Kirthar Fold Belt Research Articles

Sediment Composition and Provenance of the Pab Formation, Kirthar Fold Belt, Pakistan: Signatures of Hot Spot Volcanism, Source Area Weathering, and Paleogeography on the Western Passive Margin of the Indian Plate During the Late Cretaceous

Petrographic and geochemical data collected from the Pab Formation, a late Cretaceous clastic sequence exposed in the Kirthar Range of western Pakistan, yield important clues about the influence of the varied source regimes, transportation routes and volcanic input that have influenced the composition of sediments comprising this formation. Detrital compositional modes, petrotectonic discrimination diagrams and paleocurrent data all demonstrate that the Pab sands were ultimately derived from granitic–gneissic terranes forming the Indian Craton, exposed to the E and SE of the study area, with probable supplementary contribution from the mature, ancient sedimentary cover of the craton. These data also confirm that the two contemporaneous depositional systems operating during accumulation of the Pab Formation in this area were supplied from somewhat different sources and through different routes. Sediments deposited in the Central Kirthar sub-basin were derived from the East, while coeval deposits within the Southern Kirthar sub-basin were supplied from SSE and include relatively fresh volcanic detritus that is interpreted as the product of the major Deccan Trap volcanic episode, initiated during late Maastrichtian times. Moreover, geochemical indicators demonstrate that the ultimate composition of Pab sediments has been strongly influenced by intense chemical weathering, associated with warm/humid climatic conditions in the source areas, accompanied by significant diagenetic effects.

A prospective Neoproterozoic-Cambrian hydrocarbon/exploration play in the Kirthar Fold Belt, Pakistan

Abstract During the Late Neoproterozoic to Early Mesozoic the Indian Plate was part of Pangaea, the Palaeo supercontinent, with the African Plate to the west, as interpreted by various authors. At the same time, the Indian Plate was juxtaposed with the Central Iranian Plate, which separated it from the Arabian Plate in the vicinity of present-day Oman, c. 800 Ma ago. Between 612 and 200 Ma (Late Neoproterozoic to the end of the Triassic) these plates remained firmly attached. The changing configuration of the plates from 200 Ma to the present are provided in this paper. The Neoproterozoic–Cambrian rocks are recorded along the eastern border of Pakistan with India, extending into the Indian Territory and comprising part of the Neoproterozoic–Cambrian basin (Lower Indus Basin). The southern part of the Lower Indus Basin, from the Thar Platform in the east, deepens westwards towards Karachi (embayment) and the Kachhi Foredeep, where the Neoproterozoic–Cambrian succession is likely to be deep-seated. However, c. 5 km uplift of the Kirthar Fold Belt (KFB) across the Western Boundary Thrust (WBT) and the subsequent erosion have exposed the Middle Jurassic Chiltan Limestone, particularly in the central region of the KFB (Landsat images and domal structures with Jurassic outcrops are described in this paper) The limestone rests over older strata, with a possible presence of that of Neoproterozoic–Cambrian age, which is interpreted to be at drillable depth.

Depositional environments of Campanian–Maastrichtian successions in the Kirthar Fold Belt, southwest Pakistan: Tectonic influences on late cretaceous sedimentation across the Indian passive margin

The creation of a complex submarine morphology on the passive margin of the Indo-Pakistan continental plate during later stages of its northward drift, just prior to collision with Eurasia, is clearly demonstrated by the nature, architecture and regional distribution of sandstone bodies within the Campanian–Maastrichtian successions (Mughal Kot and Pab formations), exposed within the north–south trending Kirthar Fold Belt of southwest Pakistan. These successions range in thickness from 7 m to more than 500 m and are dominated by fine to coarse, sometimes pebbly, thin to thick-bedded sandstones with subordinate mudstones and marls, all of which were deposited on the north-facing passive margin of the Indo-Pakistan Plate. Twelve facies have been identified in these sequences and these have been grouped into nine Facies Associations, which were formed within two broadly coeval depositional systems that occupied the contiguous Southern Kirthar and Central Kirthar sub-basins. It is argued here that these sub-basins and their fill-sequences developed mainly in response to major, tectonically induced changes in both the morphology of this sector of the palaeo-margin and in the sediment-supply systems. The more proximal sequences in the east and southeast sectors of the Southern Kirthar sub-basin are dominated by fluviodeltaic deposits while more distal areas to the northwest are characterized by turbidite sandstone bodies formed in channel-levee and lobe complexes within slope and basin floor settings of a relatively confined deep marine trough. In this Southern Kirthar sub-basin, the Mughal Kot Formation comprises basin floor lobes, submarine channel-fill sand bodies and base of slope mud-rich lobes, whereas the succeeding Pab Formation reflects overall progradation of the system, being dominated by submarine slope fan lobes, channels and levee deposits. The Central Kirthar sub-basin displays a broadly east-to-west transition from shoreface (inner shelf), through shelfal delta lobes (middle shelf) and deeper shelf/ramp (outer shelf) facies associations, all formed on a gently inclined, storm- and flood-dominated clastic ramp. Synsedimentary normal faults observed in this study were controlled the depositional architecture and creation of closed deep marine southern Kirthar sub-basin during Late Cretaceous.

The effects of diagenesis on the reservoir characters in sandstones of the Late Cretaceous Pab Formation, Kirthar Fold Belt, southern Pakistan

The Maastrichtian Pab Formation in the southern part of Pakistan is composed of fine- to very coarse-grained texturally mature quartz arenite and subordinate sublitharenite varieties. The sandstones have undergone intense and complex diagenetic episodes due to burial and uplift. Diagenetic modifications were dependent mainly on the clastic composition of sandstone, burial depth and thrust tectonics. Diagenetic events identified include compaction, precipitation of calcite, quartz, clay minerals and iron oxide/hydroxide, dissolution and alteration of unstable clastic grains as feldspar and volcaniclithic fragments as well as tectonically induced grain fracturing. The unstable clastic grains like feldspar and lithic volcanic fragments suffered considerable alteration to kaolinite and chlorite. Dissolution and alteration of feldspar and volcanic lithic fragments and pressure solution were the main sources of quartz cements. Mechanical compaction and authigenic cements like calcite, quartz and iron oxide/hydroxide reduced the primary porosity, whereas dissolution of clastic grains and cements has produced secondary porosity. Chlorite coatings on clastic grains have prevented quartz cementation. Coarse-grained, thick bedded packages of fluviodeltaic, shelf delta lobe and submarine channels facies have higher average porosity than fine-grained, thin bedded and bioturbated sandstone of deeper shelf and abyssal plain environments and these facies are concluded to be possible future hydrocarbon prospects.

CLIFT, P. D., KROON, D., GAEDICKE, C. & CRAIG, J. (eds) 2002. The Tectonic and Climatic Evolution of the Arabian Sea Region. Geological Society Special Publication no. 195. vii + 525 pp. London, Bath: Geological Society of London. Price £120.00, US $200.00; members' price £60.00, US $100.00; AAPG members' price £72.00, US $120.00 (hard covers). ISBN 1 86239 111 4

The Arabian Sea region is a key area for deciphering plate tectonic reconstructions including the opening of the Red Sea/Gulf of Aden, the northward drift of India, the evolution of the Makran accretionary prism and the geometry and extent of the Indus Fan. It is also a key area for testing models of climatic–tectonic interrelationships, in particular the evolution of the Indian summer monsoon. This volume contains 26 papers documenting plate reconstructions, magnetic and gravity data, seismic surveys, magnetic isochrons, neotectonics and the Pleistocene–Holocene climatic record of the Arabian Sea. It begins with papers that include a new compilation of magnetic and gravity data used to reconstruct the Paleogene plate tectonic evolution of the Arabian Sea and East Somali basin. Multi-channel seismic surveys are used to constrain the sub-surface stratigraphy and structure. Papers document the onshore geology of the Iranian Zagros belt and Makran accretionary prism, the Kirthar fold belt along western Pakistan and the Ladakh Himalaya. Soon after the initial …

DEPOSITIONAL ENVIRONMENTS AND RESERVOIR ASSESSMENT OF LATE CRETACEOUS SANDSTONES IN THE SOUTH CENTRAL KIRTHAR FOLDBELT, PAKISTAN

Sandstones of Late Cretaceous (Campanian‐Maastrichtian) age constitute much of the Pab and Mughal Kot Formations, which are well exposed in western Pakistan. In the south central part of the Kirthar foldbelt, these units attain thicknesses ranging up to 350m and are dominated by quartzose sandstones with subordinate argillites and marls, all deposited on the western continental margin of the Indo‐Pakistan Plate. Seven sedimentologic logs, measured through this sandy sequence along a strike‐wise extent of some 290 km, provide new data on the palaeoenvironments and dispersal patterns represented in these rocks and on their reservoir potential.The eight main facies were formed by a range of sand‐transporting mechanisms that includes classical turbidity flows, storm‐ and river flood‐generated underflows, high and low‐energy tractional flows, storm‐ and fair weather wave reworking, and local slope failure and remobilisation. The four facies associations comprise a Shoreface Association, a Shelfal Delta Lobe Association, a Deeper Shelf/Ramp Association (the distal equivalent of the Shelfal Delta Lobe Association), and a deep‐water Submarine Fan Lobe Association.Facies distributions and palaeoflow patterns demonstrate the existence of two depositional systems in this area during the Late Cretaceous. Sandbodies formed in a NW‐prograding submarine fan dominate a southern system, while in the north of the study area, storm‐ and river flood‐influenced shelfal sands were conveyed to the west and WNW. Here, sediment‐gravity flows evolved from east to west, following a broadly across‐shelf pattern from cross‐bedded sandstones to graded turbidites. Sandstone petrography suggests supply from the uplifting Indo‐Pakistan Shield to the east, feeding a broad, west‐facing shelf or clastic ramp characterised by Mutti‐type “shelf‐lobes”.At outcrop, these sandstones possess low porosities but other reservoir characteristics (total sand thickness, percent sand, sand‐body geometry, vertical and lateral connectivity, The authors acknowledge the financial assistance of the Pakistan Science Foundation for the fieldwork. Most of the analytical and laboratory work was carried out at Keele University under the auspices of the Commonwealth Fellowship Scheme. The principal author thanks the Association of Commonwealth Universities for financial support and the School of Earth Sciences and Geography, Keele University, for providing facilities. Special thanks are due to P. Greatbatch, D. Wilde and A. Lawrence (Keele University) for technical and drafting assistance. Andrew Brown (ENI‐Lasmo, London), John Warburton and Simon Beswetherick of Lasmo Oil (Pakistan) Ltd. were most helpful and their sponsorship of new biostratigraphical analyses is also acknowledged. Thanks are due to the Centre of Excellence in Mineralogy, University of Balochistan for granting leave to the principal author. We much appreciated helpful discussions with John Smewing (Earth Resources Ltd, Swansea, UK) and Stuart Burley (BG Group), whose perceptive comments on an earlier draft of this paper were most valuable.

Sequence stratigraphy of the southern Kirthar Fold Belt and Middle Indus Basin, Pakistan

Abstract The southern Kirthar Fold Belt (KFB) and the contiguous Middle Indus Basin (MIB) constitute a major oil and gas province on the southern Pakistan foreland. In the Middle Indus Basin, gas is reservoired in Early Cretaceous marginal marine sandstones sealed by Paleocene shales. Reservoir quality of the Early Cretaceous sediments deteriorates towards the fold belt, but recent discoveries of gas in Upper Cretaceous sandstones sealed by Paleocene shales have highlighted its potential. To understand better the petroleum systems of this region and provide a potential correlation scheme for comparison with other areas of the country, a sequence stratigraphic interpretation was carried out on the Jurassic to Recent sediments of the KFB and MIB. On the basis of outcrop and well data, 23 depositional sequences have been identified: five in the Jurassic units, 10 in the Cretaceous units and eight in the Tertiary units. Sequence boundaries have been defined according to the Exxon method of identifying unconformities and their correlative conformities. However, equal importance has been given to indentifying the potentially more chronostratigraphically significant maximum flooding surfaces between these sequence boundaries so as to define accurately the component systems tracts of each sequence. The depositional systems are described in terms of their relationship to the existing lithostratigraphic framework and interpreted in terms of sedimentary responses to external (eustatic) or local (tectonic) events. Notwithstanding the presence of a eustatic signature on some sequences, the majority appear to be tectonically driven and can be related to plate margin events affecting the NW margin of the Indo-Pakistan Plate during its rift-drift-collision history.

Paleostress Reconstruction from Striated Fault Data Sets in the Kirthar Fold Belt, Southern Pakistan

The Kirthar fold belt (KFB) is one of the N-S-trending portions of the thrust belts of western Pakistan. In the study area (some 150 km north of Karachi), the KFB consists of large-scale, open NNW-SSE anticlines that affect the outcropping Kirthar and Nari formations. From an analysis of more than 200 minor strike-slip and reverse faults from 14 different data stations, two main σ1 directions were identified, ENE and ESE. The ESE stress is interpreted as the regional, primary stress field, and the ENE direction as a deflection of the former caused by the presence and activity of NNW-trending macrostructures (folds and strike-slip faults).