Identification Of Limestone Unit Based On Faunal Content In Khanpur-Dam Section, Khyber Pakhtunkhwa, Pakistan

Abstract

The Chorgali Formation, dating back to the Eocene period, comprises limestone beds of medium to thick thickness with shale intercalations. The main focus of the study is the Khanpur Dam section located in the Haripur District of Khyber Pakhtunkhwa. Fieldwork involved the collection of approximately twenty rock samples, followed by microscopic analysis, which led to the identification of four microfacies. These microfacies were distinguished based on their fossil content, discrete texture, and allochem type. The identified microfacies within the Chorgali Formation are as follows Larger Foraminiferal Mud-Wackstone Microfacies. This microfacies contains larger foraminifer fossils and exhibits a texture characterized by mud and wackstone. The presence of these fossils indicates deposition in a low-energy shelf environment, likely closer to the inner part. Larger Benthic Foraminiferal Wackstone Microfacies. This microfacies also contains larger foraminifer fossils but displays a wackstone texture. The prevalence of larger benthic foraminifera suggests a shallow marine environment, potentially situated in the middle part of the shelf. Bioclastic Wackstone Microfacies. Bioclastic Mud-Wackstone Microfacies. This microfacies combines the presence of Bioclasts with a texture displaying characteristics of both mud and wackstone. It signifies a transition in depositional conditions from lower energy (mud) to slightly higher energy (wackstone). Additionally, petrographic studies were conducted to examine the diagenetic variations present within the Chorgali Formation. These studies revealed various diagenetic processes that have influenced the formation. Calcite veins were observed, indicating a transition from marine diagenesis to meteoric diagenesis. The presence of larger foraminifera and Bioclasts suggests a diverse marine fauna during deposition. The diagenetic variations further support this interpretation, indicating changes in environmental conditions over time, including the transition from marine to meteoric diagenesis and the influence of tectonic activity. In conclusion, the detailed analysis of the Chorgali Formation provides insights into its depositional environment, fossil content, and diagenetic history. This analysis suggests that the formation was primarily deposited in a shallow shelf environment.