The Middle Permian (Capitanian) carbonate platform evolution and stratigraphic architecture of a Neo‐Tethys rim basin, Central Pakistan

Abstract

Here we present the stratigraphic architecture and carbonate platform evolution of the Middle Permian (Capitanian) succession (Wargal Formation) of Trans‐Indus Ranges, central Pakistan. The exposed carbonate sequence consists of thin‐ to thick‐bedded bioclastic, nodular, fine‐grained, and sandy limestone. Based on detailed petrographic studies, seven microfacies assemblages have been recognized, suggesting diverse depositional environments including mudflats, lagoon, sand shoal, and middle shelf. The identified age‐diagnostic larger benthic foraminiferal species enabled to assign a Middle Permian (Capitanian) age to the studied section of the Wargal Formation. Based on the vertical arrangements of depositional environments in time, three Transgressive Systems Tracts (TSTs), two Regressive Systems Tracts (RSTs), and 11 high‐resolution fourth/fifth‐order parasequences were delineated. The depositional and sequence stratigraphic analyses of the studied section inferred evolution of the Middle Permian carbonate platform in three stages: (i) marginal marine facies development in the lower part followed by (ii) transitional stage in the middle part, and (iii) finally, aggrading shallow marine facies stage in the upper part. The evolution of carbonate platform can be linked with the cessation of major rifting followed by thermal cooling and establishment of marine Tethyan settings at the margin of the rift flank basin. The diverse facies variation in the second stage of platform evolution argues strongly for the local intra‐plate stresses. Based on petrographic, SEM, and EDS studies, it is concluded that the studied section of Wargal Formation carries porosity values from a range of 2–8% with an average of 5% and can be called a low to moderate hydrocarbon reservoir in the study area.