Stable silicon (Si) isotopes in fluvial sediments can provide insights into understanding silicate weathering processes on the Earth's surface. However, a lack of comprehensive studies has hindered full understanding of the factors influencing Si isotope fractionation during continental weathering. In this study, through the analysis of Si isotopes in fine-grained sediments from 13 rivers surrounding the South China Sea, significant variation of Si isotopes in bulk detrital sediments (<63 μm) was observed, with δSi values ranging from −0.17‰ to −1.09‰. At basin scale, the δSi values are influenced by multiple controlling factors such as climatic conditions, lithology, and tectonic settings, which have a close relationship with the content of clay minerals. The characteristics of weathering types and intensities are ultimately reflected in the weathering products, specifically clay minerals. Compiling data across multiple grain sizes from major rivers globally, robust correlations based on clay mineral classification between δSi and Al/Si ratio have been observed, which are unaffected by regional and grain-size variations. As the dominant clay mineral group transitions from illite/chlorite to smectite and kaolinite, the degree of Si isotope fractionation increases progressively. This sequence indicates a shift from stronger physical erosion to more intensive chemical weathering, suggesting a transition in the weathering regime from weathering-limited to transport-limited. This study reveals the intrinsic link between Si isotopic compositions and clay mineral assemblages, providing implications for similar stable isotope research and offering a potential indicator for understanding continental weathering processes and their contributions to the global carbon cycle.

中文翻译：

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粘土矿物控制细粒河流沉积物的硅同位素变化：对物理侵蚀和化学风化之间权衡的影响


河流沉积物中的稳定硅 (Si) 同位素可以为了解地球表面硅酸盐风化过程提供见解。然而，缺乏全面的研究阻碍了对大陆风化过程中硅同位素分馏影响因素的全面了解。本研究通过对南海周边13条河流细粒沉积物中Si同位素的分析，观察到大块碎屑沉积物（<63μm）中Si同位素的显着变化，δSi值范围为-0.17‰到−1.09‰。在盆地尺度上，δSi值受气候条件、岩性、构造背景等多重控制因素影响，与粘土矿物含量密切相关。风化类型和强度的特征最终反映在风化产物中，特别是粘土矿物上。通过对全球主要河流的多种粒度数据进行汇编，我们观察到基于粘土矿物分类的 δSi 和 Al/Si 比率之间存在强大的相关性，并且不受区域和粒度变化的影响。随着主要粘土矿物群从伊利石/绿泥石转变为蒙皂石和高岭石，硅同位素分馏程度逐渐增加。这一序列表明从更强的物理侵蚀到更强烈的化学风化的转变，表明风化状态从风化限制到运输限制的转变。这项研究揭示了硅同位素组成和粘土矿物组合之间的内在联系，为类似的稳定同位素研究提供了启示，并为了解大陆风化过程及其对全球碳循环的贡献提供了潜在的指标。