High-resolution Luminescence Chronology And Environment Implications Of A Loess Profile In Source Regions Of The Yellow River

The extensive aeolian deposits in Qinghai-Tibet Plateau(QTP)are good environment information carrier,recording the atmospheric circulation evolution information between Asian monsoon and Westerlies,at the same time,as the ice source loess which also record the interrelationship between dust accumulation and terminus fluctuation of plateau quaternary glaciers.In northeast QTP,mantles of sandy loess form a distinct belt which covers an elevation range between 3500 to 4500 m on the east-facing slopes of the Anyemaqen Mountains,Hebei loess profile(HB)is selected as the research object,we collected 29 OSL samples,medium grain(63-90 ?m)quartz SAR protocol was employed to build the systematic dating of above samples,we established the high resolution chronology framework of HB section,on the basis of it,selecting effective environmental proxies to explore the characteristics of environment change in this region,the existing ages data on QTP were summarized to investigate its depositional model and response mechanisms.From the sedimentary age sequence of stratum,HB loess section mainly records a continuous environmental information from 46±3.2 to 27.5±2.8 ka belonging to Marine Isotope Stage(MIS)3 stage.The change of grain-size in our study area has a good response to climatic cooling events,revealing that the QTP loess has more obvious response to rapid climate cooling events than warm events.Magnetic susceptibility's response to the climate has periodic differences,the response to climatic cooling events is not obvious in cold episode,but it shows a more evidently response in warm period.On the whole,it shows such a distribution regularity that warm periods correspond to the high value and cold periods on the contrary.In comparison with magnetic susceptibility in Chinese Loess Plateau(CLP)and Qinghai lake region,we found that the average susceptibility is minimum in high area of QTP,it may be related to the high altitude and weak pedogenesis.According to the change of relationship between age and depth,the dust accumulation rate in this region can be divided into two stages: dust accumulation rate is~24.8cm/ka ranging from 46.3±3.2 ka to 36.5±2.9 ka while 27.5 cm/ka ranging from 36.5±2.9 ka to 27.5±2.8 ka,indicating the climate in middle MIS 3 is relatively better than late MIS 3.Meanwhile,the high density ages result also detected the strata of LGM in MIS 2 stage are missed,loess deposition in the whole northeast QTP also present the similar situation.Loess sediments in the QTP mainly accumulated during interstadial stages,while they were probably eroded largely during stadial stages,which is obviously different from loess sedimentation model of the CLP,showing a antiphase relation and illustrated that the northern QTP is an important dust source region for CLP especially during LGM and MIS 4 cold stadial stages et al.