Preliminary Study On Loss Deposition At Deyang In Sichuan Basin And Southwest Monsoon Evolution During 65-5Ka Period

The global climate,environmental evolution and special climatic events during the last glacial had received considerable attention for many years.Sichuan Basin was more sensitive to climate change and significant,because its locate in an area where is influenced by the southwest monsoon,southeast monsoon,westerly of Plateau and westerly,and is sensitive to climate change,therefore,it is significantly important for to do research.And also this area is indispensable for the envioronment evolution research of Titeban Plateau and it's southeasten margin.So we chose a section which depth 3.6 meters with continuously loess deposition with ontinuously loess deposition at Xinxin brickyard,Deyang,Chengdu loess District to study.With OSL dating and various of sediment index(including grain size,magnetic susceptibility,carbon content,rare earth elements,fractionated magnetic susceptibility etc.),this paper discussed paleoenvironment and paleoclimate of this region which dating was 62.4-5 ka period,explain its evolutionary relationship between loess deposits and southwest monsoon and definite the evolution of the southwest monsoon mechanism.Based on these results and environmental characteristic of the studied area,the preliminary conclusion has been achieved as following:1.OSL dating indicates that the Xinxin brick section of Chendu loess sediments spans from 62.4 to 5 ka period.2.The samples from the Xinxin brick section which were analyzed with grain size,fractionated magnetic susceptibility and rare-earth element(REE)geochemistry methods,the results suggest that the fine sediments of this section are of eolian origin and transported by the Plateau monsoon and the westerlies.3.This study area is bounded by 44 ka,the early deposition rate is slow,and most of the particles are fine.The bottom sections(270-360 cm)which was deposition during dating 62.4-44 ka period.Sediments dominated of silt(4-63 ?m)and clay(<4 ?m),an average of 68.216%and 29.446%respectively.The sand-bearing(>63 ?m)samples(average)are only 2.338%.Median particle size and Magnetic susceptibility sample(average)are 9.74 ?m and 7.97.Magnetic susceptibility and median grain size changed roughly synchronously.Total organic carbon(TOC)and total inorganic carbon(TIC)concentrations are low,an average of 0.35%and 0.01%respectively.4.The upper sections(270-85 cm)which was deposition during dating 44-5 ka period.Sediments dominated of silt(4-63 ?m)and clay(<4 ?m),an average of 70.02%and 27.492%respectively.The sand-bearing(>63 ?m)samples(average)are only 2.487%.Median particle size and Magnetic susceptibility sample(average)are10.233 ?m and 7.579.Magnetic susceptibility and median grain size changed roughly synchronously too.Total organic carbon(TOC)and total inorganic carbon(TIC)concentrations are low,an average of 0.14%and 0.02%respectively.5.Indian monsoon was mainly controlled by the change of summer solar radiation in low latitudes,and the global ice volume and the Tibetan plateau have a certain influence on it.