Evolution of the marine Permian carbonate platform in the Salt Range (Pakistan)

摘要

During the Permian, a large carbonate platform developed on Gondwana continental crust adjacent to the Indian Shield. The varous carbonates and mixed carbonate/Siliciclastic rocks record major depositional sequences, and are a sedimentary experssion of variations in the depositional environment. As a result of the facies analysis in the in Salt Range and Trans Indus Ranges several sequences, bounded by sequence boundaries, are distinguished within the Zaluch Group and the basal Kathwai Member (Mianwali Formation). The Amb Formation (Wordian) represents a complete sequence bounded by sequence boundaries associated with hiatuses. The maximum flooding occurred within marly, fossiliferous carbonates of the Jan Sukh Member. The second sequence comprises the lower Wargal Formation (Capitanian). A climatic change towards higher water temperatures took place, accompanied by decreased terrigenous input from the hinterland. A carbonate platform developed with scattered coral patches. The third sequence (Wuchiapingian) is represented by the upper part of the Wargal Formation, again a carbonate platform with coral patch reefs and abundant bars composed of echinodermal debris. Within the Chhidru Formation each member represents its own sequence with basal terrigenous sandstones and overlying mixed carbonate/sandstone associations. The "White Sandstone Unit" is interpreted as a further lowstand system tract Changhsingian age. The lowest part of the Kathwai Member of the Mianwali Formation is still Changhsingian in age, and indicates a final Permian transgression. Transgression continued during the basal Triassic.