HAL-BRGM, les publications scientifiques en libre accès du BRGM
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Decoupling of Magnetic Fabrics From Magnetic Remanences: Insights From Migmatites in Central Tianshan, NW China
No full textInternational audienceAbstract The coupling of magnetic fabrics and magnetic remanences is critical in interpreting paleomagnetic data. To estimate whether primary magnetic fabrics imply primary magnetic remanences, and to assess the practicability of metamorphic rocks in magnetic study, we carried out petrographic, geochronological, rock magnetic investigations, and analyses in anisotropy of magnetic susceptibility and paleomagnetism on migmatites in the Central Tianshan, NW China. Petrological observations indicate no significant dynamic recrystallization post to the migmatization. In‐situ monazite U‐Pb dating suggests that the migmatization happened during ∼314–297 Ma. Rock magnetic results reveal that the magnetic properties of migmatites are dominated by biotites with minor titanomagnetites. Despite the structural and compositional complexities of migmatites, a simple magnetic fabric pattern is observed with concentrated magnetic foliations and dispersed magnetic lineations. The anisotropy degree and shape parameter significantly change from leucosomes, mesosomes to melanosomes, suggesting that the magnetic fabrics should have been acquired during the migmatization. Characteristic remanent magnetization directions were isolated from a quarter of samples with anomalous shallow magnetic inclination. Combined with available geochronological and paleomagnetic results from the Central Tianshan and neighboring blocks, the magnetic remanences preserved in the migmatites were suggested to be obtained at ∼314–303 Ma, later than the acquisition of magnetic fabrics, probably due to thermal remagnetization or resulted from long‐term progressive magnetization during tectonic exhumation of migmatites. This study provides an important yet rarely reported example to manifest the decoupling of magnetic fabrics from magnetic remanences. Meanwhile, migmatites are found to be operable materials for magnetic fabric and paleomagnetic studies
What is the most relevant soil structure parameter to describe field-measured N2O emissions?
No full textInternational audienceNitrous oxide (N 2 O) emissions from soil are partly controlled by aeration and gas transfer in soil, and thus by soil structure. The intensity of N 2 O emissions is usually expressed according to the water filled pore space (WFPS), calculated using the soil bulk density. These factors, even if they describe the soil structure and the water proportion in the porous network, do not inform about porous network characteristics among scales and their connectivity. The aim of this work was therefore to determine ( 1) to what extent the soil structure of an agricultural soil controlled N 2 O emissions during a snap-shot campaign and (2) which metric of gas transfer or soil structure was the most appropriate to describe the N 2 O emission variability at field scale. N 2 O emissions were measured with a mobile chamber on a maize crop after fertilization with several soil management practices resulting in four soil states (strip-till versus tillage, compacted soil versus uncompacted) with contrasting soil structure. Soil cylinders and bulk soil were sampled from 24 plots exhibiting a strong gradient in N 2 O emissions. Classical soil physical and chemical properties were measured, including soil bulk density and water filled pore space. Soil structure also was characterized quantitatively by X-ray tomography at meso and macro scales, and indirectly by gas transfer parameters. Clear differences were observed between low and high emission plots in terms of soil structure, soil temperature and nitrate concentration. However, soil structure appeared more strongly connected to N 2 O emissions, and some thresholds on soil structural indicators were relevant to disentangle high and low N 2 O fluxes. Some structural indicators at both scales (e.g. porosity, surface density) and gas transfer parameters (relative gas diffusivity, air permeability) were good descriptors of the observed N 2 O fluxes. Nevertheless, the gas transfer parameters can be easily measured over a short period of time, whereas the soil structure indicators determined from 3D images require an acquisition and a processing phase that can be time consuming. A good compromise to evaluate the field N 2 O flux potential from an easy measure would be to evaluate the relative gas diffusivity, which directly controls the diffusion of oxygen in soil and thereby the microbial processes of N 2 O production
Exploring the combination of agroecological and conventional farming practices through the hybrid farming concept
No full textInternational audienceSubstantial improvements in resource-use efficiency and conservation are required to fulfill the rising and evolving global food demand, while addressing environmental degradation issues. Agroecology has emerged as a promising pathway to tackle these challenges. A binary stance often prevails in traditional discussions on agricultural transitions, where conventional farming is pitted against agroecological cropping. The reality is that farming practices blend conventional and agroecological features, hence are hybrid. Here we propose a conceptual representation of hybrid farming, that combines diverse farming practices from contrasting agricultural models, aiming to meet production goals. A schematic representation is provided and illustrated by a case study located in the Merguellil downstream plain region in central Tunisia. Hybrid farming involves multiple combinations of agroecological and conventional farming practices with a range of different outlooks and objectives. In the case study, farmers implemented these combinations to increase their income and mitigate risks. The blend of practices used in hybrid farming is not static and can be ever-changing. Various factors, such as shifting socioeconomic and environmental conditions, market trends and interactions with upstream and downstream supply chains fuel this dynamism
La rando hydrogéologique: un autre moyen de rendre visibles les eaux souterraines
No full textNational audienceAt a time when groundwater is increasingly being discussed due to repeated droughts, promoting its positive image through hiking, a leisure activity accessible to all, is an opportunity that the hydrogeology community should seize.A l’heure où l’on parle de plus en plus des eaux souterraines pour des raisons de crises sécheresse répétées, leur mise en visibilité positive, au travers de la pratique de la randonnée, loisir accessible à tous, constitue une opportunité dont la communauté des hydrogéologues devrait se saisir
Trois sources karstiques franc-comtoises incluses à l'inventaire mondial des sources majeures
No full textInternational audienceAmong 14 French springs proposed by the French committee of MIKAS project, and validated by the world’s committee, three are situated in the Franche-Comté region. These are the Loue, the Lison and Arcier springs, based on 5 selection criteria: historical, aesthetical, economic, scientific and ecological values.Parmi les 14 sources françaises proposées par le comité français du projet MIKAS, et validées par le comité mondial, trois sont situées en Franche-Comté. Il s'agit des sources d'Arcier, du Lison et de la Loue, retenues sur 5 critères de sélection : intérêts historique, esthétique, économique, scientifique et écologique
Comment les approches couplées, hydrogéologiques et géochimiques, peuvent-elles contribuer à la gestion efficace des ressources en eau dans un aquifère confiné ? Exemple du système aquifère multicouche de Beauce (région Centre, France)
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ACTES DU 14ème COLLOQUE DE GEOPHYSIQUE DES SOLS ET DES FORMATIONS SUPERFICIELLES (GEOFCAN 2025)
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Navigating the Mining Industry Challenges: An Introduction to the CERA 4in1 Standards
No full textInternational audienceZusammenfassung Die Bergbauindustrie steht vor erheblichen Herausforderungen, darunter Nachhaltigkeit, Umweltbelastungen und die Einhaltung sich weiterentwickelnder regulatorischer Rahmenbedingungen. Diese Herausforderungen werden durch die globale Nachfrage nach verantwortungsvoller Beschaffung und Rückverfolgbarkeit entlang komplexer Lieferketten zusätzlich verschärft. Der CERA 4in1-Standard bietet ein innovatives Zertifizierungsrahmenwerk, das diese Probleme durch die Integration von Umwelt‑, Sozial- und Governance-Kriterien (ESG) über den gesamten Lebenszyklus des Bergbaus hinweg, von der Exploration bis zur Endproduktlieferung, umfasst. Dieses System kombiniert fortschrittliche Technologien wie Material-Fingerprinting und Blockchain-basierte Rückverfolgbarkeit, um Transparenz, Compliance und das Vertrauen der Interessengruppen zu gewährleisten. Das modulare Design des CERA 4in1-Standards ist mit internationalen Vorschriften abgestimmt und bietet Unternehmen einen strukturierten Weg zur Verbesserung ihrer Betriebsabläufe bei gleichzeitiger Erfüllung regulatorischer und marktseitiger Anforderungen. Dieser Artikel beschreibt die Struktur und Entwicklung des CERA 4in1-Systems und betont dessen Potenzial, Nachhaltigkeit, betriebliche Transparenz und robuste Zertifizierungsprozesse im Bergbausektor zu fördern. Der voraussichtliche Abschluss dieses Standards bis 2025 stellt einen entscheidenden Meilenstein dar, um verantwortungsvolle Praktiken voranzutreiben und die globale Integrität von Lieferketten zu stärken.The mining industry faces significant challenges, including sustainability, environmental impact, and compliance with evolving regulatory frameworks. These challenges are compounded by the global demand for responsible sourcing and traceability across complex supply chains. The CERA 4in1 standard emerges as an innovative certification framework, addressing these issues by integrating Environmental, Social, and Governance (ESG) criteria throughout the mining lifecycle, from exploration to final product delivery. This comprehensive system combines advanced technologies, such as material fingerprinting and blockchain-based traceability, to ensure transparency, compliance, and stakeholder trust. The modular design of the CERA 4in1 standard aligns with international regulations, providing a structured pathway for organizations to improve operations while meeting regulatory and market demands. This contribution outlines the structure and development of the CERA 4in1 system, emphasizing its potential to foster sustainability, operational transparency, and robust certification processes across the mining sector. The anticipated completion of this standard by 2025 represents a critical milestone in advancing responsible practices and enhancing global supply chain integrit
Influence du manteau neigeux sur le déclenchement des glissements de terrain: Une analyse statistique
No full textInternational audienceRain precipitation is a major landslide trigger and is used operationally to anticipate landslide hazards. However, in mountainous regions, snow significantly alters hydrological processes and affects hazard prediction: precipitation is stored as snow during the cold season and released later during melt periods. Despite its importance, the role of snowpack in landslide triggering remains underexplored.With climate change, rapid snowmelt events are expected to become more frequent. These events may influence landslide occurrence, as observed in the 1997 Umbria landslides (Cardinali et al., 2001), which followed intense snowmelt. Similar early-winter peaks of landslide activity, concentrated in a just a few days, have occurred in alpine region over the last 25 years (Le Breton et al. 2024). However, no clear and quantitative correlation between landslides and major snowmelt runoff events has been established so far.In this study, we conducted a statistical analysis combining the ONF-RTM landslide event database with meteorological and snow data from the S2M reanalysis (Centre d’Études de la Neige). Our results show that early snowmelt (late December to early January) coincides with a marked rise in landslide activity. Additional events occur in spring, when melt is driven by solar radiation and rainfall.Elevation plays a key role, with most landslides occurring between 600 and 1400 meters, especially around 900 meters in early winter and higher altitudes in spring.We identified three contributing parameters: (i) melt period initiation, (ii) absence of soil ice, and (iii) infiltration of snowmelt water potentially leading to soil saturation.These findings highlight the relevance of snowpack dynamics in landslide prediction and risk assessment under evolving climatic conditions.CARDINALI, M., ARDIZZONE, F., GALLI, M., et al. Landslides triggered by rapid snow melting: the December 1996–January 1997 event in Central Italy. In: Proceedings 1st Plinius conference on Mediterranean storms. Bios Publisher, Cosenza, 2000. p. 439-448.Le Breton, M., Thiery, Y., Faillettaz, J., Villard, N., Gasc, M., 2024. Snowmelt, a major landslide triggering factor ?, in: Proceedings from the 13th International Symposium on Landslides. Presented at Chambéry, France
Exploring crystallization pressure limits via molecular simulation
No full textInternational audienceCrystallization pressure can cause significant damage to various materials, particularly cementitious materials and geomaterials. Understanding the mechanism behind this pressure is essential to preserve these materials and limit their degradation. Although the phenomenon has been known for a long time, the results from theoretical calculations and experimental observations remain very heterogeneous. The confined crystallization process relies on the presence of a nanometric wetting film at the interfaces to sustain crystal growth. The conditions for the existence and stability of these nanometric films, as well as their transport properties, remain largely unknown due to the great difficulty of studying them experimentally. In this paper, we determine by molecular simulation the limits of the crystallization pressure phenomenon at the finest scale. We perform hybrid configurational bias Monte Carlo-molecular dynamics simulations to determine the critical pressure at which the wetting film separating the crystal from the pore surface disappears under various temperature and pressure conditions. We illustrate the influence of the wetting film’s composition on the crystallization process by comparing a confined pure water film to a confined brine solution film. The obtained results enable us to establish both an upper and a lower boundary for the crystallization pressure, to define the range of applicability for the existing theoretical equations, and to identify the limiting factors affecting the transport properties in the constrained films