Study On The Evolution Of Paleoenvironment In Xiong'an New Area During The Past 40ka Years

The Xiong'an New Area is located in the northern part of the Hebei Plain,in the East Asian monsoon area,and has developed Baiyangdian,the largest modern lake system in North China.The rich Quaternary sediments are characterized by wide distribution,continuous,and large thickness.They are natural records and important carriers for restoring the history of paleoclimate and paleoenvironment evolution in eastern China,discussing important changes in ancient river channels,and other important geological scientific issues.In this paper,7 representative research sections of the Xiong'an New Area are selected.Based on detailed sedimentology studies,OSL Dating and ¹⁴C Dating are used to establish the stratigraphic framework since the mid-late late Pleistocene in the Xiong'an New Area.On this basis,take high-resolution paleoenvironmental samples,carry out test and analysis of various paleoclimate alternative indicators such as magnetic susceptibility,grain size,chromaticity,and comprehensive comparative study of high precision,multiple indicators,and multiple profiles to reconstruct the paleoenvironment of Xiong'an New Area since 40ka years evolution process.The main results achieved in this article are:?1?By analyzing the sedimentary characteristics of the profile,combined with OSL Dating and ¹⁴C Dating methods,the stratigraphic framework of the Xiong'an New Area since the mid-late Late Pleistocene period of 40ka years has been established,and the sedimentary environment has been analyzed.?2?According to the comprehensive analysis of climate alternative indicators,five climatic evolution stages in Xiong'an New Area since 40ka years have been divided.Stage?:41.16⁴0.25kaB.P.?1120cm¹000cm?,the sedimentary environment is mainly lacustrine facies,and the climate is relatively dry and cold.Stage?:40.25²8.31kaB.P.?1000cm⁷30cm?,the sedimentary environment is dominated by lacustrine facies,which is in the warmer period of the last glacial period,and the climate is relatively warm and humid.Stage?:8.31⁸.39kaB.P.?730cm³40cm?,in the colder period of the last glacial period and the post-glacial period,the climate is cold and dry.Stage?:8.39⁵.17kaB.P.?340cm²60cm?,in the Holocene warm period,the climate is warm and humid,and the lake has experienced an expansion period.Stage?:5.17kaB.P.till now?260cm⁰cm?,the sedimentary environment is mostly river facies,the climate fluctuates obviously,and the whole turns dry.?3?The evolutionary trend of the Baiyangdian Lake Group is discussed:the mid-late Late Pleistocene to early Holocene is the stage of incubation of lake prototypes;in the early Holocene,the lake was in the rising stage;in the middle of the Holocene,it reached a period of full expansion;in the late Holocene,due to climate change and human activities,the lake contracted and dried up.The results of this study will provide basic geological data for the Xiong'an New Area and advance the accuracy of the Quaternary geological research in the Xiong'an New Area to a certain extent.In addition,it also provides some reference for the study of the evolution of Baiyangdian Lake Group.