Quaternary sedimentary characteristics and paleochannel evolution in the Anqing valley of the Yangtze River

Two sets of sedimentary systems, fluvial facies and piedmont facies, are developed in the NE trending valley of the Anqing section of the Yangtze River. Based on the measured Quaternary boreholes, through comparing cross sections of the NW and NNE directional boreholes, this paper revealed the stratigraphic combination characteristics of geological and geomorphic units, such as the alluvial plain and hillock of the Yangtze River. Then, we discussed the evolution process of the paleochannel in the Yangtze River valley in combination with the regional neotectonics characteristics, climate change and other information. The results show that there are at least two river sedimentary cycles developed in the Anqing valley along the Yangtze River, ranging from gravelly coarse sand to silty clay. The Xiashu Formation and Qijiaji Formation were deposited simultaneously on both sides of the hilly land. Quaternary sediments are composed of river alluvium, aeolian sediments and other genetic types, and have experienced geological processes such as early-middle Pleistocene alluvial-proluvial process, middle-late Pleistocene aeolian accumulation, river undercutting erosion and filling. Neotectonics, climate changes during the glacial to the interglacial, sea level eustacy and other factors jointly affect the evolution of the ancient channel in the Anqing section of the Yangtze River.