CONTROLS ON SEDIMENT SUPPLY IN THE PLIOPLEISTOCENE PESHAWAR BASIN, PAKISTAN

Abstract

The Plio-Pleistocene sediments of the Peshawar basin were deposited in lacustrine-fluvialfloodplain settings in response to the uplift of the Attock-Charat Ranges, due to drainage blockage and lake formation during the late Pliocene. The detrital influx was mostly from acidic igneous rocks with some contribution from metamorphic rocks of a medium grade (Peshawar Plain Alkaline Igneous Complex and surrounded metasediments). In the southern part of the basin, the parent rock lithology is mainly sedimentary rock and low-grade metamorphic rocks. Sedimentation occurred in active continental margin settings under a cold, arid climate with poor chemical weathering due to the low ratio of Zr/Sc and Th/ Sc in the samples which indicated the sediments do not allow fairly recycling or intense chemical weathering. The drainage controls on the major elements concentration of the river sediments after the Attock–Cherat Range has been uplifted suggested the major contribution during the Plio-Pleistocene, is from the Peshawar Plain Alkaline Igneous Complex (PPAIC) and related metasediments have been transported into the Peshawar basin by the Swat- Kabul rivers and numerous small tributary of this small river system that originated in the PPAIC and surrounding mountains. On the other hand, the geochemical signatures of these sediments do not support the contribution from the Himalayas hinterland through the Indus River because all the samples negate the basic igneous geochemical signal.