Paleoclimatic Variation And Weathering Trend During Pleistocene In The Peshawar Basin, Pakistan

Abstract

The present study is an attempt to grasp the paleoclimatic variation and weathering trend in the Peshawar Basin during the Plio-Pleistocene epoch. In the northwest, Pakistan the Plio-Pleistocene siliciclastic of the Peshawar Basin provide a geological record of paleoclimatic variations and weathering trend during this time. The sequence indicates basin formation in response to the Attock-Cherat uplifting and preserves paleoclimatic indications during sedimentation. The sedimentary archives are represented in the Peshawar Basin, Pakistan, by an interbedded sequence of mostly sand, silt, and clay rhythmites with interbedded conglomerate and overlain by continuous loess. Sedimentological data suggests that glaciofluvial rhythmites make up the lower portion of the stratal package, which is then covered by floodplain clay cycles, loess deposits, and lastly recent floodplain clays. Petrographic study show that sediments were produced from the recycled orogenic belt under relatively mild weathering conditions, allowing feldspars and other heavy minerals to be preserved. The Chemical Index of Alteration (CIA) is a chemical proxy widely used to determine the degree of source area weathering, while the CIA average values of sand-silt-clay is 59.2 and the loess deposits having values of 50.23. The geochemical proxies show an overall cold arid climate with relatively low chemical weathering. The Rb/Sr ratios in the examined samples range from 0.20 to 0.93 (average: 0.53), while the Th/U ratio average is 5, which is above from the standard value (3.5 to 4.0), so it indicates low to modest degree of chemical weathering at the sediment source. The CIA and PIA values indicate primarily low to modest weather conditions. The chemical weathering history suggests that the Plio-Pleistocene epoch experienced a cool, arid, and humid climate