东非鲁伍马盆地下始新统沉积水动力学机制

Hydrodynamic of the Lower Eocene in the Ruvuma Basin, East Africa

赵文楷 许小勇 田冬梅 张颖 吴佳男

ZHAOWenkai XUXiaoyong TIANDongmei ZHANGYing WUJianan

浙江海洋大学海洋科学与技术学院, 浙江 舟山 316022 中国石油杭州地质研究院, 浙江 杭州 310023 中国地质大学(武汉) 海洋地质资源湖北省重点实验室, 湖北 武汉 430074

Marine Science and Technology College, Zhejiang Ocean University, Zhoushan, Zhejiang 316022, China Hangzhou Research Institute of Petroleum Geology, PetroChina, Hangzhou, Zhejiang 310023, China Hubei Key Laboratory of Marine Geological Resources, China University of Geosciences (Wuhan) , Wuhan, Hubei 430074, China

重力流与底流交互作用可形成不对称单向迁移水道，前人建立了单向迁移水道的演化模式，但在重力流与底流交互作用的水动力学机制研究方面较为薄弱。针对东非鲁伍马盆地下始新统沉积体系早期和晚期不同条件下的重力流与底流交互作用，开展沉积水动力数值模拟研究，结果表明，在研究区下始新统沉积体系中，底流将水道内重力流顶部的细粒沉积物裹挟并向北漂移，在水道北侧形成不对称天然堤。沉积物长期在北侧集聚形成漂积体，不对称沉积使水道北侧变陡；水道南侧则由于两反向流体的碰撞侵蚀作用增强，使该侧限制性作用减弱并形成新的负地形。在该不对称沉积模式的长期作用下水道逐渐向南迁移。通过揭示鲁伍马盆地下始新统不同沉积时期重力流与底流交互作用的水动力过程，阐明了流体结构对水道的沉积—侵蚀机制，从流体动力学角度解析了不对称单向迁移水道的成因机理。

The interaction between gravity flow and underflow can form an asymmetric unidirectional migration channel. The evolution model of unidirectional migration channel has been established by predecessors, but the hydrodynamic mechanism of the interaction between gravity flow and underflow is relatively weak. In this study, the sedimentary hydrodynamic numerical simulation of the interaction between gravity flow and underflow under different conditions in the early and late Lower Eocene in the Ruvuma Basin, East Africa was carried out. The results of the study are as follows: in the early Lower Eocene of the Ruvuma Basin, the restrictive effect of the channel is strong, and the sedimentation of gravity flow is the main effect; in the late period, Under the interaction of gravity flow and bottom current, the fine sediment at the top of gravity flow in the channel drifts northward, forming an asymmetric natural dike on the north side of the channel. Under the action of the crosswise fluid caused by the bottom current, the fine sediment at the top of the gravity flow is transported northward. As sediments gradually accumulate on the north side to form drift deposits, lateral sedimentation steepens the north side of the channel. The two opposite fluids collide in the south side of the channel, the erosion effect is enhanced, in the south side of the strong erosion, the restrictive action is weakened and a new negative terrain is formed. This asymmetric sedimentation pattern gradually migrates the sewers to the south for a long time. By revealing the depositional hydrodynamic processes of the interaction between gravity flow and bottom current in different periods of the Lower Eocene in the Ruvuma Basin, this study elucidates the sediment-erosion mechanism of the fluid structure on the channel and analyzes the genetic mechanism of the asymmetric unidirectional migration channel from the perspective of fluid dynamics.

10.11885/j.issn.1674-5086.2024.09.03.03