Chemical indices (CIA and WIP) as proxies for integrated chemical weathering in China: Inferences from analysis of fluvial sediments

Rivers play a key role in earth surface processes by weathering and eroding the upper continental crust under variable climate regimes. How to quantitatively determine the chemical weathering intensity in the drainage basins using geochemistry of fluvial sediments remains unclear. The Chemical Index of Alteration (CIA) and the Weathering Index of Parker (WIP) have been used worldwide as proxies to evaluate the chemical weathering intensity in large watersheds and in specific weathering profiles. In this study, concentrations of major oxides in the suspended particulate matter (SPM) and fine-grained floodplain sediments from 13 major rivers in China from north to south were analysed and compiled for the estimation of chemical weathering in China. The gradual increase in CIA and decrease in WIP values with decreasing latitude of the catchments suggest enhanced weathering intensity in these river basins. A combined monsoon climate effect of temperature, runoff and precipitation primarily controls the chemical weathering in China. The provenance rock types and relief play minor roles in weathering, whereas an active tectonic setting and typhoon events play key roles in the weathering process in Taiwan. The CIA values of the finer SPM samples within a given river are overall greater than those in the corresponding coarser floodplain sediments, underscoring the effect of sediment grain size on CIA values.The irregular seasonal variation of the CIA within a specific river further confirms the notion that the CIA does not reflect the instantaneous chemical weathering on continents. Although it is impossible to build a general model for regulating the chemical weathering of continents, this study reveals that the integrated chemical weathering intensity in large latitudinal watersheds can, with careful application, be quantitatively estimated using the proper geochemical proxies of river sediments.