Palaeoenvironmental significance of grain-size distribution of river flood deposits: a study of the archaeological sites of the Apengjiang River Drainage, upper Yangtze region, Chongqing, China

摘要

The grain-size distribution (based on cumulative probability curves) in the sediments produced by potential palaeofloods at the Shiniusi archaeological site is similar to that of modern flood sediments from the Wujiang River Drainage in the upper Yangtze River. There is an obvious pattern in the curves, with two segments, and the mean grain size (Mz), standard deviations (σ1), skewness, and kurtosis are all similar. Combined with the AMS~(14)C dating data and the ages judged based on the presence of cultural remains, our data suggests frequent palaeoflood events within the Wujiang River Drainage. We hypothesize the existence of seven high flood possibility layers in the QST4 unit from Shiniusi archaeological site: during the periods of the Ming Dynasty (1368-1644 AD) to the Qing Dynasty (1616-1911 AD), and the end of the Eastern Zhou Dynasty (770 BC-256 BC) to the Shang Dynasty (1600-1100 BC). We also hypothesize ten high flood probability layers in the QST2 unit from Shiniusi archaeological site: during the periods of the Ming Dynasty to the Qing Dynasty, the periods of Song Dynasty (960-1279 AD) to the Yuan Dynasty (1206-1368 AD), as well as during the Han Dynasty (207 BC-220 AD) to the Eastern Zhou Dynasty (770 BC-256 BC). These results are consistent with palaeoflood events inferred from pollen and spore analysis and from historical records in other rivers.