铀系同位素探究末次冰盛期以来东亚大陆边缘的风化沉积记录

Knowledge of source-to-sink processes along the East Asian continental margin is of profound importance to understand land-ocean interaction and sediment transport. Uranium-series disequilibrium method is an effective and valuable tool in revealing the earth surface processes, but application of this method to reconstruct paleoenvironment in continental margins is still rare. Hence, we aim to build up a proxy using the unique isotopic composition of 234U/238U in different sediment phases (terrigenous and authigenic) based on two sediment cores collected in the Zhe-Min mud deposits of the inner East China Sea shelf and around the mouth of the Chuoshui River of Taiwan Island. Combined with other sedimentary geochemical indicators, this study is devoted to investigating the weathering and sedimentary records in the East Asian continental basins and island since the Last Glacial Maximum, and also explore the implications for the evolution of sedimentary environment. Findings from this work will deepen our understanding of land-ocean interaction in general and coupled processes of tectonics, climate, and sedimentation along continental margins.

东亚大陆边缘发育活跃的河流沉积物从源到汇系统，是开展陆海相互作用和物质循环的典型区域。U系不平衡法在揭示地球表生过程方面具有很强的应用价值，但国内外运用该方法来重建大陆边缘风化沉积过程的研究工作还相对缺乏。本课题选取东海内陆架浙闽沿岸泥质区及台湾浊水溪河口近岸两个钻孔，建立沉积物中不同相态（碎屑及自生组分）234U/238U指标的测试方法，利用其独特的示踪意义，并结合传统沉积地球化学的研究手段，比较研究末次冰盛期以来大陆流域和岛屿的风化沉积过程，以及探究其对沉积环境演变的启示，由此有助于深化对陆海相互作用的认识及为大陆边缘构造－气候－沉积耦合过程研究提供新的思路。

针对该课题主要的科学目标，项目组以海陆结合和从源到汇的研究思路，以浙闽和台湾河流沉积物，以及台湾浊水溪河口钻孔样品为主要研究对象，开展了大量沉积矿物学、元素和Sr-Nd-U同位素地球化学分析。在台湾浊水溪河口钻孔运用碎屑态234U/238U比值进行了“沉积物搬运时间”的计算，揭示了自末次冰期以来，沉积物搬运时间经历了由短变长再变短的过程，初步推测河流沉积物滞留时间可能受控于气候变化所导致的地表植被类型及其覆盖率的变化。同时开展河流沉积地球化学复杂性研究，揭示了流域化学风化和水动力分选对河流沉积物地球化学组成的影响，以及对极端气候事件的快速响应过程。依托该项目，在国内外核心刊物上共发表研究论文4篇，包括国际SCI论文2篇。