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 CaCO3content 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 3200and 3000aB.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 3100aB.P.The results are of great significance in understanding the response of hydro-climatic system to global change