『Abstract
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.
Keywords: Chemical weathering index; River; China; Sediment; Monsoon;
Geochemistry』
1. Introduction
2. River settings
3. Data sources and methodology
4. Results
5. Discussion
5.1. Controlling factors of chemical weathering in continents
5.2. Constraints of CIA and WIP variations in Chinese drainage
basins
5.2.1. Climatic constraint
5.2.2. Constraints of sediment grain size on the CIA and WIP
values
5.3. Correlation between two weathering indices
5.4. Seasonal variation of CIA indicating weathering intensity?
6. Conclusions
Acknowledgements
References