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Discussion papers
https://doi.org/10.5194/se-2018-99
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/se-2018-99
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 15 Oct 2018

Research article | 15 Oct 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Solid Earth (SE).

The Ogooue Fan (Gabon): a modern example of deep-sea system on a complex sea-floor topography

Salomé Mignard1, Thierry Mulder1, Philippe Martinez1, and Thierry Garlan2 Salomé Mignard et al.
  • 1University of Bordeaux, UMR CNRS 5805 EPOC
  • 2SHOM

Abstract. The Ogooue deep-sea Fan located in the northeastern part of the Gulf of Guinea expands over more than 550km westwards of the Gabonese shelf and passes through the Cameroun volcanic line. Here are presented the first study of acoustic data (multibeam echosounder and 3.5kHz seismic data) and piston cores covering the deep-sea part of this West African system. This study led to the construction of the sedimentary processes map of this area. The overall system corresponds to a well-developed mud-sand rich deep-sea fan, fed by the Ogooue River 'sedimentary load. This system presents the typical morphological elements of clastic slope apron: tributary canyons, distributary channel-levees systems and lobes elements. However, variations on the slope gradient cumulated with the presence of numerous seamounts, including volcanic islands and mud volcanoes, led to a more complex fan architecture and sedimentary facies distribution. In particular, turbidity currents derived from the Gabonese shelf deposit across several interconnected sedimentary sub-basins located on the low gradient segments of the margin. The repeated spill-overs of the most energetic turbidite flows have notably led to the incision of a large distal valley connecting an intermediate sedimentary basin to the more distal lobe area. The sedimentary facies repartition over the fan indicates that pelagic to hemipelagic sedimentation is dominant across the area. Distribution and thickness of turbidite sand beds is highly variable along the system, however turbidite sands preferentially deposit in the bottom of channel-levee systems and on the most proximal depositional areas. The most distal depocenters receive only the upper parts of the flows, which are composed of fine-grained sediments. The Ogooue deep-sea system is predominantly active during periods of low sea-level because canyon heads are separated from terrestrial sediment sources by the broad shelf. However, the northern part of this system appears active during sea-level highstands. This feature is one deeply incised canyon, the Cape Lopez canyon, located on a narrower part of the continental shelf has a different behaviour and receives sediments transported by the longshore drift.

Salomé Mignard et al.
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Salomé Mignard et al.
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A large quantity a contiental material is transported to the oceans by the world rivers. Once in the ocean, these particles can be transported down the continental shelf thanks to underwater avalanches. The repetition of such massive events can form very important sedimentary deposits at the continent-ocean transition. Data obtained during an oceanic cruise in 2010 allowed us to study such a system located offshore Gabon and to evaluate the importance sediment transport in this area.
A large quantity a contiental material is transported to the oceans by the world rivers. Once in...
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