Climate Change Recorded By Aeolian Deposits From Eastern Qaidam Basin Since The Last Deglaciation Period

Qaidam Basin is located at the northeast of Qinghai-Tibet Plateau, surrounded by Qilian mountains, Altun mountains and Kunlun mountains. The basin is adjacent to the extreme drought of the Tarim Basin in the northwest, and in the junction of the East Asian monsoon and westerly circulation system in the southeast. Aeolian deposition and wind erosion are well developed, mainly in the southeastern, southwestern margin of the basin and “Three Lakes” of the central basin, which truely record history of sandy activities, climate evolution information in Qaidam Basin. Studying aeolian deposition in the eastern Qaidam Basin contributes to the research of the relationship and driving mechanism among sandy activities, westerly circulation system, East Asian monsoon and global climate change.This thesis conducts on detailed chronology, grain size, color, geochemistry and other climate proxies of Xiangride and Xiariha aeolian sedimentary sections in eastern Qaidam Basin, based on previous study on the aeolian section in the eastern basin. In contrast with Guliya ice cores and westerly lakes, we draw the following preliminary conclusions:(1) OSL and AMS 14 C dating show that Xiangride profile formed during 6.25 ~1.33 ka, while Xiariha profile formed during 14.13~5.83 ka, which constitute time sequence since the last deglaciation.(2) Grain size analyses show the average grain size of Xiangride profile is about 32.48μm, and sorting of sandy paleosol and sandy loess is superior than aeolian sand; while the average grain size of Xiariha section is about 194.80μm, and the sorting of aeolian sand is better than sandy paleosol. Both provenance of the two sections are from proximal and distal sources, and the sources are typical aeolian deposition. Grain size composition above 63μm is compared well with Guliya ice core and westerly lakes,revealing climate change of the eastern basin is consistent with the global climate features since the last deglaciation.(3) Geochemical datas show Xiangride profile is between the lower stage of chemical weathering and middle stage of chemical weathering, and chemical index of alteration in some sandy paleosols are higher than the average of Luochuan paleosol; Xiariha profile is at the lower stage of chemical weathering, and chemical index of alteration in sandy paleosols are lower than the average of Luochuan loess.(4) Aeolian deposits recorded by the eastern Qaidam Basin show high humidity during 14.13~10.62 ka stage, and sandy activities weakened; humidity and temperature both had increased during 10.62~7.16 ka stage, and sandy activities tended to enhance; the temperature and humidity had greatly increased during 7.16~5.83 ka period, and sandy activities sharply decreased; the eastern basin was in a suitable period of high temperatures and humidity during 5.83~1.33 ka stage, and aeolian deposits fixed into soil. “4.2 ka” event is very prominent in the eastern basin, and quartz morphology are mainly scratches and V-shaped pits during 4.16~3.8 ka stage, indicating the mutational event as flood event rather than strong sandstorm event, which plays an important role for understanding climatic instability during the late Holocene and prosperity and decadence of ancient human culture.(5) Climate change of aeolian deposits recorded by the eastern Qaidam Basin is different from record by stalagmites and solar radiation intensity, while the result is consistent with oxygen isotope of Guliya ice core, effective humidity of Bosten Lake and pollen of Hurleg Lake. Characteristics of climate change show drought during early Holocene and humid during mid-late Holocene, revealing that climate change features in eastern basin are in line with “Westerly mode” rather than East Asia monsoon.