Late quaternary geology and alluvial stratigraphy of the Ganga basin

Abstract

The Ganga basin in the Himalayan foreland is a part of the world's largest area of modern alluvial sedimentation and supports a population of over 200 million people. The Ganga plain deposits not only provide a modern analogue for the ancient fluvial sequences of the Himalayan foreland basin but they also provide one of the most significant continental records for understanding the interplay of climate, tectonics and eustatic changes in generating thick sedimentary fills in a monsoon-dominated foreland system. Given the large dimensions of the Ganga basin and the lack of an integrated approach, the available data are fragmentary, and several important questions regarding the sedimentary architecture and the process-form relationships of the parent rivers remain unanswered. This paper reviews the available information on the near-surface Late Quaternary stratigraphy of the upper, middle and lower Ganga basin, and reports new results based on studies of river cliff sections and shallow boreholes down to ~50 m depth. We record significant variation in sedimentary architecture between the upper and middle Ganga plains in the western and eastern parts of the basin, respectively. This variation reflects geomorphic diversity (linked especially to precipitation gradients) and tectonic history in the frontal orogenic areas which, in turn, impact sediment supply into the basin. Many of the alluvial sequences in the upper Ganga basin are interrupted by discontinuities that probably reflect Quaternary climatic fluctuations. In addition to controlling the long-term accumulation rate, tectonics may have had some local influence, and the effects of eustatic changes were almost certainly limited to the deltaic region of the lower Ganga plains, extending to a maximum of 300-400 km landward.