Abstract:

The Qingyijiang River, which is located in the northern piedmont of Mt. Huangshan, is the longest branch of the lower Yangtze River. Based on the field survey, a well-preserved sequence of one diluvial platform (P) and three river terraces (i.e., T3, T2 and T1) was found, and a corresponding sequence of four gravel beds was also presented, according to two natural sections of Xikou cross section and Chengbei cross section in the Jingxian Basin. In addition to the gravel fabric analysis method, the Electron Spin Resonance dating and palaeomagnetic dating were used to discuss the age, process and cause of river development of the Qingyijiang River. This study concludes that: (1) the results of the gravel fabric analysis show that the T3 terrace is the oldest terrace of the Qingyijiang River, and the T3 gravel bed is the oldest gravel bed of the same river; (2) the dating results show that the formation timing of the Qingyijiang River can be traced back to the period from ~1300 ka BP to ~900 ka BP, and the oldest timing of the river is ~1300 ka BP, whereas the most recent timing is ~900 ka BP; (3) the Qingyijiang River originated from one of the braided rivers on the diluvial fan before 1377 ka BP, and successively experienced three stages of the diluvial fan and braided rivers, the incision by the braided river and the Qingyijiang River formation, that is, the so-called development model of the Qingyijiang River from one braided river on the diluvial fan; and (4) the development of the Qingyijiang River may be a combined result of precipitation increase and tectonic uplift. This study provides a reference for the studies of the small and medium river development in eastern China.

Key words: Qingyijiang River, river terrace, gravel bed, gravel fabric analysis, age, river development