Authigenic carbonates from methane seeps of the Congo deep-sea fan

Type Article
Date 2007-06
Language English
Author(s) Pierre Catherine1, Fouquet Yves2
Affiliation(s) 1 : UPMC, UMR 7159, LOCEAN, F-75252 Paris 05, France.
2 : IFREMER, Geosci Marines, Technopole Iroise, F-29280 Plouzane, France.
Source Geo-Marine Letters (0276-0460) (Springer), 2007-06 , Vol. 27 , N. 2-4 , P. 249-257
DOI 10.1007/s00367-007-0081-3
WOS© Times Cited 54
Keyword(s) oxygen isotopes, carbon isotopes, Congo deep sea fan, gas hydrate, methane seep, authigenic carbonate
Abstract Submersible investigations with the ROV Victor 6000 of some pockmark structures on the seafloor of the Congo deep-sea fan have shown that they are active venting sites of methane-rich fluids, associated with abundant fauna and carbonate crusts. Moreover, methane hydrates have been observed both outcropping and deep in the sediments in the centre of the "Regab" giant pockmark. Authigenic carbonates, mostly calcite sometimes mixed with aragonite, are cementing the sedimentary matrix components and fauna; diatoms are abundant but only as moulds, indicating that biogenic silica dissolution occurred in situ synchronous with carbonate precipitation. The occurrence of diagenetic barite and pyrite in some carbonate crusts demonstrates that they can be formed either within the sulphate/methane transition zone or deeper in sulphate-depleted sediments. The oxygen isotopic compositions of the diagenetic carbonates (3.17-6.01 parts per thousand V-PDB) indicate that precipitation occurred with bottom seawater mixed with a variable contribution of water from gas hydrate decomposition. The very low carbon isotopic compositions of the diagenetic carbonates (-57.1 to -27.75 parts per thousand V-PDB) demonstrate that carbon derives mostly from the microbial oxidation of methane.
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