南海深海沉积定量重建及其对洋盆扩张过程的启示

“The South China Sea Deep” has funded multiple projects on sedimentology that focused on local and decentralized researches. It is time to establish a comprehensive integration issue that can explain the overall sedimentary filling characteristics of continental margins and ocean basins of the South China Sea (SCS). This project is focused on two key scientific issues of “evolutions and sedimentary records of the SCS various continental margins” as well as “sedimentary processes in response to the SCS spreading”. Taking the tectonic stratigraphy and marine sedimentology theories as a guide, this project aims to (1) summarize the tectonic evolution differences and sedimentary records over the various types of SCS continental margins (divergent, strike-slip and convergent continental margins), after following the significant tectonic transformation interfaces and seafloor spreading events; (2) ascertain the development and evolution, sedimentary filling sequences and sedimentary environment changes of the SCS margins and oceanic basins, in combination with investigating the SCS spreading, transition, closure and other tectonic events; (3) quantitatively determine the sedimentary filling difference and deposition flux variation during the SCS pre-spreading, syn-spreading and post-spreading stages; and (4) reveal the genetic relationship between the SCS marginal deep/ultra-deep water sedimentary fillings and the oceanic basin evolutions. This study is expected to further deepen the comprehensive understandings of the SCS continental margin sedimentary pattern evolutions and oceanic basin spreading dynamics, and provides a whole typical depositional infilling case of marginal sea from continental margin to oceanic basin.

“深海过程演变”重大计划项目已资助多个沉积学项目，但均为局部的、分散式研究，急需设立综合性的集成课题，从整体上查明南海陆缘及海盆沉积充填特征，形成整个南海系统的、全局性的认识。本项目围绕“南海陆缘差异演化及其沉积记录”和“南海海盆扩张过程的沉积响应”两个关键科学问题，以构造地层学和海洋沉积学理论为指导，以南海关键构造变革界面和海盆扩张事件为主线，建立南海不同陆缘（离散型、走滑型和汇聚型）整体的构造-地层等时对比框架；结合南海扩张起始、跃迁和闭合等构造事件研究，查明陆缘盆地及海盆发育演化、充填序列以及沉积环境变迁等方面的响应记录；定量确定南海前扩张期、同扩张期、后扩张期的沉积充填差异及沉积通量变化；揭示南海陆缘沉积充填与海盆演变之间的成因联系。本项研究可望进一步深化南海大陆边缘沉积格局演变和洋盆扩张动力学研究的整体性认识，并提供边缘海盆地从陆缘到海盆完整的沉积充填演化研究的典型范例。

通过海量地质和地球物理的综合分析，以南海关键构造变革界面和海盆扩张事件为主线，总结南海不同陆缘（离散型、走滑型和汇聚型）构造演化差异及其相应的沉积记录，定量确定南海前扩张期、同扩张期、后扩张期的沉积充填差异及沉积通量变化，揭示南海深海盆源-汇系统特征。取得如下创新性认识：①基于南海海域关键构造事件界面识别，系统构建了南海不同陆缘条件下陆架-陆坡-深海及海盆区构造层序界面对比框架。②发现南海发育2期岩石圈破裂事件，提出岩石圈破裂过程中所形成的不整合界面及其破裂不整合系统，揭示被动陆缘近端带与远端带不整合界面特征及其地层结构差异。③以关键构造事件为主线，编制了南海前扩张期、同扩张期和后扩张期沉积厚度图，系统地揭示了南海深海盆演变中的沉积作用和沉积量变化。④揭示了后扩张期南海深海盆源-汇系统特征，提出了南海海盆发育的3类源-汇系统充填样式和6大物源体系，其中东北缘及西北缘物源构成了西北海盆和中央海盆主要物源体系。⑤基于不同陆缘构造样式，揭示南海前扩张期、同扩张期和后扩张期伸展、走滑、碰撞挤压、俯冲四类陆缘沉积响应差异。该项目系统地揭示了南海不同陆缘及海盆沉积充填演化特征，为西太平洋边缘海沉积充填研究提供了一个典型的范例，对南海深海过程演变重大计划项目具有重要参考价值。所提出的不同陆缘地层样式及深水-超深水盆地沉积充填特征对南海海域，特别是中南部海域油气勘探具有重要的应用前景。.本项目组共发表学术论文24篇，其中SCI 收录论文18篇，中文核心期刊论文6篇。另在国际期刊“Marine Geophysical Research”组织的 “Tectonics and depositional infilling of western Pacific marginal sea” 专辑2019年即将出版（共8篇，其中7篇已经在线Online发表）。参加国际会议21人次。项目执行过程中培养毕业博士4名和硕士18名。