Variations in trace element (including rare earth element) concentrations with grain sizes in loess and their implications for tracing the provenance of eolian deposits

Abstract

The concentrations of rare earth elements (REEs) and other 28 trace elements were determined in seven grain-size fractions from four loess samples collected from the Tibetan Plateau, the Sichuan Basin and the Chinese Loess Plateau. The results indicate that concentrations of REEs, except for heavy rare earth elements (HREEs), are almost grain-size independent. However, REEs show clear fractionation with grain size. Middle rare earth element (MREE) depletion increases with decreasing grain size, whereas HREE enrichment increases with decreasing grain size. Excluding REEs and Y, most of the other trace element concentrations tend to increase with decreasing grain sizes. The trace element geochemistry indicates that the potential sources of eolian deposits from the Sichuan Basin, the Chinese Loess Plateau and the Tibetan Plateau differ from one another. This comparative study confirmed that the eolian materials from the Asian continent are the source of the terrigenous component of the central North Pacific sediments, and the loess from the Chinese Loess Plateau could represent the average composition of eolian dust from the Asian continent. In contrast, the eolian deposits in the Sichuan Basin and in the Tibetan Plateau are mainly of local origin, with short-distance eolian transport.