Fluvial incision by the Qingyijiang River on the northern fringe of Mt. Huangshan, eastern China: Responses to weakening of the East Asian summer monsoon

This paper focuses on climatic and tectonic controls to determine their relative importance to the Quaternary fluvial incision by the Qingyijiang River, eastern China. The Qingyijiang, which is one of longest tributaries of the lower Yangtze River, drains the northern piedmont of Mt. Huangshan. A field survey focused on three natural sections of the Qingyijiang in the Jingxian basin, where a well-preserved sequence of one alluvial platform (P) and three fluvial terraces (T3, T2, and T1) is presented. The heights of the platform and the terraces above river level are ~65, ~40, ~20, and ~7m respectively. In this study, electron spin resonance (ESR), optical stimulated luminescence (OSL), and palaeomagnetic dating were applied to reconstruct the fluvial incision history of the Qingyijiang and evaluate the possible influence of tectonic uplift and/or climate change on the fluvial incision. The main results show that (1) the ages of P, T3, T2, and T1 were determined to be ∼1300, ∼900, ∼600, and ∼1.5ka respectively, corresponding to four incision events in the Qingyijiang; (2) the East Asian summer monsoon (EASM) experienced four significant weakening events at ~1300, ~900, ~600, and ∼1.5ka, according to previous research. Correspondingly, we propose that four significant increased periods of regional precipitation occurred at ~1300, ~900, ~600, and ∼1.5ka in the study area because of the negative correlation between the intensity of the EASM and regional precipitation from 1960 to 2012; and (3) fluvial incision by the Qingyijiang arose as a result of the weakening of the EASM in combination with tectonic uplift, determined by matching fluvial incision history of the Qingyijiang with tectonic movement and EASM change. In addition, the weakening of the EASM climatically triggered fluvial incision by the Qingyijiang. This study supports the conclusion that major fluvial incision has been climatically triggered; however, it also suggests that the mechanism of river incision may be regionally distinctive in different climatic zones.