Grain-size Characteristics And Environmental Significance Of Sediments In The Middle And Late Last Glacial Period Of Liaohua Section In Jiujiang City

Quaternary sediments are widely distributed and record the global and regional environmental evolution process in detail.Xingzi County,Jiujiang City,Jiangxi Province,is a subtropical monsoon climate zone with a special natural geographical environment.During the late Quaternary,a series of aeolian sediments were developed on the banks of Poyang Lake under the East Asian monsoon,which is an ideal carrier for paleoenvironmental research of Poyang Lake since the late Pleistocene.On the basis of investigation on lakeside sandy land in Xingzi County,the Liaohua section near Poyang Lake in the east of Liaohua Village in Xingzi County was selected to carry out the work.The chronology framework was constructed by using photoluminescence dating results,and the grain size composition was tested.Based on the grain size results,endmember analysis and fractal dimension calculation were carried out,and the paleoclimate change characteristics of lacustrine-continental sedimentary sequence in the middle and late last glacial period of Liaohua section were studied.Combined with the summer solar radiation in the northern hemisphere,(1)Liaohua section is mainly composed of sandy silty sand and silty sand,and its formation age is between 48.8 and 17.1 ka,which belongs to the product of the middle and late last glacial period,and can be roughly divided into three stages,in which the sand dune deposition was formed in the strong winter wind period of MIS3B(48.8-39.9ka)and MIS2(28.1-17.1 ka);Paleosols and lacustrine sediments were formed in the strong summer monsoon period of MIS3A(39.9 ～ 28.1 ka).(2)The average particle size of the Liaohua section in MIS3 b stage is the coarsest,with low fractal dimension and high degree of self-organization,and the content of coarse-grained endmembers(EM2 and EM3)is dominant,indicating a dry and cold climate environment;In MIS3 a stage,the average particle size became smaller,the fractal dimension increased,and the content of fine-grained endmember(EM1)increased rapidly,indicating that the climate gradually changed from dry and cold to warm and humid.The overall average particle size of MIS2 is coarse,and the fractal dimension is lower than that of MIS3 a,and its particle size and endmember content fluctuate obviously.The average particle size in the early stage of MIS2 is coarse,the volume fraction of EM1 is low,and the volume fraction of EM2 is high.In the middle stage of MIS2,the average particle size becomes smaller,and the content of EM1 increases rapidly.EM2 decreased rapidly,and the volume fraction of EM3 did not change obviously,indicating the change of MIS2 from dry and cold environment in the early stage to cool and wet environment in the middle stage.(3)The characteristics of climate change in the middle and late last glacial period revealed by Liaohua section are basically consistent with other aeolian sedimentary records in Poyang Lake,and are also very similar to the changes of East Asian monsoon intensity recorded by summer solar radiation in the northern hemisphere,oxygen isotopes of stalagmites in YZ cave in Chongqing and Greenland ice core.