Les séries fluvio-éoliennes du "Cutler Group" :: Permien (Utah, USA). Modèle architectural et expression des unités génétiques

National audienceL'essor qu'a connu la stratigraphie séquentielle dans les environnements continentaux a permis de définir des modèles architecturaux pour des séries fluvio-lacustres. Plus récemment, les modèles proposés ont intégré les dépôts éoliens dans les systèmes continentaux côtiers ou lacustres (préservation de l'éolien vs variations de la table d'eau, e.g. Carr-Crabaugh & Kocurek, 1998) ou dans les systèmes continentaux endoréiques (préservation de l'éolien vs climat (e.g. Clemmensen et al., 1998) ou préservation de l'éolien vs accommodation et flux de sédiments, e.g. Bourquin et al., 2009). Cependant, peu de modèles discutent les variations de préservation des dépôts éoliens par rapport aux environnements continentaux associés (fluvial, lac, playa) afin de prédire un modèle architectural des dépôts éoliens (du réservoir au bassin) en fonction du contexte géodynamique. L'objectif de cet exposé est de contraindre l'expression des unités génétiques et de proposer un modèle architectural montrant les variations de préservation des dépôts éoliens en fonction du contexte tectonique, climatique et eustatique. L'étude des séries du Permien inférieur, " Cutler Group ", du " Paradox Basin " (SE Utah), caractérisées par des dépôts fluvio-éoliens (e.g. Condon, 1997), a été réalisée à partir de 5 sections sédimentologiques. Elles sont localisées sur un profil proximal représenté par des dépôts dominés fluvial jusqu'à des dépôts dominés éolien dans le domaine distal (e.g. Mountney & Jagger, 2004). Une étude sédimentologique et stratigraphique détaillée permet de proposer une évolution spatiale et temporelle des environnements de dépôt. Nous avons ainsi mis en évidence (1) les variations d'expression des unités génétiques d'un environnement proximal à un environnement distal en climat semi-aride, (2) plusieurs modèles architecturaux montrant l'évolution verticale depuis un contexte de bassin côtier, à dunes éoliennes faiblement préservées, vers des environnements plus continentaux dominés éolien puis vers des systèmes fluvio-lacustres à faible préservation des dépôts éoliens

Sequence stratigraphy architecture and variations of aeolian deposits preservation in a coastal environment (Permian Cutler Group, SE Utah, USA).

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Diagenesis of Rotliegend sandstone reservoirs (offshore Netherlands): The origin and impact of dolomite cements

The Upper Slochteren Sandstones of the Rotliegend Formation (ROSLU) were studied in offshore Netherlands to evaluate the impact of diagenesis, and more particularly of carbonate diagenesis, on sandstone reservoirs. An integrated study applying petrography, geochemistry (SEM-EDS, XRD, C & O stable isotopes, Sr isotopes), and fluid inclusion measurements, was undertaken. Early phases consisting of silica-bearing minerals (authigenic clays, quartz overgrowths), associated with mechanical compaction plus dissolution of labile grains and/or feldspars, are rare. These are succeeded by a sequence of carbonate cements including non-ferroan dolomite cement, ferroan dolomite cement, and finally siderite. Dolomite cements are associated with fracturing and bleaching of the sandstone. The latest phases consist of another set of authigenic clays, quartz overgrowths, plus sulphate cements. Carbonate pore-filling cements dominate the authigenic phases, representing >50% of the total, of which 80% is dolomite and 20% siderite. Although mechanical compaction is the dominant factor influencing porosity reduction, dolomite cements also have a negative impact on porosity and permeability properties, which do not only depend on sedimentary characteristics. Non-ferroan dolomite precipitated at approximately 100 °C, from highly saline brines migrating downward from the Zechstein. Conversely during the Mid Cimmerian Unconformity (MCU), faulting and fracturing allowed the upward migration of CO2-bearing, acidic and reducing, hotter fluids from the Carboniferous, which includes hydrocarbon source rocks. The mixing of the upward and downward migrating fluids resulted in the precipitation of ferroan dolomites. These results indicate an increased risk of encountering pore-filling dolomite cements close to fault/fractured zones in that area, where carbonate cements may not have been properly assessed. Moreover, this study emphasizes again the importance of a combined analytical approach to gain a deeper understanding of carbonate diagenesis, which should be considered with the same caution as clay diagenesis within clastic-hosted reservoirs

The Late Paleozoic Ice Age in western equatorial Pangea: context for complex interactions among aeolian, alluvial, and shoreface sedimentary environments during the Late Pennsylvanian - early Permian

The evolution of depositional environments in the Late Pennsylvanian-early Permian of the Paradox Basin in Utah, USA, is investigated through detailed sedimentological and high-resolution sequence stratigraphic analyses, in order to define a model of landscape evolution, to discuss the stratigraphic model, and to evaluate the significance of the cyclicity in the paleoclimatic context. Forty high-resolution cycles integrated in 15 minor and two major cycles are observed for the first time throughout the Late Pennsylvanian-early Permian units. A-three steps landscape evolution is recognized. First, the lower Cutler beds, mainly corresponded to a marine environment, with longshore bar, subtidal, tidal, mouth-bar, and with locally fluvial deposits. The upper part of the lower Cutler beds also contains an aeolian dune. Second, the Cedar Mesa Sandstone, corresponded to broad erg deposits which are present across the entire study area, whereas longshore bar, subtidal, mouth-bar, and some fluvial deposits are mainly preserved in the northern part of the studied area. Third, the Organ Rock Formation records decreasing aeolian dune field preservation. To the south, the aeolian environments are interbedded with shoreface deposits, whereas to the north, fluvial deposits with some mouth-bars are more developed. Semi-arid climatic conditions persisted, as indicated by the presence of calcretes. Everywhere in these three steps, root traces within sandstone bars indicate that a soil was once present above the sand dunes. This new model of landscape evolution documents complex interactions between aeolian, fluvial and marine environments within the entire Permian succession of the Paradox Basin. High-resolution stratigraphic analyses allow to discuss the significance of the cyclicity in a scenario that take into consideration sea-level variation in the Late Paleozoic Ice Age paleoclimatic context. This Late Pennsylvanian to early Permian succession reflects both relative sea-level fluctuations and the variability of sediment supply

Effect of LiNbO3 Polarity on the Structural, Optical and Acoustic Properties of Epitaxial ZnO and Mg X Zn1-x O Films

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A novel surface wave transducer based on periodically alternated piezoelectric domains

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Effect of LiNbO3 polarity on the structural, optical and acoustic properties of epitaxial ZnO and Mg x Zn1−x 0 films

International audienceThe effect of LiNbO3 substrate polarization on a charge density at the interface with epitaxial ZnO and MgxZn1−x O films was studied in comparison with ZnO films on dielectric sapphire substrates. An excitonic emission and optical properties such as band gap energy, refraction index, absorption and reflectivity of the ZnO/LiNbO3 structures were studied. The effect of interface charges on the performance of surface acoustic waves with frequency of 2.7 GHz was investigated, as well. The stimulated cavity mode emission was observed due to attained quasi-phase matching conditions for thin ZnO films on sapphire at high laser excitation power. The positive polarization of the ferroelectric substrate induced the band bending of the semiconductor layer, resulting in the accumulation of the negative charges at the ferroelectric/semiconductor interface, which induced an increased reflectivity, a generation of oxygen emission lines in PL spectra under laser excitation, and an increased electromechanical coupling of surface acoustic waves. The negative polarization of the substrate increased atomic peening during sputtering deposition, which induced deteriorated quality of texture and in-plane orientation and increased the residual stresses in ZnO and MgxZn1−x O films

Effect of LiNbO 3 polarity on the structural, optical and acoustic properties of epitaxial ZnO and Mg x Zn 1− x O films

International audienc