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Clay Mineralogy of Surface Sediments in the Three Gorges Reservoir: Implications for Sediment Provenances and Weathering Regimes

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Clays and Clay Minerals

Abstract

Knowledge of clay mineralogy is essential for understanding the source areas and weathering environments of fluvial sediments, particularly in large reservoirs facing serious problems with sediment deposition, such as the Three Gorges Reservoir (TGR) in east-central China. The purpose of the present study was to identify the sediment provenances and weathering regimes contributing to the sediment load in the TGR by determining the clay-mineral and geochemical compositions of surface sediments during various seasons. X-ray diffractometry and scanning electron microscopy (SEM) were used to identify the clay minerals. The results showed that illite was the dominant mineral, followed in order by kaolinite, chlorite, and montmorillonite. From a mineralogical perspective, distal sources were the main contributors to the TGR sediments, and regional sources (surrounding tributaries) also contributed much during the three seasons, while proximal sources (hillslope soils) supplied sediment in the flood season but not in the other two seasons. The geochemical and hydrological data generally supported the mineralogical results. In the flood season, the chemical indices of the TGR sediments were >0.4, showing that the sediments contained Al-rich illite minerals and experienced intense hydrolysis. In the other two seasons the TGR sediments were enriched in Fe- and Mg-rich illite minerals, resulting from strong physical weathering. Furthermore, precipitation, rather than air temperature or latitude, was the factor that controlled weathering intensity. These findings provide deep insights into the sediment cycle and chemical weathering in this large reservoir basin.

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Acknowledgments

This study was supported financially by the National Key Research and Development Program of China (Grant No. 2016YFC0401703), the Fundamental Research Funds for the Central Universities (B200203111), the Natural Science Foundation of Jiangsu Province (Grant No. BK20191304), the Fundamental Research Funds for the Central Universities (Grant No. 2019B45414), the Postgraduate Research & Practice Innovation Program of Jiangsu Province (KYCX20_0490), and China Scholarship Council (CSC). Dr Tianning Li and Xiaofan Ma are acknowledged for help with the experiments.

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Correspondence to Wenbo Rao.

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The authors declare that they have no conflict of interest.

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(Received 22 May 2020; revised 13 November 2020; AE: Selahattin Kadir)

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(DOC 87.3 mb)

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Wang, S., Rao, W., Qian, J. et al. Clay Mineralogy of Surface Sediments in the Three Gorges Reservoir: Implications for Sediment Provenances and Weathering Regimes. Clays Clay Miner. 69, 52–67 (2021). https://doi.org/10.1007/s42860-020-00106-5

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  • DOI: https://doi.org/10.1007/s42860-020-00106-5

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