is conformable and
transitional with the Pab Formation (Fig. 2.9). About 50 meters thick transitional
23 zone between 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), pelecypods (Fig. 2.11) and bivalves 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) and pale yellowish brown (10YR 6/2). It is thin bedded, finely laminated, massive and cleaved. Mudstone is mottled red, 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.
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.
25
Its upper contact is conformable and sharp with the Khadro Formation of Ranikot
Group. On the basis of faunal record a Maastrichtian age has been assigned to the
Pab Formation (Vredenburg, 1909; HSC, 1960; Shah, 1977; Shuaib, 1982; Bender
& Raza, 1995; 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 Fold Belt. These local names were complied in to the Ranikot Group
(Khadro, 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).
The 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 Khadro Formation
The name Khadro Formation was introduced by Williams (1959). Khadro nala
(lat. 26o 07/ 06// N: long. 67o 53/ 12// E) near Bara Nai in Laki Range is the type
section of the formation.
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
contains rip-up mud clasts. Shale is pale green, olive, greenish grey, grey,
brownish 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, Blandford 1878,
Nagappa 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 cross-laminated. Shale is bluish grey, greenish grey 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
27
talpur (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 brownish
gray, intraclastic, 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 bedded and cross-bedded.
Its upper contact is sharp and conformable with the Ghazij Formation (Fig.
2.12). The formation is highly fossilifereous and contains foraminifera, corals,
molluscs and echinoids (Davies 1927, Nuttall 1931, Duncan 1880, Vredenburg
1909b, 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).
28
Fig. 2.12: Far view of the contacts between the Lakhra Formation of Rani Kot Group, Ghazij Formation and Kirthar Formation, section-1.
29
2.2.6 Ghazij Formation
The name Ghazij Formation was proposed by Williams (1959) for the
rocks exposed at Ghazij Rud, a stream to the southeast of Spintangi Railway
station (lat. 29o 57/ N; long. 68o 05/ E). It is equivalent of the Gidar Dhor Group
(HSC, 1960), Ghazij Group (Oldhalm, 1890; Shah, 1990; Bendar & Raza, 1995;
Kazmi & Jan, 1997) and Laki Formation (Hunting Survey Corporation, 1960;
Noetling, 1903; Shah, 1977).
The formation is composed of shale, sandstone, conglomerate and coal seams. Shale is grey and greenish yellow, pale greenish grey, brown and olive grey, calcareous, flaky, ferruginous and gypsifereous. Sandstones are greenish grey, yellowish brown, pale brown, light olive brown, fine to very coarse grained, parallel-laminated, and cross-laminated and possess sole marks. Some other sandstones are white, cream and calcareous. Conglomerate is composed of fragments of limestone, sandstone and chert of older formations. It is moderately sorted, well rounded to subrounded and clast supported.
Its upper contact with the Kirthar Formation is conformable (Fig. 2.12).
Foraminifera, gastropods, bivalves, algae, echinoids, vertebrate bones and plant remains have been reported from the formation (Eames, 1952; HSC, 1960; Latif,
1964; Iqbal, 1969; Kakar, 1995; Kakar & Kassi, 1997 and Ginsberg et al., 1999).
The fossil assemblage mostly include: assilina granulose, A. postulosa, lochartiahunti, flosculina globosa, fasciolites oblonga, gisortia murchisoni, velates perversus and amblypygus subrotundus and echinolampus nummulitica
30
(HSC 1960; Iqbal 1973; Nuttall 1925; Noetling 1905; Davies 1926; Haque 1962).
This assemblage clearly suggests an Early Eocene age for the Ghazij Formation.
2.2.7 Kirthar 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 brown, orange, yellow, grey, gypsifereous and calcareous. 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/ 10// E) in the Kirthar
Range.
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
31
brown marl is also present in the formation. Shale is highly bioturbated containing
horizontal burrows. The formation is characterized by grading, parallel-
lamination, cross-lamination and sole marks. It is generally a flysch succession
showing the characters of turbidites.
Upper contact of the formation is transitional and conformable with the
Gaj Formation. 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).
2.2.9 Gaj 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 mainly consists of shale, sandstone with subordinate limestone 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 grey, yellowish brown and ferruginous. It is very coarse grained to pebbly, 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,
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
carinata 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
Blandford (1876) proposed the name Manchar Formation for rocks exposed near Manchar Lake (lat. 26o 23/ N and long. 67o 38/ E).
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. Sandstone is grey, greenish grey, coarse grained 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 the basis of which a Pliocene age is given to
the formation (Pilgrim 1908b).
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 bedded, poorly sorted and composed mostly of calcareous material with sandy matrix. Pebbles and cobbles are subangular to well rounded. Maximum clast size reaches up to 0.5 meters in diameter. Sandstone is greenish grey and brown, coarse 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).
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).
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 Name Latitude Longitude section 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 270 38/ 660 28/ Khan section 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 260 41/ 660 44/ section
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 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.
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) 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).
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 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 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). 43
Fig. 3.3: Field Photograph of mottled (Burrowed; arrows) sandstone bed (F 4), section-6 (after Khan et al., 2002).
Fig. 3.4: Field Photograph of small scale hummocky cross stratified (arrow) sandstone subfacies, (F 5y), section-9 (after Khan et al., 2002).
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 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).
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 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 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).
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 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.
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.
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).
53
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.
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.
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 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.
57
121 m
216 m F 3.11 & 3.12 S 1-19
0 m
58
S 2-10
S 2-9
S 2-8
S 2-7
S 2-6
S 2-4 & 2-5
S 2-3
S 2-2
S 2-1
m v sh c c
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- 60
S 10-5
S 10-4
S 10-3
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).
61
24 m 48 m 72 m
82 m
S 11-1
0 m 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).
62
47 m 94 m 141 m S 5-5
S 5-8
S 5-2
S 5-4 F 3.2
S 5-7
S 5-3 S 5-6
S 5-1
0 m
63
44 m 88 m 132 m
S 6-4
S 6-8
S 6-2
S 6-3
S 6-7
S 6-6
S 6-5
64
42 m 85 m S 8-7
S 8-4
S 8-3
S 8-6 119 m
S 8-2
S 8-11
S 8-5
S 8-10
S 8-9
F 3.9
S 8-1 S 8-8
0 m
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))
65
Ranikot 56 m 112 m 225 m Group 168 m
S 7-11
S 7-9, 10
S 7-13
S 7-8 S 7-5
S 7-12 F 3.1
S 7-7 F 3.6 S 7-6
S 7-4
S 7-2, 3
S 7-1
0 m 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).
66
75 m 150 m 225 m Ranikot Group
F 3.4
S 9-1 F 3.23
S 9-2
0 m
67
97 m 194 m
Ranikot Group 245 m
S 10-3
S 10-2
S 10-1
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 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).
70
Ranikot Group 7 m
7 m
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).
71
Ranikot Group
S 13-3 S 13-2
72
Ranikot Group S 14-10
S 14-9
S 14-8
S 14-5
S 14-7
S 14-6
S 14-4
73
S 15-4
Ranikot Group
F 6.9
S 15-7
S 15-6
F 3.5
F 6.10
F 6.11
S 15-1-3
S 15-5
F 3.10 F 6.5
74
S 16-1 Ranikot 4
.
6 Group
F
F 6.8 S 16-6 F 3.31 S 16-7
S 16-2,3
F 6.7 S 16-17
S 16-16
S 16-15
S 16-5 S 16-14
S 16-4
S 16-13
S 16-12 S 16-11 F 6.6 S 16-10
S 16-9 S 16-8 0 m
75
62 m 124 m 186 m 248 m
S 17-3
S 17-2
S 17-1
Ranikot Group
S 17-5
S 17-4
F 3.7 0 m
76
48 m 96 m 144 m 192 m S 18-2
S 18-1
S 18-3
S 18-4
Ranikot Group 203 m S 18-5
0 m
77
Fig. 3.31: Field photograph showing fluid escape structures (arrows) in sandstone section-16
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 79
104 m
Nari Formation 200 m
S 19-2
S 19-1
0 m
80
Nari Formation 103 m
F 6.3
S18-2
S18-1
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 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 83
78 m
S 11-5
145 m S 11-4
F 3.8
S 11-3 F 3.17
S 11-2
S 11-1
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).
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 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. 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 87
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 88
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 89
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 90
Fig. 4.1: Photomicrographs showing texture of sandstone: A) Very coarse grained; B) Very fine to fine grained; C) Well sorted; D) Poorly sorted; E) Well rounded; and F) grained supported.
91
Fig. 4.2: 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; and F. Microcline showing cross hatched twinning; all indicated by circles.
92
(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 93
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.
94
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.
95
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 96
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 97
98 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). 99
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 Q F L Qm F Lt No 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
100
A Q 100
80
60 Q F 40 L
20 F L 0 12 3 4 56 7 8910 15161718 Section No.
100 B Qm 80 Qm e 60
g F a
t 40 Lt n
e Lt
c 20 r
e F
p 0
11 13 14 15 16 17 18 n i
Section No.
n
o
i t
a Q r
t 100 n
e C
c 80 n
o 60 Q
C F 40 L
20 F L 0 1 2 3 4 5 6 7 8 9 10 11 15 16 17 18 Section No.
100 D Qm 80
60 Qm 40 F Lt Lt 20 F 0 11 13 14 15 16 17 18 Section No. Fig. 4.6: Comparison in concentrations of Q-F-L and Qm-F-Litn sandstones of Upper Cretaceous succession; A and C lower un i(tin both Northern and Southern depositional Systems); and B and D upper unit (only in Southern Depositional System) .
101
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 %).
102
Table 4.2: Major element concentrations and other geochemical parameters for mudstone samples of Upper Cretaceous succession.
Oxides/ 1-7 2-11 3-5 12-1 14-2 15-2 15-3 16-4 16-6 16-9 Parameters 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
103
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
104
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
105
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 ------
106
100
80
60
SiO2
40
20
10 20 30
Al23O+ KO2 +Na2O
Fig. 4.7: SiO22-Al O3+ K2O+Na2O diagram for the sandstone (after ,Suttner and Dutta, 1986) open circles indicate Northern and Closed circles show Southern Depositional System. 100 A
90 Original CIA Smectite 80 Illite
A
I Muscovite
C 70
60 Biotite
Plagioclase K-Feldspar 50
CN K
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.
107
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 108 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 109 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. 110
111
Qm
Craton interior
20
Quartzose Recycled
Lt F
Qm
Craton interior 20 Quartzose Transitional Recycled Continental 43 R e 42 c l Mixed y Transitiona c le Recycled d Dissected arc Basement Uplift 29
Transitional Lithic arc Recycled Undissected arc F 23 13 Lt
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 D epositional System (after, Dickinson et al., 1983 and Dickinson 1985
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- 114
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P Key Pab / Mughal Kot formations (Upper Cretcaceous succession) Location of measured stratigraphic section Cities and Towns ARABIAN SEA KK Khuzdar Knot
Paleocurrent direction
o 25 50 Km Karachi
Fig. 4.12: Map showing paleocurrent directions in the study area.
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 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. 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 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 119
Table 5.1: Conditions for identification of bulk mineralogical composition of sandstones and clay separates.
Conditions/Parameters Bulk Clay Mineralogy Mineralogy Untreated Ethylene Heated to (ubh) Glycol 5000 C treated (eth) 0 0 0 0 0 0 0 0 Interval 2O 2-65 2-65 2-26 2-26 0 0 0 0 Goniometer Speed 1.8 -2O /min 1.8 -2O /min 1.8 - 1.8 - 2O /min 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
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 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 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, 123
Fig. 5.1: Microphotograph of straight contact (arrows) between neighbouring framework grains.
Fig. 5.2: Microphotograph of concavo-convex contacts (arrows) between neighbouring framework grains.
124
Fig. 5.3: Microphotograph of sutured contacts (arrow) between neighbouring framework grains.
Fig. 5.4: Microphotograph of quartz overgrowth (arrows).
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 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).
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
128
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129
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130
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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).
132
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3 3 4 3 3 2 D-spacing (A) Fig. 5.11: X-ray Diffractogram showing peak positions of kaolinite, goethite, dolomite, calcite an dhematite in untreated, ethylene glycol treated and heated to 500 0 C samples in clay separates.
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 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).
135
Fig. 5.15: SEM photographs showing dolomite rim around volcanic fragmen
Fig. 5.16: SEM photograph showing kaolinite booklets (arrows).
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 137
Fig. 5.17: SEM photograph showing alteration and and dissolution of feldspar grains (arrows).
Fig. 5.18: SEM photograph showing chlorite (arrows) in BSC mode.
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).
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. 140
Fig. 5.21: SEM photograph showing anatase (arrows) well developed crystals
Fig. 5.22: SEM photograph showing hematite (arrows).
141
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 142
Fig. 5.23: SEM photograph showing pyrite (arrow) within a shell.
Fig. 5.24: SEM photograph showing iron oxide/hydroxide with rosette structures (arrows).
143 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 144
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 IGV Depositional setting n.% 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
145
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)
146
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 147
Table 5.3: Paragenetic sequence of sandstones of Upper Cretaceous succession.
Event Relative Timing Early Late
Mechanical Compaction ––––––––––------––––––––––– Dissolution of feldspar –––––––––––––------and volcanic fragments Kaolinite ---––––––––––––––– Chlorite -----––––––––––––––– Chemical compaction ––––––––––––––------Quartz cement ––––––––––––––––––––– Illite ----––––––––––------Calcite ------––––––––––––––––– Dolomite ----––––– Grain fracturing –––––------Iron Oxide ––––––––– Dissolution ----––––---
148
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
149
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 s Fig. 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.
150
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 151
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 152
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).
153
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 154 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 155
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.
156
Fig. 5.35: Photomicrograph of late stage dissolution (arrows).
157
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). 158
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 159
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. 160
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). 161
Northern Depositional System Southern Depositional System Fluviodeltaic facies association
F
162
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 163 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 164
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. 165
Fig. 6.2: Field photograph showing synsedimentary normal fault (ellipse), section-9
166
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
167
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
168
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.
169
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. 170
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.
171
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.
172
Fig. 6.11: Field Photograph showing view of thinning upward cycles (arrows) of Pab Turbidites, section-15, man encircled for scale.
173
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. 174
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. 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. 176
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