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 (2,
2-45 and 45Κm, 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 2Κm sub-population, coupled with our
finding of maximum Sr in the larger than 45Κm 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 2Κm 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-paleosolx
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