基于西沙群岛的“时间-海侵”白云岩化过程研究

新生代岛礁白云岩被认为是研究“白云岩问题”的天然实验室，其中白云岩化的时间是探讨岛礁白云岩化大规模驱动机制的关键。目前通常认为岛礁白云岩化的时间演化表现为不连续、多期次的“白云岩化事件”；然而，申请人近期研究发现西沙群岛黄流组的白云岩化表现为一个（半）连续的“时间-海侵”过程，且这种现象在太平洋和加勒比海的多个岛礁中均有出现。造成这种差异认识的根本原因是前者关注的是岛礁白云岩化时间地理学上的变化，而申请人则补充了其地层学上的信息。但当前尚缺少对岛礁白云岩化时间地层学上演化规律的完整认识。基于此，本项目拟利用白云石的锶同位素对西沙群岛莺歌海组的白云岩化时间开展研究，探究是否整个西沙群岛的白云岩化为一个完整的“时间-海侵”过程；再基于西沙群岛的认识，开展全球岛礁白云石锶同位素数据的对比，从地层学上完善岛礁白云岩化时间的演化过程。预期成果可为岛礁白云岩化的形成过程和驱动机制研究提供重要基础支撑。

Cenozoic island dolostones are generally considered as the natural laboratory for the resolution of the “dolomite problem”. The time of dolomitization is vital to determine the large-scale factors that controlled the development of island dolostones. At present, the time of island dolomitization in mainstream view is presented as discontinuous and multi-phase “dolomitization events”. However, we recently found that the dolostones of Huangliu Formation in the Xisha Islands were formed by a (semi-)continuous time-transgressive dolomitization process, which is also present on many islands from the Carribbean Sea and the Pacific Ocean. This dispute fundamentally comes from the former focusing on the geographic changes of dolomitization time between the different islands, whereas we add stratigraphic information. However, there is a lack of a full understanding of the stratigraphic evolution of the island dolomitization time now. Based on above, this project intends to use strontium isotope of dolomites to study the dolomitization time of Yinggehai Formation in the upper Xisha Islands, and to verify whether the dolomitization of the Xisha Islands is a whole "time-transgressive" process. Then, using the point of view from Xisha Islands, we plan to compare the strontium isotopes of global island dolomites to improve the stratigraphic time evolution of islands dolomitization. The expected results can provide an important basis for the study on the dolomitization process and mechanisms of Cenozoic islands.