Microfacies Analysis and Depositional Environment of Early Eocene Carbonates in the Balakot Region, Pakistan

Abstract

This paper examines microfacies, biostratigraphy, tectonic control and depositional setting of the Margalla Hill Limestone and Chorgali Formation in the Balakot area, Pakistan, during the Early Eocene. Based on a careful microfacies study, seven major microfacies types representing diverse energy regimes and depositional environments, extending from inner ramp-middle ramp settings to more limited, lagoonal environments, were recognized. Foraminiferal Bioclastic Wackestone, Assilina-Nummulites Bioclastic Wackestone, and Bioclastic Mudstone were the major microfacies employed for paleoenviromental and depositional environment interpretation. The work also defined the biostratigraphic zones SBZ8 and SBZ9 relying on the distribution of the main foraminiferal taxa like Nummulites, Assilina and Alveolina, thus, introducing the chronostratigra phic nomenclature for the area. The equivalent of the Margalla Hill Limestone represents the Nummulites Atacicus/Nummulites Globulus/Assilina Leymerie Biozone (SBZ8) and that of the Chorgali Formation is the Alveolina Indicatrix Biozone (SBZ9) which indicates a change in middle ramp setting to lagoonal setting. Further, the tectonic framework, driven by the Himalayan orogeny and the Main Boundary Thrust (MBT), was a key control on the carbonate sedimentation due to changes in subsidence, uplift, and erosion. The present work reconstructs the Early Eocene palaeoenvironmental conditions of the Balakot area in detail, which will improve our knowledge of the carbonate sedimentation, biostratigraphy, and tectonic control of the Himalayan foreland basins.

Keywords: Balakot region, Margalla Hill Limestone, Chorgali Formation, Early Eocene microfacies, Biostratigraphy of Nummulites, Depositional environments of the Eocene, Tectonic influence on carbonate deposition, Foraminiferal assemblages.