FACIES ANALYSIS, DEPOSITIONAL ENVIRONMENT AND DIAGENESIS OF CRETACEOUS KAWAGARH FORMATION, KOHAT RANGE, PAKISTAN

Abstract

The current research work focused on the petrographic investigation of the Cretaceous carbonate rocks of the Kawagarh Formation exposed in Kohat Kotal-Section. The Formation is mostly composed of thick to medium bedded, hard, highly fractured limestone and dolomitic limestone. An overall total of 107 representative samples were collected at regular intervals to perform detailed petrographic analyses to determine the depositional and diagenetic environments. In petrography, a large number of planktonic foraminifera, calcispheres, filament, oyster, and inoceramid shows the main skeletal grains whereas radiolarians, bioclasts, crinoid, echinoid, ostracod occur as trace species. Detrital quartz and dolomite were the main non-skeletal constituents. In sedimentary structures the Thalassinoides burrows were recorded as main sedimentary structures of the Kawagarh Formation. Based on the dominance of skeletal types and their abundance, eleven microfacies were constructed including, Planktonic Foraminiferous Packstone, Planktonic Foraminiferous Wackestone, Planktonic Foraminiferous Packstone- Wackestone, Mixed Bioclastic-Foraminiferous Wacke- to Packstone, Planktonic Foraminiferous Mudstone, Calcispheric Planktonic Foraminiferous Wackestone, Oyster- Planktonic Foraminiferous Wackestone, Filamentous-Planktonic Wackestone, Inoceramous-Planktonic Wackestone, Burrowed/Bioturbated Wackestone and Dolo- Mudstone were established. In the Kawagarh Formation, the lack of reefal facies, shoals of sandy carbonate, and sharp overlapping of shallow facies with deeper facies imply ramp settings. The petrographic analyses also show that the sediments of the Kawagarh Formation were affected by the various diagenetic processes including micritization, neomorphism, cementation, fracturing, pressure dissolution and dolomitization.