The Vema contourite fan in the South Brazilian basin
The Vema contourite fan is a Neogene mud-rich accumulation (200-400 m thick), fed by Antarctic Bottom Water bottom currents and located downstream of the Rio Grande Rise. It forms one single, mounded, fan-shaped body deposited between two major channels through which the main part of the deep AABW circulation is funneled. A suite of cores and seismic lines have been collected over the whole area. The sediments deposited below the shear zone between the two current branches consist almost exclusively of muddy contourites, either homogeneous in structure or micro-brecciated. Manganiferous deposits occur in the vicinity of the channels and on the channel floors. As a result of the morphological and hydrological background, the contourite drift has prograded mostly downstream. It is composed of several depositional units bounded by widespread discontinuities showing erosional patterns. This geometry results from an alternation of episodes of strong and unstable erosive currents, and periods of relatively weak and stable depositional currents
(Geological Society of London Memoirs. vol. 22, n° 0435-4052, pp. 209-222, 01/01/2002)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
The Columbia Channel-levee system: a fan drift in the southern Brazil Basin
The Columbia Channel is a turbiditic channel elongated W-E on the rise of the south Brazilian basin (4200 to 5000 m water depth). The whole area is swept by the northward flowing Antarctic Bottom Water. As a consequence, depositional processes have built a fan drift system. This system displays a levee along the northern flank of the channel while no levee occurs on its southern flank due to the Coriolis effect. The levee (400 km in length and 100 to 200 km in width) is bounded to the north by the Vitoria-Trindade Seamounts. It shows, first, a W-E trend parallel to the channel axis and predominantly turbiditic pattern, and then a S-N trend parallel to the rise contours with a predominant contouritic pattern. Its thickness is up to 1000 m. The distribution of sedimentary processes and associated deposits were investigated on the basis of water gun seismic and 3.5 kHz echosounding profiles, and core lithology. On the lower S-N part of the levee, the deposits consist of muddy contourites. On the shallowest part, turbidites that originate from the upper continental margin in the channel and on the southern part of the levee close to the channel, and from the Vitoria-Trindade Seamounts on the northern part of the levee, are interbedded with contouritic muds, and top-truncated silty turbidites. Areas subjected to turbidity current processes show chaotic to well-stratified, high amplitude reflections, in the subsurface, and more or less prolonged echofacies with or without sub-bottom reflectors, at the seabed. Areas subjected to contour currents show, in the subsurface, transparent seismofacies with some discontinuous low amplitude wavy reflections, and, in the surficial deposits, predominant wavy echofacies with sub-bottom relectors, frequently associated with tangential hyperbolae.
(Geological Society of London Memoirs. vol. 22, n° 0435-4052, pp. 223-238, 01/01/2002)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Sea-level and deep water temperature changes derived from benthic foraminifera isotopic records
(Quaternary Science Reviews. vol. 21, n° 0277-3791, pp. 295-305, 01/01/2002)
PALEOCEAN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, WHOI, ANU, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Isotopic evidence of methane-related diagenesis in the mud volcanic sediments of the Barbados Accretionary Prism
Extensive sampling of chosen sectors of the Barbados Accretionary Prism during four French oceanographic cruises (1985-1993) evidenced the presence of abundant diagenetic carbonate deposits associated mostly with zones of active or ancient fluid venting and mud expulsion processes (mud volcanoes, mud diapirs, diapiric ridges). Diagenetic carbonates (low- and high-Mg calcite, aragonite and low-Mg dolomite) are found to bind together dead benthic communities associated to fluid venting and to cover extensive areas of the sea floor where complete lithification of both autochtonous deposits and mud volcanic products occurs. Extreme cases of early diagenesis occur on mud dome structures on the summit of the ridge where the expelled sediments have been entirely lithified for a thickness of several metres. Low δ13C values of most dolomites (down to -60.2‰) and of most calcites and aragonites (down to -53.07‰) show the major contribution of oxidized methane to the dissolved inorganic carbon in the water from which these minerals precipitated. In contrast, a number of authigenic carbonates have δ13C values close to 0‰ and possibly precipitated from bottom waters. Unusually high δ18O values of the methane-related authigenic carbonates (up to 7.66‰ in dolomites and up to 6.98‰ in calcites and aragonites) are interpreted as due to precipitation from 18O-rich diagenetic fluids.
(Continental Shelf Research. vol. 22, n° 0278-4343, pp. 2355-2372, 21/02/2026)
LODYC, IRD, UPMC, CNRS, MNHN, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Sources of fine-sized organic matter in North Atlantic Heinrich Layers: δ 13C and δ 15N tracers
Organic carbon (OC) and total nitrogen (TN) concentrations and stable isotope ratios (δ 13C, δ 15N) of fine (<50 μm) size fractions of deep-sea sediments from the central North Atlantic were employed to identify changes in sources of organic matter over the past 50 ka BP. Ambient glacial sediments are characterised by values that reflect mixtures of marine and terrestrial inputs (averages ± 1σ: OC/TN = 7.6 ± 0.8; δ 13C = -22.8 ± 1.0‰; δ 15N = 5.5 ± 0.6‰). δ 13C, OC, and TN concentrations shift to higher values during the Holocene, indicating a gradual decrease of fine terrigenous supply to the North Atlantic. The unchanged δ 15N record between last glacial and Holocene stages indicates that the central North Atlantic region remained oligotrophic at least during the past 50 ka BP, but additional studies are required to support this result in terms of nitrogen oceanic budget. During the phases of enhanced ice-rafted detrital supply corresponding to prominent Heinrich events (HL 1, HL 2, HL 4, and HL 5), fine-sized sedimentary organic matter has lower OC and TN concentrations, contrasting sharply with those of ambient glacial sediments. Lower δ 13C (down to -28‰) and δ 15N (down to 1.6‰) values and high OC:TN ratios (up to 14.7 ± 1.1) are found for HL 1, HL 2, and with lesser extent for HL 4. These values reflect enhanced detrital supply originating from poorly differentiated soil horizons that characterise periglacial climate conditions and from organic matter-bearing rock sources of the underlying geological basement. During HL 5, only the δ 13C offset records the input of fine size ice-rafted organic matter. Gradually changing soil development conditions during the time interval covering HL 5 to HL 1 (marine isotope stages 5 to 2), as well as varying erosion levels, have been hypothesized on the basis of constant δ 13C, increasing OC/TN and decreasing δ 15N values.
(Geochimica et Cosmochimica Acta. vol. 66, n° 0016-7037, pp. 223-239, 21/02/2026)
iEES, INRA, UPMC, UPEC UP12, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Late quaternary variations of elemental ratios (C/Si and N/Si) in diatom-bound organic matter from the Southern Ocean
The carbon cycle in the Southern Ocean is considered as a major factor controlling past atmospheric CO 2 concentration variations. However, accumulation rates of biogenic opal are not linearly related to carbon burial rates. Here, we show that it is possible to measure the carbon and nitrogen content of diatom-bound organic matter (%C diat and %N diat, respectively) and that the signals recorded do not appear to be analytical artifacts. Analyses of two cores from the Atlantic and Indian sectors of the Southern Ocean show that %C diat and %N diat change on glacial-interglacial cycles by 30-40% and 120-175%, respectively. Accordingly, C/N ratios vary between 3 and 7 on glacial-interglacial timescales. If changes recorded in the occluded organic matter are representative of the changes in the diatom bulk organic matter, this provides a new tool to document the carbon cycle in the Southern Ocean and to determine its role on past atmospheric pCO 2 variations. Laboratory experiments on diatom cultures are needed to validate the use of diatom organic bound C and N as a tracer of diatom physiology and of carbon export from surface waters.
(Deep Sea Research Part II: Topical Studies in Oceanography. vol. 49, n° 0967-0645, pp. 1939-1952, 21/02/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Corrélation des niveaux fossilifères marins interstratifiés dans les gypses messiniens, entre la carrière de Los Yesos et la carrière de Molinos de Aguas (bassin de Sorbas, SE Espagne)
Deux niveaux fossilifères marins ont été récemment découverts intercalés dans la série évaporitique messinienne de la carrière de Molinos de Aguas (bassin de Sorbas, SE Espagne). Le plus ancien correspond à des marnes noires riches en poissons Clupeidae appartenant à l’espèce Sardina crassa (Sauvage, 1873), alors que le plus récent est constitué de marnes et calcaires gris pâle contenant le bivalve Neopycnodonte navicularis (Brocchi, 1814) et l’échinide Brissopsis lyrifera (Forbes, 1841). Ces interruptions de la série évaporitique par des niveaux marins fossilifères signent des remises en eau locale de l’Est du bassin de Sorbas, dans un contexte marin de salinité peu différente de la normale. Sur le plan stratigraphique et paléoenvironnemental, ces intercalations marines sont interprétées comme les équivalents latéraux de deux des trois niveaux à fossiles marins précédemment découverts interstratifiés dans la série évaporitique de Los Yesos, à l’Ouest du bassin de Sorbas : 1) les argiles noires à poissons de Molinos de Aguas pourraient constituer l’équivalent de l’un des deux faciès de sables noirs à huîtres et pectinidés de Los Yesos ; et 2) les marnes et calcaires gris à Neopycnodonte et Brissopsis de Molinos de Aguas seraient l’équivalent des marnes et calcaires gris à Neopycnodonte et Brissopsis de Los Yesos.
(Geodiversitas. vol. 24, n° 1280-9659, pp. 659-667, 21/02/2026)
GR, UR, INSU - CNRS, CNRS, GR, UR, INSU - CNRS, CNRS, LDO, INSU - CNRS, UBO EPE, CNRS, MNHN, CNRS
Combined 3D-spectrofluorometry, high performance liquid chromatography and capillary electrophoresis for the characterization of dissolved organic matter in natural waters
3D-spectrofluorometry, high performance liquid chromatography (HPLC) and capillary electrophoresis (CE) were used to differentiate between marine and fresh water samples. These three techniques were used to obtain different patterns for marine and fresh waters, thus confirming that the organic materials they contain are different. The HPLC fractionation allowed the separation of different classes of dissolved organic matter (DOM) components. Their further analyses using both 3D spectrofluorometry and CE demonstrated that the isolated fractions were specific of the water origin. Furthermore, capillary electrophoresis was shown to have a considerable potential for fingerprinting and for a better characterisation of DOM of different origins. \textcopyright 2002 Elsevier Science Ltd. All rights reserved.
(Organic Geochemistry. vol. 33, n° 0146-6380, pp. 221--236, 21/02/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Effet de la turbidité sur la dégradation des pigments phytoplanctoniques dans l'estuaire de la GirondeEffect of turbidity on phytoplanktonic pigments degradation in the Gironde Estuary
In the Gironde Estuary, most part of phytoplanktonic material carried by the rivers is mineralised in the maximum turbidity zone (MTZ). In order to follow the degradation of the phytoplanktonic material into the MTZ, we developed an in vitro approach based on the monitoring of phytoplanktonic pigments. Algal material from two chlorophytes ( Scenedesmus suspicatus Chaudat and Chlamydomonas sp.) was incubated in the dark during 28 days into water samples from the Gironde estuary MTZ, at variable suspended solid concentrations (SPM) as well as in a sterilised turbid sample. First order decay constants of chlorophylls a and b and lutein increased by a factor 3 to 5 between SPM of 0 and 3 g l-1. The production of pheophytin a in the presence of particles and the lack of degradation in the sterilised turbid sample confirmed the effect of attached bacteria on the particles. To cite this article: E. Lemaire et al., C. R. Geoscience 334 (2002) 251-258.
(Comptes Rendus. Géoscience. vol. 334, n° 1631-0713, pp. 251-258, 21/02/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Peut-on évaluer le rôle de la sédimentation sur l'effet de serre à l'échelle de temps des cycles orbitaux ?Can the role of sedimentation in the greenhouse effect at the time scale of orbital cycles be evaluated?
The evolution of the atmospheric CO 2 content is partly a response to the lack of balance between oceanic sedimentation and continental weathering, because the oceanic C reservoir tends to balance net inputs or losses from slow processes by rapid exchanges with the atmospheric reservoir. This response strongly depends on both amplitudes and time scales of the related processes. At Milankovitch or lower time scales, global models generally do neglect organic matter fossilisation, but such an assumption is only valid for oligotrophic systems. In eutrophic or mesotrophic systems, organic matter is not negligible and should be considered relatively to the carbonate sedimentation in order to know whether the impact of the sedimentation was a source or a sink for atmospheric CO 2. To cite this article: P. Bertrand, C. R. Geoscience 334 (2002) 521-528.
(Comptes Rendus. Géoscience. vol. 334, n° 1631-0713, pp. 521-528, 21/02/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS