Provenance of the Early Eocene Chashmai Formation in South-Western Kohat: Indications of an Uplifted Island Arc
The Chashmal Formation of Early Eocene age Is well exposed In the western Kohat basin and Is clastic equivalent of carbonate and evaporites In the eastern and central Kohat basin. The formation Is a coarsening upward sequence of shale, sandstone and conglomerate. Petrographic and modal compositional studies of the formation at Its stratotype show that It Is composed mainly of quartz and lithic fragments of sedimentary affiliation. Minor amount of volcanic lithic fragments were probably derived from rhyolites or dacites. Feldspar content is small and most of it has been altered or replaced by calcite cement. Detritus for these sediments was probably derived from cover sequence of an uplifted orogenic belt which was located to the west of the basin of deposition. North Wazlristan and Kurram melange zone are the probable source area for these sediments. .