西秦岭地区上新世生态环境演变的生物标志化合物证据

As an important geological climatic transition of late Cenozoic and a well analog episode for predicting the future climate change, the Pliocene and its climatic history and driving mechanisms issues are always attracting the attention of geoscientists and becoming one of the hot topics in Earth Science. However, the complex characterics of climate proxies and scarce quantitative research on Pliocene ecosystem and temperature prevent the further understanding of how the Pliocene climate evolved in East Asia. So more univocal methods or proxies should be involved to illustrate the driving mechanisms and will fill the knowledge gap. Among them, biomarker is a good candidate and has particular advantages in reconstructing the paleotemperature and paleoecology quantitatively. Here we conduct the integrated the compound-specific n-alkanes carbon isotope of leaf wax and microbial lipid paleotemperature studies on the Pliocene fluvial-lacustrine strata in the Western Qinling region, Northeastern Tibetan Plateau. These results will be utilized to (1) quantitatively reconstruct the Pliocene vegetation evolution and temperature history in the Western Qinling, (2) evaluate the detailed characteristics and sensitivity of the Pliocene climate in the Northeastern Tibetan Plateau, (3) illustrate the driving mechanisms of Pliocene environmental change based on the synthetical comparisons among the Western Qinling, other terrestrial and marine records. Furthermore, our proposal will not only provide the crucial biogeochemistry evidence for the coupled mechanisms between the climatic change and tectonic activity, but also depict the climatic background which can be consulted in predicting the future climate and evaluating the environmental effects.

作为晚新生代地质历史的重要气候转型期和未来气候预测的良好参考期，上新世生态、环境演变过程及其驱动机制一直是地学领域的前沿热点问题。然而，气候代用指标的多解和定量研究的缺乏使我国上新世气候演变过程仍不十分清楚，亟需环境意义更明确的生物标志化合物方法开展深入的古环境定量研究。本项目拟将针对青藏高原东北缘上新世季风的演化问题和定量研究较少的不足，以西秦岭地区喇嘛山剖面上新世河湖相沉积为研究对象，系统开展植物叶蜡单体碳同位素和微生物四醚膜类脂物测试分析，定量重建喇嘛山上新世古生态和古温度演变序列，厘清西秦岭地区上新世生态环境演变规律；并与周边地区和海洋记录进行对比，深入讨论区域气候变化与高原隆升历史和极地冰量之间的动力学联系，进而揭示上新世气候转型的可能驱动机制。本研究不仅为深入理解气候-构造之间的耦合关系提供生物有机地球化学证据，也为气候变化趋势预测及环境效应评估提供重要气候背景。

晚中新世-上新世古环境定量重建对深入理解青藏高原隆升、全球变冷和东亚地区生态环境演化的耦合关系提供独特视角。依照项目计划，对西秦岭地区尧店剖面和喇嘛山剖面（晚中新世-上新世河湖相沉积）开展了系统的生物标志化合物（正构烷烃、长链烯酮和微生物膜类脂物）、有机碳同位素、元素地球化学和孢粉集成研究。并基于前期高精度磁性地层学和古生物年代学框架，建立了西秦岭地区天水盆地晚中新世-上新世古温度和古生态等演变历史，深入探讨了区域气候变化的可能驱动机制。主要获得以下科学认识：1）定量重建了西秦岭地区天水盆地晚中新世-上新世以来古温度历史。天水盆地晚中新世以来温度逐渐变冷，晚上新世（3.2Ma和2.8Ma）出现两次显著降温事件，可能与全球M2事件、北极冰盖扩张事件和高原东北缘强烈隆升有关；2）利用微生物膜类脂物指标揭示了晚中新世-上新世期间两次显著干旱事件（7-6Ma和3.4-3.2Ma左右），2次降温事件均滞后于古干旱事件；3）多指标集成研究恢复了喇嘛山古湖晚上新世生态、水位和盐度演变历史。3.2-2.8Ma时期气候冷湿，碳同位素持续正偏，化学风化加强，流域降水增加导致湖水加深，盐度降低，2.8Ma左右湖泊最深；2.8Ma之后温度继续降低，碳同位素显著负偏，冷干气候致使湖泊萎缩、盐度增大；4）综合分析天水盆地古气候记录与全球其他记录的异同，认为晚上新世高原东北缘强烈隆升、北极冰盖扩张和全球变冷共同控制了西秦岭地区天水盆地上新世生态环境演变。本项目所取得的研究成果，为开展高原东北缘晚中新世以来古生态和古温度定量重建等提供重要参考，并对深入理解晚新生代以来青藏高原构造活动和气候相互耦合作用提供支持。

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