Abstract Late Cenozoic changes in chemical weathering and the dust cycle in response to the regional aridification and global cooling in the tectonically active northern Tibetan Plateau is an intriguing issue, although it remains poorly understood. The change in the 87Sr/86Sr ratio of basin water is linked to variations in the overall input of various Sr sources with different 87Sr/86Sr ratios, and analyses of such changes can be a useful tool for revealing changes in regional lithology, weathering regimes and the dust cycle linked to tectonics and climate. In this study, we collected fossil shells of ostracods and gastropods from the Miocene Dahonggou section to reconstruct the paleolake water 87Sr/86Sr ratio from 14.8 Ma to 11.1 Ma in the northern Qaidam Basin on the northeastern Tibetan Plateau. The reconstructed paleolake water 87Sr/86Sr ratios based on fossil shells and bulk carbonates from sediments display a coincident and stable 87Sr/86Sr ratio of approximately 0.7115, which did not show any detectable change in response to the enhanced aridification since ~13 Ma as inferred by the ostracod assemblage and its stable carbon and oxygen isotopes. The results indicate that the Sr influx regime from various sources did not change significantly during the aridification processes ~13 Ma, which may have been caused by a less detectable change in proportion of silicate versus carbonate weathering, and/or an overwhelming Sr source (e.g., extrabasinal eolian dust) that occurred from 14.8 Ma to 11.1 Ma. Further, the 87Sr/86Sr ratios of modern lake water and river sand carbonates in the study region are significantly higher, approximately ≥0.001, than those of the Miocene lake water. This observation can be explained by two possible mechanisms that need to be tested in the future: 1) given a Miocene Sr input regime that is similar to today, a large contribution from some extrabasinal Sr source (e.g., eolian dust) with a much lower 87Sr/86Sr ratio is expected to have prevailed from 14.8 Ma to 11.1 Ma but is absent in the modern setting or 2) given a Miocene Sr input regime that could yield an overall lower lake water 87Sr/86Sr ratio of approximately 0.7115, a significant increase in the 87Sr/86Sr ratio of catchment-scale Sr source may have occurred after 11 Ma in response to the uplift of the Qilian Mountains, which would have enhanced hydrothermal activity, metamorphism, glaciation and landslide processes, thereby resulting in more-radiogenic Sr source. Our study suggests that reconstructions of river/lake water 87Sr/86Sr ratios can place powerful constraints on the complex interactions among tectonics, climate and landscape evolution in the northeastern Tibetan Plateau based on a new perspective.

中文翻译：

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青藏高原东北部柴达木盆地北部介形动物中新世87Sr/86Sr比值及其与区域物源、风化和风积输入的联系

摘要 青藏高原北部构造活跃的区域干旱化和全球变冷对化学风化和沙尘循环的晚新生代变化是一个有趣的问题，尽管它仍然知之甚少。流域水 87Sr/86Sr 比值的变化与具有不同 87Sr/86Sr 比值的各种 Sr 源的总体输入变化有关，对这种变化的分析可以成为揭示区域岩性、风化状况和气候变化的有用工具。与构造和气候有关的尘埃循环。在这项研究中，我们收集了中新世大红沟剖面的介形动物和腹足动物的贝壳化石，重建了青藏高原东北部柴达木盆地北部从 14.8 Ma 到 11.1 Ma 的古湖水 87Sr/86Sr 比值。基于化石壳和沉积物中的块状碳酸盐重建的古湖水 87Sr/86Sr 比值显示出一致且稳定的 87Sr/86Sr 比值约为 0.7115，这没有显示出任何可检测的变化响应自 13 Ma 以来增强的干旱化介形虫组合及其稳定的碳和氧同位素。结果表明，在干旱化过程~13 Ma 期间，来自各种来源的 Sr 流入方式没有显着变化，这可能是由于硅酸盐与碳酸盐风化的比例变化较难检测，和/或压倒性的 Sr 来源（例如, 盆地外风尘）发生于 14.8 Ma 至 11.1 Ma。此外，研究区现代湖水和河砂碳酸盐岩的 87Sr/86Sr 比值明显较高，约为 ≥0.001，与中新世湖水相比。这一观察结果可以通过未来需要测试的两种可能机制来解释：1) 考虑到与今天相似的中新世 Sr 输入状态，来自一些盆地外 Sr 源（例如风尘尘）的巨大贡献，具有低得多的87Sr/86Sr 比率预计从 14.8 Ma 到 11.1 Ma，但在现代环境中不存在或 2) 考虑到中新世 Sr 输入制度可能会产生总体较低的湖水 87Sr/86Sr 比率约为 0.7115，显着增加流域尺度Sr源的87Sr/86Sr比值可能发生在11 Ma之后响应祁连山的隆升，这将加强热液活动、变质作用、冰川作用和滑坡过程，从而导致更多的放射性Sr源.