Sedimentary characteristics of lobes formed by interacting bottom currents and gravity flows: a case study from the Miocene in Rovuma Basin,East Africa
LIU Yuxing1,2,3,4, CHEN Yuhang1,2,3,4, FAN Guozhang5, LI Lin5, LU Yintao5, ZUO Guoping5, CAO Quanbin5, DING Qunfeng1,2,3
1 School of Earth Sciences and Engineering,Xi'an Shiyou University,Xi'an 710065,China; 2 Shaanxi Key Laboratory of Petroleum Accumulation Geology,Xi'an Shiyou University,Xi'an 710065,China; 3 Key Laboratory of Submarine Geosciences,Ministry of Natural Resources,Hangzhou 310012,China; 4 Xi'an Key Laboratory of Tight Oil(Shale Oil)Development,Xi'an Shiyou University,Xi'an 710065,China; 5 PetroChina Hangzhou Institute of Geology,Hangzhou 310023,China
Abstract：The interplay of bottom currents and gravity flows is an important deep-water sedimentary process,which plays an important role in redistributing submarine sediments and reshaping seafloor bedforms. At present,research on bottom currents and gravity flows interaction in deep-water channels is relatively mature,but little work has been done on the sedimentary characteristics of lobes influenced by bottom currents. Based on an integrated study of seismic facies and seismic attributes using 3D seismic and logging data,this study documents the distribution and lithological characteristics of the Miocene lobes in the Rovuma Basin(East Africa). The effect of bottom currents and gravity flows interaction on lobe sedimentation is revealed through quantitative restoration of gravity flow velocity,combined with regional ocean current data analysis. The results indicate that,early channels migrated southward due to the northward-directed bottom current,and their northern levees are well developed with a negative terrain present to the south of the channels,which led subsequent lobes to deposit to the south of these channels. Deposition of the lobes is influenced by bottom current flow direction and gravity flows forming the lobes. Velocity of the gravity flows is much higher than that of the bottom currents. Therefore,when the directions of bottom currents and the lobe propogation are opposite and oblique,the influence of bottom currents is suppressed on the side against bottom current flow direction(south side),and the lobe gradually thins from the axis to the margin,accompanied by increasing mud content;On the side downstream of bottom current flow direction(north side),gravity flows intersect obliquely with bottom currents,and the mud at the top of turbidity currents is stripped off by the bottom current,leaving sand deposited in the lobe. When bottom current flow direction and lobe propogration direction are close to orthogonal,the influence of bottom current on the lobe is consistent on the whole,and the mud at the top of gravity flows is stripped. Therefore,the lobe is mainly composed of thick sandy deposits at the side against the bottom current flow direction,and the sand content decreases towards the side downstream of the bottom current,accompanied by an increasing mud content.
LIU Yuxing,CHEN Yuhang,FAN Guozhang et al. Sedimentary characteristics of lobes formed by interacting bottom currents and gravity flows: a case study from the Miocene in Rovuma Basin,East Africa[J]. JOPC, 2024, 26(4): 1005-1016.
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