琼东南盆地深水重力流沉积旋回演化规律与形成机理

The mass transport deposits and channel leveed deposits are composed the deep-water deposits. There is a lack of overlooking the transformation between two systems in the previous research. Our proposal will aim at the transformation between two gravity flow deposit systems in the deep-water region of Qiongdongnan Basin, South China Sea. The highlights include adopting the cyclostratigraphy and building a sediment cycle from the mass transport deposits to channel-levee systems. Based on the newest 2D and 3D seismic data, deep-water drilled wells data, well logging data and sediment core, deposition and evolution of gravity flow which was formed within the adequate supply source deep-water sedimentary environment controlled by sea-level changes, will be built by the analysis of the seismic sedimentology and cyclostratigraphy. A model corresponding to completed sea-level change cycle will be established by analyzing the relationship of the different gravity flows with the relative sea-level changes of 500-100 ka scale. The result of this study will provide theoretical foundation and scientific basis for the exploration and development of deep-water oil&gas, studies on the seafloor instability and marine geological disasters.

深水重力流沉积体系包含了块体搬运沉积体系与水道-堤岸体系，传统理论并未考虑二者之间的相互转化，存在研究不足。本申请拟引入旋回地层学的研究方法，以琼东南盆地的深水区为研究靶区，从沉积体系相互转化着手，将块体搬运沉积体系与水道-堤岸沉积体系纳入一个整体——沉积旋回进行研究。以最新采集的2D/3D 高分辨率地震、测井、综合录井数据及沉积物样品测试数据为研究资料，通过地震沉积学与旋回地层学的方法与技术，获得在海平面变化主控因素控制、物源供给充足、深水沉积环境中的重力流沉积与演化规律，阐明四级海平面变化（500-100 ka）对深水重力流沉积的控制作用，建立一个与完整四级海平面变化周期对应的深水重力流沉积旋回模型，为深水油气勘探与开发、海底不稳定性及海洋地质灾害研究提供理论基础与科学依据。

根据三维地震资料、地震振幅、相干度、时厚、波形分类和地层切片，确定了琼东南盆地深层更新世层序中的旋回沉积体系，揭示了底部块体搬运沉积体系和顶部水道-堤岸沉积体系的垂向构成、旋回沉积体系的垂向演化。水道-堤岸沉积体系显示了从侵蚀型水道到堤岸型水道的演化序列。侵蚀型水道体系具有较强的下切能力，包括侵蚀水道、不发育的堤岸、平滑的侧缘、决口扇和滑坡。与侵蚀型水道系统相比，堤岸型水道体系的下切地层深度较小，包括水道、发育良好的堤岸和漫滩沉积物。运动学指标表明，形成旋回沉积体系的重力流来源于越南中部的陆架边缘/上坡体系。越南中部山区河流输送了大量陆源碎屑到陆架边缘/上坡体系。从1144个站点的1.6Ma、1Ma和0.5Ma的孢粉序列、δ13C最大值（δ13CMAX）的周期，提出了一个新的深水沉积体系演化模型。该模型中，相对海平面变化的周期是长偏心率时间尺度上的周期，沉积体系变化受相对海平面变化的不同阶段控制。根据沉积地层时间约束，推导出三个旋回沉积体系的起点分别对应于更新世1.6Ma、0.9Ma和0.4Ma的三个气候事件。