Causes of recent Himalayan uplift deduced from deposited patterns in the Ganges basin

Abstract

THE hypothesis¹ that late Cenozoic uplift of many of the world's mountain ranges was a response to climate change rather than to tectonic processes is based on the premise that enhanced erosion in an altered climate led to a reduction in both the total mass of a mountain range and its mean elevation. This reduction was coeval with increased regional relief and with passive isostatic uplift of the remaining summits. The hypothesis is difficult to evaluate because both climate and tectonic forces affect uplift in many active ranges. In the absence of sufficient denudational and uplift data from the mountains themselves, depositional patterns in adjacent basins may sometimes be used to distinguish between uplift arising from erosional or from tectonic processes. In foreland basins, uplift of the proximal basin and a reduction or absence of asymmetric subsidence are predicted responses to erosionally driven uplift². Here I show that patterns of sediment accumulation and the position of major rivers in the Neogene Gangetic foreland basin seem to have changed markedly in Plio-Pleistocene times. These changes lend support to the hypothesis that the importance of erosional unloading has increased in the Himalayas during the past 4 Myr.