By field investigation in the upper reaches of the Weihe River, the Holocene loess-soil profile containing the typical palaeoflood slackwater deposit was found in the Guchuan Basin.According to stratigraphic configuration and OSL dating for slackwater deposits and Loess-paleosol samples, the age of the extreme palaeoflood is fixed between 3 200 a B.P. and 3 000 a B.P..Through the analysis of microelements，a number of geochemical parameters were obtained. The results show that geochemical elements included in the palaeoflood slackwater deposit distinctly differ from paleosol layer below slackwater flood deposits and other loess layer in the profile. It shows the material sources of slackwater flood deposits is different from loess soil.Loess is the direct deposits of dust storms.While the slackwater flood deposits are secondary separation in the process of transporting by water,and without obvious weathering of soil improvement,so it is different from paleosol layer in physical and chemical properties.Combining with climatic change in the late Holocene, the results show that extreme floods usually occurred when the climatic changed abruptly.Because of the instable and highly variable climate change and the intensified rain,the extreme floods occurred frequently.

Holocene; loess-soil; palaeoflood slackwater deposits; geochemical characterization