Redai dili (Jan 2023)
Climatic Changes in the Middle and Late Period of the Last Glacial Period in Liaohua Section of Jiujiang, Jiangxi Province Recorded by End-Member Grain Size
Abstract
Late Quaternary aeolian sediment sequences are widely distributed in the Poyang Lake area and are good subjects for climate evolution research. However, previous studies have focused mainly on aeolian sediments and less on lacustrine facies and their overlapping accumulation with aeolian sands. Therefore, after field investigations in Shaling Mountain, Xingzi County, the Liaohua section was selected as the study area where we tested the geological age and grain size, analyzed the grain size results by end-member analysis model, and compared the end-member component content with the average grain size and standard deviation. Oxygen isotopes of stalagmites in YZ Cave, Chongqing, and Greenland ice core records were analyzed. We also discussed the climate change law in the middle and late periods of the last glacial period in this area to source basic data for the response of the last glacial deposits in the Poyang Lake area to the East Asian monsoon and even the whole world. The results show the following: 1) This section is composed of lake facies, ancient soil, dune sand, and other sedimentary facies. Combined with the dating results and deep-sea oxygen isotope records, a chronological-depth framework based on the piecewise sedimentation rate interpolation method was constructed. The dating results show that this profile was formed in the middle and late glacial stage (48.8-17.1 ka) and the grain size was mainly silt, medium sand, and fine sand. Clay was higher in the paleosol or lacustrine layer, and coarse sand had the highest volume fraction in the dune sand layer. 2) The end-member analysis model separates the granularity data into three different granularity end-members ( EM1, EM2, and EM3). The contents of different end-member components in different strata are obviously different. EM1 represents the end-member components of silt, and the peak values correspond to the development period of lacustrine facies and paleosol. EM2 and EM3 represent the end-member components of medium sand and coarse sand, respectively, and the peak values correspond to the dune sand development period. 3) The end volume fraction and average particle size sorting coefficient show obvious peak-valley alternations on the profile, and the alternation of these peak-valley cycles represents monsoon evolution and climate fluctuation in the last glacial period. On the scale of 10,000 years, the strong winter monsoon periods are LH10 (48.8-39.9 ka) and LH3-LH5 (28.1-17.1 ka), which correspond to the peak areas of EM2 and EM3. Dune sand has a high coarse grain content, small standard deviation, and good sorting, corresponding to the MIS3b and MIS2 stages of deep-sea oxygen isotopes, respectively. LH6-LH9 (39.9-28.1 ka) is a warm summer monsoon period, corresponding to the peak area of EM1, lacustrine deposition and paleosol development, many fine particle components, large standard deviation, and poor sorting, which corresponds to the MIS3a stage of deep-sea oxygen isotopes. These changes correspond with the changes in oxygen isotopes of stalagmites in the YZ cave and Greenland ice cores, which is consistent with global climate change.
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