Laurent Beccaletto

The eastern Provence in southeastern France comprises a complex fold-thrust system developed in a Mesozoic sedimentary cover detached above ductile Triassic evaporitic-carbonate levels. The timing of deformation is difficult to constrain due to the absence of syntectonic sedimentary strata. In this study, we investigate the Cannet-des-Maures structure, a key example of the eastern Provence fold-thrust belt, by integrating a balanced, sequentially restored cross-section with U-Pb calcite dating to reconstruct its structural evolution and quantify the time-dependent vertical partitioning of shortening. The present-day geometry of the structure is characterized by a large-scale NE-verging overturned anticline, with second-order SW-verging thrusts developed in its forelimb, that were subsequently tilted and sheared by anticline growth. This architecture reflects limited frontal propagation and strong internal strain localization, kinematically linked to the presence of Triassic evaporitic-carbonate layers in the core of the structure. Theses ductile units acted as décollement levels promoting vertical partitioning of the shortening (from 0.14 to 2.7km) and disharmonic folding between the basement and the overlying Jurassic cover. Structural restoration reveals that the current geometry results from the inversion of an inherited Jurassic rollover structure initially shaped by listric normal fault rooted in Triassic evaporitic-carbonate layers. The basement displays a reactivated, south-dipping extensional fault, which originally controlled the development of the rollover geometry. U-Pb ages of syn-kinematic calcite range from 94 to 4 Ma, providing a robust temporal framework linking Cretaceous extension to Provençal and Alpine compressions. These absolute ages validate the structural interpretation of inverted extensional geometries and demonstrate a long-lived deformation from Provençal to Alpine tectonic regimes. Based on these deformation ages, we propose a five-stage kinematic model identified through sequential restoration between the Late Cenomanian to the Eocene. This reconstruction highlights that the highest shortening rate occurred during the Eocene. Kinematic relationships reveal a combination of thin- and thick-skinned tectonic styles during the Provençal orogeny, later overprinted by reactivation of the Triassic décollement levels during the Alpine phase. By integrating absolute geochronology with structural restoration, this study refines the timing and mechanical understanding of tectonic inversion processes and emphasizes the long-term control of inherited basement structures and ductile Triassic units. The results further indicate southwestward propagation of Alpine deformation into the European foreland, expressed in Provence as a far-field Alpine overprint.

Geological characterization of the “Fonts-Bouillants” helium discovery - FranceRussier E1,2, Géraud Y2, Hauville B1, Tarantola A2 ,Beccaletto L3 and Diraison M11 45-8 ENERGY, France2 GeoRessources, University of Lorraine, France3 BRGM, F-45060, Orléans, France ABSTRACTHelium is essential for the manufacturing of many of our daily commodities such as optical fibres, computers or cell phones (semiconductors and processors), medical use (MRI scanners) or in other more specific applications such as airlifts, leak detection, gas chromatography or diving. Nowadays, Europe imports 100% of its helium needs from overseas and is facing regular shortages, reason why 45-8 Energy embarked five years ago on helium exploration and production in Europe. Helium is a noble gas mostly coming from the natural radioactive decay of Uranium and Thorium contained in the crust and the basement. Its migration and accumulation are strongly linked to a vector fluid that can be CO2, N2, CH4 or water. Helium and its vector fluids are then trapped and sealed in a rock reservoir. The Fonts-Bouillants area is located at the southern edge of the Paris Basin at the vicinity of the French Massif Central and Limagne rift. The 45-8 Energy project aims to jointly produce He and CO2 from a gas which is naturally seeping through the major Saint-Parize fault (SPF). Geological origin and migration pathway of He are therefore key questions to define the exploration guide, in particular to locate production wells to produce the seeping gas and process it. A multidisciplinary approach involving geology, geophysics, petrophysics and geochemistry has therefore been deployed. Because geological context was hardly documented in this area, a wide range of geophysical data were acquired or reprocessed and coupled with field geology to build a regional geological model. The initial geological model was considerably updated and a hidden and thick Late Palaeozoic depocenter was especially highlighted below the Mesozoic series. Well data in nearby analogous basins as well as outcrops enabled rock collections to conduct petrophysical and geochemical characterization. The main reservoirs discovered currently are in Triassic and Jurassic sandstones, and fault like Saint-Parize fault acted as barrier and drain. Our outcrops petrophysical and geochemical study highlight the importance of Late Palaeozoic basin for the helium system:As a potential rock source, with higher U-Th concentrations (3-13.5, 8-24 ppm) than typical crustal U-Th concentrations (1.8 and 7.2 ppm, [1]). As a potential migration pathway and reservoir, with sandstones and conglomerates porosity higher than 20% and permeability higher than 100 mD. Finally, gas sampling was performed in local natural springs, but also during well testing conducted in shallow boreholes which have encountered gas bearing reservoirs in the Mesozoic along the SPF. Helium generation system was modelled with geochemical data from the rocks and the fluids and from the volumetric capacity of the Palaeozoic basin. Keywords: Helium exploration, Geophysics, Petrophysics, GeochemistryThemes: Helium exploration References:[1] Krauskopf, K. B., & Bird, D. K. (1967). Introduction to geochemistry (Vol. 721). McGraw-Hill New York.

Heritage and culture tourism involve features that commemorate a valued past. Mining heritage tourism allows visitors to experience the past, guided by former mining landscapes and engaging interactively with material artifacts. This paper introduces the CoalHeritage European project, focusing on the promotion of coal mining heritage through the production and design of the European Visual Map Journal (EVMJ). The EVMJ is a user-friendly, web-based, interactive storytelling platform that supports the transfer of industrial and geoheritage from former coal mining areas. It aims to collect and disseminate heritage assets from post-mining coal areas, informing stakeholders and promoting these sites as tourist destinations. To further enhance public awareness, several ESRI StoryMaps web apps are being created to highlight specific features of each case study across Europe. The aim of this work is to introduce coal mining heritage as a new term, present the coal heritage platform and its importance for disseminating coal heritage aspects to the public, describe the methodology used for its design, and provide a brief overview of its evolving content.

A new structural model is presented for the Permo‐Carboniferous Lorraine Basin (NE France), a major intramountain basin that developed during the latest stages of the Variscan orogeny (ca. 315–270 Ma). Digitalized well logs and reprocessed seismic data were used to decipher the kinematic evolution of this basin located along the Rhenohercynian orogenic suture zone. The basin was initiated during the late collision stage (Early to Middle Pennsylvanian) in a wedge‐top position upon the Saxothuringian retro‐wedge. The syn‐orogenic sequence is delimited to the north by the major SE‐verging Metz Thrust, which is part of the backthrust system that propagated during Middle Pennsylvanian (Late Westphalian). Seismic data provide evidence of negative tectonic inversion, allowing the formation of syn‐rift depocenters (Late Pennsylvanian‐Early Permian) above the former anticlines. Erosion of these anticlines results in a major unconformity marking the onset of post‐orogenic collapse. The late Early Permian shortening (Saalian phase) is suggested to reactivate former thrusts and normal faults, thus generating late uplift of the basin. The post‐orogenic phase is complex and diachronous at basin scale, and both compression and extension can be recorded in the same area over a short period (<10 Myr). The Late Carboniferous negative tectonic inversion along the Rhenohercynian suture zone is proposed to result from the lithospheric delamination of the Variscan orogenic roots. The associated upwelling of asthenospheric material is recorded by intense magmatic activity, and can be, in turn, considered as the main trigger for the subsequent thermal subsidence of the Mesozoic Paris Basin.

Intramontane late Carboniferous–Permian basins of western Europe developed during the latest orogenic stages of the Variscan Mountain Belt in eastern Pangaea, at equatorial palaeolatitudes. Their stratigraphic framework is mainly based on continental subdivisions (e.g. Stephanian and Autunian continental stages), which can be contentious owing to biostratigraphic biases, resulting in long-distance diachronous subdivisions. To provide precise inter-basinal and global correlations to the internationally recognized chronostratigraphic marine stages, this study reports new U–Pb geochronology from the Aumance and Decize–La Machine basins, located in the northern French Massif Central. Zircon grains extracted from three volcanic ash-fall layers give weighted mean ²⁰⁶ Pb/ ²³⁸ U ages of 299.11 ± 0.35, 298.73 ± 0.36 and 298.59 ± 0.35 Ma (2 σ total propagated uncertainty) by the chemical abrasion isotope dilution thermal ionization mass spectrometry method, coinciding with the Carboniferous–Permian transition (Gzhelian and Asselian stages). These ages imply that the northern Massif Central basins developed synchronously in relatively short periods of time (Supplementary material: Operating conditions and complete analytical results are available at https://doi.org/10.6084/m9.figshare.c.6805228

From the end of the Carboniferous onwards, the over-thickened and hot Variscan crust collapsed (late-orogenic collapse), accompanied by the rise of high-grade metamorphic domes along low-angle detachment faults and the development of mainly half-graben or pull-apart type asymmetric intramountain coal basins.These Carboniferous-Permian late orogenic basins widely developed around 300 Ma and were filled with siliciclastic continental material, accompanied by a widespread intrusive and extrusive magmatic activity. These basins crop out in the internal parts of the belt south of the Variscan Front in several limited locations in and around the Variscan basement of Western Europe (Massif Central, Vosges-Black Forest, Alps, Harz). They occur as small isolated and disconnected “basins” with incomplete sedimentary series. Their present-day area does not reflect their initial extent and thickness, which can be explored by studying their subsurface prolongation beneath their Meso-Cenozoic sedimentary covers.We propose a geological overview of the late Variscan Carboniferous-Permian Brécy basin (SW Paris basin, France), based on the reprocessing and interpretation of vintage seismic lines and related deep boreholes. We aim (i) to discuss its sedimentary filling, which is hidden beneath the Meso-Cenozoic cover of the Paris basin, (ii) to present thickness maps of its 3.9 km-thick sedimentary filling, and (iii) to describe its structural extensional features related to a syn- to post-rift tectonic scenario. We finally compared our new results to other Carboniferous-Permian deposits in France (to discuss its lateral correlation with neighboring basins) and northwest Europe, suggesting that the Brécy Basin may represent - due to its thickness and location - a missing link between late Variscan basins in southern and northern Europe.

Deformation of intraplate sedimentary basins essentially results from tectonic stresses that propagate from plate boundaries. Yet, the detailed characteristics of this far field propagation are often poorly constrained, especially in age. Recent developments of U/Pb dating of calcite precipitations in fault planes and veins hopefully greatly help to frame the schedule of deformation. This is the case for the Meso-Cenozoic Paris basin, liable to have recorded several Cenozoic events due to its location in the western Eurasian plate, like Pyrenean and Alpine collisions and Oligocene extension (ECRIS).Our study focusses on the southern Paris basin area, north of the Morvan massif, where Alpine deformations are expected. Field data reveal almost exclusively strike-slip deformations with variable σ1 direction. These results are about to be confirmed at the microscopic scale using Anisotropy of Magnetic Susceptibility and of P-Wave Velocity methods. Associated U-Pb dating of synkinematic calcites from Jurassic strata indicates distributed Eocene deformation and an absence of Oligocene or Miocene ages. Such ages suggest the record of Pyrenean and possibly ECRIS tectonic events. Strikingly, Alpine deformation and especially stress propagation leading to the growth of the Jura fold-and-thrust belt during Miocene does not imprint the studied area although the Alpine orogen is located closer than the Pyrenean belt.

A new structural model is presented for the Permo-Carboniferous Lorraine Basin (NE France), a major intramountain basin that developed during the latest stages of the Variscan orogeny (ca 315–270 Ma). This basin is buried in NE France below the Paris Basin but outcrops in southern Germany (Saar-Nahe Basin). Digitalized well logs and reprocessed seismic data were used to decipher the kinematic evolution of this basin located along the Rhenohercynian orogenic suture zone. The basin initiated during the late collision stage (Late Namurian-Westphalian) in a wedge- top position upon the Saxothüringian retrowedge. The syn-orogenic sequences are delimited to the north by the major SE-directed Metz Thrust, which is part of the backthrust system that propagated during Late Westphalian times. Seismic data provide evidence of negative tectonic inversion, allowing the formation of syn-rift depocenters (Stephanian-Early Permian) above the former anticlines. Erosion of these anticlines results in a major unconformity (base of Stephanian) marking the onset of post-orogenic collapse stage. The late Early Permian shortening (Saalian phase) reactivated former thrusts and normal faults, thus generating uplift of the basin. The post- orogenic phase is complex and diachronous at basin scale, and both compression and extension can be recorded in the same area over a short period (<10 Ma). The Late Carboniferous negative tectonic inversion along the Rhenohercynian suture zone is proposed to result from the lithospheric delamination of the Variscan orogenic roots. The associated upwelling of asthenospheric material is recorded by intense magmatic activity, and can be, in turn, considered as the main trigger for the subsequent thermal subsidence of the Paris basin.

In the general context of the development of renewable energy in the Hauts-de-France region (N France), some growing interest has been focused recently on the potential of deep geothermy. This area displays favourable conditions due to the burial of a regionally well-defined reservoir, i.e. the Dinantian karstic and brecciated limestones (Lower Carboniferous, 360-330 Ma), below the Nord-Pas-de-Calais coal-bearing Upper Carboniferous basin, developed by flexural subsidence in the foreland of the Northern Variscan frontal thrust system. The predominance of shales within the molassic basin as well as within the basal units at the floor of the thrust wedge (the Lower Devonian clastic units) are furthermore likely to form a large-scale permeability barrier potentially favouring the localization of hot waters within the underlying carbonate reservoir. The occurrence of a Dinantian regional geothermal resource has already been proven in Southern Belgium in the Hainaut coal basin area (the eastern prolongation of the Northern France coal basin) where the temperature in three geothermal wells reaches about 70°C.To provide further constraints on such potential deep geothermal field in a structurally complex setting (a laterally segmented thrust front), the geometry of the Dinantian reservoir in northern France has been investigated through the integration and interpolation in a 3-D model of a large database including 1 128 boreholes and 532 km of reprocessed, interpreted and depth-converted seismic reflection profiles. The results of the 3-D modelling indicate that the Dinantian reservoir is present at depth over a large area covering approximately 7675 km² in northern France-southern Belgium. It extends at least 30 to 40 km south of the coal mining district area, underneath the Ardennes Allochthonous Unit of the Northern Variscan Front. The Dinantian reservoir is less than 200 m deep in the Lille metropolitan area and strongly deepens southward through a sharp flexure. It reaches 1000-3000 m depth underneath the coal basin and a maximum of 6944 m depth at the southern end of the study area. Overall, the Dinantian reservoir is structured along two main directions oriented N70-80° and N110-130°, related respectively to deep frontal Variscan thrusts and lateral-oblique ramps. The Dinantian reservoir ends west of Douai against a major complex lateral ramp system forming a first-order transfer zone within the Northern France Variscan thrust front. The latter localizes a set of strongly dipping N110-N130 faults (the Artois faults) representing second-order structures produced during subsequent deformation periods i.e. the Late Carboniferous-Permian rifting event and the Tertiary inversion related to the far-field accommodation of the Alpine-Pyrenean shortening.