HAL (Le Centre pour la Communication Scientifique Directe), 1999
On the edge of the Paris Basin, hardened red sandstone or hardpan developed on Tertiary deposits ... more On the edge of the Paris Basin, hardened red sandstone or hardpan developed on Tertiary deposits blanketing the Massif Central basement. The red sandstone surrounds the basement palaeohills and marks out a buried palaeolandscape. Well-structured palaeosols with biological ...
We tested the potential for sand calcites to serve as a novel paleoclimate archive by investigati... more We tested the potential for sand calcites to serve as a novel paleoclimate archive by investigating their age and formation conditions. Fontainebleau sand calcites are Pleistocene in age (based on 14C and U-Th dating) and were primarily formed during glacial periods. δ13C values increase with the depth at which these sand calcites formed, consistent with open and closed CO2 systems. Interpretation of the δ18O-T relationship in sand calcites points primarily to their formation at a low temperature, around 2°C in shallow ground water and at about 9°C in deeper ground-water settings. Their occurrence, characteristics, and compositions suggest crystallization from paleo-ground waters in permafrost environments. Crystallization of sand calcites was triggered by degassing of cold carbonate-containing surface waters as they infiltrated warmer subsurface ground-water environments. We consider sand calcites to be important indicators of interactions between meteoric water and ground water in Pleistocene periglacial landscapes. Their disposition may point to specific features of periglacial landscapes, and their ages could permit an assessment of landscape incision rates. Large crystals and zoned spheroliths may, in fact, encapsulate continuous high-resolution records of continental glacial and periglacial paleoenvironments.
HAL (Le Centre pour la Communication Scientifique Directe), Oct 18, 2009
International audienceUranium In Situ Recovery (ISR) today represents more than 25% of the uraniu... more International audienceUranium In Situ Recovery (ISR) today represents more than 25% of the uranium world production. ISR consists of ore mining by in situ chemical leaching with acid or alkaline solutions. The leaching solution is injected in the ore body through a number of wells and the uranium-enriched leachate is pumped in one or more distant wells. As ISR takes place underground, controls are limited to the analysis of the pumped solution, eventually leading to adjustments of the leaching solution. Therefore ISR mines management is still rather empirical. A numerical modelling has been considered to come to a more efficient management of the process. The modelling will also bring up to predict and minimize environmental impacts, as well as to design aquifer rehabilitation after the completion of mining activities. Three types of phenomena have to be considered for uranium leaching by ISR: (1) geochemical reactions occurring during the process; (2) kinetics of these reactions and (3) hydrodynamic transport with respect of the reaction kinetics. Leaching tests have been conducted on ore samples from Tortkuduk (Chu-Saryssu - Kazakhstan) uranium mine where ISR is conducted by sulphuric acid leaching. Two types of leaching experiments were conducted: batch reactors and extraction in flow through columns. For each type of experiment, two acidity concentrations were tested, as well as the addition of an oxidizing agent for the column experiments. Mineralogy of the ore and the host sediments has been conducted by XRD. A geochemical model (CHESS) was used to simulate the batch experiments in order to model the leaching solution and to calibrate the kinetic reaction laws. Kinetic reaction laws were considered for the following minerals: pitchblende, schoepite, carbonates, feldspath-K, albite, muscovite, pyrite, hematite, gypsum and kaolinite. Rate constants were taken from the literature and the reactive surfaces were adjusted to fit the experimental data. Then, the geochemical kinetic model was validated, by modelling the column experiments with a coupled hydrodynamic and geochemical model (HYTEC). It resulted in a 1D hydrogeochemical transport model of the ISR process at the laboratory-scale. Further work will be to build a 2D and a 3D reactive transport model of the ISR at field-scale based on the 1D laboratory model
HAL (Le Centre pour la Communication Scientifique Directe), May 25, 2005
... 2 m 10 m Fontainebleau Sand sandstone pan water level Page 2. ... A total of 108 ecological s... more ... 2 m 10 m Fontainebleau Sand sandstone pan water level Page 2. ... A total of 108 ecological stations have been individualized. The Sphagnum commu-nities zoning depends on the ponds morphology and is directly "plated" on the hydrology and hydrochemistry of the ponds. ...
HAL (Le Centre pour la Communication Scientifique Directe), 2005
Regional geodynamical evolution is mainly constrained by the sedimentary record in the basins. Us... more Regional geodynamical evolution is mainly constrained by the sedimentary record in the basins. Usually, little is known about geodynamics of the peripheral areas and even less on the evolution of the basement areas. Continental unconformities are essential to estimate erosion rates of basement and to model the crustal dynamics that control subsidence of surrounding sedimentary basins but also uplift and erosion on their edges. Dating such unconformities has always been the stumbling block while it is a prerequisite to constrain geodynamical models. Paleomagnetism has been proven as a suitable tool to date ferrugineous paleoweathering features. The method has been applied to paleoweathering occurrences resting on the Massif Central crystalline basement as well as to paleoweathering features affecting the crystalline basement itself. The remanence measurements were obtained at the Paleomagnetic Laboratory of the Institut Physique du Globe de Paris and data analyses were carried out using PaleoMac 5 software (Cogné, 2003). Relative dating of the paleoweathering profiles have been acquired by comparing the recorded paleomagnetic poles from the analysed samples to the apparent polar wandering path of the Eurasian plate (Edel et Duringer, 1997 ; Besse and Courtillot, 2003). Thick red kaolinitic formations rest locally on the Massif Central basement. They are generally bounded by the Tertiary grabens and buried by the Oligocene formations. Thus these azoic red formations have classically been ascribed to the "Siderolithic" formations of Eocene-Oligocene age. They show many pedogenic features (termites burrows, illuviation and hydromorphic features and nodules) and strong relationships with paleolandscape organisation (leaned against fault scarps, infilling paleovalleys, etc.). Macro and micromorphological arrangements show that these formations are in situ paleosols. Paleomagnetic ages range from 160 Ma (Late Jurassic) in the centre of the Massif Central to 140 Ma (Early Cretaceous) in the northern parts of the massif (Ricordel et al., 2005; Ricordel, 2007;). These new ages, fairly older than the expected ones, bring considerable changes in the palaeogeographic evolution of the Massif Central during Mesozoic and Cenozoic. Basement rocks (granites, gneiss, rhyolites and even Permo-Carboniferous sediments) show often pinkish facies throughout the Massif Central. It has been shown that these pink facies are albitised (mainly pseudomorphic replacement of the primary plagioclases into albite and alteration of the biotite into chlorite) (Schmitt, 1992; Parcerisa et al., 2009). These albitised facies are arranged in a clear succession against (?) the Triassic unconformity that gives significant constraints about their development in relation with the Triassic palaeosurface. Secondary albite and chlorite contain minute hematite inclusions, which have been dated, using paleomagnetism, to be Triassic in age (245 Ma) (Ricordel et al., 2007). Given that the alterations are of the same age as the unconformity, it then follows that the albitised facies be related to the Triassic palaeosurface and be used to track back the Triassic palaeosurface through wide crystalline areas, even far away from the Mesozoic cover. Palaeomagnetic analyses allowed dating a large range of paleoweathering features for which no objective datings were previously available. Spatial and temporal distributions of the paleoweathering features and related unconformities provide key arguments to unravel the geodynamic evolution of the Massif Central. Triassic, Late Jurassic and Tertiary unconformities are superimposed on large areas of the Massif Centrall. This implies very little erosion of the crystalline basement since Triassic time, as shown by the widespread preservation of the Triassic albitized facies. Since the red kaolinitic paleosols of Late Jurassic/Early Cretaceous age rest directly on the basement rocks, large areas of the Massif Central were uncovered at this period, and more importantly no Jurassic cover was preserved (if such a cover was even deposited?) on the massif. Consequently, the Massif Central probably never did support an important (more than 500 m) sedimentary cover during the Mesozoic. These paleosurface ages provide important constraints to crustal dynamics modeling. Identification and dating of the successive continental unconformities are evidence for long lasting continental evolution and landscape stability of large areas of the Massif Central during the Mesozoic. The alternative hypothesis was that the Massif Central was subsidizing during Mesozoic time and covered with a 2,000 m thick sedimentary series, which was fairly quickly eroded during early Tertiary (Barbarand et al., 2001). In the future, making substantial progress in paleoweathering profiles dating, especially in the scope of improving time resolution, will allow attempting efficient correlation between the continental records and the diverse ...
HAL (Le Centre pour la Communication Scientifique Directe), Oct 6, 2017
Thiry M., Liron M.N., Dubreucq P., Polton J.-C., 2017, Curiosites geologiques du massif de Fontai... more Thiry M., Liron M.N., Dubreucq P., Polton J.-C., 2017, Curiosites geologiques du massif de Fontainebleau, Guide geologique, BRGM Editions., 115 p.
On the edge of the Paris Basin, hardened red sandstone or hardpan developed on Tertiary deposits ... more On the edge of the Paris Basin, hardened red sandstone or hardpan developed on Tertiary deposits blanketing the Massif Central basement. The red sandstone surrounds the basement palaeohills and marks out a buried palaeolandscape. Well-structured palaeosols with biological ...
HAL (Le Centre pour la Communication Scientifique Directe), 1999
On the edge of the Paris Basin, hardened red sandstone or hardpan developed on Tertiary deposits ... more On the edge of the Paris Basin, hardened red sandstone or hardpan developed on Tertiary deposits blanketing the Massif Central basement. The red sandstone surrounds the basement palaeohills and marks out a buried palaeolandscape. Well-structured palaeosols with biological ...
We tested the potential for sand calcites to serve as a novel paleoclimate archive by investigati... more We tested the potential for sand calcites to serve as a novel paleoclimate archive by investigating their age and formation conditions. Fontainebleau sand calcites are Pleistocene in age (based on 14C and U-Th dating) and were primarily formed during glacial periods. δ13C values increase with the depth at which these sand calcites formed, consistent with open and closed CO2 systems. Interpretation of the δ18O-T relationship in sand calcites points primarily to their formation at a low temperature, around 2°C in shallow ground water and at about 9°C in deeper ground-water settings. Their occurrence, characteristics, and compositions suggest crystallization from paleo-ground waters in permafrost environments. Crystallization of sand calcites was triggered by degassing of cold carbonate-containing surface waters as they infiltrated warmer subsurface ground-water environments. We consider sand calcites to be important indicators of interactions between meteoric water and ground water in Pleistocene periglacial landscapes. Their disposition may point to specific features of periglacial landscapes, and their ages could permit an assessment of landscape incision rates. Large crystals and zoned spheroliths may, in fact, encapsulate continuous high-resolution records of continental glacial and periglacial paleoenvironments.
HAL (Le Centre pour la Communication Scientifique Directe), Oct 18, 2009
International audienceUranium In Situ Recovery (ISR) today represents more than 25% of the uraniu... more International audienceUranium In Situ Recovery (ISR) today represents more than 25% of the uranium world production. ISR consists of ore mining by in situ chemical leaching with acid or alkaline solutions. The leaching solution is injected in the ore body through a number of wells and the uranium-enriched leachate is pumped in one or more distant wells. As ISR takes place underground, controls are limited to the analysis of the pumped solution, eventually leading to adjustments of the leaching solution. Therefore ISR mines management is still rather empirical. A numerical modelling has been considered to come to a more efficient management of the process. The modelling will also bring up to predict and minimize environmental impacts, as well as to design aquifer rehabilitation after the completion of mining activities. Three types of phenomena have to be considered for uranium leaching by ISR: (1) geochemical reactions occurring during the process; (2) kinetics of these reactions and (3) hydrodynamic transport with respect of the reaction kinetics. Leaching tests have been conducted on ore samples from Tortkuduk (Chu-Saryssu - Kazakhstan) uranium mine where ISR is conducted by sulphuric acid leaching. Two types of leaching experiments were conducted: batch reactors and extraction in flow through columns. For each type of experiment, two acidity concentrations were tested, as well as the addition of an oxidizing agent for the column experiments. Mineralogy of the ore and the host sediments has been conducted by XRD. A geochemical model (CHESS) was used to simulate the batch experiments in order to model the leaching solution and to calibrate the kinetic reaction laws. Kinetic reaction laws were considered for the following minerals: pitchblende, schoepite, carbonates, feldspath-K, albite, muscovite, pyrite, hematite, gypsum and kaolinite. Rate constants were taken from the literature and the reactive surfaces were adjusted to fit the experimental data. Then, the geochemical kinetic model was validated, by modelling the column experiments with a coupled hydrodynamic and geochemical model (HYTEC). It resulted in a 1D hydrogeochemical transport model of the ISR process at the laboratory-scale. Further work will be to build a 2D and a 3D reactive transport model of the ISR at field-scale based on the 1D laboratory model
HAL (Le Centre pour la Communication Scientifique Directe), May 25, 2005
... 2 m 10 m Fontainebleau Sand sandstone pan water level Page 2. ... A total of 108 ecological s... more ... 2 m 10 m Fontainebleau Sand sandstone pan water level Page 2. ... A total of 108 ecological stations have been individualized. The Sphagnum commu-nities zoning depends on the ponds morphology and is directly "plated" on the hydrology and hydrochemistry of the ponds. ...
HAL (Le Centre pour la Communication Scientifique Directe), 2005
Regional geodynamical evolution is mainly constrained by the sedimentary record in the basins. Us... more Regional geodynamical evolution is mainly constrained by the sedimentary record in the basins. Usually, little is known about geodynamics of the peripheral areas and even less on the evolution of the basement areas. Continental unconformities are essential to estimate erosion rates of basement and to model the crustal dynamics that control subsidence of surrounding sedimentary basins but also uplift and erosion on their edges. Dating such unconformities has always been the stumbling block while it is a prerequisite to constrain geodynamical models. Paleomagnetism has been proven as a suitable tool to date ferrugineous paleoweathering features. The method has been applied to paleoweathering occurrences resting on the Massif Central crystalline basement as well as to paleoweathering features affecting the crystalline basement itself. The remanence measurements were obtained at the Paleomagnetic Laboratory of the Institut Physique du Globe de Paris and data analyses were carried out using PaleoMac 5 software (Cogné, 2003). Relative dating of the paleoweathering profiles have been acquired by comparing the recorded paleomagnetic poles from the analysed samples to the apparent polar wandering path of the Eurasian plate (Edel et Duringer, 1997 ; Besse and Courtillot, 2003). Thick red kaolinitic formations rest locally on the Massif Central basement. They are generally bounded by the Tertiary grabens and buried by the Oligocene formations. Thus these azoic red formations have classically been ascribed to the "Siderolithic" formations of Eocene-Oligocene age. They show many pedogenic features (termites burrows, illuviation and hydromorphic features and nodules) and strong relationships with paleolandscape organisation (leaned against fault scarps, infilling paleovalleys, etc.). Macro and micromorphological arrangements show that these formations are in situ paleosols. Paleomagnetic ages range from 160 Ma (Late Jurassic) in the centre of the Massif Central to 140 Ma (Early Cretaceous) in the northern parts of the massif (Ricordel et al., 2005; Ricordel, 2007;). These new ages, fairly older than the expected ones, bring considerable changes in the palaeogeographic evolution of the Massif Central during Mesozoic and Cenozoic. Basement rocks (granites, gneiss, rhyolites and even Permo-Carboniferous sediments) show often pinkish facies throughout the Massif Central. It has been shown that these pink facies are albitised (mainly pseudomorphic replacement of the primary plagioclases into albite and alteration of the biotite into chlorite) (Schmitt, 1992; Parcerisa et al., 2009). These albitised facies are arranged in a clear succession against (?) the Triassic unconformity that gives significant constraints about their development in relation with the Triassic palaeosurface. Secondary albite and chlorite contain minute hematite inclusions, which have been dated, using paleomagnetism, to be Triassic in age (245 Ma) (Ricordel et al., 2007). Given that the alterations are of the same age as the unconformity, it then follows that the albitised facies be related to the Triassic palaeosurface and be used to track back the Triassic palaeosurface through wide crystalline areas, even far away from the Mesozoic cover. Palaeomagnetic analyses allowed dating a large range of paleoweathering features for which no objective datings were previously available. Spatial and temporal distributions of the paleoweathering features and related unconformities provide key arguments to unravel the geodynamic evolution of the Massif Central. Triassic, Late Jurassic and Tertiary unconformities are superimposed on large areas of the Massif Centrall. This implies very little erosion of the crystalline basement since Triassic time, as shown by the widespread preservation of the Triassic albitized facies. Since the red kaolinitic paleosols of Late Jurassic/Early Cretaceous age rest directly on the basement rocks, large areas of the Massif Central were uncovered at this period, and more importantly no Jurassic cover was preserved (if such a cover was even deposited?) on the massif. Consequently, the Massif Central probably never did support an important (more than 500 m) sedimentary cover during the Mesozoic. These paleosurface ages provide important constraints to crustal dynamics modeling. Identification and dating of the successive continental unconformities are evidence for long lasting continental evolution and landscape stability of large areas of the Massif Central during the Mesozoic. The alternative hypothesis was that the Massif Central was subsidizing during Mesozoic time and covered with a 2,000 m thick sedimentary series, which was fairly quickly eroded during early Tertiary (Barbarand et al., 2001). In the future, making substantial progress in paleoweathering profiles dating, especially in the scope of improving time resolution, will allow attempting efficient correlation between the continental records and the diverse ...
HAL (Le Centre pour la Communication Scientifique Directe), Oct 6, 2017
Thiry M., Liron M.N., Dubreucq P., Polton J.-C., 2017, Curiosites geologiques du massif de Fontai... more Thiry M., Liron M.N., Dubreucq P., Polton J.-C., 2017, Curiosites geologiques du massif de Fontainebleau, Guide geologique, BRGM Editions., 115 p.
On the edge of the Paris Basin, hardened red sandstone or hardpan developed on Tertiary deposits ... more On the edge of the Paris Basin, hardened red sandstone or hardpan developed on Tertiary deposits blanketing the Massif Central basement. The red sandstone surrounds the basement palaeohills and marks out a buried palaeolandscape. Well-structured palaeosols with biological ...
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