Regional sediment sources versus the Indus River system: The Plio-Pleistocene of the Peshawar Basin (NW-Pakistan)

Abstract

Abstract Sedimentary archives within the Peshawar Basin in northwest Pakistan preserve a record of siliciclastic supply patterns during the Plio-Pleistocene epoch. The basin fill consists of fluvial-floodplain clays overlain by thick lacustrine-glaciofluvial rhythmites with deposits of multiple alluvial fans in the southern parts of the basin and topped by loess deposits in ideal vertical successions. Framework mineralogical composition and bulk sediment geochemical proxies of these sediments indicate detritus derivation from dominantly acidic igneous sources with contribution from medium-grade metamorphic rocks. There appears to be no significant contribution from ultramafic-mafic or very high grade metamorphic sources. In addition, sediments from the southern part of the basin support supply from low-grade metamorphic rocks and carbonate sediments. Overall sedimentation occurred in an active continental margin setting under conditions of insignificant chemical weathering. The uplift of the Attock–Cherat Range during the late Pliocene (2.8\u202fMa) restricted the Indus River from shedding its detritus into the basin. Therefore, the sediments of the Peshawar Basin do not reflect signatures of the Indus River siliciclastics and thus lack the basic igneous geochemical signal, which is otherwise typical for the Himalayas hinterland. On the contrary, the geochemical signatures of these sediments favour predominant detritus flux from the acidic rocks of the Peshawar Plain Alkaline Igneous Complex (PPAIC) and associated metasediments. Therefore, the Kabul-Swat River and other local tributaries of this smaller river system that originated within the PPAIC and associated mountains are considered the major transporting agents which contributed siliciclastics into the Peshawar Basin during the Plio-Pleistocene. Additionally, in the southern part of the basin the uplifting Attock–Cherat Range appeared to have contributed detritus in the form of alluvial-fluvial fan deposits.