Late Pleistocene Climatic Events Recorded By Lacustrine Sediments In Hexigten Qi Of Inner Mongolia

Hexigten Qi is located in the eastern part of Inner Mongolia Autonomous Region,the southwest of Daxing'anling,and the Otindag Sandy Land in the west.It is located in the monsoon edge area of arid and semi-arid climate transition zone,which is sensitive to climate response.The lacustrine sedimentary in this area is a good record carrier of paleoclimate and paleoenvironment and also a natural database.Based on previous studies,this paper regards Qinghuagoumen lacustrine sedimentary as the research area.In the field,we sampled and measured this section with patience and meticulousness.And a time frame of this section was established by OSL method in laboratory.Meanwhile,magnetic susceptibility,chroma and particle size experiments were carried out in school.The above data were analyzed synthetically to discuss the evolution of lake environment from its formation to extinction in late Pleistocene.The main findings are as follows:1.Based on the field survey,we studied and sampled the Qinghuagoumen section in detail,and combined with the analysis of indoor climate proxy index.The results showed that the thickness of the section was 29.70 m:There were about 1.60 m of fluvial sediments at the bottom of Qinghuagoumen section,and 28.10 m above were lacustrine sediments developed by horizontal bedding and parallel bedding.2.Based on the sedimentary characteristics,particle size,chromaticity analysis and the chronology framework established by OSL,the results show that the section records the climate evolution history of 41.37-20.22 ka B.P.,that is,the climate events occurred during the MIS3 to MIS2 transition period in the late Pleistocene.3.Based on the comprehensive analysis of the sedimentary characteristics,particle size and chromaticity of the section,and combined with the chronology framework,the climatic evolution of Qinghuagoumen section is divided into three stages:Stage ?: Buried depth 29.70-25.00m(41.37-32.55 ka B.P.),this part is the transition period from fluvial sediments to lacustrine sediments;the climate isrelatively dry and cold,corresponding MIS3 b.stage ?: Buried depth 25.00-3.45 m(32.55-22.13 ka B.P.),this part is lakeshore deposits;the climate is complex and the sand is prevailing.stage ?: Buried depth 3.45-0 m(22.13-20.22 ka B.P.),climate tends to be dry and cold,which is consistent with the background of climate change in the MIS2,which shows that the lake shrinks until it dies out.4.A total of seven times climate warming events and three times climate cooling H events have been recorded in the section since the late Pleistocene.Climate warming events correspond to the warming events of Greenland ice core GISP2 and Guizhou Qixing Cave stalagmites,respectively,occurred in 23.0 ka B.P.? 27.2 ka B.P.?29.2 ka B.P.?32.6 ka B.P.?33.5 ka B.P.?34.6 ka B.P.?38.3 ka B.P.,H events occurred in 24 ka B.P.(H2),30.9 ka B.P.(H3),39.5(H4).This reflects the widely recorded climate instability in the study area as well as in various regions of the northern hemisphere,revealing the frequent occurrence of climate fibrillation in a short time scale during the MIS3 to MIS2 transition period.