Les structures de déformation pré-lithification s’enregistrent dans les sédiments meubles. Ces structures sont abondantes dans les domaines sous-glaciaires et marins profonds en raison du développement de surpressions de fluide. A partir de cas d’études choisis dans ces deux environnements, leurs implications sur les (1)reconstructions paléoenvironnementales, leurs impacts sur la (2) morphologie glaciaire, et sur les (3) propriétés pétrophysiques ont pu être définis.(1) L’analyse de ces structures de déformation a permis de mieux contraindre les paléoenvironnements sédimentaires. Ces structures de déformation ont été utilisées comme des «proxy » permettant d’estimer les variations de la vitesse d’écoulement, de l’épaisseur de glace, de la production d’eaux de fonte et de la position de la marge glaciaire.(2) Les séries sédimentaires des vallées tunnels ordoviciennes enregistrent la mise en place de nombreuses structures de déformation liées aux surpressions de fluides. L’analyse de ces structures a permis de proposer un nouveau modèle de creusement des vallées tunnels induits par des pressions de fluides élevées. Ce modèle de creusement, lié aux surpressions de fluide, est favorisé dans les zones d’inter ice-stream. A l’inverse, sous les ice-stream, l’écoulement des eaux de fonte se produit à l’interface glace-substrat et favorise d’autres modèles de formation des vallées tunnels.(3) Les processus de remobilisation sédimentaire ont un impact sur les propriétés pétrophysiques des réservoirs sableux. Les études pétrophysiques menées sur des grès déposés en environnements marins profonds et glaciaires ont permis de mettre en évidence l’impact des surpressions de fluides sur les propriétés réservoirs des sables. Les processus de fluidisation sont capable de créer de bons réservoirs, tandisque les processus d’élutriations ont tendance a réduire la porosité/perméabilité. / Soft-sediment deformation structures (SSDs) occur in unconsolidated sediments, during or shortly after deposition. SSDs are abundant in subglacial and deep-marine environments because of the development of fluid overpressure. Case studies of these two sedimentary environments were used (1) to reconstruct palaeoenvironments from SSDS, and (2) to define the impacts of SSDS on glacial morphologies and (3) petrophysical properties.(1) Analyses of strain regimes, deformation mechanisms, and chronologies in SSDs served to improve palaeoenvironmental reconstructions. These structures were used as proxys to estimate variations of ice flow velocities, ice thickness, meltwater production, and position of the ice margin.(2) The sedimentary series of ordovician tunnel valleys record numerous SSDs induced by fluid overpressure. A new model of tunnel valley formation controlled by the increase of porewater pressure in the bed is proposed. This model of formation occurs in inter-ice stream zones, where meltwater is transferred to the substratum. In ice-stream corridors, meltwater circulates at the ice-bed interface and promotes the formation of tunnel valleys controlled by meltwater processes.(3) Remobilisation processes triggered by the increase of fluid pressure have an impact on the granular framework and on the geometry of reservoirs. Petrophysical studies of subglacial and deep-marine sandstones demonstrated the impact of fluid overpressure on reservoir properties. Processes of fluidisation are responsible for the increase in porosity/permeability, while elutriation processes lead to a decrease in these petrophysical properties.

Ce travail a pour but d’étudier les paramètres physico-chimiques qui contrôlent les transferts de matière ainsi que la formation et l’évolution des argiles dans des failles chevauchantes en environnement sédimentaire. Deux failles chevauchantes pyrénéennes de faible grade métamorphique ont été étudiées : la faille de Millaris (cf. Mont Perdu) et le chevauchement du Pic-de-Port-Vieux (cf. Gavarnie). Dans la faille de Millaris, la déformation s’accompagne principalement d’une dissolution de la calcite matricielle par pression-solution induisant un changement de volume de la roche de 20 à 40%. Le chevauchement du Pic-de-Port-Vieux enregistre des modifications importantes au coeur de la faille mais aussi dans la zone d’endommagement. Dans les calcaires du mur du chevauchement, une mylonitisation est associée à une dissolution partielle des dolomites en présence de fluides ne dépassant pas 320-340°C. Dans les pélites du toit du chevauchement, la dissolution de l’hématite par un fluide réducteur entraine un changement de l’état redox de la roche (confirmé par spectroscopie Mössbauer) et la précipitation de chlorite dans des veines syncinématiques. Des chlorites à zonations chimiques oscillatoires présentes dans certaines veines révèlent, en combinant cartographie chimique à la microsonde, mesures de l’état redox par μXANES et thermométrie, des variations cycliques de température d’au moins 50°C au cours de la cristallisation. Un processus de valves sismiques pourrait donc être associé à la mise en place du chevauchement du Pic de Port Vieux. / This work aims to study the physical and chemical parameters that control the mass-transfer and the clays formation and evolution in sedimentary environment thrust faults. Two Pyrenean thrust faults in low metamorphic grade were studied: the Millaris fault (related to Mont Perdu) and the Pic-de-Port-Vieux thrust (related to Gavarnie). In the Millaris fault, the deformation is accompanied mainly by dissolution of the matrix calcite by pressure-solution which induces a volume change of the rock from 20 to 40%. The Pic-de-Port-Vieux thrust records significant changes in the fault core-zone, but in the damaged zone also. In the footwall limestone, a mylonitisation is associated with a partial dissolution of dolomite in the presence of not exceeding 320-340°C fluids. In the hanging-wall pelites, the hematite dissolution by a reducing fluid causes a redox state change of the rock (confirmed by Mössbauer spectroscopy) and chlorite precipitation in synkinematic veins. Oscillatory zoning pattern chlorites located in some shearing veins revealed, by combining chemical mapping microprobe, redox state measurements with μ-XANES and thermometry, cyclic temperature variations of at least 50°C during the crystallization. A seismic valves process could be associated to Pic-de-Port-Vieux thrusting.

The aim of this work was to study the separate effect of fission fragment damage on the structural integrity and matrix dissolution of uranium dioxide in water. Radiation damage similar to fission damage was created by irradiating bulk undoped and doped ‘SIMFUEL’ disks of UO2, undoped bulk CeO2 and thin films of UO2 and CeO2 with high energy Xe and U ions. The UO2 thin films, with thicknesses in the range of 90 – 150 nm, were deposited onto (001), (110) and (111) orientations of single crystal LSAT (Al10La3O51Sr14Ta7) and YSZ (Yttria-Stabilised Zirconia) substrates. The CeO2 thin films were deposited onto single crystal silicon (001) substrates. Part of the bulk UO2 and CeO2 samples, the thin films of UO2 on the LSAT substrates and the thin films of CeO2 were irradiated with 92 MeV 129Xe23+ ions to a fluence of 4.8 × 1015 ions/cm2 to simulate the damage produced by fission fragments in uranium dioxide nuclear fuel. Part of the bulk UO2 and CeO2 samples and the thin films of UO2 on the YSZ substrates were irradiated with 110 MeV 238U31+ ions to a fluence of 5 × 1010, 5 × 1011 and 5 × 1012 ions/cm2 to study the accumulation of the damage induced. The irradiated and unirradiated samples were studied using scanning electron microscopy (SEM), focused ion beam (FIB), atomic force microscopy (AFM), energy dispersive X-ray (EDX) spectroscopy, electron probe microanalysis (EPMA), X-ray diffraction (XRD), electron backscatter diffraction (EBSD), secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS) techniques to characterise the as-produced samples and assess the effects of the ion irradiations. Dissolution experiments were conducted to assess the effect of the Xe ion irradiation on the dissolution of the thin film UO2 samples on the LSAT substrates and the bulk and thin film CeO2 samples. The solutions obtained from the leaching of the irradiated and unirradiated samples were analysed using inductively coupled plasma mass spectrometry (ICP-MS). XRD studies of the bulk UO2 samples showed that the ion irradiations resulted in an increased lattice parameter, microstrain and decreased crystallite size, as expected. The irradiated UO2 thin films on the LSAT substrates underwent significant microstructural and crystallographic rearrangements. It was shown that by irradiating thin films of UO2 with high energy, high fluence ions, it is possible to produce a structure that is similar to a thin slice through the high burn-up structure. It is expected that the ion irradiation induced chemical mixing of the UO2 films with the substrate elements (La, Sr, Al, Ta). As a result, a material similar to a doped SIMFUEL with induced radiation damage was produced.