Evaluation of multiple weathering indices of fine-grained river sediments as climate proxies in subtropical and tropical South China

Geochemical and mineral compositions of river sediments are crucial for the understanding of continental weathering and climate changes in the past. Although fined-grained sediments were generally considered as reliable archives of past weathering history, the effectiveness of weathering indices and potential interference factors were rarely discussed seriously. This paper chooses modern river basins in subtropical–tropical South China to evaluate the effectiveness of multiple weathering indices of fine-grained fractions (<31 μm) as climate indicators. Results show that the CIA (chemical index of alteration) and WIP (weathering index of Parker) values of fine-silt fractions (2–31 μm) deviate the weathering trend of the clay fraction due to mineral sorting and sediment recycling. Chemical weathering intensity of clay fractions in river sediments agrees with soil data and shows positive correlations with modern temperature and precipitation in South China. However, multiple weathering indices of clay minerals are weakly correlative to climatic parameters due to the influence of parent rocks. We conclude that elemental proxies of clay fractions in fluvial deposits can better record the present-day weathering conditions in South China. For reconstructing the past climate changes in those small regions, the CIA of clay fractions is the most reliable climate indicator.