Mineralogy and geochemistry of modern Yellow River sediments: Implications for weathering and provenance

摘要

This study illustrates the textural, mineralogical and geochemical signatures of sediments from the upper Yellow River. Sediments of major tributaries have also been examined to study the influence of provenance, weathering intensity, and hydraulic sorting on the spatial compositional variability of sediments. Similarly to floodplain sediments, riverbed deposits are strongly depleted in MgO and Na2O, and enriched in CaO and Si2O relative to the upper-continental-crust standard. The pattern of rare earth elements (REE) indicates LREE enrichment and negative Eu anomaly (Eu/Eu*=0.54-0.68). Low CIA (Chemical Index of Alteration) values indicate that the sediments from the trunk-river channel, floodplain, and major tributaries have not experienced intense chemical weathering in arid to semi-arid climatic conditions. The distribution of chemical elements shows a significant increase of Zr and Hf with coarsening of grain-size, whereas Rb, Ni, and V are associated with finer sediment fractions supplied by adjacent dune fields and tributaries. The Al/Si ratio (a proxy for grain size) correlates positively with CIA, Fe2O3, MgO, and K2O, but not with Na2O, reflecting grain-size control. Clay mineral assemblages in the upper Yellow River and in tributaries draining the Loess Plateau (e.g., Qingshui and Zuli Rivers) are dominated by illite and chlorite, whereas the abundance of smectite characterizes the middle reaches of the Yellow River and the Ten tributaries draining the Ordos Plateau.