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

Abstract 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 T 1 to T h , 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 10 Be exposure and 14 C show abandoned ages of ~2.1 ka for T 1 , ~4.1 ka for T 2 , ~4.2 ka for T 3 , ~8.2 ka for T 4 , ~18.1 ka for T 5 , ~18.8 ka for T 6 , ~102.1 ka for T 7 , ~100.6 ka for T 8 1 , ~113.9 ka for T 8 2 , ~144.6 ka for T h 1 , ~210.7 ka for T h 2 , and ~284.3 ka for T h 3 . 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.