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.
The Malta Horst is a NW-SE trending, 30 km-wide structural high situated on the southern Hyblean-Malta Plateau, which is an African continental indenter in collision with Eurasia. Sediments consist of a shallow marine carbonate platform succession (Mesozoic to Oligocene) capped by Miocene pelagic carbonates and marl. Utilizing seismic profiles, well data, and outcrop observations, this study provides the first description of kilometre-scale contractional structures within the horst and analyses the reactivation of normal faults by transcurrent movement under NW compression. The tectonic evolution of this foreland region is defined by five distinct phases (A through E), alternating between extension and compression. This cyclicity reflects the interplay between the migrating Calabrian Arc and the converging African craton. Initial NE-SW trending faults (Phases A and B) developed during the Late Oligocene to Early Miocene, coinciding with platform drowning. Following Tortonian uplift (Phase C), accelerated migration of the Calabrian Arc during Phase D triggered N-S extension, establishing the NW-SE and NE-SW normal faults that bound the Malta Horst. The neotectonic regime (Phase E) marks a return to dominance of the NW-directed compression by the African craton as the Calabrian Arc migration decelerated. This regional stress field has reactivated the NW-SE marginal normal faults through strike-slip motion. The combination of transcurrent drag and regional compression has inverted Phase A NE-SW normal faults into oblique reverse faults. These thrusts sole along a weak top Eocene evaporite décollement, producing a series of folds and inverted basins within 10 km of the horst's northeast margin. Onshore, these structures are manifest as en echelon, non-cylindrical, and doubly plunging folds that define the topography of Malta's northeast coast. These shear zone structures are thin-skinned deformations in Oligo-Miocene sediments controlled by thick-skinned, W-E transcurrent movement in the crust and Mesozoic sediments. Ongoing compression suggests an increase in seismic risk proximal to the Maltese Islands, with significant implications for local geohazard frequency and magnitude.
The gold-rich Kett & eacute; formations belong to the Adamawa-Yad & eacute; block of the Neoproterozoic Central Africa Orogenic Belt. They consist of a complex association of tonalite, granodiorite, and heterogeneous granite including rafts of metapyroxenite, amphibolite, paragneiss and migmatite. Metapyroxenite and amphibolite are metaluminous (A/CNK: 0.65-0.95), calc-alkaline, enriched in LILE and LREE, with epsilon Nd-610 < 0 and T-DM ages of 1.7 Ga, highlighting their enriched mantle source. Paragneiss are rich in LREE, Cr, V, Sc and Ni and display A/CNK (1.06-1.08) and A/NK (1.5-3.49) ratios consistent with a sedimentary protolith made of poorly sorted greywackes and litharenites with a contribution from mafic rocks of the juvenile crust. Granitoids display a variety of signatures, ranging from metaluminous to peraluminous (A/CNK: 0.94-1.04), calc-alkaline to alkaline. The heterogeneous granite in diffuse contact with migmatite have epsilon Nd-654 values of -9.61 and -8.11, and are interpreted to reflect local magma collection within the zone of dominant partial melting of the paragneiss. The tonalite and granodiorite, characterized by magmatic textures, display Mg# of 39.9-48.8, low HFSE contents, and enrichment in LILE and LREE. They were likely formed by the fractional crystallisation of a dioritic magma derived from the partial melting of amphibolite. The main structure of the migmatite is a shallow- to moderately dipping NE-SW trending syn-migmatitic foliation S-mgm, marked by alternating leucosome and mesosome layers, with relics of an S-0/S-1 foliation locally preserved within the mesosome. Granulite-facies relics with a peak at 8-10 kbar/>= 800 degrees C are preserved in metapyroxenite. Networks of texturally continuous leucosome veins concordant to discordant to the syn-migmatitic foliation, localization of granitic veins in shear zones and fold axial planes, attest for deformation in the presence of melt. Granitoids form kilometre-scale plutons with gently dipping magmatic fabrics (S-m-S-m/C-2) concordant to the syn-migmatitic foliation. These fabrics are transposed into a steeply dipping (47 degrees-74 degrees) E-W to NW-SE trending mylonitic fabric (S-myl-S-3/C-3), bearing a moderately plunging (15 degrees-49 degrees) stretching lineation L-3, marking the folded Mama Shear Zone (MaSZ). These data indicate that the Kett & eacute; region has recorded magmatic accretion of a mafic crust originating from an enriched mantle source. This crust and its associated sediments were subsequently tectonically thickened during the Pan-African orogeny and affected by partial melting. Migration of dioritic to granitic magmas from the partially molten orogenic root led to syntectonic crustal differentiation.
The Sioule region in the northern part of the French Massif Central of the Variscan belt hosts the Echassières complex, where a large W(-Sn) quartz vein system was intruded by the Beauvoir rare-metal granite (RMG) hosting disseminated Sn, Nb-Ta and Li mineralization. We combined whole-rock geochemical data, zircon U-Pb geochronology of migmatites and felsic igneous rocks of the Sioule area, along with U-Pb dating of cassiterite, wolframite, and apatite in the Echassières complex to reconstruct the regional magmatic and metallogenic evolution. Results reveal: (i) early W mineralization at 351 ± 9 Ma, coeval with peraluminous granite magmatism (Chantelle and St-Gervais massifs) and a N115-striking dextral shear zone; (ii) a second W mineralization phase at 329 ± 5 Ma, linked to rare-metal-rich rhyolitic dykes and the Colettes granite during NW-SE extension, synchronous with regional biotite microgranites (Pouzol-Servant Massif) and trachy-dacitic tuffs and lavas; and (iii) late-orogenic emplacement of the Beauvoir RMG with minor hydrothermal Sn and W at ca. 320-310 Ma, synchronous with biotite granites hosting quartz-tourmaline orbicules (Champs Massif) and pyroclastic flows. Our study reveals a 40 Myr-long metallogenic evolution with hydrothermal W mineralization preceding hydrothermal Sn and magmatic Li-Sn-Nb-Ta. Each mineralization period coincided with widespread crustal magmatism involving the anatexis of late-Ediacaran metasedimentary rocks and Cambrian-Ordovician metagranites, as shown by the dating of zircon in migmatites and inherited zircon in Variscan igneous rocks. However, rare-metal-enriched magmas remained spatially confined to the Echassières complex suggesting a structural corridor that repeatedly focused magmas and fluids from a localized fertile source.
The sub-continental lithospheric mantle (SCLM) beneath the Cameroon Volcanic Line (CVL) is vertically and laterally heterogeneous, consisting of a complex mixing of DMM, HIMU, and EM1, affected by modal or cryptic metasomatism, depending on the area. The petrography, whole-rock geochemical data, and minerals’ chemical composition of lavas and mantle xenoliths from the Bini Warack area, combined with Sr isotope compositions, provide constraints on the origin and thermochemical evolution of the SCLM beneath this sector of the CVL. The host lavas are basanite, basalt, and latite with OIB affinity, characterized by moderate to high silica and alkali contents (SiO2 = 42.35–56.56 wt%, K2O+Na2O = 2.34–7.07 wt%), a high Ba/Rb ranging from 12.2 to 26.1, a low Rb/Sr from 0.03 to 0.08, strong enrichment in LREE relative to HREE (LaN/YbN: 9.3–30), and moderate enrichment in radiogenic isotopes (e.g., 0.702987 < 87Sr/86Srinitial < 0.703206; 0.512854 <143Nd/144Ndinitial < 0.512918) with positive εNdinitial (+4.84 to +6.09). These features are consistent with an origin of the lavas by a low degree of partial melting (<2%) of a lherzolitic mantle source containing 2% to 6% garnet. These lavas have then evolved by fractional crystallization without any evidence of crustal contamination. The studied mantle xenoliths are spinel-bearing lherzolites, characterized by U/Th ratios typically lower than 1, a slight enrichment in LILE relative to HFSE, and mainly consist of minerals with fertile composition (Fo84-91; spinel Cr#: 0.1–0.22; Al-rich pyroxenes). They are consistent with refractory mantle peridotite that evidences low partial-melting degrees. Trace element concentrations of host lavas (high Ba/Rb: 12.2–26.1 and low Rb/Sr: 0.03–0.08), together with olivine’s crystals chemical features (high Ca/Fe and 100*Mn/Fe ratios; low 100*Ni/Mg ratios) and low Ca/Al ratios (<5) of clinopyroxenes in spinel-bearing lherzolite xenoliths suggest that the SCLM beneath the Bini Warack area is likely a juvenile lithospheric mantle which that undergone a carbonate-rich metasomatism.
The Malta Horst is a NW-SE-trending, 30 km wide structural high situated on the southern Hyblean-Malta Plateau, which is an African continental indenter in collision with Eurasia. Sediments consist of a shallow marine carbonate platform succession (Mesozoic to Oligocene) capped by Miocene pelagic carbonates and marl. Utilizing seismic profiles, well data, and outcrop observations, this study provides the first description of kilometer-scale contractional structures within the horst and analyzes the reactivation of normal faults by transcurrent movement under NW compression. The tectonic evolution of this foreland region is defined by five distinct phases (A through E), alternating between extension and compression. This cyclicity reflects the interplay between the migrating Calabrian Arc and the converging African craton. Initial NE-SW trending faults (Phases A and B) developed during the Late Oligocene to Early Miocene, coinciding with platform drowning. Following Tortonian uplift (Phase C), accelerated migration of the Calabrian arc during Phase D triggered N-S extension, establishing the NW-SE and NE-SW normal faults that bound the Malta Horst. The neotectonic regime (Phase E) marks a return to dominance of the NW-directed compression by the African craton as the Calabrian Arc migration decelerated. This regional stress field has reactivated the NW-SE marginal normal faults through strike-slip motion. The combination of transcurrent drag and regional compression has inverted Phase A NE-SW normal faults into oblique reverse faults. These thrusts sole along a weak top Eocene evaporite d & eacute;collement, producing a series of folds and inverted basins within 10 km of the horst's northeast margin. Onshore, these structures are manifest as en echelon, non-cylindrical, and doubly plunging folds that define the topography of Malta's northeast coast. These shear zone structures are thin-skinned deformations in Oligo-Miocene sediments controlled by thick-skinned, W-E transcurrent movement in the crust and Mesozoic sediments. Ongoing compression suggests an increase in seismic risk proximal to the Maltese Islands, with significant implications for local geohazard frequency and magnitude. Le Horst de Malte est un haut-fond structural de 30 km de large, orient & eacute; NO-SE, situ & eacute; sur la partie sud du plateau Hybl & eacute;en-Maltais, qui constitue un poin & ccedil;on continental africain en collision avec l'Eurasie. La s & eacute;dimentation se compose d'une succession de plateforme carbonat & eacute;e marine peu profonde (du M & eacute;sozo & iuml;que & agrave; l'Oligoc & egrave;ne), surmont & eacute;e par des carbonates p & eacute;lagiques et des marnes du Mioc & egrave;ne. En s'appuyant sur des profils sismiques, des donn & eacute;es de puits et des observations d'affleurements, cette & eacute;tude fournit la premi & egrave;re description de structures de contraction & agrave; l'& eacute;chelle kilom & eacute;trique au sein du horst et analyse la r & eacute;activation de failles normales par un mouvement transcurrent sous une compression NO. L'& eacute;volution tectonique de cette r & eacute;gion d'avant-pays est d & eacute;finie par cinq phases distinctes (A & agrave; E), alternant entre extension et compression. Cette cyclicit & eacute; refl & egrave;te l'interaction entre la migration de l'arc calabrais et la convergence du craton africain: Phases A et B (Oligoc & egrave;ne sup & eacute;rieur & agrave; Mioc & egrave;ne inf & eacute;rieur); D & eacute;veloppement des premi & egrave;res failles orient & eacute;es NE-SO, co & iuml;ncidant avec l'ennoiement de la plateforme; Phase C (Tortonien), soul & egrave;vement tectonique; Phase D, l'acc & eacute;l & eacute;ration de la migration de l'arc calabrais d & eacute;clenche une extension N-S, & eacute;tablissant les failles normales NO-SE et NE-SO qui d & eacute;limitent le horst de Malte et, Phase E, (r & eacute;gime n & eacute;otectonique) marque le retour & agrave; la dominance de la compression dirig & eacute;e vers le NO par le craton africain, alors que la migration de l'arc calabrais ralentit. Ce champ de contraintes r & eacute;gional a r & eacute;activ & eacute; les failles normales marginales NO-SE par un mouvement de d & eacute;crochement. La combinaison de l'entra & icirc;nement transcurrent et de la compression r & eacute;gionale a invers & eacute; les failles normales NE-SO de la Phase A en failles inverses obliques. Ces chevauchements s'enracinent le long d'un niveau de d & eacute;collement ductile d'& eacute;vaporites du sommet de l'& Eacute;oc & egrave;ne, produisant une s & eacute;rie de plis et de bassins invers & eacute;s & agrave; moins de 10 km de la marge nord-est du horst. & Agrave; terre, ces structures se manifestent par des plis en & eacute;chelon, non cylindriques et & agrave; double plongement, qui d & eacute;finissent la topographie de la c & ocirc;te nord-est de Malte. Ces structures de zone de cisaillement sont des d & eacute;formations de couverture (thin-skinned) dans les s & eacute;diments oligo-mioc & egrave;nes, contr & ocirc;l & eacute;es par un mouvement transcurrent E-O de socle (thick-skinned) dans la cro & ucirc;te et les s & eacute;diments m & eacute;sozo & iuml;ques. La compression actuelle sugg & egrave;re une augmentation du risque sismique & agrave; proximit & eacute; des & icirc;les maltaises, avec des implications significatives pour la fr & eacute;quence et l'ampleur des risques g & eacute;ologiques locaux.
We collected quartz veins and meteoric waters at alike altitudes on the Mont Blanc and the Chenaillet massifs in the French Alps to reconstruct the paleoaltimetry of these massifs. We analyzed 17 modern meteoric waters in total; the isotopic ratios of the MBM samples show a negative correlation with sample elevation defining a linear trend varying from the low values (δ2H = −144.3‰; δ18O = −18‰) at high elevation (3759 m) to higher values (δ2H = −33.3 ‰; δ18O = −4.9‰) at lower altitudes (1200 m) comparable to the Global Meteoric Water Line. The isotopic composition of Chenaillet samples collected at elevations ranging from 2160 to 2600 meters showed lower dispersion, with δ18O values ranging from −11.8‰ to −15.9‰ and δ2H values ranging from −83 ‰ to −108.1 ‰. The quartz veins from the Mont Blanc massif (MBM) and the Chenaillet massif (CM) used in this work cements tectonic fissures formed during compressive or extensive events associated with the exhumation of the massifs. To recover the water from quartz FIs and obtained their isotopic composition, we used two distinct extraction methods (thermal decrepitation and crushing) and two distinct analytical methods (the conventional one: equilibration/reduction and the one developed in this study combining H and O analysis). Three separate laboratories, the LGL-TPE and ISA in Lyon and the CRPG in Nancy performed the analyses. The FIs contained in the quartz of the MBM provide δ18O values ranging from −5 ‰ to −10.5 ‰ and δ2H values ranging from −33 ‰ to −76 ‰. The FIs from the CM have an isotopic composition ranging from −6.4 to −16.9% for the δ18O values and from −83 ‰ to −120.3 ‰ for the δ2H values. The results indictae that the water in the FIs is meteoric in origin. The presence of adularia associated with quartz in the MBM samples allow to date the formation of the veins between 14 and 11 Ma. Based on data from the literature, we suggest an age of 22 Ma for the formation of the veins in the CM. A comparison of the isotopic compositions of the FIs waters with modern precipitations suggests that the MBM was at low elevation (between 0 and 1156 m) during the Middle Miocene, while the CM was already uplifted at an elevation between 2250 m and 3750 m. Finally, we demonstrate that H and O analysis of aqueous fluid inclusions from quartz veins is an effective method for mountain range paleo-altimetry reconstruction.
Paleontology is a natural science discipline based on the observation of fossils. Therefore, paleontology education requires extensive training, and thus significant time, dedicated to observing and describing fossils. In the classroom, teachers often lack sufficient time to showcase the vast majority of key and basic fossil diversity typically encountered in the field. Moreover, students cannot spend enough time in class to properly study each sample. This challenge becomes even more critical in remote learning settings where access to fossils is limited. To address these limitations, we present a remote class dedicated to invertebrate paleontology bachelor’s students, based on a collection of 3D fossils. These models are reconstructed using photogrammetry and hosted online on the Sketchfab web platform. We present a comprehensive Moodle remote course, so-called VirtualPal, that seamlessly integrates instructional videos, interactive 3D fossil models, specific lessons, and formative and summative quizzes. The VirtualPal model can be easily adapted to other observational disciplines such as micropaleontology or petrology but still requires a proper evaluation of its effectiveness using educational science methodologies.
Hydrothermal groundwater systems are key to renewable energy due to their high thermal efficiency. Effective geothermal resources require not only a heat source but also permeable geological formations and appropriate flow patterns. Fault zones, play a critical role in this process, potentially acting as either drains or barriers. This study investigates the origins of heat flow in geothermal reservoirs by comparing the Bresse, Limagne, and Upper Rhine Grabens within the European Cenozoic Rift System (ECRIS), using a multidisciplinary approach to examine thermal properties, subsurface structure, and the role of fault zones in surface heat flow anomalies. Surface heat flow data from 943 points, geological maps, seismicity databases, and stress orientation data characterize crustal structures and fault networks, while seismic tomography, gravimetric maps, Moho and LAB depths, and SKS splitting measurements provide insights into mantle density variations, structural boundaries, and flow directions—together informing the model of heat distribution and high-temperature fluid migration. This synthesis highlights different scale of heat flow anomalies above the continental average of 67 mW/m2: (i) a long-wavelength anomaly, (ii) three high-wavelength anomalies, and (iii) seven areas with very high-wavelength anomalies exceeding 175 mW/m2. High surface heat flow anomalies are linked to fault zones, such as the Sillon Houiller fault. In contrast, the long wavelength anomaly at the scale of the French Massif Central (FMC) is probably not linked to a lithospheric fault. Characterizing the lithosphere-asthenosphere architecture reveals that the long-wavelength thermal anomaly aligns with a thin lithosphere-crust corridor and a positive seismic velocity anomaly, indicating an increase in the mantle heat flux beneath the thin lithosphere of the FMC and the Rhine Graben. In Upper Rhine and Bresse Grabens areas, high crustal fault density network connecting with major lithospheric discontinuities often corresponds to high surface heat flow. The active and crustal faults (Sillon Houiller, La Marche, and Vittel) facilitate the upward migration of high temperature fluid. Finally, this study highlights the importance of integrating multidisciplinary methods to understand surface heat flow and its implications for geothermal energy.
The Le Teil (Rhône Valley) earthquake of magnitude 4.9 on November 11, 2019, located on the Cévennes fault system has raised many questions about how regional intraplate structures may be reactivated and how they could potentially trigger strong and shallow earthquakes. This study aims to better understand the geodynamic evolution of this major structure of France’s geology over geological time. A structural study was carried out between Alès and Cruas localities, and synkinematic calcite samples were collected on fault planes and dated using the U-Pb method at LA-HR-ICPMS. Four major geodynamic episodes between 110 and 25 Ma were identified. In addition to recording tectonic events related to plate boundary geodynamics, the Cévenol Fault System appears to be a key structure in accommodating vertical motion differentials between the Massif Central, the Pyrenean domain and the South-East basin.
Tephrostratigraphy in marine cores is an important tool for dating sedimentary sequences along the North Atlantic and in Western Europe. Most previously analyzed marine tephra were produced by Icelandic volcanoes, albeit rarely from the Krafla volcano, and require land-based records for validation. Two series of rhyolitic tephra emitted to the east of the Krafla volcano were recorded in the Eemian Rangá Formation in Northern Iceland, the two series being separated by the Grímsvötn 1 tephra known as “5e low bas IV” in marine core (∼127 ka). These rhyolitic deposits were seemingly ejected from the Hágangnahali paleocrater row (North of the Hágöng) and overlay the older Halarauður Ignimbrite. This rhyolitic activity persisted for ∼20 ka to the end of the Eemian last thermal optimum. probably initiated by deglaciation (MIS 6a/5e). It postdated the Halarauður ignimbrite. The ignimbrite and caldera formation were correlated with an ODP907 tephra, yielding a possible 207 ka age, but possibly older. These results constrain the main rhyolitic activity of Krafla to after the mid-Pleistocene transition, as observed for other “two-magma” volcanoes. Rhyolitic activity is non-systematically triggered by deglaciation, at least as analysed during the period 80–400 ka, but this genetic link is possibly valid for the late Pliocene of Iceland.
Many papers refer in a revised way to the two-step scenario of the Messinian Crisis conceived by Clauzon et al. (1996). The present paper recalls the basis for the two-step scenario and discrepancies with the later modified version, completed by new data supported by extensive micropaleontological analyses. Our interpretation of the Sicilian Eraclea Minoa section as belonging to a peripheral basin is the centre of the debate. We show the great amplitude of fluvial erosion during the peak of the crisis, which for the Rhône River, exceeded 400 km upstream of the present shoreline. Based on dinoflagellate cysts, we also recall the reasons for supporting the occurrence of three successive Lago Mare episodes of two different origins. The first and third episodes constitute phases of high sea-level exchanges between the Mediterranean and the Paratethys respectively just before the onset of paroxysm and after it. The second episode is due to overflowing Paratethyan waters from the Aegean Basin just before the end of paroxysm. Similarly, the demonstration of the marine reflooding of the Mediterranean Basin prior to the Zanclean is repeated. We emphasize dissimilarity between basins, focussing in particular on those, isolated or perched ones, which were continuously filled by waters during the desiccation phase: western part of the Alboran Sea and southeastern part of the Levantine Basin (marine waters), Apennine Foredeep (fresh waters), and Aegean Basin (brackish waters). The Apennine Foredeep cannot be the reference for the entire Mediterranean with respect to its evolution during the crisis. During the crisis, water exchanges between the Aegean Basin and the Eastern Paratethys (Dacic Basin, Black Sea) were impossible through the Marmara region because of the development of two opposed fluvial networks. Such exchanges existed thanks to a gateway that was probably located within the Balkans. Investigations around the Levantine Basin point to areas submitted to fluvial erosion during the crisis paroxysm and nearby areas, which might have received marine waters from the Red Sea. Much information is still to be discovered and that more progress is still needed in order to fully decipher this outstanding event.
The Central High Atlas of Morocco is the result of the Alpine tectonic inversion of an intracontinental Mesozoic basin, the infill of which started with thick Upper Triassic clay and evaporite deposition. This slightly deformed mountain range is characterized by narrow ENE-WSW ridges that expose a Triassic core. These ridges bound unique synclines filled by thick Jurassic successions showing well-preserved halokinetic depositional sequences, interpreted as salt-related minibasins. This paper aims to describe and analyze the evolution of diapiric movements and their interactions with Lower and Middle Jurassic carbonate dominated sedimentation in the Imilchil area, which corresponds to the axial part of the Atlas basin. Four diapiric ridges have been identified in this region: the Tasraft, Tassent, Ikkou, and Amagmag, which expose Triassic shales and are intruded by Triassic and Jurassic magmatic rocks. These ridges delineate three minibasins: Ikassene, Lakes (Lake Plateau), and Tilmi (Ikkou), each 5 to 10 km wide, preserving over 6,000 m of Upper Liassic and Dogger deposits. The Atlas basin is filled with five third-order transgression-regression cycles organized as one regressive megasequence. This long regressive trend is expressed by the succession of three depositional systems: i) a distal to proximal carbonate ramp system from the Toarcian to Late Bajocian; ii) a shallow mixed carbonate-siliciclastic system from the Late Bajocian to Early Bathonian; and iii) a fluvial system from the Bathonian to Early Callovian. Throughout this period, the development of coeval diapiric ridges significantly influenced these sedimentary systems, though the intensity of the diapiric activity varied over time. During the Late Bajocian, ridge growth slowed considerably amid the peak progradation of the carbonate systems. It then increased significantly from the latest Bajocian onward, due to a drastic rise in siliciclastic flux and sedimentation rate in the Atlas basin. The effects of diapirism on sedimentation are observed regionally (several kilometers), as minibasins evolve as depocenters, each exhibiting distinct subsidence rates and sedimentary thicknesses. Despite these local variations, the regional scale paleogeography and the sequential organization of the deposits remained largely unaffected. On a smaller scale (hectometers to kilometers), diapiric structures are always characterized by halokinetic depositional patterns. Internal angular unconformities only occur in very shallow-marine to continental deposits during periods of maximum ridge growth and subaerial exposure (notably in the Bathonian). At this scale, diapiric movements lead to local facies variations within shallow-marine deposits, fostering the development of bioconstructed or grainy carbonate sediment bodies along the ridges. However, in outer ramp environments, the submarine topographies created by ridge growth were generally insufficient to induce similar facies variations.
The volcanic island complex of Milos, situated ∼200 km north of the Hellenic subduction zone, records the interplay of volcanic, tectonic, and gravitational processes within multidirectional, polyphased rift systems that developed throughout the Mio–Plio–Quaternary. Its active and seismogenic fault network hosts both perennial and transient hydrothermal venting zones, offering a natural laboratory to examine fluid circulation within a volcanic arc built on stretched continental crust. This study refines the relationships between magmatism, seismicity, and hydrothermal activity, with implications for local geological hazards. Two new morpho-tectonic sketches are presented. The first places the Milos volcanic center within the structural framework of the Aegean microplate; the second illustrates the spatial organization of the Milos tectono-hydrothermal-volcanic system. These reconstructions integrate detailed physiographic analyses (relief, slope), field observations, and multidisciplinary datasets on seismicity, hydrothermalism, and mineralization. At the scale of the Aegean microplate, (i) NE–SW faults are attributed to extensional deformation along the Mid-Cycladic Lineament; (ii) E–W faults relate to the opening of the Milos, Cretan, and Christiana basins, parallel to the mid-Miocene West Cycladic Detachments; (iii) NW–SE faults correspond to the Myrtoon Basin and Gulf of Milos openings, the latter being closed to the south by the Fyriplaka volcano; and (iv) N–S faults controlling the Zephyria graben and the eastern margin of Milos are continuous with Cretan fault systems and are parallel both to the Eocene trans-Cycladic thrust in the region and to magnetic anomalies in the subducted Tethyan oceanic crust south of the Hellenic subduction zone. At the archipelago scale, seismicity, hydrothermal venting, alteration zones, and phreatic explosions are concentrated in the hanging wall of the Achivadolimni fault, along or near the intersections of the N–S Zephyria and NW–SE Fyriplaka grabens, directly above the inferred magma chamber. Microearthquake hypocentres, likely linked to fluid-induced fault dilation, occur beneath the Gulf of Milos (∼7 km) and Fyriplaka volcano (∼5 km). Their distribution suggests a genetic link between the intersecting grabens, cooling of isotherms beneath the gulf by descending seawater, surface hydrothermal manifestations, and tectonic earthquakes (e.g., Mw 5.3 Milos, 1992). A shallow hydrothermal convection loop (<3 km) probably overlies a magmatic reservoir where fluids accumulate beneath a self-sealed, low-permeability cap, possibly corresponding to a thermal brittle-ductile transition (370–450 °C). Co-seismic ruptures may locally breach this barrier, inducing “arterial fault” behaviour along the Achivadolimni fault. Pulsating hydrothermal activity and historical phreatic eruptions are interpreted as surface expressions of transient injections of over-pressurized magmatic fluids, leading to decompression, phase transitions, and fluid expulsion during seismic events. These coupled magmatic-hydrothermal-tectonic processes should be integrated into future hazard assessments for Milos.
The offshore western Sicily region is located at the active Africa-Eurasia plate boundary, between the southern Tyrrhenian backarc basin and the African continental margin, where tectonic processes make this sector prone to strong earthquakes and tsunamis. In the area, positive inversion structures have been documented due to a contractional reactivation of pre-existing normal faults. However, a detailed geological study of the inversion features addressing the structural inheritance, timing, regional tectonic framework and the geodynamic significance is still absent. The comprehensive interpretation of a dense seismic grid, calibrated by dredges, deep well logs and onshore geology, documents a great variability of the inversion structures during the Quaternary. We characterize different fault and fold families, unravelling the basin architecture, and providing a new tectonic scenario for the region. The role of inversion tectonics in the recent tectonic frame of the study area has been investigated. The development of the Quaternary inversion structures occurred within a complex structural pattern of faults characterised by E-W strike-slip faults, en-échelon folds, and negative flower structures. All the recognized structures are compatible with a dextral wrench zone that developed along the plate boundary offshore western Sicily. In this frame, the pre-existing normal faults represent important crustal discontinuities for the development of the new generated structures; furthermore, the inversion structures developed in agreement with the new structural frame growing in correspondence with the pre-existing normal faults. This tectonic frame furnishes new geologic constraints for the Recent geodynamic evolution of a key area of the Central Mediterranean. We suggest a link between the complex tectonic evolution of the upper crust and the development of the subducting slab to unravel the possible triggering factors responsible for these crustal deformations.
The Lorraine Coal Basin (LCB), filled with continental clastic formations of the Upper Carboniferous-Permian age, developed along the Metz-Hunsrück-Fault-Zone (MHFZ). Despite the structural studies, the structure of the basement which control the total sedimentary thickness variations, and the Alsting fold structure and formation remains poorly constrained. In this study, the analysis of gravity data has allowed to map the MHFZ and more regionally the top basement structures beneath the basin. The analysis of 2D seismic lines and well data analysis has allowed to constrain the structure and formation of the Alsting fold. The top basement map highlights the presence of highs (−1, 5 km) and deeps (−6, 5 km) trending NE-SW, NNE-SSW to N-S and NW-SE. This structuration explains the global sedimentary thickness variation of the sedimentary series in place. The first vertical derivative of the Bouger anomaly suggests that the MHFZ is continuous throughout the LCB and the SNCB. Furthermore, seismic interpretations show that the Alsting fold is a thrust fold whose formation and post-compression erosion occurred during the Stephanian. After this deformation phase, subsidence and deposition restarted during the late Stephanian. This study highlights a different Stephanian geological history of the BHL compared with other basins of the same age due to its structural position.
Although foreland regions are often perceived as stable zones, the Sicily Channel—situated in the central Mediterranean between Sicily and Tunisia and regarded as the continental foreland of the Sicilian Maghrebian chain—reveals significant tectonic complexity. It comprises three major tectonic troughs (Pantelleria, Malta, and Linosa grabens) formed by the ongoing extension of Africa. This area includes a foreland-foredeep-chain system encompassing the Pelagian foreland, the Gela foredeep Basin, and the offshore section of the Neogene-Quaternary Sicilian-Maghrebian chain. Based on an extensive review of available literature, including previously published multichannel seismic reflection profiles and structural maps, we provide a detailed analysis of the stratigraphic architecture and key tectonic features that have influenced the Sicily Channel during the Plio-Quaternary. Furthermore, we assess the timing of these events to gain a comprehensive understanding of the region's Plio-Quaternary tectonic evolution. Our findings demonstrate that the Sicily Channel is not merely a simple rifted foreland zone but is characterized by recurrent extensional and compressional phases during the late Neogene/Plio-Quaternary. This evidence indicates that distinct tectonic regimes can coexist within a foreland area, reinforcing the idea that foreland zones actively record dynamic processes driving lithospheric deformation and are prone to tectonic reactivation
This study investigates the structurally-controlled fluid flow of the Lake Abhe Geothermal Field (LAGF), using multiscale structural lineament distribution mapping and field observations. The LAGF lies within the Gob Aad graben in the Afar depression, at the junction of three rifts, along the Djibouti-Ethiopia border. Numerous hydrothermal surface manifestations on the lake’s eastern shore, including steam vents, hot springs and carbonate chimney structures, reflect the geothermal activity of this area. Structural features of the LAGF area are dominated by ESE-extensional faults that form a series of narrow elongated horst, graben and half-graben structures. Fault interaction and accommodation zones, such as fault intersections and relay ramps, as well as possible breaching faults are also identified in the area. The control of the main ESE-structural direction over the distribution of hydrothermal chimneys and hot springs indicates these faults to be the primary permeability fluid pathways of the LAGF. Signs of enhanced hydrothermal activity at fault intersections further suggest that structural intersections locally increase fracture-related permeability. Field observations combined with satellite image analysis also reveal a lateral migration of the hydrothermal outflows over a short period of time (during the past several thousands to tens of thousands of years) from the SE to the NW. Finally, this study discusses the potential role of N-striking faults, which may either act as vertical drains channeling fluids from south to north or as barriers preventing eastward fluid migration. Overall, this study provides new insights into the tectonically driven fluid flow dynamics of the LAGF, which may support further exploration of this remarkable site and promote its geothermal development.
The Lorraine Coal Basin, recognized as the most promising coal bed methane basin in France, holds significance for the energy transition after more than a century of coal mining until 2004 and renewed interest in oil and gas exploration in the 80 s and 90 s. New data from an ongoing exploration campaign within this basin rise new opportunities in the assessment of gas resources. In the scope of this evaluation the determination of Total Organic Carbon (TOC) content using well-log data is a necessary step. The study employs a methodology encompassing Schmoker’s method, ΔlogR, and multivariate regression, focusing on two reference boreholes. While TOC calculations techniques are usually developed for marine shale deposits, an adaptation to highly heterogeneous fluviatile deposits is presented. Schmoker’s method provides the most accurate TOC values, consistent with Rock-Eval data. However, the ΔlogR method underestimates TOC values, particularly for coal lithologies, for which logarithmic equations are proposed for proportional corrections. Moreover, new equations based on multivariate regression of gamma-ray, sonic, and resistivity logs are developed for TOC estimation. Schmoker’s method proves to be the most reliable with available density logs in the Lorraine Coal Basin. Alternatively, the modified ΔlogR equations or those derived from the multivariate regression of gamma-ray, sonic, and resistivity logs can be used. These new equations represent an alternative approach and identify new possibilities for estimating TOC in hetereogenous coaly formations. Based on TOC, lithologies of the investigated sedimentary series are classified from lean to fair source-rocks for shaly lithologies to excellent for the coal layer.
