Two unique weathering regimes in the Changjiang and Huanghe drainage basins: geochemical evidence from river sediments

Abstract

The present research reconstructs the histories of chemical weathering in the drainage basins of the Changjiang and Huanghe based on the chemical compositions of the river sediments. The silicate weathering of the Changjiang Basin is strong and Na-and Ca-silicate minerals are considerably dissolved, while other silicate minerals are less attacked. In comparison, the Huanghe Basin is characterized by very weak silicate weathering, and the weathering degree corresponds well with that of the loess which is the predominant source of the Huanghe sediment. Overall, the Changjiang and Huanghe basins constitute a consistent weathering spectrum from the early to intermediate stage. The similarity of chemical compositions between upper continental crust and the Huanghe sediments as well as the low degree of chemical weathering in the Huanghe Basin imply that the river sediments can be considered to be the representative of UCC and are suitable for studying the evolution of continental crust. Our observations indicate that climate is the predominant factor controlling silicate weathering in both river basins, while controls by source rocks and relief are subordinate. Highly erosive river basins such as the Huanghe produce poorly weathered materials, which casts doubt on the idea that strong physical weathering naturally contributes much to chemical weathering. Differences in silicate weathering processes between the Changjiang and Huanghe basins may provide more constraints in estimating atmospheric CO2 budget in China. (C) 2003 Elsevier B.V. All rights reserved.