Sedimentary Characteristics, Physicochemical Properties And Environmental Evolution Of The Last Glacial Period In The Houtian Section Of Nanchang

After several field investigations of the aeolian sediment——"Sand Mountain"developed around Poyang Lake,the aeolian sediment profile located in the east of Houtian Sandy Land in Xinjian District,Nanchang City is selected as the research object.Climate proxies such as trace elements,heavy minerals and chroma are used.Based on the results of photoluminescence dating,a geochronological framework was established to determine that the sedimentary sequence of dune sand-sandy paleosoil in Houtian section was the eolian sediment of the last glacial age.Combined with the paleoclimatic indicators,such as magnetic susceptibility of Luochuan loess,δ¹⁸O content of Guliya ice core,the total solar radiation in the northern Hemisphere and the summer monsoon strong period recorded by stalagmite in Hulu Cave,This paper inverts the evolution process of the paleoenvironment in this region during the last glacial period and its internal relationship with the East Asian monsoon.According to the experimental results and data analysis,the following conclusions are obtained:（1）The sedimentary sequence of dune sand-sandy paleosol in Houtian section was formed in the last glacial age,and the formation age was between 77.0～14.9 ka,which was divided into three stages:HTS4,HTS3 and HTS2.HTS3 can also be divided into three sub-stages:HTS3a,HTS3b and HTS3c.The development period of dune sand layer is HTS4（77.0～57.1 ka）,HTS3b（49.7～36.8 ka）,early HTS2（29.7～26.5 ka）and late HTS2（19.0～14.9 ka）.The development period of sandy paleosoil layer is HTS3c（57.1～49.7ka）,HTS3a（36.8～29.7 ka）and middle HTS2（26.5～19.0ka）.（2）The types and contents of trace elements in sand-sandy paleosoils formed in different sedimentary ages are different under the influence of climate and environment changes.Rb/Sr is a good indicator of the variation of summer monsoon intensity.In the warm and humid environment where summer monsoon prevailed,the decomposition of unstable minerals such as potassium feldspar and plagioclase released rubidium and strontium,which increased with the intensification of weathering.Differences in geochemical behavior made rubidium more easily adsorbated in the weathering process,while strontium was often lost.It can be seen that during the formation period of dune sand layer,Rb/Sr curve decreases,ZTR index is low,and HW index is high,which indicates the degree of weathering is low,indicating the dry and cold climate.On the contrary,in the formation period of sandy paleosoil layer,Rb/Sr value curve appears a peak,HW index is obviously low,and ZTR index is high,indicating a high degree of weathering,indicating a warm and wet climate.（3）The response mechanism of various color parameters to different environmental conditions is different:the high value of L^*appears in the formation period of dune sand layer（HT7,HT5,HT3 and HT1）,indicating that MIS4 stage,MIS3b stage,early and late stages of MIS2 are dry and cold climate environment,and the winter wind is enhanced.The high values of a^*,b^*,C^*and h^*mainly occurred in the formation period of sandy paleosoil layer（HT6,HT4 and HT2）,indicating that MIS3c,MIS3a and middle MIS2stages were warm and humid climates with enhanced summer monsoon,reflecting the climatic evolution pattern of this region during the last glacial period influenced by alternating winter monsoon and summer monsoon.（4）Through the analysis of trace chemical elements,heavy minerals,chroma and other indicators in the full text,it can be seen that the region has experienced several cold and warm oscillation processes:HTS4（dominated by winter monsoon and poor hydrothermal conditions）→HTS3c（favorable hydrothermal conditions in strong summer monsoon）→HTS3b（weakened summer monsoon and reduced precipitation）→HTS3a（strengthened summer monsoon and increased precipitation,Temperature rise）→early HTS2（warm and wet transition to dry and cold）→middle HTS2（summer monsoon began to weaken but still dominated）→late HTS2（strong winter monsoon）,reflecting the climatic fluctuations that occurred during the last glacial period on a 10,000-year time scale.（5）The sedimentary characteristics and physical and chemical properties of Houtian section at different stages are different.The paleoenvironment of Houtian section is compared with several climatic indicators in Poyang Lake and East Asian monsoon region.It is found that the development stage of Houtian section is basically synchronized with that of the sand mountain around Poyang Lake.The results show a high consistency with the magnetic sensitivity of Luochuan loess,theδ¹⁸O content of Guliya ice core,the total solar radiation in the northern hemisphere and the intensity of the East Asian summer monsoon recorded by the stalagmite in Hulu Cave,indicating that the climate change in Houtian area during the last glacial period was influenced by the solar radiation and the East Asian summer monsoon.