Éditeur(s) : Gauthier-Villars
Résumé : Analysis of Geosat sea level data over the period November 1986-November 1987 has evidenced long, low-frequency equatorial wave propagations over most of the equatorial Pacific basin (Delcroix et al.,1991). The succession of downwelling Kelvin, upwelling Kelvin, and upwelling Rossby waves has raised a series of questions. Is the observed upwelling Rossby wave due to a reflection process on the eastern boundary, or due to wind forcing near the equator? Why is there no evidence of a reflection of the downwelling Kelvin wave? Is this wave sequence a feature of the 1986-1987 El Nino phenomenon or is it to be found in the mean seasonal cycle? We used a linear model forced by the FSU wind stress to study these questions. The results, during the period November 1986-November 1987, show the successive downwelling/ upwelling Kelvin waves and upwelling Rossby wave as in the Geosat observations. Another test was made, using only the part of the forcing responsible for creating Kelvin waves, in order to evaluate the portion of the signals that was due to the reflection process and the part due to local forcing. It appears that wind forcing favourable to upwelling in the eastern part of the equatorial basin is the main mechanism which both generates the upwelling Rossby wave and inhibits the reflection of the downwelling Kelvin wave. However, the reflection of the upwelling Kelvin wave contributes to the upwelling Rossby wave signal, and makes it visible all the way from the eastern to the western sides of the equatorial Pacific. Results of a climatological run show that the successive downwelling/upwelling Kelvin and Rossby wave propagations are present in the mean seasonal cycle. However, the corresponding model signals, as well as the wind forcing anomalies, show a larger amplitude in 1986-1987.
Oceanologica Acta (0399-1784) (Gauthier-Villars), 1992 , Vol. 15 , N. 5 , P. 545-554

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00101/21180/18797.pdf
http://archimer.ifremer.fr/doc/00101/21180/

Éditeur(s) : Pergamon-elsevier Science Ltd
Résumé : Quantitative analyses on calcareous nannofossil assemblages on high temporal resolution (600-800 years) have been carried out from Core KC01B in the Ionian Sea (Eastern Mediterranean) throughout Marine Isotope Stage (MIS) 13-9, between 500 and 300 ka. This is an interval of considerable climate changes, known as the Mid-Brunhes event, which includes MIS 11, considered as a possible analogue for future interglacial conditions. In the Mediterranean core, the interval is characterized by the dominance of Gephyrocapsa spp., as also known from ocean records. Calcareous nannofossil abundance fluctuations have been interpreted in terms of modification of sea surface primary productivity/water stratification and temperature. Specifically, the increase in abundance of Gephyrocapsa caribbeanica and small Gephyrocapsa coupled with decreases of Florisphaera profunda, Syracosphaera spp. and Rhabdosphaera spp. suggests enhanced primary productivity/mixed surface waters during interglacial stages and at the Terminations, which can be interpreted in terms of interaction between climate changes and mesoscale oceanographic circulation. On the other hand, distributions of Calciosolenia spp., Oolithotus spp. and Umbilicosphaera sibogae, which are in phase with delta O-18 curve showing higher abundances at the lighter values of the marine isotope record, are considered as warm-water indicators. Biotic proxies point to peculiar climate dynamics through the MIS 12-11 transition (i.e. Termination V). High productive, cool, low salinity and turbid surface waters characterize the early MIS 11(421-408 ka) and likely reflect enhanced continental humidity/monsoon activity over North Africa and increased runoff into the basin. A late surface water warming with respect to Termination V is established at about 403 ka, during a period of low insolation forcing, almost coeval with the deposition of sapropel S11. A climate optimum, lasting about 15 ky (403-389 ka), is then recorded during a period of low insolation forcing centred at 398 ka. The later part of MIS 11 is characterized by climate deterioration at about 389 ka. Comparison with results from subtropical to polar Atlantic records suggests a remarkable relation between Mediterranean and Atlantic climate regimes.
Quaternary International (1040-6182) (Pergamon-elsevier Science Ltd), 2013-03 , Vol. 288 , P. 97-111

Droits : 2011 Elsevier Ltd and INQUA. All rights reserved.
http://archimer.ifremer.fr/doc/00181/29194/27593.pdf
DOI:10.1016/j.quaint.2011.12.007
http://archimer.ifremer.fr/doc/00181/29194/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Karukéra spur is an easternmost submerged rise of the Lesser Antilles fore-arc in the Guadeloupe archipelago, culminating about 4000 m above the fore-arc basin 150 km west of the deformation front. The analysis of 3500 km 2D high-resolution multichannel seismic reflection and multibeam bathymetric data, and the study of 14 core samples, allow for the first time to reconstruct its sedimentary anatomy and tectonic evolution. Seven seismic units (US1 to US7) are evidenced, organised into four major depositional sequences separated by erosional surfaces. Units US1 to US4 thicken to the south-southeast on the spur. The sedimentary deposits rest upon a deeply eroded metamorphic basement of the Caribbean Plate as in La Désirade Island. Sequence 1 (units US1 and US2) remains unknown in its lower part because it does not outcrop. Its upper part comprises early Miocene shallow water carbonates. Sequence S2 (Unit US3) only comprises an upper Miocene transgressive systems tract deposited into basinal environment. It is bounded by major erosional surfaces SB2 and SB3. Sequence 3 (US4 to US6) is Zanclean to Pleistocene. It is dominantly composed of shallow water, reefal deposits. Sequence 4 corresponds to recent deposits. The Karukéra spur experienced three main extensional episodes with alternations between uplift and subsidence periods. Uplifts are responsible for emersions and erosions. Subsidence severely drowned shallow water deposits. The first extensional episode led to the formation of horsts and grabens in the basement, prior to early Miocene deposits. The second extensional episode occurred during upper Miocene, in accordance with data in surrounding islands. The third tectonic episode developed since Calabrian. Noticeable is the constant reactivation of N130°–N150°, N150°–N180° and N40° trending faults since early Miocene and the neoformation of E–W trending faults since Calabrian. Our results suggest that at the latitude of Guadeloupean archipelago the Lesser Antilles subduction zone is an erosional margin because of the successive sweepings of the Santa Lucia then Tiburon Ridges.
ISSN: 0025-3227

hal-01172231
https://hal.archives-ouvertes.fr/hal-01172231
DOI : 10.1016/j.margeo.2015.02.007

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
This paper presents a reappraisal of the tectonic evolution of the Zanhuang Massif that lies at the eastern margin of the Trans-North China Orogen, a continent–continent collision belt that marked the amalgamation of the North China Craton in Late Paleoproterozoic. Detailed field work with focus on geometries of structures and kinematics was performed. This was completed with LA-ICP-MS U–Pb analyses on zircon, EPMA U–Th/Pb dating on monazite and 40Ar/39Ar dating on amphibole. These studies led us to propose a new three-fold litho-tectonic subdivision of the massif: The Western Zanhuang Domain (WZD) made of TTG, migmatite and pink anatectic granite is correlated to the Fuping Massif that crops out to the north-west. Both areas represent a continental block, called the Fuping Block, which acquired most of its architecture around 2100 Ma ago. The Eastern Zanhuang Domain (EZD) made of TTG and migmatite represents the western edge of an Eastern Neoarchean Block. In between, the Central Zanhuang Domain (CZD) is a NE–SW trending stack of supracrustal, gneiss and mafic magmatic rocks thrust sheets displaced toward the ESE upon the Eastern Block. The lithological features suggest that the CZD represents the remnant of an oceanic basin, called the Taihang Ocean that closed during the amalgamation of the Eastern Block and the Fuping Block around 1880–1850 Ma. In agreement with recent work done along the western margin of the belt, in the Lüliang Massif, this study documents the amalgamation of the North China Craton in response to the closure of two oceanic basins, namely the Lüliang Ocean and the Taihang Ocean. West-dipping subductions and collisions involving three distinct continental blocks, called the Western, the Fuping and the Eastern Blocks, took place around 1880–1850 Ma.
ISSN: 0301-9268

insu-00403871
https://hal-insu.archives-ouvertes.fr/insu-00403871
https://hal-insu.archives-ouvertes.fr/insu-00403871/document
https://hal-insu.archives-ouvertes.fr/insu-00403871/file/Trap-PrecambrianResearch-2009.pdf
DOI : 10.1016/j.precamres.2009.03.011

Éditeur(s) : Amer Geophysical Union
Résumé : The objective of the paper is to analyze the degree of realism of the Parallel Ocean Program ( POP) model of the Los Alamos Laboratory using the combined TOPEX/Poseidon and ERS-1/2 (TPERS) sea level anomaly (SLA) data sets and to present a detailed study of mesoscale characteristics in the North Atlantic. This description spans 8 years of data from 1993 to 2000. At first, we focus on the analysis of the mean eddy kinetic energy ( EKE) and show that the major characteristics of mesoscale variability are realistically simulated despite an overestimation of the EKE model in the Gulf Stream region. We then describe the SLA space and timescales and propagation velocities at a resolution never achieved before. There is a high level of agreement between the model and altimeter values regarding spatial scales and propagation velocities. POP timescales are, however, significantly longer in the subtropical regions. The westward zonal propagation velocity of both the model and the observations are higher than the speed computed from standard Rossby wave theory. The effect of mean current advection on POP and TPERS propagation velocities is also clearly seen in the Labrador Current and in the Gulf Stream and its recirculations. Finally, a study of the seasonal and interannual variability of the high-frequency (HF) EKE is carried out. The model reproduces accurately most of the HF-EKE seasonal variations in the Caribbean Sea and at high latitudes despite a phase advance. A clear HF-EKE interannual variability is then evidenced. Our hypothesis is that a contraction of the subpolar and subtropical gyres due to the North Atlantic Oscillation (NAO) could explain a reduction of the eddy activity in the North Atlantic Current, in the Newfoundland basin, and in the Azores Current. In the Caribbean Sea, the interannual variability of the EKE for both POP and TPERS seems to be caused by an interannual variability of the wind stress.
Journal Of Geophysical Research-oceans (0148-0227) (Amer Geophysical Union), 2004-12 , Vol. 109 , N. C1205 , P. 16 PP.

Droits : 2004 AGU
http://archimer.ifremer.fr/doc/00087/19841/17491.pdf
DOI:10.1029/2004JC002360
http://archimer.ifremer.fr/doc/00087/19841/

Éditeur(s) : HAL CCSD
Résumé : International audience
In orogens, shortening is mainly accommodated by thrusts, which constitute preferential zones for fluid–rock interactions. Fluid flow, mass transfer, and mineralogical reactions taking place along thrusts have been intensely investigated, especially in sedimentary basins for petroleum and uranium research. This study combines petrological investigations, mineralogical quantifications, and geochemical characterizations with a wide range of analytical tools with the aim of defining the fluid properties (nature, origin, temperature, and redox) and fluid–host rock interactions (mass transfers, recrystallization mechanisms, and newly formed synkinematic mineralization) in the Pic-de-Port-Vieux thrust fault zone (Pyrenees, Spain). We demonstrate that two geochemically contrasted rocks have been transformed by fluid flow under low-grade metamorphism conditions during thrusting. The hanging-wall Triassic red pelite was locally bleached, while the footwall Cretaceous dolomitic limestone was mylonitized. The results suggest that thrusting was accompanied by a dynamic calcite recrystallization in the dolomitic limestone as well as by leaching of iron via destabilization of iron oxides and phyllosilicate crystallization in the pelite. Geochemical and physical changes highlighted in this study have strong implications on the understanding of the thrust behavior (tectonic and hydraulic), and improve our knowledge of fluid–rock interactions in open fluid systems in the crust.
Contributions to Mineralogy and Petrology

hal-01575548
https://hal-univ-fcomte.archives-ouvertes.fr/hal-01575548
DOI : 10.1007/s00410-017-1394-5

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The paleostorm history of coastal lagoon environments (Pierre Blanche Lagoon, central part of the Gulf of Lions) has been established by integrating clay mineralogy and geochemical analysis. Clay mineralogy combined with bulk major and trace elements concentrations allow for the definition of four different end members: the Mosson drainage basin, the sandy barrier, the biogenic and the anthropic components. The two main sedimentary sources of the lagoonal system are the Mosson drainage basin which has a high concentration of smectite and Al2O3, and the sandy barrier characterized by high contents of illite, chlorite, SiO2 and Zr. Smectite/(illite + chlorite), SiO2/Al2O3 and Zr/Al2O3 ratios can be used to reconstruct the past storm history of the Pierre Blanche Lagoon. Our results indicate that the sensitivities of the clay mineralogy and geochemistry proxies are different. These sensitivities could be related: 1) first, to the comparison between different grain size for geochemistry and for clay mineralogy: 2) second, to the complexity of the mix (four end-members for the geochemistry and two end-members for the clay minerals): and 3) third, by the storm's ability to transport sediment of different sizes. (C) 2010 Elsevier B.V. All rights reserved.
ISSN: 0037-0738

hal-00512614
https://hal.archives-ouvertes.fr/hal-00512614
DOI : 10.1016/j.sedgeo.2010.04.012

Éditeur(s) : Walter De Gruyter & Co
Résumé : The section of the Liguro-Provencal basin north of the Balearic Islands is one of the most productive sites in the whole Mediterranean Sea, with intense phytoplankton bloom lasting about 2 months in late winter-early spring. The phytoplankton species composition of the area was investigated using light and electron microscopy to analyze bottle and net samples collected at several stations in spring 2000 and 2003. Serial dilution cultures established from bottle samples were also examined. A total of 168 phytoplankton taxa was identified, consisting of 73 Coscinodiscophyceae, 47 Dinophyceae, 25 Coccolithophyceae and 4 Prymnesiophyceae, 5 Prasinophyceae, 3 Chrysophyceae, 2 Cryptophyceae, 2 Dictyochophyceae, 1 Euglenophyceae, 1 Pelagophyceae, 1 Choanoflagellidea, 1 Filosea and 3 incertae sedis. We also provided a brief taxonomic description and original micrographs for 25 of the smallest and/or less known species identified in the study area, which may go undetected during routine microscopical analysis of fixed samples. Among these, 10 species were recorded for the first time in the Mediterranean Sea, confirming the need of detailed studies to reveal the biodiversity and biogeography of Mediterranean phytoplankton.
Botanica Marina (0006-8055) (Walter De Gruyter & Co), 2011-06 , Vol. 54 , N. 3 , P. 243-267

Droits : 2011 by Walter de Gruyter
http://archimer.ifremer.fr/doc/00038/14916/12245.pdf
DOI:10.1515/BOT.2011.033
http://archimer.ifremer.fr/doc/00038/14916/

Résumé : Spiny lobsters are an important component of the coastal fisheries around the Martinique island. This study aimed to assess the contamination by kepone of the two main species Panulirus argus and P. guttatus in the main fishery area laying along the eastern coast of Martinique. The objectives of the study were to describe the distribution of the spiny lobster contamination in the area, to explore possible relationships with some biological parameters such as individual size, sex and colour of tegument, as well as characterize difference of kepone concentration between the muscle and soft flesh of the head, in view of helping the definition of further fishery management measures. The analyses were done from chemical analyses of 125 samples of spiny lobsters gathered from 2008 to 2010 all around the island, and from a specific set of 200 new observations from a specific survey carried out in 2011 in the study area. For both species, the results show a diffusion of the contamination all over the coral shoals, close to contaminated catchment basins, with a strong decrease just outside these areas. For the Caribbean spiny lobster, a strong relationship between kepone concentration and individual size was identified, and less for the Spotted spiny lobster. For the two species, the concentration of kepone found in soft flesh of the head was more than twice as in the muscle. Finally, the difference of contamination between the two species appeared strongly linked with their biology.
La langouste blanche Panulirus argus et la langouste brésilienne P. guttatus représentent environ 25 % du chiffre d’affaires des pêcheurs professionnels de Martinique. Une part très importante des captures de ces espèces proviennent du platier continental de la zone centre-atlantique de l’île. L’étude réalisée en 2011 visait à approfondir les connaissances sur la distribution de la contamination par la chlordécone des langoustes dans la zone centre- atlantique de la Martinique, d’explorer d’éventuelles relations entre cette contamination et des paramètres biologiques des individus comme la taille, le sexe et leur pigmentation tégumentaire, et d’analyser la différence de contamination entre la queue et les chairs molles du céphalothorax, en vue d’aider à la définition de mesures de réglementation de la pêche dans ce secteur. L’étude s’appuie sur un ensemble de 125 échantillons rassemblés de 2008 à 2010 pour les deux espèces autour de la Martinique, complétés par 200 échantillons constitués pour la présente étude dans la zone centre-atlantique en 2011. Le rapport est précédé d’un rappel d’éléments sur la biologie et sur l’état de la pêche des langoustes en Martinique. Pour les deux espèces, l’étude met en évidence une extension de la contamination à l’ensemble du platier corallien au pied des bassins versants contaminés, puis une nette diminution au-delà. Pour la langouste blanche, cette contamination est en relation avec la taille des individus, en liaison avec leur plongée progressive vers le large. Cette relation avec la taille est moins marquée pour la langouste brésilienne, espèce beaucoup plus inféodée aux eaux littorales. Pour les deux espèces, les chairs molles du céphalothorax apparaissent plus de deux fois plus contaminées que le muscle caudal. Les différences de contamination observées entre langouste blanche et la langouste brésilienne sont cohérentes avec les connaissances sur la biologie de chaque espèce.

Droits : Délégation Antilles
http://archimer.ifremer.fr/doc/00088/19971/17638.pdf
http://archimer.ifremer.fr/doc/00088/19971/

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) : Université de Bucarest - Université de Bretagne occidentale
Résumé : This study is focusing on the architecture and recent sedimentary evolution of the Danube channel, the youngest channel-levee system in the Danube deep-sea fan. The study was conducted as part of the BlaSON French-Romanian Project, and combined high-resolution seismic-reflection profiles and chirp profiles with multibeam bathymetry and piston cores. This data set was acquired in 1998 during a joint survey IFREMER-GeoEcoMar of the north-western Black Sea. Previous seismic and acoustic data were also used. The Danube deep-sea fan is a large passive-margin mud-rich fan. Like the other systems of this type (Amazon fan, Mississippi fan or Indus fan) the Danube fan consists of stacked channel-levee systems intercalated with mass-transport deposits. Seismic and sedimentary facies in the Danube fan are similar to those identified in most of the mud-rich systems. Nevertheless, the Danube fan is distinguished by a specific feature: its development in a freshwater environment. This is due to the peculiar water-level history of the Black Sea controlled by the link to the Mediterranean through the Strait of Bosphorus and the Sea of Marmara. This connexion was successively interrupted (during sea level lowstands) and re-established (when the sea level was rising above the Bosphorus). Temporary absence of marine water influx during lowstands together with large freshwater inputs from the Danube and other major rivers changed the Black Sea into a freshwater lake during times of fan activity. This peculiarity possibly favourised the development of hyperpycnal flow at the Danube mouth and the initiation of turbidity currents in the deep-sea fan. The Danube channel is directly connected to the large shelf-indenting Danube canyon (also known as Viteaz canyon). The Danube canyon is deeply incised into the shelf margin for 26 km landward of the shelfbreak. During lowstands this canyon acted as the most important path for sediment supply to the deep sea in this part of the continental margin. It consists of a main trough with steep flanks, and a meandering thalweg cut into the flat canyon floor, attesting for the development of the canyon by erosion in the entrenched axial thalweg. Sections with specific morphology, orientation and gradient identified along the canyon, are interpreted as phases of landward expansion of the canyon. Internal structure of the canyon shows several erosional surfaces, which indicate that the present morphology of the canyon is the result of its polyphasic evolution. Instability in the zone of the canyon is related to the important sediment supply at the Danube mouth, to the presence of the gas in the surficial sediment, and possibly under a structural control. The upper part of the Danube channel (between the Danube canyon and ~1400 m depth) consists in a single leveed-channel that has undergone significant overbank deposition, as attested by the well-developed levees. The levees are strongly asymmetrical, being higher and wider on the right-hand side looking downstream. This type of asymmetry is rather common in deep-sea fans, and is generally attributed to the Coriolis effect (Menard, 1955). The channel is slightly sinuous, partially filled and incised by an entrenched thalweg, connected to the axial thalweg of the Danube canyon. Detailed seismic investigation inside the channel trough documented several depositional phases within the channel fill, separated by erosional surfaces. These surfaces are associated with distinct terraces identified on the multibeam bathymetry, that can be followed downward along the main trough axis. The valley fill deposits (where not removed by the subsequent erosional event) show an axial HAR (High Amplitude Reflections) seismic facies with lateral lower amplitude continuous reflections consisting in a levee facies, as proved by sampling. This indicates that filling up was associated with flow within the channel, and not with interruption of fan activity. On the middle slope below 1400 m, this single channel bifurcates through repeated avulsions. As a result, several highly meandering channels developed. The onlap relationships between these channels indicate that only one channel was active at a time. Each phase of avulsion resulted in a depositional unit consisting in a basal unchannelized lobe defined as High Amplitude Reflection Packets (HARP, Flood et al., 1991) that underlies a channel-levee system. The deposition of HARPs was associated with the readjustment of the longitudinal profile of the channel after the breaching of a levee, which resulted in remobilization of upslope channel deposits and eroded levees. When this adjustment was complete, erosion ceased and levees began to develop above the HARPs (Pirmez et al., 1997). All the identified phases of avulsion followed the same pattern: (1) breaching of the lower and narrower left levee; (2) building of a unit of High Amplitude Reflector Packets (HARP) basinward of the bifurcation point by the unchannelized flow, while the former channel was abandoned; and (3) initiation of a new meandering leveed channel. The northward migration of the resulting units through repeated bifurcations is influenced by the asymmetry between levees (hence by the Coriolis effect), and confined between the high levees of the initial phase of the Danube channel (to the south) and the steep relief of the Dniepr fan (to the north). Structure of the fan valley fill indicate that the erosional surfaces inside the upper channel could be formed in response of successive avulsions, by the adjustment of the longitudinal profile of the channel following the breaching of a levee wall. Sediments removed by erosion formed the HARP lobes basinward of the avulsion point. When this adjustment was complete, a channel-levee system developed downward of the bifurcation, overlying the HARPs, but also upward of this point, as a confined channel-levee system inside the erosional trough of the fan valley. Fluvial incisions identified on the continental shelf, together with the coastline location during the last active period of the Danube channel, indicated that the paleo-Danube was directed towards the head of the Danube canyon. Paleo-Danube mouth was fairly close (ca. 10 km) to the Danube canyon, supplying sediment to the Danube channel. Furthermore, hyperpycnal flow probably prevailed in the freshwater environment that characterized the Black Sea during times of fan activity. These conditions would have enabled the development of a quasi-continuous river-canyon-deep-sea fan system, ensuring the effective transfer of the sediment between the coastal zone and the deep sea.
Ce travail est consacré à l'étude de l'architecture et de l'évolution sédimentaire récente de l'éventail profond du Danube, en particulier de son dernier système chenal-levée: le chenal du Danube. L'étude a été réalisée dans le cadre du projet de coopération franco-roumaine BlaSON, à partir des données sismiques, bathymétriques-acoustiques et sédimentologiques acquises en 1998 lors d'une campagne en mer Noire réalisée par IFREMER et GeoEcoMar. Des données sismiques et acoustiques antérieures ont été également utilisées. L'éventail profond du Danube s'enserre dans la catégorie des grands éventails vaseux. Comme les autres systèmes de ce genre (tel que les éventails de l'Amazone, du Mississippi ou de l'Indus) il est constitué d'une succession de systèmes chenaux-levées intercalés avec des dépôts de transport en masse. Le fonctionnement de l'éventail était conditionné par la baisse du niveau marin lors des périodes glaciaires. Ses faciès sismiques et sédimentaires s'apparentent aux faciès qui caractérisent la plupart des éventails de ce type. L'éventail du Danube constitue néanmoins un cas particulier parmi les autres systèmes étudiés, du fait de son fonctionnement dans un bassin lacustre. Ceci est dû à la situation spécifique de la mer Noire dont la connexion avec la Méditerranée, par le détroit de Bosphore et la mer de Marmara, a été successivement interrompue (au cours de périodes de bas niveau) et reprise (quand le niveau marin remontait en dépassant le seuil du Bosphore). L'absence de l'apport d'eau salée pendant les périodes glaciaires, associée avec l'augmentation de l'apport fluvial, ont déterminé l'installation d'un milieu d'eau douce dans la mer Noire à chaque fois que la baisse du niveau permettait la reprise du fonctionnement de l'éventail profond. Cette situation particulière aurait favorisé la formation des courants hyperpycnaux à l'embouchure d'un fleuve du débit du Danube qui déversait ses eaux turbides dans un bassin lacustre, et aurait donc influencé l'apparition de courants de turbidité dans l'éventail profond. Le chenal du Danube s'est développé sur la pente continentale en prolongation du canyon du Danube (ou Viteaz) auquel il est directement connecté. Le canyon est incisé de manière significative (26 km) dans la plate-forme continentale. Au cours de bas-niveaux marins il constituait la principale voie de transfert des sédiments terrigènes vers le bassin profond dans cette partie de la marge. Le canyon est constitué par une entaille avec des flancs abrupts et un talweg axial incisé, qui montre l'importance du processus d'érosion du fond pour le développement du canyon. Les segments qui ont été identifiés le long du canyon, avec des morphologies, des orientations et des pentes spécifiques, sont interprétés comme des phases d'avancement du canyon vers la côte. Plusieurs incisions sont visibles dans la structure interne du canyon et témoignent que la morphologie actuelle du canyon est le résultat de son évolution polyphasée. L'instabilité de la zone du canyon est en relation avec les apports sédimentaires importants à l'embouchure du Danube, avec la présence du gaz dans les sédiments superficiels, et possiblement sous un contrôle structural. Sur la pente supérieure (entre le canyon du Danube et environ 1400 m de profondeur) le chenal du Danube présente des levées bien développées et fortement asymétriques, avec la levée droite plus haute et plus large que la levée gauche. Ce type d'asymétrie, fréquemment décrit dans les éventails profonds est généralement attribué à l'effet Coriolis (Menard, 1955). Le chenal est légèrement sinueux, partiellement comblé et incisé par un talweg axial qui représente la continuation sur la pente du talweg incisé dans le canyon du Danube. L'analyse sismique détaillée du remplissage de la vallée montre plusieurs phases de dépôt, séparées par des discontinuités érosives. Ces surfaces d'érosion correspondent à des terrasses emboîtées, relativement parallèles le long de la vallée, visibles dans la bathymétrie. Les dépôts qui constituent le remplissage du chenal présentent un faciès sismique de type HAR (High Amplitude Reflections) dans l'axe du chenal, partiellement (ou parfois totalement) enlevé par les phases d'érosion subséquentes, qui continue latéralement avec des réflexions litées correspondant à un faciès sédimentaire de levée. Le remplissage de la vallée a été donc associé avec des écoulements dans le chenal, et non pas avec l'interruption de son fonctionnement. Sur la pente inférieure, le chenal unique bifurque plusieurs fois par avulsion et forme de nouveaux systèmes chenaux-levées méandriformes. Ces systèmes se succèdent verticalement en onlap, ce qui montre qu'un seul chenal a été actif à la fois. Chaque phase d'avulsion a eu comme résultat la mise en place d'une unité constituée par un lobe défini comme "High Amplitude Reflection Packets" (HARP, Flood et al., 1991) à la base, et un système chenal-levée au sommet. Le dépôt d'un lobe HARP est associé avec de l'érosion dans le chenal en amont du point d'avulsion pour l'ajustement de son profil après la rupture de la levée. Quand le chenal a retrouvé son profil d'équilibre, l'érosion a cessé et des levées ont commencé à se développer au-dessus des HARPs (Pirmez et al., 1997). Toutes les phases d'avulsion se sont développées d'après le même modèle: (1) la rupture de la levée gauche, plus étroite; (2) le dépôt d'un lobe HARP par les écoulements non-chenalisés en aval du point d'avulsion, et l'abandon de l'ancien chenal; (3) l'initiation d'un nouveau système chenal-levée. La migration systématique du chenal vers le nord est influencée par l'assymétrie des levées (donc par la force de Coriolis), et confinée entre les grandes levées de la phase initiale du chenal du Danube, au sud, et le relief abrupt de l'éventail du Dniepr au nord. La structure sédimentaire du chenal du Danube indique que les surfaces érosives à l'intérieur du remplissage du chenal se seraient formées en réponse aux avulsions, du fait de l'ajustement du profil du chenal après la rupture d'une levée. Les sédiments du chenal érodés au cours de ce processus ont formé les lobes HARP. Quand le chenal a retrouvé son profil d'équilibre, un système chenal-levée s'est développé en aval du point d'avulsion au dessus du lobe HARP, mais aussi en amont de ce point, où il se trouve confiné dans la vallée érosive. Les incisions fluviatiles identifiés sur la plate-forme continentale et la position de la ligne de côte pendant la dernière période d'activité du chenal du Danube montrent que le paléo-Danube se dirigeait directement vers la tête du canyon du Danube. Son embouchure était située à proximité du canyon, qui alimentait le chenal du Danube. Cependant, les courants hyperpycnaux devaient prévaloir dans le milieu de salinité réduite qui caractérisait la mer Noire lors des périodes actives de l'éventail. Ces conditions auraient favorisé la mise en place d'un système quasi-continu fleuve-canyon-éventail profond, qui contrôlait le transfert des sédiments entre la côte et le bassin profond.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/2002/these-1206.pdf
http://archimer.ifremer.fr/doc/00000/1206/

Éditeur(s) : Taylor & Francis Ltd
Résumé : A new method is developed to estimate daily turbulent airsea fluxes over the global ocean on a 0.25 degrees grid. The required surface wind speed (w(10)) and specific air humidity (q(10)) at 10m height are both estimated from remotely sensed measurements. w(10) is obtained from the SeaWinds scatterometer on board the QuikSCAT satellite. A new empirical model relating brightness temperatures (T-b) from the Special Sensor Microwave Imager (SSM/I) and q(10) is developed. It is an extension of the author's previous q(10) model. In addition to T-b, the empirical model includes sea surface temperature (SST) and airsea temperature difference data. The calibration of the new empirical q(10) model utilizes q(10) from the latest version of the National Oceanography Centre airsea interaction gridded data set (NOCS2.0). Compared with mooring data, the new satellite q(10) exhibits better statistical results than previous estimates. For instance, the bias, the root mean square (RMS), and the correlation coefficient values estimated from comparisons between satellite and moorings in the northeast Atlantic and the Mediterranean Sea are 0.04gkg(1), 0.87gkg(1), and 0.95, respectively. The new satellite q(10) is used in combination with the newly reprocessed QuikSCAT V3, the latest version of SST analyses provided by the National Climatic Data Center (NCDC), and 10m air temperature estimated from the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalyses (ERA-Interim), to determine three daily gridded turbulent quantities at 0.25 degrees spatial resolution: surface wind stress, latent heat flux (LHF), and sensible heat flux (SHF). Validation of the resulting fields is performed through a comprehensive comparison with daily, in situ values of LHF and SHF from buoys. In the northeast Atlantic basin, the satellite-derived daily LHF has bias, RMS, and correlation of 5Wm(2), 27Wm(2), and 0.89, respectively. For SHF, the statistical parameters are 2Wm(2), 10Wm(2), and 0.94, respectively. At global scale, the new satellite LHF and SHF are compared to NOCS2.0 daily estimates. Both daily fluxes exhibit similar spatial and seasonal variability. The main departures are found at latitudes south of 40 degrees S, where satellite latent and sensible heat fluxes are generally larger.
International Journal Of Remote Sensing (0143-1161) (Taylor & Francis Ltd), 2013-07 , Vol. 34 , N. 14 , P. 5243-5261

Droits : 2013 Taylor & Francis
http://archimer.ifremer.fr/doc/00137/24825/23575.pdf
DOI:10.1080/01431161.2013.787502
http://archimer.ifremer.fr/doc/00137/24825/

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Brecciated and fractured peridotites with a carbonate matrix, referred to as ophicalcites, are common features of mantle rocks exhumed in passive margins and mid-oceanic ridges. Ophicalcites have been found in close association with massive peridotites, which form the numerous ultramafic bodies scattered along the North Pyrenean Zone (NPZ), on the northern flank of the Pyrenean belt. We present the first field, textural and stable isotopic characterization of these rocks. Our observations show that Pyrenean ophicalcites belong to three main types: (1) a wide variety of breccias composed of sorted or unsorted millimeter- to meter-sized clasts of fresh or oxidized ultramafic material, in a fine-grained calcitic matrix; (2) calcitic veins penetrating into fractured serpentine and fresh peridotite; and (3) pervasive substitution of serpentine minerals by calcite. Stable isotopic analyses (O, C) have been conducted on the carbonate matrix, veins and clasts of samples from 12 Pyrenean ultramafic bodies. We show that the Pyrenean ophicalcites are the product of three distinct genetic processes: (1) pervasive ophicalcite resulting from relatively deep and hot hydrothermal activity; (2) ophicalcites in veins resulting from tectonic fracturing and cooler hydrothermal activity; and (3) polymictic breccias resulting from sedimentary processes occurring after the exposure of subcontinental mantle as portions of the floor of basins which opened during the mid-Cretaceous. We highlight a major difference between the eastern and western Pyrenean ophicalcites belonging, respectively, to the sedimentary and to the hydrothermal types. Our data set points to a possible origin of the sedimentary ophicalcites in continental endorheic basins, but a post-depositional evolution by circulation of metamorphic fluids or an origin from relatively warm marine waters cannot be ruled out. Finally, we discuss the significance of such discrepancy in the characteristics of the NPZ ophicalcites in the frame of the variable exhumation history of the peridotites all along the Pyrenean realm.
ISSN: 1437-3254

insu-00944405
https://hal-insu.archives-ouvertes.fr/insu-00944405
https://hal-insu.archives-ouvertes.fr/insu-00944405/document
https://hal-insu.archives-ouvertes.fr/insu-00944405/file/clerc-etal-IJES-Review.pdf
DOI : 10.1007/s00531-013-0927-z

Éditeur(s) : HAL CCSD AGU and the Geochemical Society
Résumé : International audience
A NE-SW magnetotelluric 110 km-long profile including 18 sites was acquired across the western Rif Cordillera along the Eurasian-African plate boundary, allowing to constrain its poorly known deep structure. It extends from the Internal Zones, close to the Alboran coast, crossing the External Zones and up to the Gharb foreland basin. The periods recorded range from 0.001 s to 1000 s. The combination of magnetotelluric data with available geological data provides new insight regarding the relationship between deep and shallow crustal structures of the Rif Cordillera. Analyses of structural dimensionality suggest a preferential NW-SE direction, and a 2D joint inversion was performed. A 3D inversion extending the 2D model along the strike confirmed the reliability of this approach. The magnetotelluric model shows a heterogeneous upper crust in agreement with the geological structures observed at surface. The Internal Zones correspond to resistive (metamorphic rocks) and conductive (peridotites) bodies, while the External Zones and the foreland basin are characterized by large conductive bodies of variable thickness. A crustal detachment level separating shallow geological units from a probable variscan basement was inferred. At depth, the most relevant feature consists of large resistive bodies with a shallow irregular top, located below the frontal part of the Rif. The outcrops of exotic metapelitic, granitic and gneissic blocks in the frontal part of the Cordillera suggest that these large resistive bodies may correspond to a gneissic or granitic basement surrounded by metapelitic rocks. Late contractive thrust and diapiric processes were responsible for their uplift and shallow emplacement. The Rif constitutes an active southwestward vergent orogenic wedge, oblique to the present-day NW-SE convergent Eurasian-African plate boundary.
ISSN: 1525-2027

hal-00670999
https://hal.archives-ouvertes.fr/hal-00670999
DOI : 10.1029/2011GC003783

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
From outcrops located in Provence (South-East France), we describe the distribution, the microstructures, and the petrophysical properties of deformation band networks related to both contractional and extensional tectonic events. In contraction, pervasively distributed networks of reverse-sense compactional shear bands are observed in all folded sand units of the foreland, whereas localized networks of clustered reverse-sense shear bands are only observed close to a large-scale thrust. In extensional setting, networks of clustered normal-sense shear bands are generally observed adjacent to map-scale faults (100 m–10 km scale), although some randomly distributed bands are also observed between these faults. Normal-sense cataclastic faults, i.e. zone of deformation bands containing a localized slip-surface, are also observed to be restricted to sand units, suggesting that faults initiated in the sands during extension, but not during contraction. Shear bands and faults show cataclastic microstructures with high-permeability reduction whereas compactional shear bands show crush microbreccia or protocataclastic microstructures with moderate permeability reduction. This basin-scale analysis underlines the major role of tectonic settings (thrust-fault versus normal-fault andersonian-stress regime) and the influence of inherited large-scale faults on the formation/localization of low-permeability shear bands. We also provide a geometrical analysis of the band network properties (spacing, thickness, shear/compaction ratio, degree of cataclasis, petrophysical properties) with respect to the median grain size, porosity and grain sorting of host sand. This analysis suggests that grain size, although less important than stress-state conditions and the presence of large-scale faults, has a non-negligible effect on band network geometry. No correlations are observed between the grain sorting, porosity and band network geometry.
ISSN: 0264-8172

hal-01116421
https://hal.archives-ouvertes.fr/hal-01116421
DOI : 10.1016/j.marpetgeo.2013.12.020

Éditeur(s) : Elsevier Science Bv
Résumé : The Var turbiditic system located in the Ligurian Sea (SE France) is an intermediate mud/sand-rich system. The particularity of the Var deep-sea fan is its single channel with abrupt bends and its asymmetric and hyper-developed levee on the right hand side: the Var Sedimentary Ridge. Long-term sediment accumulation on the Var Sedimentary Ridge makes this an ideal target for studying the link between onshore climate change and deep-sea turbidite stratigraphy. This paper focuses on the establishment of the first detailed stratigraphy of the levee, which is used to analyze the timing of overbank deposition throughout the last deglaciation. Main results indicate that high variability in turbidite frequencies and deposition rates along the Var Sedimentary Ridge are determined by two main parameters: 1) the progressive decrease of the levee height controlling the ability of turbidity currents to spill out from the channel onto the levee, and 2) climatic variations affecting the drainage basin, in particular changes in glacial condition since late Last Glacial Maximum to early Holocene. Compared to other deep-water areas, this study confirms the ability of turbiditic systems to record past climatic events on millennial timescales, and underlines the influence of European deglaciation on the observed decrease in turbidite activity in the Var canyon. The presence of a very narrow continental shelf and a single, large channel-levee system makes the Var Sedimentary Ridge a unique example of climate-controlled turbiditic accumulations. (C) 2010 Elsevier B.V. All rights reserved.
Marine Geology (0025-3227) (Elsevier Science Bv), 2011-01 , Vol. 279 , N. 1-4 , P. 148-161

Droits : 2010 Elsevier Ltd All rights reserved.
http://archimer.ifremer.fr/doc/00030/14104/11370.pdf
DOI:10.1016/j.margeo.2010.10.021
http://archimer.ifremer.fr/doc/00030/14104/

Éditeur(s) : HAL CCSD Wiley
Résumé : [b]Aim[/b][br/] [br/] The phylogeographical history of Neotropical species can be difficult to reconstruct because of superimposed Neogene and Quaternary histories, and because of taxonomic uncertainty. We analysed range-wide genetic diversity in a widespread pioneer tree species, Jacaranda copaia (Aubl.) D. Don, to characterize phylogeographical structure, date the evolutionary relationships among lineages, and evaluate the role of dispersal and vicariance in establishing the present geographical range.[br/] [br/] [br/] [b]Location[/b][br/] [br/] Guiana Shield; central, southern and western Amazon Basin; Chocó region; Central America.[br/] [br/] [br/] [b]Methods[/b][br/] [br/] We analysed nine nuclear simple sequence repeat loci (nuSSR), eight chloroplast SSRs (cpSSR), and two cpDNA intergenic sequences in 341 adult trees. Genetic differentiation at nuSSRs was inferred using Bayesian clustering. Dating of chloroplast lineage divergence was obtained using a range of published mutation rates and Bayesian coalescence analyses. Population divergence dating was performed using an isolation-with-migration model for eight loci (one cp sequence and seven nuSSRs).[br/] [br/] [br/] [b]Results[/b][br/] [br/] Nuclear SSR variation identified three geographically overlapping clusters (nu-1, nu-2, nu-3). Twelve cpDNA haplotypes were clustered into two haplogroups (cp-1, cp-2) with the central Amazon harbouring the highest diversity. Molecular dating analysis suggests that cpDNA haplotype diversification started around the end of the Pliocene (2.61 Ma on average), whereas population divergence was more recent and occurred during the mid-Quaternary (point estimates between 357 and 436 ka).[br/] [br/] [br/] [b]Main conclusions[/b][br/] [br/] The genetic variation of J. copaia in the Neotropics was shaped mainly by Pleistocene events. Chloroplast diversity did not display the expected cis/trans Andean disjunction, indicating recent dispersal. Nuclear variation revealed that separate regions share a recent history, with a centre of diversity in the central Amazon Basin. The geographical pattern of diversity is congruent with the distribution of the two subspecies, J. copaia copaia and J. copaia spectabilis, and evidence of nuSSR admixture between the two taxa supports their classification as subspecies.
ISSN: 0305-0270

hal-01032410
https://hal.archives-ouvertes.fr/hal-01032410
DOI : 10.1111/j.1365-2699.2012.02797.x

Éditeur(s) : HAL CCSD
Résumé : This historical perspective provides an overall view of the main steps that led to the acceptance of the concept of mantle exhumation accompanying lithosphere stretching and extreme crustal thinning. We first remember that the presence of exposures of mantle rocks along oceanic spreading ridges was early reported in the 60's due to the results of sediment cores and dredge hauls collected along the Mid-Atlantic Ridge. In the meantime, detailed analysis of the relationships between oceanic sediments of Late Jurassic age and their primary basement in the Apennine ophiolites led many authors to point to the importance of exhumation of mantle rocks on ancient seafloors. By contrast to the thick sections of classical ophiolites (e.g. Oman), the Alpine-Corsican-Appennine ophiolites are characterized by a relatively small amount of mafic rocks (gabbros and basalts), by the absence of any sheeted dyke complex and by the frequent occurrence of oceanic sediments stratigraphically overlying mantle-derived peridotites and associated gabbroic intrusions. They display some of the characteristics of slow-spreading ridge systems, but, due to their highly tectonized character, they have been interpreted successively either as remnants of oceanic fracture zones of normal ocean or as remnants of very-poorly organized, abnormal oceanic basement. This review shows how the concept of mantle exhumation has been elaborated more or less in the same period both by marine geoscientists and by geologists conducting investigations in ophiolitic units of the Alps-Apennines mountain belt. Dredging and diving results from the Gorringe Bank, the Iberia margin, the Thyrrenian Sea and the Central Atlantic in the 1980's and 1990's provided additional proofs that the mantle is currently exhumed in various oceanic environments, including distal continental margins, back-arc basins and slow-spreading ridges of wide oceans. It is shown finally how renewed cross-information from mountain belts and the oceans, multiplying the examples of sedimentary reworking of mantle material, help better constrain the mechanisms of mantle exhumation. This mechanism progressively appeared as a fundamental step during the processes of extension of both continental and oceanic lithospheres in numerous geological situations worldwide.
Bollettino della Società Geologica Italiana

hal-00475653
https://hal.archives-ouvertes.fr/hal-00475653
DOI : 10.3301/IJG.2009.128.2.279

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) : Gauthier-Villars
Résumé : Seismic data from the deep Gulf of Mexico basin indicate: 1) inferred ocenaic crust in the deep central Gulf (5 to 6 km thick; 6.8 to 7.1 km/sec.) is flanked symmetrically on the north and south by inferred transitional crust (8 to 15 km thick; 6.4 to 6.8 km/sec.); 2) acoustic basement seen on the reflection data in the central Gulf is an irregular reflector and probably represents the top of an oceanic volcanic (basaltic) layer (layer 2); 3) northof the Campeche Escar pment the top of transitional crust is represented by a strong, smooth reflector/unconformity that truncates rift basins and is onlapped by a thick salt and sedimentary section; 4) in the southeastern Gulf transitional crust consists of tilted basement blocks probably representing a thinned and rifted continental crust; lows between the blocks are filled with synrift sediments; 5) thick salt symmetrically flanks the north and south sides of the oceanic crust; 6) seismic stratigraphic analysis suggests that early sediments in the Gulf in areas of transitional crust represent an upward gradation from volcanics and nonmarine sediments including evaporites to shallow marine and then to deep marine; only deep marine sediments occur in the central Gulf overlying oceanic crust.
Oceanologica Acta, Special issue (0399-1784) (Gauthier-Villars), 1981

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00246/35679/34187.pdf
http://archimer.ifremer.fr/doc/00246/35679/