Natural hydraulic fractures in the Wessex Basin, SW England: widespread distribution, composition and history

International audienceBedding-parallel veins of fibrous calcite ('beef') are historical in the Wessex Basin. The veins are common in Mesozoic mudstones and shales, especially of Liassic to Mid-Cretaceous ages. Cone-in-cone structures, which consist of multiple nested cones, are also well developed within the 'beef'. To investigate the distribution and the context of formation of 'beef' in the basin, we have made several field studies and analysed numerous samples. The veins are widespread vertically and horizontally in the sedimentary sequence, but they are especially common near or within potential source rocks for petroleum or near major tectonic faults. The internal structures of some 'beef' veins have revealed that they formed during Late Cretaceous to Tertiary compressional inversion of the basin. The typical composition for 'beef' is of calcite, with some pyrite and fragments of shale. However, inclusions or patches of hydrocarbons (liquid or solid) occur within calcite crystals or between fibres, respectively. According to some previous studies, as well as ours, 'beef' veins of the Wessex Basin represent natural hydraulic fractures, which formed as a result of fluid overpressure. This may have resulted in part from chemical compaction of petroleum source rocks, during Late Cretaceous to Tertiary times. Indeed, source rocks at outcrop in the Wessex Basin could be more mature than previously thought and the 'beef' veins may be good markers of maturation

Cenozoic reactivation of the Great Glen Fault, Scotland: additional evidence and possible causes

International audienceThe Great Glen Fault trends NNE-SSW across northern Scotland. According to previous studies, the Great Glen Fault developed as a left-lateral strike-slip fault during the Caledonian Orogeny (Ordovician to Early Devonian). However, it then reactivated right-laterally in the Tertiary. We discuss additional evidence for this later phase. At Eathie and Shandwick, minor folds and faults in fossiliferous Jurassic marine strata indicate post-depositional right-lateral slip. In Jurassic shale, we have found bedding-parallel calcite veins ('beef' and 'cone-in-cone') that may provide evidence for overpressure development and maturation of organic matter at significant depth. Thus, the Jurassic strata at Eathie and Shandwick accumulated deeper offshore in the Moray Firth and were subject to Cenozoic exhumation during right-lateral displacement along the Great Glen Fault, as suggested by previous researchers. Differential sea-floor spreading along the NE Atlantic ridge system generated left-lateral transpressional displacements along the Faroe Fracture Zone from the Early Eocene to the Late Oligocene (c. 47-26 Ma), a period of uplift and exhumation in Scotland. We suggest that such differential spreading was responsible for reactivation of the Great Glen Fault. Indeed, leftlateral slip along the Faroe Fracture Zone is compatible with right-lateral reactivation of the Great Glen Fault

Physical modelling of chemical compaction, overpressure development, hydraulic fracturing and thrust detachments in organic-rich source rock

International audienceGeological evidence for overpressure is common worldwide, especially in petroleum-rich sedimentary basins. As a result of an increasing emphasis on unconventional resources, new data are becoming available for source rocks. Abnormally high values of pore fluid pressure are especially common within mature source rock, probably as a result of chemical compaction and increases in volume during hydrocarbon generation. To investigate processes of chemical compaction, overpressure development and hydraulic fracturing, we have developed new techniques of physical modelling in a closed system. During the early stages of our work, we built and deformed models in a small rectangular box (40 40 10 cm), which rested on an electric flatbed heater; but more recently, in order to accommodate large amounts of horizontal shortening, we used a wider box (77 75 10 cm). Models consisted of horizontal layers of two materials: (1) a mixture of equal initial volumes of silica powder and beeswax micro-spheres, representing source rock, and (2) pure silica powder, representing overburden. By submerging these materials in water, we avoided the high surface tensions, which otherwise develop within pores containing both air and liquids. Also we were able to measure pore fluid pressure in a model well. During heating, the basal temperature of the model surpassed the melting point of beeswax (w62 C), reaching a maximum of 90 C. To investigate tectonic contexts of compression or extension, we used a piston to apply horizontal displacements. In experiments where the piston was static, rapid melting led to vertical compaction of the source layer, under the weight of overburden, and to high fluid overpressure (lithostatic or greater). Crosssections of the models, after cooling, revealed that molten wax had migrated through pore space and into open hydraulic fractures (sills). Most of these sills were horizontal and their roofs bulged upwards, as far as the free surface, presumably in response to internal overpressure and loss of strength of the mixture.We also found that sills were less numerous towards the sides of the box, presumably as a result of boundary effects. In other experiments, in which the piston moved inward, causing compression of the model, sills also formed. However, these were thicker than in static models and some of them were subject to folding or faulting. For experiments, in which we imposed some horizontal shortening, before the wax had started to melt, fore-thrusts and back-thrusts developed across all of the layers near the piston, producing a high-angle prism. In contrast, as soon as the wax melted, overpressure developed within the source layer and a basal detachment appeared beneath it. As a result, thin-skinned thrusts propagated further into the model, producing a low-angle prism. In some experiments, bodies of wax formed imbricate zones within the source layer. Thus, in these experiments, it was the transformation, from solid wax to liquid wax, which led to chemical compaction, overpressure development and hydraulic fracturing, all within a closed system. According to the measurements of overpressure, load transfer was the main mechanism, but volume changes also contributed, producing supra-lithostatic overpressure and therefore tensile failure of the mixture

Surpression de fluides et fracturation de roches mères en différents contextes tectoniques (modélisation analogique et exemples de terrain)

L'étude des surpressions de fluide et de fracturation hydraulique des roches mères peut nous renseigner sur les mécanismes de génération qui en sont à l'origine. Ces dernières années, l'intérêt pour ces phénomènes s'est largement accru, notamment sous l'influence des sociétés pétrolières qui exploitent les ressources non-conventionnelles au cœur des problèmes énergétiques actuels. Dans ce travail de thèse, nous avons choisi deux approches différentes pour l'étude de ces mécanismes : (1) des exemples de cas géologiques naturels, et (2) le développement de la modélisation analogique. Ainsi, nous montrons que ces phénomènes sont très répandus au sein des bassins sédimentaires et que leurs manifestations s'expriment notamment par la génération de veines fibreuses parallèles à la stratification de la roche (beef), mais également par la formation de veines d'hydrocarbures solides (bitume). Nous démontrons également que les surpressions de fluides peuvent profondément changer le style de déformation d'un bassin sédimentaire par la génération de niveaux de décollement localisés au sein même des roches mères. Enfin, à l'aide de la modélisation analogique, nous avons pu identifier les mécanismes à l'origine des surpressions de fluide et de la fracturation hydraulique. En effet, lors de la génération d'hydrocarbures la transformation de solide à liquide de la matière organique conduit à la compaction chimique des sédiments. Par un mécanisme de transfert de charge lors de ce processus, ainsi que par l'accroissement de volume associé, des surpressions de fluides se développent et atteignent des pressions lithostatiques, capables de fracturer hydrauliquement les roches.The study of fluid overpressures and hydraulic fracturing in source rocks can help us to understand the mechanisms, which are responsable for these phenomena. During the last few years, the interest in such processes has highly grown, especially through the influence of petroleum companies, which extract hydrocarbons from unconventional reservoirs. In this work, we have chosen to develop two different approaches for the study of these mechanisms: (1) field studies and (2) physical modelling. Thereby, we show that fluid overpressures and hydraulic fracturing are common in sedimentary basins worldwide. Bedding-parallel fibrous veins (beef) and solid hydrocarbon veins (bitumen) are the resulting structures. We also show that fluid overpressures can highly affect the deformation style in sedimentary basins, especially by causing thrust-detachments within source rocks. By the using of a new physcial modelling technique, we have identified the mechanisms, which are responsible for fluid overpressures and hydraulic fracturing. Indeed, during hydrocarbon generation, the solid organic matter becomes liquid, which leads to chemical compaction of the sediment. By a mechanism of load transfer, fluid overpressures rise to lithostatic values. However, volume changes also contribute, and are able to induce hydraulic fractures in the rocks.RENNES1-Bibl. électronique (352382106) / SudocSudocFranceF

Structural analysis of sulfate vein networks in Gale crater (Mars)

The Curiosity rover's campaign in the Gale crater on Mars provides a large set of close-up images of sedimentary formations outcrops displaying a variety of diagenetic features such as light-toned veins, nodules and raised ridges. Through 2D and 3D analyses of Mastcam images we herein reconstruct the vein network of a sample area and estimated the stress field. Assessment of the spatial distribution of light-toned veins shows that the basin infillings, after burial and consolidation, experienced a sub-vertical compression and lateral extension coupled with fluid overpressure and cracking. Overall, rock failure and light-toned veins formations could have been generated by an overload produced by infilling material within the basin

Исследование ультрадисперсных оксидов меди, полученных плазмодинамическим методом

The synthesis of copper oxides has a great importance due to the fact these materials are widely used in superconductors manufacturing. It’s known that properties of materials in nanodispersed conditions are improved. In this article, an analysis of ultradispersed plasmodynamic synthesis product obtained using coaxial magnetoplasma accelerator with copper electrodes was carried out. The obtained powder was analyzed by X-ray diffractometer Shimadzu XRD 7000 using the temperature consoles Anton Paar TTK450. Using this analysis such phases as copper Cu, copper oxide (I) Cu2O, copper oxide (II) CuO, and copper hydroxide hydrate Cu(OH)[2]•H[2]O were identified in the product. By gradually heating, the powder to the temperature of 800 °С the phase change was observed. The mass of copper oxide increased up to 96% and copper hydroxide hydrate

Typologie des formes d’humus forestières (sous climats tempérés)

National audienceLe présent chapitre actualise la typologie des formes d'humus forestières dans le cadre du Référentiel Pédologique 2008. Les horizons de référence O et A sont définis sur la base de caractères directement observables sur le terrain, avec une liste de qualificatifs permettant de décrire toutes les variantes possibles des formes d'humus forestières présentes en climat tempéré. Des clés d'identification sont fournies pour les formes d'humus aérées et hydromorphes, ainsi que des tableaux synoptiques

Autour du fonds Poinssot

Julien Poinssot (1844-1900), Louis Poinssot (1879-1967) et Claude Poinssot (1928-2002), archéologues de père en fils, ont été, à des titres divers, des acteurs et des témoins privilégiés de l’histoire de l’archéologie en Tunisie. Entre les années 1870 et 1990, ils ont réuni un ensemble documentaire exceptionnel et original sur l’histoire de l’Afrique du Nord, de l’Antiquité au XXe siècle. Constitué d’une bibliothèque de plus de 4 500 volumes, de 25 mètres-linéaires d’archives issues de leurs recherches et de celles de leurs confrères – Bernard Roy (1846-1919), Paul Gauckler (1866-1911), Alfred Merlin (1876-1965) – le fonds Poinssot offre aux chercheurs d’aujourd’hui une documentation sans équivalent sur l’archéologie française en Afrique du Nord. Les contributions présentées ici explorent l’activité de trois générations de chercheurs, mus autant par le culte de l’archéologie que par le respect du document. Elles mettent au jour les multiples aspects de l’activité scientifique de cette famille d’archéologues, tout autant que les contraintes intellectuelles, matérielles et économiques qui pesaient sur elle

The First Cellular Models Based on Frataxin Missense Mutations That Reproduce Spontaneously the Defects Associated with Friedreich Ataxia

BACKGROUND:Friedreich ataxia (FRDA), the most common form of recessive ataxia, is due to reduced levels of frataxin, a highly conserved mitochondrial iron-chaperone involved in iron-sulfur cluster (ISC) biogenesis. Most patients are homozygous for a (GAA)(n) expansion within the first intron of the frataxin gene. A few patients, either with typical or atypical clinical presentation, are compound heterozygous for the GAA expansion and a micromutation. METHODOLOGY:We have developed a new strategy to generate murine cellular models for FRDA: cell lines carrying a frataxin conditional allele were used in combination with an EGFP-Cre recombinase to create murine cellular models depleted for endogenous frataxin and expressing missense-mutated human frataxin. We showed that complete absence of murine frataxin in fibroblasts inhibits cell division and leads to cell death. This lethal phenotype was rescued through transgenic expression of human wild type as well as mutant (hFXN(G130V) and hFXN(I154F)) frataxin. Interestingly, cells expressing the mutated frataxin presented a FRDA-like biochemical phenotype. Though both mutations affected mitochondrial ISC enzymes activities and mitochondria ultrastructure, the hFXN(I154F) mutant presented a more severe phenotype with affected cytosolic and nuclear ISC enzyme activities, mitochondrial iron accumulation and an increased sensitivity to oxidative stress. The differential phenotype correlates with disease severity observed in FRDA patients. CONCLUSIONS:These new cellular models, which are the first to spontaneously reproduce all the biochemical phenotypes associated with FRDA, are important tools to gain new insights into the in vivo consequences of pathological missense mutations as well as for large-scale pharmacological screening aimed at compensating frataxin deficiency

Surpression de fluides et fracturation de roches mères en différents contextes tectoniques : modélisation analogique et exemples de terrain

The study of fluid overpressures and hydraulic fracturing in source rocks can help us to understand the mechanisms, which are responsable for these phenomena. During the last few years, the interest in such processes has highly grown, especially through the influence of petroleum companies, which extract hydrocarbons from unconventional reservoirs. In this work, we have chosen to develop two different approaches for the study of these mechanisms: (1) field studies and (2) physical modelling. Thereby, we show that fluid overpressures and hydraulic fracturing are common in sedimentary basins worldwide. Bedding-parallel fibrous veins (beef) and solid hydrocarbon veins (bitumen) are the resulting structures. We also show that fluid overpressures can highly affect the deformation style in sedimentary basins, especially by causing thrust-detachments within source rocks. By the using of a new physcial modelling technique, we have identified the mechanisms, which are responsible for fluid overpressures and hydraulic fracturing. Indeed, during hydrocarbon generation, the solid organic matter becomes liquid, which leads to chemical compaction of the sediment. By a mechanism of load transfer, fluid overpressures rise to lithostatic values. However, volume changes also contribute, and are able to induce hydraulic fractures in the rocks.L'étude des surpressions de fluide et de fracturation hydraulique des roches mères peut nous renseigner sur les mécanismes de génération qui en sont à l'origine. Ces dernières années, l'intérêt pour ces phénomènes s'est largement accru, notamment sous l'influence des sociétés pétrolières qui exploitent les ressources non-conventionnelles au cœur des problèmes énergétiques actuels. Dans ce travail de thèse, nous avons choisi deux approches différentes pour l'étude de ces mécanismes : (1) des exemples de cas géologiques naturels, et (2) le développement de la modélisation analogique. Ainsi, nous montrons que ces phénomènes sont très répandus au sein des bassins sédimentaires et que leurs manifestations s'expriment notamment par la génération de veines fibreuses parallèles à la stratification de la roche (beef), mais également par la formation de veines d'hydrocarbures solides (bitume). Nous démontrons également que les surpressions de fluides peuvent profondément changer le style de déformation d'un bassin sédimentaire par la génération de niveaux de décollement localisés au sein même des roches mères. Enfin, à l'aide de la modélisation analogique, nous avons pu identifier les mécanismes à l'origine des surpressions de fluide et de la fracturation hydraulique. En effet, lors de la génération d'hydrocarbures la transformation de solide à liquide de la matière organique conduit à la compaction chimique des sédiments. Par un mécanisme de transfert de charge lors de ce processus, ainsi que par l'accroissement de volume associé, des surpressions de fluides se développent et atteignent des pressions lithostatiques, capables de fracturer hydrauliquement les roches