Morphology, structure, composition and build-up processes of the active channel-mouth lobe complex of the Congo deep-sea fan with inputs from remotely operated underwater vehicle (ROV) multibeam and video surveys
Morphology, structure, composition and build-up processes of the active channel-mouth lobe complex of the Congo deep-sea fan with inputs from remotely operated underwater vehicle (ROV) multibeam and video surveys
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DOI：
10.1016/j.dsr2.2017.03.010
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发表时间：
2017-08-01
影响因子：
3
通讯作者：
Rabouille, Christophe
中科院分区：
文献类型：
--
作者：
Dennielou, Bernard;Droz, Laurence;Rabouille, Christophe
浊积水道河口叶状体的详细结构和成分在很大程度上仍然未知，因为它们通常位于深海深度，非常薄，因此超出了船载声学工具的分辨率。利用船载条带测深、气枪地震、3.5 kHz浅地层剖面仪、沉积活塞岩芯，以及高分辨率多波束测深和遥控潜水器（ROV）获取的视频，对刚果浊积水道河口叶状体复合体（90×40千米；2525平方千米）的形态、结构和成分进行了研究。该叶状体复合体位于安哥拉深海平原，距刚果河口760千米，深度在4740米至5030米之间。它是活跃的，由浊流提供物质，每世纪沉积几厘米的沉积物。该叶状体复合体被细分为五个进积的叶状体。这些叶状体主要是泥质的。砂约占沉积物的13%，且局限于补给河道和分流河道。整个叶状体由薄的泥质到粉质浊积岩组成。整个叶状体复合体的特征是原地物质坡移（滑坡、泥石流）。1米分辨率的测深显示，在补给河道和河口边缘普遍存在滑动和块状崩塌，这表明在叶状体堆积过程中滑动很早就开始且持续发生。物质坡移被解释为极高的堆积速率、河道过度变陡和侵蚀的结果，因此是叶状体形成的一个内在过程。当一个叶状体顶部的分流河道坡度变缓，且浊流在叶状体一侧较高的坡度上找到路径时，补给河道的分叉可能就会被触发。它也可能由叶状体一侧的物质坡移触发。当一个新的叶状体发育时，被遗弃的叶状体继续从补给河道的溢出物中收集大量浊积物，因此整个叶状体复合体仍然保持活跃。针对五种形态 - 沉积环境：叶状体边缘、叶状体主体、分流河道、天然堤、补给河道，提出了一个概念性的岩石地层模型。这项研究表明，高分辨率测深和ROV观测对于充分理解现代水道河口叶状体的形成过程是必要的。
The detailed structure and composition of turbiditic channel-mouth lobes is still largely unknown because they commonly lie at abyssal water depths, are very thin and are therefore beyond the resolution of hull-mound acoustic tools. The morphology, structure and composition of the Congo turbiditic channel-mouth lobe complex (90x40 km; 2525 km(2)) were investigated with hull-mounted swath bathymetry, air gun seismics, 3.5 kHz sub bottom profiler, sediment piston cores and also with high-resolution multibeam bathymetry and video acquired with a Remote Operating Vehicle (ROV). The lobe complex lies 760 km off the Congo River mouth in the Angola abyssal plain between 4740 and 5030 m deep. It is active and is fed by turbidity currents that deposit several centimetres of sediment per century. The lobe complex is subdivided into five lobes that have prograded. The lobes are dominantly muddy. Sand represents ca. 13% of the deposits and is restricted to the feeding channel and distributaries. The overall lobe body is composed of thin muddy to silty turbidites. The whole lobe complex is characterized by in situ mass wasting (slumps, debrites). The 1-m-resolution bathymetry shows pervasive slidings and block avalanches on the edges of the feeding channel and the channel mouth indicating that sliding occurs early and continuously in the lobe build-up. Mass wasting is interpreted as a consequence of very-high accumulation rates, over-steepening and erosion along the channels and is therefore an intrinsic process of lobe building. The bifurcation of feeding channels is probably triggered when the gradient in the distributaries at the top of a lobe becomes flat and when turbidity currents find their way on the higher gradient on the lobe side. It may also be triggered by mass wasting on the lobe side. When a new lobe develops, the abandoned lobes continue to collect significant turbiditic deposits from the feeding channel spillover, so that the whole lobe complex remains active. A conceptual lithostratigraphic model is proposed for five morpho-sedimentary environments: lobe rims, lobe body, distributaries, levees, feeding channel. This study shows that high resolution bathymetry ROV observations are necessary to fully understand the build-up processes of modern channel-mouth lobes.