Origin and distribution of the organic matter in the distal lobe of the Congo deep-sea fan – A Rock-Eval survey

Type Article
Date 2017-08
Language English
Author(s) Baudin Francois1, Stetten Elsa1, 2, Schnyder Johann1, Charlier Karine3, Martinez Philippe3, Dennielou BernardORCID4, Droz Laurence5
Affiliation(s) 1 : Sorbonne Univ, UPMC Univ Paris 06, CNRS, Inst Sci Terre ISTeP,UMR 7193, 4 Pl Jussieu, F-75005 Paris, France.
2 : Sorbonne Univ, CNRS, UPMC Univ Paris 06, Observ Oceanol,UMR 8222,Lab Ecogeochim Environm B, Banyuls Sur Mer, France.
3 : Univ Bordeaux, CNRS, EPOC, UMR 5805, Allee Geoffroy St Hilaire, F-33615 Pessac, France.
4 : IFREMER, Dept REM, Unite Geosci Marines, F-29280 Plouzane, France.
5 : Univ Bretagne Occidentale, Inst Univ Europeen Mer, MRS, LDO,UMR 6538, F-29280 Plouzane, France.
Source Deep-sea Research Part Ii-topical Studies In Oceanography (0967-0645) (Pergamon-elsevier Science Ltd), 2017-08 , Vol. 142 , P. 75-90
DOI 10.1016/j.dsr2.2017.01.008
WOS© Times Cited 17
Keyword(s) Recent sediments, Congo turbidite system, Organic matter, Rock-Eval pyrolysis
Abstract The Congo River, the second largest river in the world, is a major source of organic matter for the deep Atlantic Ocean because of the connection of its estuary to the deep offshore area by a submarine canyon which feeds a vast deep-sea fan. The lobe zone of this deep-sea fan is the final receptacle of the sedimentary inputs presently channelled by the canyon and covers an area of ~2500 km². The quantity and the source of organic matter preserved in recent turbiditic sediments from the distal lobe of the Congo deep-sea fan were assessed using Rock-Eval pyrolysis analyses. Six sites, located at approximately 5000 m water-depth, were investigated. The mud-rich sediments of the distal lobe contain high amounts of organic matter (~3.5 to 4% Corg), the origin of which is a mixture of terrestrial higher-plant debris, soil organic matter and deeply oxidized phytoplanktonic material. Although the respective contribution of terrestrial and marine sources of organic matter cannot be precisely quantified using Rock-Eval analyses, the terrestrial fraction is dominant according to similar hydrogen and oxygen indices of both suspended and bedload sediments from the Congo River and that deposited in the lobe complex. The Rock-Eval signature supports the 70% to 80% of the terrestrial fraction previously estimated using C/N and δ13Corg data. In the background sediment, the organic matter distribution is homogeneous at different scales, from a single turbiditic event to the entire lobe, and changes in accumulation rates only have a limited effect on the quantity and quality of the preserved organic matter. Peculiar areas with chemosynthetic bivalves and/or bacterial mats, explored using ROV Victor 6000, show a Rock-Eval signature more or less similar to background sediment. This high organic carbon content associated to high sedimentation rates (> 2 to 20 mm.yr−1) in the Congo distal lobe complex implies a high burial rate for organic carbon. Consequently, the Congo deep-sea fan represents an enormous sink of terrestrial organic matter when compared to other turbiditic systems over the world.
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Baudin Francois, Stetten Elsa, Schnyder Johann, Charlier Karine, Martinez Philippe, Dennielou Bernard, Droz Laurence (2017). Origin and distribution of the organic matter in the distal lobe of the Congo deep-sea fan – A Rock-Eval survey. Deep-sea Research Part Ii-topical Studies In Oceanography, 142, 75-90. Publisher's official version : https://doi.org/10.1016/j.dsr2.2017.01.008 , Open Access version : https://archimer.ifremer.fr/doc/00369/48018/