Terrace sequence along the Yushanguxi River in the southern piedmont of Tian Shan and its relationship to climate and tectonics in northwestern China

Controversies persist regarding the formation of terraces under the control of tectonic factors or climatic changes. This work focuses on the Yushanguxi River in the southern piedmont of Tian Shan, which is an intense tectonic uplift area where the terraces are very developed and the river has deeply downcut. Nine main terraces are distinguished (labelled T1 to Th, from youngest to oldest) based on the interpretation of a high-resolution remote sensing image, field investigations and detailed surveying with differential GPS. The results of the determination of 10Be exposure and 14C show abandoned ages of ~2.1 ka for T1, ~4.1 ka for T2, ~4.2 ka for T3, ~8.2 ka for T4, ~18.1 ka for T5, ~18.8 ka for T6, ~102.1 ka for T7, ~100.6 ka for T81, ~113.9 ka for T82, ~144.6 ka for Th1, ~210.7 ka for Th2, and ~284.3 ka for Th3. Since ~18 ka, the incision rate began to increase from ~0.6 mm a−1 to ~12 mm a−1, which is obviously higher than the fault slip rate of ~0.7 mm a−1. We suggest that the rapid downcutting along the Yushanguxi River during the Holocene has mainly been caused by frequent climate fluctuations.