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Carte géologique de la France à 1/50 000, feuille Mézidon (n°146).
... Additional dating information comes from correlation of palaeovalley remnants in the chain with foothills fluvial deposits infill. In the foothills, Upper Tortonian to Messinian fluvial deposits (Goguel, 1963) unconformably overly : (i) Mesozoic marine formations near Oloron-Sainte-Marie ( Castéras et al., 1970b), and (ii) Lutetian-Bartonian ( Hourdebaigt et al., 1986) to Burdigalian-Lower Tortonian fluvial deposits further north (Goguel, 1963, ;Fig. 6.20). ...
... Additional dating information comes from correlation of palaeovalley remnants in the chain with foothills fluvial deposits infill. In the foothills, Upper Tortonian to Messinian fluvial deposits (Goguel, 1963) unconformably overly : (i) Mesozoic marine formations near Oloron-Sainte-Marie ( Castéras et al., 1970b), and (ii) Lutetian-Bartonian ( Hourdebaigt et al., 1986) to Burdigalian-Lower Tortonian fluvial deposits further north (Goguel, 1963, ;Fig. 6.20). ...
The late to post-compressive evolution of the Pyrenees is characterized by the formation of a planation surface whose relics are observed today on top of the range. This surface is the subject of an abundant literature, where authors focused on the characterization of its geometry, extent and on the age and mechanism of its formation. The most recent studies showed that the planation surface probably formed at high elevation during the Oligocene - Upper Miocene interval. However, this elevation remains unconstrained.
Our work brings a new qualifying element of the relics of the pyrenean planation surface, which is the description of subtractive weathering profiles developed on these surfaces. Weathering in samples collected below surface remnants was dated by the 40Ar/39Ar method applied to potassic manganese oxides. A Cretaceous age, consistent with the timing of the Pyrenean rifting during which the top of tilted blocks surfaced, and a quaternary age were obtained. The lack of geochronological information between those two ages is interpreted as a result of the reactivation of weathering profiles due to uplift during the post-compressive period. These results show that weathering continued until Quaternary times in the Pyrenees.
The geomorphological analysis of the dismantling of the planation surface, based on Miocene to present-day fluvial incisions analysis in the Western Pyrenees reveals the occurrence of an uplift of the range, which started during middle Miocene times. This uplift is confirmed for present-day by the analysis of a new InSAR dataset. The forcing mechanism of this uplift is discussed ar the African and Eurasian plates-scale. The middle Miocene to present-day uplift of the Pyrenees which provokes the dismantling of the planation surface may be explained by a propagation of the deformation from active plates boundaries toward intraplate areas caused by a reorganization of African - Eurasian plate motion.
... Espitalié, 1967, 1981;Bordes and Labrot, 1967;Bordes, 2002) what has been identified, through macroscopic observation, as Calcédoine de Bord collected at Domme. It is a light gray to pale yellow chalcedony from a tertiary lake environment that was used as a grindstone in the 18th and 19th centuries, and so the outcrop's location is very well known in Dordogne, France (Grandvoinnet, 1870;Labrot and Rey, 1976;Demars, 1982;Capdeville and Rigaud, 1986;Turq, 1992), being located about 10 km from Le Bois de Milhac. Some archaeological pieces with porcelain patina were broken during clandestine excavations, revealing the cross section of the flakes. ...
... The geological samples presented less than 10% of allochems: rare gyrogonites, very rare stem fragments of Charophyta, and very rare gastropods. This paleontological content was typical of a lake environment formation and consistent with previous descriptions of Calcédoine de Bord (Capdeville and Rigaud, 1986). The archaeological samples also presented less than 10% of allochems. ...
Chert alteration in Paleolithic contexts, generally known as “patina” by prehistorians, has long been recognized. Originally, different types of “patina” were defined as “white patina”, “glossy patina”, or “porcelain-like patina”, all of which involved changes in the color and/or roughness of the initial raw material. Alteration degrees are used in many research fields like taphonomy, petroarchaeology or use-wear analysis; however most of these studies are still based on qualitative descriptions using a wide range of terms that bring about confusion. In this paper, we present first the results of an inter-observer's blind-test where color and roughness are described at macroscopic scale. Secondly, we use quantitative methods to compare archaeological and experimental altered silicifications: light spectrometry and confocal microscopy are used to quantify color and roughness. We show here how macroscopic qualitative descriptions could lead to confusion because of the lack of calibration and the number of terms used differently by each one. We demonstrated the efficiency of quantitative methods as light spectrometry and confocal microscopy that will significantly enhance studies of surface alteration in terms of taphonomy, use-wear analyses, and petroarchaeology issues as well as interdisciplinary discussions.
... In addition, the altitude of the transmitter is also inverted. Results were first obtained with a smooth inversion (19 layers for each 1D model) in order to pre-evaluate the Figure 1 Simplified geological map of the study area (modified from Pomerol, 1988). Flight lines are displayed in gray and boreholes are indicated by black triangles. ...
We investigate a novel way to introduce resistivity models deriving from airborne electromagnetic surveys into regional geological modelling. Standard geometrical geological modelling can be strengthened using geophysical data. Here, we propose to extract information contained in a resistivity model in the form of local slopes that constrain the modelling of geological interfaces. The proposed method is illustrated on an airborne electromagnetic survey conducted in the region of Courtenay in France. First, a resistivity contrast corresponding to the clay/chalk interface was interpreted confronting the electromagnetic soundings to boreholes. Slopes were then sampled on this geophysical model and jointly interpolated with the clay/chalk interface documented in boreholes using an implicit 3D potential-field method. In order to evaluate this new joint geophysical–geological model, its accuracy was compared with that of both pure geological and pure geophysical models for various borehole configurations. The proposed joint modelling yields the most accurate clay/chalk interface whatever the number and location of boreholes taken into account for modelling and validation. Compared with standard geological modelling, the approach introduces in between boreholes geometrical information derived from geophysical results. Compared with conventional resistivity interpretation of the geophysical model, it reduces drift effects and honours the boreholes. The method therefore improves what is commonly obtained with geological or geophysical data separately, making it very attractive for robust 3D geological modelling of the subsurface.
... In addition, the altitude of the transmitter is also inverted. Results were first obtained with a smooth inversion (19 layers for each 1D model) in order to pre-evaluate the Figure 1 Simplified geological map of the study area (modified from Pomerol, 1988). Flight lines are displayed in gray and boreholes are indicated by black triangles. ...
Standard geological modelling based on boreholes and geological maps can be strengthened using geophysical data. Constrains such as gravity, magnetic and seismic data have already been used. We propose a novel method combining boreholes and the resistivity model resulting from inversion of airborne time domain electromagnetic data. First, the "geophysical" top of the chalk has been identified in the resistivity model after a detailed crossanalysis of resistivities versus boreholes. Then, we jointly interpolated slopes extracted from this geophysical surface together with the top of the chalk in boreholes. Comparison of uncertainties between this model together with pure geological and geophysical models shows that the joint modelling yields the most accurate top of the chalk. A cross-section, intersecting five boreholes (two used as control boreholes) and displaying each of the three surfaces, highlights the usefulness to take into account "geophysical slopes" when modelling. The proposed joint modelling improves what is commonly obtained with geological or geophysical data. This makes the method very attractive for detailed 3D geological modelling.
While early maps are known from all over the world, the key questions always involve: what exactly do they show? And what spatial extent do they cover? In this context, we recently used 3D‐modelling to re‐examine a carved stone slab datable to the Early Bronze Age (c.2150–1600 BC) that was found at Saint‐Bélec in Brittany. We show that the surface of the slab had been shaped in three dimensions to represent the relief of the surrounding landscape in which it was found, while several engraved motifs on it evoke contemporary structures known archaeologically. We argue that the Saint‐Bélec slab represents an area of c.545 km2 corresponding to the extent of a prehistoric political entity. The carving and subsequent burying of the slab can be linked to the postulated rise and fall of hierarchical societies and raises many wider questions about socio‐economic structures in temperate Europe at that time.
Bathonian from the Grands Causses area (southern France) is characterized by the "Calcaires à stipites" Formation, which is formed by an alternation of limestones representing brackish, costal marshland, or proximal marine environments, with some marls levels rich in organic matter and lignite. Those alternations in facies illustrate a changing environment, ranging from lagoons to emerged areas, as supported by the more or less advanced pedogenetic horizons rich in root-casts. We describe sedimentology of this formation as well as we note and measure some tridactyl and egg-shaped, ovoid marks supposedly of dinosaurian origin. Those marks are located on four sites (Garène, Capellan, Gayrand and Saint-Sulpice) in the valleys of the Dourbie, Jonte and Trévezel rivers. Here we confirm that the tridactyl footprints belong to theropod dinosaurs and we compare them to a database of other Liassic Causses' footprints. Statistical tests and multivariate analyses warrant identification to the ichnotaxon Eubrontes giganteus. These footprints have probably been made while the dinosaur was walking on a substrate covered by water. As for the ovoid marks, several hypotheses can be formulated for their origin: abrasion, pressure figures, or plant-related bioturbation in the substratum during emerged periods, but no element allows us to discriminate a hypothesis among the others. Overall, it seems that theropod dinosaurs were walking on this environment. We also highlight the presence of dense mangrove-like vegetation.
De par leurs magnitudes élevées et leur potentiel tsunamigénique, les séismes qui se produisent en contexte de subduction présentent un risque majeur pour les villes côtières souvent densément peuplées. La compréhension de la géométrie et du fonctionnement des zones de failles associées à ces ruptures sismiques a donc fait l'objet de nombreuses recherches sismologiques et géologiques.L’objectif de cette thèse est centré sur la caractérisation des zones de failles paléo-sismiques traversant des formations ophiolitiques subductées puis exhumées en surface des continent et sur leur comparaison avec les zones sismogéniques actuelles. Elle s’appuie sur une approche multi-échelle faisant intervenir les outils de la géologie structurale, de la pétrographie microstructurale, de la minéralogie, de la géochimie ainsi que les données de la géophysique. Le cas de la Corse alpine, de par la présence de nombreuses pseudotachylytes (étant considérées comme des fossiles de séismes) mafiques et ultramafiques constitue un cas d’étude idéal.La rupture sismique dans la nappe du Cima di Gratera est matérialisée par des réseaux de pseudotachylytes parallèles ou à fort pendages situées de part et d’autre de la discontinuité tectonique séparant les unités ultramafiques et mafiques formant la nappe. Le système de faille est caractérisé par une cinématique vers l’ouest associée à la subduction de la plaque océanique liguro-piémontaise sous la plaque adriatique. Les analyses minéralogiques des microlites présentes dans les pseudotachylytes mafiques indiquent une formation des veines en contexte de pression et température du facies eclogite, correspondant à une profondeur comprise entre 60 et 70 km, soit le début de la zone de sismicité dite de profondeur intermédiaire. La géométrie du système de faille a également pu être comparée à des géométries observées via la géophysique au large du nord-est Japon et à des profondeurs similaires.A également été mis en lumière l’impact de la serpentinisation sur le caractère sismique / asismique des discontinuités tectoniques faisant intervenir des formations mafiques et ultramafiques. En effet, la fusion frictionnelle issue des ruptures sismiques et responsable de la formation des veines de pseudotachylytes n’a été observée que dans le cas où était mis en contact la péridotite fraiche ou faiblement serpentinisée et le métagabbro. Les contacts impliquant la serpentinite et le métagabbro n’en présentent jamais et peuvent donc être considérés comme asismiques. Au regard de l’épaisseur des réseaux de pseudotachylytes dans les masses de péridotite et de leur absence dans les serpentinites, les masses de péridotites peuvent donc être assimilées à des aspérités au sein même de la plaque plongeante.
The prehistoric site of "la Terre-des-Sablons" is located near by the palaeontological Site of Rosières at Lunery (Cher department, France). During 1980's, about 50 prehistoric artifacts were discovered in a quarry at the base of a sandy fossil fluvial formation. The lithic assemblage show similar techno-typological characters as Early Palaeolithic European industries (Mode 1). Since 2003, multidisciplinary studies were coordinate in the prehistoric Site. Three stepped fossil fluvial formations were recognized and their dating by ESR method applied on fluvial grain quartz indicated that they were deposited at the end of Early Pleistocene since 1.1 to 0.8 Ma. During sampling for these geochronological studies, prehistoric artifacts were recovered again at the bottom of the oldest fluvial formation (1.166 ± 0.140 Ma), 12 m deep under the initial topographical surface. Between 2006 and 2011, excavations revealed presence of four archaeological levels with cores and flakes associated with a stratified layers of pebbles and cobbles (Unit a, layers 1 and 2) deposited on the incision floor and laid under this lower sandy formation. The technics used for flaking take place in the technics variability describe for the assemblages present in the European Early Pleistocene Sites. Geoarchaeological studies of this gravelly unit a permit to determine the source and phases of the deposits of raw materials gathered by Hominins, especially Jurassic silicifications ("chailles") and millstone. The prehistoric artifacts were observed in secondary position in the polygons or in the stone clusters (level 3) and on the eroded surfaces of layers 1 and 2 (levels 1 and 2).
Situé près du site paléontologique de Rosières, le site préhistorique de « la Terre-des-Sablons » à Lunery (Cher) a été découvert dans les années 1980 et environ 50 pièces taillées préhistoriques typologiquement attribuables à un Paléolithique très ancien (Mode 1) y avaient alors été récoltées dans une sablière exploitant des formations alluviales fossiles du Cher. A partir de 2003, des études pluridisciplinaires y ont été organisées en vue de mieux comprendre la situation géologique et structurale du site et de préciser le mode de dépôt et la position des formations sédimentaires qui y sont observées afin de les replacer dans le système fluviatile du Cher. Trois formations fluviatiles fossiles superposées ont ainsi été reconnues et leur datation par la méthode ESR sur quartz fluviatile optiquement blanchis a montré qu’elles avaient été toutes trois déposées par le Cher au cours du Pléistocène inférieur entre 1,1 et 0,8 Ma. Lors des prélèvements associés à cette étude géochronologique, des pièces d’industrie préhistorique furent de nouveau récoltées à la base de la formation fluviatile la plus ancienne (1,166 ± 0,140 Ma), à 12 m de profondeur sous la surface topographique initiale. Les fouilles menées entre 2006 et 2012 dans cette formation ont révélé la présence de quatre niveaux archéologiques associés à deux cailloutis stratifiés déposés sur le plancher d’incision et recouverts par cet ensemble fluviatile inférieur. Les techniques de débitage utilisées dans ces assemblages d’artefacts préhistoriques (blocs débités et éclats) rentrent dans la variabilité des techniques de Mode 1 reconnues dans les sites préhistoriques du Pléistocène inférieur européen. Une étude géoarchéologique de cette unité grossière a permis de déterminer les matériaux siliceux, essentiellement des chailles jurassiques et des meulières, récoltés sur place par les homininés et de caractériser la situation des artefacts dans des cellules de cryoturbation ou sur des surfaces d’érosion.
Des résultats des investigations sédimentologiques, essentiellement des observations sur terrain, et magnétiques, avec l´etude de 27 échantillons de la Bretagne et d´un de la Normandie sont présentées. Des valeurs de la susceptibilité magnétique de roches-mères recherchés d´après la littérature sont donnés pour la comparaison avec valeurs élevés qui indiquent probablemt une influence anthropogène.
The paleogeographic reconstructions that have been proposed for the Paleozoic generally agree upon the existence of two major distinct paleogeographic units in Europe: Baltica and North Gondwana, separated by a mid-European Rheic Ocean. The evolution of this ocean, from its opening in the earliest Paleozoic until its closure during the Carboniferous, influenced the geological development of the entire Armorican Massif and more generally that of southwestern Europe. This evolution controlled: (1) the thick accumulation of sediments during the initial period of rifting and those which were possibly related to marginal accretionary prisms (Ardennes?); (2) the successive latitudinal positions of the distinct paleogeographic units and the resulting climatic conditions which influenced the distribution of facies and faunas; (3) the igneous activity, especially in relation with subduction zones; and (4) the tectonic and metamorphic processes when the ocean closed and the continents collided.
The May sandstone which crops out in the Paleozoic synclines south of Caen (France) is characterized by ferruginous red-brown veinlets in a predominantly light gray quartzite. Petrographic analysis of the beds reveals a succession of three zones which have certain characteristics in common: quartz grains interpenetrating and shaping each other; grains with radial fissures; and grains including heavy mineral incrustations. These characteristics indicate mechanical action imposed on the sands after their deposition. Three stages in the formation of the sandstone are distinguished. The first phase includes sedimentation, burial and compaction of the deposits, resulting in the formation of stylolites in the biotite layers and establishing variable degrees of cementation as illustrated by the passage of sandstone and quartzite into orthoquartzite. Fracturing during the Hercynian orogeny marks the second phase. In the last phase, meteoric water circulated through the diaclases perforated by stylolites. The biotite was then hydrolyzed, liberating iron which was carried by the water and deposited as hematite veinlets which give the May sandstone its peculiar red color.
