Latest Quaternary rapid river incision across an inactive fold in the northern Chinese Tian Shan foreland

This work focuses on the incision process over the Tuostai anticline, a fold of the proximal structure Belt I in the northern Chinese Tian Shan foreland, where the Sikeshu River has incised deeply into the alluvial gravels and the fold's underlying bedrock strata. Field investigation and geomorphic mapping define five terraces of the Sikeshu River (designated as T-1 to T-5 from oldest to youngest) preserved within the Tuostai anticline. Be-10 surface exposure dating and optically stimulated luminescence dating constrain stabilization of the highest three terrace surfaces at about 80 ka (T-1), 16 ka (T-2), and 15 ka (T-3), respectively. Around 16 ka, the calculated river incision rates significantly increase from <2 mm/yr to >6 mm/yr. Undeformed longitudinal profiles of terraces T-2, T-3 and T-4 over the Tuostai anticline suggest that this structure may have been tectonically inactive since stabilization of these three terraces. We thus think that the observed rapid river incision over the Tuostai anticline has not been largely forced by tectonic uplift. Instead, the progressively warmer and wetter palaeoclimatic condition within the Tian Shan range and its surrounding area during the period of similar to 20-10 ka may have enhanced river incision across the Tuostai anticline. A reduced sediment/water ratio might have lowered the gradient of the Sikeshu River. (C) 2017 Elsevier Ltd. All rights reserved.