Temporal variations in Pb isotopes and trace element concentrations within Chinese eolian deposits during the past 8 Ma: Implications for provenance change

The Pb isotopes and trace element compositions of the silicate fraction of airborne dust from the Chinese Loess Plateau were analyzed to infer provenance change during the past 8 Ma. The results indicate that the composition of eolian dust changed at 2.6 Ma, coincident with initiation of the Northern Hemisphere ice sheet. The change in trace element composition at 2.6 Ma indicates that a larger component of the eolian dust was derived from felsic rocks after this time. Pb isotopic evidence demonstrates that the source material of Tertiary Red Clay differs to some extent from that of Quaternary eolian deposits. Although chemical weathering may result in compositional changes in eolian deposits, such a scenario is not supported by the present evidence. Given that glacial grinding and frost-weathering processes have been active in the peaks of high mountains during the Quaternary, eolian dust of this age contains a large proportion of material derived from areas of high topographic relief and relatively little material from low-lying cratonic regions. Such alpine processes played an important role in controlling the distinct changes in Pb isotopes and trance element concentrations recorded at around 2.6 Ma.