Rock magnetism in loess from the middle Tian Shan: Implications for paleoenvironmental interpretations of magnetic properties of loess deposits in Central Asia

Considerable attention has recently been paid to the magnetic properties of loess deposits in Central Asia. However, paleoenvironmental interpretations of magnetic properties of loess deposits in South Tajikistan, the Ili Basin, and the Tarim Basin remain controversial. Current meteorological observations demonstrate that the mean annual precipitation in the Junggar Basin exceeds that in the Tarim Basin and falls below that in the Ili Basin and South Tajikistan. This study of rock magnetism in loess from the Junggar Basin improves our understanding of the complicated relationships between magnetic properties, climate, and source materials for loess deposits of Central Asia. This study involved multiparameter investigations of rock magnetism in a 71 m loess section in the Dongwan area, on the northern slope of the middle Tian Shan (in the Junggar Basin). Variations in concentration of coarse eolian ferrimagnetic minerals appear to provide the main control over the magnetic properties of loess in this area. The contribution of ultrafine pedogenically produced magnetic grains to the magnetic susceptibility (chi) is minimal. Furthermore, long-term increasing trends in the chi and the saturation isothermal remanent magnetization (SIRM) were found in the Dongwan loess section. These trends may be linked with intensified aridification of Central Asia in the mid-Pleistocene. This study suggests that reduced precipitation of westerly moisture from Tajikistan into the Tarim Basin might play a critical role in the paleoenvironmental interpretations of magnetic properties in the loess deposits of Central Asia.