东非鲁伍马盆地海底峡谷发育特征及成因机制

Developmental Characteristics and Genesis Mechanisms of Submarine Canyons in the Rovuma Basin, East Africa

马宏霞 朱越越 许小勇 何云龙 王红平

MAHongxia ZHUYueyue XUXiaoyong HEYunlong WANGHongping

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

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

针对鲁伍马盆地海底峡谷的发育特征和成因机制认识尚不全面，利用三维地震资料，结合深水沉积学的相关理论与前人研究成果，开展了对海底峡谷外部形态特征、内部充填结构和成因机制的研究。结果表明，研究区内鲁伍马盆地发育10个峡谷，整体呈东西走向；垂向上呈上游尖窄V形、下游宽缓U形特征，平面上呈孤立—合并—分散特征；峡谷内部充填沉积类型包括底部滞留沉积、滑塌及块体流搬运体沉积；峡谷外部可见漂积体、麻坑。结合研究区海底峡谷发育背景，认为其可能存在两种成因机制：一是由于下伏地层中天然气向上逃逸形成麻坑，造成地层薄弱易侵蚀，相邻麻坑串联沟通形成峡谷雏形，并在后期含沉积物流体改造与侵蚀下逐渐形成；二是由于下陆坡大型断层的活动导致下陆坡沉积物失稳，导致原始沉积层崩塌形成的重力流事件，在重力流侵蚀作用下而形成。

The external morphological characteristics, internal filling structure and genetic mechanism of submarine canyons in the Rovuma Basin are not fully understood. We make a study on the external morphological characteristics, internal filling structure and genetic mechanism of submarine canyons by using three-dimensional seismic data, combined with the relevant theories of deep-water sedimentology and previous research results. The results indicate that there are 10 canyons in the Rovuma Basin, trending east-west, with a V-shaped narrow upstream and U-shaped gentle downstream profile vertically, and showing an isolated-merged-dispersed pattern on the horizontal plane. The internal filling sediment types in the canyons include basal lags, slides and MTDs. Outside the canyons, sediment drifts and pockmarks are observed. Considering the developmental background of submarine canyons in the study area, it is believed that there may be two genesis mechanisms at play. One involves the escape of natural gas from the underlying strata, leading to the formation of pockmarks and subsequent erosion of weak layers, with interconnected pockmarks forming the initial shape of the canyon, gradually evolving under the influence of sediment-laden fluid flow and erosion. The second mechanism involves destabilization of sediment on the lower slope due to the activity of large-scale faults, resulting in gravity flow events and subsequent erosion leading to canyon formation.

10.11885/j.issn.1674-5086.2024.08.28.07