A new scenario for the Domerian-Toarcian transition

Pour tenter de mieux comprendre l’événement d’anoxie océanique globale au Toarcien inférieur, il convient de remonter aux changements environnementaux qui ont précédé cette phase paroxysmale. En effet, la comparaison des séquences sédimentaires et biostratigraphiques du passage Domérien-Toarcien entre la Téthys occidentale (Maroc, Espagne, Portugal) et l’Europe du Nord-Ouest (Causses, Allemagne, Angleterre) fait apparaître une importante lacune dans la région septentrionale. La faune d’Arieticeratinae (Emaciaticeras, Canavaria, Fontanelliceras) et d’Harpoceratinae (Lioceratoides, Neolioceratoides), accompagnée ensuite de Dactylioceras particuliers (groupe mirabile-polymorphum = sous-genre Eodactylites), fait presque totalement défaut en Europe du Nord-Ouest, alors qu’elle abonde dans les dernières alternances marno-calcaires, sans changement lithologique notable avec le Domérien des coupes téthysiennes. Cette faune est intercalée entre les derniers Pleuroceras et les Dactylioceras du groupe tenuicostatum. Ces derniers apparaissent dans les argiles succédant immédiatement au dernier banc calcaire à Dactylioceras mirabile au Portugal notamment. C’est là le diachronisme déjà reconnu entre les limites lithostratigraphique (disparition des bancs calcaires) et biostratigraphique (apparition du genre Dactylioceras) au passage Domérien-Toarcien. Cette observation peut s’intégrer dans un nouveau scénario paléo-océanographique prenant en compte à la fois la tendance régressive majeure du Domérien supérieur (conduisant à une lacune régionale importante), l’abondance de matière charbonneuse dans les premiers dépôts transgressifs du Toarcien et l’événement anoxique global subséquent. Dans la partie supérieure du Domérien, l’existence d’un fort volcanisme peut être déduite des données relatives aux variations des isotopes du strontium [McArthur et al., 2000]. A ce pic de strontium sont associées une faible anomalie négative du δ13 C à la limite Domérien-Toarcien et des valeurs particulièrement élevées du δ18 O [Morettini et Bartolini, 1999]. Nous pensons que cette activité volcanique débute par des émissions massives de SO2 induisant des pluies acides, un obscurcissement et un refroidissement. A cette phase de refroidissement correspond une augmentation de l’englacement des pôles et une régression responsable de la lacune majeure évoquée plus haut, particulièrement sensible dans les mers épicontinentales. Bien que les preuves directes d’une glaciation fini-domérienne fassent actuellement défaut [Hallam, 2001], le glacio-eustatisme nous semble le seul mécanisme permettant d’expliquer une oscillation marine importante mais de courte durée [Brandt, 1986 ; Dewey et Pitman, 1998]. En effet, le cycle régression-transgression s’étale sur environ deux zones d’ammonites, la lacune sédimentaire en elle-même recouvrant essentiellement les sous-zones à Elisa et Mirabile. Ce premier épisode serait suivi, dans la zone à Tenuicostatum, par une importante perturbation du cycle du carbone responsable d’un effet de serre. Le réchauffement, provoquerait alors la transgression bien connue du Toarcien inférieur, cachetant le hiatus sédimentaire dans la province nord-ouest européenne. L’intervalle de temps correspondant à cette lacune aurait permis à la végétation de coloniser les immenses surfaces nouvellement émergées. C’est le lessivage et l’oxydation de la matière organo-humique et bactérienne accumulée pendant cette période, associée à une élévation de la température, qui aurait enclenché le mécanisme d’anoxie lors du paroxysme de la transgression

The melting curve of Ni to 1 Mbar

International audienceThe melting curve of Ni has been determined to 125 GPa using laser-heated diamond anvil cell (LH-DAC) experiments in which two melting criteria were used: firstly, the appearance of liquid diffuse scattering (LDS) during in situ X-ray diffraction (XRD) and secondly, plateaux in temperature vs. laser power functions in both in situ and off-line experiments. Our new melting curve, defined by a Simon–Glatzel fit to the data where T M ( K ) = [ ( P M 18.78 ± 10.20 + 1 ) ] 1 / 2.42 ± 0.66 × 1726 , is in good agreement with the majority of the theoretical studies on Ni melting and matches closely the available shock wave melting data. It is however dramatically steeper than the previous off-line LH-DAC studies in which determination of melting was based on the visual observation of motion aided by the laser speckle method. We estimate the melting point ( T M ) of Ni at the inner-core boundary (ICB) pressure of 330 GPa to be T M = 5800 ± 700 K ( 2 σ ) , within error of the value for Fe of T M = 6230 ± 500 K determined in a recent in situ LH-DAC study by similar methods to those employed here. This similarity suggests that the alloying of 5–10 wt.% Ni with the Fe-rich core alloy is unlikely to have any significant effect on the temperature of the ICB, though this is dependent on the details of the topology of the Fe–Ni binary phase diagram at core pressures. Our melting temperature for Ni at 330 GPa is ∼2500 K higher than that found in previous experimental studies employing the laser speckle method. We find that those earlier melting curves coincide with the onset of rapid sub-solidus recrystallization, suggesting that visual observations of motion may have misinterpreted dynamic recrystallization as convective motion of a melt. This finding has significant implications for our understanding of the high-pressure melting behaviour of a number of other transition metals

Attribute Controlled Reconstruction and Adaptive Mathematical Morphology

ISBN : 978-3-642-38293-2International audienceIn this paper we present a reconstruction method controlled by the evolution of attributes. The process begins from a marker, propagated over increasing quasi-flat zones. The evolution of several increasing and non-increasing attributes is studied in order to select the appropriate region. Additionally, the combination of attributes can be used in a straightforward way. To demonstrate the performance of our method, three applications are presented. Firstly, our method successfully segments connected objects in range images. Secondly, input-adaptive structuring elements (SE) are defined computing the controlled propagation for each pixel on a pilot image. Finally, input-adaptive SE are used to assess shape features on the image. Our approach is multi-scale and auto-dual. Compared with other methods, it is based on a given attribute but does not require a size parameter in order to determine appropriate regions. It is useful to extract objects of a given shape. Additionally, our reconstruction is a connected operator since quasi-flat zones do not create new contours on the image

Durability improvement of wood by treatment with Methyl Alkenoate Succinic Anhydrides (M-ASA) of vegetable origin

Methyl Alkenoate Succinic Anhydride (M-ASA) is the product of the reaction between methyl esters of fatty acids and maleic anhydride. Crude M-ASA was synthesized from rapeseed oil methyl esters. The main compounds in this adduct are methyl oleate succinic anhydride (30%), methyl linoleate succinic anhydride (24%), unreacted methyl esters (41%) and unreacted maleic anhydride (4%). The treatment of wood at high temperature with crude M-ASA conferred protection against fungal decay and insects. Biological tests were carried out on Scots pine (Pinus sylvestris) sapwood and beech (Fagus sylvatica) according to European standards. M-ASA treatment was efficient against mould fungi (BS 3900), blue staining (EN 152), white and brown rot fungi (EN 113), longhorn beetle larvae (EN 46 and 47) and termites (EN 117). This treatment delayed the degradation of wood by soft rot (ENV 807) but it did not prevent it. Therefore, M-ASA combines all the necessary conditions to fulfil the requirements of the biological use classes 2 and 3, but not for class 4

Patterns of eukaryotic diversity from the surface to the deep-ocean sediment

Remote deep-ocean sediment (DOS) ecosystems are among the least explored biomes on Earth. Genomic assessments of their biodiversity have failed to separate indigenous benthic organisms from sinking plankton. Here, we compare global-scale eukaryotic DNA metabarcoding datasets (18S-V9) from abyssal and lower bathyal surficial sediments and euphotic and aphotic ocean pelagic layers to distinguish plankton from benthic diversity in sediment material. Based on 1685 samples collected throughout the world ocean, we show that DOS diversity is at least threefold that in pelagic realms, with nearly two-thirds represented by abundant yet unknown eukaryotes. These benthic communities are spatially structured by ocean basins and particulate organic carbon (POC) flux from the upper ocean. Plankton DNA reaching the DOS originates from abundant species, with maximal deposition at high latitudes. Its seafloor DNA signature predicts variations in POC export from the surface and reveals previously overlooked taxa that may drive the biological carbon pump

Acute partial Budd-Chiari syndrome and portal vein thrombosis in cytomegalovirus primary infection: a case report

BACKGROUND: Splanchnic vein thrombosis may complicate inherited thrombotic disorders. Acute cytomegalovirus infection is a rare cause of acquired venous thrombosis in the portal or mesenteric territory, but has never been described extending into a main hepatic vein. CASE PRESENTATION: A 36-year-old immunocompetent woman presented with acute primary cytomegalovirus infection in association with extensive thrombosis in the portal and splenic vein. In addition, a fresh thrombus was evident in the right hepatic vein. A thorough evaluation for a hypercoagulable state was negative. The clinical course, biological evolution, radiological and histological findings were consistent with cytomegalovirus hepatitis complicated by a partial acute Budd-Chiari syndrome and portal thrombosis. Therapeutic anticoagulation was associated with a slow clinical improvement and partial vascular recanalization. CONCLUSION: We described in details a new association between cytomegalovirus infection and acute venous thrombosis both in the portal vein and in the right hepatic vein, realizing a partial Budd-Chiari syndrome. One should be aware that this rare thrombotic event may be complicated by partial venous outflow block