Depositional Setting Of The Datta Formation In The Western Salt Range, Pakistan

Abstract

The aim of the present work is to investigate the depositional setting of the Jurassic Datta Formation in the western Salt Range of Pakistan. In the western Salt Range, the Jurassic Datta Formation is comprised of quartz rich conglomerates, dolomite, shale, and coarse to fine sandstones of white, light and dark gray in colors having cross-bedding, ripple marks, bioturbation, mud cracks and plants remains are the common sedimentary structures. Based on field observation the Datta Formation in the studied section is divided into five lithofacies and three lithofacies associations. The channel belt lithofacies association predominates in the bottom portion of the lithological section, it consists of conglomerate lithofacies and medium to coarse grained sandstone lithofacies. It displays lenticular bedding with pinching behavior, having trough cross-bedding, illuminating sandstone deposition in a constrained environment. This association is overlain by channel margin and flood plain lithofacies association. The sandstone of this association is different from the channel belt facies association. Mud cracks, ripple marks, and bioturbation are the common feature which show low energy conditions than channel belt facies associations. Channel margin lithofacies association is overlain by lagoonal lithofacies associations, which is comprised of interbedded shale and dolomite with some minor sandstone/siltstone lithofacies. It has vertical and inclined burrows which show calm conditions. Moreover, the sedimentlogical feature of sandstone and siltstone of the studied area composed of dominantly cross-bedded sandstone reveal the flow direction of sediments in the north northwest. The petrographic study shows that the sediments are sub-sorted to well sorted and contain more than 90% of quartz, other minerals such as feldspar and lithic fragments are also observed but they are minor. The geochemical data shows that the sediments are highly weathered and recycled and the sediments were deposited in passive margin setting. The combined lithofacies associations, petrographic studies and geochemistry data indicate that the Jurassic Datta Formation in the western Salt Range exists probably in fluvial-deltaic environment