The Research On Environmental Change Of Southeastern Badain Jaran Desert During The Last Glacial Period

The Badain Jaran desert is China's third largest desert,which has the highest megadune in China even all over the world.It is also the world's only desert with dense megadunes.The extraction on the environmental and other geological information in the area is still very difficult so far.If we can use new methods,new technology to rebuild and obtain the environmental evolution records of the Badain Jaran desert,the results will play an important part in the research of quaternary geology,geomorphology and global climate change.Based on this,this paper chooses the Barunbaoritaolegai profile as the research object.Barunbaoritaolegai profile is located in the east of Barunbaoritaolegai singing sand mountain in the southeast of the Badain Jaran desert,which is a shrinking sedimentary outcrop on the edge of the modern lake.We also can find similar outcrops in the areas in the southeast of the Badain Jaran desert,such as Baoritaolegai,Shuanghaizi and the central Zhalate,Bagajilin,Badan,Tamayin and Yindeertu Lake areas.In September 2013,the profile BRBG with a long of 280cm was obtained.Through the interpretation of Optically Stimulated Luminescence,we establish the temporal framework of the profile.Combining the grain size,magnetic susceptibility,mineral composition analysis,and geochemical indexes with different grain sizes and composition and the measurements of carbonate and silicate strontium isotope,we reconstruct the environmental change in the southeast of the Badain Jaran desert during the last glacial period.The conclusions and innovations are as follows:1.The environmental change in the southeast of the Badain Jaran desert during the last glacial period can be divided into the following stages.During 79.3 ka⁶6.8 ka,the climate is cold and dry.At the same time winter wind prevailing,physical weathering is strong while chemical weathering is weak.There is less rain,the salinity of lake water increases.This phase corresponds to the global oxygen isotope stage 4?MIS 4?,which belongs to early glacial staircase of the last glacial period.During 66.8 ka⁴1.0 ka the climate is warm and wet,with weak physical weathering and strong chemical weathering.The rain increased and the recharge of lake increases,the lake expands.This phase response to oxygen isotopic stage3?MIS 3?,which belongs to the interstage of the last glacial period,and this phase can be continue to divided into three period.During 41.0 ka³5.2 ka,the climate has characteristics of cold and dry.Physical weathering is strong while chemical weathering is weak.Lake shrinks and the lake salinity increase.This phase corresponds to the global oxygen isotope stage 2?MIS 2?,which belongs to great ice age of the last glacial period.2.The ⁸⁷Sr/⁸⁶Sr values in inland lake are the proxy of chemical weathering intensity.The values of acid soluble fraction indicate the strontium isotope change in the sedimentary area while the values of acid insoluble fraction indicate the change in provenance area.The result shows the opposite trend,which indicates that the different material composition in the provenance sedimentary area have different response to chemical weathering.3.The experimental comparison shows that the geochemical indicators in whole sample have little response.However,the innovative experiment method adopted in this paper has a very good effect and is more sensitive to climate change.So,this method can be as a new method to use in the later experiment.According to the research results,Sr and K content and Sr/Ca values with less than 125 microns in the residue composition,K content of more than125 microns in acid soluble components and the content of Al with less than 125 microns?containing acid soluble components and residual components?are more sensitive to climate change.We also can see that fine grained components had more effects on the direction of environmental change.Through the innovative experiment of this study,we also find that the change tendency of Ba in acid soluble components whether is fine or coarse grained components,has high consistency with magnetic susceptibility.Whether the Ba index can be,or even replace susceptibility this controversial indicators as a new,is the further work.4.From 66.8 ka,the study area began to develop lakes or again.This profile contains the MIS 4^MIS 2 three stages.In the MIS 3,this place develops lakes and its scale must be greater than today.And other areas the results are consistent with that in northwest China.5.The environmental change of Barunbaoritaolegai area is fairly similar with the typical indexes of the globe.This reflects the Badain Jaran desert has a response on global climate change.At the same time,it also has particularity.The result of comparison shows that MIS 3stage in the region stopped early.The reason lies in two points:First,Barunbaoritaolegai area is located in the intersection of three major monsoon?the southwest monsoon from Indian Ocean,east Asia monsoon and westerly winds from central Asia?,namely the particularity of geographic location.Second,the southwest monsoon from the Indian Ocean play a leading role in the regional climate evolution,in other words,the uplift of the Qinghai-Tibet Plateau has had a huge impact to the region climate evolution of Barunbaoritaolegai area.