Geochemical Differentiation and Tectonic Evolution of Flood Plain Sediments of Southern Ganga Plain, India: Implication to Provenance and Weathering Processes

The Ganga plain is an active foreland basin formed as a result of continent-continent collision between the Indian and the Eurasian plates. The Ganga foreland Basin (GFB) provides a unique opportunity to study the response of fluvial system to foreland basin processes, namely intra-and extra-basinal tectonics, climatic variability and base level changes. The Ganga River receives sediments from Himalayas in the north and the Peninsular (cratonic) region in the south, encompassing heterogenous lithologies belonging to differing geological origin. The nature and proportion of Himalayan as well as peninsula derived sediments have varied with time in response to prevailing tectonic and climatic conditions. In this study, a systematic sedimentological and geochemical investigation has been carried out on a chronologically well constrained sediments deposited in the southern Ganga plain in Varanasi region, to decipher the source of sediments, and its link with climate and tectonic evolution of Ganga River basin. Based on the sediment texture and structures, two sediment packages could be identified belonging to different ages. The geochemical investigation further confirmed the compositional variability in these sediment packages. Sediments deposited before 40ka (sediment package 1) shows higher trace elements (Sc, Co, Ni, Ti and Cr) and weak Eu anomaly suggesting mafic sediment source. On the other hand, the sediments deposited after 40ka (sediment package 2) shows lower abundance of trace elements with insignificant Eu anomaly indicating mixed type sediment source. This implies that the sediment contribution to Varanasi region in the southern Ganga Plain were chiefly through Peninsular Rivers before 40ka, and the Himalayan derived sediments dominated after 40ka, possibly associated with the intra-basinal tectonic activity in the Ganga Basin.