Geochemical characteristics of the Tertiary and Quaternary eolian deposits in eastern Gansu province: Implications for provenance and weathering intensity

Abstract

An eolian deposit section named Shaozhai, which has been developed since the Tertiary in eastern Gansu province, was analyzed for major-trace elements and Sm-Nd isotopic compositions to explore the relationship for the provenance and weathering intensity between the Tertiary red clay and Quaternary loess. The magnetostratigraphy data indicates that the basal age of the typical eolian deposits is about 5.23 Ma B.P.. We observed both similarities and obvious differences in the Tertiary red clay and Quaternary loess. Specifically, the Tertiary red clay has similar UCC-normalized major-trace element abundances and chondrite-normalized rare earth element abundances as the Quaternary loess, demonstrating that dust materials making up these sediments likely have experienced similar and numerous recycling processes prior to deposition. The Tertiary red clay has relatively high abundances of MgO, Li, Cs, Bi and low abundances of Na2O, La-Lu, Y. In comparison with the Quaternary loess, chemical weathering parameters such as Na2O/Al2O3, CIA, combined with the A-CN-K diagram suggest that the Tertiary Red clay has experienced a stronger weathering intensity. There is not much difference in the TiO2/Al2O3, SiO2/Al2O3, SiO2/TiO2, Zr/Hf, Nb/Ta, Lu/Hf, Y/Ho, Th/Nb, Hf/Nb, total rare earth elements, differentiation degree between the light and heavy rare earth element, internal differentiation degree of the light rare earth element, abnormal degree of Ce and Eu, εNd(0) of the Tertiary red clay and Quaternary loess, demonstrating a similar provenance for them. The finer grain size and stronger weathering of the Tertiary red clay may be responsible for the difference in major and trace element content for the Tertiary red clay and Quaternary loess.

Keywords

• eolian deposits
• red clay
• geochemistry
• provenance
• chinese loess plateau