Sedimentary records of palaeofloods during the late Holocene along the lower Yellow River, China: A comprehensive study based on multi-proxy

In this paper we propose a new super-comprehensive proxy that integrates the sedimentary rhythm indicators of grain size, black carbon, anthropogenic elements, and pollen for the division of alluvial sedimentary rhythms suitable for use on sediments that have or have not been disturbed by past human activity. The new proxy was applied in the analysis of sedimentary records from two boreholes (identified as JM and SZ) in the Kaifeng area of the lower Yellow River, an area that has received less research attention in terms of flood events and sedimentary records compared to its middle and upper reaches. From this analysis, flood events that occurred in the lower Yellow River since the late Holocene were reconstructed. The results suggest there are 15 and 14 sedimentary rhythms in the cores of JM and SZ, respectively. Based on historical documents, archaeological excavation data from the vicinity of the core sites, and AMS14C dating, we established the chronological framework of sedimentary rhythms in both JM and SZ cores. Using this information, we then reconstructed six Yellow River flood events impacting Kaifeng that occurred after the Warring States period in the years 225 BCE, 1387 CE, 1399 CE, 1461 CE, 1642 CE and 1841 CE. Among the six flood events, except for the flood of 225 BCE which was directly caused by human factors, the rest were caused by natural factors, mainly from prevailing climatic conditions but superimposed by human activities. The research results, therefore, can provide a scientific basis for flood prediction, prevention and risk assessment in the Yellow River Basin under the background of global change, and also provide support for clarifying the relationship between regional climate background and human activities in abnormal flood events.