摘要： 东非陆缘深水盆地具有巨大油气资源潜力,但对陆坡峡谷沉积特征研究较少,制约有利储集层预测。本研究利用三维地震资料,对东非坦桑尼亚滨海盆地陆坡峡谷开展精细研究。结果表明:(1)研究区陆坡发育多条大型海底峡谷;上陆坡处,坡度较陡,峡谷内以侵蚀作用为主,沉积物主要局限在褶皱推覆带的翼部;褶皱推覆带之外的下陆坡区,坡度变缓,峡谷末端发育席状砂质沉积及砂泥混杂的碎屑流沉积,同时在峡谷北侧发育向北延伸的泥质漂积体;在陆坡边缘,发育海底滑塌,形成块体搬运沉积。(2)峡谷沉积受陆源物质供给、褶皱推覆带、北大西洋底流以及陆坡边界断层等因素控制。受东非裂谷海域分支活动影响,研究区陆架窄、陆坡陡,陆源物质可迅速通过陆架,进入陆坡峡谷:与河流相连的峡谷,物源充足、规模较大,有沉积物发育而没有与河流直接相连的峡谷物源有限、规模较小,峡谷内无明显沉积;褶皱推覆带通过改变海底地形来控制峡谷内沉积分布,褶皱翼部发育沉积,核部则以侵蚀为主;褶皱推覆带外,北大西洋底流与峡谷末端重力流发生交互作用,细粒物质被搬运至峡谷北岸形成漂积体;陆坡边缘断层活跃,峡谷被断层切割,形成断崖,并引发海底滑塌,陆坡处不发育水道及朵体沉积,陆源物质通过峡谷被搬运至更深的深海盆地内。

关键词: 东非, 陆缘, 陆坡峡谷, 沉积特征, 控制因素

Abstract: The East African continental margin deep-water basins have great oil and gas potentials. However,only few studies were carried on the sedimentary features of slope canyon and prohibit the prediction of favorable reservoir. We use 3D seismic data to investigate the sedimentary characteristics of slope canyon in the offshore of the Tanzania Coastal Basin. The result are as follows. (1)Large submarine canyons are developed in the study area. The upper slope is steep,where the canyon is dominated by erosional process,with limited deposition at the limb of fold and thrust belt. The gentle lower slope area is outside the fold and thrust belt,where the sheet-like sandy deposits and sand-mud mixed debris-flow deposits accumulated. Meanwhile,the mound-shaped muddy drift is developed on the northern canyon bank and extends northward. Slumps occur at the edge of slope margin,forming the mass transport deposits. (2)The sedimentary feature of the canyon is controlled by multiple factors,including terrigenous sediment supply,fold and thrust belt,North Atlantic Deep Water,and slope margin fault. Influenced by the activity of the offshore branch of East African Rift System,the study area is characterized by a narrow continental shelf and steep slope. Consequently,the terrigenous material can easily pass through the continental shelf and enter the continental canyon. The canyons connected with the river have sufficient sediment supply and are in large scale,while the canyons disconnected with the river have limited terrigenous sediment supply and are in small scale with no obvious sediment found in the canyon. Fold and thrust belt controls the sedimentary distribution in the canyon by changing the seafloor topography,with erosions occurred on the core and depositions occurred on the wings of the fold. Outside the fold and thrust belt,the North Atlantic Deep Water interacts with the gravity flow at the end of the canyon,transporting fine particles to the northern canyon bank and forming drifts. The fault activity at slope margin cut the canyons and triggers the sediment collapses. No channels and lobes formed on the continental slope,and the terrigenous material are transported to the deeper basin through the canyons.

Key words: East Africa, continental margin, continental slope canyon, sedimentary characteristics, controlling factor

中图分类号: 

• P531