First geomorphological and sedimentological evidence for the combined tectonic and climate control on Quaternary Yarlung river diversion in the eastern Himalaya

Abstract

This study investigates the combined effects of Quaternary climate change and tectonically induced topography on the Yarlung River drainage-system evolution in the eastern Himalaya. Our work integrates field mapping, geomorphological analysis, stratigraphy, sedimentology, optically stimulated luminescence dating, radiocarbon dating, and detrital-zircon dating of a Holocene valley-fill sequence in a Yarlung River tributary. This holistic approach reveals an aggradational event, which started at or soon after 24–20 k.y. B.P. and continued to or after 9.2–8.0 k.y. B.P. across the Himalayan drainage divide between the east-flowing Yarlung River in the north and the south-flowing Subansiri River in the south. The aggradational event was associated with a major phase of glacier advance during a period of warm and wet climate conditions in the eastern Himalaya; it was expressed by the deposition of a valley-fill sequence across the modern Yarlung-Subansiri drainage divide. South-flowing fluvial sediments across the divide and the elevation distribution of the fluvial terraces require the existence of a major glacier dam that either blocked a tributary or the main trunk of the Yarlung River. Although we are unable to differentiate the two competing scenarios, our work reveals that combined Holocene climate change and tectonically induced topography have played a major role in controlling rapid shifts in drainage geometry at a time scale of <10 k.y. across the Himalaya.