Insight to the geological character of the Early Triassic strata in the Western Salt Range, Pakistan: A comparative study

Abstract

The sedimentary strata along the Permian–Triassic Boundary in the Western Salt Range of the sub‐Himalayas were analysed to gain an insight of its geological character regarding palaeoenvironments, palaeoclimate, and sequence stratigraphic attributes. The Early Triassic Mianwali Formation is dominated by shallow marine facies with transgressive phases, differentiation in facial character, and palaeowater depth among different sections. The study suggests that compared to the siliciclastic‐dominated Nammal Gorge Section, the Zaluch Nala Section is more carbonate‐dominated, representing algal‐laminated limestones, dolomitic marls, and siliciclastics – mainly restricted to the Mittiwali Member. There is a general decrease in ammonoids and increase in thickness from east to west, that is believed to be due to algal‐induced rapid sedimentation in the shallow marine environments as compared to deeper marine in the east. The Mianwali Formation has been deposited in two transgressive systems tracts, two highstand systems tracts, and one falling‐stage regressive systems tract. Two flooding surfaces, one each in the Mittiwali and Narmia members, have been recognized. The maximum regressive surfaces at the bottom (with the Chhidru Formation) and top (with the Tredian Formation) mark second‐order eustatic falls. The study also advocates for existence of a low‐energy platform in the temperate waters of the Palaeo‐Tethys. The sediments have similarities with various sections of Gondwanaland having the same trend of shallow marine facies and presence of algal‐laminated deposits. In the Middle Triassic, the gradual loss of sediment binding organisms shifted the low‐energy meandering patterns to high‐energy braided systems.