Geochemical and magnetic characteristics of fine-grained surface sediments in potential dust source areas: Implications for tracing the provenance of aeolian deposits and associated palaeoclimatic change in East Asia

摘要

We investigated the geochemical and magnetic characteristics of fine-grained surface sediments (fractions <63μm) of 182 samples collected at 20 sites in potential dust source areas of arid China (along the southern border of Mongolia). We found coefficients of variation ranging from 2.8 to 35.2% for the four magnetic parameters (χ _(lf), ARM, SIRM, and the S-ratio) in these samples, and this variation may have great significance for interpreting the magnetic characteristics of aeolian deposits far from their source regions. In addition, the results also show that chemical weathering in the potential dust source areas did not play a major role in pedogenesis and evolution of the characteristics of the fine-grained surface sediments because there were variations of only 5% in the values of the chemical index of alteration, which is usually considered to indicate the intensity of chemical weathering, versus variations of 14% in the Rb/Sr ratio. In addition, there was no significant positive correlation between the magnetic susceptibility and the Rb/Sr ratio, which shows that in the source areas, weathering caused little magnetic enhancement in the fine-grained surface sediments. Therefore, in addition to pedogenesis effects on the windblown sediments deposited far from their source regions, the geochemical and magnetic characteristics of fine-grained surface sediments in source areas exhibited complicated patterns.