Magnetic Susceptibility Record Of Loess-Paleosol Sequence In Yili Basin, Central Asia

In recent years, loess-paleosol sequences have been received significant attention for their detailed records of local and regional climatic and environmental changes superimposed on a global signal(Oches and Banerjee, 1996). Magnetic susceptibility, regarded as a simple, rapid and low-cost method, is a very useful proxy to characterize both terrestrial and ocean climatic changes and lithostratigraphic correlation. In some loess- paleosol sequences, including those of the Chinese Loess Plateau, Tajikistan and the Czech Republic, maxima in magnetic susceptibility values correspond with the paleosol horizons, and minima with the least-weathered loess layers. In other loess-paleosol sequences, including those of Siberia, Alaska and Argentina, the relationship is completely opposite, with susceptibility minima associated with the most developed paleosols (Maher et al, 1998). Here, we present the results of magnetic susceptibility of loess-paleosol sequences since the last interglacial period in Yili basin, North Xinjing, central Asia. We selected two loess-paleosol sections at different altitudes in Yining basin surrounded by Tianshan, Central Asia. Talede (TLD) section (N43.34, E83.02) is located the fourth terrace at 850 m altitude with 350mm annual precipitation and annual temperature 8¡æ. Kurdenengbula(KD) section (N43.46, E83.92) is located at 1400 m altitude with 550mm annual precipitation and annual temperature 5¡æ. Magnetic susceptibility was measured at 5 cm intervals, using a Bartington Instruments magnetic susceptibility meter and MS2B sensor. The results show that the relationship between susceptibility values and loess-paleosol layers varies with sections. In TLD section, the maxima of magnetic susceptibility occur at L1 loess layer (with an average value 68.18 SI) not at S1 paleosol (45 SI), which is similar to that of Alaska loess, but the maxima of susceptibility in KD section is correspond with the S1 paleosol, which is similar to the loess-paleosol sequence of Chinese Loess Plateau. The differences of precipitation and altitude between the two sections are responsible for their difference of magnetic susceptibility. High altitude and relative abundant precipitation is helpful to develop soil layers. However, more factors such as tectonic, mountain shade should be considered, and also more study of rock magnetism and mineral are necessary to confirm this case.