Climatic Records And Environmental Evolution Of The Desert-Loess Transitional Zone In The North Of Shaanxi Province Since The Last Glacial

Climatic Records and Environmental Evolution of the Desert-Loess Transitional Zone in the North of Shaanxi Province since the Last GlacialThe desert-loess transitional zone is located at margin region of East Asian monsoon system. This region is dominated by the monsoon-desert system. The aeolian sedimentary sequences of sand-sandy loess-sandy soil are very sensitive to climatic changes and very important in studying the high-resolution past global changes and reconstruction desert evolution.The studies of loess-paleosol sequences have been developed at present, and some efficient climate-environment proxies, special for the Loess Plateau, have been constructed. For desert and its peripheral loess form a coupled system, the great progresses in the Loess Plateau have supplied wide space of working and subject for comparison for the research of desert-loess transitional zone. Climatic proxies used well in the Loess Plateau have been continually used in the desert-loess transitional zone at the very beginning, but some problems occurred consequently especially in using grain-size proxies. For the reason of the dominance of monsoon-desert system, the grain-size compositions of aeolian deposits of desert-loess transitional zone are apparently different from that of the Loess Plateau, which is characterized by mainly composed of coarse-sand particle and wide grain-size range from very fine to very coarse. Such grain-size proxies as Mz and Md are not sensitive to the transitional zone, especially when recording the increase of fine particles that implied the warming of climate. It is very crucial to construct climatic proxies suitable for transitional zone, which is the important base to carry on deeply researching.In the light of the above consideration, the transitional zone of the Mu Us Desert and the Loess Plateau has been collected as researching region for this paper after the expedition of Junggar Basin, Tuha Basin, Hexi Corridor, Alxa Plateau, Erduosi Plateau, Bashang Plateau and Xilingele Plateau. Having surveying the researching region in detail, 5 sections are chosen as studying location that possess continue and distinct sedimentary sequences. Grain-size, magnetic susceptibility, CaCO3 and TFe proxies are planned to measure. After finishing the sampling, measurement and analyzing, the changing property and environmental implications of the above proxies were re-explained for desert-loess transitional zone. The elementary proxy system of the transitional zone was constructed including grain-size, magnetic susceptibility, CaCO3 and TFe content. Proxies are as follows: >63 u m and 2-10um are positive and negative grain-size proxies for winter monsoon intensity respectively; although the data of magnetic susceptibility is much lower than loess region, it can still infer the summer monsoon intensity variation and thechanging amplitude between glacial and interglacial interval is apparent. The change of CaCO3 and TFe content can infer variation of temperature and humidity of transitional zone. High data in warm period and low data in cold period in transitional zone are on the contrary with the Loess PlateauAccording to the proxies mentioned above, climatic records of transitional zone are analyzed since the last glacial. It is found that not only long time-scale environmental circle, but also short, rapid climate events can all be recorded in sedimentary sequences of transitional zone, which prove the ability to imply the high-resolution environmental oscillation.At last, it is discussed that ancient aeolian sand in transitional zone caused by the desert variation has great effect on modern dersitification.