Éditeur(s) : Elsevier
Résumé : 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.
Marine Geology (0025-3227) (Elsevier), 2009-06 , Vol. 261 , N. 1-4 , P. 92-104

Droits : 2009 Elsevier B.V. All rights reserved.
http://archimer.ifremer.fr/doc/2009/publication-6586.pdf
DOI:10.1016/j.margeo.2008.10.008
http://archimer.ifremer.fr/doc/00000/6586/

Éditeur(s) : Springer
Résumé : The Var turbidite system is a small sandy system located in the Ligurian Basin. It was deposited during the Pliocene-Quaternary in a flat-floored basin formed during the Messinian salinity crisis. The system was fed through time by the Var and Paillon canyons that connect directly to the Var and Paillon rivers. It is still active during the present sea-level highstand. Two main mechanisms are responsible for gravity-flow triggering in the Var turbidite system: (1) mass-wasting events affect mainly the upper part of the continental slope, in areas where volumes of fresh sediment delivered by rivers are highest, and result from the under-consolidation state of slope sediments and earthquakes, and (2) high-magnitude river floods resulting from melting of snow and convective rainfall during fall and spring seasons, and generating hyperpycnal turbidity currents at river mouths when the density of freshwater transporting suspended particles exceeds that of ambient seawater. Failure- and flood-induced gravity flows are involved through time in the construction of the Var Sedimentary Ridge, the prominent right-hand levee of the Var system, and sediment waves. Processes of construction of both the Var Ridge and sediment waves are closely connected. Sandy deposits are thick and abundant in the eastern (downchannel) part of the ridge. Their distribution is highly constrained by the strong difference of depositional processes across the sediment waves, potentially resulting through time in the individualization of large and interconnected sand bodies.
Geo-Marine Letters (0276-0460) (Springer), 2006-12 , Vol. 26 , N. 6 , P. 361-371

Droits : 2006 Springer
http://archimer.ifremer.fr/doc/2006/publication-2258.pdf
DOI:10.1007/s00367-006-0047-x
http://archimer.ifremer.fr/doc/00000/2258/

Éditeur(s) : Springer
Résumé : Based on new multibeam bathymetric data, seismic-reflection profiles and side-scan sonar images, a great number of submarine failures of various types and sizes was identified along the northern margin of the Ligurian Basin and characterized with 3 distinct end-members concerning their location on the margin, sedimentary processes and possible triggering mechanisms. They include superficial landslides mainly located in the vicinity of the main mountain-supplied rivers and on the inner walls of canyons (typically smaller that 10(8) m(3) in volume: Type 1), deep scars 100-500 m high along the base of the continental slope (Type 2), and large-scale scars and Mass Transport Deposits (MTDs) affecting the upper part of the slope (Type 3 failures). The MTDs are located in different environmental contexts of the margin, including the deep Var Sedimentary Ridge (VSR) and the upper part of the continental slope in the Gulf of Genova (Finale Slide and Portofino Slide), with volumes of missing sediment reaching up to 1.5 x 10(9) m(3). High sedimentation rates related to hyperpycnal flows, faults and earthquake activity, together with sea-level fluctuations are the main factors invoked to explain the distribution and sizes of these different failure types.
Marine Geophysical Research (0025-3235) (Springer), 2011-03 , Vol. 32 , N. 1-2 , P. 225-243

Droits : Springer Science+Business Media B.V. 2011
http://archimer.ifremer.fr/doc/00043/15387/14028.pdf
DOI:10.1007/s11001-011-9123-3
http://archimer.ifremer.fr/doc/00043/15387/

Éditeur(s) : HAL CCSD Société Géologique de France
Résumé : Les fluides géologiques dans les bassins sédimentaires
ISSN: 0037-9409

hal-01685491
https://hal.archives-ouvertes.fr/hal-01685491
DOI : 10.1051/bsgf/2017200

Éditeur(s) : HAL CCSD Société géologique de France
Résumé : International audience
EISSN: 1777-5817

hal-01672822
https://hal-amu.archives-ouvertes.fr/hal-01672822
DOI : 10.1051/bsgf/2017183