HAL-BRGM, les publications scientifiques en libre accès du BRGM
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Precambrian crustal architecture of Malawi: a keystone in SE Africa
No full textInternational audienceThe results of a major geological mapping project in Malawi have produced a new model of the Precambrian structural architecture of this small country, with major implications for the whole of central-eastern Africa. In the north, the oldest rocks of the Palaeoproterozoic Ubendian Domain (c. 2150-1950 Ma), the traditional division into the Mbozi, Ufipa and Nyika “terranes” (here termed “subdomains - SD”) is confirmed, but with one important proviso. Geophysical data indicate that the Nyika SD extends westwards without break into the “Bangweulu Block” in northern Zambia, suggesting that they are one and the same and the name “Bangweulu-Nyika block” (BaNy) is proposed for the combined entity. The extended Nyika SD is considered to be the central zone of the orogen, with the other two being the steeply dipping root zones of nappes that were transported NE over the Tanzanian Craton during the Ubendian collision phase. The Ubendian Domain returns Neoarchaean to Palaeoroterozoic Nd model ages. It is unconformably overlain by the low-grade Mafingi Group metasedimentary rocks, seen as equivalents of parts of the Muva Supergroup in Zambia.The Irumide Domain in central Malawi is separated into the Mzimba, Kasungu and Mchinji subdomains. They are characterized by Nd model ages between 1.5 and 2.7 Ga, no Ubendian magmatism, voluminous collision-related granitoid magmatism between 1070 and 1030 Ma and medium to high-grade metamorphism. The South Irumide Domain in southern Malawi is subdivided into the Lilongwe, Unango and Nampula subdomains, characterized by Nd model ages between 1.1 and 1.5 Ga, indicating generation in a juvenile island arc geodynamic setting with little evidence of older crustal involvement. The Irumide orogeny is marked by tectonic stacking at ∼1070 Ma with polyphase reactivation at the end of the main collision at ∼1020 Ma and overprinting during the Pan-African event at ∼560 Ma. Structural younging of the Irumide thrust stack implies subduction of the South Irumide Domain to the north below the Irumide Domain, with the latter constituting an active continental margin SE of the Congo-BaNy craton. The main collision phase and prograde metamorphism between 1050 and 1020 Ma are interpreted as evidence of collision between the Congo-BaNy-Tanzania Craton (upper plate), and the subducting Proto-Kalahari Craton margin.The three fundamental Proterozoic domains of Malawi were intruded by several polyphase Neoproterozoic (Tonian) alkaline igneous plutons (Nyassa Suite) between ∼850 and 700 Ma, implying that the domains formed a contiguous block of continental crust in Rodinia at c. 1000 Ma. The Nyassa Suite represents a failed continental rift associated with Rodinia break-up between c. 700-640 Ma. To the west of Malawi, this event was manifested in a confined oceanic basin between the Kalahari and Congo cratons and represented by the Zambezi-Lufilian-Damara belts. This basin closed between 590 and 520 Ma resulting in the re-amalgamation of Congo and Kalahari during the later phases of the Pan-African orogeny and variable tectonic (shear zones), magmatic (Blantyre Suite) and metamorphic effects in Malawi increasing in intensity towards the south
Spatial predictions and uncertainty maps of global fallout radionuclides (137Cs and 239+240Pu) for the Southern Hemisphere
No full textInternational audienceThis repository contains high-resolution (1 km) spatial datasets for global fallout radionuclides across the Southern Hemisphere (extending to 20°N). The data includes spatial predictions, uncertainty estimates, and model applicability assessments for Cesium-137 () and Plutonium-239+240 () inventories in soil
Effects of temperature variations on aquifer biogeochemistry during high-temperature thermal energy storage operation: flow-through laboratory experiment insights
No full textInternational audienceReducing the carbon footprint of building heating and cooling is essential for reaching climate change mitigation goals. Seasonal High-Temperature Aquifer Thermal Energy Storage (HT-ATES) is a promising method to achieve these goals. However, the injection of high-temperature water may significantly alter aquifer geochemistry and microbiology by influencing redox equilibria and mineral solubility, and by strongly impacting the structure and activity of microbial communities, favouring shifts toward thermophilic microorganisms and changes in metabolisms. Although microbial life is ubiquitous in aquifers, biogeochemical processes occurring under HT-ATES conditions remain poorly understood, raising concerns regarding environmental impacts, system performances and long-term sustainability.We investigated the effects of heating and cooling cycles on the structure and functions of aquifer microbial communities. HT-ATES conditions were simulated in the laboratory using a pressurised (13 bar) flow-through column with the BRGM’s BioREP platform. Groundwater from a monitoring HT-ATES well in TU Delft campus (Netherlands) was injected through the aquifer sediments while the temperature of the experimental device varied cyclically within a range typical of HT-ATES warm wells (30°C to 50°C), before a last phase returning to the natural aquifer temperature (12°C). Geochemical parameters, such as pH, redox potential, conductivity, redox-sensitive elements were monitored in circulating water at the inlet and outlet points of the column. Changes in microbial community composition of sediments and circulating water were assessed through 16S rRNA genes Illumina sequencing.Preliminary results indicate that the aquifer sediments are quartz-rich, with presence of carbonates and clay minerals, and that the groundwater is of reduced brackish Na-Cl type. While intermediate and final sediment mineralogy analysis are still ongoing, groundwater analysis show that the chemistry remained stable throughout the experiment. A gradual clogging of the column (increase of the inlet pressure) was observed. Upon opening the experimental setup, precipitates were observed at the outlet of the column. Their origin, whether chemical or biological, are under investigation.Initial microbial analysis of the groundwater revealed a dominance of bacteria (89%), with major phyla including Firmicutes, Bacteroidota, Proteobacteria, Desulfobacterota, and Spirochaetota along with Halobacterota. Many of these taxa are associated with anaerobic and slightly saline environments and include fermentative microorganisms. Several dominant groups are mesophilic and/or non-spore forming taxa. Higher and fluctuating temperatures may promote alternative, more thermotolerant microbial assemblage. Ongoing metagenomic analyses aim to determine how temperature perturbations under HT-ATES conditions influence microbial communities’ composition and possible functions and assess the implications for associated biogeochemical processes.Acknowledgements: Funded by the European Union under grant agreement 1011096566 (PUSH-IT project). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or CINEA. Neither the European Union nor CINEA can be held responsible for them
D’albâtre et d’eau : le transport fluvial comme clé du rayonnement des gisements européens d’albâtre du XIVe au XVIIe siècle
No full textInternational audienceL’albâtre a été un matériau de prédilection pour la sculpture européenne dès la fin du Moyen Âge. Ses qualités intrinsèques en faisaient un matériau aussi recherché que le marbre mais avantagé par la répartition plus égale de ses gisements sur le continent européen. La longévité et le rayonnement des exploitations dépendaient de leur connexion au réseau fluvial. Nous comparons les gisements d’albâtre ayant un accès direct aux voies navigables à ceux dépendants du transport terrestre. La carrière de Notre-Dame-de-Mésage qui approvisionnait l’Avignon papal des XIVe et XVe siècles via la Romanche, le Drac, l’Isère et le Rhône, a dominé la sculpture française pendant cinq-cents ans. Elle concurrençait l’albâtre anglais arrivant en France et aux Pays-Bas par la rivière Trent et la Manche. Moselle et Rhin constituaient les axes de diffusion de la production lorraine. L’importance des albâtres jurassiens et provençaux, dont Saint-Lothain et Malaucène, restait, au contraire, surtout régionale
Block-Additive Gaussian Processes under Monotonicity Constraints
No full textInternational audienceWe generalize the additive constrained Gaussian process framework to handle interactions between input variables while enforcing monotonicity constraints everywhere on the input space. The block-additive structure of the model is particularly suitable in the presence of interactions, while maintaining tractable computations. In addition, we develop a sequential algorithm, MaxMod, for model selection (i.e., the choice of the active input variables and of the blocks). We speed up our implementations through efficient matrix computations and thanks to explicit expressions of criteria involved in MaxMod. The performance and scalability of our methodology are showcased with several numerical examples in dimensions up to 120, as well as in a 5D real-world coastal flooding application, where interpretability is enhanced by the selection of the blocks
Les formations agricoles dans le monde à l’épreuve de l’agroécologie
No full text[Articles publiés progressivement par la revue] Dans le cadre de l'approche des comparaisons internationales, ce dossier spécial de la revue Cahiers Agricultures vise à analyser les évolutions des curriculums des formations agricoles à travers le monde, tant dans les pays du Nord que du Sud, dans le contexte de montée en puissance des politiques de « transition agroécologique ». Il s'agit de comprendre les enjeux de l’élaboration des programmes des formations en agroécologie en fonction des définitions de l’agroécologie selon les contextes nationaux ou locaux, leur adoption et appropriation par les personnels de formation et leur réception par les publics concernés. Face à la prise de conscience croissante des enjeux environnementaux liés à l’agriculture, les politiques publiques réorientent les formations agricoles vers l’adaptation aux changements climatiques, la réduction d’usages des pesticides à travers l’intégration de nouveaux savoirs agronomiques en cours d’élaboration. Le premier axe propose d’interroger la manière dont les programmes d’enseignement (ou référentiels de formation) sont conçus pour répondre aux enjeux de la « transition agroécologique » (Métral, et all, 2016). Il s’agit d’analyser la traduction curriculaire des différentes conceptions de l’agroécologie. En effet, les définitions multiples de l’agroécologie (scientifique, politique, sociale, etc.), sa traduction en principes (HLPE 2019, FAO 2020, Wezel et al. 2020) se reflètent dans les contenus de formation, ce qui peut être source de tensions ou permettre au contraire d’intégrer une diversité de points de vue, de référentiels. Il s’agit aussi d’interroger les mécanismes qui permettent de sourcer plus rapidement les enseignements agronomiques sur les conditions d’activation d’innovations agroécologiques que documentent différents acteurs (recherche agronomique, organisations professionnelles, société civile). Le deuxième axe invite à examiner la manière dont les personnels de formation — enseignants, formateurs, conseillers, maîtres de stage — s’approprient et traduisent dans leurs pratiques pédagogiques ou professionnelles les référentiels et les orientations curriculaires liés à l’agroécologie (Gaborieau, Peltier, 2024). L’enjeu est de comprendre comment ces acteurs, situés à l’interface entre prescriptions institutionnelles et réalités locales, participent à la mise en œuvre effective des transformations attendues. Le troisième axe s’intéresse à la manière dont les publics en formation — élèves, étudiants, agriculteurs en reconversion, adultes en formation continue — reçoivent, interprètent et s’approprient (ou non) les savoirs agroécologiques transmis. L’objectif est d’analyser comment ces nouveaux contenus, porteurs de transformations profondes des pratiques agricoles, résonnent avec les trajectoires sociales (Sahuc, 2017), les représentations professionnelles et les projets de vie des apprenants
Evaluation multi-méthodes du risque de mouvement de terrain lié à d'anciennes carrières sur un ancien site militaire à Châlons-en-Champagne (51)
No full textNational audienceThe possible presence of large underground cavities (measuring several thousand cubic metres) at the site of an urban regeneration project in Châlons-en-Champagne prompted the urban community to commission a detailed study from BRGM. A review of existing knowledge and geophysical investigations using microgravimetry (4,377 stations covering an area of 65 ha) were followed by topographical surveys (accessible cavities) and geotechnical investigations with the aim of verifying the presence of underground voids, understanding the origin of gravimetric anomalies and assessing residual risks. The study focused on two sites, considered representative of two notable negative gravimetric anomalies. Each site was surveyed using a profile of surveys covering the areas without anomalies and the most pronounced anomalies (northern site: 14 boreholes over a 110 m profile; southern site: 30 boreholes over 134 m). Three drilling techniques were used to optimally interpret the geotechnical configuration of the sites (destructive surveys to search for voids, core sampling to directly visualise the ground, CPT to finely measure transitions between materials). No clear voids were identified during drilling. However, for the southern anomaly, 13 out of 23 boreholes show low resistance up to a depth of 18-23 m, which closely coincides with the location of the gravimetric anomaly. These results reveal the presence of an old backfilled openpit quarry: a completely new configuration in this location, as it never appears in the numerous archive documents consulted. For the northern anomaly, the results of the surveys, particularly CPT: 1) coincide almost perfectly with the gravimetric anomaly; 2) rule out geotechnical risks associated with former mining operations; 3) reinforce the hypothesis of a purely geological anomaly. The analyses carried out open up the possibility of simplified development and allow for the consideration of a precise measurement protocol to continue the analysis of this sector.La présence possible de grandes cavités souterraines (crayères de plusieurs milliers de mètres cubes) au droit d'un projet de réhabilitation urbaine à Châlons-en-Champagne a motivé la Communauté d'Agglomération à confier une étude approfondie au BRGM. Un état des connaissances et des investigations géophysiques par microgravimétrie (4377 stations sur une surface de 65 ha) ont été suivis de levés topographiques (cavités accessibles) et d'investigations géotechniques avec l'objectif de vérifier la présence de vides souterrains, de comprendre l'origine des anomalies gravimétriques et d'évaluer les risques résiduels. L'étude s'est concentrée sur deux sites, jugés représentatifs de deux anomalies gravimétriques négatives notables. Chacun des sites a fait l'objet d'un profil de sondages qui recoupent les zones sans anomalies et les anomalies les plus marquées (site nord : 14 sondages sur un profil de 110 m ; site sud : 30 sondages sur 134 m). Trois techniques de sondages ont été mises en oeuvre pour interpréter de manière optimale la configuration géotechnique des sites (sondages destructifs pour rechercher des vides, carottés pour visualiser directement les terrains, CPT pour mesurer finement les transitions entre matériaux). Aucun vide franc n'a été identifié en sondage. Pour l'anomalie sud, 13 sondages sur 23 présentent toutefois de faibles résistances jusqu'à 18-23 m de profondeur avec une forte coïncidence avec la localisation de l'anomalie gravimétrique. Ces résultats révèlent la présence d'une ancienne carrière à ciel ouvert remblayée : configuration totalement inédite à cet endroit car n'apparaissant jamais dans les nombreux documents d'archives consultés. Pour l'anomalie nord, les résultats des sondages, notamment CPT : 1) coïncident quasi parfaitement avec l'anomalie gravimétrique ; 2) écartent les risques géotechniques liés à d'anciennes exploitations ; 3) renforcent l'hypothèse d'une anomalie purement géologique. Les analyses effectuées ouvrent la possibilité d'un aménagement simplifié et permettent d'envisager un protocole précis de mesures pour poursuivre l'analyse de ce secteur
Uncertainty sources in a large ensemble of hydrological projections: Regional Climate Models and Internal Variability matter
No full textInternational audienceMulti-scenario, multi-model ensembles of hydrological projections are widely used to describe possible futures of regional hydrology and inform adaptation strategies. The Explore2 dataset is such an ensemble of river flow projections in Metropolitan France. It provides future simulations for 1735 catchments with modeling chains composed of different hydrological models forced by 36 regional climate projections based on bias-adjusted EUROCORDEX simulations. This study assesses the uncertainties of this ensemble with QUALYPSO, a method specifically designed to deal with incomplete ensembles and to disentangle and quantify all uncertainty sources, including that due to internal variability. Focusing on results obtained at the end of the century, this study shows a strong agreement between modeling chains towards decreases in low flows in a large southern part of France for a high-emission scenario, and very uncertain changes for the annual mean and high flows. Emission scenario uncertainty is the dominant source of uncertainty for low flows over the whole of France, and for mean annual flows in southeastern France. The contribution of the global and regional climate models is important for mean and high flows, especially in rainfall-dominated areas. Regional climate models contribute considerable uncertainty to low flows, much more than global models. The contribution of hydrological model uncertainty is large for low flows, moderate for mean annual flows, and small for high flows. For all climate and hydrological indicators, internal variability is often large and cannot be overlooked. It is often of the same order and sometimes larger than the uncertainty on the climate change response
Proposed survey sites for the FIQUgS project multi-physics carrier
No full textInternational audienceOne of the main objectives of the FIQUgS project is to deploy the Differential Quantum Gravimeter (DQG) in the field, to conduct geophysical surveys for various applications. Developed by exail, this instrument represents a major advancement over conventional gravimeters by simultaneously measuring gravity (g) and its vertical gradient (Γ zz ). To facilitate its handling due to its important weight, a robotic carrier was specifically designed to operate the DQG in the field. Furthermore, to enhance the imaging resolution in the near surface, a ground penetrating radar system, specifically developed for the project, is also operated on the robotic carrier.Here, we present the three sites to be surveyed by the multi-physics carrier within the project, and the survey strategy at each site. The first site, in Reims, France, pertains to the detection and characterization of a medieval moat for archeological applications. The second site is in the Netherlands and will allow to test the detection threshold of the instrument over an underground dipping tunnel. In the third site, in Nièvre, France, a regionally complex geological structure will be surveyed. These sites will be surveyed in the spring and summer of 2026, and will serve to showcase the enhanced imaging capabilities of the developed instrument</p
Experimental Assessment of hydrogen consumption by microbial communities from underground reservoirs: a European case study
No full textInternational audienceUnderground hydrogen (H2) storage is a promising solution for storing large amounts of energy and addressing the intermittency of renewable energy sources. However, H2 can be metabolized by part of the indigenous microbial communities inhabiting deep subsurface environments. Microbial H₂ consumption poses several risks, including loss of stored H2, deterioration of gas quality due to the production of secondary gases (e.g., H₂S, CH₄), and alterations of the physicochemical properties of the reservoirs. Through the HyLife CETP project, four potential hydrogen storage reservoirs (3 depleted reservoirs and 1 aquifer), exhibiting contrasting characteristics (temperatures ranging from 13°C to 70°C, salinity from 0.02% to 2%, etc.), were thoroughly investigated to characterize their hydrogenotrophic microbial communities and assess their capacity for H2 consumption. Experiments were achieved by the four microbiology laboratories involved in the project (NORCE, BRGM, TUL, and Isodetect). A series of triplicate batch experiments were conducted in serum flasks to monitor H₂ consumption over time under varying conditions: temperature shifts (+10°C and −10°C compared to on-site temperature), pH variations (+1 and −1 unit), presence of mixed rocks, and a second H₂ injection. Gas composition, aqueous geochemistry, and microbial DNA were analyzed to track changes in geochemical parameters and microbial diversity. Methanogenesis, sulfate reduction, and acetogenesis were the main microbial metabolic pathways involved. For all the samples from the depleted hydrocarbon reservoir, H₂ was completely consumed within 20 days, with a maximum consumption rate of approximately 1.6 mmol/L/day. In contrast, H2 consumption in the aquifer was significantly lower, with only 20% of the injected H₂ metabolized after 100 days. H₂ consumption was strongly influenced by experimental conditions. For depleted reservoirs, temperature variations reduce hydrogenotrophic methanogenesis and promote acetogenic pathways and the accumulation of organic acids. The presence of rocks also significantly influenced microbial diversity and metabolic activity by promoting the reduction of sulfate and fermentation. A re-feed of H₂ into the bottles revealed variable H2 consumption rates depending on the timing of the reinjection and the availability of CO2. These findings highlight the importance of considering transient states and temporal dynamics when evaluating H2 behavior in deep environments