副特提斯海对塔里木环境演化的影响：地质证据和数值模拟

Numerical simulations suggested that the Paratethys retreat is a major contributor of the central Eurasian aridification, however,there exists much uncertainty as proposed by geologic evidence of drying events from the surroundings.The Cenozoic sediments in the Tarim basin trapped the trans-/regression history of the Paratethys, as well as regionally environmental responses to the retreat, as the intracontinental sea once extended into as far as the basin interior during the Palaeogene.We firstly select the Baxbulak section, located on the seaway connecting the Paratethys to the Tarim, to reconstruct in detail the retreat processes based on Sr isotope of shells and sulfur isotope of evaporites. Meanwhile, the terrestrial Kuqa section, next to the east shore of the sea during the Palaeogene, is selected to reconstruct the responses of regional vegetation and surface processes to the retreat. With these constraints,a fully coupled ocean-atmospheric circulation model HadCM3 is used to evaluate the impacts of the Paratethys on the Tarim aridity, as well as Eurasian climatic pattern.

数值模拟认为，副特提斯海退缩是欧亚大陆中部干旱环境形成的重要原因，但现有地质证据显示，海退过程、干旱化时间及机制都有很大的不确定性。在古近纪，副特提斯海东端一度深入塔里木盆地，盆地周边巨厚新生代沉积物保存了海水进退和环境演化的直接记录。本项目选择位于副特提斯海－塔里木海水通道的巴什布拉克剖面，利用生物壳体的锶同位素和石膏的硫同位素，重建海水从塔里木盆地逐渐退出的过程。同时，选择濒临古近纪副特提斯海东缘的库车剖面，利用孢粉学和地球化学手段，恢复区域植被和地表环境对海退的响应。结合巴什布拉克剖面重建的海退历史，以库车剖面的环境记录为约束条件，利用HadCM3海气耦合环流模式评价副特提斯海分布变化对早渐新世以来塔里木盆地干旱气候形成，以及欧亚大陆气候的影响。

在面上项目的支持下，过去四年里我们在塔里木盆地西缘的巴什布拉克剖面成功地确认陆相沉积记录开始于26Ma，表明副特提斯洋一直到晚渐新世才退出塔里木盆地。同时，库车盆地的地球化学以及孢粉记录表明，与现今相似的干旱环境记录至少开始于30Ma之前。这些结果表明，塔里木盆地的干旱状况可能完全独立于副特提斯海的范围，严重挑战了副特提斯退缩是塔里木盆地干旱环境形成重要原因的数值模拟结果。我们的数值模拟结果显示，使用不同的干旱化指标，如降水量 vs 蒸发与降水的差值，可能得到相反的结果。这一结果为理解数值模拟与地质记录的异同，提供了新的视角和思路。