冲绳海槽中南段陆坡海底峡谷侵蚀-沉积结构与形成演化机制

Submarine canyon is a natural transport channel for terrigenous detritus from land to deep sea，and is also an important carrier and potential inducing factor of landslide hazard. Its formation and evolution record geological history information, such as sea level eustacy, climate change, tectonic movement and so on. Therefore, studying the formation and evolution process of the submarine canyon on the continental margin and revealing its genetic mechanism not only promote the scientific understanding of the origin and evolution of the submarine canyon, but also have a realistic significance for assessing the climate and hazard effects of the submarine canyon. The project intends to focus on the sedimentary stratigraphic sequence in the mid-southern continental slope of the Okinawa Trough, determining the sequence record, stratigraphic position and geologic age of key tectonic and sedimentary transformative events, establishing a time-space frame of submarine canyon distribution and evolution by combining drilling well/borehole and seismic, describing the morphological structure and erosional-depositional characteristics of the submarine canyon and reconstructing its temporal-spatial evolution history. Based on the above research, a three-dimensional depositional dynamics model is constructed to simulate the formation and evolution of the submarine canyon, and to analyze the controls of fracture, sediment supply, sea level change, geomorphology and methane fluid leakage events, revealing the genetic mechanism of the submarine canyon in the mid-southern continental slope of Okinawa Trough.

海底峡谷是陆源碎屑物质由陆地向深海输运的天然通道，也是海底滑坡灾害的重要载体和潜在诱因，其形成演化记录了海平面升降、气候变化和构造活动等地质历史信息。因此，研究大陆边缘海底峡谷的形成演化过程并揭示其成因机制，不仅可以提升对海底峡谷起源和演化的科学认识，而且对评估海底峡谷的气候环境和地质灾害效应具有现实意义。本项目拟以冲绳海槽中南段陆坡沉积地层序列为重点研究对象，厘定关键构造沉积变革事件的层序旋回记录和层位时限，钻井/钻孔-地震联合确立海底峡谷分布和演化的时空格架，识别刻画海底峡谷的形态结构与侵蚀-沉积特征，重建海底峡谷的时空演化历史，并以此为基础，构建三维沉积动力学模型模拟海底峡谷的形成演化过程，剖析断裂、沉积物供给、海平面变化、地貌以及甲烷流体渗漏事件等因素对海底峡谷发育演化的控制作用，揭示冲绳海槽中南段陆坡海底峡谷的形成机制。

海底峡谷是陆源碎屑物质由陆地向深海输运的天然通道，也是海底滑坡灾害的重要载体和潜在诱因，其形成演化记录了海平面升降、气候变化和构造活动等地质历史信息。因此，研究大陆边缘海底峡谷的形成演化过程并揭示其成因机制，不仅可以提升对海底峡谷起源和演化的科学认识，而且对评估海底峡谷的气候环境和地质灾害效应具有现实意义。本项目以冲绳海槽中南段陆坡沉积地层序列为重点研究对象，厘定关键构造沉积变革事件的层序旋回记录和层位时限，钻井/钻孔-地震联合确立海底峡谷分布和演化的时空格架，识别刻画海底峡谷的形态结构与侵蚀-沉积特征，重建海底峡谷的时空演化历史，并以此为基础，构建三维沉积动力学模型模拟海底峡谷的形成演化过程，剖析断裂、沉积物供给、海平面变化、地貌以及甲烷流体渗漏事件等因素对海底峡谷发育演化的控制作用，揭示冲绳海槽中南段陆坡海底峡谷的形成机制。.结果显示，冲绳海槽陆坡海底峡谷开始形成于更新世中期并持续发育至今，海底峡谷的头部多是由LGM时期形成的古下切水道进一步演化形成的。海底峡谷的形成时间与欧洲阿尔卑斯山脉、新西兰南阿尔卑斯山脉以及东非高山记录的第四纪冰期启动时间相当，且海底峡谷谷壁上与BSRs相伴生、内部呈叠瓦状杂乱反射特征的MTD块体和谷壁上的气体逃逸“缺口”等地质特征，均说明海底峡谷的侵蚀-沉积演化与海底甲烷渗漏系统存在着复杂的成因联系，其耦合演化模式可以划分为四个阶段：①中更新世冰期海平面下降-水合物分解-海底峡谷启动形成阶段；②海底峡谷持续下切、溯源侵蚀-水合物稳定带动态迁移阶段；③峡谷谷壁沉积物失稳、滑塌-甲烷逃逸渗漏的互促阶段；④峡谷侵蚀减弱、水道砂体充填-水合物再赋存阶段。