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Shahid Ghazi ¹, Nigel P. Mountney ²

Affiliations
1 Institute of Geology, Punjab University, Quaid-i-Azam Campus, Lahore-54590, PK
2 School of Earth and Environment, Earth Science Building, The University of Leeds, Leeds LS2 9JT, GB

Abstract

The Early Permian Warchha Sandstone is well preserved in subsurface in the Potwar Basin and the Punjab Plain of Pakistan. However, this succession is only exposed in the Salt Range, and within this region, only a modest number of the many outcrops are of sufficient quality to enable the preparation of lateral and vertical log profiles. From the subsurface, data from five wells drilled in the Salt Range and Potwar Basin have been analysed. Although they are of restricted coverage, these subsurface data - which take the form of gamma ray logs and well cuttings - provide a valuable addition to the outcrop dataset of the Warchha Sandstone as they provide useful information about vertical textural changes, type and thickness of bedding and the nature of sandbody contacts with underlying strata. Overall, the Warchha Sandstone succession is composed of repeated fining-upwards cycles indicative of a meandering fluvial succession. Sub-components of each cycle are themselves classified into six subsurface sedimentary facies. Through comparison with outcropping parts of the succession, the origin and significance of these subsurface facies can be related to specific architectural elements within the meandering fluvial system responsible for generating the Warchha Sandstone succession.

Keywords

Cyclicity, Gamma-Ray Log, well Cuttings, Facies, Fluvial.

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Shahid Ghazi ¹, Shakeel Ahmad ¹, Muhammad Riaz ², Tehseen Zafar ¹

Affiliations
1 Institute of Geology, University of the Punjab, Lahore 54590, PK
2 Department of Earth Sciences, Abbottabad University of Science and Technology, Havelian 22500, PK

Abstract

Comprehensive sedimentological and sequence stratigraphic analyses of the Kussak Formation were carried out at the Nilawahan Gorge, the Karuli Section and the Khewra Gorge, Pakistan. The studied Kussak Formation has been grouped into: (1) bioturbated mudstone, (2) interbedded sandstone/shale, (3) sandy dolomite, (4) glauconitic sandstone and (5) laminated sandstone and siltstone. Hard to friable sandstone is present with condensed neobolus beds in the mud at the top. Bioturbation and glauconite are in middle parts, while a few beds of sandy dolomite are also present in the upper and middle parts of the Kussak Formation. These five depositional sequences had developed during the phase of transgression. Mineralogically, the average modal composition classifies it as quartz arenite. Rock fragments belong to the igneous origin, and feldspar grains most likely indicate an igneous and metamorphic source. The field and petrographic study indicate that the source area belongs to arid and semi-arid environments. Presence of wavy and flaser bedding indicates tidal flat deposition. Burrows, mud cracks, and synaeresis cracks indicate supra-tidal environment. Subsurface data show the finning upward sequence that confirms the deposition during transgression. In summary, the environment of deposition is subtidal, intertidal to supra-tidal environment. Palaeogeographic setting shows that the Kussak Formation source belongs to Aravalli and Malani ranges.

Keywords

Depositional Environment, Lithofacies, Provenance, Sedimentology, Sequence Stratigraphy.

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