Holocene Paleoflood Slackwater Deposit in Lower Reaches of Weihe River

The Holocene palaeoflood slackwater deposit(SWD) was found in the lower reaches of the Weihe river by field investigations.Sedimentary samples were taken after detailed observations and pedo-stratigraphic subdivisions.Grain-size distribution,magnetic susceptibility,loss-on-ignition and CaCO3 content were measured in the laboratory.The results show that these bedded palaeoflood slackwater deposits are silty clay,very dense and hard,with blocky structure and low magnetic susceptibility,which are very different from the aeolian loess and soils overlying on the river terraces.Optically stimulated luminescence(OSL) dating shows that these palaeoflood events occurred between 3200 and 3000 a B.P.,exactly the same time as that documented in the upper reaches of the Weihe river.This time was the ending of the mid-Holocene climatic optimum,and also the ending of the Shang Dynasty in Chinese history.These palaeofloods are closely related with the global climatic decline at about 3100 a B.P.The results are of great significance in understanding the response of hydro-climatic system to global change.