Genesis of the Qingyijiang River on the northern fringe of Mt. Huangshan, China, based on a combined analysis of gravel fabrics and ESR dates

The Qingyijiang River, which originates from the northern fringe of Mt. Huangshan, is an important tributary of the lower Yangtze River. A field investigation focused on the natural outcrops of the Qingyijiang in the Jingxian Basin, where a well-preserved sequence of three gravel beds of fluvial terraces is present. Based on gravel fabric analysis and ESR dating, this paper discusses the genesis of the Qingyijiang on the northern fringe of Mt. Huangshan. The main results show that (1) the diameter of the gravels is mainly medium and coarse, showing that the hydrodynamic conditions were strong in the formation periods of the terrace gravel beds, especially for the T3 terrace gravel bed; (2) the gravel orientations in the gravels of the T3 and T2 terraces are 191° and 250°, which are to the SSW and SWW, respectively, and are similar to the present flow, which is from southwest to northeast; (3) the roundness of the gravels is mainly subrounded or rounded, implying that these gravels were transported significant distances from their provenances; (4) the terrace gravels contain mainly quartz sandstone, sandstone, vein quartz and quartzite, which account for 90% of the rudaceous clasts in each terrace gravel, which shows that there was no significant provenance change; (5) the gravels of the T2 and T1 terraces are typical fluvial sediments, whereas that of the T3 terrace is a product of superimposition of debris flow and fluvial deposits; and (6) the Qingyijiang originated from a braided river on an alluvial (or pluvial) fan, and the timing of the Qingyijiang can be traced back at least to 905.4 ± 272.4 kyr ago when the Yangtze cut through the Three Gorges.