Sedimentary characteristics and its controlling factors of continental slope canyons in Tanzania Coastal Basin
Chen Yu-Hang1,2,3, Yao Gen-Shun4, Shao Da-Li4, Lu Yin-Tao4, Lü Fu-Liang4, Cao Quan-Bin4, Tang Peng-Cheng4, Li Shi-Fang5
1 School of Earth Sciences and Engineering,Xi’an Shiyou University,Xi’an 710065,China; 2 Key Laboratory of Marine Geology and Environment,Institute of Oceanology,Chinese Academy of Sciences,Shandong Qingdao 266071,China; 3 Shaanxi Key Laboratory of Petroleum Accumulation Geology,Xi’an Shiyou University,Xi’an 710065,China; 4 PetroChina Hangzhou Research Institute of Geology,Hangzhou 310023,China; 5 The Tenth Oil Plant of PetroChina Changqing Oilfield Company,Gansu Qingcheng 745100,China
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.
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