Abstract:
The late Permian age Chhidru Formation, exposed in Nammal Gorge, Western part of Salt Range Upper Indus Basin of Pakistan was studied for detailed microfacies analysis and petrographic study. The Chhidru Formation exposed in the study area constitutes a siliciclastic mixed carbonate sequence and consists of mixed lithologies containing white sandstone and beds of calcareous sandstone with sandy limestone. The upper most part of the studied formation marks an unconformity (P-T Boundary) with overlying Mainwali Formation, at the base, the formation has shale unit of grey to dark grey color with some dolomite and at bottom the Chhidru Formation is conformable with Wargal Formation. The thickness of studied formation is 66m reported and Chhidru Formation marks the termination of Paleozoic Era. As a result of microfacies analysis carried out, five microfacies i.e. CF-1 to CF-5 have been identified on the basis of fossils content, distinct textures and composition. These microfacies include CF-1microfacies, which corresponds bio-clasticwackestonefacies, CF-2 corresponds quartz rich sandstone facies, CF-3 corresponds forams’ rich calcareous sandstone facies, CF-4 corresponds forams’ rich bio-clastic sandy limestone facies and CF-5 corresponds bryozoans’ rich mudstone-wackestonefacies. The depositional characteristics of these facies are consistent with the proximal inner shelf to distalmiddle shelf settings of a siliciclastic-carbonate mixed platform.
