Éditeur(s) : HAL CCSD
Résumé : The DRADEM campaign was performed from July 9th to 21th 2016 on board the Pourquoi Pas?, in the Exclusive Economic Zones of Suriname and French Guyana. This campaign belongs to a program dedicated to geological investigations of the Demerara plateau, following the GUYAPLAC (2003) and IGUANES (2013) campaigns, and before the MARGATS campaign (2016). The aims of the DRADEM campaign were to map the continental slope of the transform margin north of the Demerara plateau, and to dredge the rocks outcropping in the slope.We completed the bathymetric mapping of the continental slope, including part of the edged of the Demerara plateau. These new bathymetric data confirm the segmentation of the transform margin in three parts with very different morphologies. In addition, two circular structures were interpreted as mud volcanoes, one on the northern edge of the plateau, the other one in the distal part of the Orinoco deep sea fan.Twelve dredges were performed between 4700 and 3500 m depths. Four from these twelve did not recovered rocks. The eight others brought back variables amounts of rocks, often encrusted, but of various natures: sediments (breccia, coarse sandstones, sandstones with plants debris, sandstones with shells, clayey ooze), micro-granular rocks and metamorphic rocks (including mylonite). The nature of the rocks was determined from macroscopic observation of the rocks, which are currently altered. Of course, these determinations need to be validated and specified by onshore further studies. Anyway, most of these rocks were previously unknown in this area, and they will strongly influence our understanding of the structure and evolution of this margin. They evidence huge vertical displacements that brought back to the surface some of these rocks that formed in a deep setting.
https://hal.archives-ouvertes.fr/hal-01418244

Droits : http://creativecommons.org/licenses/by-nc/
hal-01418244
https://hal.archives-ouvertes.fr/hal-01418244
https://hal.archives-ouvertes.fr/hal-01418244/document
https://hal.archives-ouvertes.fr/hal-01418244/file/DRADEM-Campaign%20Report.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The analysis of 2D deep-seismic-reflection profiles across the slope and abyssal plain of the Angola oceanic basin reveals the existence of a significant and formerly unknown depocentre beneath the giant Cenozoic Congo deep-sea fan, between 7000 m and 9000 m depth, deposited directly onto the Aptian oceanic crust. The unit, which is up to 2.5 km thick and extends for more than 200 km basinwards of the Continent-Ocean boundary, is probably aged Albian-Turonian. Its radial fan-shaped depocentre is centred on the present-day Congo River outlet and contains at least 0.2 Mio km(3) of sediments. These observations and the results from flexural modelling indicate that (1) the location of the Congo River's outlet has remained fairly stable since the Late Cretaceous, and (2) the basal unit was indeed sourced by a palaeo-Congo River probably located nearby the present-day one. Thus, the Atlantic sedimentary system related to the exoreism of the Congo River is much older than previously thought. Thermal modelling indicates that the maturation history of this upper-Cretaceous deposits is highly influenced by the interaction between the initial high heat flow of the young oceanic crust and further increase in sediment supply due to the progradation of the overlying Tertiary deep-sea fan during the Miocene. Hence, despite low present-day heat-flow values, should the unit have source rock potential, its basal section may be currently generating hydrocarbons.;All in all, the results from our models also suggest that the interplay between an initially high heat flow and the further high sediment supply in areas of major river input, may be a key factor for the thermal maturation of potential source rocks deposited onto a present-day "cold" oceanic crust.
ISSN: 0264-8172

hal-00475541
https://hal.archives-ouvertes.fr/hal-00475541
DOI : 10.1016/j.marpetgeo.2009.08.015

Éditeur(s) : HAL CCSD AGU and the Geochemical Society
Résumé : International audience
Mélange rocks outcrop widely in the central and western frontal sectors of the Betic Cordillera, as in many other collisional orogens where they form part of the accretionary wedges. Extrusion of Triassic plastic clays and evaporites was favored by the progressive accretion of the Betic External Zones, mixing rocks of different provenance and forming a synorogenic frontal mélange unit. MT data coupled with gravity data are a valid combined methodology to characterize the geometry of these mélange units, since the characterization of plastic rocks geometry is usually uncertain using seismic techniques. The results correlate well with known geological features (sedimentary basins, calcareous ranges, evaporitic rocks) and reveal the deep geometry. A resistive body, slightly dipping toward the SE, points to the continuity of the Iberian Massif below the Guadalquivir basin (2°) and the External Zones (6-8°). To the south, gravity models show the Iberian continental crust subducting below the Internal Zones with a roughly 20-35° slope. The main conductive bodies are related to the location of evaporitic rocks involved in the frontal mélange. They overlie the Iberian Massif and, southwards, the frontal Jurassic and Cretaceous limestone sequences of the External and Median Subbetics. In this setting, thick plastic rock units placed above the foreland could act as a lubricant facilitating continental subduction, and being progressively accreted toward a frontal mélange.
ISSN: 1525-2027

hal-00750364
https://hal.archives-ouvertes.fr/hal-00750364
DOI : 10.1029/2012GC004153

Éditeur(s) : The American Association of Petroleum Geologlists
Résumé : The west African continental margin between Abidjan (Ivory Coast) and Walvis Boy (Southwcst Africa) was surveyed in 1971 by the R/V Jean Charcot. Fiftyeight seismic-reflection (flexotir source), bathymetric (3.5 and 12 kc), gravimetric, and magnetic profiles were obtained. The seaward limit of an evaporitic zone outlined during the survey is at the boundary between continental slope and continental rise. Variation of depth of this limit as a function of latitude shows the presence of a large offset at 11°S which seems to be related to an east-east-southeast line of magnetic seamounts cutting into the continental slope. The Annobon-Cameroun volcanic axis separates the salt zones of the Nigerian basin and Congo-Angola basin. The northern limit of Salt deposition in the Congo-Angola basin is marked near 1°N by a strong southwest-northeast magnetic trend. On the south it extends to necr 14°s. The Walvis Ridge, located farther south, does not seem to have an effect on evaporite deposition. [NOT CONTROLLED OCR]
The American Association of Petroleum Geologlists Bulletin (The American Association of Petroleum Geologlists), 1973 , Vol. 57 , N. 9 , P. 1658-1671

Droits : The American Association of Petroleum Geologlists
http://archimer.ifremer.fr/doc/1973/publication-5123.pdf
http://archimer.ifremer.fr/doc/00000/5123/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The active collision zone around Taiwan orogen receives a variety of sedimentary inputs, including terrigenous flux from Taiwan and Chinese rivers, oceanic currents and atmospheric dust. In order to determine the present-day respective contributions of these different sources, we analysed the Pb and Sr isotopic compositions of late Quaternary sediments accumulated offshore east Taiwan. Samples from the Taiwan Coastal Range (andesites, sandstones, conglomerate and Peinan River terraces and suspended loads) have also been analysed to constrain the mean Taiwan isotopic signature. Mixing lines between the different sources of material indicate that the core located in the Okinawa Trough represents a mixture of about 60% of Taiwan, 30% of Chinese Loess and 10% of Yangtze River contributions. The southernmost core, located close to Luzon Are, is influenced by Taiwan (60%) and volcanic material (40%). The Sr and Pb isotopic compositions of samples cored in the Manila Trench and in the Huatung Basin are strongly influenced by the Taiwan signature, while the Ryukyu Trench core samples point to significant but variable contributions of Chinese Loess and Yangtze River. This work also reports Zn isotopic variations in the silicate fraction of these marine core samples. The overall variation in Zn isotopic compositions (expressed as 666 Zn) is greater than 0.3 per mil (parts per thousand) for an analytical precision of +/- 0.05 parts per thousand. The Zn isotopic signal for most of the marine core samples is similar to the literature data measured on sedimentary material, except for the Manila Trench core samples and the older sample from the Huatung Basin: they present values heavier by 0.2-0.3 parts per thousand, close to those obtained on all Taiwan rocks and Peinan River particulates. These results show: 1- the particular characteristics of Taiwan Zn isotopic compositions on a large scale; and: 2- the possible use of Zn isotopes as a tracer of material sources.
ISSN: 0009-2541

hal-00412214
https://hal.archives-ouvertes.fr/hal-00412214
DOI : 10.1016/j.chemgeo.2007.10.024

Éditeur(s) : HAL CCSD Springer-Verlag
Résumé : International audience
With hull-mounted multibeam echosounder data, wereport for the first time along the active Ecuadorian margin,acoustic signatures of water column fluid emissions and seep-relatedstructures on the seafloor. In total 17 flare-shaped acousticanomalies were detected from the upper slope (1250 m) to the shelfbreak (140 m). Nearly half of the flare-shaped acoustic anomaliesrise 200–500 m above the seafloor. The base of the flares is generallyassociated with high-reflectivity backscatter patchescontrasting with the neighboring seafloor. We interpret these flaresas caused by fluid escape in the water column, most likely gases.High-resolution seismic profiles show that most flares occur closeto the surface expression of active faults, deformed areas, slopeinstabilities or diapiric structures. In two areas tectonic deformationdisrupts a Bottom Simulating Reflector (BSR), suggesting thatburied frozen gas hydrates are destabilized, thus supplying free gasemissions and related flares. This discovery is important as it opensthe way to determine the nature and origin of the emitted fluids andtheir potential link with the hydrocarbon system of the forearcbasins along the Ecuadorian margin.
ISSN: 0033-4533

insu-01267238
https://hal-insu.archives-ouvertes.fr/insu-01267238
DOI : 10.1007/s00024-015-1230-7

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
This paper focuses on the analyses of the clastic sedimentary infill of the Coastal Plain of Eastern Mexico, which initiated synchronously with the Laramide orogeny in the vicinity of the Golden Lane. Results of these analyses are used as boundary conditions for calibrating/interpreting seismic profiles across more distal depocenters in the offshore of the Gulf of Mexico, from the sea shore and continental slope in the west to the abyssal plain in the east. The objective of the study is to better predict the reservoir distribution in the Deep offshore Basin of the Gulf of Mexico (DBGM), in order to explore for petroleum. The Coastal Plain is underlain by three morpho-tectonic domains: the tectonic front of the Sierra Madre Orientale (SMO), the Chicontepec deep water flexural basin, and the Tuxpan Platform (also known as the Golden Lane). Each domain is characterized by a distinct, dominantly siliciclastic Cenozoic lithostratigraphy. After a Jurassic rifting episode, followed by thermal subsidence, the oceanic basin and its western passive margin were deformed during the Upper Cretaceous and Paleogene, by far field stresses associated with the Cordilleran-Laramide Orogeny. Starting in the Late Cretaceous-Early Paleogene and during the Early Eocene, the tectonic load associated with the Laramide Orogen (Sierra Madre Oriental, SMO) caused flexural subsidence of the foreland located under the Coastal Plain. During this period, a massive transfer of siliciclastic sediments occurred from the Laramide foothills into the adjacent foreland. Sediments were eroded of the Sierra Madre tectonic wedge. Loading by these sediments pushed source units associated with the former passive margin down ward. The first syn-tectonic sediments of the Laramide orogeny were turbiditic silt layers in submarine fans which record also numerous collapse episodes and gravity slides. During the Late Eocene and Oligocene, the flexural subsidence stopped in the hinterland, whereas the subsidence of the passive margin resumed. This resulted in a change in the overall sedimentary architecture of the basin. Paleo-highs and reefs facies of the Golden Lane were flooded. Clastics by-passed the reefs and progradational clastic stratification formed as sediment moved towards the DBGM in the east. The final depositional environment of the continental platform/Coastal Plain became deltaic, marked by a succession of sand bars, levees and channels systems. From Miocene times onward, a system of gravitational listric faults developed near the platform to slope transition, resulting in a coeval compressional system at the transition between the slope and the abyssal plain. This system is driven by sediments charge. Because the sedimentation rate is larger than the subsidence, a large amount of clastics and slumped sediments are deposited in hangingwall basins.
ISSN: 0264-8172

hal-00424586
https://hal.archives-ouvertes.fr/hal-00424586
DOI : 10.1016/j.marpetgeo.2008.03.009

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/

Éditeur(s) : Yale University
Résumé : Data from a hydrographic section carried out in January-March 1994 offshore from the eastern coast of South America from 50S to 10N, are used to quantify the full-depth exchanges of water between the western boundary currents and the ocean interior. In the upper and intermediate layers, the westward transport associated with the southern branch of the South Equatorial Current was 49 Sv at the time of the cruise. The transports of the central and northern branches in the upper 200 m were 17 Sv and 12 Sv, respectively. After subtraction of the parts that recirculate in the subtropical, subequatorial, and equatorial domains, the fraction of the South Equatorial Current that effectively contributes to the warm water export to the North Atlantic is estimated at 18 Sv. The poleward boundary of the current southern branch is at 31S through the whole thickness of the subtropical gyre, but the latitude of the northern boundary varies from 7 degrees 30'S at the surface to 27S at 1400 m depth. The estimated latitude of its bifurcation into the Brazil Current and North Brazil Undercurrent also varies downward from about 14S at the surface to 28S at a depth of 600 m.In the North Atlantic Deep Water, eastward flows exceeding 10 Sv are observed at 3 degrees -4 degrees of latitude in both hemispheres, at 10S, and at 34S-30S. Between 4S and 17S, a net westward flow with an estimated transport of 19 Sv reinforces the southward deep western boundary current. Cyclonic circulations of Antarctic Bottom Water along the western boundaries of the Argentine and Brazil basins have amplitudes of 15 Sv and 13 Sv, respectively, exceeding those of the interbasin exchanges. The net alongshore transport of this water mass between the hydrographic section and the continental slope reverses to a southward direction from 13S to 27S, probably in relation with an eastward shift of the equatorward near-bottom boundary current at these latitudes.
Journal of Marine Research (0022-2402) (Yale University), 2000-11 , Vol. 58 , N. 6 , P. 1007-1039

Droits : 2000 Yale University
http://archimer.ifremer.fr/doc/2000/publication-803.pdf
DOI:10.1357/002224000763485782
http://archimer.ifremer.fr/doc/00000/803/

Éditeur(s) : Elsevier
Résumé : The multi-component aspect of species diversity of groundfish assemblages was examined on the basis of a set of experimental trawl surveys conducted on the east coast of Corsica. We analysed and compared the structuration of diversity within three different bathymetric strata: the continental shelf (60-120 m depth), the upper slope (250-400 m) and the lower slope (450-570 m). For each of these three bathymetric strata, we simultaneously analysed 12 indices that are theoretically complementary and relate to 4 diversity components: (1) the number of species, (2) rarity, (3) evenness and (4) taxonomic diversity. Principal component analysis based on Spearman's correlation coefficients was carried out to investigate empirical relationships between the selected indices. Our results showed not only that a single diversity index cannot provide a complete view of the groundfish diversity along the east coast of Corsica, but also that-in some cases-one index cannot even encapsulate a complete description of a specific diversity component. We also found that the nature and the number of independent diversity components slightly varied from one bathymetric stratum to another. The main differences-which mainly occurred in the deepest bathymetric stratum-might be associated with lower density of individuals and lower dominance of some species at deeper depths. Finally, this study is the first dealing with groundfish diversity in this area, which is currently characterized by one of the lowest fishing intensity rates in the northern Mediterranean Sea. It might be considered as a first '' reference state '' with a view to monitoring the spatio-temporal changes in species diversity patterns along the east coast of Corsica in the future. (C) 2007 Elsevier B.V. All rights reserved.
Fisheries Research (0165-7836) (Elsevier), 2007-12 , Vol. 88 , N. 1-3 , P. 120-132

Droits : 2007 Elsevier B.V. All rights reserved.
http://archimer.ifremer.fr/doc/2007/publication-3512.pdf
DOI:10.1016/j.fishres.2007.08.003
http://archimer.ifremer.fr/doc/00000/3512/

Éditeur(s) : Institut de Ciències del Mar de Barcelona, CSIC
Résumé : Acoustic and core data have recently been collected on the shelf break and the upper part of the slope of the south Aquitaine continental margin. They reveal the major role played by mass-flow gravity processes in deposit erosion and redistribution, modelling of the sea-bed, and transfer of sediment toward the deep-sea. The study region is bounded in the south by the Capbreton canyon. The northern area, which shows a smooth morphology, is characterised by small-scale deformations due to sediment creep or low-amplitude slide processes. The deformations are associated with mini listric-like faults that bound packets of sediments in which the deposit geometry is typical of constructional sediment waves. These sediment waves result from the interaction of depositional and gravity deformation processes. In the southern area, closer to the canyon, wave-like structures are still present but mostly of smaller size. They only result from gravity deformation processes without any evidence of constructional processes. In the vicinity of the Capbreton canyon, the shelf break and upper slope have a much more uneven morphology with sedimentary reliefs, escarpments and depressions directed toward the canyon thalweg. The depressions look like slide scars, and could be the result of regressive slides initiated at the top of the canyon flank. The age of the sliding event responsible for the formation of the depression observed today could be middle to upper Quaternary. Since their formation, these depressions act as conduits that channel the transfer of shelf sediment into the canyon, as demonstrated by the occurrence of a meandering channel on the sea-floor of one depression.
Scientia Marina (0214-8358) (Institut de Ciències del Mar de Barcelona, CSIC), 2006-06 , Vol. 70 , N. 1 , P. 89-100

Droits : 2006 Institut de Ciències del Mar de Barcelona
http://archimer.ifremer.fr/doc/2006/publication-3960.pdf
http://archimer.ifremer.fr/doc/00000/3960/

Éditeur(s) : HAL CCSD Elsevier
Résumé : We have integrated the relatively unknown distal domains of the Lower Congo basin, where the main depocenters of the Congo submarine fan are located, with the better-constrained successions on the shelf and upper slope, through the analysis of thousands of km of 2D seismic reflection profiles off-shore the Congo-Angola passive margin. The basin architecture is depicted by two ca. 800-km-long regional cross sections through the northern (Congo) and southern (Angola) margin. A large unit deposited basinward of the Aptian salt limit is likely to be the abyssal-plain equivalent of the upper-Cretaceous carbonate shelf that characterized the first post-rift deposits in West-equatorial African margins. A latest-Turonian shelf-deepening event is recorded in the abyssal plain as a long period (Coniacian-Eocene) of condensed sedimentation and basin starvation. The onset of the giant Tertiary Congo deep-sea fan in early Oligocene following this event reactivates the abyssal plain as the main depocenter of the basin. The time-space partitioning of sedimentation within the deep-sea fan results from the interplay among increasing sediment supply, margin uplift, rise of the Angola salt ridge, and canyon incision throughout the Neogene. Oligocene-early Miocene turbidite sedimentation occurs mainly in NW-SE grabens and ponded inter-diapir basins on the southern margin (Angola). Seaward tilting of the margin and downslope salt withdrawal activates the up-building of the Angola escarpment, which leads to a northward (Congo) shift of the transfer zones during late Miocene. Around the Miocene-Pliocene boundary, the incision of the Congo submarine canyon confines the turbidite flows and drives a general basinward progradation of the submarine fan into the abyssal plain The slope deposition is dominated by fine-grained hemipelagic deposits ever since. Results from this work contribute to better understand the signature in the ultra-deep deposits of processes acting on the continental margin as well as the basin-wide sediment redistribution in areas of high river input.
ISSN: 0040-1951

hal-00424533
https://hal.archives-ouvertes.fr/hal-00424533
DOI : 10.1016/j.tecto.2008.04.009

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The base of the Faro contouritic drift (IODP Site U1386) on the northern margin of the Gulf of Cádiz (Algarve margin) is characterized by two sequences of frequent gravity deposits with different ages and compositions. Among these gravity deposits, several relatively thick debrites (up to 12 m) have been observed and studied in detail.Sedimentological analyses have been performed and because of non-turbulent behavior of debris flows, detailed micropaleontological studies could be realized. Planktonic foraminifera thus allowed establishing a detailed biostratigraphy of these deposits. Benthic foraminifer and ostracod assemblages were used to evaluate the origin of the sediment composing these debris flows and estimate their run-out distance.These debrites are dated from Early Pliocene and early Pleistocene, and were deposited in a mesobathyal environment. They comprise silty mud clasts and matrixes with sand content up to 34%. The Early Pliocene debrites are bioclast-rich whereas the Early Pleistocene debrite is enriched in terrigenous particles. The data indicates that these debrites were triggered on the continental shelf and traveled less than 100 km, eroding the seafloor all along their path for the Early Pliocene debrites and only the first part of their path for the early Pleistocene debrite. Matrixes originate from failure areas whereas eroded sediments along the flow pathway are incorporated into the flow as clasts.High abundance of shelf fauna during the Early Pliocene and great supply of terrigenous particles from rivers during the early Pleistocene in the south-western Iberian margin have favored gravity flows from the continental shelf to the slope. The contouritic paleo-moat of the Faro drift has been a determining channeling feature for gravity flows along the Algarve margin during the early Pleistocene, testifying of the strong interaction between MOW circulation and down-slope processes. Tectonic and diapiric activities were significant during Early Pliocene and early Pleistocene on the Algarve margin and could have been triggering parameters of failures related to these debris flows.
ISSN: 0025-3227

hal-01356172
https://hal.archives-ouvertes.fr/hal-01356172
DOI : 10.1016/j.margeo.2015.08.018

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) : Elsevier
Résumé : The present work is based on a set of bottom trawl surveys performed in the Gulf of Lions between 1983 and 1992. A new method which couples the STATIS multitable approach with the logic of correspondence analysis (CoA) is proposed to study the stability of spatial organization of demersal assemblages in terms of species composition. This CoA version of STATIS has provided a clear representation of the stable part of the spatial structure of the assemblages. In addition, it gave an insight into the interannual variations of the distribution of each population around the reference structure. Our results showed that the demersal assemblages of the Gulf of Lions exhibited strong spatial structuring, mainly orientated along a bathymetric gradient. This gradient is structured around three major regions: the coast, the continental shelf and the continental slope. Despite sampling variations that occurred during the course of the study, the analysis showed a high degree of reproducibility for this spatial pattern. With the exception of Mullus surmuletus, the species considered in this investigation exhibit limited variations in their spatial distribution. Finally, in the absence of log-books covering the activities of commercial fishing vessels, these findings constitute a base of reference for the analysis of the dynamics of fishing fleets exploiting the demersal resources of the Gulf of Lions.
Ce travail porte sur une série de campagnes de chalutage de fond réalisé dans le golfe du Lion entre 1983 et 1992. Une nouvelle méthode fondée sur le couplage de la technique multitableaux STATIS et de l'analyse factorielle des correspondances (AFC) est proposée afin d'étudier l'organisation spatio-temporelle des assemblages démersaux, poissons et quelques céphalopodes, en terme de composition spécifique. Cette version AFC de STATIS a fourni une représentation claire de la part stable de l'organisation spatiale des assemblages. De plus, elle nous a permis d'appréhender les variations interannuelles de la distribution de chaque population autour de la structure de référence. Nos résultats montrent que les assemblages démersaux du golfe du Lion présentent une forte structuration spatiale, principalement orientée selon un gradient bathymétrique. Ce dernier est structuré en trois grandes régions: la côte, le plateau continental et le talus continental. En dépit des variations d'échantillonnage survenues au cours de la période d'étude, l'analyse a mis en évidence une forte reproductibilité de ce schéma d'organisation. A l'exception de Mullus surmuletus, les espèces considérées dans ce travail présentent des variations limitées de leur distribution spatiale. Enfin, en l'absence de livres de bord sur l'activité des navires professionnels, ces résultats constituent une base de référence pour l'analyse de la dynamique des flottilles exploitant les ressources démersales dans le golfe du Lion.
Aquatic Living Resources (Elsevier), 1998-03 , Vol. 11 , N. 2 , P. 75-85

Droits : 1998 Published by Elsevier SAS
http://archimer.ifremer.fr/doc/1998/publication-875.pdf
DOI:10.1016/S0990-7440(98)80063-6
http://archimer.ifremer.fr/doc/00000/875/

Éditeur(s) : Public Library Science
Résumé : Like hydrothermal vents along oceanic ridges, cold seeps are patchy and isolated ecosystems along continental margins, extending from bathyal to abyssal depths. The Atlantic Equatorial Belt (AEB), from the Gulf of Mexico to the Gulf of Guinea, was one focus of the Census of Marine Life ChEss (Chemosynthetic Ecosystems) program to study biogeography of seep and vent fauna. We present a review and analysis of collections from five seep regions along the AEB: the Gulf of Mexico where extensive faunal sampling has been conducted from 400 to 3300m, the Barbados accretionary prism, the Blake ridge diapir, and in the Eastern Atlantic from the Congo and Gabon margins and the recently explored Nigeria margin. Of the 72 taxa identified at the species level, a total of 9 species or species complexes are identified as amphi-Atlantic. Similarity analyses based on both Bray Curtis and Hellinger distances among 9 faunal collections, and principal component analysis based on presence/absence of megafauna species at these sites, suggest that within the AEB seep megafauna community structure is influenced primarily by depth rather than by geographic distance. Depth segregation is observed between 1000 and 2000m, with the middle slope sites either grouped with those deeper than 2000m or with the shallower sites. The highest level of community similarity was found between the seeps of the Florida escarpment and Congo margin. In the western Atlantic, the highest degree of similarity is observed between the shallowest sites of the Barbados prism and of the Louisiana slope. The high number of amphi-atlantic cold-seep species that do not cluster according to biogeographic regions, and the importance of depth in structuring AEB cold-seep communities are the major conclusions of this study. The hydrothermal vent sites along the Mid Atlantic Ridge (MAR) did not appear as "stepping stones" for dispersal of the AEB seep fauna, however, the south MAR and off axis regions should be further explored to more fully test this hypothesis.
Plos One (1932-6203) (Public Library Science), 2010-08 , Vol. 5 , N. 8 , P. 1-11

Droits : © 2010 Olu et al.
http://archimer.ifremer.fr/doc/00011/12207/8975.pdf
DOI:10.1371/journal.pone.0011967
http://archimer.ifremer.fr/doc/00011/12207/

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Selected high-resolution seismic-reflection profiles and multibeam bathymetry acquired along the convergent Ecuador margin during the ATACAMES cruise on onboard the R/V L’Atalante (Jan.15–Feb.18, 2012) allow a preliminary evaluation of the neotectonic development and stratigraphic evolution of the margin based on the sismo-stratigraphic analysis of Quaternary sediment preserved on the margin shelf and upper slope. We present three major preliminary results. (1) The evolution of the Esmeraldas, Guayaquil and Santa Elena canyons. The head of the Esmeraldas canyon is the location of a continuous significant sediment transport. The Guayaquil canyon shows several episodes of deposition and incision. Aggrading sedimentation pattern in the canyon records several changes in relative sea-level. The subsidence of the Gulf of Guayaquil probably contributes to the good preservation of the canyon filling stages. The Santa Elena canyon is controlled by a SW–NE trending normal fault. (2) Variations of sediment accumulation and relative vertical motions are shown along-strike the shelf edge. Offshore the uplifted Manta peninsula, a pronounced subsidence of the shelf edge is documented by sedimentary clinoforms that have deposited in a morphological reentrant, and have migrated upslope testifying of a local subsidence meanwhile the adjacent La Plata Island area underwent uplift. In the Esmeraldas canyon area, a local uplift of the shelf is documented. (3) Two neotectonic fault systems with a possible transcurrent component are imaged across the shelf edge and upper margin slope offshore Jama, and Cape Galera. This possible transcurrent motion could be related to the reactivation of ancient faults of the upper plate by the subduction. These preliminary results indicate that the ATACAMES data set has a strong potential to evaluate the spatial and temporal contribution of tectonic and climate changes on the structural development and stratigraphic evolution of the Ecuador continental margin.
ISSN: 0025-3235

insu-01131151
https://hal-insu.archives-ouvertes.fr/insu-01131151
DOI : 10.1007/s11001-014-9231-y

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We analyze in this study a new set of marine data including 3D local tomography, 1992-2008 relocated earthquakes and two recent multichannel seismic lines to characterize the deformation style in the collision area offshore east Taiwan. We have mapped in detail the Mohos of the converging plates as well as the subduction interface with a resolution never reached before. We show that the sharp continental subduction of the Eurasia plate, beneath the middle part of the Central Range, indents the Philippine Sea plate (PSP) as attested by intra-oceanic slicing and incipient subduction of the PSP beneath the east coast of Taiwan. The westernmost part of the PSP slab is probably experiencing a beginning of break-off as attested by NW-trending en-échelon shear zones beneath the southern slope of the southern Ryukyu arc (SRA). These en-échelon shear zones have a sinistral component favored by the "collision-free" subduction of the PSP north of 24°30′N. The down-faulting of the subduction interface forms ramps along which earthquakes clusterize. Three M7 subduction earthquakes occurred offshore Suao city along these ramps with a recurrence interval of about 40 years: 1920 Mw7.7, 1963 Mw7.2 and 2002 Mw7.1 events. The 1966 Mw6.0-7.5 earthquakes sequence likely outlines a WNW-ESE left-lateral intra-slab shear zone. The SRA upper plate accommodates the complex geometry and deformation of the subducting PSP through seismic deformation. Shallow high velocities fringing the Luzon volcanic arc (LVA) beneath the Longitudinal Valley and north of the southernmost Ryukyu forearc basins are interpreted as relics of the LVA forearc basement squeezed in the collision zone. Based on the accommodation of a large part of the convergence through shortening within the PSP and the subsequent segmentation of the shallow subduction interface, we consider that the nucleation of a Mw ≥ 8 earthquake along the southernmost Ryukyu megathrust is unlikely.
ISSN: 0040-1951

hal-00853365
https://hal.archives-ouvertes.fr/hal-00853365
https://hal.archives-ouvertes.fr/hal-00853365/document
https://hal.archives-ouvertes.fr/hal-00853365/file/publallemandifremer.pdf
DOI : 10.1016/j.tecto.2013.03.020

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Multi-proxy analysis of two marine sediment cores (MS27PT and MD04-2726) from the Nile continental slope provides evidence of changes in Nile sediment discharge related to changes in Ethiopian African Monsoon (EAM) precipitation, and allows us to reconstruct changes in Nile River runoff, vegetation and erosion in the Nile headwaters. Sediment element composition and neodymium isotopic composition reveal significant changes in clastic sediment provenance, with sources oscillating between a Saharan aeolian contribution during the Last Glacial Maximum/deglacial transition and during the Late Holocene, and a Blue/Atbara Nile fluvial contribution during the African Humid Period (AHP). This study provides a new understanding of past environmental changes. Between 14.6 and 14.13 ka there was a major input of sediments from the Ethiopian Highlands, consistent with a stronger EAM at that time. Climate in the Nile basin was wetter between 14.8 and 8.4 ka, with a corresponding increase in Blue Nile water and sediment discharge via the main Nile into the Eastern Mediterranean. The gradual climatic transition from the AHP to the present-day dry climate was reflected in a decrease in Blue Nile sediment deposition and flood discharge between 8.4 and 3.7 ka, with aridity at a maximum between 3.7 and 2.6 ka. The onset of drier conditions in the Blue Nile basin seems to have begun before the 8.2 ka cooling event in the North Atlantic. We speculate that the climatic change from the wet AHP to the dry late Holocene may have been a result of a break in the low latitude dynamic equilibrium between climate, vegetation and erosion, which may in turn have affected the climate in higher latitudes. Reduced Nile flow may also have had an impact on Levantine Intermediate Water originating in the Eastern Mediterranean through an increase in intermediate water formation.
ISSN: 0277-3791

hal-01277950
https://hal.archives-ouvertes.fr/hal-01277950
DOI : 10.1016/j.quascirev.2015.10.030

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/