Mass mortality or exceptional fossilization? The case of the early and middle Toarcian fossiliferous beds from the Digne-Les-Bains area (southeastern France)

La série sédimentaire d’âge domérien supérieur à toarcien supérieur (de –190 à –180 Ma) dans la Réserve Géologique de Haute-Provence (Sud-Est de la France) a l’intérêt de présenter deux types de gisements fossilifères remarquables. Le premier type, d’âge toarcien inférieur, a la particularité de présenter des restes d’ichtyosaures (dans au moins six sites) en plus de très nombreux autres fossiles. Le deuxième type, d’âge toarcien moyen, est caractérisé par l’abondance et la présence presque exclusive d’ammonites et de nautiles. Des études lithostratigraphiques, biostratigraphiques, paléontologiques, sédimentologiques et géochimiques, ont permis de savoir si ces accumulations résultaient de mortalité en masse ou bien si elles n’étaient dues qu’à des fossilisations exceptionnelles d’organismes à taux de mortalité normal. Les accumulations d’âge toarcien inférieur se sont effectuées, après mortalité normale, par piégeage avec des sédiments terrigènes dans des hémigrabens à la suite de jeu de blocs basculés et pendant une période d’anoxie ou d’hypoxie. Les gisements d’âge toarcien moyen correspondent à des condensations et concentrations fauniques lors de sédimentation carbonatée très réduite en liaison avec une transgression marine de grande ampleur. Diverses conditions, tectoniques locales de rifting, eustatiques régionales liées à l’évolution du domaine liguro-piémontais, océanographiques globales d’anoxie et de crise de production carbonatée, ont toutes joué un rôle dans la genèse des gisements fossilifères. Tout lien avec des extinctions massives, en rapport ou non avec des crises biologiques, est exclu

Mise en évidence d’un Sénonien gypseux sous la série phosphatée du bassin des Ouled Abdoun: Un nouveau point de départ pour l’origine des zones dérangées dans les mines à ciel ouvert de Khouribga, Maroc

In the Ouled Abdoun sedimentary basin (Morocco), the phosphatic series is composed of regular interbedded phosphatic and marly limestone layers. Exploitation of the phosphate in some deposits in this basin collides frequently with problems bound to the existence, in the phosphatic series, of disturbed areas (sterile bodies) qualified as derangements by the mining engineers of the Office Cherifian Phosphate Group (OCP). Their presence in the phosphatic layers causes two kinds of problems: (1) since the whole phosphatic sequence is overlain by a Quaternary cover, we do not know their volume proportion in the phosphatic layers, and therefore the reserves estimations can be wrong (2) they are generally hard, so they complicate the phosphate extraction. Indeed, in an area containing sterile bodies, boring grid may always be tightened and boreholes filled with dynamite. The required borehole tools and use of explosives are time consuming and therefore increase drastically the cost of phosphate extraction. Their localisation would permit the mining engineers to get around them during the exploitation. Several geophysical works have carried out in the achieved in Khouribga area to localize and delimit these sterile bodies. Electric resistitivy was established as a suitable geophysical parameter to map them, but the slowness and difficulty of data collection hinders the application of these geophysical methods to the whose phosphatic deposits area (about 25000 ha). Their application in all the Ouled Abdoun basin requires the comprehension of the origin of the sterile bodies, in order to specify their formation process and to predict consequently their spacial distribution in each phosphatic deposit. Our study concerns to sedimentological and diagenetic analysis of disturbed aereas and their immediate vicinity. It made it possible to identify for the first time the existence of an evaporitic series intensely karstified at the top of the Senonian, under the phosphatic series. The senonian karsts are undoubtedly at the origin of the derangements, which are defined as the collapsing phenomena at the base of underground cavities. These bodies have a polyphase structuring and a genesis that is the consequence of on several processes (fracturing, infiltration, dissolution, collapse). Their installation began from the end of Senonian, and continues up to the Quaternary.[fr] Dans le bassin sédimentaire des Ouled Abdoun (Maroc), la série phosphatée est formée d’une intercalation régulière de niveaux phosphatés et marno-calcaires sur environ 50m de puissance. Localement, cette régularité est perturbée par la présence fréquente de structures communément appelés «dérangements». Il s’agit de masses non stratifiées, stériles, qui perturbent et alourdissent les travaux d’exploitation des couches phosphatées. Les études géophysiques expérimentales, réalisées dans les zones dérangées de la série phosphatée, ont démontré la possibilité de les cartographier sous couvertures à l’échelle décamétrique. Leur généralisation sur toute la superficie du bassin des Ouled Abdoun, nécessite une compréhension du phénomène à l’origine de ces structures. Notre étude concerne l’analyse sédimentologique et diagénétique des zones dérangées et de leur voisinage immédiat. Elle a permis d’identifier pour la première fois l’existence d’une série évaporitique intensément karstifiée au sommet du Sénonien, sous la série phosphatée. Les karsts sénoniens sont incontestablement à l’origine des dérangements ou fontis que l’on défini comme étant des phénomènes de collapses à l’aplomb de cavités souterraines. Ces fontis ont une structuration polyphasée et une genèse au dépend de plusieurs processus (fracturation, infiltration, dissolution, effondrement). Leur mise en place a débuté dès la fin du Sénonien et s’est poursuivie jusqu’au quaternaire

The skeleton of the staghorn coral Acropora millepora: molecular and structural characterization

15 pagesInternational audienceThe scleractinian coral Acropora millepora is one of the most studied species from the Great Barrier Reef. This species has been used to understand evolutionary, immune and developmental processes in cnidarians. It has also been subject of several ecological studies in order to elucidate reef responses to environmental changes such as temperature rise and ocean acidification (OA). In these contexts, several nucleic acid resources were made available. When combined to a recent proteomic analysis of the coral skeletal organic matrix (SOM), they enabled the identification of several skeletal matrix proteins, making A. millepora into an emerging model for biomineralization studies. Here we describe the skeletal microstructure of A. millepora skeleton, together with a functional and biochemical characterization of its occluded SOM that focuses on the protein and saccharidic moieties. The skeletal matrix proteins show a large range of isoelectric points, compositional patterns and signatures. Besides secreted proteins, there are a significant number of proteins with membrane attachment sites such as transmembrane domains and GPI anchors as well as proteins with integrin binding sites. These features show that the skeletal proteins must have strong adhesion properties in order to function in the calcifying space. Moreover this data suggest a molecular connection between the calcifying epithelium and the skeletal tissue during biocalcification. In terms of sugar moieties, the enrichment of the SOM in arabinose is striking, and the monosaccharide composition exhibits the same signature as that of mucus of acroporid corals. Finally, we observe that the interaction of the acetic acid soluble SOM on the morphology of in vitro grown CaCO3 crystals is very pronounced when compared with the calcifying matrices of some mollusks. In light of these results, we wish to commend Acropora millepora as a model for biocalcification studies in scleractinians, from molecular and structural viewpoints

Transfer of hexazinone and glyphosate through undisturbed soil columns in soils under Christmas tree cultivation

International audienceField studies monitoring pesticide pollution in the Morvan region (France) have revealed surface water contamination by some herbicides. The purpose of this study was to investigate in greater detail the transport of two herbicides, used in Christmas tree production in the Morvan, under controlled laboratory conditions. Thus, the leaching of hexazinone (3-cyclohexyl-6-dimethyl-amino-1-methyl-1,3,5-triazine-2,4 (1H,3H) dione) and glyphosate (N-(phosphono-methyl-glycine)) through structured soil columns was studied using one loamy sand and two sandy loams from sites currently under Christmas tree cultivation in the Morvan. The three soils were cultivated sandy brunisol [Sound reference base for soils, D. Baize, M.C. Girard (Coord.), INRA, Versailles, 1998, 322 p] or, according to the FAO [FAO, World reference base for soil resources, ISSS-ISRIC-FAO, FAO, Rome, Italy, 1998], the La Garenne was an arenosol and the two other soils were cambisols. The clay contents of the soils ranged from 86 to 156 g kg -1 and the organic carbon ranged from 98 to 347 g kg -1. After 160 mm of simulated rainfall applied over 12 days, 2-11% of the applied hexazinone was recovered in the leachate. The recovery was much higher than that of glyphosate, which was less than 0.01%. The greater mobility of hexazinone might be related to its much lower adsorption coefficient, Koc , 19-300 l kg -1 , compared with 8.5-10 231 l kg -1 for glyphosate (literature values). Another factor that may explain the higher amounts of hexazinone recovered in the leachates of the three soil columns is its greater persistence (19.7-91 days) relative to that of glyphosate (7.9-14.4 days). The mobility of both herbicides was greater in the soils with higher gravel contents, coarser textures, and lower organic carbon contents. Moreover, glyphosate migration seems negatively correlated not only to soil organic carbon, but also to aluminium and iron contents of soils. This soil column study suggests that at the watershed scale, surface water contamination by hexazinone could occur via the horizontal subsurface flow in upper centimeters of soil. In contrast, the surface water contamination with glyphosate by this mechanism appears unlikely

Estimating the impact of early diagenesis on isotope records in shallow-marine carbonates: A case study from the Urgonian Platform in western Swiss Jura

14 pagesInternational audienceThe poor preservation of sedimentological and geochemical evidence often hampers the identification of subaerial exposure surfaces in carbonate platform successions. Such discontinuities may represent significant time gaps, justifying the quest for diagnostic indications. We investigated a lower Hauterivian to upper Barremian sedimentary succession from Switzerland to highlight the stratigraphic impact of meteoric diagenesis on platform carbonates. Petrographic observations revealed the presence of five generations of calcitic cements. Spot measurement of carbon and oxygen stable isotope compositions (δ13C and δ18O values, respectively) measurements relate them to specific diagenetic environments: selected blocky calcite cements exhibit an enrichment in light isotopes (12C, 16O), indicative of meteoric eogenesis, whereas very negative δ18O values link the last phase of cementation to mesogenesis. Meteoric calcitic cements formed during karstification of the top of the upper Barremian succession; burial diagenetic phases overlap these eogenetic phases, which thus cannot be related to recent telogenesis. We estimated the ratio of early meteoric versus burial cements within the studied succession: its stratigraphic repartition reveals that lower Aptian eogenesis influenced the geochemistry of platform carbonates as deep as 45 m below the exposure surface. In this interval, negative whole-rock δ13C values do not reflect contemporaneous variations of the δ13C curves documented in sections devoid of strong diagenetic impact. Such an impact is a function of the amount of meteoric cement filling pore space as well as of the primary carbon isotope composition of the carbonate sediments and of the meteoric cement. The vertical influence of a karst event is not restricted to the first metres directly below the exposure surface. Although meteoric diagenesis may not significantly alter microfacies, it may strongly perturb isotope systems. Building onto this case study, the application of δ13C chemostratigraphy to platform carbonates can only be performed with great caution and after a careful examination of diagenetic features

Petrography and biosedimentology of the Rosso Ammonitico Veronese (Middle-Upper Jurassic, Northeastern Italy

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The ‘Rosso Ammonitico’ Veronese (Jurassic, Italy): Diagenesis and Microbial Content

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