Geochemical Compositions of Size‐Fractioned Sediment Samples From the Yangtze and Yellow Rivers: Implications for Chemical Weathering, Fractionation Behavior of Provenance Tracers, and Sources of Radial Sand Ridges

Abstract

Abstract River sediments are valuable archives of the environmental conditions within their catchments. The Yangtze and Yellow Rivers are the most active fluvial systems for sediment transport in East Asia, and they are regarded as potential sediment sources for the radial sand ridges (RSRs) in the southwestern Yellow Sea. We used the geochemical compositions of size‐fractioned sediment samples from the Yangtze and Yellow Rivers to characterize chemical weathering, the fractionation behavior of provenance tracers, and the sources of RSRs. For the Yangtze and Yellow River sediments, the (Rb + Sr)/Ti ratio is a reliable chemical weathering proxy that is grain‐size independent. The chemical indices of Chemical Index of Alteration, Rb/Sr, (Rb + Sr)/Ti, and acid‐leached elements from common grain‐size fractions together reveal that the Yangtze River basin undergoes stronger chemical weathering than the Yellow River basin, indicating that the chemical weathering is dominated by latitudinally‐dependent climatic variations. The dissolution and precipitation of amorphous Fe‐Mn oxides can result in the significant fractionation of La/Y, La/Sc, Nb/Co, La/Co, (La/Sm)N, (La/Yb)N, Ti/Sc, Zr/Y, Zr/Co, and Cr/Ta, whereas Zr/Ti and Zr/Nb are largely unaffected. Based on the robust provenance tracers of Zr/La, La/Hf, (La/Yb)N, Zr/Nb, Ti/Zr, and Hf/Ta, we conclude that the RSRs in the southwestern Yellow Sea are mainly derived from Yangtze River sediments, and that part of the clay fraction is from the Yellow River. In future research, we suggest that established geochemical indicators of chemical weathering and sediment provenance can be applied to the deposits of the Yangtze and Yellow River Deltas, the Yellow Sea, and the East China Sea.