Caractérisation de l'organisation spatiale de la couverture pédologique par mesure de la résistivité électrique: Application à la cartographie des sols en contexte agricole

Maintenant à l'Université de Clermont AuvergneThe increasing importance of environmental issues has led to a renewed interest in soils. Soils are subjected to numerous hazards that may threaten their quality and affect their properties. An optimal management and protection of soils goes through an accurate knowledge of their spatial variability and the identification of vulnerable areas. The goal of the presented work is to make use of electrical survey data through relying on the discriminating power of electrical resistivity towards the different horizons composing the soil cover in order to characterize their geometrical and typological properties.First of all, modeling of multi-depth electrical resistivity measurements was performed in order to 1)define an optimal survey strategy and 2)assess the efficiency and limitations of electrical method. This step allowed us to estimate what were the minimal dimensions of a pedological heterogeneity that could be detected and the influence of the following different parameters on its detectability: inter-profiles spacing used during measurements, depth and thickness of the heterogeneity, resistivity contrast between heterogeneity and surroundings.The experimental study of a trench dug along several metres, including soil sampling and resistivity measurements, permitted us to characterize the vertical and lateral variability of the soil cover’s horizons. Relationships between electrical resistivity and pedological properties such as mass water content, volume water content or soil bulk density were established.Finally, a new and original method for exploiting data generated by multi-depth electric resistivity survey was put forward. The method is based on the confrontation of geophysical and pedological taxonomies, and on the mapping of vertical apparent resistivity profiles. It allowed finding back soil cartographic unit outlines that were coherent with the previously available soil map. This approach is a valuable tool for studying soil cover spatial variability and has potential for setting up a (semi-)automated method of soil mapping.L’importance croissante des problématiques environnementales entraîne un regain d’intérêt pour les sols. Les nombreux aléas auxquels ils sont soumis les fragilisent et affectent leurs propriétés. Une gestion et une protection optimales des sols passe par une connaissance approfondie de leur variabilité spatiale, y compris l’identification de zones vulnérables. L’objectif des travaux présentés est d’exploiter les données issues de la prospection électrique, afin d’exploiter le pouvoir discriminant de la résistivité électrique vis-à-vis des différents horizons d’une couverture pédologique, en vue d’en caractériser les propriétés géométriques.Tout d’abord, une modélisation de mesures de résistivité électrique multi-profondeurs a été réalisée en vue 1)de définir une stratégie de prospection optimale, et 2)d’évaluer les performances et limites de la méthode électrique. Cette étape a permis d’évaluer les dimensions minimales détectables d’une hétérogénéité pédologique ainsi que l’impact, sur sa détection, de différents paramètres : espacement inter-profils utilisé lors des mesures, profondeur et épaisseur de l’hétérogénéité, contraste de résistivité entre celle-ci et l’encaissant.L’étude expérimentale d’une tranchée ouverte sur plusieurs mètres, couplant prélèvements de sols et mesure de résistivité, a permis de caractériser la variabilité verticale et latérale des horizons de la couverture pédologique. Des relations entre résistivité électrique et propriétés pédologiques telles que teneur en eau massique, teneur en eau volumique ou masse volumique apparente de sol ont également été établies.Enfin, une méthode originale d’exploitation de données électriques issues d’une prospection multi-profondeurs a été proposée. Basée sur une taxonomie géophysique et pédologique, elle a permis, par la cartographie de profils verticaux de résistivité apparente, de retrouver des délinéations concordantes avec celles d’une carte des sols. Cette approche constitue un outil précieux pour l’étude de la variabilité spatiale de la couverture pédologique

Approximate three-dimensional resistivity modelling using Fourier analysis of layer resistivity in shallow soil studies

International audienceThe approximate forward modelling method using Fourier analysis has been used in 2-D applications for several decades. It involves decomposition of the terrain parameters, either the resistivity or the layer thickness, into a Fourier series expansion to simplify the problem to that of a 1-D situation. In this study, the Fourier analysis is applied to 3-D forward modelling for the purposes of shallow DC resistivity imaging with pole-pole array. Our work is to assess advantages and drawbacks of the simplified approach by comparing to exact 3-D solutions, method of moments (MoM) and surface integrals and to the Born approximation applied to MoM. While the Fourier analysis method offers very short calculation times, it shows a significant, albeit systematic, reduction of the anomaly amplitudes; and its ability to delineate anomaly sources is lower than the other methods. Nevertheless, its rapidity makes it an interesting first approach in the modelling of DC resistivity results

Self-potential dataset for mapping groundwater flow patterns in the Chaîne des Puys (Auvergne, France)

The present Self-Potential (SP) dataset acquired in the Chaîne des Puys is the result of four decades of measurements carried out by master's students, PhD students, researchers, and engineering offices under the auspices of the Laboratoire Magmas et Volcans (LMV) and the Observatoire de Physique du Globe de Clermont-Ferrand (OPGC). Acquired in the 1980s by Maurice Aubert and his collaborators (e.g. [1–3]), this Self-Potential dataset was completed as part of the CAPRICE project focused on the hydrosystem of the Chaîne des Puys. The methodology and equipment used for data acquisition has remained unchanged since the first measurement in 1987. As a result, this dataset compiles more than 20,000 SP measurements and covers an area of almost 200 km².The SP data are intended to serve as the basis for geological models, coupled with geological and other geophysical data, according to the method described in Aubert and Atangana, 1996. After interpolation, SP data can be used to identify preferential groundwater flow paths and to delineate the surface of hydrogeological watersheds. As indicated in the literature, they also be used to identify possible recharge zones or areas of permeability contrast

Structuration tertiaire et quaternaire du Plateau des Dômes (Chaîne des Puys, Massif central, France)

International audienceThe Plateau des Dômes overhangs the Limagne graben by several hundred metres and represents the basement of a Quaternary volcanic chain oriented north-south, the Chaîne des Puys (CdP), consisting of about 80 volcanic edifices spread linearly over thirty kilometers. Since its final emersion in the late Cretaceous, the Plateau des Dôme has been mainly affected by two tectonic events: the formation of the West European Rift (ROE), with its associated volcanism, and a late surrection that is still ongoing. To unravel the Tertiary and Quaternary geological history of the Plateau, a structural approach was defined. At the scale of the Massif central, four families of Variscan crustal faults can be described : 1. the Sillon Houiller family oriented N20E (dir.SH), 2. the Cévennes fault family oriented NE-SW (dir.C), 3. the Villefort fault fa­mily oriented N160-170E (dir.V) and 4. the Armorican family, which oscillates between N110E and N140E (dir.A) due to the orientation of the North and South Armorican Shear Zone. This network of crustal faults can be observed at any scale.It is shown that the Plateau des Dômes is crossed by such a network of variscan faults, which was reactivated during the Tertiary and Quaternary tectonic events occurring in the studied zone. No new faults were created in response to the different stress patterns that prevailed in the Tertiary and Qua­ternary periods.The main conclusions of this study can be summarized as follows :1. The Variscan basement of the Plateau des Dômes was tilted westwards at the end of the Eocene by the formation of the Olby half-graben controlled by the reactivation of the Pontgibaud fault [FdP (dir.SH)]. It was limited to the east by the Limagne fault (FdL), which reactivated two Variscan directions (dir.SH and dir.V), the only two compatible with the east-west extension. At that time, the future plateau was emerged, but at an altitude close to sea level.2. The cessation of the FdP and the continued activity of the FdL in the Oligocene caused the eastern edge of the future plateau to be dissected and lowered down by the activation of FdL's secondary (dir.SH) faults. The future plateau remained close to sea level. The main outlines of its present topography were acquired at the end of the sedimentation period.3. The plateau was uplifted shortly before the emission of the last Montdorian lava flows, dated at 3.5/3 Ma. To the east, the FdL was not reactivated during the regional uplift and the Plateau des Dômes appears as such due to erosion of the Limagne weak sediments, which cleared the fault scarp. The Plateau des Dômes is part of a larger ensemble (i.e. a larger plateau) bounded by the Morge dir.C fault to the north and the Sillon Houiller to the west. Through the coeval reactivation of these two faults, this large north-western quadrant has undergone differential uplift bringing it to a high position relative to areas further north and west. To the south, the Plateau des Dômes is dominated by the large Monts Dore stratovolcano. In this sector, a series of parallel dir.A faults, oriented N110E, as well as the reactivation of the Nébouzat fault, have ensured the differential surrection of the basement in a way similar to successive steps of a staircase.4. The volcanoes of the CdP are aligned along a main fault (the Beauregard fault), which is the backbone of the chain, and along several secondary faults, dir.SH to the NE and dir.A to the SE, all connected to the main fault. The lava flows follow paleo valleys that were dug along the weak zones constituted by the Variscan faults. The north of the plateau, dominated by dir.SH faults, exhibits lava flows that are generally oriented NE-SW, in sharp contrast to the south, dominated by dir.A faults, where the flows are oriented NW-SE.Le Plateau des Dômes surplombe le graben de la Limagne de plusieurs centaines de mètres et supporte une chaîne volcanique quaternaire orientée nord-sud, la Chaîne des Puys (CdP), constituée d’environ 80 édifices répartis linéairement sur une trentaine de kilomètres. Ce plateau est traversé par un réseau de failles crustales où se reconnaissent les grandes familles varisques, représentées dans le Massif central par des failles emblématiques telles que le Sillon Houiller, la Faille des Cévennes ou la Faille de Villefort. Depuis son émersion définitive vers la fin du Crétacé, le Plateau des Dômes a été principalement affecté par deux événements tectoniques : la formation du Rift Ouest Européen (ROE), avec son volcanisme associé, et une surrection tardive qui se poursuit actuellement.Par une synthèse des données existantes et une réappréciation des cartes géologiques et de l’analyse de la topographie (analyse des MNT : Modèles Numériques de Terrain), cet article montre que la structuration tertiaire et quaternaire du Plateau des Dômes s’est entièrement effectuée par la réactivation de quelques failles varisques majeures qui ont 1) permis le basculement du socle lors de la formation des grabens, 2) assuré sa surrection différentielle par rapport à d’autres secteurs limitrophes et 3) contrôlé l’ascension des magmas vers la surface. Une évolution structurale du plateau est proposée résumant les étapes majeures depuis l’Eocène

Structuration tertiaire et quaternaire du Plateau des Dômes (Chaîne des Puys, Massif central, France)

International audienceThe Plateau des Dômes overhangs the Limagne graben by several hundred metres and represents the basement of a Quaternary volcanic chain oriented north-south, the Chaîne des Puys (CdP), consisting of about 80 volcanic edifices spread linearly over thirty kilometers. Since its final emersion in the late Cretaceous, the Plateau des Dôme has been mainly affected by two tectonic events: the formation of the West European Rift (ROE), with its associated volcanism, and a late surrection that is still ongoing. To unravel the Tertiary and Quaternary geological history of the Plateau, a structural approach was defined. At the scale of the Massif central, four families of Variscan crustal faults can be described : 1. the Sillon Houiller family oriented N20E (dir.SH), 2. the Cévennes fault family oriented NE-SW (dir.C), 3. the Villefort fault fa­mily oriented N160-170E (dir.V) and 4. the Armorican family, which oscillates between N110E and N140E (dir.A) due to the orientation of the North and South Armorican Shear Zone. This network of crustal faults can be observed at any scale.It is shown that the Plateau des Dômes is crossed by such a network of variscan faults, which was reactivated during the Tertiary and Quaternary tectonic events occurring in the studied zone. No new faults were created in response to the different stress patterns that prevailed in the Tertiary and Qua­ternary periods.The main conclusions of this study can be summarized as follows :1. The Variscan basement of the Plateau des Dômes was tilted westwards at the end of the Eocene by the formation of the Olby half-graben controlled by the reactivation of the Pontgibaud fault [FdP (dir.SH)]. It was limited to the east by the Limagne fault (FdL), which reactivated two Variscan directions (dir.SH and dir.V), the only two compatible with the east-west extension. At that time, the future plateau was emerged, but at an altitude close to sea level.2. The cessation of the FdP and the continued activity of the FdL in the Oligocene caused the eastern edge of the future plateau to be dissected and lowered down by the activation of FdL's secondary (dir.SH) faults. The future plateau remained close to sea level. The main outlines of its present topography were acquired at the end of the sedimentation period.3. The plateau was uplifted shortly before the emission of the last Montdorian lava flows, dated at 3.5/3 Ma. To the east, the FdL was not reactivated during the regional uplift and the Plateau des Dômes appears as such due to erosion of the Limagne weak sediments, which cleared the fault scarp. The Plateau des Dômes is part of a larger ensemble (i.e. a larger plateau) bounded by the Morge dir.C fault to the north and the Sillon Houiller to the west. Through the coeval reactivation of these two faults, this large north-western quadrant has undergone differential uplift bringing it to a high position relative to areas further north and west. To the south, the Plateau des Dômes is dominated by the large Monts Dore stratovolcano. In this sector, a series of parallel dir.A faults, oriented N110E, as well as the reactivation of the Nébouzat fault, have ensured the differential surrection of the basement in a way similar to successive steps of a staircase.4. The volcanoes of the CdP are aligned along a main fault (the Beauregard fault), which is the backbone of the chain, and along several secondary faults, dir.SH to the NE and dir.A to the SE, all connected to the main fault. The lava flows follow paleo valleys that were dug along the weak zones constituted by the Variscan faults. The north of the plateau, dominated by dir.SH faults, exhibits lava flows that are generally oriented NE-SW, in sharp contrast to the south, dominated by dir.A faults, where the flows are oriented NW-SE.Le Plateau des Dômes surplombe le graben de la Limagne de plusieurs centaines de mètres et supporte une chaîne volcanique quaternaire orientée nord-sud, la Chaîne des Puys (CdP), constituée d’environ 80 édifices répartis linéairement sur une trentaine de kilomètres. Ce plateau est traversé par un réseau de failles crustales où se reconnaissent les grandes familles varisques, représentées dans le Massif central par des failles emblématiques telles que le Sillon Houiller, la Faille des Cévennes ou la Faille de Villefort. Depuis son émersion définitive vers la fin du Crétacé, le Plateau des Dômes a été principalement affecté par deux événements tectoniques : la formation du Rift Ouest Européen (ROE), avec son volcanisme associé, et une surrection tardive qui se poursuit actuellement.Par une synthèse des données existantes et une réappréciation des cartes géologiques et de l’analyse de la topographie (analyse des MNT : Modèles Numériques de Terrain), cet article montre que la structuration tertiaire et quaternaire du Plateau des Dômes s’est entièrement effectuée par la réactivation de quelques failles varisques majeures qui ont 1) permis le basculement du socle lors de la formation des grabens, 2) assuré sa surrection différentielle par rapport à d’autres secteurs limitrophes et 3) contrôlé l’ascension des magmas vers la surface. Une évolution structurale du plateau est proposée résumant les étapes majeures depuis l’Eocène

Structuration tertiaire et quaternaire du Plateau des Dômes (Chaîne des Puys, Massif central, France)

International audienceThe Plateau des Dômes overhangs the Limagne graben by several hundred metres and represents the basement of a Quaternary volcanic chain oriented north-south, the Chaîne des Puys (CdP), consisting of about 80 volcanic edifices spread linearly over thirty kilometers. Since its final emersion in the late Cretaceous, the Plateau des Dôme has been mainly affected by two tectonic events: the formation of the West European Rift (ROE), with its associated volcanism, and a late surrection that is still ongoing. To unravel the Tertiary and Quaternary geological history of the Plateau, a structural approach was defined. At the scale of the Massif central, four families of Variscan crustal faults can be described : 1. the Sillon Houiller family oriented N20E (dir.SH), 2. the Cévennes fault family oriented NE-SW (dir.C), 3. the Villefort fault fa­mily oriented N160-170E (dir.V) and 4. the Armorican family, which oscillates between N110E and N140E (dir.A) due to the orientation of the North and South Armorican Shear Zone. This network of crustal faults can be observed at any scale.It is shown that the Plateau des Dômes is crossed by such a network of variscan faults, which was reactivated during the Tertiary and Quaternary tectonic events occurring in the studied zone. No new faults were created in response to the different stress patterns that prevailed in the Tertiary and Qua­ternary periods.The main conclusions of this study can be summarized as follows :1. The Variscan basement of the Plateau des Dômes was tilted westwards at the end of the Eocene by the formation of the Olby half-graben controlled by the reactivation of the Pontgibaud fault [FdP (dir.SH)]. It was limited to the east by the Limagne fault (FdL), which reactivated two Variscan directions (dir.SH and dir.V), the only two compatible with the east-west extension. At that time, the future plateau was emerged, but at an altitude close to sea level.2. The cessation of the FdP and the continued activity of the FdL in the Oligocene caused the eastern edge of the future plateau to be dissected and lowered down by the activation of FdL's secondary (dir.SH) faults. The future plateau remained close to sea level. The main outlines of its present topography were acquired at the end of the sedimentation period.3. The plateau was uplifted shortly before the emission of the last Montdorian lava flows, dated at 3.5/3 Ma. To the east, the FdL was not reactivated during the regional uplift and the Plateau des Dômes appears as such due to erosion of the Limagne weak sediments, which cleared the fault scarp. The Plateau des Dômes is part of a larger ensemble (i.e. a larger plateau) bounded by the Morge dir.C fault to the north and the Sillon Houiller to the west. Through the coeval reactivation of these two faults, this large north-western quadrant has undergone differential uplift bringing it to a high position relative to areas further north and west. To the south, the Plateau des Dômes is dominated by the large Monts Dore stratovolcano. In this sector, a series of parallel dir.A faults, oriented N110E, as well as the reactivation of the Nébouzat fault, have ensured the differential surrection of the basement in a way similar to successive steps of a staircase.4. The volcanoes of the CdP are aligned along a main fault (the Beauregard fault), which is the backbone of the chain, and along several secondary faults, dir.SH to the NE and dir.A to the SE, all connected to the main fault. The lava flows follow paleo valleys that were dug along the weak zones constituted by the Variscan faults. The north of the plateau, dominated by dir.SH faults, exhibits lava flows that are generally oriented NE-SW, in sharp contrast to the south, dominated by dir.A faults, where the flows are oriented NW-SE.Le Plateau des Dômes surplombe le graben de la Limagne de plusieurs centaines de mètres et supporte une chaîne volcanique quaternaire orientée nord-sud, la Chaîne des Puys (CdP), constituée d’environ 80 édifices répartis linéairement sur une trentaine de kilomètres. Ce plateau est traversé par un réseau de failles crustales où se reconnaissent les grandes familles varisques, représentées dans le Massif central par des failles emblématiques telles que le Sillon Houiller, la Faille des Cévennes ou la Faille de Villefort. Depuis son émersion définitive vers la fin du Crétacé, le Plateau des Dômes a été principalement affecté par deux événements tectoniques : la formation du Rift Ouest Européen (ROE), avec son volcanisme associé, et une surrection tardive qui se poursuit actuellement.Par une synthèse des données existantes et une réappréciation des cartes géologiques et de l’analyse de la topographie (analyse des MNT : Modèles Numériques de Terrain), cet article montre que la structuration tertiaire et quaternaire du Plateau des Dômes s’est entièrement effectuée par la réactivation de quelques failles varisques majeures qui ont 1) permis le basculement du socle lors de la formation des grabens, 2) assuré sa surrection différentielle par rapport à d’autres secteurs limitrophes et 3) contrôlé l’ascension des magmas vers la surface. Une évolution structurale du plateau est proposée résumant les étapes majeures depuis l’Eocène

Imaging probes and modalities for the study of Solute Carrier O (SLCO)-transport function in vivo

International audienceTransporters of the Solute Carrier O (SLCO) family, former organic anion-transportingpolypeptides (OATP), are now recognized as key players in pharmacokinetics. Imagingis increasingly regarded as a relevant method to elucidate and decipher the intrinsicrole of SLCO in controlling drug disposition in plasma and tissues. Current research inthis representative field of translational research is based on different imagingmodalities including nuclear imaging, such as Single Photon Emission ComputedTomography (SPECT) or Positron Emission Tomography (PET), as well as MagneticResonance Imaging (MRI). Imaging modalities can be compared in terms of sensitivity,quantitative properties, spatial resolution, variety of ligands and radiation exposure. Allof these approaches rely on the use of SLCO-substrates that are detected usingcorresponding modalities. The present review aims at reporting and comparing theimaging probes that have been proposed to study SLCO-transport function, in termsof $in\ vitro$ specificity, $in\ vivo$ behavior and clinical validation

Structuration tertiaire et quaternaire du Plateau des Dômes (Chaîne des Puys, Massif central, France)

International audienceThe Plateau des Dômes overhangs the Limagne graben by several hundred metres and represents the basement of a Quaternary volcanic chain oriented north-south, the Chaîne des Puys (CdP), consisting of about 80 volcanic edifices spread linearly over thirty kilometers. Since its final emersion in the late Cretaceous, the Plateau des Dôme has been mainly affected by two tectonic events: the formation of the West European Rift (ROE), with its associated volcanism, and a late surrection that is still ongoing. To unravel the Tertiary and Quaternary geological history of the Plateau, a structural approach was defined. At the scale of the Massif central, four families of Variscan crustal faults can be described : 1. the Sillon Houiller family oriented N20E (dir.SH), 2. the Cévennes fault family oriented NE-SW (dir.C), 3. the Villefort fault fa­mily oriented N160-170E (dir.V) and 4. the Armorican family, which oscillates between N110E and N140E (dir.A) due to the orientation of the North and South Armorican Shear Zone. This network of crustal faults can be observed at any scale.It is shown that the Plateau des Dômes is crossed by such a network of variscan faults, which was reactivated during the Tertiary and Quaternary tectonic events occurring in the studied zone. No new faults were created in response to the different stress patterns that prevailed in the Tertiary and Qua­ternary periods.The main conclusions of this study can be summarized as follows :1. The Variscan basement of the Plateau des Dômes was tilted westwards at the end of the Eocene by the formation of the Olby half-graben controlled by the reactivation of the Pontgibaud fault [FdP (dir.SH)]. It was limited to the east by the Limagne fault (FdL), which reactivated two Variscan directions (dir.SH and dir.V), the only two compatible with the east-west extension. At that time, the future plateau was emerged, but at an altitude close to sea level.2. The cessation of the FdP and the continued activity of the FdL in the Oligocene caused the eastern edge of the future plateau to be dissected and lowered down by the activation of FdL's secondary (dir.SH) faults. The future plateau remained close to sea level. The main outlines of its present topography were acquired at the end of the sedimentation period.3. The plateau was uplifted shortly before the emission of the last Montdorian lava flows, dated at 3.5/3 Ma. To the east, the FdL was not reactivated during the regional uplift and the Plateau des Dômes appears as such due to erosion of the Limagne weak sediments, which cleared the fault scarp. The Plateau des Dômes is part of a larger ensemble (i.e. a larger plateau) bounded by the Morge dir.C fault to the north and the Sillon Houiller to the west. Through the coeval reactivation of these two faults, this large north-western quadrant has undergone differential uplift bringing it to a high position relative to areas further north and west. To the south, the Plateau des Dômes is dominated by the large Monts Dore stratovolcano. In this sector, a series of parallel dir.A faults, oriented N110E, as well as the reactivation of the Nébouzat fault, have ensured the differential surrection of the basement in a way similar to successive steps of a staircase.4. The volcanoes of the CdP are aligned along a main fault (the Beauregard fault), which is the backbone of the chain, and along several secondary faults, dir.SH to the NE and dir.A to the SE, all connected to the main fault. The lava flows follow paleo valleys that were dug along the weak zones constituted by the Variscan faults. The north of the plateau, dominated by dir.SH faults, exhibits lava flows that are generally oriented NE-SW, in sharp contrast to the south, dominated by dir.A faults, where the flows are oriented NW-SE.Le Plateau des Dômes surplombe le graben de la Limagne de plusieurs centaines de mètres et supporte une chaîne volcanique quaternaire orientée nord-sud, la Chaîne des Puys (CdP), constituée d’environ 80 édifices répartis linéairement sur une trentaine de kilomètres. Ce plateau est traversé par un réseau de failles crustales où se reconnaissent les grandes familles varisques, représentées dans le Massif central par des failles emblématiques telles que le Sillon Houiller, la Faille des Cévennes ou la Faille de Villefort. Depuis son émersion définitive vers la fin du Crétacé, le Plateau des Dômes a été principalement affecté par deux événements tectoniques : la formation du Rift Ouest Européen (ROE), avec son volcanisme associé, et une surrection tardive qui se poursuit actuellement.Par une synthèse des données existantes et une réappréciation des cartes géologiques et de l’analyse de la topographie (analyse des MNT : Modèles Numériques de Terrain), cet article montre que la structuration tertiaire et quaternaire du Plateau des Dômes s’est entièrement effectuée par la réactivation de quelques failles varisques majeures qui ont 1) permis le basculement du socle lors de la formation des grabens, 2) assuré sa surrection différentielle par rapport à d’autres secteurs limitrophes et 3) contrôlé l’ascension des magmas vers la surface. Une évolution structurale du plateau est proposée résumant les étapes majeures depuis l’Eocène

The use of magnetic susceptibility and viscosity measurements as a mapping tool for soil properties: DIGISOIL field results

International audienceThe clay (paramagnetic) and iron oxides (ferrimagnetic) contents carry the magnetic properties of soils. Changes in the local redox conditions influence the iron oxides fatum and, then, the magnetic properties of soils. Consequently, many processes (air circulation, microbial activities, heavy metal accumulation...) can influence the magnetic behaviour. The aim of this study is to evaluate which soil property(ies) (carbon content, bulk density, clay content...) can be mapped with the help of magnetic properties measurements (magnetic susceptibility, magnetic viscosity and there ratio). The survey has been achieved on the validation site defined in the DIGISOIL project and located in Luxembourg. This site is about 4 ha in area, it is cultivated and ploughed. We made 231 measurements with 5 devices (MS2D Bartington ltd, DECCO, TS6 Protovale, CS60 and VC100 prototype) in 7 configurations. 30 calibration cores were also collected to characterize soil properties (carbon content, clay content, stone content and water content) in the field. The results are used to analyse the relationship between soil and magnetic properties. When a relation appears, soil property maps derived from magnetic property ones are plotted and confronted with collected sample results

Medium-frequency electromagnetic device to measure electric conductivity and dielectric permittivity of soils

International audienceAn electromagnetic (EM) tool working in the medium-frequency range allows the determination of the electric conductivity and dielectric permittivity of soils with a single measurement. It brings information about different state parameters of soils, especially their water and clay contents for a significant volume of investigation. To investigate these properties, a medium-frequency-range EM prototype, the CE120, was built using a perpendicular coil Slingram configuration with a working frequency of 1.56 MHz and a fixed coil spacing of 1.2 m. This configuration was chosen using modeling with the purpose of measuring electric resistivities up to a few thousands of ohm-meters and relative dielectric permittivities as low as two. These thresholds match the expected parameters values in the medium frequency range. Moreover, the CE120 characteristics allowed for an investigation depth between 2 and 2.5 m, depending on the nature of the soil. The prototype was tested on two different soils with water variations: sandy alluvia and clay-loam soil