Depositional Sedimentary Facies, Stratigraphic Control, Paleoecological Constraints, and Paleogeographic Reconstruction of Late Permian Chhidru Formation (Western Salt Range, Pakistan)

The Upper Indus Basin, in Pakistan's western Salt Range, is home to the Zaluch Gorge. The sedimentary rocks found in this Gorge, belonging to the Chhidru Formation, were studied in terms of sedimentology and stratigraphy, and provide new insights into the basin paleogeographic evolution from the Precambrian to the Jurassic period. Facies analysis in the Chhidru Formation deposits allowed the recognition of three lithofacies (the limestone facies-CF1, the limestone with clay interbeds facies-CF2, and the sandy limestone facies-CF3) with five microfacies types (mudstone biomicrite-MF-1, wackestone-biomicrite-MF-2, wackestone-biosparite-MF-3, pack-stone-biomicrite-MF-4, and packstone-biosparite-MF-5), as well as their depositional characteristics. The identified carbonate and siliciclastic formations display various facies in a shallow marine environment, with different lithologies, sedimentary features, and energy conditions. It is thought that the depositional characteristics of these microfacies are closer to those of the middle to outer shelf. Because of the progressively coarsening outcrop sequence, this formation seems to be at the very top of the high stand system tract (HST). A modified dynamic depositional model of the Chhidru Formation is further built using outcrop data, facies information, and stratigraphy. According to this concept, the formation was deposited in the middle to inner shelf area of the shallow marine environment, during the Late-Permian period. The Permo-Triassic Boundary (PTB), which is the end of the type-1 series, is marked by this formation's top.

Automated summary

The study of the sedimentary rocks in the Zaluch Gorge in the Upper Indus Basin of Pakistan provides new insights into the paleogeographic evolution of the basin from the Precambrian to the Jurassic period. The facies analysis of the Chhidru Formation deposits reveals three lithofacies and five microfacies types, suggesting deposition in a shallow marine environment closer to the middle to outer shelf. The depositional characteristics of the formation point to it being at the top of the high stand system tract during the Late-Permian period.