Li,F., Jin,Z., Xie,C., Feng,J., Wang,L. and Yang,Y.(2007): Roles of sorting and chemical weathering in the geochemistry and magnetic susceptibility of Xiashu loess, East China. Journal of Asian Earth Sciences, 29, 813-822.

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wAbstract
@Uncertainties in paleoenvironmental interpretations for traditional chemical analysis of bulk samples result from different grain-size sub-populations of sediments containing variable distributions of elements and minerals. Therefore, it is important to understand the elemental and mineral distribution in different grain sizes in determining the quantitative relationship between chemical weathering and climatic change. We sieved a series of Xiashu loess samples into three sub-populations of different grain sizes (ƒ2, 2-45 and „45ƒΚm, respectively), and then analyzed each population for rubidium (Rb), strontium (Sr), rare earth elements and magnetic susceptibility. In comparison with elemental concentrations of bulk samples, clay mineralogy and illitic crystallinity, our results show that distinct elemental distributions and magnetic susceptibilities for different grain-size sub-populations are controlled by sorting and/or chemical weathering, although we also suggest that the Xiashu loess may have the same provenance as the Central Chinese Loess. Maximum concentrations of Rb and fine-grained magnetic minerals in the less than 2ƒΚm sub-population, coupled with our finding of maximum Sr in the larger than 45ƒΚm fraction, indicate that Sr was lost during chemical weathering. Grain-size sub-population analysis is, therefore, an effective method for extracting paleoenvironmental information, because individual sub-populations show minimal variations in initial Rb/Sr ratios compared to bulk analysis of all sizes together. Furthermore, a negative correlation between Rb/Sr ratios and Sr concentrations for the ƒ2ƒΚm fraction (R2 = 0.97) may indicate that clay is a sensitive indicator of intensity of chemical weathering and is an ideal sub-population for determining Rb/Sr ratios, but not for magnetic susceptibility.

Keywords: Grain-size sub-population; Rb/Sr ratio; Magnetic susceptibility; Clay minerals; Loess-paleosolx

1. Introduction
2. Sampling and methods
3. Results and discussion
@3.1. REE and eolian provenance
@3.2. Clay minerals and illite crystallinity (IC)
@3.3. Rb, Sr distribution and Rb/Sr ratio in different size sub-populations
@3.4. Relationship between magnetic susceptibility and size
4. Conclusions
Acknowledgements
References


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