Mineral magnetic variation of the Jiaodao Chinese loess/paleosol sequence and its bearing on long-term climatic variability

[ 1] To retrieve reliable long-term paleoclimatic signals from the Chinese loess/paleosol sequences deposited over the past 2.6 Myr, multiparameter mineral magnetic investigations have been conducted on the Jiaodao section on the Chinese central Loess Plateau. First, the lithogenic magnetic components and the pedogenic overprinting were chemically separated by the citrate-bicarbonate-dithionite (CBD) method. The magnetic properties of the least pedogenically altered loess units and post-CBD loess/paleosols are dominated by coarse-grained lithogenic magnetite. Increasing degree of pedogenesis increases both the concentration and grain size of pedogenic magnetite/maghemite. Longterm changes of the pre-CBD magnetic properties suggest a long-term decrease in summer monsoon intensity and a long-term increase in winter monsoon intensity from the late Pliocene to the late Pleistocene. Long-term variations of the post-CBD magnetic properties suggest an increase in both concentration and grain size of coarse-grained lithogenic PSD/MD magnetite grains, and hence indicate a long-term increase in winter monsoon intensity over that period. The coercivity decrease of the lithogenic component for the loess unit L15 may be related to the accelerated uplift of the Tibetan Plateau and its adjacent regions during the period of L15 deposition. From paleosol S5 to loess L1, higher values of coercivity of the lithogenic component occur in typical loess and paleosols, and lower values are found at the loess/paleosol transition. These coercivity variations are thought to be related to significant changes in the source region as well as dust deposition in the Loess Plateau caused by changes in ice/snow or vegetational cover. These new results lead to a better understanding of the relationships between the effects of tectonic, paleoclimatic, and paleoenvironmental processes in northwestern China.