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1. Coupled study of water-stable isotopes and anions in porewater for characterizing aqueous transport through the Mesozoic sedimentary series in the eastern Paris Basin

Author

F. Bensenouci, Jean-Michel Matray, M. Massault, Jean-Luc Michelot, S. Savoye, Agnès Vinsot, Laboratoire d'Etude et de recherche sur les Transferts et les Installations dans les Sols (IRSN/PRP-DGE/SRTG/LETIS), Institut de Radioprotection et de Sûreté Nucléaire (IRSN), Géosciences Paris Sud (GEOPS), Université Paris-Sud - Paris 11 (UP11)-Centre National de la Recherche Scientifique (CNRS), GéoHydrosystèmes COntinentaux (GéHCO EA6293), Université de Tours (UT), Laboratoire de Mesures et Modélisation de la Migration des Radionucléides (L3MR), Service d'Etudes du Comportement des Radionucléides (SECR), Département de Physico-Chimie (DPC), CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire) (CEA-DES (ex-DEN)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire) (CEA-DES (ex-DEN)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Département de Physico-Chimie (DPC), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay, Laboratoire d'Etude des Transferts dans les Sols et le sous-sol (DEI/SARG/LETS), and Université de Tours

Subjects
Stratigraphy, 0207 environmental engineering, Borehole, Geochemistry, [SDU.STU]Sciences of the Universe [physics]/Earth Sciences, Aquifer, 02 engineering and technology, 010502 geochemistry & geophysics, Oceanography, 01 natural sciences, Chloride, medicine, Diffusion (business), 020701 environmental engineering, Geomorphology, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences, geography, geography.geographical_feature_category, Advection, Stable isotope ratio, Geology, 6. Clean water, Geophysics, 13. Climate action, Economic Geology, Sedimentary rock, Groundwater, medicine.drug
Abstract

This study presents data on chloride and bromide concentrations in porewater, water and anion diffusion coefficients, and their accessible porosities based on radial diffusion experiments on rock samples collected from a 2000 m-deep borehole (EST433) drilled by Andra in the eastern Paris Basin. The distributions of water stable isotope and chloride concentrations in porewater along this column reveal transient flows of water and solutes between the aquitard layers and the surrounding aquifers. These distributions confirm the occurrence of two separate aquitard/aquifer systems: “Oxfordian/Callovo–Oxfordian/Dogger” and “Dogger/Liassic/Rhaetian”. This separation is confirmed by Cl−/Br− ratios, which are low in Liassic and Dogger porewater, suggesting the influence of primary brines, and which are close to the marine ratio in the Dogger groundwater. Based on these results, transport simulations in the two systems were carried out according to different scenarios. The simulation results confirm that transport properties obtained in the laboratory at sample scale may be extrapolated to the formation scale. It is highly probable that diffusion is the main transport process in the Callovo–Oxfordian formation. This may also be the case in the Dogger/Liassic layer, although a limited contribution from advection cannot be totally excluded. By testing different scenarios of boundary conditions in diffusive models, it is proposed that the Dogger aquifer was first activated in the Early Miocene.

Published
2014
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2. Geochemical characterization and modelling of the Toarcian/Domerian porewater at the Tournemire underground research laboratory

Author

David Arcos, Christophe Tournassat, Eric C. Gaucher, Joachim Tremosa, Jebril Hadi, Jean-Michel Matray, F. Bensenouci, Structure et fonctionnement des systèmes hydriques continentaux (SISYPHE), Université Pierre et Marie Curie - Paris 6 (UPMC)-École pratique des hautes études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-MINES ParisTech - École nationale supérieure des mines de Paris, Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), AMPHOS, XXI Consulting, Laboratoire d'Etude des Transferts dans les Sols et le sous-sol (DEI/SARG/LETS), Institut de Radioprotection et de Sûreté Nucléaire (IRSN), Interactions et dynamique des environnements de surface (IDES), Université Paris-Sud - Paris 11 (UP11)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Bureau de Recherches Géologiques et Minières (BRGM) (BRGM), Université Pierre et Marie Curie - Paris 6 (UPMC)-École Pratique des Hautes Études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Mines Paris - PSL (École nationale supérieure des mines de Paris), and Laboratoire d'Etude et de recherche sur les Transferts et les Installations dans les Sols (IRSN/PRP-DGE/SRTG/LETIS)

Subjects
Calcite, [SDU.STU]Sciences of the Universe [physics]/Earth Sciences, Mineralogy, 010501 environmental sciences, engineering.material, 010502 geochemistry & geophysics, 01 natural sciences, Pollution, chemistry.chemical_compound, chemistry, Hydraulic conductivity, Geochemistry and Petrology, Illite, engineering, Environmental Chemistry, Pyrite, Porosity, Clay minerals, Quartz, Water content, ComputingMilieux_MISCELLANEOUS, Geology, 0105 earth and related environmental sciences
Abstract

For safety evaluation of hazardous waste repositories in clay-rocks, a thorough assessment of porewater chemistry and water–rock interactions is required. However, this objective is a challenging task due to the low hydraulic conductivity and water content of such rocks, which subsequently renders porewater sampling difficult (without inducing perturbations). For this reason, an indirect approach was developed to determine porewater composition of clay-rocks, by a geochemical model of water–rock interaction using some properties of the rock and the solution. The goal of this paper is to obtain the porewater composition of the Toarcian/Domerian argillaceous formation at Tournemire (South of France), for which a reliable model is still lacking. The following work presents a comprehensive characterization of the geochemical system of the Tournemire clay-rock, including mineralogy, petrology, mobile anions, cation exchange properties, accessible porosity and CO 2 partial pressure. Perturbation corrections from fracture water sampling were also computed. These water were found in sealed fractures ( Beaucaire et al., 2008 ) and their radiocarbon apparent age is estimated at 20 ka. Their age together with their equilibrium situation allow considering these fracture waters as representative of the formation porewater. The model developed to calculate the Tournemire porewater composition is essentially based on cation exchange by a multi-site approach, but equilibrium with some mineral phases (calcite, quartz and pyrite) is also considered. Different exchange sites of different affinities towards cations are used, which proportions are given by the mineralogy. Exchange on illite is performed with a three-sites model, while one site is considered for smectite phases. Multi-site model results are compared with corrected fracture water data and two other models: a model only based on mineral equilibrium and a model using cation exchange on one global site. The best results were obtained with the models that take into account cation exchange and particularly with the multi-site model. The interest in considering a model with exchange sites of different affinities is particularly obvious for a satisfactory representation of the K + content in solution. A dependence of K + content to the amount of high affinity sites was observed, leading to an improvement of its simulation when uncertainty on mineralogical data is considered. Once validated, the multi-site model was applied at different levels of the Tournemire argillaceous formation to obtain a profile of the porewater composition.

Published
2012
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3. A profile of helium-4 concentration in pore-water for assessing the transport phenomena through an argillaceous formation (Tournemire, France)

Author

Bertrand Thomas, F. Bensenouci, Jean-Michel Matray, Sébastien Savoye, P. Dick, B. Lavielle, Jean-Luc Michelot, Interactions et dynamique des environnements de surface (IDES), Université Paris-Sud - Paris 11 (UP11)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Géosciences Paris Sud (GEOPS), Université Paris-Sud - Paris 11 (UP11)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Recherche sur le Stockage géologique des déchets et les transferts dans les Sols (IRSN/DEI/SARG/LR2S), Institut de Radioprotection et de Sûreté Nucléaire (IRSN), Laboratoire de Mesures et Modélisation de la Migration des Radionucléides (L3MR), Service d'Etudes du Comportement des Radionucléides (SECR), Département de Physico-Chimie (DPC), CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire) (CEA-DES (ex-DEN)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire) (CEA-DES (ex-DEN)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Département de Physico-Chimie (DPC), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay, Chimie Nucléaire Analytique et Bio-environnementale (CNAB), Université Sciences et Technologies - Bordeaux 1 (UB)-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'Etude des Transferts dans les Sols et le sous-sol (DEI/SARG/LETS), and Université Sciences et Technologies - Bordeaux 1-Centre National de la Recherche Scientifique (CNRS)

Subjects
Hydrogeology, Core samples, 02 engineering and technology, 010501 environmental sciences, Steady state, 01 natural sciences, Rock sample, Diffusion, argillaceous deposit, Solid-phase, Helium-4, Vertical distributions, Midi-Pyrenees, Preliminary model, Diffusion (business), 020701 environmental engineering, porewater, geography.geographical_feature_category, argillite, Small scale, In-situ, Diffusion Coefficients, Helium 4, Chlorine compounds, Water isotope, 6. Clean water, Aquifers, Geophysics, Deposition (aerosol physics), Uncertainty analysis, France, Transport phenomena, Diffusion time, Geology, porosity, water chemistry, Argillites, 0207 environmental engineering, chemistry.chemical_element, Mineralogy, borehole, Experimental data, Aquifer, helium, Modelling, Pore water pressure, Complex profiles, Geochemistry and Petrology, Aveyron, Formation scale, Transport process, Pore waters, Argillaceous formations, Helium production, Isotopes of helium, Helium, 0105 earth and related environmental sciences, geography, aquifer, Transport parameters, modeling, Deuterium, Tournemire, Natural tracers, chemistry, [SDU]Sciences of the Universe [physics], Clay
Abstract

International audience; A vertical distribution of helium-4 was obtained in pore-water from the Toarcian/Domerian argillaceous formation at Tournemire (South Aveyron, France). Most of the studied core samples were collected from two vertical air-drilled boreholes across the impervious argillaceous formation and penetrating the bounding aquifers. Accessible porosities for helium were assumed similar to those of water and calculated by weighting before and after heating the core samples. Helium-4 concentrations were obtained after out-gassing the rock samples in tight containers. The comparison of the total amount of 4He produced since the deposition of the formation with that presently measured in the rock reveals that more than 97% of 4He has been lost from the solid phase to pore-water and afterwards to the surrounding aquifers. Helium distribution in pore water shows a complex profile because of the presence of unexpectedly 4He-rich samples in the lower part of the Upper Toarcian level. In order to understand this distribution and to assess the transport of helium at the formation scale, a series of preliminary model calculations were performed using helium diffusion coefficients three times higher than those of water isotopes. The comparison between simulated and experimental data indicates that: (1) the helium profile could be similar to those of deuterium and chloride in pore-water if some unexpectedly 4He-rich samples are not considered; (2) the estimated transport parameters (at small scale) may be transposable at the formation scale with some uncertainties; (3) a steady state has most probably been reached between the in situ helium production and its loss towards the aquifers; (4) only 17-30Ma of diffusion time would be necessary to obtain steady state; this is short compared to the formation age (180Ma) and thus the helium profile cannot give very precise information about diffusion time in the massif, but is in agreement with the hypothesis that transport processes are dominated by diffusion. © 2011 Elsevier Ltd.

Published
2011
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4. Transfers through argillaceous rocks over large space and time scales: Insights given by water stable isotopes

Author

Sébastien Savoye, Jean-Michel Matray, Justo Cabrera, F. Bensenouci, Jean-Luc Michelot, Institut de Radioprotection et de Sûreté Nucléaire (IRSN), Interactions et dynamique des environnements de surface (IDES), and Université Paris-Sud - Paris 11 (UP11)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)

Subjects
geography, Hydrogeology, geography.geographical_feature_category, Stable isotope ratio, Petrophysics, 0207 environmental engineering, Borehole, [SDU.STU]Sciences of the Universe [physics]/Earth Sciences, Mineralogy, Aquifer, 02 engineering and technology, 010502 geochemistry & geophysics, 01 natural sciences, Pore water pressure, Geophysics, Geochemistry and Petrology, Geotechnical engineering, Diffusion (business), 020701 environmental engineering, Oil shale, ComputingMilieux_MISCELLANEOUS, Geology, 0105 earth and related environmental sciences
Abstract

In order to characterize the large-scale transport properties of the Toarcian/Domerian formation in the Tournemire Underground Research Laboratory, the isotopic composition ( δ 18 O and δ 2 H) of pore water was determined on samples from a 250 m borehole drilled from the tunnel ground down to the lower aquifer. The isotope data were obtained from core samples by diffusive vapour exchange. The comparison with previous profiles obtained from vacuum distillation shows a clear discrepancy for all the stratigraphic levels. This demonstrates that artefacts, induced by distillation and already highlighted on only one stratigraphic level, occurred all over the shale sequence. Moreover, diffusion parameters were derived from both radial diffusion experiments and petrophysical determinations. To evaluate the large-scale transport properties of the formation, we performed a series of diffusive model calculations and compared them to experimental data. In agreement with the hydrogeological history, the best simulations considered an activation of the embedding aquifers 11–13 Ma ago, corresponding to the beginning of the diffusive process through the argillaceous formations.

Published
2008
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5. Chlorine transport processes through a 2000 m aquifer/aquitard system

Author

Shaun K. Frape, Jean-Luc Michelot, Philippe Jean-Baptiste, Joël Lancelot, R. Rebeix, Jean-Michel Matray, Elise Fourré, F. Bensenouci, Orfan Shouakar-Stash, Philippe Landrein, Véronique Lavastre, Laboratoire de Géochimie Isotopique Environnementale (GIS) / Université de Nîmes (GIS), Université de Nîmes (UNIMES)-Centre National de la Recherche Scientifique (CNRS), Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Glaces et Continents, Climats et Isotopes Stables (GLACCIOS), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Laboratoire Magmas et Volcans (LMV-ENSMSE), École des Mines de Saint-Étienne (Mines Saint-Étienne MSE), Institut Mines-Télécom [Paris] (IMT)-Institut Mines-Télécom [Paris] (IMT)-SPIN-Centre National de la Recherche Scientifique (CNRS)-Laboratoire Magmas et Volcans (LMV), Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet [Saint-Étienne] (UJM)-Institut de Recherche pour le Développement et la société-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Institut national des sciences de l'Univers (INSU - CNRS)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet [Saint-Étienne] (UJM)-Institut de Recherche pour le Développement et la société-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Institut national des sciences de l'Univers (INSU - CNRS)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'Etude des Transferts dans les Sols et le sous-sol (DEI/SARG/LETS), Institut de Radioprotection et de Sûreté Nucléaire (IRSN), Géosciences Paris Sud (GEOPS), Université Paris-Sud - Paris 11 (UP11)-Centre National de la Recherche Scientifique (CNRS), Agence Nationale pour la Gestion des Déchets Radioactifs (ANDRA), University of Waterloo [Waterloo], Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Institut de Recherche pour le Développement et la société-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Institut national des sciences de l'Univers (INSU - CNRS)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Institut de Recherche pour le Développement et la société-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), and Laboratoire d'Etude et de recherche sur les Transferts et les Installations dans les Sols (IRSN/PRP-DGE/SRTG/LETIS)

Subjects
010504 meteorology & atmospheric sciences, Stratigraphy, Borehole, [SDU.STU]Sciences of the Universe [physics]/Earth Sciences, Context (language use), Aquifer, Structural basin, engineering.material, 010502 geochemistry & geophysics, Oceanography, 01 natural sciences, Petrology, 0105 earth and related environmental sciences, Hydrology, geography, geography.geographical_feature_category, Advection, Geology, 6. Clean water, Geophysics, 13. Climate action, engineering, Halite, Economic Geology, Sedimentary rock, Groundwater
Abstract

International audience; In the Paris Basin, in France, the Callovo-Oxfordian (COx) is currently studied over a 250 km2 surface area by the French national radioactive waste management agency in order to assess the feasibility of long-term underground nuclear waste repository. The COx is a 140 m thick clay-rich layer, which is part of the 2000 m aquitard/aquifer system constituting the sedimentary cover. In such sedimentary context, the transport processes of potential contaminants can be represented by both vertical diffusion and horizontal advection through the most permeable layers. Chloride is used as a natural conservative tracer, and is monitored in term of concentrations and isotopic composition (δ37Cl) for both pore and groundwater. During this study, the samples were collected from three boreholes located in the center of the studied zone, one of them (EST433) going down to 2000 m depth. The main solute transport process is shown to be vertical diffusion from the massive Keuper halite level to the rest of the sedimentary pile. This global diffusive system can be occasionally disturbed by horizontal circulation of groundwater occurring in the Oxfordian and Dogger limestone formations. Therefore, these circulations cut the global diffusive system in a succession of independent diffusive systems. In this study the data set was implemented in a simplified 2D solute transport model and scenarii reproducing known history in term of paleo circulations inside the system, were applied and allowed to obtained a good fit of the data. Model results showed that paleo circulations, occurring between −145 Ma and −110 Ma, still have an impact on current distribution of chloride in the system, especially for δ37Cl. The model highlights the need of the presence of a circulation spatially limited at the base of the Liassic formation to fit the data. The best fit obtained indicated current residence time of 500 ka in the Dogger and Oxfordian, with respective onset of the circulations at −20 Ma and −5 Ma.

Published
2014
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6. Profiles of chloride and stable isotopes in pore-water obtained from a 2000m-deep borehole through the Mesozoïc sedimentary series in the eastern Paris Basin

Author

Stéphane Gaboreau, Jean-Luc Michelot, Joachim Tremosa, S. Savoye, Jean-Michel Matray, F. Bensenouci, Interactions et dynamique des environnements de surface (IDES), Université Paris-Sud - Paris 11 (UP11)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'Etude et de recherche sur les Transferts et les Installations dans les Sols (IRSN/PRP-DGE/SRTG/LETIS), Institut de Radioprotection et de Sûreté Nucléaire (IRSN), Laboratoire de Mesures et Modélisation de la Migration des Radionucléides (L3MR), Service d'Etudes du Comportement des Radionucléides (SECR), Département de Physico-Chimie (DPC), CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire) (CEA-DES (ex-DEN)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire) (CEA-DES (ex-DEN)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Département de Physico-Chimie (DPC), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay, and Laboratoire d'Etude des Transferts dans les Sols et le sous-sol (DEI/SARG/LETS)

Subjects
geography, geography.geographical_feature_category, Global meteoric water line, δ18O, Stable isotope ratio, 0207 environmental engineering, Geochemistry, [SDU.STU]Sciences of the Universe [physics]/Earth Sciences, Aquifer, 02 engineering and technology, 010502 geochemistry & geophysics, 01 natural sciences, Chloride, 6. Clean water, Pore water pressure, Geophysics, Geochemistry and Petrology, medicine, Sedimentary rock, 020701 environmental engineering, Geomorphology, Groundwater, Geology, 0105 earth and related environmental sciences, medicine.drug
Abstract

International audience; Water stable isotopes and chloride profiles in pore-water through more than 800 m of sediments were obtained from a 2000 m-deep borehole (EST 433) drilled by Andra in the eastern Paris Basin. Vapour exchange method and aqueous leaching were used to obtain the stable isotope and chloride concentrations of pore-water from 24 rock samples. Petrophysical measurements included water contents, grain densities and porosities of the studied formations. Pore-water and some groundwater samples collected during the drilling are mainly of meteoric origin: they plot near the Global Meteoric Water Line, distributed between heavy-isotope depleted Oxfordian groundwater and enriched Triassic groundwater, in good agreement with previous data. The δ2H and δ18O values describe curved profiles in the Callovo-Oxfordian formation, and show an increase with depth below this formation (Dogger and Liassic). Similar trends were observed for the chloride concentrations, except in the Liassic formation where they are more or less constant. The low chloride concentrations in the basal Jurassic layers indicate that the source of salinity to the Dogger aquifer is likely the middle Liassic formation and not the Triassic salt as previously suggested. A preliminary modelling exercise showed that currently available diffusion parameters (diffusion coefficients and accessible porosities) might be used to properly simulate these exchanges for deuterium. This is not the case for chloride, perhaps because the used values for anion accessible porosity were not relevant and/or the applied modelling conditions were unsuitable.

Published
2013
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