Éditeur(s) : AGU
Résumé : Submarine canyons are narrow but deep submarine valleys that extend for hundreds of meters. They represent the most impressive structures that shape the present morphology of passive continental margins. They can occur off the mouth of rivers: the Tagus, Zaire, Amazon, and Orinoco in the Atlantic; the Indus in the Indian Ocean; and the Var, Rhone, and Ebro in the Mediterranean. Some are at times disconnected from any stream mouth such as the Nazare canyon, off Portugal, despite the fact that it is close to the coast. Some were connected to a river mouth during lowstands of sea level, such as the Wilmington canyon in the northwest Atlantic, or the Blackmud canyon in the northeast Atlantic.
EOS, Transactions American Geophysical Union (0096-3941) (AGU), 2004-07-06 , Vol. 85 , N. 27 , P. 257

Droits : 2004 AGU
http://archimer.ifremer.fr/doc/00071/18201/15769.pdf
DOI:10.1029/2004EO270001
http://archimer.ifremer.fr/doc/00071/18201/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Gulf of Cadiz lies astride the complex plate boundary between Africa and Eurasia west of the Betic-Rif mountain belt. We report on the results of recent bathymetric swathmapping and multi-channel seismic surveys carried out here. The seafloor is marked by contrasting morphological provinces, spanning the SW Iberian and NW Moroccan continental margins, abyssal plains and an elongate, arcuate, accretionary wedge. A wide variety of tectonic and gravitational processes appear to have shaped these structures. Active compressional deformation of the wedge is suggested by folding and thrusting of the frontal sedimentary layers as well as basal duplexing in deeper internal units. There is evidence for simultaneous gravitational spreading occurring upslope. The very shallow mean surface and basal slopes of the accretionary wedge (1° each) indicate a very weak decollement layer, geometrically similar to the Mediterranean Ridge accretionary complex. Locally steep slopes (up to 10°) indicate strongly focused, active deformation and potential gravitational instabilities. The unusual surface morphology of the upper accretionary wedge includes “raft-tectonics” type fissures and abundant sub-circular depressions. Dissolution and/or diapiric processes are proposed to be involved in the formation of these depressions.
ISSN: 0264-8172

insu-00401683
https://hal-insu.archives-ouvertes.fr/insu-00401683
DOI : 10.1016/j.marpetgeo.2007.11.008

Éditeur(s) : Elsevier Science Bv
Résumé : In this study, the Capbreton canyon head, just off the coast, is investigated using high-resolution multibeam bathymetry datasets, sediment samples and numerical modeling. The HR bathymetry analysis reveals a morphological connection between the longshore trough and the head of the canyon. The analysis of recent sediment samples shows a clear correlation between the sediment of the canyon head and that of the nearshore. Hydrodynamic modeling (a coupled wave-flow model) shows that for high-energy waves, the rotational nature of surf-zone circulation reverses and wave-induced currents have the potential to transport large quantities of nearshore sands toward the canyon head. All these arguments support the assumption that the canyon head captures a part of the sand transported by longshore drift. Over the 15 years of observation (1998–2013), time-lapse bathymetry shows that the floor of the canyon head and one lateral gully network experienced significant morphological reworking. In terms of hazards, despite this strong activity, the position of the canyon head and the profile of its longitudinal slope remained stable and appears as a comforting factor. However, the activity of unusual lateral erosions needs to be monitored.
Marine Geology (0025-3227) (Elsevier Science Bv), 2014-05 , Vol. 351 , P. 1-12

Droits : 2014 Elsevier B.V. All rights reserved.
http://archimer.ifremer.fr/doc/00180/29118/27524.pdf
DOI:10.1016/j.margeo2014.03.001
http://archimer.ifremer.fr/doc/00180/29118/

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) : Elsevier
Résumé : Foraminifera and ostracods have been quantitatively studied in core MD01-2472, from the upper continental slope (at water depth of 501 m), to evaluate their relationship with bottom water condition variability and decipher the control of the Levantine Intermediate Water (LIW) current on benthic faunas. The occurrence of reworked ostracod species (originating from the continental shelf) and, the presence of shallow water Elphidium/Ammonia benthic foraminifera are used to estimate the degree of along-slope transport at the core site. This has revealed two intervals of along-slope transport also associated with coarse-grained contourite deposits, deposited during the YD and HS2 episodes. Planktonic-benthic foraminiferal and ostracod assemblages reflect climate oscillations. Peaks of the polar planktonic Neogloboquadrina pachyderma (left-coiling S) may be used to identify Heinrich Events. Interstadials are marked by abundant ostracod species such as Paracypris sp., Argilloecia acuminata, and Cytheropteron alatum and the presence of benthic foraminifera like Bulimina marginata, Bulimina costata and Gyroidina altiformis. The B–A and Holocene are characterized by abundant warm water species of planktonic foraminifera and by the ostracod species Polycope sp. We hypothesize that there is relationship between LIW intensification during cold rapid climate events and benthic fauna assemblage variations due to changes in: 1) bottom water ventilation; and 2) the export of nutrients and/or sediment particles by bottom currents.
Quaternary International (1040-6182) (Elsevier), 2015-01 , Vol. 357 , P. 295-313

Droits : 2014 Elsevier Ltd and INQUA. All rights reserved.
http://archimer.ifremer.fr/doc/00245/35648/34208.pdf
DOI:10.1016/j.quaint.2014.11.038
http://archimer.ifremer.fr/doc/00245/35648/