Reorganization of antecedent rivers in response to the evolving landscape at the northeastern margin of the Tibetan Plateau

Abstract

Drainage reorganization is generally associated with the coupling of crustal movements and climatic influences, although, in terms of landscape evolution, the responses of river systems to these competing roles remain elusive. Here, we focus on patterns of drainage reorganization in relation to rivers interacting with uplifting mountains, aiming to establish processes and patterns of drainage reorganization in the mountainous fringe of the northeastern Tibetan Plateau during episodes of arid or semi-arid climate during the Quaternary. This work has used sedimentary and geomorphological data from north–south oriented gaps through recently uplifted mountains, with copious geochronological constraint from optically stimulated luminescence, ¹⁴C and cosmogenic nuclide exposure dating, the last involving ¹⁰Be exposure and ¹⁰Be depth-profile analysis. We find that these gaps, now with uplifting mountains on both sides, were initially the lowland courses of rivers originating from the Qilian Shan mountain-range at the northeastern plateau margin. Gravels representing Qilian Shan rivers following these lowland courses have been dated to ∼200 ka, 120–100 ka and 80–50 ka. As the newly formed mountains uplifted further and coalesced, in combination with a cooling and drying climate, the rivers draining through the gaps were forced to reorganize by means of valley deepening and diversion. Two episodes of such reorganization are seen from our geochronology: at 119 ka and 30 ka. It can be concluded that the initial river pattern was driven by tectonic activity, but was later adjusted as part of complex landscape evolution in response to the coupling of surface uplift and climate change. Our results imply that drainage reorganization is primarily driven by crustal movements, although the potential influence of climate change on this process in the region cannot be entirely excluded.