Late Pleistocene history of aggradation and incision within a bedrock gorge, Narmada River, central India: implications for resurgent tectonic activity and changing climate

Abstract

Bedrock gorges occurring on the Indian Peninsula are sites of intense erosive activity where thick sequences of fluvial sediments are conspicuously absent. We identified unusually thick and coarse fluvial sequences within the Dhadgaon (DG) gorge in the lower reaches of the Narmada River in central India. Stratigraphic interpretations, sediment character and optically stimulated luminescence (OSL) ages revealed episodic aggradation at ~70 ka and ~28 ka in response to tectonically induced steepening of the upstream channel gradient. Incision of the DG gorge and sedimentation of the alluvial fan downstream was facilitated by a climatically induced decrease in the sediment supply/discharge ratio in addition to the tectonic slope. The final evacuation of sediments from the DG gorge and incision of the Banganga channel occurred during the early Holocene. Collectively, the results show a major influence of tectonics, hillslope processes and lithology on aggradation-incision patterns supported by climatic conditions during the late Quaternary.