Fluid circulation at basin–basement interfaces in rift systems is primarily controlled by brittle fault networks evolution and major interfaces. In the Upper Rhine Graben (Vosges, France), fractured crystalline basement rocks host major geothermal reservoirs, although the relationship between present-day fluid circulation and inherited, relict hydrothermal pathways remains debated. This study investigates the structural and hydrothermal evolution of the Villé Basin (Vosges Massif, France), located on the western shoulder of the Upper Rhine Graben, and provides a natural analogue for fractured basement reservoirs. The Villé Basin exposes the unconformity between the granitic basement and Stephanian sedimentary cover, allowing direct observations of faulted basement–cover interfaces. An integrated approach combining structural field analysis, petro-mineralogical characterization, and geochronological dating was applied to constrain fault activity and fluid circulation episodes. Two main brittle fault systems are identified: (i) An E–W-oriented fault network is pervasive at the basin scale and connects the basement to the sedimentary cover. These normal faults with metric vertical displacements are associated with hematite mineralization, and localized late barite mineralization event, indicating several hydrothermal circulations. Rb–Sr ages on muscovite and biotite suggest fault activity during Carboniferous–Permian times associated with N020°E extensional constrains. (ii) A later N–S-oriented fault network is localized along major basin-bounding faults associated to kilometric vertical displacement related to the formation of the Rhine Graben. U–Pb dating of newly-formed anatase (TiO2) yields Jurassic-Cretaceous ages (142 ± 66 Ma) questioning the activation of brittle N-S faults, low-temperature clay assemblages (kaolinite, illite/smectite, calcite) indicate late fluid circulation during late stages of URG (Upper Rhine Graben) evolution. These results demonstrate that the structural architecture of fractured basement reservoirs is controlled by evolution of fault systems and their episodic (re-)activation. The Villé Basin highlights the importance of structural control when interpreting geochronological data and provides key insights into fluid flow processes relevant to better understand complex geothermal systems of the Upper Rhine Graben.
Rocky shore platforms are critical coastal landforms whose morphology reflects the interplay between geological inheritance, sea-level history, and erosional processes. While Sunamura’s (1992) classification distinguishes three main platform types (A, B, C), the detailed morphology of these features—especially their submerged components—remains poorly understood due to limited access. Here, we investigate the geological and geomorphological controls on shore platform development along the Basque Coast (France), using high-resolution bathymetric data acquired during the SPLASHALIOT-1 cruise (R/V Haliotis, 2014). Our study focuses on two sites near Saint-Jean-de-Luz: Socoa (a long-term monitoring site of the Dynalit national observatory) and Kokotia, both underlain by Cretaceous–Paleogene turbidites deformed during the Pyrenean orogeny. By integrating bathymetric mapping, and geological observations, we reveal that both sites exhibit the characteristics of a Type A platform (sensu Sunamura, 1992): a planar, gently sloping surface (1–2°) extending 100–500 m offshore. The platform morphology is strongly influenced by lithological layering, with resistant turbidite beds shaping roughness and structural features. Notably, we observe no seaward cliff, challenging the hypothesis of ubiquity of low-tide cliffs in models of rocky coast evolution. Geological mapping extends onshore stratigraphy offshore, highlighting thrusts and normal faults ( e.g ., the Bidart–Pointe Sainte Anne Fault) that compartmentalize the platform. Our results suggest that platform morphology primarily records Holocene sea-level stabilization, with limited evidence of deeper terraces from the Last Interglacial (MIS5). The absence of prominent scarps or stepped features implies that cliff retreat rates (4–20 cm/a) have been insufficient to preserve older morphologies. We further discuss how structural roughness and lithological contrasts modulate wave energy dissipation, with implications for future cliff retreat under sea-level rise. This study underscores the need to account for geological heterogeneity in predictive models of rocky coast evolution.
We report on the area of the Jausiers-Col de la Bonette road, which is the highest of Europe, based on personal observations and the literature, including the published geological maps (BRGM Infoterre application). The tectonic pile comprises, 1) the folded Barcelonnette Autochthon (Keuper evaporites to marly Upper Jurassic-Lower Cretaceous); 2) various Subbriançonnais units (Séolanes platform facies), 3) some slivers from the classical Briançonnais (e.g., Ventebrun sliver); 4) the Roche Chevalière sliver described since years as originating from the Acceglio domain of eastern Briançonnais ; 5) the unconformable Neoauochthon Priabonian-Rupelian of the Grès d’Annot Basin ; 6) various sub-units of the Parpaillon Flysch, i.e., the Cretaceous-Paleocene turbidites that form the bulk of the Embrunais-Ubaye (Emb-Ub) Nappe (Flysch and basal Subbriançonnais-Briançonnais slivers). The Chevalier sub-unit of the Parpaillon Flysch (ParC) extends on top of and below the Roche Chevalière sliver, whereas the main Parpaillon sub-units extend further ENE. The sheared, brecciated « Schistes à blocs » and « Restefond Tectonic mélange » (uncorrectly described as « Autapie nappe » in previous works) underlie the Parpaillon units when they extend on top of the Neoautochthon formations. The Roche Chevalière sliver is non-metamorphic contrary to the blueschist facies Acceglio-type units of eastern Briançonnais. Sampling of Roche Chevalière by the WNW-going Flysch prism occurred before the eastward subduction of the Briançonnais margin at c. 37 Ma. The Roche Chevalière sliver remained at low temperature close to 260 °C when it crossed the exhumed Briançonnais units (cf. Furfande klippes) ; it reached its frontal position at c. 30 Ma, when the Rupelian sediments were still rich in interstitial water. The complex setting of the area is linked to the post-Rupelian folding and faulting that affected the Flysch and underlying units.
The Cigéo project, led by the French National Radioactive Waste Management Agency (Andra), involves the future disposal of high-level and long-lived radioactive waste in a deep geological repository. The site is located between the departments of Meuse and Haute-Marne in north-eastern France. In order to better monitor local seismicity and enhance the discrimination between natural and anthropogenic seismic events in the vicinity (<40 km) of the future Cigéo site, a dedicated network of four seismic stations – known as the Réseau d'Ecoute Sismique (RES) – was installed in 2002 and has been operated since then by the French Alternative Energies and Atomic Energy Commission (CEA). Over the past 60 years, the CEA has recorded 268 natural seismic events within a 90 km radius of the Cigéo site, with the largest reaching a local magnitude (ML) of 3.9. The closest recorded earthquake occurred about 20 km from the site, with a magnitude of ML 1.7. Historical and early instrumental records indicated that seismic activity in this region was low, a finding confirmed following the implementation of the RES network which significantly improved the detection and location of small earthquakes and identification of numerous quarry explosions in this region. This enhancement has finally increased the number of seismic events processed annually with more than 1,000 quarry blasts detected annually and allowed to reduce the completeness local magnitude down to approximately ML 1.5. We highlight the improvements in terms of event location and hypocentral depth accuracy provided by the RES network by comparing the median primary and secondary azimuthal gaps and the dimensions of the error ellipses before and after its deployment. Furthermore, we relocate the entire catalogue using a 3D location algorithm along with a 3D global velocity model to obtain more reliable estimates of event locations and hypocentre depth and to better quantify the uncertainties.
Although 3D and even 4D seismic imaging have advanced significantly, some acoustic patterns in carbonate reservoirs remain poorly understood. Diagenetic effects are still largely overlooked in interpreting reflectors within these complex sedimentary systems. We present a field study based on an outcrop of a well-known carbonate formation, the “Oolithe Blanche” of the Paris Basin (Burgundy, France). This formation is currently one of the preferred targets for medium enthalpy geothermal exploitation in the Paris Basin. A quarry working face is meshed with a decimetric resolution. Each cell of the grid is characterized from a sedimentological point of view and assigned to a dominant facies. Using a portative device, the 2D section is acoustically investigated by measuring horizontal and vertical P- and S- waves velocities. P-wave velocities measurements contribute to calculate synthetic seismic using a wavelet frequency allowing to highlight reflectors and seismic facies inside the section. Comparison between the synthetic seismic profile and the facies description provides us three main results. Firstly, the study allows us to characterize the acoustic role of the cross-beds visible in two carbonate facies of the site. These structures preferentially accelerate acoustic waves, suggesting lower porosity and permeability in this facies. Secondly, the seismic reflectors align with the boundaries of rudstone facies. The initial lithological contrast is amplified by a firm ground atop the underlying structure, increasing acoustic impedance and enhancing the seismic response beyond that of a simple facies change. Finally, small-scale karst structures have been described and appear to generate a chaotic seismic facies at the outcrop scale.
