Late Quaternary fluvial landform evolution and controlling factors along the Yulin River on the Northern Tibetan Plateau

Abstract

The Yulin River in the northern Tibetan Plateau, consists of multiple geomorphological features, including alluvial fans, fluvial terraces, and river profile knickpoints. Collectively, these provide a natural laboratory for exploring the late Quaternary fluvial landform evolution in response to both climatic change and tectonic activities in the region of the Altyn Tagh Fault. In this study, we investigated the distribution, sequences and sediment characteristics of the fluvial landforms along the Yulin River based on high-precision (0.5 m-resolution) Worldview satellite images and field observations. Mid-Pleistocene alluvial fans formed the highest fluvial landform surface into which ten major inset fluvial terraces were developed, distributed along three stream segments. Real-time kinematic global positioning system (RTK-GPS) measurement of terrace surfaces and the modern river longitudinal profiles was conducted across the Dongbatu Shan to show fluvial landform geometry and tectonic deformation. Fluvial terrace surfaces were deformed due to fault uplift as illustrated by spatially variable surface geometries. The chronological sequences of terraces along the Yulin River since 160 ka were reconstructed based on 10Be terrestrial cosmogenic nuclides (TCNs) dating. Results indicated that river incision occurred mainly during periods of climate transition, suggesting that terrace evolution was partly controlled by climate changes. Moreover, terrace exposure ages showed an upstream younging trend along the river, demonstrating a probable response to knickpoint retreat. Combined with terrace deformation and ages, fault uplift rates were constrained, which were lower than the river incision rates during the Late Quaternary, indicating that crustal shortening was mainly absorbed by the growth of the regional anticline. Collectively, our results suggest that the evolution of fluvial landforms along the Yulin River is a function of interplay between regional tectonic activities and climatic changes, which is significant to understand the NW-outward splay of the Altyn Tagh Fault.