青藏高原腹地始新世-渐新世古海拔演化的介形类和同位素证据

Whether the Tibetan Plateau hinterland had uplifted in large scale before the end of Eocene has been an important area of research in the geological sciences in recent years. Both animal fossils analysis and oxygen isotopic analysis are popular and reliable methods to estimate the palaoelevation. The ostracod fossils from the Eocene and Oligocene strata in the Tibetan Plateau hinterland are ideal materials for this study. We plan to compare these fossils to the same age ostracod fossils from the mid-south China, sort out the different evolution rules of species and slight shape structure of these ostracod fossils in two regions. The progress of the ecology difference evolutionary based on the ostracods shape functional analysis can provide the qualitative evidence of large scale uplifting time of Tibetan Plateau hinterland. The oxygen isotope and clumped isotope paleotemperature analysis of calcareous gastropoda fossil shell collected from the same layers can be applied to the suitable Rayleigh fractionation model for palaoelevation calculation of Tibetan Plateau hinterland, which can provide quantitative results of palaoelevation during different period. Based on these two methods of palaoelevation reconstruction, we can describe the detailed progress of the uplifting of Tibetan Plateau hinterland during the Eocene-Oligocene and provide exact evidence for the Qinghai-Tibet Plain uplifting model research.

青藏高原腹地是否在始新世晚期欧亚大陆碰撞之前就已发生大幅度抬升是近年来地质学界一个重要的争议热点。动物化石分析和氧同位素分析是恢复古海拔的热门且可靠手段。本次研究拟以青藏高原腹地的始新世至渐新世介形类动物群为主要研究对象，对比同时代中南地区介形类动物群，研究两区域介形类属种和细微形态构造演化规律，从形态功能分析角度重建古生态差异演化过程，找出差异分化时间节点，为确定青藏高原腹地的大幅隆升时间提供定性证据。同时对相同层位腹足类钙质壳体进行氧元素和二元同位素古温度分析，将其应用在已建立的适用于西藏腹地的瑞利分馏理论模型，以期定量恢复不同时期的古海拔。通过以上两种古海拔重建的手段，精细描绘青藏高原腹地始新世-渐新世海拔变化细节，为青藏高原隆升模式提供确切证据。

青藏高原古海拔定量重建是近十多年以来的研究热点，然而当前古高程数据资料分析多集中于氧同位素、古植物、氢同位素和二元同位素古高程计等方法，并采用单一手段为主，与研究区生物组合和古气候数据结合的综合分析较弱。本项目以青藏高原腹地的始新世至渐新世介形类化石和孢粉化石组合为主要研究对象，对比同时代百色盆地介形类化石和孢粉化石组合，并辅以抚顺盆地始新世孢粉化石研究，定性得出了始新世时期青藏高原腹地已经有了一定隆升但规模与现今差异较大的结论。同时对相同层位碳酸盐岩和腹足类钙质壳体进行氧元素和二元同位素古温度分析，将其应用在已建立的适用于西藏腹地的瑞利分馏理论模型，定量恢复始新世的古海拔为1382m(σ=453m)。通过以上两种古海拔重建的手段，确定青藏高原腹地在晚始新世前仅发生小规模隆升，为青藏高原隆升模式提供确切证据。