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

Type Article
Date 2017-08
Language English
Author(s) Dennielou BernardORCID1, Droz Laurence2, Babonneau Nathalie2, Jacq Celine1, 2, Bonnel Cedric1, 3, Picot Marie1, 2, Le Saout Morgane1, Saout Yohan1, Bez Martine4, Savoye Bruno1, Olu Karine5, Rabouille Christophe5, 6
Affiliation(s) 1 : IFREMER, Ctr Brest, Unite Rech Geosci Marines, F-29280 Plouzane, France.
2 : Univ Brest, UMR Geosci Ocean 6538, UBO, Inst Univ Europeen Mer, Pl Copernic, F-29280 Plouzane, France.
3 : Univ Pau & Pays Adour, UMR 5150, Lab Fluides Complexes & Leurs Reservoirs, IPRA, BP 1155, F-64013 Pau, France.
4 : Ctr Sci & Tech Jean Feger, TOTAL, Ave Larribau, F-64018 Pau, France.
5 : IFREMER, Ctr Brest, Unite Rech Etud Ecosyst Profonds, F-29280 Plouzane, France.
6 : UMR CEA CNRS UVSQ, LSCE, F-91198 Gif Sur Yvette, France.
Source Deep-sea Research Part Ii-topical Studies In Oceanography (0967-0645) (Pergamon-elsevier Science Ltd), 2017-08 , Vol. 142 , P. 25-49
DOI 10.1016/j.dsr2.2017.03.010
WOS© Times Cited 28
Keyword(s) Congo deep-sea fan, Lobe, Lobe complex, Channel, Channel-Lobe Transition Zone, Angola basin, Slump, Slide, Debrite, Turbidite, ROV, Bathymetry, Seismic, Sediment core
Abstract

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 (90×40 km; 2525 km2) 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.

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Dennielou Bernard, Droz Laurence, Babonneau Nathalie, Jacq Celine, Bonnel Cedric, Picot Marie, Le Saout Morgane, Saout Yohan, Bez Martine, Savoye Bruno, Olu Karine, Rabouille Christophe (2017). 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. Deep-sea Research Part Ii-topical Studies In Oceanography, 142, 25-49. Publisher's official version : https://doi.org/10.1016/j.dsr2.2017.03.010 , Open Access version : https://archimer.ifremer.fr/doc/00378/48976/