『Abstract
Quaternary loess-soil sequences in China and Tajikistan are valuable
archives of the chemical weathering history for arid and semi-arid
regions of Asia. The development of new proxies independent of
grain size are vital to reconstruct the long-term chemical weathering
history of eolian deposits. In this study, we analyze major elemental
and Rb, Sr, and Ba concentrations of decarbonated residue from
representative loess and soil units along a north-south transect
on the Chinese Loess Plateau and compare these concentrations
among different grain-size fractions. Results show that most of
the elemental abundances and ratios vary considerably among different
grain-size fractions for both loess and paleosols, indicating
transport-driven compositional differentiation of minerals during
subaerial transport. However, (CaO + Na2O
+ MgO)/TiO2 ratios show little variation
among different size fractions for the loess-soil transect. Loess-soil
sequences at Lingtai (northern China) and Chashmanigar (southern
Tajikistan) for the past 1.50-1.77 Ma show lower (CaO + Na2O + MgO)/TiO2 ratios in
soil units than in adjacent loess horizons, in good agreement
with greater weathering intensity in soils than in loess units.
The (CaO + Na2O + MgO)/TiO2
ratio of the decarbonated residue is therefore a reliable proxy
for chemical weathering of loess deposits that is independent
of grain size. The (CaO + Na2O + MgO)/TiO2 ratios of the Lingtai and Chashmnanigar sections
display a relatively regular oscillation within a narrow range
in the early Pleistocene, and a rapid increase in average values
and in variance from 0.85-0.6 Ma to the present, indicating lowered
chemical weathering intensity in both the dust source regions
and the depositional areas. This event may be causally related
to the expansion of northern hemisphere ice and/or the regional
tectonic uplift of high mountains in Asia since the mid-Pleistocene.』
1. Introduction
2. Site locations and lithostratigraphy
3. Sampling and analytical procedures
4. Characteristics of elemental depletions in loess deposits
4.1. Major element and Rb, Sr, and Ba abundances of the Lingtai
and Chashmanigar sections
4.2. Changes in major element concentrations during pedogenesis
5. Major element and Rb, Sr, and Ba characteristics in different
size fractions for the loess transect
5.1. Elemental abundances and ratios
5.2. The relationship between elemental differentiation and mineralogical
constituent among different grain-size fractions
6. A new proxy for chemical weathering intensity
7. Pleistocene chemical weathering history recorded in loess deposits
of China and Tajikistan
7.1. Comparison of elemental ratio records
7.2. Pleistocene chemical weathering history
8. Discussion
9. Conclusions
Acknowledgments
Appendix A. Supplementary data
References