Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
An original karstic system in a coastal alluvial plain located in a carbonate environment (Cassis, Provence -- SE France) was studied using a multi-method approach (electrical resistivity tomography, gravimetric, passive seismic survey), combined with geomorphologic methods, surface observations and drilling. Limestone dissolution and/or cavity collapse led to the development of a polje, which was filled rapidly by erosion of Aptian marls. The combination of several dating and paleoenvironmental proxies indicates that the polje was filled during a glacial period (MIS 6, 8 or 10, i.e. in the 130-360 ka age range). This discovery has implications for the understanding of karst processes. The connection between the polje and the three km-long Bestouan underwater karstic conduit with submarine outlet is strongly suggested by sedimentological studies and geophysical prospections.
ISSN: 0169-555X

hal-01054334
https://hal.archives-ouvertes.fr/hal-01054334
DOI : 10.1016/j.geomorph.2014.02.021

Éditeur(s) : HAL CCSD
Résumé : The Firouzkuh Fault in most of its extension is located at the southern side of Firouzkuh Valley in west of the Central Alborz. It is a SW - NE prominent structure with a 70 km long on a sinistral -normal fault. It has been known as a south-dipping reverse fault.Paleoseismic analysis and C14 dating along the Firouzkuh left -lateral strike-slip fault indicate that Central Alborz has been shaken by large earthquakes during the Holocene. Here we present the data carried out of one of the two excavated trenches with 15 m long, 2m wide, ~ 4m deep in the east of Firouzkuh, where we found some evidence for last paleoearthquake associated to seismic re-activity on Firouzkuh Fault in the second trench (F2) that dug across a gauge zone. The last event is evidenced by cutting young superficial deposit where this faulted unit stratigrafically covered alluvium deposits yielded dated human bones fragments. The bones found in 60-70cm-deep of trench which a C14 age of 1159 ± 28 BP. Regarding to estimated slips per event on paleoseismological log of eastern wall of trench F1, event magnitudes for each paleoearthquakes are M≈7.
Geosciences Scientific Quarterly Journal

hal-00800375
https://hal.archives-ouvertes.fr/hal-00800375

Éditeur(s) : HAL CCSD
Résumé : International audience
We present an overview of the Mid-Cretaceous hyper-extended rift systemexposed in the northern part of the Pyrenean mountain range. Itsinversion during the Pyrenean orogeny allows for precious observationsof the deep-seated processes occurring at the foot of distal margins.Some peculiar aspects characterizing the pre-Alpine hyper-extended domainare examined throughout the 400 km long suture that is fossilizedin the North Pyrenean Zone (NPZ). The high temperature/low pressure(HT/LP) thermal imprint of the extensional event is studied thanksto a dataset of more than hundred peak temperature measurementsby Raman spectroscopy of the carbonaceous material (RSCM). Thepre- and syn-rift metasediments are characterized by an intense, synmetamorphicductile deformation. Focusing on several key-localitiesof the NPZ, we examine the emplacement conditions of the peridotitesin response to this extreme crustal thinning. Geological evidencessuch as the occurrence of peridotite bodies directly underlying metamorphicpre-rift sediments indicate an early attenuation of the rifted continentalcrust. Moreover, syn-rift, Albian-Cenomanian flysch sequenceswere deposited synchronously with the syn-metamorphic ductile deformationof the pre-rift sequences. All along the Internal MetamorphicZone (IMZ), the base of the flysch deposits also recorded the HT tectonicevent. Such a synchronicity between geological events, which aregenerally separated in time, is not common in mountain belts. We examinehow tectonics, metamorphism and sedimentation may be activein a single basin during extension. We propose an original mechanismfor the evolution of the basins involving continuous basal extraction ofthe pre-rift metamorphic sediments. This early HT deformation eventrelates to the « phase anté-Cénomanienne » described by Pyrenean geologistssince 1930.
24 ème Réunion des sciences de la Terre 2014
Pau, France

insu-01080795
https://hal-insu.archives-ouvertes.fr/insu-01080795

Éditeur(s) : HAL CCSD National Academy of Sciences
Résumé : International audience
The Isua Supracrustal Belt, Greenland, of Early Archean age (3.81-3.70 Ga) represents the oldest crustal segment on Earth. Its complex lithology comprises an ophiolite-like unit and volcanic rocks reminiscent of boninites, which tie Isua supracrustals to an island arc environment. We here present zinc (Zn) isotope compositions measured on serpentinites and other rocks from the Isua supracrustal sequence and on serpentinites from modern ophiolites, midocean ridges, and the Mariana forearc. In stark contrast to modern midocean ridge and ophiolite serpentinites, Zn in Isua and Mariana serpentinites is markedly depleted in heavy isotopes with respect to the igneous average. Based on recent results of Zn isotope fractionation between coexisting species in solution, the Isua serpentinites were permeated by carbonate- rich, high- pH hydrothermal solutions at medium temperature (100-300 degrees C). Zinc isotopes therefore stand out as a pH meter for fossil hydrothermal solutions. The geochemical features of the Isua fluids resemble the interstitial fluids sampled in the mud volcano serpentinites of the Mariana forearc. The reduced character and the high pH inferred for these fluids make Archean serpentine mud volcanoes a particularly favorable setting for the early stabilization of amino acids.
ISSN: 0027-8424

insu-00674714
https://hal-insu.archives-ouvertes.fr/insu-00674714
DOI : 10.1073/pnas.1108061108

Résumé : Les forêts côtières inondables (FCI) des régions tropicales et subtropicales remplissent des fonctions écologiques nécessaires aux écosystèmes marins côtiers situés en aval et aux populations humaines vivant à proximité Aux Antilles, les mangroves et les forêts marécageuses à Pterocarpus officinalis sont structurés par des espèces ligneuses qui ont développé des adaptations particulières à la salinité, à l’inondation et aux substrats meubles sur lesquels elles reposent. Dans des contextes climatiques à forte saisonnalité, les saisons sèches prolongées entraînent de fortes variations de la salinité et du niveau de la nappe, que le changement climatique devrait amplifier. Les modèles climatiques de la région Caraïbe prévoient des saisons sèches plus sèches liées à une baisse des précipitations de 20 à 50 %. Or, la question des capacités de résistance et d’acclimatation des espèces ligneuses des FCI à des variations saisonnières marquées de leur environnement édaphique a été peu traitée dans la littérature scientifique.L’objectif de ce travail de thèse a été double. Il s’est agi, d'une part, de caractériser la structure et la croissance de faciès de végétation représentatifs des FCI antillaises et de mettre en évidence leurs déterminants. A cet effet, des individus adultes, des espèces ligneuses dominantes des FCI, (Avicennia germinans, Laguncularia racemosa, Pterocarpus officinalis, Rhizophora mangle), dans cinq faciès de végétation sur le gradient terre-mer, ont été suivis sur l'île de Grande-Terre (Guadeloupe). D’autre part, les effets de variations salines extrêmes sur la croissance et l’écophysiologie de ces quatre espèces ont été évalués au stade plantule par une expérience en conditions contrôlées.A travers cette étude, il a été montré que les différences de salinité et de fertilité entre les stationspermettent d’expliquer la composition et la structure des peuplements de FCI. Cette étude a égalementmontré que P. officinalis peut se maintenir dans une gamme de salinité plus large que ne l'indiquait lalittérature.Dans le contexte des Antilles où les marnages sont faibles, la saisonnalité du climat entraine des variations saisonnières importantes d’un ensemble de descripteurs édaphiques tels que le niveau de la nappe, la salinité du sol, le pH et le potentiel RedOx. L’inondation et la salinité des sols sont fortement corrélées aux variations mensuelles des précipitations. Les périodes sèches sont accompagnées de salinités élevées et d’une baisse du niveau de la nappe allant jusqu’à l’exondation des sols dans toutes les stations suivies. Les stress environnementaux liés à la saisonnalité entrainent une baisse de la production primaire. L’accroissement cambial mensuel des individus est fortement corrélé avec les précipitations et l’intensité du vent. Dans les stations de mangrove, la sècheresse édaphique régule la production primaire des palétuviers. En forêt marécageuse, la part de la sècheresse atmosphérique semble plus importante pour expliquer la production de P. officinalis. Aussi, les sècheresses édaphique et atmosphérique doivent être prises en compte toutes deux pour modéliser efficacement la croissance des peuplements des FCI.Lors de la saison sèche, le stress le plus important est le stress hydrique, lié à la diminution de la teneur en eau du sol et à l’augmentation de la salinité, qui entraine des contraintes physiologiques sur les palétuviers (ajustements stomatiques, pertes de surface foliaire et de conductivité hydraulique). Le stress ionique, lié à la toxicité des ions Na+ et Cl-, permet aussi d’expliquer une partie de la contrainte sur l’assimilation en carbone. En saison sèche, l’aération des sols ne se traduit pas par une amélioration des performances de croissance chez toutes les espèces. Aussi, la croissance cambiale maximale de toutes les espèces de FCI est réalisée en saison des pluies lorsque la salinité est faible et les niveaux d’inondation élevés.
In tropical and subtropical regions, flooded coastal forests provide essentials goods and services to local communities. In the Antilles, mangrove forests and the Pterocarpus officinalis swamp forest host tree species that are adapted to salinity, flooding and loose substrates. In areas were climatic seasonality is strong, dry seasons lead to strong fluctuations of soil salinity and water table level ; that climate change is likely to make stronger again. Climate model for the Caribbean project drier dry seasons with a decease of 20 to 50 % in annual rainfall amounts. However, resistance and acclimation ability of flooded coastal forest’s species to strong environmental fluctuations still remain poorly studied.This thesis aims two objectives. On the one hand, it aims to characterize the forest structure and monthly growth of vegetation structures representative of the Antillean flooded coastal forests and to highlight their determinants. In this respect, adult trees of the four dominant species of local flooded coastal forest (Avicennia germinans, Laguncularia racemosa, Pterocarpus officinalis, Rhizophora mangle), in five stations along a sea – land gradient were monitored on the Grande-Terre island (Guadeloupe). On the other hand, the effects of salinity variation patterns and salinity levels on growth performances and physiology of seedlings from the four same species were investigated through a greenhouse experiment.This study shows that differences among average salinity and soil fertility explain the vegetation structure of flooded coastal forest. It also extents, in the literature, the range of salinity in which P. officinalis can stand at the tree stage.In the Antilles were tidal range is small, climate seasonality lead to strong edaphic seasonal variations in water table level, soil salinity, pH and RedOx potential. Flooding and soil salinity are strongly correlated to monthly rainfall amounts: dry periods lead to high salinity and to a decrease in water table level under the soil surface. Seasonal environmental stresses lead to a decrease of primary production. Cambial growth was strongly correlated to monthly precipitation and average wind speed. In mangrove stations, edaphic drought determines primary production of mangrove trees, when, in swamp forest stations, atmospheric drought determines an important part of P. officinalis’ primary production.During the dry season, water stress is the more important environmental stress, both by the decrease in soil humidity and the increase in soil salinity, and leads to physiological strains (stomatal adjustment, loss of leaf area and hydraulic conductivity) for mangrove trees. Ionic toxicity of ions Na+ and Cl- also explains a part of the strain on carbon assimilation. During the dry season, re oxygenation of soils via low water table level does not lead to an increase of physiological traits. Thus, maximum cambial growth of all species is observed during the rainy season, when salinity is low and water table level is high.Flooded coastal forest’s species do not have the same ability to recover after a dry episode. In all the studied stations, A. germinans’ cambial growth rises back as soon as the rainy season starts, when, for one station, cambial growth of L. racemosa and R. mangle stay null during the three first month of the rainy season. This low ability to recover after a dry episode is correlated to a stronger impact of the dry season on the physiological traits of these two species.The greenhouse experiment shows that salinity variation patterns are to be taken into consideration for explaining seedlings’ growth and salinity tolerance. A stronger salinity increase impacts the growth of all the studied species; a punctual drop of salinity highlights that flooded coastal forest’s species differ in ability to take advantage of a low salinity episode. These results are coherent with field observations as cambial growth was fairly explained by monthly precipitation.

http://www.theses.fr/2013AGUY0674/document

Éditeur(s) : Elsevier
Résumé : in this study we evaluated the effects of the probiotic Pediococcus acidilactici MA18/5M on shrimp, Litopenaeus stylirostris (also called Penaeus stylirostris), first on antioxidant defences and secondly on the oxidative stress status in the shrimps' haemolymph and digestive gland. We conducted two experiments with the same protocol in which shrimps were fed two diets for three weeks: a control diet and a probiotic diet containing 1 g of live P. acidilactici MA18/5M kg(-1). In the first experiment, the shrimps were found to be healthy over the trial period; no mortalities and non-detectable signs of infection were recorded. These resulted in high final survival rates (above 90% in both treatments). On the other hand, during the second trial, carried out at a period of increased risk for an outbreak of the summer syndrome, higher mortalities were recorded, associated with high V. nigripulchritudo prevalence and loads in the shrimp haemolymph. In healthy shrimps (trial 1), no detectable response of the antioxidant defence system and of oxidative stress bio-indicators were observed. However, feeding the probiotic significantly increased the total antioxidant status (TAS) and glutathione peroxidase activity, while all other parameters remained significantly unchanged. In the shrimps exposed to V nigripulchritudo (trial 2), the antioxidant response was characterized by higher antioxidant enzyme activities (superoxide dismutase and catalase) and higher oxidative stress level in the digestive gland (higher oxidized/reduced glutathione ratio, higher malonclialdehyde and carbonyl protein contents) compared to levels found in trial 1. However, shrimps fed the probiotic diet exhibited (i) significantly higher final survival rates (67 +/- 3%) compared to the control (47 +/- 4%) and (ii) a lower prevalence of V nigripulchritudo throughout the trial. Moreover, the antioxidant response and the oxidative stress level recorded in the digestive gland with shrimps submitted to the probiotic diet were lower. In the light of these results, we confirm that P acidilactici enrichment in shrimps' diet seems an effective way of reducing the susceptibility of shrimps to bacterial pathogens. (c) 2009 Elsevier B.V. All rights reserved.
Aquaculture (0044-8486) (Elsevier), 2009-09 , Vol. 294 , N. 3-4 , P. 306-313

Droits : 2009 Elsevier B.V. All rights reserved.
http://archimer.ifremer.fr/doc/2009/publication-6780.pdf
DOI:10.1016/j.aquaculture.2009.06.016
http://archimer.ifremer.fr/doc/00000/6780/

Éditeur(s) : HAL CCSD Geological Society
Résumé : International audience
Palaeoclimate and sea-level studies commonly rely on interpretations based on depth. The location and quantity of core recovered during a drilling expedition has direct implications for subsequent applications of core measurements. A key objective of Integrated Ocean Drilling Program (IODP) Expedition 3 10 is to establish the course of postglacial sea-level rise for Tahiti in the South Pacific, for which assigning the correct depth to recovered core is fundamental. By convention, core is placed at the top of the core barrel run from which it was collected. Unless core recovery is 100%, this results in depth errors that are inversely proportional to the recovery. The difficulties of locating core are compounded for the Tahiti boreholes, where primary cavities in the carbonate reef successions are frequently present. Only through the integration of core with continuous geophysical measurements of the borehole can accurate depth positioning be achieved. High-resolution optical and acoustic images of the borehole wall allow effective visual correlation of the core and logging datasets. The final integrated depths form the underlying framework for all subsequent scientific analyses of recovered core employing evaluations that rely on depth. Furthermore, the integration process allows true core recoveries to be accurately estimated.
ISSN: 0016-7649

hal-00411915
https://hal.archives-ouvertes.fr/hal-00411915
DOI : 10.1144/0016-76492007-041

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Heletz sandstone (Israel) reactivity is studied by means of CO2-rich brine percolation experiments and modeling. Experiments are performed at in situ temperature and pressure conditions with two distinctly different injection flow rates and for two different brine compositions: the genuine Heletz brine and a similar brine but in equilibrium with gypsum. The Heletz sandstone is composed of quartz, dolomite, ankerite, K-feldspar, clay minerals and minor amounts of gypsum and pyrite. The main reaction is the dissolution of the carbonates which is fastest for the highest flow rate injection and for the genuine Heletz brine. Permeability increases during the five percolation experiments, regardless of flow rate and brine type. This increase in permeability is associated to a decrease in porosity during the gypsum-equilibrated brine experiments due to gypsum precipitation. The precipitation of secondary minerals (kaolinite, muscovite and smectite) is mainly controlled by the dissolution of K-feldspar and largest at low flow rate injection, indicating that these precipitation processes are diffusion-controlled and localized in immobile zones where favorable chemical micro-environments exist. These processes are quantified by means of a reactive transport model. These results indicated that the CO2 injection at the Heletz site should trigger both permeability increase in interface between brine and CO2, which may extend over a large extension and where mixing processes are very active, especially near the well under intermittent injection conditions.
ISSN: 1750-5836

hal-01356329
https://hal.archives-ouvertes.fr/hal-01356329
DOI : 10.1016/j.ijggc.2015.10.023

Résumé : Le mérou géant, Epinephelus itajara, espèce en danger critique d’extinction au niveau mondial, est présent dans les eaux turbides et saumâtres de la Guyane française où l’espèce est exploitée par une pêcherie côtière. Dans la partie est du plateau continental guyanais, les mérous géants se localisent autour de tous les sites rocheux marins où ils se répartissent en fonction de la profondeur et du faciès (éboulis ou tombant). Les analyses des isotopes stables du carbone et de l’azote suggèrent qu’environ 30 % des mérous géants < 115 cm présents sur ces sites rocheux, proviendraient des mangroves alentours. Les analyses de contenus stomacaux révèlent un changement ontogénétique du régime alimentaire. Les petits individus (< 90 cm) s’alimentent principalement de Crustacés puis intègrent progressivement les poissons à leur alimentation jusqu’à devenir essentiellement piscivores au-delà de 140 cm. La population de Guyane est principalement composée d’individus juvéniles : seulement 8,5 % des individus capturés en Guyane a plus de 6 ans. Ces jeunes mérous sont très territoriaux durant les 4-5 premières années de leur vie puis ne sont plus retrouvés sur les sites rocheux. Le devenir de ces juvéniles est incertain, soit ils sont pêchés, soit ils migrent vers d’autres sites ou vers les agrégations de reproduction. Cependant, les mérous géants ne semblent pas se reproduire en Guyane. Il est possible que les conditions environnementales (forte turbidité et température) ne favorisent pas le développement gonadique, ce qui engendrerait une omission totale de reproduction. Le suivi par tags satellite suggère que les mérous géants migrent dans le sens des courants marins vers Trinidad-et-Tobago, potentiellement pour la reproduction. Aucun mouvement vers le Brésil n’a été mis en évidence bien que les stocks de mérous géants du Brésil et de Guyane semblent liés. En effet, ces deux stocks évoluent conjointement avec un déclin des populations au début des années 90. Le maintien de la population de mérou géant en Guyane se ferait grâce à l’apport de larves des sites d’agrégation du Brésil par le courant marin. La mortalité totale des mérous géants (0,65) est aussi élevée au sein de la réserve marine ainsi que sur les sites de pêche. Cela suggère que l’interdiction de pêche à la réserve n’est pas respectée et que les grands individus quittent la réserve pour des sites plus spacieux. En supposant que la population de mérous géants adultes a été réduite à cause de la pêche, une protection régionale des individus > 150 cm doit être instaurée afin de régénérer le stock d’individus matures. Il semble nécessaire de développer une politique de gestion internationale de l’espèce, surtout entre la Guyane et le Brésil, afin de conserver les populations de mérous géants d’Amérique du Sud.
The critically endangered Goliath Grouper, Epinephelus itajara, is found in the turbid and brackish waters of French Guiana, where the species is subject to a coastal fishery. Goliath Grouper populations inhabit all rocky habitats and exhibit increasing abundance with depth. Around 30% of individuals less than 115 cm may derive from the abundant mangrove habitat along the french Guiana coast. There is a ontogenetic shift of the diet, primarily crustacivorous, individuals >140 cm become piscivorous. The Goliath Grouper population in French Guiana is composed primarily og juvelines. The fate of the juvelines is unknonw, some may be caught in the fishery, others may move to other habitat. No evidence of spawning or gonadal readiness was found in french Guiana. it is possible that environmental conditions (high turbidity and temperature) are not conducive to reproductive activity. Goliath Grouper may migrate down current from French Guiana to Trinidad and Tobago or further. No movement of Goliath Grouper was found against the current toward Brazil. French Guiana juveniles may be derived from spawns occuring off Brazil. Calculated total mortality of Goliath Grouper off French Guiana is high (0.65) in both fished and protected areas suggesting that illegal fishing is occuring within the protected area, or that emigration rates are high. Assuming that the adult population of Goliath Grouper in French Guiana has been reduced due to fishing, protection of spawning-size adults (larger than about 150 cm TL) should be instated.

http://www.theses.fr/2014AGUY0721/document

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Cyanobacteria are ubiquitous microorganisms considered as important contributors to the formation of Earth's atmosphere and nitrogen fixation. However, they are also frequently associated with toxic blooms. Indeed, the wide range of hepatotoxins, neurotoxins and dermatotoxins synthesized by these bacteria is a growing environmental and public health concern. This paper provides a state of the art on the occurrence and management of harmful cyanobacterial blooms in surface and drinking water, including economic impacts and research needs. Cyanobacterial blooms usually occur according to a combination of environmental factors e.g., nutrient concentration, water temperature, light intensity, salinity, water movement, stagnation and residence time, as well as several other variables. These environmental variables, in turn, have promoted the evolution and biosynthesis of strain-specific, gene-controlled metabolites (cyanotoxins) that are often harmful to aquatic and terrestrial life, including humans. Cyanotoxins are primarily produced intracellularly during the exponential growth phase. Release of toxins into water can occur during cell death or senescence but can also be due to evolutionary-derived or environmentally-mediated circumstances such as allelopathy or relatively sudden nutrient limitation. Consequently, when cyanobacterial blooms occur in drinking water resources, treatment has to remove both cyanobacteria (avoiding cell lysis and subsequent toxin release) and aqueous cyanotoxins previously released. Cells are usually removed with limited lysis by physical processes such as clarification or membrane filtration. However, aqueous toxins are usually removed by both physical retention, through adsorption on activated carbon or reverse osmosis, and chemical oxidation, through ozonation or chlorination. While the efficient oxidation of the more common cyanotoxins (microcystin, cylindrospermopsin, anatoxin and saxitoxin) has been extensively reported, the chemical and toxicological characterization of their by-products requires further investigation. In addition, future research should also investigate the removal of poorly considered cyanotoxins (β-methylamino-alanine, lyngbyatoxin or aplysiatoxin) as well as the economic impact of blooms.
Environment International

hal-00875835
https://hal-univ-rennes1.archives-ouvertes.fr/hal-00875835
https://hal-univ-rennes1.archives-ouvertes.fr/hal-00875835/document
DOI : 10.1016/j.envint.2013.06.013
PUBMED : 23892224

Éditeur(s) : HAL CCSD Wiley
Résumé :  
Positive aboveground biomass trends have been reported from old-growth forests across the Amazon basin and hypothesized to reflect a large-scale response to exterior forcing. The result could, however, be an artefact due to a sampling bias induced by the nature of forest growth dynamics. Here, we characterize statistically the disturbance process in Amazon old-growth forests as recorded in 135 forest plots of the RAINFOR network up to 2006, and other independent research programmes, and explore the consequences of sampling artefacts using a data-based stochastic simulator. Over the observed range of annual aboveground biomass losses, standard statistical tests show that the distribution of biomass losses through mortality follow an exponential or near-identical Weibull probability distribution and not a power law as assumed by others. The simulator was parameterized using both an exponential disturbance probability distribution as well as a mixed exponential-power law distribution to account for potential large-scale blowdown events. In both cases, sampling biases turn out to be too small to explain the gains detected by the extended RAINFOR plot network. This result lends further support to the notion that currently observed biomass gains for intact forests across the Amazon are actually occurring over large scales at the current time, presumably as a response to climate change.
ISSN: 1354-1013

hal-01032162
https://hal.archives-ouvertes.fr/hal-01032162
DOI : 10.1111/j.1365-2486.2009.01891.x

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Timétrine massif exposed west of the Pan-African suture zone in northeastern Mali belongs to the passive margin of the West African craton facing to the east intra-oceanic arc assemblages and 730 Ma old pre-collisional calc-alkaline plutons. The Timétrine lithologic succession includes from the base to the top Mesoproterozoic cratonic to passive margin formations overlain by deep-sea Fe-Mg schists. Submarine metabasalts and two ultramafic massifs of serpentinized mantle peridotites are inserted as olistoliths towards the top whereas turbidites of continental origin represent the younger unit. Field and petrological data have revealed a distinct metasedimentary sequence attached to the serpentinized peridotites. It essentially consists of impure carbonates, Fe jaspers and polymictic breccias containing altered blocks of mantle peridotites, most rocks being enriched in detrital chromite. This association is interpreted as reworked chemical and detrital sediments derived from the alteration of mafic-ultramafic rocks. It is argued that mantle exhumation above sea floor took place during the Neoproterozoic rifting and crustal thinning period under possible tropical conditions, as suggested by the large volume of silicified serpentinites. In spite of greenschist facies metamorphic overprint characterized by widespread Fe-rich blue amphiboles that are not diagnostic of high-pressure conditions, it is possible to reconstruct a former ocean-continent transition similar to that evidenced for the Mesozoic period, followed by the deposition of syn-to post rift terrigeneous turbidites roughly coeval with ocean spreading some time before 800 Ma. It is concluded that the serpentinite massifs were tectonically emplaced first in an extensional setting, then incorporated within deep-sea sediments as olistoliths and finally transported westward during late Neoproterozoic collisional tectonics onto the West African craton.
ISSN: 0899-5362

hal-00985586
https://hal.archives-ouvertes.fr/hal-00985586
DOI : 10.1016/j.jafrearsci.2013.11.004

Éditeur(s) : HAL CCSD
Résumé :  
In tropical rainforests, the origin of the interspecific variability in trunk CO2 efflux (Et) and of seasonal variations in Et have not yet been explained. We conducted a study to test which biotic and abiotic determinants would contribute to these variations. Et and a set of wood anatomical and functional characteristics were measured on trees in two habitats (Terra Firme forest vs. seasonal flooded forest) in a Neotropical rainforest over a 18-months' period including a range of climatic and soil water conditions. The large variability in Et (0.33 to 3.15 μmol CO2 m-2 s-1 in Terra Firme forest) was associated with tree diameter and growth respiration (Eg), although maintenance respiration (Em) was the main component of Et. Neither wood properties nor sapflow density were correlated with trunk CO2 efflux. The large seasonal variations in Et were correlated with diameter growth and surface soil water content (SWC). These data underlined the absence of clearly identified biotic determinants, beside growth, to explain the interspecific variability in Et. We emphasized the fast response of growth and maintenance respiration processes to seasonal variations in SWC that potentially has consequences on the carbon cycle in the ecosystem under upcoming climatic changes.
23. New Phytologist Symposium. Carbon cycling in tropical ecosystems
Guangzhou, China

hal-01032199
https://hal.archives-ouvertes.fr/hal-01032199

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The barrier reef tract of New Caledonia is the second largest in the world enclosing lagoons of variable width. The Late Quaternary evolution of these barrier reefs and lagoons is poorly known. A recent high resolution seismic and multibeam bathymetry survey was carried out in the south-western lagoon from shoreline to open ocean across the barrier reef pass systems to perform sequence stratigraphy and to better understand the Quaternary evolution of the lagoon. Two depositional sequences bounded by type-1 erosional surfaces can be identified. The bounding surfaces delineate the bottom of two generations of incised valleys. System tracts comprising a complete succession of regressive, lowstand, transgressive and highstand tracts were observed only in the upper sequence. Chronostratigraphic and sedimentological interpretations of the seismic data are based on correlations with the chronology defined in the nearby cores drilled through the reefs and in the gravity cores previously recovered in the inner lagoon. Interpretation of seismic data is also carried out on the basis of correlation with multibeam bathymetric data. Our results indicate that the history of the New Caledonian lagoon probably does not exceed 200ka marked by two or three brief episodes each of immersion of about ten thousand years. The bathymetric data reveal that during successive low sea level stands, the lagoon was dependent upon erosional fluvial networks. The deep fluvial valleys were connected to the continental slope through the passes. Seismic records reveal that upstream palaeo-channels are not connected to the modern coastal rivers. In contrast, many aggrading deposits, including numerous stacking channels, and extending across the proximal part of the outer lagoon, can be identified. Examination of drainage network morphology suggests a progressive tilt of the outer lagoon. Such evolution reveals that the Nouméa lagoon which is one of the widest in the world is an exceptional modern example of a rimmed shelf providing data to analyze the past counterparts.
ISSN: 0031-0182

insu-00338953
https://hal-insu.archives-ouvertes.fr/insu-00338953
DOI : 10.1016/j.palaeo.2008.08.012

Éditeur(s) : HAL CCSD
Résumé : International audience
Sub-continental lithospheric mantle rocks are exhumed at the foot of magma-poor distal passive margins as aresponse to extreme stretching of the continental crust during plate separation. Remnants of the Northern Iberianpaleo-passive margin are now exposed in the North-Pyrenean Zone (NPZ) and represent field analogues to studythe processes of continental crust thinning and subcontinental mantle exhumation. The NPZ results from theinversion of basins opened between the Iberia and Europa plates during Albo-Cenomanian times. In the westernNPZ, the ‘Chaînons Béarnais’ ranges display a fold-and-thrust structure involving the Mesozoic sedimentarycover, decoupled from its continental basement and associated with peridotite bodies in tectonic contact withPalaeozoic basement lenses of small size. Continental extension developed under hot thermal conditions, asdemonstrated by the syn-metamorphic Cretaceous ductile deformation affecting both the crustal basement and theallochthonous Mesozoic cover.In this study, we present structural and geochemical data providing constraints to reconstruct the evolution ofthe northern Iberia paleo-margin. Field work confirms that the pre-rift Mesozoic cover is intimately associatedto mantle rocks and to thin tectonic lenses of crustal basement. It also shows that the pre-rift cover was detachedfrom its bedrock at the Keuper evaporites level and was welded to mantle rocks during their exhumation atthe foot of the hyper-extended margin. The crust/mantle detachment fault is a major shear zone characterizedby anastomosed shear bands defining a plurimetric phacoidal fabric at the top of the serpentinized mantle. Thedetachment is marked by a layer of metasomatic rocks, locally 20 meters thick, made of talc-chlorite-pyrite-richrocks that developped under greenschist facies conditions. Raman Spectroscopy on Carbonaceous Materials(RSCM), performed on the Mesozoic cover reveal that the entire sedimentary pile underwent temperatures rangingbetween 200C and 480C.We show that: (i) at the site of mantle rocks exhumation, the boudinaged pre-rift sediments have undergone drasticsyn-metamorphic thinning with the genesis of a S0/S1 foliation and, (ii) the Paleozoic basement has been ductilelydeformed, into thin tectonic lenses that remained welded to the exhumed mantle rocks. Therefore the overallcrustal rheology appears dominated by shallow levels having a ductile behavior. This rheology is related to thepresence of a thick pre- and syn-rift decoupled cover acting as an efficient thermal blanket. This new geologicaldata set highlights important characteristics of ductile-type hyper-extended passive margin that cannot be obtainedfrom the study of seismic lines. Finally, we stress that studying field analogues represents a major tool to betterunderstand the mechanisms of extreme crustal thinning associated with mantle exhumation and their structuralinheritance during tectonic inversion.
Geophysical Research Abstracts
Vienne, Austria

insu-01510103
https://hal-insu.archives-ouvertes.fr/insu-01510103

Éditeur(s) : HAL CCSD Nature Publishing Group
Résumé : International audience
Iron is an essential micronutrient involved in many biological processes and is often limiting for primary production in large regions of the World Ocean. Metagenomic and physiological studies have identified clades or ecotypes of marine phytoplankton that are specialized in iron depleted ecological niches. Although less studied, eukaryotic picophytoplankton does contribute significantly to primary production and carbon transfer to higher trophic levels. In particular, metagenomic studies of the green picoalga Ostreococcus have revealed the occurrence of two main clades distributed along coast-offshore gradients, suggesting niche partitioning in different nutrient regimes. Here, we present a study of the response to iron limitation of four Ostreococcus strains isolated from contrasted environments. Whereas the strains isolated in nutrient-rich waters showed high iron requirements, the oceanic strains could cope with lower iron concentrations. The RCC802 strain, in particular, was able to maintain high growth rate at low iron levels. Together physiological and transcriptomic data indicate that the competitiveness of RCC802 under iron limitation is related to a lowering of iron needs though a reduction of the photosynthetic machinery and of protein content, rather than to cell size reduction. Our results overall suggest that iron is one of the factors driving the differentiation of physiologically specialized Ostreococcus strains in the ocean.
ISSN: 2045-2322

Droits : http://creativecommons.org/licenses/by/
hal-01502140
http://hal.upmc.fr/hal-01502140
http://hal.upmc.fr/hal-01502140/document
http://hal.upmc.fr/hal-01502140/file/acclimation.pdf
DOI : 10.1038/s41598-017-00216-6

Éditeur(s) : HAL CCSD Société géologique de France
Résumé : The Maguelone shore extends along the northern coast of the Gulf of Lions margin, West of the Rhone delta and East of some high gradient coastal streams that have been providing most of the elastic sediments to the Gulf of Lions margin since the early Miocene. This 10 km wide area comprises an onshore small coastal watershed (15 km long) in low-lying carbonate hills, kilometer wide marshes, sandy beach and shoreface featuring local low sedimentation. Deposit architecture in such a coastal zone records dynamics of incised valley fill under the influence of rivers and wave/current hydrodynamics in a microtidal environment during an eustatic cycle.;A detailed analysis of about 250 km of very high resolution seismic profiles, tens of cores and outcrops data revealed the evolution of the Maguelone coastal system from Late-Quaternary to present-day. It highlighted also dominant denudation processes in the upstream catchments associated to the formation of incised valley seaward during Quaternary. Combination of this inherited morphology together with hydrodynamics controlled the lagoonal environment evolution since the last transgression. In particular, the Maguelone shore is characterized by the formation of built-over-rias lagoonal systems and records an evolution from partially protected lagoon to isolated lagoon environment. These two stages of lagoon evolution correspond to distinct deposit environments. Correlation of fauna contents with deposit geometry improves lagoonal environment models.
EISSN: 1777-5817

hal-00486370
https://hal.archives-ouvertes.fr/hal-00486370
DOI : 10.2113/gssgfbull.181.2.211

Éditeur(s) : HAL CCSD Society of Exploration Geophysicists
Résumé : Read More: http://library.seg.org/doi/10.1190/geo2015-0411.1
International audience
Understanding the role of the unsaturated zone in aquifer recharge and contaminant attenuation processes is a major challenge for the protection and management of karstic water resources. We present the potential of the magnetic resonance soundings (MRS) geophysical method for characterizing the vadose zone of karst aquifers composed of epikarst and infiltration layers. To investigate the hydraulic functioning of the Durzon karst system located on the Larzac plateau (southern France), we used the MRS method at 16 sites. The MRS results have been compared with available geologic information and to core water content measurements. The remarkable spatial variability of the MRS response observed in the study area makes it possible to determine ranges of water storage properties in relation to the lithology of the investigated carbonate formations (dolomite, marly, and siliceous limestone). All soundings found either constant or increasing MRS water content with depth, which demonstrates that the infiltration zone might be the major water storage entity for permanent water storage, with important consequences for recharge quality and quantity. These results show the feasibility and potential of the MRS method for the characterization of the karst unsaturated zone and for understanding the vertical distribution of water content, which impacts the overall functioning of karst systems.Read More: http://library.seg.org/doi/10.1190/geo2015-0411.1
ISSN: 0016-8033

hal-01412654
https://hal.archives-ouvertes.fr/hal-01412654
https://hal.archives-ouvertes.fr/hal-01412654/document
https://hal.archives-ouvertes.fr/hal-01412654/file/mazilli2016.pdf
DOI : 10.1190/GEO2015-0411.1

Éditeur(s) : HAL CCSD
Résumé : International audience
Tin mineralization in Achmmach deposit (NE of Moroccan Central Massif) is associated with tourmaline-rich alteration halos and faults, within N70 shear zones, hosted in sandstones and metapelites of the Upper Visean-Namurian. Such deposits were reported as late-Variscan in age and related to the emplacement of late orogenic granite not outcropping in the studied area.From field constraints, it appears that the late Variscan phase is marked by a transition from transpression to extension with conditions of deformation evolving from ductile to brittle environments. During the transpressive phase (horizontal shortening direction roughly trending E-W), pervasive tourmaline is deposited under the form of metasomatic halos around fractures in the upper levels relative to the deep batholith. This hydrothermal activity is coeval with ductile shear zones within a large corridors trending N70. Tourmaline-rich alteration appears as a hardening stage contributing to the modification of the tectonic style of rocks. Thereafter, a strong brecciation occurs in response of re-using and re-opening of the strike-slip structure. The result is (1) the formation of dextral (N070, N020) and sinistral (N120) shears, and (2) the circulation of fluids within early tourmalinites and formation of tourmaline-rich breccia. Subsequently, during the late orogenic extensional phase, tourmalinite breccias reopened as normal faults acting as overpressure fluid pathways for developing other breccias and veins. Such event is marked by deposition of tin mineralization i.e., cassiterite followed by sulphides, and then fluorite and carbonates at the end.From analysis of the shear-zone structure and superimposition of tourmalines and tin mineralization in the same structures, it is possible to suggest a structural control continuum. Such control is well expressed during metasomatism and deposition of hydrothermal tourmaline under the transpressive phase. Thereafter, under the extensive phase allowing open-space, tin-mineralization were trapped.This study has been supported by AI MA/09/210
24ème RST
Pau, France

insu-01546927
https://hal-insu.archives-ouvertes.fr/insu-01546927

Éditeur(s) : HAL CCSD Elsevier
Résumé : We present comparative field studies in folded areas (Southern France. Moroccan Western Atlas and Abruzzo, Italy) giving new insights into fracture distribution within folded rocks of the shallow brittle crust. We show that the curvature in folds formed in brittle mechanical units is usually accommodated by multiple "dip-domain boundaries" (appearing as curvature discontinuities at fold scale) corresponding to relatively narrow and dense fracture zones, striking parallel or slightly oblique to the fold axis. They separate "dip-domains" where curvature is absent or moderate. It is shown that the dip-domain boundaries (which are obvious in the case of kink folds or box-fold anticlines) are currently present as multiple subtle hinges even when the curvature appears continuous at first sight. The nature of dip-domain boundaries is studied, they often cut through the whole thickness of the mechanical units Their internal structure varies, and a non-exhaustive typology is proposed For each type, an interpretative kinematic scenario shows how the dip-domain boundaries could initiate and develop. We suggest two kinds of origins (1) they could correspond to the reactivation of inherited, along-strike fracture zones (opening-mode fracture concentrations such as big joints, fracture corridors. Inherited faults, etc), (2) they could be created as mechanical instabilities during the fold formation (syn-folding origin), in particular through small reverse faults. In both cases, early zones of weakness localize the dip-domain boundaries, and control the Increase in curvature in association with increasing fracture density within the boundary. Because they represent well-defined vertically and axially persistent sub-seismic fracture zones generally limited to the thickness of the folded unit, dip-domain boundaries could enhance the axial permeability of folded and fractured reservoirs.
ISSN: 0191-8141

hal-00512651
https://hal.archives-ouvertes.fr/hal-00512651
DOI : 10.1016/j.jsg.2010.03.002