Bureau de Recherches Géologiques et Minières

Manganese (Mn) removal in passive mine water treatment remains a challenge due to its slow oxidation kinetics, requiring specific biogeochemical conditions. Constructed wetlands are often the key functional units enabling Mn removal in full-scale passive treatment plants. This study examines the key biogeochemical factors influencing Mn removal in a full-scale passive mine water treatment plant located in Alès (South-East France). Over one year, monitoring of physicochemical parameters, microbial communities, and Mn speciation in solid phases was conducted every two months. Results highlight temporal variations in Mn removal efficiency, with two main mechanisms identified: (1) Mn carbonate (MnCO₃) precipitation, likely influenced by high carbonate concentrations in mine water, and (2) Mn oxide (δ-MnO₂) formation, mainly associated with reed rhizosphere, where it accumulates as mineral plaque. In mine water, Mn removal correlates with Fe particle concentrations, suggesting a catalytic effect, as well as with alkalinity and the abundance of microorganisms affiliated to Alteromonadaceae, suggesting a microbial influence. Mn removal appears to be primarily abiotic, driven by favourable pH and alkaline conditions that promote Mn carbonate precipitation, by autocatalytic oxidation reactions occurring on rhizosphere surfaces and by plant's design including surface area and hydrological conditions. Microbial communities may facilitate certain Mn removal processes depending on environmental conditions.

Deep-seated landslides in high mountain terrain typically deform slowly over years to decades, making their internal kinematics difficult to characterise from field observations alone. Here we investigate the Leo Pargil landslide on the southwestern flank of the exhumed Leo Pargil gneiss dome in the northwestern Indian Himalaya, a large active deep-seated gravitational slope deformation (DSGSD) in the region. Multi-temporal persistent scatterer interferometric synthetic aperture radar (PS-InSAR) analysis of Sentinel-1 data is combined with geological and structural information to characterise the landslide's present-day kinematics and internal segmentation. Ascending and descending Sentinel-1 data from 2018 to 2023 are combined to decompose InSAR-derived displacement into vertical and horizontal components, allowing spatial variations in displacement magnitude and direction to be resolved across the landslide body. The displacement field is strongly segmented, with faster-moving sections separated by sharp displacement gradients and relatively stable zones, indicating the presence of distinct internal sectors within the landslide. The upper part of the slope shows displacement patterns consistent with a rotational component near the headscarp, whereas the lower part is characterised by predominantly slope-parallel motion. Spatial variations in motion broadly follow mapped structural and lithological boundaries, indicating that inherited structures and slope geometry may influence the present-day deformation pattern. The results show that the Leo Pargil landslide is a segmented deep-seated gravitational slope deformation on the flank of an exhumed gneiss dome, with its present-day kinematics consistent with consistent with inherited structural heterogeneity and ongoing geomorphic processes.

Droughts are a growing concern for water managers, as climate change is expected to intensify both their severity and frequency. Accurately forecasting these events is crucial to mitigate their impacts. Semi-distributed hydrological modelling, by dividing the catchment into interconnected hydrological units, provides flow estimation at gauged and ungauged locations and explicitly accounts for some physical and climatic spatial variability across the catchment.In this study, four semi-distributed models (GRSD, MORDOR-TS, PRESAGES, RAMEAU) are implemented in the Meuse River catchment at Chooz, an area characterized by contrasting geological, topographic, and meteorological conditions. The models differ in their structural assumptions, notably regarding groundwater exchanges beyond topographic boundaries and the potential use of piezometric data during calibration.Following a joint calibration exercise, the four models provide consistent results on streamflow across the entire catchment and comparable performance at the outlet at Chooz in comparison to their lumped-model counterparts. Similar biases are observed among the models, which may reflect common limitations in their assumptions or uncertainties in flow measurements and meteorological data. The case study of the 2022 low-flow event highlights variability in simulated low flows, linked in particular to the choice of model and to the climate data used for calibration. Gauging measurements taken during low-flow periods would help strengthen these results. Future work should focus on improving the understanding and the representation of groundwater flows in semi-distributed hydrological models.

Aquifers may naturally contain undesirable and toxic trace elements, known as geogenic contaminants. The presence of these micropollutants poses a major challenge for groundwater management, and has health, economic, and environmental consequences.Areas with high concentrations, either elevated or exceed the guideline value of water standards, are generally identified through the analysis of groundwater data. However, it should be possible to predict these occurrences based on their presence in the solid matrices of aquifers and their mobilization controlled by the physicochemical conditions of the water.To better predict the occurrence of inorganic natural pollutants, we have developed a methodology, based on an integrated approach to better understand the distribution of these elements in aquifers, the conditions controlling their presence, and their evolution in groundwaters.The methodology combines two complementary approaches: i) predictions of geogenic elements content in rocks, including their speciation, using a source to sink methodology are cross-correlating with ii) hydrogeochemistry to identify water-rock interaction processes and the potential mobility of the elements according to physicochemical conditions (e.g., redox conditions). This makes it possible to predict the spatial distribution of geogenic elements (e.g. As, Se, F, etc.) as well as the processes of mobilization in groundwater.Using a geographic information system (GIS), this study compares predicted occurrences using a source-to-sink (S2S) approach with available data including a large dataset on groundwater quality data (ADES data base, a national database publicly available). By interpretating the chemical composition of water, geochemical modelling via PHREEQC and geological data, it is possible to confirm but also to contribute to the S2S modelling.The study focuses on aquifers linked to the Massif Central (France). Geological source-to-sink paleomaps and drilling data are used to correlate the availability in sedimentary deposits of elements such as arsenic (As), selenium (Se), fluorine (F), with the main periods of erosion, transfer, deposit and remobilisation between the end of the Cretaceous and the Miocene. Arsenic, in particular, is studied in various geological layers with a focus on its speciation and mobilization in confined aquifers such as the Beauce calcareous confined aquifer (Southern Paris Basin).This approach presents a real interest in terms of groundwater quality, as it helps to anticipate water quality degradation linked to groundwater exploitation in aquifer impacted by the natural presence of geogenic metals.This work is part of the PEPR OneWater DEESAC project (France 2030), illustrating a transdisciplinary approach combining geology, geophysics, geochemistry, and hydrogeology.

Tidal stress is a periodic stress acting globally on the Earth, driven primarily bythe gravitational forcing of the Moon and the Sun. Understanding how tidalstress can trigger seismic events is essential for constraining tectonicenvironments that are sensitive to small, periodic stress perturbations.Here we investigate tidal triggering on stable sliding, velocity-weakening (VW)rate-and-state frictional (RSF) faults using a spring-block framework. We firstapply idealized step-like and boxcar normal stress perturbations todemonstrate a resonance-like amplification of slip rate when the perturbationduration approaches the intrinsic RSF time scale. Building on this observation,we perform non-dimensional analyses and numerical simulations withsinusoidal tidal-like perturbations to identify the key parameters controllingtidal triggering and their admissible ranges. We further characterize thetriggered events through observable quantities, including radiation efficiencyand tidal phase. Our results show that resonance effects allow tidal stress to trigger bothregular periodic and complex temporal slip events on otherwise stable slidingVW faults. The triggering behavior is primarily controlled by two non-dimensional parameters: the normalized perturbation period and thenormalized perturbation amplitude. Increasing the normalized period shiftsevent timing from peak tidal stress toward the maximum stress rate, whereasincreasing the normalized amplitude promotes a transition from slow to fastslip events. The parameter space permitting tidally triggered slip eventssuggests that the RSF parameter,$a\sigma$, which characterizes theinstantaneous frictional strength of an interface, should not exceed tens tohundreds of kilopascals, and that the characteristic slip distance for frictionalweakening is likely on the order of micrometers.

Around the Late Priabonian-Early Rupelian, the Paris Basin is characterized by an incomplete succession of sediments deposited at the marine-continent interface. In the overall marine record, this interval is marked by the Eocene-Oligocene Transition (EOT), characterized by a climate deterioration and a significant sea level drop, associated with the permanent establishment of the Antarctic ice cap. Nevertheless, the EOT is poorly documented and understood in terrestrial areas.Located between the active tectonic regions of the Pyrenean and Alpine orogens and the West-European Cenozoic Rift Systems, the lagoon to lacustrine deposits of the Paris Basin therefore enable to acutely record both global and local processes (glacio-eustasy, climate, tectonic). A detailed stratigraphic framework is consequently necessary to estimate the contribution of each of these controls. This study is based on: 1) a large-scale correlation of boreholes in order to study the 3D organization of deposits and their lateral and vertical variations, and 2) an elementary and isotopic geochemical, mineralogical, and paleontological study to clarify the depositional environments and the causes of the observed variations (sea level, tectonic and hydrological changes). The analyzed sites are located around tectonic structures (the Bray, Beynes-Meudon, and Remarde anticlines and the Saint-Denis syncline) and in various areas, ranging from the edges to the center of the Paris Basin.We established a correlation between lagoon-marine deposits of the center of the basin and lacustrine deposits of its southern and eastern edges. Detailed sedimentological studies of the sites reveal a two-steps evolution. The first step is marked by marls deposited during the latest Priabonian. Their mineralogical and chemical composition indicates a deposition evolving from a clastic to a chemical-dominated system in a wetter to drier climate. The second step, during Early Rupelian times, shows the return to detrital deposition in a wetter climate. More specifically, the sections show a mineralogical, chemical and environmental separations. The Priabonian cycle is influenced by sea level variations (marine incursion, then confinement of the basin) and a climate changing from wetter to drier. The Rupelian cycle shows a global transgression in a wetter climate, briefly interrupted by a confinement of the basin, but above all the reactivation of tectonic structures linked to the Pyrenean compression, which caused palustrine deposits on the anticlines and marine deposits in the synclines.The Paris Basin shows to a lesser extent the same record of the EOT as several marine sites. The major regression is only illustrated by the confinement and partial emersion of the basin in the latest Priabonian; the cooling seems to be recorded by the progressive increase in oxygen isotope values, and the aridification by mineralogical proxies and the known floral evolution. The basin also reflects the west-European regional geodynamics with the recurrence of tectonic structures in the Early Rupelian associated with the African-Eurasian convergence, illustrated for instance as well by the inversion of the Cotentin and Hampshire basins, further north of the Paris Basin.

Earthquake rupture propagation speed is an essential source factor that largely controls hazard and risk. However, measuring rupture speeds of natural earthquakes is often challenging and ambiguous. Near-fault seismic waveforms (recorded within several km) are believed to have high capability for resolving rupture process. In this study, we probe the feasibility of using near-fault data signatures to directly infer rupture speeds in continental strike-slip earthquakes. To thoroughly understand near-fault features, we synthesize the near-fault seismic waves for kinematic source models on a strike-slip fault under different rupture speeds in a 3D medium. We identify the dependence of velocity waveform and particle motion on rupture speed in both amplitude and shape. In addition, we compare our results with the analytical solution with steady-state constant rupture speed. The discrepancies between the kinematic model and the analytical model indicate the contribution of radiation from different configurations. With inspecting the near-fault dataset of eight M>7 strike-slip earthquakes, we find that instead of dealing with the velocity waveforms with multiple high-frequency spikes, the features of the particle motion shape are easier to identify. Then we apply the particle-motion-based criterion to identify signatures associated with supershear, subshear, and other complexities such as multiple rupture fronts and initial-stage rupture phase. Our study highlights the further application of near-fault seismic data in studying earthquake sources.

Debris flows are a significant geohazard in the semi-arid mountain belts of southwestern Türkiye, where short-duration, high-intensity rainfall frequently triggers rapid sediment mobilization, generating destructive debris-flow hazards that threaten settlements, transportation corridors, and agricultural land. The catastrophic 6-7 August 2018 debris-flow event, reported to have caused severe damage to agricultural fields, livestock, and road infrastructure (in both two villages, one day apart) together with more recent rainfall-triggered events in the area, highlights the vulnerability of the region; since these basins drain into the Elmalı polye, a critical agricultural hub, assessing debris-flow susceptibility is essential for future risk mitigation. This study presents a regional debris-flow susceptibility assessment for the Elmalı Basin (Western Taurus Mountains) in Antalya, Türkiye. Using a 5m resolution DEM, NDVI-based vegetation change analyses, topographic thresholds (slope, curvature, flow accumulation), and lithological data, potential source areas were identified, and runout paths were modeled with the empirical Flow-R approach. Model calibration was supported by geomorphic evidence of the 2018 event, and NDVI difference maps provided an effective tool for evaluating the accuracy of runout angle calculations. The results highlight several channels where steep, concave slopes coincide with high-susceptibility zones, indicating that certain settlements and agricultural fields lie within potential impact zones.

Extreme value theory provides effective approaches and methods for estimating return levels RL (with a typical return period >100 years) of extreme events. However, the lack of sufficiently representative observations to properly fit extreme value distributions (EVDs) is a recurring problem for any metocean engineer in situations where the number of observations is limited or of poor quality [1]. To overcome this problem, augmenting the set of observations with complementary information sources is an interesting option. In this paper, we address this problem by fitting EVDs to both observations and predictions from machine learning models using the approach developed by [2]. By design, however, the predictions of machine learning models are uncertain because they are learned from a limited number of training samples. We therefore propose to explicitly take this error into account when inferring the EVD parameters within an approximate Bayesian computation (ABC) scheme combined with the Wasserstein distance [3].The added value of this ML approach, which takes prediction uncertainty into account, is shown for cyclone-induced waves in Guadeloupe (Lesser Antilles) using a large database of extreme waves (representative of 1,000 years of cyclonic activity) that were numerically calculated within [4]. A random forest (RF) regression model is trained to link cyclone characteristics (radius, atmospheric pressure, distance to the eye of the hurricane) to significant wave height, and the quantile variant of the RF model is then used to model prediction error within the ABC scheme. Comparison with the 100-year and 500-year RL reference solutions (calculated using the complete database) shows that the ML-based approach results in low bias and high reliability of RL estimates as well as gain in computational efficiency, even when the sample size is reduced by a factor up to 10 and even when the RF prediction error remains moderate with cross-validation coefficient of determination of 70–75%. The benefit of integrating the ML prediction error is shown in different contexts, both along Guadeloupe coasts and in deep ocean environments.[1] Jonathan et al. (2021). Ocean Engineering, doi:10.1016/j.oceaneng.2020.107725[2] Rohmer et al. (2023). Ocean Modelling, doi:10.1016/j.ocemod.2023.102275[3] Bernton et al. (2019). Journal of the Royal Statistical Society Series B, https://doi.org/10.1111/rssb.12312[4] Interreg Carib-Coast program, https://www.carib-coast.com/en/

The early Eocene long-term warming was punctuated by relatively short (50 to 200 kyr) and abrupt warming events, which are used as analogues to understand current anthropogenic global warming. Among these hyperthermal events, the Eocene Thermal Maximum 2 (ETM2) corresponds to an orbitally paced release of 2,600 to 3,800 Gt of carbon at 54.1 Ma. It has primarily been identified in deep oceanic settings, while terrestrial and coastal records of this event remain scarce. Indeed, the ETM2 has only been identified in shallow marine settings in a few locations (Arctic, USA Atlantic coast, Egypt, India, and New Zealand), hindering a full understanding of its environmental impact.Here, we present a high-resolution multi-proxy record from a newly drilled 25-m-long core in southwest Belgium (Mons Basin), at a paleolatitude of ~40°N, combining Gamma-ray spectrometry, mineralogy (XRD bulk-rock and clays, TEM, grain-size) and organic geochemistry (δ13Corg, Rock-Eval®, and palynofacies). Sedimentological interpretation indicates a siliciclastic tidal shallow marine environment (a few tens of meters water depth). Using an age model based on nannofossils, dinocysts and cyclostratigraphy, the ETM2 is recorded over approximately 2.5 m by a ~1‰ negative carbon isotope excursion (CIE) located within the NP11 nannofossil biozone. The peak of this CIE corresponds, with a slight delay, to an increase in carbonate content and nannofossil abundance, suggesting enhanced primary productivity related to an intensified hydrological cycle and higher nutrient inputs during the ETM2. An increase in detrital input is also suggested by the transition to coarser grain size. After a progressive decline in kaolinite, illite, and chlorite contents in the clay fraction, smectite becomes the dominant clay mineral during the CIE, possibly pointing to a transgressive event in relation with the ETM2, as also suggested by palynofacies and dinocyst assemblages.This study presents the first high-resolution record of the ETM2 in the coastal environments of the southern North Sea Basin, preserved in the Mons Basin. In these settings, the ETM2 is associated with a deepening trend, possibly related to sea-level rise, as well as with increased primary productivity and detrital inputs, which point to an enhanced hydrological cycle.