Multi-disciplinary investigation of fluid seepage on an unstable margin: The case of the Central Nile deep sea fan
|Author(s)||Bayon Germain1, Loncke L.2, Dupre Stephanie1, 3, Caprais Jean-Claude4, Ducassou E.5, Duperron Sebastien6, Etoubleau Joel1, Foucher Jean-Paul1, Fouquet Yves1, Gontharet S.7, Henderson G. M.8, Huguen Caroline9, Klaucke I.10, Mascle J.11, Migeon S.11, Olu-Le-Roy Karine4, Ondreas Helene1, Pierre C.7, Sibuet Myriam4, Stadnitskaia A.12, Woodside J.3|
|Affiliation(s)||1 : IFREMER, Dept Geosci Marines, Brest, France.
2 : Univ Picardie Jules Verne, UMR 8110, Amiens, France.
3 : Vrije Univ Amsterdam, Sedimentol & Marine Geol Dept, Amsterdam, Netherlands.
4 : IFREMER, Dept Etud Ecosyst Profonds, Brest, France.
5 : Univ Bordeaux 1, EPOC, UMR 5805, F-33405 Talence, France.
6 : Univ Paris 06, UMR 7138, Paris, France.
7 : Univ Paris 06, LOCEAN, Paris, France.
8 : Univ Oxford, Dept Earth Sci, Oxford OX1 2JD, England.
9 : Univ Perpignan, LEGEM, F-66025 Perpignan, France.
10 : IFM GEOMAR, Kiel, Germany.
11 : Geosci Azur UMR 6526, Villefranche Sur Mer, France.
12 : Royal Netherlands Inst Sea res, Texel, Netherlands.
|Source||Marine Geology (0025-3227) (Elsevier), 2009-06 , Vol. 261 , N. 1-4 , P. 92-104|
|WOS© Times Cited||76|
|Keyword(s)||Authigenic carbonate, U Th, Cold seep, Continental margin, Nile|
|Abstract||We report on a multidisciplinary study of cold seeps explored in the Central Nile deep-sea fan of the Egyptian margin. Our approach combines in situ seafloor observation, geophysics, sedimentological data, measurement of bottom-water methane anomalies, pore-water and sediment geochemistry, and Th-230/U dating of authigenic carbonates. Two areas were investigated, which correspond to different sedimentary provinces. The lower slope, at similar to 2100 m water depth, indicates deformation of sediments by gravitational processes, exhibiting slope-parallel elongated ridges and seafloor depressions. In contrast, the middle slope, at similar to 1650 m water depth, exhibits a series of debris-flow deposits not remobilized by post-depositional gravity processes. Significant differences exist between fluid-escape structures from the two studied areas. At the lower slope, methane anomalies were detected in bottom-waters above the depressions, whereas the adjacent ridges show a frequent coverage of fractured carbonate pavements associated with chemosynthetic vent communities. Carbonate U/Th age dates (similar to 8 kyr BP), pore-water sulphate and solid phase sediment data suggest that seepage activity at those carbonate ridges has decreased over the recent past. In contrast, large (similar to 1 km(2)) carbonate-paved areas were discovered in the middle slope, with U/Th isotope evidence for ongoing carbonate precipitation during the Late Holocene (since similar to 5 kyr BP at least). Our results suggest that fluid venting is closely related to sediment deformation in the Central Nile margin. It is proposed that slope instability leads to focused fluid flow in the lower slope and exposure of 'fossil' carbonate ridges, whereas pervasive diffuse flow prevails at the unfailed middle slope.|