Abstract:Paleoflood sediment is an important carrier to study extreme precipitation events and paleoenvironmental evolution in geological history.The study of paleoflood reconstruction based on geological records can provide basis for revealing the historical process and mechanism of regional flood,and has important practical significance for water resources utilization and engineering construction.In this paper,the Lidicheng village profile,which is well exposed on the north bank of the ancient channel of Caohe River,is taken as the research object.Based on the analysis of stratigraphic sequence,field sedimentary characteristics,sedimentary structure and sediment grain size,the ancient flood events recorded by the ancient channel of Caohe River in Baiyangdian area are identified.It is found that the profile has the following main characteristics:there are obvious scouring and erosion surfaces between the paleoflood sedimentary layers and the underlying strata,and the sedimentary body is lenticular in shape,which is composed of muddy gravel,charcoal fragments,bivalves and grayish black silt-fine sand,and medium-and small-sized cross-bedding is developed;The grain size indexes of flood sediment (median grain size,sand content,clay/silt and Q90) have high values,with fine sand as the dominant component,mixed silt and a small amount of clay,and poorly sorted;Ancient trees and bivalves are intensively buried in the paleoflood sediments in a directional arrangement,and the direction is consistent with that of ancient river channels revealed by remote sensing images.Based on the sedimentary characteristics of the profile and AMS 14C age analysis,it is determined that four paleoflood events occurred in Caohe at about 10.8~9.6 ka BP in the early Holocene,which can be compared with other paleoflood events in North China during this period.It is inferred that the paleoflood events in Baiyangdian area were the product of the climate in the early Holocene.At that time,the East Asian summer monsoon was strengthened,with frequent fluctuations in temperature and precipitation.
