Abstract. The effects of changes in slope gradient on deposition
processes and architecture have been investigated in different deep-sea
systems both in modern and ancient environments. However, the
impact of subtle gradient changes (< 0.3∘) on sedimentary
processes along deep-sea fans still needs to be clarified. The Ogooue Fan,
located in the northeastern part of the Gulf of Guinea, extends over more
than 550 km westwards of the Gabonese shelf and passes through the Cameroon
volcanic line. Here, we present the first study of acoustic data (multibeam
echosounder and 3.5 kHz, very high-resolution seismic data) and piston cores
covering the deep-sea part of this West African system. This study documents
the architecture and sedimentary facies distribution along the fan. Detailed
mapping of near-seafloor seismic-reflection data reveals the influence of
subtle slope gradient changes (< 0.2∘) along the fan
morphology. The overall system corresponds to a well-developed deep-sea fan,
fed by the Ogooue River sedimentary load, with tributary canyons,
distributary channel–levee complexes and lobe elements. However, variations
in the slope gradient due to inherited salt-related structures and the
presence of several seamounts, including volcanic islands, result in a
topographically complex slope profile including several ramps and steps. In
particular, turbidity currents derived from the Gabonese shelf deposit cross
several interconnected intra-slope basins located on the low gradient
segments of the margin (< 0.3∘). On a higher gradient
segment of the slope (0.6∘), a large mid-system valley developed
connecting an intermediate sedimentary basin to the more distal lobe area.
Distribution and thickness of turbidite sands is highly variable along the
system. However, turbidite sands are preferentially deposited on the floor
of the channel and the most proximal depositional areas. Core description
indicates that the upper parts of the turbidity flows, mainly composed of
fine-grained sediments, are found in the most distal depocenters.
We are thankful to Dr Hogdson for his interest in our paper and for his helpful and constructive comments. We have made efforts to clarify the parts of the manuscript that, in light of the reviewer's comment, needed to be more accurate and more detailed, escpecially by giving much more quantitative information. Here, we report below the reviewers' comments answers concerning the main issues.General comments: The manuscript by Mignard et al. presents recently collected bathymetry, sidescan, and core data from the understudied Ogooue Fan, offshore Gabon. These data permit the authors to present an interesting case study clearly.
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