Sedimentary Characteristics,Physicochemical Property And Environmental Evolution Of Houtian Section In North Jiangxi Province During The Last Glacial Period

The study area is located on the southwestern edge of Poyang lake in northern Jiangxi,in which it is influenced by the east asian monsoon.As the special geographical position,not only are a series of friable aeolian sandy hills and mounds generally distributes along the banks of Poyang Lake's estuary,but also it spreads the central lakeside and the middle and lower reaches of the Ganjiang and Fuhe rivers.The aeolian sediments implies rich environmental evolution information,providing ideal recording materials for paleoclimate changes in the region.On the basis of multiple comprehensive investigations of the aeolian sedimentary sequence developed around Poyang lake,the Houtian section was selected to carry out the work,which located on the east side of the Houtian desert in the Xinjian district of Nanchang.Through the climate substitutes such as grain size,chromaticity,calcium carbonate,and p H value,basing on the results of Optically Stimulated Luminescence(OSL)age,the palaeoclimate change characteristics of the dune sand-sandy paleosol sequence were worked by the Houtian section,at the same times,combining with the northern hemisphere summer solar radiation,Luochuan loess magnetic susceptibility flux and the oxygen isotope curve of stalagmites in the Nanjing Hulu cave,the area is preliminarily explained the environmental evolution process since the Last Glacial Period.The results were as following:(1)The aeolian sediments on the Houtian section are the products of the Last Glacial Period,and developing dates are between 77.0 and 14.9 ka,that can be divided into 3stages of MIS4,MIS3 and MIS2,and 6 sub-stages.Among them,the development period of the dune sand layer is MIS4(77.0—57.1 ka),MIS3b(49.7—36.8 ka)and late MIS2(19.0—14.9 ka);the development period of the sandy paleosol layer is MIS3c(57.1—49.7ka),MIS3a(36.8—26.5 ka),and early MIS2(26.5—19.0 ka).(2)There are differences in sedimentary characteristics and physicochemical property at different stages of the Houtian section in northern Jiangxi.At the MIS4 stage,Mz(1.50?)is the coarsest,fractal dimension value that have a good fractal structure is 2.2,coarse-grained end-member components CEM1 and CEM2(86.10%)content are the main advantage,at the same time,it is the high L*value,Ca CO₃content and p H,which indicating the dry and cold climate environment;At the MIS3c stage,Mz(2.78?)gets smaller,fractal dimension value increases,fine-grained end-member components CEM3(61.25%)content increases rapidly,L*value and Ca CO₃content decreases,which indicating a gradual change from dry and cold to warm and humid climate;At the MIS3b stage,fractal dimension value is larger,coarse-grained end-member component CEM2content rises,Mz and L*value increases,while a*value and b*value increases slightly,which indicating that the climate at this stage fluctuates greatly,and the climate environment is generally dry and cold;At the MIS3a stage,Mz is relatively fine,fractal dimension value is larger,fine-grained end-member component CEM3 content(94.44%)is the highest,L*value(60.53)is the lowest,a*value and b*value become larger,Ca CO₃content and p H value decrease,which indicating a warm and humid climate environment;At the early MIS2 stage,Mz(3.62?)is the finest,and fractal dimension value(2.59)is the largest,although fine-grained end-member component CEM3 content decreases,that is still at a higher value,L*value and Ca CO₃content increases,b*value decreases,which indicating that the climate is changing from warm and humid to warm and dry;At the later MIS2 stage,Mz is relatively coarse,fractal dimension value decreases,fine-grained end-member component CEM3 content is higher,a*value and b*value decrease significantly,Ca CO₃content and p H value rises,which indicating that the changing trend of the climate to dry and cold.(3)Comparing the Houtian section with Poyang lake and the east asian monsoon,which is found that it is basically consistent with the sedimentary development period of the Poyang lake sand hills,which is consistent with the changes in the intensity of the east asian summer monsoon recorded by the northern hemisphere summer solar radiation,Luochuan loess magnetic susceptibility flux and the stalagmite oxygen isotope in Nanjing Hulu cave.The high consistency indicates that the paper is regionally comparable to the climate change stages of the Houtian sandy land.