OSL and radiocarbon dating of flood deposits and its paleoclimatic and archaeological implications in the Yihe River Basin, East China

Flood is a kind of serious nature disaster, so studies on the palaeofloods are the keys to understand the mechanisms and their relationships with climatic change, geomorphologic evolution and civilization evolution are of great importance. The floods happened frequently in the Yihe-Shuhe River Basin in history, forming the alluvial plain and affecting the evolution of the ancient civilization. However, the complex sediment sources and depositional processes make the flood deposits difficult to be dated and consequently hinder our understanding to the palaeofloods. In this study, we present twelve Optically Stimulated Luminescence (OSL) ages and four AMS 14C ages of flood deposits to study the palaeoflood activities in the Yihe River Basin and its palaeoclimatic and archaeological implications. The youngest OSL age of 0.19 ± 0.02 ka at the depth of 0.5 m shows that the residual OSL age, if any, must be much smaller than this amount, and the well comparison between OSL ages and AMS 14C ages further confirm that the flood deposits could be well bleached before buried and consequently the OSL ages are not overestimated. The source of sediments from ground surface in the mountain regions in the upper stream and the special characteristic of quartz might have contributed to the sufficiently bleaching. Consequently, OSL dating has the potential to offer reliable chronology for the flood deposits. The extraordinary floods happened at 4.1-3.8 ka, 3.3-3.0 ka and 0.9-0.1 ka correspond to the global abrupt climatic events, demonstrating that the extreme floods might be caused by or be parts of these climatic instabilities in monsoonal China. The flood happened at 4.1-3.8 ka might have directly caused the decline of the highly developed late Neolithic civilization (Longshan Culture) in the Yihe-Shuhe River Basin.