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Apports en matière organique marine et terrigène sur la marge équatoriale ouest africaine : rôle joué par le canyon sous-marin du Zaïre.
Approche par les biomarqueurs lipidiques

Abstract : The Zaire deep-sea fan (South-East Atlantic) is one of the world's largest active fans. It is fed by a unique canyon extending across the West Equatorial African margin, creating a direct connection between the Zaire River estuary and the abyssal plains. The canyon drives a substantial amount of terrigenous sediment down to the deep sea, mainly via turbidity currents. The initial goal of the French BIOZAIRE project initiated by IFREMER is to study the benthic ecosystem in relation to the organic matter inputs, which quantity and quality may influence its development.
Sediment traps and surface sediments collected along the Zaire River submarine canyon and adjacent area were investigated for n-alcohol biomarkers to identify the sources of organic matter.
The main part of this work is devoted to the study of the abundance of short- (C22) n-alcohols, derived from marine organisms and higher plants, respectively, in order to evaluate i) marine vs. terrestrial inputs to the sediments, ii) their transport pathways, and iii) the dynamics in terms of preferential accumulation of turbiditic material. The spatio-temporal variability of marine and terrestrial inputs was assessed using the same approach.
The n-alcohol results exhibit mixed organic matter inputs of marine and terrestrial origins, with the terrigenous contribution predominant in the channel surficial deposits (83% of long-chain biomarkers). The marine inputs are related to the Zaire River plume, whereas the terrestrial material is mostly carried seaward via turbidity currents. Indeed, the material derived from a turbidity current observed in March 2001 shows a strong terrigenous contribution. The turbidity current overflowed the channel flanks onto the levee in a <400 m thick layer. The levee deposits show a different composition compared with those within the channel. Despite the abundance of terrigenous material, an extensive degradation is observed upon settling: 92 and 47% of the C22 n-alcohols are degraded, respectively. Assuming a first order degradation rate, it leads to degradation constants of 3.4 and 0.9 y-1, respectively. The area is characterised by a strong temporal variability. On the levees adjacent to the Zaire submarine channel, this latter is due to the overflow of turbidity currents.
The last part of this study examines the sterol and hydroxy acid biomarkers released simultaneously with the n-alcohols, performing principal component analysis. This method enables the reliability of the source assignment of the biomarkers, and would help towards the interpretation of the sterol data.
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Submitted on : Wednesday, October 4, 2006 - 11:11:06 AM
Last modification on : Wednesday, January 13, 2021 - 11:12:03 AM
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  • HAL Id : tel-00103360, version 1

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Claire Treignier. Apports en matière organique marine et terrigène sur la marge équatoriale ouest africaine : rôle joué par le canyon sous-marin du Zaïre.
Approche par les biomarqueurs lipidiques. Géochimie. Université Pierre et Marie Curie - Paris VI, 2005. Français. ⟨tel-00103360⟩

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