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The French scientific expedition, commanded by Captain Nicolas Baudin, which visited Australia between 1801 and 1803, carried out the first geological surveys along the continent's western and southern margins. Louis Depuch and Charles Bailly, the expedition's geologists, were educated at the École des mines and the École polytechnique respectively. Their ideas, and those of the expedition's zoologist François Péron, were influenced by the teachings of Dolomieu and the works of de Saussure. They followed the Neptunist school of thought with regard to the origin of granite, but rejected this theory for volcanic rocks in assigning their formation to lavas of subterranean origin. The geological discoveries made in Australia were not, at the time of the expedition's return, received with much appreciation. This was largely due to death of Depuch on the return voyage and to the loss of his journal. In time, a number of scholars recognised the importance of the work of these pioneers of Australian geology., L'expédition scientifique française, sous le commandement du capitaine Baudin, visita l'Australie entre 1801 et 1803. Parmi les savants, il y avait Louis Depuch (1774-1803) et Charles Bailly (1777-1844), les premiers géologues à étudier l géologie le long des côtes de ce continent. Leurs travaux en Australie furent fortement influencés par les idées des célèbres géologues Dolomieu (1750-1801)et Horace-Bénédict de Saussure (1740-1790), qu'ils appliquèrent aux roches de ce continent. Les écrits de Depuch et Bailly, et ceux du zoologiste de l'expédition, François Péron, démontrent qu'ils acceptaient la théorie neptuniste pour l'origine des granites, qu'ils considéraient comme les roches les plus anciennes. Cependant ils réfutaient cette théorie pour la formation des basaltes, qu'ils considéraient comme des produits des feux souterrains. Après le retour de l'expédition en France, la collection géologique ne suscita pas un grand intérêt. La mort de Depuch à l'île de France (île Maurice) et la perte regrettable de son journal, ont contribué au manque d'appréciation de leurs découvertes. Avec le temps, quelques-uns des savants européens ont cependant reconnu l'importance des travaux de ces pionniers de la géologie australienne.

The reconstruction of gap-free signals from observation data is a critical challenge for numerous application domains, such as geoscience and space-based earth observation, when the available sensors or the data collection processes lead to irregularly-sampled and noisy observations. Optimal interpolation (OI), also referred to as kriging, provides a theoretical framework to solve interpolation problems for Gaussian processes (GP). The associated computational complexity being rapidly intractable for n-dimensional tensors and increasing numbers of observations, a rich literature has emerged to address this issue using ensemble methods, sparse schemes or iterative approaches. Here, we introduce a neural OI scheme. It exploits a variational formulation with convolutional auto-encoders and a trainable iterative gradient-based solver. Theoretically equivalent to the OI formulation, the trainable solver asymptotically converges to the OI solution when dealing with both stationary and non-stationary linear spatio-temporal GPs. Through a bi-level optimization formulation, we relate the learning step and the selection of the training loss to the theoretical properties of the OI, which is an unbiased estimator with minimal error variance. Numerical experiments for 2D+t synthetic GP datasets demonstrate the relevance of the proposed scheme to learn computationally-efficient and scalable OI models and solvers from data. As illustrated for a real-world interpolation problems for satellite-derived geophysical dynamics, the proposed framework also extends to non-linear and multimodal interpolation problems and significantly outperforms state-of-the-art interpolation methods, when dealing with very high missing data rates.

International audience; Since its landing in Jezero crater in February 2021, the western delta of Jezero has been one of the main targets for the Perseverance rover to explore and sample sedimentary rocks that lead us to better understand the environmental evolution of the region, and could host traces of past biosignatures.During the first year, the rover explored the floor of Jezero crater, focusing on aqueously altered igneous rocks. It also provided the opportunity to remotely observe the main delta front and its remnants (e.g., the Kodiak butte). This allowed us to distinguish several beds of sandstones (with local occurrences of boulders up to 30 cm) arranged into bottomsets, foresets and topsets morphologies. This tripartite geometry and steep slopes of foresets are characteristic of a Gilbert-type delta, formed by the deposition of fluvial sediments prograding into a standing body of water, here a paleolake whose level can be constrained by the transition from the foresets to topsets. Massive beds of boulder conglomerates (with boulders up to 1.5 m) have also been observed at or close to the top of many locations along the delta’s front, hinting at a transition to higher energy flows. Collectively, these elements argue for a polyphase complex depositional history of the delta through time.The toe of the current delta front was reached by the rover on Sol 422 (April 2022) when Perseverance arrived at the Enchanted Lake outcrop, at the base of the southeastern end of the promontory informally named Cape Nukshak on the distal end of the delta. The first in-place sedimentary rocks that were observed were a succession of thinly-laminated medium/coarse sandstones and mudstones. Then, Perseverance pursued its route towards the delta and started its ascension at Hawksbill Gap to assess the first half of the lower delta succession. Strata at the base of Hawksbill Gap are mostly composed of fine to coarse-grained rocks ranging from mudstones to granule conglomerates, displaying planar to low-angle cross-stratifications.These fine-grained detrital rocks are likely to have been deposited by fluvial to deltaic processes. There, the rover collected the first sets of paired sedimentary rock samples (coarse sandstone to micro-conglomerate) that will represent the fine- and coarse-grained lower delta succession once returned to Earth.

International audience; The Cenozoic history of the Tibetan Plateau topography is critical for understanding the evolution of the Indian-Eurasian collision, climate, and biodiversity. However, the long-term growth and landscape evolution of the Tibetan Plateau remains ambiguous, it remains unclear if plateau uplift occurred soon after the India-Asia collision in the Paleogene or later in the Neogene. As the landscape evolution is controlled mainly by mountain uplift and surface processes, the present-day river profiles and the drainage basin geometries preserve important information that can be extracted to infer the long-term history of mountain uplift with numerical models. Here we focus on the southeastern Tibetan Plateau where three of the world’s largest rivers draining the Tibetan Plateau (the Yangtze, Mekong, and Salween Rivers, i.e., Three Rivers) have incised deep valleys with distinctive geomorphic signatures. We reproduce the uplift history of the southeastern (SE) Tibetan Plateau using a 2D landscape evolution model, which simultaneously solves fluvial erosion and sediment transport processes in the drainage basins of the Three Rivers region. Our model was optimized through a formal inverse analysis with a large number of forward simulations, which aims to reconcile the transient states of the present-day river profiles. The modeling results were ultimately compared to existing thermochronologic and paleoelevation datasets to help decipher between competing tectonic models that predict contrasting topographic evolutions. Our results suggest initially low elevations during the Paleogene, followed by a gradual southeastward propagation of topographic uplift of the plateau margin until present day. Our modeling thus does not support Paleogene formation of the SE Tibetan Plateau with a major subsequent degradation via upstream fluvial erosion. The quantitative constraints on landscape evolution achieved based on drainage patterns in SE Tibet indicate a powerful tool potentially applicable to other regions to infer important implications for the evolution of Indian-Eurasian collision, Asian monsoons, and biodiversity, as well as the geodynamic forces involved in collisional orogens.

International audience; Navigable canals contribute to the improvement of connectivity between marine, coastal and inland waterways networks. This paper questions the location of active canals during the Roman period in relation to their archaeological and geographical contexts in which they were excavated. During the Roman period, literary and archaeological evidence reveal that most of the canals were dug in lowlands, coastal plains, and especially in river deltas. Locally, canals connected fluvial and/or coastal port-cities to inland waterways and maritime routes (e.g. Ostia-Portus, Ravenna, Aquileia, Alexandria). Additionally, some canals could have had a regional relevance in interconnecting fluvio-coastal port systems or possibly organising wider port systems. We identified three types of coastal settings that hosted regional projects of canals or actual constructed canals: (1) river deltas with the Nile delta as the archetype; (2) overlapping or contiguous deltaic plains similar to the Northern Adriatic coastal plain; and (3) separated coastal or deltaic plains, categories in which most of the Mediterranean port systems fit, especially the coastal port system of Rome. This paper explores the potential of these fluvio-coastal landscapes in which canals may have contributed in establishing interconnected port systems.

International audience; The terminal migration of Homo erectus in Southeast Asia during Early Pleistocene is cardinal to our comprehension of the evolution of the genus Homo. However, the limited consideration of the rapidly changing physical environment, together with controversial ages of hominin bearing sites, make it challenging to secure the necessary robust timeline. Here, we reappraise the first appearance datum of Javanese H. erectus by adding to a compilation of earlier estimates the most reliable age constraints based on cosmogenic nuclides 10 Be and 26 Al produced in situ. We find that H. erectus reached Java and dwelled at Sangiran, Java, at least ⇠1.4 Ma ago and more probably around 1.8 Ma. Using this age as a baseline, we develop a probabilistic approach to reconstruct their dispersal routes, coupling ecological movement simulations to landscape evolution models. We demonstrate that the hospitable terra firma conditions of Sundaland facilitated the prior dispersal of hominins to the edge of Java, where they conversely could not settle until the Javanese archipelago emerged from the sea and connected to Sundaland. We estimate a characteristic dispersal time of H. erectus across Sundaland of a few tens to hundreds kyrs, indicating that changes in their physical environment, whether climatic or physiographic, cannot be ignored. Our comprehensive reconstruction method to unravel the peopling timeline of SE Asia provides a novel framework to evaluate the evolution of early humans.

International audience; Understanding mechanical properties and their microscopic origins is fundamental for multiple fields in condensed matter research. They are controlled by defects, dislocations, diffusion, as well as microstructures, which are not trivial to study under extreme conditions. This chapter summarizes the last 25 years of advances in high pressure devices, x-ray measurements, and data interpretation capabilities for addressing the deformation and plasticity of materials under extreme conditions, from experiments in large volume presses or diamond anvil cells, texture and stress analysis in powder x-ray diffraction, multi-grain crystallography, to self consistent models of materials behavior. Examples of applications are then provided in the fields of geophysics and materials science along with perspectives for studies of plastic deformation under extreme conditions in the coming years.

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International audience; Les collections du Laboratoire Magmas & Volcans (LMV) sont méconnues du monde scientifique et du grand public. Elles font néanmoins partie des vingt collections françaises référencées dans le “World Directory of Mineral Collections”. Les collections ont la particularité d’être hétérogènes, reflétant l’évolution dans le temps des thématiques scientifiques abordées.En 2016, le laboratoire a déménagé dans un bâtiment neuf dans lequel un lieu de stockage de 600 m2 est dédié aux collections : 100 m2 pour la collection de minéralogie (+ de 6000 échantillons), et cinq salles de lithothèque (500 m2) où sont rassemblés les roches, fossiles et vieux instruments.Les collections remontent au XIXème siècle. Elles se sont enrichies à la suite de legs d’éminents scientifiques, d’acquisitions (collections Deyrolles, Pisany, Demarty...) et d’apports réguliers des membres successifs du laboratoire. Les échantillons présents dans nos collections ont donc des origines diverses, provenant notamment d’anciennes études (publiées ou non), travaux de thèses ou d’excursions géologiques.Un grand nombre de pièces rassemblées ont été collectées dans le Massif Central, avec une abondante collection de minéraux du métamorphisme, du volcanisme, et de minerais. Ce fond régional est très riche, et à peu près complet pour les variétés existantes. Il comprend des échantillons “historiques”: exemple du saphir du Sioulot, des cristaux maclés d’orthose de Four la Brouque, de minerais des gisements miniers auvergnats (Pontgibaud, Brioude-Massiac, etc.). Il comprend également de nombreux échantillons d'anciennes colonies (pays d’Afrique, Madagascar), dans lesquelles les géologues clermontois ont travaillé.La prise de conscience d’une gestion des collections au laboratoire est apparue seulement depuis le déménagement des locaux. Une Commission des Collections, interne au laboratoire, composée de six enseignants-chercheurs n’ayant aucune décharge, et d’un personnel technique à temps partiel sur cette mission, a été créée. Notre première difficulté est l’élaboration d’une stratégie d’inventaire et de stockage, devant un nombre considérable d’échantillons (~63 000) “historiques” et “actuels”. Nous devons concilier les différents inventaires, selon les échantillons et leurs usages potentiels.Néanmoins, le laboratoire est doté d’une bibliothèque crée en 1856, ce qui permet d’optimiser l’inventaire, et d’enrichir les collections avec des documents anciens.

International audience

For more than 20 years, nadir satellite altimetry has revolutionized our understandingof mesoscale ocean dynamics by producing highly accurate sea surface height (SSH) measurements.For a large number of applications, one-dimensional SSH data must be interpolatedonto two-dimensional gridded maps regular in space and time. Today, these mapsare generated at a daily frequency at 1/4° resolution by an optimal interpolation algorithmoperationally implemented within the DUACS system. However, the spatial resolution ofthese maps, mainly limited by nadir altimetry sampling, does not allow to properly observesub-mesoscale structures, which are known to be essential for understanding, modeling andforecasting the climate system. The new Surface Water Ocean Topography (SWOT) wideswath altimetry mission will be launched in late 2022. SWOT will allow the observation ofprocesses on spatial scales of 15-30 km. However, the linear interpolation algorithm currentlyimplemented in the DUACS system needs to be improved to account for the non-linear dynamicsof fast sub-mesoscale structures. In addition, it will be necessary to distinguish motionsaround geostrophic balance from those of internal tides to properly study the associateddynamics.In this thesis, we explored the ability of the SWOT mission to meet its scientific objectivesby developing innovative tools to map SSH at high resolution while separating balanced andinternal tide dynamics. To do so, the strategy has been to include the ocean dynamics in theSSH mapping tools in the form of data assimilation with simple physical models adapted toeach dynamics.The first step of the PhD work was to apply the Back-and-Forth-Nudging (BFN) methodalong with a one-and-a-half layer Quasi-Geostrophic model (the so-called BFN-QG method)to map the balanced dynamics of the SSH. This technique is tested with both simulatedand real observations. The results show that BFN-QG substantially reduces mapping errorscompared to DUACS and this reduction is amplified when SWOT is added to the nadiraltimeter constellation. Also, the BFN-QG method can be adapted to combine large-scalecorrections from nadir data and small-scale corrections from SWOT data so as to reducethe impact of SWOT correlated noises and still provide accurate SSH maps. However, theperformance of BFN-QG applied to real nadir observations is reduced in low energy regions.In a second step, we focused on the issue of separating balanced and internal tidesdynamics from SWOT data. In particular, we developed a 4Dvar technique to assimilate SSHobservations into a linear Shallow-Water model to estimate the internal tidal dynamics (theso-called 4Dvar-SW method). A key strength of the 4Dvar-SW is its ability to estimate thenon-stationary internal tide. Two separation strategies are presented. The first implementsan alternating minimization algorithm that iteratively combines BFN-QG and 4Dvar-SWmethods. Although tested in an idealized experimental set-up, this technique seems promisingfor mapping and separating the contributions of the two dynamics. The results also indicatethat the temporal sampling of the observations is crucial to correctly estimate the internaltidal dynamics, and by extension the balanced dynamics. The second strategy relies on theimplementation of a global 4Dvar in reduced bases and an additive contribution of the tworeduced models. This technique is tested in the realistic framework of the calibration andvalidation phase off the coast of California and the performances are once again promising,in particular for estimating non-stationary internal tides dynamics., Depuis plus de 20 ans, l’altimétrie satellitaire nadir a révolutionné notre compréhension de la dynamique océanique de mésoéchelle en produisant des mesures très précises du niveau de la mer (SSH; pour Sea Surface Heigh). Pour un grand nombre d’applications, les données 1D de SSH doivent être interpolées sur des cartes 2D régulières en temps et en espace. Aujourd’hui, ces cartes sont générées quotidiennement à une résolution de 1/4° par un algorithme d’interpolation optimale implémenté de manière opérationnelle au sein du système DUACS. Cependant, la résolution spatiale de ces cartes, principalement limitée par l’échantillonnage de l’altimétrie nadir, ne permet pas d’observer convenablement les structures de sous-mésoéchelle, que l’ont sait essentielles pour la compréhension, la modélisation et la prévision du système climatique. La nouvelle mission altimétrique à large fauchée SWOT (pour Surface Water Ocean Topography) sera lancée à la fin de l’année 2022. SWOT permettra l’observation de processus à des échelles de 15-30 km. Cependant, l’algorithme d’interpolation linéaire actuellement implémenté dans la chaîne DUACS doit être amélioré pour tenir compte de la dynamique non-linéaire des structures rapides de sous-mésoéchelle. De plus, il faudra distinguer les mouvements autour de l’équilibre géostrophique de ceux des ondes de marée interne pour étudier convenablement les dynamiques associées.Dans cette thèse, nous avons exploré la capacité de la mission SWOT à répondre à ses objectifs scientifiques en développant des outils innovants pour cartographier la SSH à haute résolution tout en séparant les dynamiques équilibrée et ondulatoire. Pour cela, la stratégie a été d’inclure la dynamique de l’océan dans les outils de cartographie de SSH sous forme d’assimilation de données avec des modèles physiques simples et adaptés à chaque dynamique.La première étape de notre travail a été d’appliquer la méthode du Back-and-Forth-Nudging (BFN) appliqué à un modèle Quasi-Géostrophique à une couche et demie (méthode dite du BFN-QG) pour cartographier la dynamique équilibrée de la SSH. Cette technique est testée avec des observations simulées et réelles. Les résultats montrent que le BFN-QG permet de réduire substantiellement les erreurs de cartographie comparé au système DUACS et que cette réduction est amplifiée lorsque SWOT est ajouté à la constellation d’altimètres nadirs. Par contre, les données nadirs se révèlent nécessaires pour contraindre les grandes échelles spatiales lorsque les données SWOT sont polluées par des erreurs spatialement corrélées. De plus, les performances sont réduites lorsque la dynamique équilibrée est faiblement énergétique.Dans un second temps, nous avons traité la problématique de séparation des dynamiques équilibrée et ondulatoire. Pour cela, nous avons développé un 4Dvar assimilant les observations de SSH dans un modèle Shallow-Water linéaire pour estimer la dynamique de marée interne (méthode dite du 4Dvar-SW). Un atout essentiel du 4Dvar-SW est sa capacité à estimer la marée interne non-stationnaire. Deux stratégies de séparation sont présentées. La première implémente un algorithme de minimisation alternée qui combine itérativement le BFN-QG et le 4Dvar-SW. Bien que testée dans un contexte idéalisé, cette technique semble prometteuse pour cartographier et séparer les contributions des deux dynamiques. Les résultats montrent que l’échantillonnage temporel des observations est déterminant pour estimer correctement la dynamique de marée interne, et par extension la dynamique équilibrée. La seconde stratégie repose sur l’implémentation d’un 4Dvar global en bases réduites et une contribution additive des deux modèles réduits. Cette technique est testée dans le cadre réaliste de la phase de calibration et validation au large de la Californie et les performances sont une nouvelles fois prometteuses, en particulier pour estimer la composante non-stationnaire de la marée interne.

International audience; The Anthropocene, a new geological period when human actions are altering the habitability of the Earth for all forms of life, raises new challenges in terms of knowledge integration that fragmented approaches cannot overtake. Due to complex interactions within geo-eco-socio-systems (GESS), a “whole system” approach is required to answer societal concerns around soil capital, water resources, chemical pressure and biodiversity.To address these challenges, the TERRA FORMA project will design and test in-situ observation plateform coupling sensor viewpoints on human, biotic and abiotic dynamics. This project builds on pioneering and mature technological advances (optical sensors, 3D printing, IoT, AI) to design and probe a scalable network of smart sensors. We will develop a new generation of smart, connected, low-cost, low-impact and socially appropriated environmental sensors, adapted to field conditions, dedicated to capture the behavior, metabolism and trajectory of GESS emerging from states and fluxes of liquid, gas and solid matter and biota. These new technologies will contribute to shed light on “essential variables” for GESS and evaluate the descriptive and predictive potential of models over a wide range of contexts. TERRA FORMA gathers scientists, in an interdisciplinary effort at the crossroad of Earth, environmental, technological, computer and social sciences.In this presentation, we will show how instrumental developments (spectroscopy, lab on a chip, …) and methodological developments (biogeophysics, …) contributes to the construction of the observation plateform.

The stratigraphic interval spanning the Aptian-Albian transition is marked by a cluster of short-lived marine anoxic episodes referred to as Oceanic Anoxic Event 1b (OAE 1b). These short-lived episodes are, from the oldest to the youngest, the Jacob, Kilian, Paquier and Leenhardt events. We here aim at testing the impact of the long Milankovitch cycles (1.2-Myr and 2.4-Myr) on the recurrence of these oxygen-deficiency episodes by establishing a precise astrochronology of the OAE 1b interval from the Col de Pré-Guittard section (Albian GSSP, Vocontian Basin, SE France). The section belongs to the “Marnes Bleues Formation”, which is a thick (several hundred metres) clayey formation, interrupted by thin limestone beds and black shale layers, slumps and turbidites, all deposited in the hemipelagic part of the Vocontian Basin. Organic-matter carbon isotope ratios and Total Organic Carbon have been measured to precisely locate these events within the Col de Pré-Guittard section. A magnetic susceptibility signal was obtained from 3500 bulk rock samples collected every 5 cm. The sampling was performed on two parts of the Col de Pré-Guittard section to avoid a multi-decametric slump outcropping in one of the two section below the Kilian Level. However, two thin turbidite layers, near the Jacob and the Paquier events, remained unavoidable. Spectral analyses were performed using the Multi-Taper Method and the evolutive Fourier Transforms. These spectral analyses show the pervasive control of the 100-kyr eccentricity cycle and demonstrates a duration of (i) 1.6 Myr from the Jacob to the Kilian events, (ii) 1.5 Myr from the Kilian to the Paquier events, and (iii) 1.0 Myr from the Paquier to the Leenhardt events. Duration do not correspond to long Milankovitch cycles and thus do not favour the sole orbital control on the pacing of the anoxic events of the Aptian-Albian transition. Thus, other global forcing factors, as the volcanism, or local factors, as basin-scale paleoceanographic and climatic changes, have to be considered to explain this recurrence of anoxic conditions in the Vocontian Basin.

The size distribution of sediments together with their shape inform on their transport history, are important factors controlling the efficiency of erosion and transport, and control the quality of aquatic ecosystems. However, the size distribution of sediments is generally assessed using poorly representative field measurements and determining the grain-scale shape of sediments remains a real challenge in geomorphology. To tackle this issue, we develop a new methodological approach based on the segmentation and geomorphological fitting of 3D point clouds. Point cloud segmentation into individual grains is performed using a watershed algorithm applied here to 3D point clouds. Once the grains are individualized into several sub-clouds, the morphology of each grain is determined by fitting a 3D ellipsoid to each sub-cloud. These 3D models are then used to extract the size distribution and the grain-scale shape of the sediment population. The algorithm is validated against field data acquired by Wolman counts in coastal and fluvial environments. The main benefits of this automatic and non-destructive method are that it provides, with a fast and efficient approach, access to 1) an un-biased estimate of surface grain-size distribution on a large range of scales, from centimeters to tens of meters; 2) a very large number of data, only limited by the number of grains in the point-cloud dataset; 3) the 3D morphology of grains, in turn allowing to develop new metrics characterizing the size and shape of grains; and 4) the in-situ orientation and organization of grains and grain clusters. The main limit of this method is that it is only able to detect grains with a characteristic size significantly greater than the resolution of the point cloud.

Watershed management is an important issue throughout Europe. A key point is that business activities that prosper through fluvial transport require optimal conditions of navigation, leading to a double problematic. On one hand, urbanization, industrial, and agricultural activities have evolved to intensifying inflow to water ways (run off and effluents). Input of particulate matter to river networks has hampered functionality of water gates and fluvial circulation. On the other hand, due to human activities (industry, wastewater treatment plants, domestic and agricultural drains), particulate matter may become a contamination vector in the fluvial realm and thus may degrade sediment and water quality.The territorial direction of the Voies Navigables de France (VNF) of the Nord-Pas-de-Calais is responsible of the maintenance of all water ways in the Northern France region. Regular dredging campaigns are necessary to maintain optimal navigation conditions, which produces ~100.000 m3 of sediment waste each year. VNF has the ambition to both prevent particle and contaminant inputs into the water ways and valorize the dredged sediments. However, this is not feasible without a detailed knowledge of the contribution of particulate matter sources, which requires a source-to-sink approach for both sediments and contaminants. The present study aims to spatialize and quantify the contribution of particulate matter sources and their role on the sediment contamination using a sediment fingerprint approach (e.g. Haddadchi et al., 2013). The focus is on the canalized Denain-Trith reach of the Scheldt River which presents an important sediment accrual (about 18.000 m3/year) contaminated by heavy metals (Zn, Pb, Cd) and organic compounds.Geochemical and mineralogical analyses were performed on about 200 riverbed sediments and 30 topsoil samples by powder X-ray diffraction, X-ray fluorescence, ICP-MS, and chemo-analytical methods adapted to organic compounds (RRLC-MS/MS, HPLC-MS). This set of analyses is used as tracers of the different particulate sources. Effluent samples are also analyzed to evaluate the contribution of anthropogenic inputs. Preliminary results have already demonstrated the spatial distribution of metal contamination in the reach, which can be related to spot sources, and led to a first estimation of their respective contributions. Geostatistical analyses (such as kriging) will be further used to assess the impact of contaminant sediment accrual on the sediment source quantification (Alary and Demougeot-Renard, 2010).Alary, C., Demougeot-Renard, H., 2010. Factorial Kriging Analysis As a Tool for Explaining the Complex Spatial Distribution of Metals in Sediments. Environ. Sci. Technol. 44, 593–599. https://doi.org/10.1021/es9022305Haddadchi, A., Ryder, D.S., Evrard, O., Olley, J., 2013. Sediment fingerprinting in fluvial systems: review of tracers, sediment sources and mixing models. International Journal of Sediment Research 28, 560–578. https://doi.org/10.1016/S1001-6279(14)60013-5

The interplay between uplift, which is mostly controlled by tectonics or deep-seated mechanisms and the efficiency of surface processes, which is primarly set by climate, modulates the growth and the decay of topography across diverse temporal and spatial scales. In active orogens, tectonic and climatic forcings are the dominant processes in controlling the landscape evolution and the creation of topographic relief, as largely demonstrated by numerical and quantitative investigations. Conversely, in tectonically quiescent settings, a few field-based studies have documented that the main control on topography is exerted by bedrock erodibility and to a minor extent by climate. Regions that experienced an increase in uplift rates (i.e., topographic rejuvenation) are in disequilibrium and are characterized by the coexistence of a transient landscape that is still recording the previous boundary conditions and a steep topography that has already adjusted to the new uplift rates. Consequently, the landscape of the renjuvineted regions contains at the same time information on present and past uplift (and erosion) conditions and hence represents a first-order geomorphological archive. To explore the landscape dynamics of a rejuvenated topography, we investigated the Atlas-Meseta system of Morocco, which represents a large-scale orographic system characterized by active orogens and quiescent domains. Particularly, it includes the High and the Middle Atlas, which represent active orogens, and the Anti-Atlas and the Western and Estern Meseta, which are tectonically incactive domains. The entire Atlas system has undergone a Cenozoic phase of topographic resurgence as testified by geological, geomorphological and volcanological contraints. However, the low amount of crustal shortening and the presence of an anomalous thinning of the lithosphere beneath suggest an important contribution of deep-seated processes in generating and supporting the topography of this orographic system.Here I combine a quantitative analysis of regional and basin-scale topography, stream profiles analysis (knickpoints characterization, longitudinal profiles and -plot) and landscape modelling, with denudation rates inferred from 10Be concentrations from bedrocks and watersheds in the quiescent Anti-Atlas and Western Meseta. The results of this study allow deciphering and quantifing the erosional dynamics that control the topographic relief production and the landscape uplift history for shorter and longer time scales. This approach further provides the possibility to dechiper, quantify, and differentiate the deep-seated, large wavelength signal, from the shallower contributions (i.e., tectonics and possibly magma injection) in the Atlas-Meseta system., L'interaction entre le soulèvement, principalement contrôlé par la tectonique ou les mécanismes profonds liés à la dynamique du manteau, et l'efficacité des processus de surface, principalement déterminée par le climat, module la croissance et la décroissance de la topographie à diverses échelles temporelles et spatiales. Dans les orogènes actifs, les forçages tectoniques et climatiques sont les processus dominants dans le contrôle de l'évolution du paysage et de la création du relief topographique, comme le démontrent largement les études numériques et quantitatives. A l'inverse, dans les contextes tectoniquement calmes, quelques études de terrain ont montré que le contrôle principal de la topographie est exercé par l'érodabilité du substratum rocheux et, dans une moindre mesure, par le climat. Les régions qui ont connu une augmentation des taux de soulèvement (c'est-à-dire un rajeunissement topographique) sont en déséquilibre et sont caractérisées par la coexistence d'un paysage transitoire qui conserve encore les conditions aux limites précédentes et d'une topographie abrupte qui s'est déjà adaptée aux nouveaux taux de soulèvement. Par conséquent, le paysage des régions rajeunies contient en même temps des informations sur les conditions de soulèvement (et d'érosion) présentes et passées et représente donc une archive géomorphologique de premier ordre. Pour explorer la dynamique du paysage d'une topographie rajeunie, nous avons étudié le système Atlas-Meseta du Maroc, qui représente un système orographique à grande échelle caractérisé par des orogènes actifs et des domaines quiescents. En particulier, il comprend le Haut et le Moyen Atlas, qui représentent des orogènes actifs, et l'Anti-Atlas et la Meseta occidentale et orientale, qui sont des domaines tectoniquement inactifs. L'ensemble du système Atlas a subi une phase cénozoïque de résurgence topographique comme en témoignent les contraintes géologiques, géomorphologiques et volcanologiques. Cependant, la faible quantité de raccourcissement crustal et la présence d'un amincissement anormal de la lithosphère sous-jacente suggèrent une contribution importante des processus profonds dans la génération et le soutien de la topographie de ce système orographique.Ici, nous combinons une analyse quantitative de la topographie régionale et à l'échelle du bassin, une analyse des profils de rivières (caractérisation des knickpoints, profils longitudinaux et -plot) et une modélisation du paysage, avec les taux de dénudation déduits des concentrations en nucléide cosmogénique 10Be produit in situ dans les roches du substratum rocheux et les sédiments modernes transportés dans les bassins versants de l'Anti-Atlas et de la Meseta occidentale. Les résultats de cette étude permettent de déchiffrer et de quantifier la dynamique érosive qui contrôle la production du relief topographique et l'histoire du soulèvement du paysage pour des échelles de temps courtes et longues. Cette approche offre en outre la possibilité de déchiffrer, de quantifier et de différencier le signal profond de grande longueur d'onde des contributions moins profondes (c'est-à-dire la tectonique et éventuellement l'injection de magma) dans le système Atlas-Meseta.

For several years, the problematic about soil-structure interaction (SSI) have been studied in order to refine the evaluation of the seismic risk at local scale. This thesis particularly focuses on the quantification of the effects induced by the presence of buildings on the local seismic hazard in a sedimentary valley and on the characterization of dynamic parameters sensitive to soil-structure interaction from experimental ambient vibration data and 3D numerical models.Developed within the framework of the Ritmica project supported by the IDEX JEDI of the University Côte d’Azur, the objective of this thesis is to assess the respective impact of the site stratigraphy, of the geology and of the building on the seismic hazard. To do this, one of the highest seismic risk area in France mainland is chosen as study case: the lower Var valley. Many experiments have been carried out there for several years, including instrumentation of buildings, engineering structures and free field sites which have made it possible to define and describe the geological configuration of the valley and the dynamic behavior of some of the surrounding structures.In the aim of better characterize the seismic hazard in the Var valley taking into account the presence of existing buildings, multiple campaigns of ambient vibration measurements were performed on the basin and on the rock of the valley and also, at the level and inside the highest buildings in the valley. These data allow first, to define the 3D geotechnical model of the valley from available geotechnical and geophysical data and second, to calibrate simplified numerical model of building in order to establish a 3D finite element model of the valley including building at the top. This model is used to numerically simulate the seismic wave propagation in the Var valley using simulated earthquake. The soil model of the valley permits to better delimit the basin-bedrock interface and the seismic wave velocities that constitute important elements in the study of site effect. This model shows that the basin thickness increases from North to South from 50 m deep to more than 100 m under the Nice airport with average Vs velocity around 400 m.s-1. A numerical study done on five finite element models of building (4 low-rise and one high-rise, reinforced concrete and masonry) shows that bending type buildings are the most prone to SSI and that stiffness horizontal irregularities play a major role in SSI. The instrumentation campaigns of buildings in the Var valley allow to get a large set of data for the identification of the dynamic behavior of buildings, the study of SSI and the characterization of the spatial variability of the ground motion. These dense instrumentation campaigns allow to check that the first mode shape of building, thereafter used in the calibration of simplified model through simple relationship, corresponds to a bending mode. The analysis of the rocking spectral ratio and of random decrement functions is useful for the characterization of SSI from vertical temporal series at the base of buildings. To study the influence of lithological site effect and buildings on the surface ground motion, seismic wave propagation has been numerically simulated in five different 3D finite element site-city models characterized using ambient vibration recordings and including various city configurations., Depuis plusieurs années, les problématiques portant sur l’interaction sol-structure (ISS) sont étudiées afin d’affiner l’évaluation du risque sismique à l’échelle locale. Cette thèse s’intéresse particulièrement à la quantification des effets de la présence du bâti sur l’aléa sismique local dans une vallée sédimentaire et à la caractérisation de paramètres dynamiques sensibles à l’interaction sol-structure à partir de données expérimentales de vibrations ambiantes et de modèles numériques 3D. Elaboré dans le cadre du projet Ritmica soutenu par l’IDEX JEDI de l’Université Côte d’Azur, l’objectif de ce travail de thèse, financée par le Cerema, est d’évaluer l’impact respectif de la stratigraphie du site, de la géologie et du bâti sur l’aléa sismique. Pour cela, une des zones les plus sismiques et à enjeux forts en France métropolitaine est choisie pour cas d’étude : la basse vallée du Var. De nombreuses expérimentations y ont été réalisées depuis plusieurs années, incluant des instrumentations de bâtiments, d’ouvrages d’art et de sol qui ont permis de définir et décrire la configuration géologique de la vallée et le comportement dynamique de certaines des structures environnantes.Dans l’objectif de mieux caractériser l’aléa sismique dans la vallée du Var en prenant en compte la présence des constructions existantes, plusieurs campagnes de mesures de vibrations ambiantes ont été réalisées sur le bassin et sur le rocher de la vallée et également, au niveau et au sein des plus hauts bâtiments de la zone. Ces données permettent d’une part, de définir le modèle géotechnique 3D de la vallée à partir des données géotechniques et géophysiques disponibles et d’autre part, de calibrer un modèle numérique simplifié de bâtiment dans le but d’établir un modèle 3D en élément finis de la vallée intégrant le bâti en surface. Ce modèle sert ensuite à simuler numériquement la propagation des ondes sismiques dans la vallée du Var en utilisant un séisme simulé. Le modèle de sous-sol de la vallée permet de mieux délimiter l’interface bassin-substratum et les vitesses d’ondes sismiques qui constituent des éléments importants dans l’étude des effets de site. Ce modèle montre que l’épaisseur du bassin augmente du Nord vers le Sud allant de 50 m d’épaisseur à plus de 100 m sous l’aéroport de Nice avec des vitesses Vs moyennes aux alentours de 400 m.s-1. Une étude numérique réalisée à partir de cinq modèles de bâtiment en éléments finis (4 de faible hauteur et un de grande hauteur, en béton armé et maçonnerie) montre que les effets de l’ISS sont plus importants pour les bâtiments de type cantilever et que les irrégularités horizontales de rigidité jouent un rôle majeur dans l’ISS. Les campagnes d’instrumentation de bâtiments dans la vallée du Var ont permis d’obtenir un large jeu de données pour l’identification des comportements dynamiques des bâtiments, l’étude de l’ISS et la caractérisation de la variabilité spatiale du mouvement du sol. Ces campagnes denses permettent de vérifier que le premier mode de déformée des bâtiments, par la suite utilisé dans la calibration de modèle simplifiés à partir d’une relation simple, correspond à un mode de flexion. L’analyse du spectre de basculement et des fonctions du décrément aléatoire est utile pour la caractérisation de l’ISS à partir des séries temporelles verticales à la base des structures. Afin d’étudier l’influence combinée des effets de site et du bâti sur le champ d’ondes sismiques en surface, la propagation des ondes sismiques a été numériquement simulée dans cinq modèles 3D en éléments finis différents calibrés à partir d’enregistrements de vibration ambiante et incluant ou non plusieurs types de configurations de villes.

In the proposed discussion we stress the possibility to use maps fromSpaceborne Digital Elevation Models (DEMs) to analyse the topography of craters or crater-like structures. The Digital Elevation Model here used is that proposed by Yamazaki, Ikeshima, Tawatari, Yamaguchi, O'Loughlin, Neal, Sampson, Kanae and Bates, in the Geophysical ResearchLetters, 2017, and implemented at the web site it-ch.topographic-map.com . Crater-like structures can be observed in visible satellite images, but elevation profiles are fundamental to understand their geological nature. Here we will show that the DEM maps are able to easily evidence the elevation features, giving the possibility of a first remote analysis of them.

International audience

Covered by ultrabasic units for more than a third of its surface, the New Caledonia (South West Pacific) is one of the largest world producers of Ni-ore from lateritic deposits. Almost all outcrops of geological units and open mines contain serpentine and amphibole, also as asbestos varieties. In this geological context, in which weathering processes had a great contribution in the production and dispersion of mineral fibres into the environment, the development of a routinely analytical strategy, able to discriminate an asbestiform fibre from a non-harmful particle, is a pivotal requisite. However, the acquisition of all these parameters is necessary for determining the risk associated to fibres exposition. A multidisciplinary routinely approach, based on the use of complementary simply-to-use but reliable analytical methods is the only possible strategy. In addition, the instrumental apparatus must be easily transportable on the field, directly on the mining site. The employment of specialized tools such as Polarized Light Microscopy associated to Dispersion Staining method (PLM/DS) and portable Raman spectroscopy for identification of environmental asbestos, are proved extremely effective in the improvement of the performance and rapidity of data acquisition and interpretation. Both PLM/DS and handheld Raman devices confirmed to be discriminant in the detection and characterization of asbestos fibres for both serpentine and amphibole. Furthermore, these techniques proved extremely effective even in the presence of strongly fibrous and altered samples. Keywords: Asbestos, Fibrous antigorite, In situ monitoring, Dispersion staining, Portable Raman, New Caledonia

The External Crystalline Massifs (ECMs) of the Western Alps form the outcropping portions of the Paleozoic basement involved in the Alpine collision. Like a large part of the continental basement of Western Europe, these massifs were structured by the Variscan orogeny during the Devonian-Carboniferous period (~380-300 Ma). However, several questions remain regarding the age of deformation and the degree of metamorphism associated with Variscan events in the ECMs. In particular, high pressure relics (eclogites and HP granulites) outcrop in the ECMs, but the age and P-T conditions of this metamorphism remain poorly constrained. Furthermore, these massifs were affected by wrenching tectonics during the Late Carboniferous and early Permian, and were subsequently reworked by Alpine tectonics, which complicates their integration within the Variscan system. Thus, the significance of ECMs and their relation with major tectonic blocks and Variscan sutures in Europe remain poorly defined.This thesis aims to provide new geochronological and thermobarometric constraints on Variscan tectonic and magmatic events in the ECMs, in order to propose a coherent geodynamic model. This work was carried out on the Belledonne and Oisans massifs, in parallel with a second thesis (Jonas Vanardois) carried out on the basement of the Mont Blanc and Aiguilles-Rouges massifs, within the framework of the RGF Alpes project led by the BRGM.The petrochronological study of the high-pressure (HP) relics revealed a HP metamorphic stage of Visean age, with age estimates and P-T conditions consistent across the ECMs (~330-340 Ma, 1.4-1.8 GPa and 650-750°C). The preservation of prograde relics marks an early metamorphic stage at 460-550°C and 0.4-1.0 GPa, which is incompatible with a cold subduction context, and rather marks a crustal thickening context by underthrusting of the lower plate.The exhumation of deep metamorphic units from the lower crust is controlled by a large, late Variscan strike-slip shear zone (325-300 Ma) running through the ECMs. Comparison of the HP relics of the Belledonne and Oisans massifs reveals contrasting exhumation paths. In the Belledonne Massif, the deep units were exhumed following relatively isothermal path (peak temperature ~750 °C) in the core of the shear zone, whereas the units of the Oisans Massif, located at the margin of this system, were exhumed later and underwent significant heating (to 800-870 °C) during exhumation.A second part of the thesis concerns the petrographic and geochemical study of enclaves of peridotites discovered in the Oisans massif, embedded in migmatites. These peridotites bear the traces of a mantle metasomatism by continental material, characterised by the crystallisation of phlogopite/pargasite, a marked enrichment in incompatible elements (LILE, LREE), and low radiogenic Nd signatures (-8.12, Les massifs cristallins externes (MCE) des Alpes occidentales forment les portions affleurantes du socle Paléozoïque impliqué dans la collision alpine. A l’instar d’une grande partie du socle continental ouest-européen, ces massifs ont été structurés par l’orogenèse varisque au cours du Dévonien et du Carbonifère (~380–300 Ma). Cependant, plusieurs points d’ombre demeurent concernant l’âge des déformations et le degré de métamorphisme associé aux événements varisques dans les MCE. En particulier, des reliques de haute pression (éclogites et granulites HP) affleurent dans les MCE, mais l’âge et les conditions P-T de ce métamorphisme restent mal contraints. Par ailleurs, ces massifs ont été affectés par des grands décrochements au cours du Carbonifère supérieur et du Permien, et ont ensuite été remaniés par la tectonique alpine, ce qui complique leur intégration au sein du système varisque. Ainsi, la signification des MCE par rapport aux grands blocs tectoniques et aux sutures varisques en Europe reste mal définie.Cette thèse vise à apporter de nouvelles contraintes géochronologiques et thermobarométriques sur les événements tectono-métamorphiques et magmatiques varisques dans les MCE, afin de proposer un modèle géodynamique cohérent. Ce travail a été mené sur les massifs de Belledonne et de l’Oisans, en parallèle d’une seconde thèse (Jonas Vanardois) réalisée sur le socle des massifs du Mont Blanc et des Aiguilles-Rouges, dans le cadre du chantier RGF Alpes piloté par le BRGM.L’étude pétrochronologique des reliques de haute pression (HP) a permis de mettre en évidence un stade métamorphique HP d’âge Viséen, avec des estimations d’âge et de conditions P-T cohérentes sur l’ensemble des MCE (~330-340 Ma, 1.4-1.8 GPa et 650-750°C). La préservation de reliques progrades marque un stade métamorphique précoce à 460-550 °C et 0.4-1.0 GPa, incompatible avec un contexte de subduction froide, et marquant plutôt un contexte d’épaississement crustal par sous-charriage de la plaque inférieure.L’exhumation des unités métamorphiques profondes issues de la croûte inférieure est contrôlée par un grand système décrochant tardi-varisque (325-300 Ma) parcourant l’ensemble des MCE. La comparaison reliques HP des massifs de Belledonne et de l’Oisans révèle des chemins d’exhumation contrastés. Dans le massif de Belledonne, les unités profondes ont été exhumées de manière relativement isotherme (pic de température ~750 °C) au cœur de la zone de décrochement, alors que les unités du massif de l’Oisans, situées en marge de ce système, ont été exhumées plus tardivement et ont subi un échauffement important (800–870 °C) lors de l’exhumation.Un second volet de la thèse concerne l’étude pétrographique et géochimique d’enclaves de péridotites découvertes dans le massif de l’Oisans, emballés dans des migmatites. Ces péridotites portent les traces d’un métasomatisme mantellique d’origine continentale, caractérisé par la cristallisation de phlogopite/pargasite, un enrichissement marqué en éléments incompatibles (LILE, LREE), et des signatures en Nd peu radiogéniques (-8.12

Piton de la Fournaise is one of the most active volcanoes in the world with a mean of 2.3 eruptions/yr since 1998. Typical activity is characterized by the opening of eruptive fissures along a main arcuate preferential intrusion zones NE and SE of the summit crater. In March-April 2007 the largest eruption of the last hundred years took place, characterized by the output of 220x106 m3 of lava, and a collapse of the summit crater by 300 m. During the eruption, an aseismic slip of the Eastern Flank up to 1.4 m toward the sea was measured by satellite RADAR interferometry (InSAR). Since then, InSAR and GNSS data show that slip is still going at a rate of 1.4 cm/yr. The slip was related to a fault or to sheared intrusion depending on authors. In order to estimate the impact of intrusive activity on the Eastern Flank movement and the mechanisms related to instabilities, displacement field analysis and inverse modeling were performed for 60 intrusive events that occurred between 1998 and 2021. The modelled intrusions reveal a major NE-SE intrusive zone, a sill zone, and four secondary intrusion zones radiating from the summit cone. The NE-SE major intrusive zone is connected at depth to the sill zone located below the eastern flank. Together they form a continuous intrusive zone characterized by a convex, seaward spoon shape. It has sub-vertical walls at its head, accommodating the opening of the dykes. Towards the east, the intrusive structure becomes horizontal and accommodates shear-associated intrusions indicating a pre-existing discontinuity guiding their emplacement. At the eastern end of the structure, two slip regimes separated by a N60° axis are identified: sheared sills (coeval opening and slip) to the north of the axis; and faulting behavior (≈pure shear) to the south. In addition, stress modeling associated with the intrusions shows that the emplacement of intrusions in the preferential intrusion zones is controlled by the inherited stress history of previous intrusions and that there is a positive feedback between dyke opening in the rift zones and slip along the sills and the fault. Thus, the major spoon-shaped structure probably acts as a destabilization surface. On the geologic time scale, repeated intrusions into the structure can lead to catastrophic flank collapse generating earthquakes and tsunamis. This model of long-term evolution of the edifice is consistent with the presence of debris avalanche deposits in the bathymetry and allows to explain the formation of the Enclos Fouqué., Le Piton de la Fournaise est l'un des volcans les plus actifs au monde avec en moyenne 2.3 éruptions/an depuis 1998. L'activité typique est caractérisée par l'ouverture de fissures éruptives le long d'une rift zone principale arquée vers le NE et le SE du cratère sommital. En mars-avril 2007, la plus grande éruption des cent dernières années a eu lieu. Elle s'est caractérisée par l'émission de 220x106 m3 de lave et par un effondrement du cratère sommital de 300 m. Pendant l'éruption, un glissement asismique du Flanc Est de 1.4 m vers la mer a été mesuré par interférométrie RADAR (InSAR). Depuis lors, les données InSAR et GNSS montrent que le glissement se poursuit à un taux de 1.4 cm/an. Le glissement a été relié à une faille ou à une intrusion cisaillée suivant les auteurs. Afin d'estimer l'impact de l'activité intrusive sur les mouvements du flanc Est et les mécanismes liés aux instabilités, une analyse des champs de déplacements et des modélisations inverses ont été réalisées pour 60 événements intrusifs survenus entre 1998 et 2021. Les intrusions modélisées révèlent une zone intrusive majeure orientée NE-SE, une zone de sills et quatre zones d'intrusions secondaires rayonnant à partir du cône sommital. La zone intrusive majeure NE-SE est connectée en profondeur à la zone de sills se localisant sous le flanc est. Ensemble, elles forment une zone intrusive continue caractérisée par une forme de cuillère convexe, orientée vers la mer. Elle présente des parois sub-verticales à sa tête, accommodant l'ouverture des dykes. Vers l'est, la structure intrusive s'horizontalise et accommode des intrusions associées à du cisaillement indiquant une discontinuité préexistante guidant leur mise en place. A l'extrémité est de la structure, deux régimes de glissement séparés par un axe N60° sont identifiés: des sills cisaillés (cisaillement synchrone de l'ouverture) au nord de l'axe; et un comportement de failles (≈purement en cisaillement) au sud. De plus, la modélisation des contraintes associées aux intrusions montre que la mise en place des intrusions dans les zones d'intrusions préférentielles est contrôlée par l'historique des contraintes héritées des intrusions précédentes et qu'il existe une rétroaction positive entre l'ouverture des dykes dans les rift zones et le glissement le long des sills et de la faille. Ainsi, la structure majeure en forme de cuillère agit probablement comme une surface de déstabilisation. A l'échelle des temps géologiques, les intrusions répétées dans la structure peuvent conduire à un effondrement catastrophique des flancs générant des séismes et des tsunamis. Ce modèle d'évolution long terme de l'édifice est en accord avec la présence de dépôts d'avalanche de débris dans la bathymétrie et permet d'expliquer la formation de l'Enclos Fouqué.

Phosphorites composed by linguliform brachiopod shells represent a poorly known phosphorus source. As mineral precursors for P-fertilizers, they are an increasingly important resource for agricultural activities. inguliform brachiopod shells have a stratiform organo-phosphatic microstructure, which produces bioclasts characterized by their low density and laminar shape; as of yet, no other studies on their hydrodynamic behaviour have been carried out. The objective of this work is to shed some light on the concentration mechanisms acting on organo-phosphatic particles and finally leading to phosphorite formation; and also, to betterunderstand general processes of segregation in mixed bioclastic-siliciclastic sediments. In this work we present preliminary results of experiments made on fragments of Lingula anatina shells, a modern linguliform brachiopod species. We performed settling velocity and entrainment velocity measurements, as well as current-flow experiments on a mixed-sediment bed to investigate particle segregation. Lingula anatina shells show a variable degree of mineralization, and thus density, throughout the shell: measured densities ranged from 1010 – 1330 kg/m3 in marginal areas to 1370 – 1730 kg/m3 in the central part of the shell. Their fragments have platy shapes, with shape factors between 0.02 – 0.39, a range similar to the one reported for platy carbonate bioclasts (Li et al., 2020). Settling velocity values were about 50% of similarly shaped and sized carbonate bioclasts, and 20% of similarly sized quartz sand. Settling velocities are controlled jointly by particle diameter, shape and density, which are strongly variable in Lingula anatina bioclasts; when plotted against each other, these parameters show high dispersion and complex interrelationships. By contrast, the ratio between the particle mass and its maximum projected area (M:A) shows a strong correlation with settling velocity. Drag coefficients were calculated by nonlinear regression. The obtained values are comparable with those calculated from the data of Li et al. (2020), suggesting that the lower settling velocities in organo-phosphatic bioclasts are explained mostly by their lower density and not by differences in their falling behaviour. Threshold near-bed velocities (u*c) ranged between 1.0 – 4.3 cm/s for organo-phosphatic bioclasts ranging between 0.7 – 5 mm (sieve-diameter). The obtained values are comparable with those of carbonate bioclasts and quartz-sand with similar diameters ( Weill et al. 2013, Rieux et al. 2018). Dual-behaviour has been noted in carbonate bioclasts, where low settling velocities and significant resistance to erosion contributes to their segregation from siliciclastic sediments ( Weill et al. 2013, Li et al. 2020); this type of behaviour should be more pronounced in organo-phosphatic bioclasts given their smaller settling velocities. Entrainment and segregation experiments were conducted on a mixed-sediment bed composed of fine siliciclastic sand and organo-phosphatic particles (3 mm-sieve diameter). For the bed set-up, a concentrated slurry of siliciclastic and organo-phosphatic particles was set on the empty flume, which was later filled with water. At sub-threshold velocities, little sand transport took place with no bioclast motion; this was followed by incipient migration of small sandy ripples, occasional bioclast motion and imbrication. At this stage, armoured bioclast-rich patches developed through sand winnowing. Above threshold velocities the sandy ripples grew taller; bioclasts were not easily eroded, excepted in high-shear and turbulence areas such as stoss faces and downstream of lee faces of ripples. Once incorporated into the flow they were rapidly transported downstream and redeposited in bioclast-rich areas (with higher bed rugosity) or out of the test section. By contrast, sand seemed to be transported with a lower velocity corresponding to that of the migrating ripples. The final rippled bed was noticeably sandier than the original mixed-sediment massif; by contrast, a bioclast-rich deposit was formed downstream of the test section. Contrasting hydrodynamic behaviour in terms of settling and entrainment velocities favoured the segregation between both sediment fractions; however, sorting mechanisms are also strongly dependent on less predictable sedimentary processes such as bed armouring, and increased form-related shear stress and turbulence due to ripple migration. Extensive experimental studies should be carried out to further investigate segregation in mixed bioclasticsiliciclastic sediments.

La géothermie (ou chaleur de la Terre) fait partie des nouvelles formes d'énergies souvent évoquées depuis l'avènement de la transition énergétique qui presse l'humanité à changer ses modes de production et de consommation énergétiques. L'utilisation de la géothermie est une pratique qui est néanmoins connue depuis des siècles avec l'utilisation notable des sources thermales, et qui a connu ces dernières décennies un essor tout particulier. La Programmation Pluriannuelle de l'Energie (PPE) en France vise à augmenter la part des énergies renouvelables dans la consommation de chaleur qui reste aujourd'hui nettement dépendante des centrales thermiques fonctionnant au gaz. Malgré le fait que 99 % du volume de la Terre soit à une température supérieure à 100 °C, la chaleur est répartie de manière inégale à la surface du globe. Les grands mouvements tectoniques aux frontières et à l'intérieur des plaques tectoniques, le volcanisme, ou encore l'hydrothermalisme sont autant de facteurs favorisant la circulation de chaleur depuis les profondeurs. Faisons le point sur cette ressource aux différentes facettes, et qui reste malgré tout encore mal connue. Les évènements des dernières années, faisant état de sismicité en lien avec l'exploitation géothermale de certains sites, ont participé à ternir l'image de la géothermie

For some time, allotment gardens have often been established on urban soils without prior health risk assessment. Soil analysis revealing contamination by trace elements such as lead (Pb) may now compromise the practice of gardening. To prevent a restriction or change of soil use, the introduction of industrial compost to the soil can be efficient, but the potential of composts self-produced by the gardeners themselves must be evaluated. The first objective of this thesis was to analyze composting practices in allotment gardens and select self-produced composts with different biochemical properties and trace element content. The composting practices and the quality of these composts are very variable. Composts self-produced in the garden (home composts) are generally poor in organic matter and sometimes contaminated,contrary to composts self-produced at the foot of buildings or in restoration (community composts) also used in gardens. The second objective was to assess the potential health risk of consuming vegetables from allotment gardens moderately contaminated with Pb (100 - 200 mg.kg-1) amended with self-produced composts. In an attempt to improve remediation, biochar was also introduced into the soil. A diet composed essentially of self-produced vegetables in the garden would not present a health risk, but the addition of self-produced composts at a high dose (10-20 kg.m-2) could increase the bioavailability of As in allotment garden soils. In contrast, the combined addition of self-produced compost and biochar limited the transfer of both As and Pb while simultaneously increasing the biomass of self-produced vegetables., Les jardins familiaux ont souvent été installés sur des sols urbains sans évaluation préalable du risque sanitaire. Le diagnostic de contamination du sol par des éléments trace comme le plomb (Pb) peut compromettre la poursuite du jardinage. Pour éviter un changement d’usage, l’apport au sol de compost industriel peut être efficace mais le potentiel des composts autoproduits par les jardiniers eux-mêmes doit être évalué. Ce travail de thèse a eu pour premier objectif d’analyser les pratiques de compostage dans les jardins familiaux et sélectionner des composts autoproduits différents en termes de propriétés biochimiques et de contenu en éléments trace. Les pratiques de compostage et la qualité des composts sont très variables. Les composts autoproduits au jardin (domestiques)sont généralement pauvres en matière organique et parfois contaminéscontrairement aux composts autoproduits en pied d’immeuble ou en restauration (collectifs) également utilisés au jardin. Le second objectif a été d’évaluer le risque sanitaire potentiel lié à la consommation de légumes de jardins familiaux modérément contaminés en Pb (100-200 mg.kg-1) amendés avec des composts autoproduits. Pour tenter d’améliorer la remédiation, du biochar a aussi été introduit. Une alimentation composée essentiellement des légumes autoproduits au jardin ne présenterait pas de risque sanitaire mais l’apport de composts autoproduits à une dose élevée (10-20 kg.m-2) a pu augmenter la biodisponibilité de As dans des sols de jardins familiaux. L’apport combiné d’un compost autoproduit et d’un biochar a toutefois limité les transferts de As et de Pb tout en augmentant la biomasse des légumes autoproduits.

Sediment transport modeling in shallow coastal waters is a challenging topic, especially in macrotidal environments where large intertidal areas are subjected to rapid wave transformation and breaking, complex patterns of tidal currents, and dynamic bedforms. Quantifying the sediment fluxes from the inner shelf to the shoreface is crucial to understand the long-term evolution of such embayment. The bay of Somme, facing the English Channel in North-West France, is a particularly relevant environment to tackle these issues. Known for its megatidal range (up to 10m in spring tides), it is in front of a large subtidal sediment source known as the Picard prism. The intertidal area, more than 6 km-wide, features highly dynamic dune fields and tidal channels. The aim of the study is to evaluate the sediment fluxes between the Picard prism and Bay of Somme using numerical modeling and in-situ observations. The first step is to build a numerical configuration which combines the hydrodynamic model CROCO, the spectral wave model WaveWatch-III and the USGS sediment transport model. Three nested grids have been created (100m, 30m, 10m) that are forced at the boundaries by tide, wind, wave spectra and fluvial discharge. Numerical results were tested against ADCP and tidal gauge data. The main conclusions are: i) the flow velocity and the sea surface height are in agreement with observations with a mean RMSE around 0.1m/s and 0.17m for current velocity and sea surface height, respectively ii) a time delay varying between 10 and 30 minutes is observed at some locations, iii) the contribution of the Somme River has very little influence on the results due the low flow discharge for the considered period, iv) the longshore current is well simulated by the coupled model. One of the main limitations of our modeling is due to a bathymetry that was not recorded at the same time as the measurements. Prospects for future work will be to add the USGS sediment transport model in the coupling and to simulate sediment fluxes.

Les Eléments de Terres Rares sont distribués à faibles teneurs dans grand nombre de roches. Pour en augmenter les concentrations et en faire une ressource exploitable, de multiples processus géologiques sont à l’œuvre. Charles et al. font l’inventaire exhaustif des domaines européens où des concentrations intéressantes en Eléments de Terres Rares sont reconnues.

The moderately siderophile and volatile elements are strong tracers of condensation, accretion-collision and metal-silicate differentiation processes in the earliest history of the solar nebula, and of terrestrial planets, the Moon, and asteroids, respectively. Among them, germanium, with T 50% cond = 825 K and metal-silicate partition coefficient of 17 for the Earth, show significant isotopic fractionation (Δ 74 Ge metal/silicate) at two scales, namely (1) at a meteorite scale between metal and silicate phases in ordinary chondrites or pallasites, and (2) at reservoir scales, between iron meteorites taken as proxies for core and the silicate Earth. Establishing the isotopic budget of planetary mantles (e.g.Earth, Mars, Vesta) and the Moon implies to determine the isotopic composition of chondrites as proxy for undifferentiated parent bodies. Here we present new high precision germanium isotopic data obtained on (1) bulk carbonaceous (CC) and ordinary chondrites (OC), (2) Howardite-Diogenite meteorites though to originate from Vesta, (3) Martian meteorites (shergottite, nackhlites) and (4) lunar basalt meteorite, They will be compared with Ge isotopic composition of iron meteorites and Earth silicate mantle (peridotites, basalts) [3,4] to assess parent bodies composition. Samples and methods: Variable quantities of sample, from 80 mg for CC (CI, CM, CV, CO), OC (H, L, LL) and martian meteorites (shergottite, nackhlites), to up to 2 g for Ge-depleted HED (unbrecciated and brecciated eucrites, diogenite) and lunar basalt, were analyzed for Ge concentrations at the SARM (ICP-MS, CRPG-Nancy), and for bulk Ge isotopic compositions by using Ge chemistry and MC-ICPMS techniques (Hydride Generator System coupled to NeptunePlus) developed at CRPG (δ 74/70 Ge NIST3120a ≤0.1‰, 2σSD) [1,2,3]. Results and discussion: OC and CC type chondrites present fundamental Ge isotopic dichotomy that follow O and Cr isotopic anomalies [4]. Bulk ordinary chondrites values display negative values from-0.51±0.16 ‰ in H OC,-0.29±0.05‰ in L to-0.33±0.14‰ in LL, that agree within error with data on metal phase of OCs (Florin et al., 2020), then confirming that the metal phase hosts the Ge isotopic budget. By contrast, carbonaceous chondrites have positive δ 74 Ge values and show exceptional large variations of ≈1‰, from CI (Orgueil) with the heaviest composition (δ 74 Ge=0.901±0.06‰) toward lighter composition in CV (Allende) (δ 74 Ge=+0.096±0.12‰). The δ 74 Ge values and matrix fraction (%) of OCs and CCs are positively correlated and describe a mixing line between CI composition and expected chondrule composition (Fig.1). In addition large Ge isotopic composition in CC are exceptionally well correlated with Δ 17 O (Fig. 1) and ε 54 Cr, then constraining the origin and/or processes that lead to Ge isotopic signatures in the Solar System. Planetary mantles, except the Moon, have Ge isotopic compositions that are lighter than the iron meteorites, thus confirming the positive Δ 74 Ge metal/silicate during core formation [2]. In addition, distinct Ge isotopic signatures are recorded: Mars has δ 74 Ge values that overlap terrestrial mantle and crustal values, and reveals a dichotomy between shergottites with higher δ 74 Ge, lower Ge contents (+0.84‰, 0.73 ppm) than nakhlites (+0.35‰, 2.2 ppm), thus emphazing degazing processes [6]. The highly depleted HED and lunar samples (Ge =

In the context of climate change, it is essential to estimate precisely and be able to monitor over time the energy balance of the Earth at the top of the atmosphere and at the surface. In terms of measurement, obtaining a correct estimate of the radiative balance requires a precise determination of the shortwave (solar) and longwave (infrared) radiative fluxes. The objective of this thesis is to assess the solar radiative fluxes obtained from the French radiometer POLDER on board the PARASOL microsatellite supported by CNES. A first part of the thesis presents a comparison between the operational products computed from POLDER observations with the reference fluxes obtained through the broadband radiometers CERES on the NASA space platforms Aqua and Terra. The comparisons are made over two periods: first a period with coincident measurements (2005-2009), then a second period which corresponds to the drift of the PARASOL satellite (2010-2013). We show that this drift had an impact on the observations, with strong repercussions on the calculated fluxes. Over the period of coincidence of the measurements, POLDER fluxes are very close to the fluxes from CERES for two of the products studied (CERES SSF1deg and CERES SYN1deg) with relative differences under 2% until December 2009. After 2010, the relative difference increases with the drift. A land/ocean compensation effect is also revealed. The results obtained through these comparisons led us to study in detail the component of the algorithm used to obtain the monthly means of POLDER shortwave fluxes. This part of the algorithm is the diurnal extrapolation, used to estimate a value of albedo at all hours of the day from a single observation using models that are scene-dependent. The models used for the operational products were built using four months of POLDER-1 observations (1996-1997). We decided to take advantage of the data obtained throughout the entire PARASOL mission to improve these models. The shortwave fluxes obtained with the new models show less dependence on the drift over oceans but a drift is still present over lands. These results led to several propositions that could improve POLDER's shortwave fluxes, mainly by increasing the number of POLDER models. This work, based on measurements from POLDER-3, which was shut down in December 2013, but whose data is available, will be largely reusable for the future multispectral, multi-angular and polarized radiometer 3MI, developed by ESA and EUMETSAT and which will fly onboard the EPS-SG mission supported by EUMETSAT from 2024, for approximately 20 years., Dans le contexte actuel du changement climatique, il est essentiel de bien caractériser et de pouvoir suivre dans le temps le bilan d'énergie radiative terrestre au sommet de l'atmosphère et à la surface. Du point de vue de la mesure, obtenir une estimation correcte du bilan radiatif passe par la détermination précise des flux radiatifs solaire et infra-rouge. L'objectif de cette thèse est d'étudier les flux radiatifs solaires obtenus à partir du radiomètre français POLDER embarqué sur le microsatellite PARASOL du CNES. Une première partie des travaux de thèse présentés consiste à comparer les produits opérationnels actuels de POLDER avec les flux de référence obtenus par les radiomètres à large bande spectrale CERES sur les plates-formes spatiales américaines Aqua et Terra. La comparaison est faite sur deux périodes, la première pour laquelle nous disposons de mesures coïncidentes (2005-2009), et la seconde qui correspond à une période de dérive du satellite PARASOL (2010-2013). Nous montrons que cette dérive a eu un impact direct sur les observations, avec des répercussions sur les flux calculés. En effet, sur la période de coïncidence des mesures les flux POLDER sont très proches des flux CERES pour deux des produits étudiés (SSF1deg, SYN1deg) avec des différences relatives inférieures à 2% jusqu'en décembre 2009. Après cette date, la différence relative augmente. Un effet de compensation terres/océans est par ailleurs mis en évidence. Les résultats obtenus suite à cette comparaison nous ont menés à étudier plus particulièrement la composante de l'algorithme qui permet d'obtenir les moyennes mensuelles des flux POLDER. Celle-ci concerne l'extrapolation diurne, utilisée pour obtenir des estimations de l'albédo à toutes les heures de la journée à partir d'une seule observation en utilisant des modèles qui dépendent de la scène observée. Les modèles utilisés actuellement sont issus de quatre mois d'observations POLDER-1 (1996-1997) et nous avons décidé de mettre à profit les données obtenues sur l'ensemble de la mission PARASOL pour améliorer ces modèles. Les flux solaires obtenus avec les nouveaux modèles présentent moins de dépendance à la dérive au-dessus des océans mais une tendance encore visible au-dessus des terres. Ces résultats nous ont amenés à proposer plusieurs pistes d'amélioration, principalement en augmentant le nombre de modèles POLDER. Ces travaux, basés sur les mesures de POLDER qui a cessé de fonctionner en décembre 2013 mais dont les données sont disponibles, seront en grande partie réutilisables pour le futur radiomètre multispectral, multi-angulaire et polarisé 3MI, développé par l'ESA et EUMETSAT et qui sera embarqué sur la prochaine mission spatiale opérationnelle EPS-SG d'EUMETSAT à partir de 2024 pour une durée d'environ 20 ans.

International audience; L’objectif de cette communication est de présenter les avancées récentes sur la caractérisation de la contamination par la chlordécone (CLD) des eaux souterraines (ESO) qui sont un vecteur clé « invisible » de sa dispersion dans l’environnement. Ce travail se base sur des suivis pluri annuels des ESO des îles de Martinique et Guadeloupe, ainsi que des suivis physico-chimiques de l’Observatoire des Pollutions Agricoles (OPALE). L’analyse des tendances pluri-annuelles montre que contrairement aux points d’eau plus faiblement contaminés avec des tendances à la baisse, des tendances à la hausse ou l’absence de tendance sont détectées pour les points les plus contaminés. Cette variabilité est à rattacher au temps de résidence des aquifères, les concentrations les plus fortes étant généralement observées pour des eaux s’étant infiltrées lors de la phase d’application de la CLD (1970-1990). Un schéma de la contamination des ESO est proposé afin d’identifier les facteurs d’exposition des écosystèmes qui en dépendent.

Ce document traite des transferts de chaleur dans la Terre, enseignés aux étudiants en Sciences de la Terre à l’École de l’OPGC (Université Clermont Auvergne).

Geological descriptions are written in natural language by different geologists during the acquisition process, without any constraints on the format or the content of the descriptions As a result, the records are highly heterogeneous, ranging from brut observations to high level interpretations and all the nuances in between. This heterogeneity imposes manual reprocessing of the data by experts to avoid mistakes occurring in downstream applications. Instead, we try to automate this process via Natural Language Processing (NLP) techniques

The PhD work aims at studying the role of volcanism in influencing winter climate variability (especially, NAO) over the North Atlantic-Mediterranean sector at inter-annual scale. The first part is devoted to characterizing the simulated NAO signal in winters following stratospheric volcanic eruptions using three long transient simulations of the past millennium (500-1849 CE) by IPSL-CM6A-LR in the frame of PMIP4. The robustness and sensitivity of the response related to the latitude, season and strength of the eruptions are also explored. The second part extends further to decrypt the physical mechanism regarding different components of volcanic radiative forcing (the surface cooling and stratospheric warming). The work focuses on three 25-members ensemble simulations by IPSL-CM6A-LR following the VolMIP protocol for the well observed Mt. Pinatubo tropical eruption (Philippines, June 1991). Sensitivity experiments indicate that the surface positive NAO signature in our model experiments is primarily attributable to heating in the lower tropical stratosphere which generates stronger subtropical zonal winds through the thermal wind balance and accelerates the polar vortex. Stationary planetary wave propagations are also playing indispensable modulations effects., La thèse vise à étudier le rôle du volcanisme ainsi ses impacts sur la variabilité climatique hivernale (spécialement l'ONA) dans le secteur Atlantique Nord-Méditerranée à l'échelle interannuelle. La première partie est consacrée à la caractérisation du signal d'ONA en hiver à la suite d'éruptions volcaniques stratosphériques grâce à trois simulations transitoires du dernier millénaire (500-1849 CE) par IPSL-CM6A-LR dans le cadre de PMIP4. La robustesse et la sensibilité de réponse liée à la latitude, la saison et la magnitude des éruptions sont ainsi explorées. La deuxième partie étend plus loin pour décrypter le mécanisme concernant différentes composantes radiatives du forçage volcanique (le refroidissement de la surface et le réchauffement du stratosphère). Le travail est axé sur trois 25-membres ensembles de simulation par IPSL-CM6A-LR suivant le protocole VolMIP sur l'éruption tropicale Mt. Pinatubo (Philippines, juin 1991), la meilleure observée. Les expériences de sensibilité indiquent que la signature d’ONA positive de surface dans nos expériences de modèle est principalement attribuée au réchauffement dans la basse stratosphère tropicale qui génère des vents zonaux subtropicaux plus forts à travers le bilan de vent thermique et accélère le vortex polaire. Les propagations d'ondes planétaires stationnaires jouent également des effets de modulations indispensables.

When a seismic wave propagates in a wet porous medium, the transient movement of ions inside the pores will give rise to an electromagnetic (EM) wavefield that accompanies the seismic field. This coseismic field, due to electrokinetic phenomena, carries valuable information about the fluid content and the petrophysical properties. Additionally, when the seismic disturbance reaches an interface, where either the petrophysical, the fluid, or both properties change, another EM wave will be generated, due to the electric charge imbalance across the interface. This second wave propagates independently and carries information about the discontinuity where it was generated. While the first contains mainly information about the physical properties around the receivers, the second is a noteworthy alternative to near surface exploration since it can be detected away from the interface generating it. Moreover, it can detect layers thinner than what the seismic resolution allows, being specially sensitive to fluid changes. Seeking to extend the understanding of seismoelectric phenomena we developed a experimental setup able to detect both seismo-EM effects. To record seismic displacement we use a laser vibrometer and for the EM signals we measure (approximate) absolute potentials using stainless steel electrodes. We study two cases, the first is a saturated homogeneous sand, and the second includes a thin sandstone layer buried inside the sand. The experimental dataset confirms that measuring absolute potentials allows the interface-generated EM wave to be detected by receivers ten wavelengths away from its origin, whereas it is hardly detected when using dipolar arrays (which are common practice) located near the layer. Using a benchmarked numerical code we quantitatively compare theoretical predictions and experimental data, finding that seismo-EM amplitudes agree within a factor of 2. While this result validates the seismoelectric theory that the code is based on, it also opens the path for future upscaling of the experimental workflow used in the comparison and show that absolute potentials should be systematically measured. Finally, our study supports that thin layers can be detected by this method.

International audience; Better understanding of the mechanisms that control microplastic (MP) transport in streams is vital to predict their movement in river systems. MPs are abundantly found in streambed sediments, including small and low-density particles of neutral and positive buoyancy. Hyporheic exchange, which occurs in most rivers, is the two-way movement between the overlying water and the streambed sediments. It is driven by both turbulence in the near bed region and pressure variations at the streambed surface that force water and particulate matter (e.g., microplastics, fine sediments, microbes) into and out of the sediment porewater, leading to accumulation of very small particles with very low settling rates within the hyporheic region. Recently, hyporheic exchange has been shown to substantially increase the retention of MPs in rivers. Subsequently, models need to incorporate hyporheic exchange to avoid underestimating the deposition, retention, and long-term accumulation of MPs in streambed sediments.Additionally, MP remobilization caused by flood events through turbulence or bed sediment transport is yet to be quantified. The extent of remobilization is dependent on both the increase in magnitude of the flow and the number of accumulated MPs in streambed sediments prior to the event. Therefore, in order to accurately predict the persistence and fate of MP in streams it is crucial to not only include hyporheic exchange, but also consider both baseflow and stormflow processes within a model framework.We present multi-scale mobile-immobile models combined with direct measurements of MP accumulation, deposition, and resuspension rates from mesocosm to reach-scale. The models account for the exchange between the surface water and streambed sediments, deposition, and resuspension during baseflow and stormflow conditions. We used this approach to relate in-stream MP transport for varying polymer shapes and types to spatial and temporal scales of retention. Linking transport mechanisms across scales advances our ability to predict MP fate in streams. These results demonstrate the complex relationship between microplastic transport and retention characteristics that lead to the heterogeneous distribution of microplastic accumulation and persistence in streambed sediments.

The use of flammable substances (e.g. powders, liquids, gases or vapors) in synthetic roofing membranes and flexible geomembranes is likely to generate a risk of ignition of explosive atmosphere (ATEX) hazards. Regulation which is imperative upon industries aims at improving protection of workers considering operational health and safety issues. Typical and recurring accident are demonstrating of constraints and obstacles that industrial plant operators of this equipment, are facing. Based on lessons learned from feedback, Ineris organized and facilitated a working group including the French Geosynthetics Committee which made it possible to identify the associated means of prevention of these ATEX hazards while collecting the existing good practices relating to the use of such equipment., Les installations intégrant les membranes synthétiques de couverture et de géomembranes souples et dédiées à la mise en oeuvre de substances inflammables sont susceptibles de générer un risque d’inflammation d'atmosphères explosives (ATEX). La réglementation qui s’impose aux exploitants industriels vise à améliorer la protection en matière de sécurité et de santé des travailleurs susceptibles d'être exposés à ces risques. Une accidentologie typique et récurrente témoigne des difficultés auxquels sont confrontés les industriels exploitants de ces produits. En se basant sur le retour d’expérience, l’Ineris a organisé et animé un groupe de travail en liaison avec le Comité Français des Géo synthétiques1 qui a permis d’identifier les moyens de prévention de ces risques ATEX tout en recueillant les bonnes pratiques existantes relatives à la mise en oeuvre de tels équipements.

Through the analysis of high frequency physico-chemical time series at the Fontaine de Nîmes spring (South of France), we aim to improve our understanding of the hydrogeological responses and water origins in an urban karst catchment. Based on the study of 28 major flood events we shed light on relationships between solutes (electrical conductivity), particles (turbidity), or wastewater leaching from urban areas (natural fluorescence). We find that a seasonal flood typology helps explain the observed physico-chemical variability. Overall, this paper highlights the benefit of a multi-parameter monitoring at high resolution in order to better characterize water origin, depending on the seasonality for Mediterranean karst urban systems.