FACIES DISTRIBUTION, DEPOSITIONAL ENVIRONMENTS, PROVENANCE AND RESERVOIR CHARACTERS OF UPPER CRETACEOUS SUCCESSION KIRTHAR FOLD BELT PAKISTAN BY MUHAMMAD UMAR THESIS PRESENTED TO THE CENTRE OF EXCELLENCE IN MINERALOGY UNIVERSITY OF BALOCHISTAN QUETTA FOR THE DEGREE OF DOCTOR OF PHILOSOPHY NOVEMBER 2007.
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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
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CONTENTS Page No.
LIST OF CONTENTS LIST OF FIGURES LIST OF TABLES LIST OF APPENDICES ACKNOWLEDGEMENT ABSTRACT CHAPTER 1- INTRODUCTION
1.1 AIMS AND OBJECTIVES OF THE STUDY 1.2 LOCATION AND ACCESSIBILITY 1.3 PREVIOUS WORK 1.4 METHODS OF STUDY
CHAPTER 2- GEOLOGIC SETTING AND STRATIGRAPHY
2.1 GEOLOGIC SETTING 2.2 STRATIGRAPHY OF THE KIRTHAR FOLD BELT
3.3 FACIES ASSOCIATIONS: THEIR NATURE AND DESCRIPTION
3.3.1 Shoreface facies Association 3.3.2 Shelfal Delta lobe Association 3.3.3 Deeper Shelf or Ramp Association 3.3.4 Submarine channels facies Association 3.3.5 Levee facies Association 3.3.6 Submarine fan lobe facies Association 3.3.7 Submarine base of slope mud lobe facies
Association 3.3.8 Submarine slope sandstones facies Association 3.3.9 Fluviodeltaic to shoreface facies association
3.4 FACIES VARIATIONS 3.4.1 Facies variations in the northern sequences 3.4.2 Facies Variations in the southern sequences
CHAPTER 4 –PETROGRAPHY, GEOCHEMISTRY AND
PROVENANCE 4.1 INTRODUCTION
4.1.1 Methods Used 4.2 SANDSTONE PETROLOGY
4.2.1 Texture 4.2.2 Characters of framework grains
6.1 INTRODUCTION 6.2 NORTHERN DEPOSITIONAL SYSTEM 6.3 SOUTHERN DEPOSITIONAL SYSTEM 6.3.1 Mughal Kot Turbidites 6.3.2 Pab Turbidites 6.4 SUMMARY
CHAPTER 7 –CONCLUSIONS REFERENCES
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Figure No.
LIST OF FIGURES Page No.
1.1
2.1
2.2
2.3
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2.5
2.6
2.7
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2.9
2.10
2.11
2.12
Map showing location of the study area in Kirthar Fold Belt. Map showing generalized major tectonic zones of Pakistan and location of Kirthar Fold Belt (modified after Kazmi and Snee, 1989). The map showing major tectonic features of Kirthar Fold Belt Pakistan and location of the study area (modified after Bannert et al., 1992). Geological map of the study area showing important tectonic location of measured stratigraphic sections (modified after Bakr and Jackson, 1964). Disconformable contact between the Sembar Formation (arrow) and Anjira Formation (dip direction is shown by symbols) of the Ferozabad Group section-5. Bioturbation (arrow) in shale of Sembar Formation section 16. Parallel-lamination (arrows) in limestone of Goru Formation section-9. Contacts between the Goru Formation, Parh Limestone, Mughal Kot Formation and Pab Formation section-9. Parallel-lamination (arrows) in limestone of the Parh Limestone section-16. Gradational and conformable contact between the Mughal Kot Formation and Pab Formation section-9, two persons in the circle are shown for scale. Pelecypods (arrow) on top of limestone bed of the Mughal Kot Formation section-1. Close up view of nautilus (arrow) at the top most limestone bed of the Mughal Kot Formation section-1. Far view of the contacts between Lakhra Formation of Rani Kot Group, Ghazij Formation and Kirthar Formation section- 1.
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3.1
3.2
3.3
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3.13
3.14
Field Photograph of parallel lamination (arrow) in sandstone (F 2), section-7; after Khan et al., 2002). Field Photograph showing amalgamated, thick, massive (arrow) sandstone bed (F 3), section-5 (after Khan et al., 2002). Field Photograph of mottled (Bioturbated) sandstone bed (F 4), section-6 (after Khan et al., 2002). Field Photograph of small scale hummocky cross stratified (arrow) sandstone subfacies (F5a), section-9 (after Khan et al., 2002). Field Photograph of sandstone with hummock-type bed forms subfacies (F5b), section-15. Field Photograph of Mudstones, Marls (arrows) with Sandstone interbeds facies (F6), section-7 (after Khan et al., 2002). Field Photograph of normally graded (arrow) sandstone (F8), section-17. Field Photograph of large scale planar cross-bedding (arrows) in sandstone of fluviodeltaic facies (F11), section-11. Field Photograph showing sandstone dikes and sills (F 12), section-8 (after Khan et al., 2002) Field Photograph showing rounded slumped bodies (F 12), section-15 (after Khan et al., 2002). Field Photograph of cross bedded sandstone in shoreface facies association, section-1. Field Photograph showing vertical cross cut burrows within cross bedded sandstone of shoreface facies association, section-1. Sedimentary log of section-1 measured at Langerchi, grid ref. 710190, showing shoreface facies association (see Fig. 2.3 for location). Sedimentary log of section-2 measured at Karkh nala, grid ref. 596185, showing shoreface facies association (see Fig.
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3.15
3.16
3.17
3.18
3.19
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2.3 for location and 3.13 for legends; modified after Khan et al., 2002). Sedimentary log of section-3 measured at Bhalok, grid ref. 584205, showing shelfal delta lobe facies association (see Fig. 2.3 for location and 3.13 for legends). Sedimentary log of section-4 measured near Khori village, grid ref. 553228, showing shelfal delta lobe facies association (see Fig. 2.3 for location and 3.13 for legends). Sedimentary log of section-5 measured at Siman Jhal, grid ref. 059163, showing shelfal delta lobe facies association (see Fig. 2.3 for location and 3.13 for legends; modified after Khan et al., 2002). Sedimentary log of section-6 measured near Pirmal village, grid ref. 984070, showing shelfal delta lobe facies association (see Fig. 2.3 for location and 3.13 for legends; modified after Khan et al., 2002). Sedimentary log of section-8 measured near Ferozabad village, grid ref. 050321, showing dominantly shelfal delta lobe facies association (see Fig. 2.3 for location and 3.13 for legends; modified after Khan et al., 2002). Sedimentary log of section-7, measured at Tibbi Jhal, grid ref. 860350, showing deeper shelf or ramp facies association (see Fig. 2.3 for location and 3.13 for legends; modified after Khan et al., 2002). Sedimentary log of section-9 measured at Chashma Murrad Khan, grid ref. 978137, showing deeper shelf or ramp facies association (see Fig. 2.3 for location and 3.13 for legends). Sedimentary log of section-10 measured near Nal village, grid ref. 541443, showing deeper shelf or ramp facies association (see Fig. 2.3 for location and 3.13 for legends). Field Photograph showing flute marks at the base of sandstone bed, section-9, current direction towards west (after Khan et al., 2002). Sedimentary log of section-12, measured at Naka Pabni, grid ref. 290545, showing thin channelized succession of Pab Turbidite System in most proximal setting (see Fig. 2.3 for location and 3.13 for legends).
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3.25
3.26
3.27
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3.29
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3.34
Sedimentary log of section-13 measured at Akri Dhora, grid ref. 58590, showing proximal channelized succession of Pab Turbidites (see Fig. 2.3 for location and 3.13 for legends). Sedimentary log of section-14 measured at Korara Lak, grid ref. 366611, showing submarine channels with slope-fan lobes of Pab Turbidites (see Fig. 2.3 for location and 3.13 for legends). Sedimentary log of section-15 measured at Jakker Lak grid ref. 69780, showing both Mughal Kot and Pab Turbidites (see Fig. 2.3 for location and 3.13 for legends). Sedimentary log of section-16 measured at Sandh Dhora, grid ref. 401078, showing both Mughal Kot and Pab Turbidites (see Fig. 2.3 for location and 3.13 for legends). Sedimentary log of section-17, measured at Zarro Range, grid ref. 388780, showing both Mughal Kot and Pab Turbidites (see Fig. 2.3 for location and 3.13 for legends). Sedimentary log of section-18, measured at Khude Range, grid ref. 547729, showing both Mughal Kot and Pab Turbidites (see Fig. 2.3 for location and 3.13 for legends). Field Photograph showing fluid escape structures (arrows) in sandstone, section-16. Sedimentary log of section-19 measured at Kalghalo Jhal, grid ref. 051263, showing basin floor-fan lobes of Mughal Kot Turbidites and submarine slope-fan lobes of Pab Turbidites in distal settings (see Fig. 2.3 for location and 3.13 for legends). Sedimentary log of Mughal Kot Turbidite System measured at section-20 Pundu Pash Jhal, grid ref. 101255, showing basin-floor and fan-lobe facies in most distal setting (see Fig. 2.3 for location and 3.13 for legends). Sedimentary log of section-11 measured at Bur Nai, grid ref. 336353, showing fluviodeltaic facies association, proximal component of Southern Depositional System (see Fig. 2.3 for location and 3.13 for legends).
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4.1
4.2
4.3
4.4
4.5
4.6
4.7
4.8
4.9
Photomicrographs showing texture of sandstone: A) Very coarse grained; B) Very fine to fine grained; C) Well sorted; D) Poorly sorted; E) Well rounded F) Grain supported. Photomicrographs showing varieties of framework grains: A) Undulose monocrystalline quartz; B); Polycrystalline quartz consists of two sub grains; C) Polycrystalline quartz consists of more than two sub grains; D) K-feldspar; E) Plagioclase showing albite type twinning in central part; F) Microcline showing cross hatched twinning all indicated by circles. Photomicrographs showing varieties of framework grains: A) Sedimentary fragment (siltstone); B to E); Various forms of fossil fragments; F) Chert; all shown by arrows. Photomicrographs showing: A) Volcanic lithic fragment; B) Mica grain (lower central part: arrow); C) Micritic calcite (arrow): D) Sparry calcite (arrow); E) Iron oxide/hydroxide cement (arrow); F) Well rounded quartz grain with overgrowth (arrow) showing reworking. Classification of sandstone samples of Upper Cretaceous succession (after Folk, 1974), open circles indicate lower unit of both the Northern and Southern Depositional Systems. Closed circles indicate Upper unit of Southern Depositional System. Comparison in concentration of Q-F-L and Qm-F-Lt in sandstones of Upper Cretaceous succession; A and C lower unit (in both Northern and Southern depositional Systems); and B and D upper unit (only in Southern Depositional System). SiO2-Al2O3+K2O+Na2O diagram for the sandstone (after Suttner and Dutta, 1986); open circles indicate Northern and closed circles show Southern Depositional system. The A-CN-K diagram of mudstone samples, showing high CIA values (after Nesbitt and Young, 1984); open circles indicate Northern and closed circles show Southern Depositional system. QFL plot for detrital modes of sandstone showing Craton Interior and Recycled Orogen provenance (after Dickinson et al., 1983 and Dickonson, 1985), Open circles indicate lower
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4.10
4.11
4.12
5.1
5.2
5.3
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5.6
5.7
5.8
5.9
unit of both the Northern and Southern Depositional system, closed circles show upper unit of Southern Depositional System. Qm-F-Lt plot for detrital modes of sandstone showing Craton Interior and Recycled Orogen provenance (after Dickinson et al., 1983 and Dickonson, 1985), Open circles indicate lower unit of both the Northern and Southern Depositional system, closed circles show upper unit of Southern Depositional System. Qp-Lv-Ls triangle for detrital modes of upper unit of Southern Depositional System (after Dickinson et al., 1983 and Dickonson, 1985). Map showing paleocurrent directions in study area. Microphotograph of Straight contact (arrows) between neighboring framework grains. Microphotograph of concavo-convex contacts (arrows) between neighboring framework grains. Microphotograph of sutured contacts (arrow) between neighboring framework grains. Microphotograph of Quartz overgrowth (arrows). SEM image quartz overgrowth along C-axis (arrows). SEM photograph of Quartz overgrowth obstructed by early formed clay minerals (arrows). X-ray Diffractogram showing peak positions of feldspar, mixed clay layers, goethite and plagioclase (albite) in untreated, ethylene glycol treated and heated to 500 0C samples in clay separates. X-ray Diffractogram showing peak positions of illite, plagioclase (albite) in untreated, ethylene glycol treated and heated at 500 0C sample in clay separates. X-ray Diffractogram showing peak positions of chlorite and plagioclase (albite) in untreated, ethylene glycol treated and heated to 500 0C samples in clay separates.
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5.10
5.11
5.12
5.13
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SEM image of albite showing plagioclase laths (arrows) within volcanic fragments. X-ray Diffractogram showing peak positions of kaolinite, goethite, dolomite, calcite and hematite in untreated, ethylene glycol treated and heated to 500 0C samples in clay separated. Photomicrograph of calcite replaced framework grain at margins (arrows). Photomicrograph of calcite replaced framework grain in core (arrows). SEM of calcite replaced framework grain in core (encircled). SEM photograph showing dolomite rim around volcanic fragment. SEM photograph showing kaolinite booklets (arrows). SEM photograph showing alteration and dissolution of feldspar grain (arrows). SEM photograph showing chlorite (arrows) in BSC mode. SEM photograph showing illite-smectite mixed layer in SEI mode. SEM photograph showing brush and hairy illite (arrows). SEM photograph showing anatase (arrows) well developed crystals. SEM photograph showing hematite (arrows). SEM photograph showing pyrite (arrows) within a shell. SEM photograph showing iron oxide/hydroxide with rosette structures (arrows). SEM photograph showing randomly oriented (arrows) iron oxide/hydroxide. SEM photograph of iron oxide laths showing little dissolution (arrows).
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5.27
5.28
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6.1
6.2
6.3
6.4
6.5
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SEM photograph of later stage iron oxide/ hydroxide (arrows) into early calcite cement. Photomicrograph of microfractures (arrows) in framework grains. A sketch of microfractures in framework grains perpendicular to maximum stress axis (same thin section as in Fig. 5.28). SEM photograph showing dissolution (arrows) of calcite along microfractures. SEM photograph of physically fractured feldspar grain (within ellipse). SEM photograph showing calcite penetration within early formed kaolinite booklets (arrows). SEM photograph of massive calcite cementation (arrows) which reduced porosity of sandstone. SEM photograph of dissolution (arrows) of unstable framework grains enhanced porosity of sandstone. Photomicrograph of late stage dissolution (arrows). Depositional model of Upper Cretaceous succession showing two contrasting, coeval depositional Systems. Field photograph showing synsedimentary normal fault (ellipse), section-9. Field Photograph showing basin-floor lobes of Mughal Kot Turbidites, section-20 (line across strike). Field Photograph showing laterally continuous beds (line), section-16, person encircle for scale. Field Photograph showing view of thinning upward (arrow) trend in Mughal Kot Turbidites, section-15. Field Photograph of channels (arrows) within mud rich lobes of Mughal Kot Turbidites, section-16.
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6.7
6.8
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6.10
6.11
Field Photograph showing mud rich lobes and channels (C)-levee (L) in Mughal Kot Turbidites, section-16. Field Photograph showing individual channel (arrow) within mud rich lobes of Mughal Kot Turbidites, section-16. Field Photograph of thickening upward cycle (arrow) of slope fan lobes of Pab Turbidites, section-15. Field Photograph showing laterally continuous beds of submarine slope fan lobes of Pab Turbidites, section-15. Field Photograph showing view of thinning upward cycle (arrows) of Pab Turbidites, section-15, man encircled for scale.
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Table No.
List of Tables Page No.
2.1
3.1
4.1
4.2
4.3
4.4
4.5
5.1
5.2
5.3
Generalized Stratigraphic succession of the Kirthar Fold Belt showing the stratigraphic position of Upper Cretaceous succession. Location of measured sections and logged through Upper Cretaceous succession in Central and Southern Kirthar Fold Belt (see Fig. 2.3). Average of point counting results in percentages (Fig. 4.6) of measured sections in lower units of both Northern and Southern Depositional Systems. Note that Upper unit is observed only in Southern Depositional System Major element concentrations and other geochemical parameters for mudstone samples of Upper Cretaceous succession. Major element concentrations for sandstones. Average major element concentrations for mudstone and sandstone samples. Point counting results of sandstone samples in percentages (Qp-Lv-Ls diagram) of measured sections. Conditions for identification of bulk mineralogical composition of sandstones and clay separates. Showing burial depths (B. Depth), mean porosity (n), Intergranular Volume (IGV) and depositional settings of Upper Cretaceous succession. Paragenetic sequence of sandstones of Upper Cretaceous succession.
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Appendix No.
LIST OF APPENDICES
Page No.
4.1
4.2
Results of point counting of sandstone of the Upper Cretaceous succession, Central and Southern Kirthar Fold Belt. Results of point counting in percentages (for Figs. 4.5, 4.9, 4.10) of sandstone.
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ACKNOWLEDGEMENT
I am indebted to my research supervisor, Dr. Abdul Salam Khan,
Professor and Director Centre of Excellence in Mineralogy, for proposing
research project, his guidance, valuable suggestions, discussions and cooperation
during fieldwork, laboratory work and writing up of this thesis. I am grateful to
my Co-Supervisor, Prof. Dr. Akhtar Muhammad Kassi, who equally contributed
and guided me in the field, laboratory and during writing up of the thesis. The
guidance of Professor Henrik Friis is specially acknowledged during my six
month research visit to Aarhus University, Denmark. I really appreciate the
cooperation of Professor Rasmussen, Anne Thoisen, Charlotte Rasmussen, Lab
Staff for their assistance in XRD analyses. The cooperation of Lab staff of Keele
University U.K., and Geoscience Laboratory Pakistan are appreciated for making
good thin sections and polished thin sections.
The research carried out for this thesis was partly funded by Pakistan
Science Foundation under a Project awarded to Dr. Abdul Salam Khan, Professor,
Centre of Excellence in Mineralogy. I acknowledge the financial assistance of the
Pakistan Science Foundation. I acknowledge the University of Balochistan for
granting funds for six months split PhD. The cooperation of Mr. Jiand Khan
Jamaldini, Treasurer University of Balochistan and Mr. Ghulam Nabi Chairman
Geology Department, during split Ph.D. case is highly appreciated. I would like to
thank Mr. Aimal kassi Assistance Professor Centre of Excellence for guidance in
computer softwares used to prepare this dissertation. I acknowledge the
cooperation of Mr. Alam Baloch, Registrar, Balochistan University of
Engineering and Technology, Khuzdar, for providing accommodation during
fieldwork. Ali Muhammad Driver is acknowledged here for safe driving and
making food during field.
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
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volcanic fragments, which were most probably caused by Deccan Trap volcanism in
south-southeast to the studied area.
Low K2O/Al2O3 ratio in mudstones, high values of CIA (Chemical Index of
Alteration) and SiO2 – Al2O3+K2O+Na2O diagram suggest the initial feldspar deficiency
was caused by intense chemical weathering due to warm humid paleoclimatic conditions
in source area. Further reduction of feldspar was caused by long transport distance and
most effectively by diagenetic dissolution, alteration and replacement.
The sandstones have undergone intense and complex diagenetic changes due to
framework composition of sandstones, burial depth and thrusting of Bela Ophiolites. The
unstable grains like feldspar and lithic volcanic fragments were dissolved considerably
and altered to a variety of clay minerals. Compaction, authigenic cementation, dissolution
and grain fracturing are important diagenetic events identified. Calcite, quartz, clay
minerals and iron oxide are the common authigenic cements. Dissolution and alteration
of feldspar and volcanic lithic fragments and pressure solution were the main sources of
quartz cements. Mechanical compaction, authigenic cements like calcite and quartz
reduced the primary porosity of the sandstones, whereas, dissolution of feldspar and
volcanic grains have enhanced and produced secondary porosity up to 15.53% (average
2.77 to 10.61%). Chlorite coating has prevented the quartz cementation, so some
microporosity was preserved. Some microporosity in interbooklets of kaolinite is
observed.
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
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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 –
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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, and ocation of the study area (Modified Bannert et al., 1992)
: Pakistan l after .
9
670660
O
NL
UL
BL
KHI
Uthal
Bela
Karachi
Sehwan
28o
27o
26o
66o
68o
67o
25o
ARABIAN SEA
50 Km0
Fig.2.3:.Geological Map of the study area showing important tectonic features andlocation of measured stratigraphic sections (modified after Bakr and Jackson, 1964).
12
14
Location of stratigraphic sections measuredCities and Towns
Northern Depositional System
Southern Depositional System
1
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 Formation
Sandstone and shale interbedded with subordinate conglomerate
Unconformity Miocene Gaj Formation Shale, sandstone with
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. 2.5: Bioturbation (arrows) in shale of Sembar Formation, section-16.
Fig. 2.4: Disconformable contact between the Sebmar Formation (arrow) and Anjira Formation (dip direction is shown by symbols) of the Ferozabad Group, section-5.
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. 2.7: Contacts between the Goru Formation, Parh Limestone, Mughal Kot Formation and Pab Formation, section-9.
Fig. 2.6: Parallel-lamination (arrows) in limestone of Goru Formation, section-9.
21
Fig. 2.9: Gradational and conformable contact between the Mughal Kot and Pab formations, section-9, two persons in circle are shown for scale.
Fig. 2.8 Parallel-lamination (arrows) in limestone of the Parh Limestone, section-16.
22
The formation has been assigned Barremian to Campanian age by Kazmi (1955 &
979) in the Kach-Ziarat area of the Sulaiman Fold Belt and Senonian by
illiams (1959).
.2.3 Mughal Kot Formation
Williams (1959) proposed the name Mughal Kot Formation for the rocks
xposed between 2 to 5 kilometers west of Mughal Kot Fort along Zhob–Dera
mail Khan road (lat. 31o 26/ 52// N; long. 70o 02/ 58// E).
The formation within the study area comprises marl, mudstone and
ccasional limestone. Marl is white (N9), bluish white (5B 9/1), light brownish
rey (5YR 6/1), greyish orange (10Y 7/4), greenish grey (5GY 4/1) and dark
ellowish orange (10YR 6/6). Marl is massive, parallel and cross-laminated. The
eds of marl are lenticular, thin bedded, ranging from 5 to 50 centimeters in
ickness. The frequency and thickness of marl beds decreases upward and
radually changes to mudstone completely. Marl is highly cleaved, homogeneous
nd partly laminated. Upper 30-35 meters part of the formation is composed of
in to thick bedded arenaceous limestone, which is graded, parallel-cross and
ummocky cross-laminated. Occasional sandstone beds are also present in the
rmation. Mudstone is olive grey (5Y 4/1), dark greenish grey (5GY 4/1), olive
Mughal Kot Formation is conformable and
transitional with the Pab Formation (Fig. 2.9). About 50 meters thick transitional
1
W
2
e
Is
o
g
y
b
th
g
a
th
h
fo
green (5GY 3/2), calcareous and flaky. Limestone is brownish grey (5YR 4/1),
light brownish grey (5YR 6/1), medium light grey (N6), medium grey (N5) and
biomicritic.
Upper contact of the
23
zone be
pelecypods (Fig. 2.11)
and bi
and pale yellowish brown (10YR 6/2). It is thin bedded, finely
d r
tween the underlying Parh Limestone and Mughal Kot Formation can be
seen in places. Vertical, horizontal and inclined burrows of up to 6 centimeters in
diameter are present. Brachiopods, Nautiliods (Fig. 2.10),
valves are present in the formation. On the basis of various types of
foraminifera a Campanian to Maastrichtian age has been assigned to the Mughal
Kot Formation (Williams, 1959; Fatmi, 1977).
2.2.4 Pab Formation
The name Pab Sandstone was introduced by Vredenburg (1907) and is
derived from the Pab Range in Kirthar Fold Belt. Williams (1959) designated its
type locality as a section along the route to Somalji Trail west of Wirhab Nai (lat.
25o 31/ 12// N; long. 67o 00/ 19// E). Later the name Pab Formation was introduced
as it comprises various lithologies like sandstone, mudstone and marl.
The sandstone is light brownish grey (5YR 6/1), very light grey (N8),
medium grey (N5), moderate yellowish brown (10YR 5/4) and pale red purple
(5PR 6/2). It is very fine to very coarse-grained and in places pebbly. Marl is
Table 3.1: Location of measured sections logged through the Upper Cretaceous succession in Central and Southern Kirthar Fold Belt (see Fig. 2.3). No. of section
Name Latitude Longitude
1 Langerchi section 270 41/ 670 10/
2 Karkh Nala section 270 41/ 670 05/
3 Bhalok section 270 39/ 670 03/
4 Khori section 270 44/ 670 01/
5 Siman Jhal section 270 37/ 660 31/
6 Pirmal village section 270 35/ 660 31/
7 Tibbi Jhal section 270 03/ 660 22/
8 Ferozabad section 270 45/ 660 31/
9 Chashma Murrad Khan section
270 38/ 660 28/
10 Nal section 270 47/ 660 08/
11 Bur Nai section 260 04/ 670 54/
12 Naka Pabni section 250 16/ 660 56/
13 Akri Dhora section 250 19/ 660 58/
14 Korara Lak section 250 20/ 660 58/
15 Jakker Lak section 250 31/ 670 00/
16 Sandh Dhora section 250 46/ 670 00/
17 Zarro Range section 260 24/ 660 55/
18 Khude Range section 260 26/ 670 04/
19 Kalghalo Jhal section 260 38/ 660 46/
20 Pundu Pash Jhal section
260 41/ 660 44/
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
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
216 m
121 m
0 m
S 1-19
F 3.11 &3.12
58
sh m c vc
S 2-2
S 2-3
S 2-4 & 2-5
S 2-6
S 2-7
S 2-8
S 2-9
S 2-10
S 2-1
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
Fig. 3.15: Sedimentological log of section-3 measured at Bhalok, grid ref 584205-35M/2, showing shelfal delta lobe faies association (see Fig. 2.3 for location and 3.13 for legends).
S 10-5
S 10-4
S 10-3
61
Fig. 3.16: Sedimentary log of section -4 measured near Khori village, grid ref. 553228, showing shelfal delta lobe facies association (see Fig. 2.3 for location and 3.13 for legends).
82 m
S 11-1
0 m
24 m48 m
72 m
62
141 m94 m47 m
0 m
S 5-1
F 3.2
S 5-3
S 5-2
S 5-4
S 5-5
S 5-6
S 5-7
S 5-8
63
132 m
S 6-2
S 6-3
S 6-4
S 6-8
S 6-5
S 6-6
S 6-7
44 m 88 m
64
Fig. 3.19: Sedimentary log of section-8 measured near Ferozabad village, grid ref 050321, showing shelfal delta lobe association (see Fig. 2.3 for location and 3.13 for legends; modified from Khan et al., 2002))
119 m
S 8-1
F 3.9
S 8-2
S 8-3
S 8-4
S 8-5
S 8-6
S 8-7
S 8-8
S 8-9
S 8-10
S 8-11
42 m 85 m
0 m
65
Fig 3.20: Sedimentary log of section-7 measured at Tibbi Jhal, grid ref. 860350, showing deeper shelf or ramp facies association, (see Fig. 2.3 for location and 3.13 for legends; modified from Khan et al., 2002).
225 mRanikotGroup56 m 112 m 168 m
S 7-1
S 7-2, 3
S 7-4
F 3.6
S 7-5
S 7-6
S 7-7
S 7-8
S 7-9, 10
F 3.1
S 7-11
S 7-12
S 7-13
0 m
66
S 9-1
F 3.4
S 9-2
F 3.23
0 m
75 m 150 m 225 m Ranikot Group
67
245 m
S 10-1
S 10-2
S 10-3
97 m 194 m
Ranikot Group
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
Fig. 3.24: Sedimentary log of section-12 measured at Naka Pabni, grid ref. 290545, showing thin channelized succession of Pab Turbidites in most proximal setting (see Fig. 2.3 for location and 3.13 for legends).
7 m
7 m
Ranikot Group
71
S 13-3 S 13-2
Ranikot Group
72
Ranikot Group
S 14-4
S 14-5
S 14-10
S 14-9
S 14-8
S 14-7
S 14-6
73
Ranikot Group
F 3.5
S 15-1-3
S 15-5
S 15-6
S 15-7
S 15-4
F 3.10
F 6.10
F 6.5
F 6.11
F 6.9
74
S 16-1
F 6
.4
S 16-2,3
F 6.8
RanikotGroup
S 16-17
S 16-16
S 16-15
S 16-14
S 16-13
S 16-12
F 6.6S 16-11
S 16-8S 16-9
S 16-10
S 16-7
S 16-5
F 3.31
S 16-6
S 16-4
F 6.7
0 m
75
Ranikot Group
S 17-5
F 3.7
S 17-4
S 17-3
S 17-2
S 17-1
0 m
62 m 124 m 186 m 248 m
76
203 mRanikot Group
0 m
48 m 96 m 144 m 192 m
S 18-5
S 18-4
S 18-3
S 18-2
S 18-1
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
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
Fig. 3.34: Sedimentary log of section-11 measured at Bur Nai, grid ref.336353 showing fluviodeltaic facies association, proximal component of Southern Depositional System (see Fig. 2.3 for location and 3.13 for legends).
F 3.17
145 m
S 11-5
S 11-4
S 11-3
S 11-2
S 11-1
F 3.8
78 m
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
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) Verycoarse 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) Undulosemonocrystalline quartz; B) Polycrystalline quartz consists of two sub grains;C) Polycrystalline quartz consists of more than two sub grains; D) K-feldspar; E) Plagioclase showing albite type twinning in central part; and F. Microclineshowing cross hatched twinning; all indicated by circles.
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
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
Fig. 4.8: The A-CN-K diagram of mudstone samples, showing high CIA values (after Nesbitt and Young, 1984); open circles indicate Northern and Closed circles show Southern Depositional System.
Al O + K O+Na O2 3 2 2
20
40
60
80
100
10 20 30
SiO2
Fig. 4.7: SiO -Al O + K O+Na O diagram for the sandstone (after, Suttner and Dutta, 1986)2 2 3 2 2 open circles indicate Northern and Closed circles show Southern Depositional System.
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
Craton interior
TransitionalContinental
Basement Uplift
Mixed
Dissected arc
Transitionalarc
Undissected arc
Recycled
QuartzoseRecycled
TransitionalRecycled
LithicRecycled
Qm
F Lt23 13
29
42
20
43
20
Craton interior
QuartzoseRecycled
Qm
LtF
112
Table 4.5: Point counting results of sandstone samples in percentages (Qp-Lv-Ls diagram) of measured sections.
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: traight contact between neighbouringframework grains.Microphotograph of s (arrows)
Fig. 5.2: oncavo-convex contacts betweenneighbouring framework grains. Microphotograph of c (arrows)
124
Fig. 5.3: utured contacts between neighbouringframework grains.Microphotograph of s (arrow)
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
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
Plag
iocl
ase
6.56
12.2
5
4.18
3.34
13.0
3.24
3.18
4.25
Qua
rtzFe
ldsp
ar
Goe
thite
Qua
rtz
Mix
ed il
lite-
smec
tite
Mix
ed il
lite-
smec
tite
Mix
ed il
lite-
smec
tite
c = samples heated at 500 C0
b = samples treated with ethylene glycol
a = untreated samples
a
b
c
D-spacing (A)Fig. 5.7: X-ray Diffractogram showing peak positions of feldspar, mixed clay layers, goethite and plagioclase (albite) in untreated, ethylene glycol treated and heated to 500 C samples in clay separates.0
129
Illite
Illite Qua
rtz
Illite
Plag
iocl
ase
c = samples heated at 500 C0
b = samples treated with ethylene glycol
a = untreated samples
D-spacing (A)
a
bc
10.0
5.0 3.3
Fig. 5.8: X-ray Diffractogram showing peak positions of illite, plagioclase (albite), in untreated, ethylene glycol treated and heated to 500 C samples in clay separates.0
4.25
130
Quar t
z
Chlo
rite
Plag
ioclas
e
Chlor
ite
Chl
orite
Chl
orite
Qua
rtz
Chl
orite
D-spacing (A)
c = samples heated at 500 C0
b = samples treated with ethylene glycol
a = untreated samples
a
b
c
14.0 7.0
3.34 3.18
3.524.
7
4.25
Fig. 5.9: X-ray Diffractogram showing peak positions of chlorite and plagioclase (albite) in untreated, ethylene glycol treated and heated to 500 C samples in clay separates.0
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
Kao
linite
Goet
hite
Kaol
inite
Calc
ite
Dol
omite
Hem
atite
Qua
rtz
3.587.
1
4.18
3.34
3.03
2.89 2.
7
3.52
D-spacing (A)
Chlo
rite
a
b
c
c = samples heated at 500 C0
b = samples treated with ethylene glycol
a = untreated samples
Fig. 5.11: X-ray Diffractogram showing peak positions of kaolinite, goethite, dolomite, calcite and hematite in untreated, ethylene glycol treated and heated to 500 C samples in clay separates.0
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. 5.18: SEM photograph showing chlorite (arrows) in BSC mode.
Fig. 5.17: SEM photograph showing alteration and and dissolution of feldspar grains (arrows).
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
n.% IGV Depositional setting
Northern Depositional System 1-19 2893m 7.42 20.2 Shoreface facies association 2-2 2916 m 8.70 17.0 Shoreface facies association 5-2 2792 m 9.96 24.0 Shelfal delta lobe facies
association 5-8 2710 m 9.25 19.6 Shelfal delta lobe facies
association 6-2 2812 m 8.04 34.0 Shelfal delta lobe facies
association 6-5 2747 m 8.59 29.0 Shelfal delta lobe facies
association 7-1 2825 m 7.63 34.2 Deeper shelf facies association 7-7 2757 m 9.51 23.0 Deeper shelf facies association 8-1 2835 m 7.84 33.8 Shelfal delta lobe facies
association 8-5 2790 m 10.61 34.6 Shelfal delta lobe facies
association 9-2 2743 m 2.77 25.2 Deeper shelf facies association 10-1 2824 m 10.11 20.2 Deeper shelf facies association
Southern Depositional System 11-3 3252 m 8.52 22.2 Fluvio-deltaic facies association 11-5 3185 m 10.30 14.8 Fluvio-deltaic facies association 13-3 2754 m 9.47 6.2 Submarine slope channels-fan lobe
facies association 14-7 2704 m 6.98 24.2 Submarine slope channels-fan lobe
facies association 16-5 2765 m 6.74 33.0 Submarine basin floor and slope
fan lobes and channels turbidites. 18-1 2777 m 8.83 15.2 Submarine basin floor and slope
fan lobes and channels, turbidites. 19-2 2760 m 3.29 10.2 Submarine basin floor and slope
fan lobes and channels, turbidites. 20-1 2780 m 6.65 26.2 Basin floor fan lobe facies
association
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.
Relative Timing Event Early Late
Mechanical Compaction Dissolution of feldspar and volcanic fragments Kaolinite Chlorite Chemical compaction Quartz cement Illite Calcite Dolomite Grain fracturing Iron Oxide Dissolution
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 sFig. 5.29: A sketch of microstructures in framework grains perpendicular to maximum stress axis (same thin section as in Fig. 5.28).
Fig. 5.30: SEM photograph showing dissolution (arrows) of calcite along microfractures.
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
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
Southern Depositional SystemNorthern 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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