关键词: 西风区, 黄土, 磁化率, 新疆

Abstract: The magnetic susceptibility has been used as an index of summer monsoon strength which varies with orbitally forced solar radiation in the Loess Plateau. Many scientists think that the precipitation-driven pedogenesis is largely responsible for the production of ultrafine-grained magnetic minerals that strongly influence the strength of the magnetic susceptibility signal in the loess and paleosol sequence. For this reason, paleosols usually have higher magnetic susceptibility than the loess. The stronger the summer monsoon is, the higher the magnetic susceptibility is. Variations in magnetic susceptibility correlate closely with the global marine ¹⁸O record too. The Heinrich events and the interstadials happened at the North Atlantic Ocean and Greenland have left their signature in the Chinese loess records. This implies that the climate changes in the high latitude Northern Hemisphere may significantly affect the intensity of the Chinese monsoon systems and the climates of the North Atlantic and China were linked by the effect of westerly winds. However, few studies on the magnetic susceptibility of loess and paleosol have been done in the westerly region of Xinjiang. This will hinder the understanding to the global change well.;The investigation of two typical loess sections in Yili area where the westerly circulation is prevailing shows that there are some differences on magnetic susceptibility of loess and paleosol between monsoon region and westerly region and regional features as well. Zeketai section is located in the desert steppe zone where the annual precipitation is lower than 300 mm. It is different from the monsoon areas that most pedogenic layers during the Last Glaciation have relatively low magnetic susceptibility values, whereas the values of the loess layers are relatively high. On the contrary, the contents of the carbonate of the poorly developed paleosols are higher than those of the loess. The content of carbonate is negatively related to the value of magnetic susceptibility. At the upper of the paleosol that formed during the interglaciation the magnetic susceptibility is lower than the value of loess. Kuerdenengbulake section is situated at the steppe zone where the annual precipitation is larger than 400mm. Being similar to the Loess Plateau, the peaks in magnetic susceptibility and pedogenic layers identified in the field coincide very well. Contrast to that of desert steppe, the paleosols from steppe zone can be distinguished from the loess by decarbonation and high magnetic susceptibility values.;On the one hand the regional features of magnetic susceptibility from both loess sections may mean the differences of the precipitation-driving pedogenisis, on the other hand it indicates that the origin of magnetic susceptibility is complex. At the inland the climate was dry whether the cold or warm periods during the Last Glaciation. During the cold periods the temperature was low and the evaporation was weaker, thereby the humid may be relatively high. In contrast to the cold periods, both the evaporation and carbonate accumulation were stronger. This may result in the low humid. The author do not think it is good to directly adopt the method that have been used in the monsoon region when the studies are done in the westerly region, but the magnetic susceptibility can be an indicator of humid change to a certain degree.

Key words: westerly region, loess, magnetic susceptibility, Xinjiang