深水单向迁移水道的成因机理及其内的浊流、内潮流与等深流交互作用研究

The interplay of turbidity flows, tidal bottom currents and bottom currents are the frontier area of the submarine sedimentology, while the ultimate decoding of the genesis and depositional model of deposits created by this depositional process has huge significance to the industrial and academic communities. Unidirectionally migrating deep-water channels are textbook examples of deposits created by interplay of turbidity and bottom currents and are the natural laboratory for the stduies of the interplay of turbidity, tidal bottom currents and bottom currents. A series of unidirectionally migrating deep-water channels developed in the Baiyun Depression, northern South China Sea. Compared with sinuous deep-water channels, which are characterized by: (1) overall steepened northeastern compared to the southwestern flanks; (2) migration progressive northeastward since Late Miocene with maximum northeastward migration of 5 km; and (3) short and steep morphology and a lack of levees. Newly available high-quality 3D database acquired during the the geophysical and geological surveying of LW3-1 gas field cruise, including hydrographic survey, multibeam bathymetry, side-scan sonar images (200 kHz), sub-bottom profiles (10 kHz), six longer drillings with the average depth of 200 meters, etc. These high-quality 3D data sets allow us to: (1) investigate products deposited by bottom currents observed on seafloor, and recogniz the diagnostic criteria of these products; (2) detailed investigate morphology and architectural stylesof the unidirectionally migrating deep-water channels; (3) reconstruct the sedimentary processes operating within unidirectionally migrating deep-water channels; (4) discuss the possible controls on the development on the development of the unidirectionally migrating deep-water channels, investigate the genesis of the unidirectionally migrating deep-water channels; (5) investigate the depositional models of unidirectionally migrating deep-water channels and the distribution pattern of the sand bodies with within these channels. Our results will lead to a better understanding of deep-water sedimentation on continental margins and will help to obtain a better understanding of the origin and distribution patterns of non-turbidite reservoirs in deep-water settings.

浊流、内潮流与等深流交互作用是当今深水沉积学理论研究的前缘和薄弱环节，而深水单向迁移水道体现了浊流、内潮流及等深流的综合效应，是开展浊流、内潮流与等深流交互作用及其沉积模式研究的天然实验室。白云深水区发育了一系列与深水浊流水道特征迥异的深水单向迁移水道，其东陡西缓、自晚中新世以来持续向东迁移。拟利用"荔湾3-1气田工程勘察"丰富的海流观测、多波束、旁测声纳、钻孔（单个长约200米）等高精度观测数据，从"交互作用"的角度对深水单向迁移水道进行高精度解剖：开展现今海底各种沉积作用的沉积响应分析，建立水道内不同类型沉积响应的相标志；对上新世以来的水道充填结构进行精细刻画，研究深水单向迁移水道内的浊流、内潮流及等深流交互作用的沉积作用过程及演化,进而分析各种沉积响应的发育背景及控制因素，从交互作用的角度揭示深水单向迁移水道的成因机理，建立相应的沉积模式和砂体展布模式。

本基金项目（41372115）利用高精度地质与地球物理资料，探讨了重力流与底流（内潮流和等深流）交互作用有利的形成发育场所，研究了典型交互作用的产物—深水单向迁移水道的沉积构成和成因机理，揭示了交互作用形成的底流改造砂的分布模式和识别相标志，并分析了重力流与底流交互作用的沉积动力学机制。不发育堤岸且持续地向一个方向迁移的深水单向迁移水道是重力流与底流交互作用有利的形成发育场所。深水单向迁移水道内充填发育一个由底流改造砂、滑塌/碎屑流沉积和深海披覆泥组成的向上变细的沉积序列。在缺少离心力作用的顺直的深水单向迁移水道内，流向水道迁移一侧（凹岸）的底流能够驱动重力流以2°～15°斜交凹岸，从而形成一个由流速较大的流向凹岸的表层流和流速较小的流向凸岸的底层流构成的横向环流，这一底流诱发的横向环流的高速涡流区出现在水道的凹岸，以侵蚀作用为主；而其低速涡流区出现在水道的凸岸，以沉积作用为主。该横向环流所伴生的“凹岸侵蚀—凸岸沉积”驱动水道及其所伴生的底流改造砂向参与其沉积建造的底流流向一侧持续、稳定地迁移、叠加，同时该横向环流的流体厚度小于水道的深度，从而形成不发育堤岸且持续地向一个方向迁移的深水单向迁移水道。底流改造砂是顺物源方向的重力流、潮汐底流交和内波互作用及垂直于物源方向的等深流和低能的浊流交互作用共同作用的产物，内潮沉积相标志和牵引流沉积构造是其最重要的识别相标志。深水单向迁移水道内的沉积物能够被发育在凹岸一侧的高速涡流区更充分地分选、淘洗和改造，细粒的泥质沉积物被淘洗掉，从而使得底流改造砂在平面上总是沿着与水道轴向平行的、靠近水道迁移一侧呈条带状展布而在剖面上底流改造砂总是向水道迁移方向不断迁移、叠加。