Detailed investigations of sedimentary rocks from the Tibetan Plateau interior, which has been shaped by plateau development and climate change, will provide new insights into its uplift history. However, few continuous environmental records with clear climatic significance and precise age controls from the Tibetan Plateau hinterland exist, particularly in the early Cenozoic. This shortage hinders a full understanding of the impact of uplift on regional climate change. In this study, we present detailed mineralogical, micromorphological and geochemical investigations of the middle–upper Eocene (∼39.6–35.3 Ma) lacustrine sediments from the well-dated Dayu section in the Lunpola Basin, central Tibetan Plateau, to explore the paleoenvironmental evolutionary history of the middle–late Eocene from paleoweathering and paleohydrological perspectives. The results reveal that regional weathering process continuously weakened, as indicated by a long-term decrease in the (smectite + mixed-layer illite–smectite)/(illite + chlorite) ratio. The quantitative reconstruction of salinity variations via clay boron-based paleosalimeters reveals long-term salinization of paleolakes from freshwater–mesosaline conditions (averaging 9.0 psu) at ∼39.6–37.8 Ma to freshwater–polysaline conditions (averaging 13.4 psu) at ∼37.8–35.3 Ma. The long-term continuous weakening of the weathering intensity and lake salinization collectively suggests a secular drying trend in the central Tibetan Plateau. This drying was consistent with the climatic evolution of the southeastern and northern Tibetan Plateau, which is attributed primarily to global cooling, with secondary contributions from the increasing distance from moisture sources in the Paratethys and regional tectonics.

中文翻译：

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全球降温控制青藏高原中部 Lunpola 盆地始新世环境变化：来自盐度和风化重建的证据


青藏高原内部的沉积岩受高原发展和气候变化的影响，对沉积岩的详细研究将为了解其隆起历史提供新的见解。然而，青藏高原腹地具有明确气候意义和精确年龄控制的连续环境记录很少，尤其是在新生代早期。这种短缺阻碍了对上升对区域气候变化影响的充分理解。在这项研究中，我们详细介绍了青藏高原中部伦波拉盆地大禹剖面中上始新世 （∼39.6–35.3 马） 湖泊沉积物的矿物学、微形态学和地球化学研究，从古风化和古水文的角度探索中晚期始新世的古环境演化历史。结果表明，区域风化过程持续减弱，表现为（蒙脱石 + 混层伊利石-蒙脱石）/（伊脱石 + 绿泥石）比值的长期降低。通过基于粘土硼的古盐度仪对盐度变化进行定量重建，揭示了从 ∼39.6-37.8 马 的淡水-中盐水条件（平均 9.0 psu）到 ∼37.8-35.3 马的淡水-多盐条件（平均 13.4 psu）的古湖泊长期盐化。风化强度长期持续减弱和湖泊盐碱化共同表明青藏高原中部长期呈干旱趋势。这种干燥与青藏高原东南部和北部的气候演变一致，这主要归因于全球变冷，次要原因是与帕拉提斯和区域构造中水分源的距离越来越远。