HAL-BRGM, les publications scientifiques en libre accès du BRGM
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Impact of tectonics and fluid circulations on shale gas isotope geochemistry – A case study of the Rietheim Member at the Mont Terri anticline (Switzerland)
No full textInternational audienceIn the framework of the hydrological survey of the Mont Terri anticline (Mont Terri rock Laboratory in the Folded Jura, Switzerland), a 58 m-deep borehole (BHS-1) was drilled through the Jurassic low permeability shale sequence. Dedicated sampling was carried out to characterize gases within a 13 m-thick unit of organic matter-rich Early Jurassic Rietheim black shales and adjacent units, including the underlying Beggingen aquifer. A cone-in-cone calcite, observed at the bottom of the black shale, as identified as an indicator of oil-window conditions and records a maximal burial temperature of ~80-90°C. Two fracture zones within the black shales, marked by calcite infillings, provide evidence for at least two episodes of water paleocirculations: (1) an early circulation between fractures at the top of black shales and the Main Fault, and (2) a later circulation between fracture zones within the black shales and the lower Beggingen aquifer. Gas migration was investigated within the complex geological context of regional uplift, Jura folding and thrusting, and associated water flows. Alkane data reveal a partial carbon isotope reversal of thermogenic gases within the black shales between the two fracture zones, strongly suggesting alkane migration linked to the second water paleocirculation episode
Sediment routing and palaeogeographic evolution of the Western Alpine Foreland Basin during the early collisional stage
No full textInternational audienceIn the Western Alpine Foreland Basin (WAFB), Late Eocene and Miocene periods were characterized by longitudinal sediment routing systems: The first one was situated within the turbidite basin during the underfilled phase and exhibited a northward orientation toward the Swiss Basin, whereas the second was located in the Rhône Valley during the overfilled phase and was directed southward toward the Mediterranean Sea. The transition between these two periods occurred during the Oligocene, which corresponds to both the underfilled/ overfilled transition and the early overfilled period. In this study, we provide new fieldwork observations, seismic and well data interpretations, biostratigraphic analyses and a literature synthesis to reconstruct the palaeogeographic and source-to-sink evolution of the WAFB from Priabonian to Aquitanian. The aim is to discuss this reorganisation of sediment routing in relation to the evolution of the Alpine orogenic wedge, as well as the structural inheritance and the suite of geodynamic events that affected southeastern France during the mid-Cenozoic. We divided the WAFB sedimentary formations into four depositional sequences (S1 to S4). During the deposition of the first two sequences (Priabonian to early late Rupelian; ~37.4-28.8 Ma), the WAFB routing system was influenced by the end of the Pyrenean-Provençal orogeny, the European Cenozoic Rifting System (controlling the Rhône Valley s.l.) and the Alpine orogenic wedge (controlling the Alpine foredeep). The very first connection between the Alpine domain and the Rhône Valley is established at ~30 Ma, during the late Rupelian (S2 highstand), controlled by E-W inherited Pyrenean-Provençal structures implying a 'broken foreland'. In the meanwhile, from the Dévoluy Basin and northward, the orogenic wedge controlled a classical, although thin, foreland basin characterized by a northward sediment routing connected to the Northern Alpine Foreland Basin. Most of the S3 sequence (Latest Rupelian to middle Chattian; ~28.8-23.25 Ma) corresponds to a decrease of clastic Alpine inputs throughout SE France caused by a reorganisation of the drainage network related with the exhumation of the southern External Crystalline Massifs. S3 highstand and S4 sequence (late Chattian to Aquitanian; from ~23.25 Ma) correspond to the establishment of a longitudinal sediment routing system in the Rhône Valley, with material flowing southwards toward the Gulf of Lion, and supplied by the Palaeo-Isère to the north and potentially by the Palaeo-Durance to the south. This final stage in the reorganisation of the drainage network is clearly associated with the post-rift phase of the Gulf of Lion, which facilitated the opening of a new sink and the ultimate southward migration of the sedimentary area
Soil organic matter decomposition in semi-arid mangrove stands (New Caledonia)
No full textInternational audienceOrganic matter (OM) dynamics in mangrove forests have been studied extensively in terms of the capacity of their soils to store organic carbon. While δ13C, δ15N, and C/N values for mangrove soils and sources are well reported, other indicators of OM maturity and composition are lacking. In this study, soil OM decomposition processes were investigated for a semi-arid bay head mangrove forest in New Caledonia. Mangrove tissues and 20-cm soil cores were collected in monospecific stands of Avicennia marina and Rhizophora stylosa. The isotopic compositions of the samples were assessed, along with their molecular compositions (lignin-derived phenols and neutral carbohydrates). Rock-Eval analysis was also performed on the samples to investigate OM characteristics. Results showed that stable isotope ratios and Rock-Eval parameters followed similar vertical trends beneath both species indicating the influence of depth on OM state. However, the more anoxic conditions beneath R. stylosa limited OM decomposition as shown by the lower TpS2 values (indicator of OM thermal stability). Neutral carbohydrates and, surprisingly, lignin-derived phenols, were lost at higher rates than bulk organic carbon beneath both mangrove species. Selective degradation of individual compounds was observed, and species-dependent variations associated with the redox conditions and the OM sources were identified. We suggest that lignin was degraded, even in anoxic environments, because of the amount of labile lignocellulosic components in the soil. These findings enhance our understanding of OM dynamics in mangrove ecosystems, shedding light on the mechanisms underlying carbon cycling and their implications for global carbon storage and ecosystem management
RECHARGE, a model of potential recharge of aquifers applied to mainland France
No full textInternational audienceCalculating aquifer recharge provides a means of estimating the renewable fraction of groundwater resources, which is often difficult to quantify. This paper introduces the RECHARGE method, developed to calculate potential groundwater recharge from precipitation infiltration, and its application across mainland France over an extended historical period.The method relies on a simple soil water budget approach to estimate effective precipitation, using meteorological data and a spatial parameter that accounts for land cover and allows the seasonal variability of evapotranspiration to be reflected. An effective precipitation infiltration ratio (EPIR) is then derived for catchments with homogeneous geological lithology, based on linear regressions involving the baseflow index and a GIS-derived parameter. Given the low interannual variability of the baseflow index, the EPIR is assumed to remain constant over time and is subsequently used to convert effective precipitation into potential recharge at the scale of all groundwater bodies in mainland France.To validate this approach, annual effective precipitation estimates were compared for 556 selected catchments, both with observed annual river flows and with outputs from the physically based SURFEX model. The calculated potential recharge was also evaluated at both annual and seasonal scales for the entire French territory, using SURFEX as a reference. Results demonstrate that the RECHARGE model can effectively estimate annual and seasonal potential aquifer recharge. It is suitable for large-scale applications without requiring detailed knowledge of aquifer properties. Future improvements are envisioned, particularly to enhance monthlyscale accuracy in mountainous regions.</p
Response of an active fault to hydraulic stress in the context of future geothermal development
No full textInternational audienceGeothermal development in faulted basin environments presents specific challenges related to induced seismicity. This study investigates the hydro-mechanical behavior of the Vuache fault, located within the Annecy Basin (France), to assess the potential seismic hazard associated with future geothermal exploitation of the fractured and karstified carbonate aquifer. Based on an integrated dataset combining geological, geophysical, and hydrochemical observations, a 3D conceptual model of deep fluid circulation was constructed to guide numerical hydro-mechanical simulations. The results highlight a heterogeneous permeability structure controlled by three main fracture sets (NW–SE, NNE–SSW, ESE–WNW) and the presence of a conductive zone (~20–30 Ω·m) beneath Épagny at 1–1.5 km depth, spatially coincident with the 1996 Mw 5.3 earthquake area. Preliminary simulation outcomes suggest that significant fault reactivation would only occur under overpressures of approximately 10 Mpa, well above typical operational pressures expected in permeable carbonate systems. Consequently, the Épagny sector appears as a favorable target for medium-depth geothermal development. Further refinement of the geological and hydro-mechanical models is recommended to better constrain overpressure thresholds and fault stability
Constraints of basement geometry and supra-salt cohesion on deformation of salt-bearing fold-and-thrust belts: a discrete-element study
No full textInternational audienceSalt-bearing fold-and-thrust belts (FTBs) in foreland basins exhibit complex structural architectures, primarily governed by the interplay among basement geometry, supra-salt mechanical strength, and the detachment behavior of intervening salt layers. However, the respective roles of basement surface geometry and supra-salt cohesion in controlling deformation localization, thrust segmentation, and fold development remain poorly constrained, particularly in regions with limited subsalt seismic imaging. To address this gap, we conducted two-dimensional discrete element method (DEM) simulations to systematically assess how variations in basement surface geometry and supra-salt cohesion influence the structural evolution of salt-bearing FTBs. The results show that lateral variations in basement morphology produce significant heterogeneity in salt layer thickness, thereby strongly influencing salt particle rearrangement and deformation localization. Redistribution of salt particles from thick to thin zones leads to compression and uplift in the overburden, while reverse movement induces extension and subsidence. A relatively low supra-salt cohesion promotes more rapid deformation front propagation, increased fold density, and more frequent salt piercement, whereas a relatively high cohesion delays deformation front propagation and favors fewer but higher-amplitude folds and enhanced thrust faulting. Comparisons with representative natural examples demonstrate that the models broadly capture the main structural features of salt-related FTBs at a regional scale, including large-scale thrust systems and salt-cored folds. Overall, our findings highlight that basement relief and supra-salt cohesion are first-order controls on structural evolution in compressional salt-bearing systems, thereby enhancing the understanding of deformation localization, thrust segmentation, and fold development
Effect of Minor Components on the Density of Geothermal Fluids Dominated by NaCl, KCl and CaCl2 Dissolved Salts
No full textInternational audienceGeothermal fluids are highly variable in chemical composition and ion concentration. Parametrising density, as one of the most important fluid properties for geothermal reservoir development, is therefore challenging. The purpose of this paper is to test the hypothesis that saline geothermal fluids can well be characterised for density when only the dominating dissolved salts (i.e., NaCl, KCl, and CaCl 2 ) are taken into account, thus neglecting any minor fluid constituents. For the example of four geothermal sites with known chemical fluid composition and significant differences in total salt content (Groß Schönebeck and Insheim, Germany, Balmatt, Belgium, and Heemskerk, The Netherlands) synthetic aqueous solutions of the main salts without and with three different other salts (i.e., LiCl, SrCl 2 , and MgCl 2 ) representing the minor fluid constituents were parametrised for density at atmospheric pressure and temperatures between 293 K and 353 K. Moreover, density was derived numerically using the PHREESCALE chemical code and evaluated against the analytical data. The results demonstrate that: (1) an effect of the ion type is evident with density increasing in the order of added LiCl, MgCl 2 , and SrCl 2 at a given concentration. (2) The uncertainty in density when neglecting any minor fluid components is at most 2 % which indicates that fluid density can be well characterised when applying the database of the main salts only. (3) The match between analytical and numerical data is excellent with differences generally less than 1 % evidencing that PHREESCALE permits to reliably predict the density of complex and multicomponent geothermal fluids
Microstructural, compositional and textural inheritance in deformed mafic amphibolites
No full textInternational audienceThis study investigates the scales of compositional equilibria and the role of early hydration for the development of microstructures and mineral fabric in mafic amphibolites, all deformed along a major tectonic plate boundary (Hokkaido, Japan). From fractured domains to mm-size shear bands and meter-size shear zones, element and cathodoluminescence mapping, as well as thermodynamic modelling show that both in plagioclase and in amphibole, strong compositional gradients were observed at the smallest (10 to 200 micron) scale, which in many instances are inherited from an early, static stage of fracturing, hydration and replacement of igneous minerals.Phase distribution and grain sizes in shear bands and shear zones were also inherited this early metamorphic stage, giving rise to: (1) monomineralic amphibole layers derived from amphiboles replacing aggregates of Fe-Mg igneous minerals in metagabbros, (2) monomineralic plagioclase layers derived from plagioclase-rich domains of metagabbros that experienced limited early breakdown reactions and (3) intimately mixed and fine-grained amphibole-plagioclase layers developed only where symplectites after igneous minerals were previously formed.While crystallographic and shape preferred orientations of amphibole were acquired from early fracture-driven reactions, and then strengthened in shear bands/zones by dissolution-precipitation, nucleation and oriented growth, the ones of plagioclase, whose reaction was incomplete in fractured domains, continued to evolve with increasing viscous strain and reaction progress. Where plagioclase experienced early, partial breakdown, viscous strain was further accommodated by dissolution-precipitation and phase nucleation. In contrast, where igneous plagioclase was largely preserved, crystal plastic deformation accompanied dissolution-precipitation. Heterogeneous early hydration of mafic rocks led therefore to a patchwork of local reacted domains, where inherited microstructures gave rise to heterogeneous phase distribution, grain sizes, fabrics and preconditioned the rock for strain J o u r n a l P r e -p r o o f 2 partitioning, and hence, strain localization at a scale of hundreds of microns. In particular, phase mixing was the product not of strain, but rather of an initial stage of chemical reactions.</p
La gestion de l’eau : défi majeur pour l’humanité, nouvel enjeu de recherche sur l’innovation
No full textInternational audienceLa gestion de l’eau est devenue un enjeu majeur pour l’innovation, du fait de la pression anthropique croissante sur cette ressource, accentuée par le changement climatique. Elle constitue un domaine particulier d’innovation car l’eau est un bien commun, qui circule sur la planète, qui est nécessaire à la vie et à tous les secteurs économiques, et dont la gestion combine étroitement des dimensions technologiques, organisationnelles, institutionnelles et sociales. L’article précise ces enjeux et appelle à un renforcement des échanges entre « Water Studies » et « Innovation Studies », l’objectif qui a motivé le forum innovation 2023 « innover pour une gestion durable et concertée de l’eau ». Après une synthèse des fronts possibles de recherche entre ces deux communautés, l’article introduit les articles de ce numéro spécial d’ Innovations , en montrant leurs contributions complémentaires pour une analyse des innovations dans des situations contrastées de gestion de l’eau sur la planète
Microplastics quantification in organic-rich samples: the relevance of testing substrate-specific calibration curves
No full textInternational audienceUrban agriculture could rely on waste-based substrates, but potential contaminants such as microplastics should be evaluated for safe public use. However, quantifying macroplastics in these substrates is challenging due to their high organic matter content, which is difficult to remove completely, leading to interfering compounds and unreliable results. This study investigated the underexplored effects of organic matter on microplastics quantification employing pyrolysis-GC-MS. Natural organic matter (NOM) removal methods were tested on organic-rich peat-based substrate, reaching up to 46% of reduction with Fenton’s reaction. Then, calibration curves were prepared in two inorganic matrices, silicon dioxide and glass fiber powders, for high density polyethylene (HDPE), polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS) and polyvinyl chloride (PVC) across nine concentrations, from 0.01 to 10 µg/mg, adding polyflurostyrene (PFS) as internal standard. The selectivity of several polymer pyrolytic markers was compared. Polymer-spiked samples were subjected to Fenton’s oxidation and quantified with both inorganic calibration curves, overestimating polymer contents, up to four times for PET and PVC. The preparation of a third calibration curve, specific for peat, improved results for PS, but not for PP, PET, and PVC. For the first time, the three calibration curves were tested on untreated polymer-spiked (HDPE, PP, PS) waste-based substrates, and resulted in a better estimation closer to the expected polymer concentrations when substrates closely matched the curve’s matrix composition. The comparison of three calibration curves made with different matrices showed that the quantification of plastic polymers in organic-rich samples could be improved using matrix-specific calibration curves even without a complete NOM removal. This represents a novel methodological approach for plastic polymers quantification in complex matrices, minimizing the sample pre-treatment that could cause the loss of nanoparticles during filtration, evidencing that matrix similarity is key for reliable quantification in NOM-rich samples, even without its complete removal