Search

Peer Reviewed Objectius de Desenvolupament Sostenible::12 - Producció i Consum Responsables Objectius de Desenvolupament Sostenible::12 - Producció i Consum Responsables::12.2 - Per a 2030, assolir la gestió sostenible i l’ús eficient dels recursos naturals

Mapping the subsurface temperatures can efficiently lead to identifying the geothermal distribution heat flow and potential hot spots at different depths. In this paper, an advanced adaptive multitask deep learning procedure for 3D spatial mapping of the subsurface temperature was proposed. As a result, predictive 3D spatial subsurface temperatures at different depths were successfully generated using geolocation of 494 exploratory boreholes data in Catalonia (Spain). To increase the accuracy of the achieved results, hybridization with a new modified firefly algorithm was carried out. Subsequently, uncertainty analysis using a novel automated ensemble deep learning approach for the predicted temperatures and generated spatial 3D maps were executed. Comparing the accuracy performances in terms of correct classification rate (CCR) and the area under the precision–recall curves for validation and whole datasets with at least 4.93% and 2.76% improvement indicated for superiority of the hybridized model. According to the results, the efficiency of the proposed hybrid multitask deep learning in 3D geothermal characterization to enhance the understanding and predictability of subsurface spatial distribution of temperatures is inferred. This implies that the applicability and cost effectiveness of the adaptive procedure in producing 3D high resolution depth dependent temperatures can lead to locate prospective geothermally hotspot active regions.

Subsidence is an important environmental and safety issue in the mining sector, yet there remain voids in knowledge in terms of management and prediction. This study aims to improve knowledge on the impact of mining operations on the surface, reducing their effect on the environment, increasing the safety of mining operations, monitoring stress behavior and predicting rock mass. Therefore, an analysis was carried out to process and analyze the measured subsidence data and, subsequently, create a numerical model to predict the surface subsidence of a case study mine. The model was developed based on a finite element method (FEM). It was achieved by considering the geological characteristics of the area, the design features of the mine, the surface subsidence measured over twelve years and the time-dependent behavior of the geological layers. The correlation obtained between the measured subsidence and the modelling results was very satisfactory, with a 90% confidence level, over the years analyzed. Hence, the efficiency of the system was confirmed, enabling the evaluation and the prediction of potential surface effects, and therefore improving the safety and environmental levels of the mining area.

This is a post-peer-review, pre-copyedit version of an article published in International Journal of Earth Sciences. The final authenticated version is available online at: http://dx.doi.org/10.1007/s00531-019-01764-0. Extensive areas of the Variscan granitic basement in NE Spain display profiles of red-stained albitized facies characterized by albitization of Ca-plagioclase, chloritization of biotite and microclinization of orthoclase, along with the alteration of igneous quartz to secondary CL-dark quartz. These profiles have a geopetal structure beneath the Triassic unconformity, with a very intense and pervasive alteration in the upper part that progressively decreases with depth to 150–200 m where the alteration is restricted to the walls of fractures. The red albitized facies contains secondary maghemite and hematite that indicate oxidizing conditions. Dating of microclinized orthoclase and secondary monazite that have formed in the red-stained albitized facies yielded K–Ar and U–Th–Pbtotal ages of 240 and 250 Ma, respectively, suggesting that the alteration developed during the Permian–Triassic period. The geopetal disposition of the red albitized profile with respect to the Triassic unconformity, its large regional extent, and the fracture-controlled alteration in the lower part of the profile indicate groundwater interaction. The d18O values of albitized plagioclase (+¿11‰), microclinized orthoclase (+¿13‰), and secondary CL-dark quartz (+¿12‰) suggest that the alteration temperature was about 55 °C. This “low” temperature suggests that the alteration occurred during interaction of the granitic rocks with Na-rich fluids below a surficial weathering mantle on the Permian–Triassic palaeosurface. The latter is possibly related to Triassic evaporitic environments in long-lasting, stable landscapes in which Na-rich solutions infiltrated deep regional groundwaters.

The Port del Comte Massif (SE, Pyrenees) contains one of the most important vulnerable and strategic karst aquifers for supplying freshwater to the city of Barcelona (Spain). It is a fragile system, whose possible environmental impact is highly conditioned by land use. To improve the hydrogeological knowledge of the system, between September 2013 and October 2015, a detailed fieldwork was carried out for the revision of the geological model, the inventory of water points, and the in situ physico-chemical characterization on major elements and isotopes of up to a total of 43 springs, as well as precipitation water. This paper focuses on the characterization of the geochemical processes that allow explanation of the observed chemical variability of groundwater drained by the pristine aquifer system to determine the origin of salinity. The results show that the main process is the dissolution of calcite and dolomite, followed by gypsum and halite, and a minor cation exchange-like process. Sulfur and oxygen isotopes from dissolved sulfate in the studied springs point out a geogenic origin related to the dissolution of gypsum from Triassic and Tertiary materials, and that the contribution from anthropogenic sources, like fertilizers, is lower. Nitrate in groundwater is not an important issue, with a few localized cases related with agricultural activities. The multidisciplinary approach has allowed the development of a consistent hydrogeological conceptual model of the functioning of the aquifer system, which can be replicated in other places to understand the geogenic character of the hydrogeochemistry.

The hydrogeological processes driving the hydrochemical composition of groundwater in the alpine pristine aquifer system of the Port del Comte Massif (PCM) are characterized through the multivariate statistical techniques Principal Component Analysis (PCA) and Gaussian Mixture Models (GMM) in the framework of Compositional Data (CoDa) analysis. Also, the groundwater Natural Background Levels (NBLs) for NO3 and SO4 and Cl are evaluated, which are specially important for indicating the occurrence of groundwater contamination derived from the anthropic activities conducted in the PCM. The different hydrogeochemical facies found in the aquifer system of the PCM comprises low mineralized Ca-HCO3 water for the main Eocene karst aquifer, and Ca-SO4 and highly mineralized Na Cl water types in the minor aquifers discharging from the PCM. The NBL values of SO4, Cl and NO3 obtained for the main karst aquifer are 14.33, 4.06 and 6.55 mg/L, respectively. These values are 35, 3 and 1.2 times lower than the respective official NBLs values that were determined by the water administration to be compared with in the case of conducting a pollution assessment characterization in the main karst aquifer. Official overestimation of NBLs can put important groundwater resources in the PCM at risk.

Near-surface diagenesis has been studied in the Langhian siliciclastic rocks of the Montju&iuml, c Hill (Barcelona Plain) by means of petrographical (optical and cathodoluminescence) and geochemical (electron microprobe, &delta, 18O, &delta, 13C, &delta, 34S and 87Sr/86Sr) analyses. In the hill, these rocks are affected by strong silicification, but the same unit remains non-silicified at depth. The results reveal that fracturing took place after lithification and during uplift. Fracture cementation is clearly controlled by the previous diagenesis of the host rock. In non-silicified areas, cementation is dominated by calcite, which precipitated from meteoric waters. In silicified areas, fractures show multiepisodic cementation produced firstly by barite and secondly by silica, following the sequence opal, lussatite, chalcedony, and quartz. Barite precipitated only in fractures from the mixing of upflowing seawater and percolating meteoric fluids. The presence of silica stalactites, illuviation, and geopetal structures, and &delta, 18O values indicate that silica precipitation occurred in the vadose regime from low-temperature percolating meteoric fluids, probably during a glacial period. Moreover, the presence of alunite suggests that silica cement formed under acidic conditions. Karst features (vugs and caverns), formed by arenisation, reveal that silica was derived from the dissolution of surrounding silicified host rocks.

Instrumental mass fractionation (IMF) of isotopic SIMS analyses (CAMECA 1280HR, CRPG Nancy) was predicted by response surface methodology (RSM) for the 18O/16O determination of plagioclase, K-feldspar, and quartz. The three predictive response surface models combined instrumental and compositional inputs. The instrumental parameters were: (i) X and Y stage positions, (ii) the values of LT1DefX and LT1DefY electrostatic deflectors, (iii) chamber pressure, and (iv) primary-ion beam intensity. The compositional inputs included: (i) anorthite content (An%) for the plagioclase model, and (ii) orthoclase (Or%) and barium (BaO%) contents for the K-feldspar model. The three models exhibited high predictive power. The coefficients R2 and prediction-R2 were, respectively, 90.47% and 86.74% for plagioclase, 87.56% and 83.17% for K-feldspar, and 94.29% and 91.59% for quartz. The results show that RSM can be confidently applied to IMF prediction in stable isotope SIMS analyses by the use of instrumental and compositional variables.

An improved approach is presented to model the product particle size distribution resulting from grinding in high-pressure roll crusher with the aim to be used in standard high-pressure grinding rolls (HPGR). This approach uses different breakage distribution function parameter values for a single particle compression condition and a bed compression condition. Two materials were used for the experiments, altered Ta-bearing granite and a calc-silicate tungsten ore. A set of experiments was performed with constant operative conditions, while varying a selected condition to study the influence of the equipment set-up on the model. The material was comminuted using a previously determined specific pressing force, varying the feed particle size, roll speed and the static gap. A fourth group of experiments were performed varying the specific pressing force. Experimental results show the high performance of the comminution in a high-pressure environment. The static gap was the key in order to control the product particle size. A mathematical approach to predict the product particle size distribution is presented and it showed a good fit when compared to experimental data. This is the case when a narrow particle size fraction feed is used, but the fit became remarkably good with a multi-size feed distribution. However, when varying the specific pressing force in the case of the calc-silicate material, the results were not completely accurate. The hypothesis of simultaneous single particle compression and bed compression for different size ranges and with different parameters of the distribution function was probed and reinforced by various simulations that exchanged bed compression parameters over the single particle compression distribution function, and vice versa.

The Penouta Sn-Ta deposit, in the northwest of Spain, is a greisenized granitic cupola where Ta minerals occur mainly as disseminations in a leucogranite body intruded in Precambrian–Lower Cambrian gneisses and mica-schists. This leucogranite is a medium- to fine-grained inequigranular rock consisting mainly of quartz, albite, K-feldspar and muscovite. Accessory minerals are mainly of spessartine, zircon, cassiterite, Nb-Ta oxides, monazite, xenotime, native bismuth and pyrite. The alteration processes were mainly albitization, muscovitization and kaolinitization.This leucogranite is peraluminous and P-poor, with 0.03–0.07 wt.% P2O5, 900–1500 ppm Rb, 30–65 ppm Cs, 120–533 ppm Li, 80–140 ppm Ta, 51–81 ppm Nb and up to 569 ppm of Sn.Mineralogical characterization of Nb-Ta oxide minerals was determined by X-ray diffraction, scanning electron microscopy, electron microprobe analysis and mineral liberation analysis. Mn-rich members of the columbite-group minerals (CGM) are the most common Ta-bearing phases, but microlite, wodginite, tapiolite and Ta-rich cassiterite occur also. CGM crystals are commonly zoned concentrically, with a Nb-rich core surrounded by a Ta-rich rim, with a sharp boundary between them. Convoluted zoning occurs also. Dissolution textures resulting from the corrosion of columbite and tantalite rims, in particular, are common. The Mn/(Mn + Fe) ratio varies between 0.33 and 0.97 and the Ta/(Ta + Nb) ratio between 0.07 and 0.93. Wodginite and microlite formed as late replacements of CGM and occur associated with tantalite and cassiterite. Subhedral to anhedral cassiterite crystals, usually up to 200 μm across, occur in two generations: the earlier one is Nb,Ta-poor whereas in the later generation, the Ta content can reach >9 wt.% of Ta2O5and 1.7 wt.% of Nb. The presence of a fluid phase in the apical zone of the granite, probably related to the separation of a fluid/vapour of the melt, could explain the sponge-like textures, the Ta enrichment associated with these textures, the occurrence of Ta-enriched mineral phases (microlite and wodginite) and their common interstitial character.

The modelling of high pressure grinding rolls is described by the population balance model, a mass balance which includes several functions that are related to the mineral characteristics, material kinetics and operative conditions of the device. The breakage distribution function is one of these functions and refers to the way in which the daughter particles are generated by the process of comminution. The piston-die press is presented as a methodology to determine the breakage distribution function of two different materials, from the mechanical response point of view: altered granite and a cal-silicate material. The aim is to determine the relation between the operative conditions and the mineral characteristics in order to explain and predict the breakage function parameters. The materials were characterised using XRD and single compression strength tests. The altered granite is a brittle material, which generates more fines under single compression conditions compared to bed compression conditions, mainly due to the mineral composition and the response of the material to the breakage action. The cal-silicate material shows a normal trend in its breakage behaviour. As is expected, the mineralogical characterisation is a useful tool to predict the values of the parameters of the breakage distribution function.

A database of tourist mines and caves has been created to investigate the requirements of an integrated monitoring system with the aim of ensuring the safety of visitors and preserving the environment of the activities. It contains the main features of each site, in particular the physical, geological and technical information. The results unfold the main characteristics of these sites and give an insight of the parameters to be monitored: number of visitors, temperature, noise, gas concentrations, ground movements, among other factors. All these features are crucial for the safety of tourists and guides, as well as for the preservation of biodiversity and geodiversity. This information will be used to create a system capable of controlling the entire underground activity, such as the one tested in the two case studies. Resumen Se ha creado una base de datos de cuevas y minas turísticas para investigar los requerimientos necesarios para implementar un sistema integrado de monitorización capaz de mantener las condiciones de seguridad de los visitantes y el ambiente adecuado de la actividad. Dicho sistema controla las principales características físicas, geológicas y de información del sitio. Los resultados detallan las principales condiciones de las cuevas y minas turísticas, mostrando los parámetros importantes a controlar: Número de visitantes, temperatura, ruido, concentraciones de gas y movimientos del terreno, entre otros. Todos estos parámetros son fundamentales para mantener la seguridad de los turistas y guías, así como para preservar la biodiversidad y formaciones geológicas particulares de cada sitio. La información incluida en este estudio se usará para obtener un producto similar al mostrado en los casos de estudio.

Preservation of the architectural integrity of archaeological sites requires detailed information about the properties of the building materials and their decay processes. This study investigates the petrophysical properties of the Eocene nummulitic limestone rock used in the construction of the Roman City of Dougga (Tunisia) and its resistance to various factors of decay. The petrographical study is carried out using standard microscope techniques and the petrophysical behaviour by a combination of techniques focusing on hydric and mechanical properties. The pore network is studied by fluorescence microscopy and mercury intrusion porosimetry. Durability was assessed by ice crystallization and SO2 attack ageing tests. The results allowed the identification of four main building lithotypes and their exact stratigraphic point of mining in the ancient quarries. The petrographic variations between lithotypes correlate well with their physical properties. In addition, the four lithotypes show high resistance to ageing tests, confirming the excellent characteristics of the studied nummulitic limestones as a building rock.

International audience

Kaolin is a widespread authigenic clay mineral in the Permo-Triassic sandstones from the marginal areas of the SE Iberian Basin. However, relatively more extensive illitization of kaolin occurs in the SW basin margin compared with the slight occurrence in the NE margin. SEM analysis of sandstones reveals that illite replaced small kaolinite crystals while blocky dickite remained unaltered. Kaolin illitization is suggested to take place in relation to the maximum burial depth reached during Late Cretaceous post-rift stage. Vitrinite reflectance data denotes a maximum burial temperature of 118 °C and 144 °C in the NE basin margin and in the SW basin margin, respectively. Thus, the extent of illitization in the SW margin is attributed to the higher T peak reached by the Permo-Triassic succession. Regarding the lack of K-feldspars observed in the sandstones and interbedded mudrocks, the source of K + is mainly related to the alteration of detrital mica.

Fe and Mn occur in calcite cements depending on the oxidizing–reducing conditions of cementing waters, which may change according to depositional and diagenetic environments. In red beds, Mn and Fe are available from the ferruginous matrix. Thus, it is possible to know the oxidizing–reducing conditions of fluids that precipitated calcite as a function of Mn and Fe content in calcite cement. A detailed petrological (with special attention to cathodoluminescence) and geochemical analysis of these cements is a useful tool to constrain the diagenetic evolution of red beds and the history of the basin where they deposited.

The Valles-Penedes half-graben developed during a Neogene extensive period as part of the Catalan Coastal Ranges in the northwestern edge of the Valencia Trough. The Neogene deposits of the Valles-Penedes half-graben consist of, from base to top, three lithostratigraphic complexes: i) a lower continental complex of Aquitanian?–early Langhian age; ii) a continental to marine complex with reefal carbonate platforms of Langhian age and; iii) an upper continental complex of middle Serravallian–Tortonian age. This study focuses on the calcite cements of the lower continental complex consisting of red beds (mudstones, sandstones and conglomerates) and lacustrine limestones deposited in alluvial fan environments. The studied materials are cemented by calcite precipitated from meteoric waters that circulated through the sediments during the early diagenesis at shallow burial depths. The calcite cement was studied by means of petrographic, cathodoluminescence, microprobe and δ18O and δ13C isotopic analysis. The petrographic and geochemical results show that these cements vary according to the sedimentary environment: (i) sandstones deposited in proximal alluvial fan environments cemented by calcite with low contents of Mg, Fe, Mn, Sr and Na, δ13C values of − 7,4‰PDB and δ18O values from − 6.5 to − 6.2‰PDB; (ii) sandstones sedimented in medium to distal alluvial fan environments cemented by Mn-rich and Mg, Fe, Sr and Na-poor calcite with δ13C values from − 7.9 to − 6.9‰PDB and δ18O values from − 10.5 to − 8.6‰PDB; and (iii) lacustrine limestones of distal alluvial fan environments cemented by Fe-rich calcite with variable contents of Mn and low contents of Mg, Sr and Na. The distribution of these calcite cements allows us to propose a model of fluid circulation and early calcite cementation within an alluvial fan indicating spatial and temporal variations in chemical composition of meteoric water during migration from proximal to distal alluvial fan environments. Residence time of waters, Eh–pH conditions, and the degree of sediment–water interactions, influenced by the mineral composition of the host sediments, are the most important parameters controlling variations in calcite cement composition.

The Montjuic hill is part of the Neogene horst and graben system of the Catalan Coastal Ranges at the northwestern edge of the Valencia Trough. It is located to the SE of Barcelona City and consists of a 200 m thick strongly silicified detrital succession (mainly conglomerate and sandstone units alternating with lutitic units) of Miocene age. The geological constraints of this area (young age, shallow depositional environment and no evidence of burial processes) ensure that authigenic minerals formed during silicification have not been modified by further diagenetic processes and allow to constrain the age and nature of the silicification. Silicification has strongly increased the hardness of the original sediment. Textural effects of mechanical compaction are rare, testifying that burial processes had no effect on diagenesis and pointing towards an early and/or shallow cementation. Two main diagenetic facies with characteristic associations of authigenic minerals can be identified, namely: (1) non silicified facies are present in ochre-coloured, fine-grained sandstones with high clay and carbonate content. In these facies, cementation is scarce and generally forms minor feldspar overgrowths around detrital K-feldspar as well as layers or nodules of calcite spar cement mainly filling interparticle porosity; (2) silicified facies are red, purple-coloured and characterized by the presence of opal, microquartz and quartz overgrowths as well as other minor authigenic minerals such as Ti and Fe oxides and alunite. Particularly, alunite and opal appear often at the boundary of the silicified/non silicified facies, coming with the development of bleached facies and are replaced by silica. In this paper, a detailed sampling of the silicification fronts has been made, in order to establish the main silicification pathways. In the sampled zone the non silicified sandstones are mainly made up of quartz, K-feldspar, muscovite, phyllite fragments and bioclasts and cemented by thin K-feldspar overgrowths and decimetric concretions of intergranular calcite spar with spherical and tabular shapes. Sandstones contain some pyrite pseudomorphs and 20 to 30% of clay minerals, essentially illite-mica. Samples collected perpendicular to the silicification fronts reveal significant textural, compositional and petrographical transformations, namely: (1) The color of the sample varies strongly from ochre in the non silicified facies to white and red in the bleached weakly silicified front and finally to red, purple and grey in the massively silicified facies; (2) The siliciclastic framework of Montjuic sandstones remains stable during the silicification, only detrital feldspars are partially altered into illite, and biotites are completely altered. The detrital carbonate components disappear quickly towards silicified facies; (3) Within the silicification front, either bleached or not, authigenic minerals show quite important variability. Calcite disappears progressively. The first silicification stage is built by incipient quartz overgrowths, then microquartz develops towards the massively silicified facies. Alunite and opal are usually present in samples collected in this silicification boundary; (4) In the massively silicified facies quartz overgrowths and microquartz take up almost all the intergranular volume of sandstones. Clay content is strongly reduced to 5-10% (mainly illite), so the primary clay-carbonate matrix has been replaced and/or transformed to microquartz. Iron oxides appear around feldspar and phyllite fragments. Because of the geological constraints Montjuic sandstones silicification was a surface/sub-surface phenomenon. Therefore, silicification occurred at relatively low temperature and pressure conditions. Partly, silica may have an internal origin (supplied by clay and feldspar hydrolysis). Supposing that diagenetic transformations inside sandstones are made at steady state conditions it is necessary to consider a strong external supply of silica. The presence of alunite points to acidic fluids with pH between 1,5 and 4. In these conditions, quartz solubility is unaffected, but the aluminium becomes mobile, thus aluminosilicate minerals (like feldspars) are hydrolyzed and clay minerals are transformed into opal CT. A feasible process which may have contributed to the acidification is the oxidation of the pyrite and organic matter present in the original sediments, testified by numerous pyrite ghosts in the non silicified and silicified sandstones. Silicification occurred in an oxidizing environment where sulfides were oxidized and iron oxides precipitated, explaining the colour of these materials. At the basin scale, different models can be considered: (a) a topographic driven flow that moved groundwater from the horst towards the basin; (b) a thermoconvective driven flow that moved phreatic and formation waters along the main faults of the graben or (c) a compaction driven flow that also moved formation waters. Only shallow systems driven by topographic flows can explain the oxidizing nature of the silicification solutions of Montjuic. Conclusions. The Montjuic sandstone silicification is remarkable in several aspects. (1) The lack of compaction and the oxidizing nature of the silicification indicate that this diagenesis was induced by subsurface groundwater, in shallow environments. (2) Silicification is pervasive in medium and coarse-grained sandstones and conglomerates. On the contrary, silicification is restricted to fracture zones in fine-grained sandstones.

Olianatrivia riberai n. gen., n. sp. (Mollusca, Caenogastropoda), a singular Ovulidae from the Bartonian (middle Eocene) of Catalonia (Spain). Shells of an Ovulidae species with unusual morphological features have been collected in the axial part of the Oliana anticline, Catalonia: Olianatrivia riberai n. gen., n. sp. (Mollusca, Caenogastropoda) whose shape and ornamentation remind some Triviinae. According to the chronostratigraphy of the South-Pyrenean basin, it belongs to a subrecifal facies, reworked by storm dynamics, of a Late Bartonian age (Middle Eocene). It is proposed to place O. riberai n. gen., n. sp. within the Pediculariinae, a subfamily of Ovulidae (Cypraeoidea), close to Cypropterina ceciliae (De Gregorio, 1880) from the Veronese Early Lutetian.

Widespread albitization has been recorded on Variscan granitoids of the Catalan Coastal Ranges (CCR) and the Eastern Pyrenees. Field observations suggest that albitization display a profile-like shape beneath Triassic, Cretaceous and Paleocene unconformities, decreasing in intensity forward the internal areas of the pristine granitoids. Petrographic, cathodoluminescence, SEM, microprobe and geochemical analyses show that albitization of Ca-plagioclase occurs as a pseudomorphic dissolution-reprecipitation mechanism and is mainly accompanied by biotite chloritization and Feoxides precipitation, giving a characteristic red-pink colour to the Na-metasomatized rock. Palaeomagnetic data suggest a Triassic age for the Fe-oxides and so for albitization. Triassic severe environmental conditions are characterized by high atmospheric and oceanic CO2 levels and global warming, besides acidification and salinisation of marine waters. All these features, possibly coupled with the granitoids long-lasting exposure due to smooth palaeoreliefs, could have played a major role in the development of these unusual shallow albitization profiles during Triassic times.

International audience

International audience

International audience; The Fontainebleau Sand contains tightly cemented sandstone lenses, which form spectacular elongated ridges that are up to 10 km long and 0.5 km wide. Denudation of the sandstone pans leads to a highly contrasted landscape, with sandstone ridges towering over sandy depressions. However, little is known about the erosion processes that have built up this landscape. Periglacial processes, including aeolian ones, appear to have been significant in the development of the massif's physiography. The topography of the massif has played an important role in controlling the aeolian processes. The upwind westerly front face of the massif displays numerous deflation features, such as blowout hollows, high sandstone scarps with numerous overhangs and spectacular talus screen, and a wide uncovered sandstone plateaux. In the eastern downwind district the landforms are more subdued and the sandstone plateaux and their scarps are partly sanded up. Sand dunes have built up directly downwind from the westerly scarps. Further onto the plateaux, loess has been deposited in a relatively regular cover. Finally, in the low areas downwind from the plateaux, there are fine sand dune fields and loess covers. The layouts and arrangements inherited from the aeolian action partly command the present-day relief and the plant biodiversity. There are oak and beech groves on the aeolian calcareous sand deposits, birch and pine trees on the quartzose sand forming the upwind scarps, and wet peaty moors as well as dry moors with heather and birch on the uncovered sandstone plateaux. Thus, the landscape features inherited from the periglacial aeolian action contribute to the striking biodiversity of the Fontainebleau Massif.

International audience

International audience

International audience; The Carboniferous Morvan Massif, in the northern part of the French Massif Central, consists of granite and some rhyolite. A Triassic erosional unconformity has developed on the massif which is covered by Mesozoic sediments of the Paris Basin. The igneous rocks of the Morvan Massif show a strong alteration with pseudomorphic replacement of the primary plagioclases into albite, pseudomorphic replacement of primary biotite into chlorite and minor precipitation of neogenic minerals like albite, chlorite, apatite, haematite, calcite and titanite. The geometry and arrangement of these alterations give significant constraints about their development. Some of the altered facies develop in a pervasive manner; others are restricted to centimetric to metric-wide joints that imply fluid-flow phenomena. Moreover, the alteration facies are arranged in a clear succession with strongly altered facies at the top and weakly altered facies towards the depth, which point to a genetic relationship with the Triassic unconformity. Regional distribution of the alterations, which affect the Carboniferous igneous and volcanic formations beneath the Jurassic sedimentary cover, also leads to associate these alterations with the Triassic unconformity. Dating of the alterations provides even a further constraint, alterations are of Triassic age, that means the same age as the unconformity. Taking into account all these geological constraints, it is proposed that albitisation of the Morvan Massif was developed under low temperature subsurface conditions in relation to the Triassic palaeosurface.

International audience; The Morvan massif, located in the northern part of the French Massif Central, shows widespread unusual deep alteration profiles in the Palaeozoic basement rocks (gneisses, granites and rhyolites). They are characterised by overall albitization, chloritisation and haematisation. Albite and chlorite constitute their characteristic mineral paragenesis. Haematite pigmentation comes with this paragenesis and gives an overall pink coloration to the weathered rocks. A paleomagnetic analysis was conducted after detailed petrographical and mineralogical studies of the alteration that lead to the albitized profiles. Special attention was devoted to the occurrence of haematite, the main paleomagnetism carrier, with the though to date this palaeoweathering event. Petrographical checking after heating treatments showed that deshydroxylation of chlorite also led to the formation of secondary haematite. This haematite formed by recrystallization acquired remanence properties and thus superimposed and hided the original magnetic signal. This problem has prevented the extraction of the original magnetic signal especially in the sections made up of rhyolites. Virtual Geomagnetic Poles (VGPs) obtained from the characteristic directions carried by haematite have been compared to the European Apparent Polar Wander Path (APWP). An Early Triassic magnetic overprint has been recorded in the albitized basement rocks of the Morvan massif. The age obtained for this albitization phenomena, strengthens the hypothesis that albitization developed in relation with palaeoweathering processes linked with the Triassic palaeosurface. Therefore, large scale continental weathering could be the main mechanism for Late Permian/Early Triassic remagnetizations which are widespread throughout the Palaeozoic formations of western Europe. As far as we know, this is the first time that deep palaeoweathering phenomena affecting hard and non-disaggregated weathered rocks of the basement have been directly dated. Palaeomagnetism appears as a precious tool to date alteration events developed in widely and long-lasting emerged areas of the basement. © 2007 Elsevier B.V. All rights reserved.

The Oligocene deposits of Montgat are integrated in a small outcrop made up of Cenozoic and Mesozoic rocks located in the Garraf-Montnegre horst, close to the major Barcelona fault. The Oligocene of Montgat consists of detrital sediments of continental origin mainly deposited in alluvial fan environments; these deposits are folded and affected by thrusts and strike-slip faults. They can be divided in two lithostratigraphic units separated by a minor southwest-directed thrust: (i) the Turó de Montgat Unit composed of litharenites and lithorudites with high contents of quartz, feldspar, plutonic and limestone rock fragments; and (ii) the Pla de la Concòrdia Unit composed of calcilitharenites and calcilithorudites with high contents of dolosparite and dolomicrite rock fragments. The petrological composition of both units indicates that sediments were derived from the erosion of Triassic (Buntsandstein, Muschelkalk and Keuper facies), Jurassic and Lower Cretaceous rocks (Barremian to Aptian in age). Stratigraphic and petrological data suggest that these units correspond to two coalescent alluvial fans with a source area located northwestwards in the adjoining Collserola and Montnegre inner areas. Micromammal fossils (Archaeomys sp.) found in a mudstone layer of the Pla de la Concòrdia Unit assign a Chattian age (Late Oligocene) to the studied materials. Thus, the Montgat deposits are the youngest dated deposits affected by the contractional deformation that led to the development of the Catalan Intraplate Chain. Taking into account that the oldest syn-rift deposits in the Catalan Coastal Ranges are Aquitanian in age, this allows to precise that the change from a compressive to an extensional regime in this area took place during latest Oligocene-earliest Aquitanian times. This age indicates that the onset of crustal extension related to the opening of the western Mediterranean Basin started in southern France during latest Eocene-early Oligocene and propagated southwestward, affecting the Catalan Coastal Ranges and the northeastern part of the Valencia trough during the latest Chattian-earliest Aquitanian times.

The Chattian (Upper Oligocene) deposits of Montgat consist of continental detrital sediments deposited mainly in alluvial fan environments. Stratigraphic and petrographic data allow identification of two lithostratigraphic units: the Turo de Montgat unit and the Pla de la Concordia unit. These units are interpreted as two coalescent alluvial fans deposited synchronously. The catchment areas of these alluvial fans were located between the Collserola and Montnegre highs and consisted of a Mesozoic cover overlying a Paleozoic basement. Intrabasinal limestones interbedded in the two alluvial fan deposits of the Montgat area have been analyzed geochemically, and three groups are distinguishable. The first group is composed of the oncolites of the Turo de Montgat unit, which were formed in ponding zones in the channel or disconnected pools in a fluvial setting where waters remained under closed conditions. The second group is composed of the lacustrine limestones and the oncolites of the Pla de la Concordia unit, which were formed in an open and permanent fluvial setting. The third group is composed of the palustrine limestones and tufa-oncolites of the Pla de la Concordia unit; these were formed in ephemeral fluvial settings concurrent with development of calcrete soils. The geochemistry of the intrabasinal limestones deposited in the Chattian alluvial fans of the Montgat area is mainly controlled by the fluvial regime and the lithology and altitude of the catchment areas and the sedimentary basin.

The Valles-Penedes neogene half-graben (NE of Spain) is filled with a thick succession of terrigenous rocks, the lowermost unit of the basin consists of red-coloured clays, sandstones and conglomerates (red beds) formed in an alluvial fan environment. In the upper part of this unit some vertical joints are filled with blue sand (sand dikes). Sand dikes are interpreted as having been formed in an early stage after sedimentation. Despite the colour difference, the common sediment source of both, red-coloured sediments and blue-coloured sand dikes is evidenced by almost identical results obtained by using different techniques: Petrographic microscope, Cameca electron microprobe, XRD and SEM. Mossbauer spectrometry has proven to be a useful technique providing significant data to explain the colour difference and helping to understand the diagenetical processes involved herein.

International audience

International audience

The Miocene siliciclastic sediments infilling the Vallès-Penedès half-graben are affected by two sets of structures developed during the extensional tectonics that created the basin. The first set, represented by extension fractures infilled with mud and sands, is attributed to seismically induced liquefaction. The second set, represented by normal faults, corresponds to a high-permeability horsetail extensional fracture mesh developed near the surface in the hanging walls of normal faults. The incremental character of the vein-fills indicates episodic changes in the tectonic stress state and fault zone permeability. Two episodes of fluid migration are recorded. The first episode occurred prior to consolidation and lithification when shallow burial conditions allowed oxidizing meteoric waters to flow horizontally through the more porous and permeable sandy layers. Development of clastic dikes allowed local upward flow and dewatering of the sandy beds. Liquefaction and expulsion of fluids were probably driven by seismic shaking. During the first episode of fluid migration there was no cementation of the sandstone or within the fractures, probably because little fluid was mobilized by the predominantly compaction-driven flow regime. The second episode of fluid migration occurred synchronously with normal fault development, during which time the faults acted as fluid conduits. Fluids enriched in manganese, probably leached from local manganese oxyhydroxides soon after sedimentation, moved laterally and produced cementation in the sandstone layers, eventually arriving at the more porous and permeable fault pathways that connected compartments of different porosities and permeabilities. Carbonate probably precipitated in fractures saturated with meteoric water near the ground surface at a transitional redox potential. Once the faults became occluded by calcite cement, shortly after fault development, they became barriers to both vertical and horizontal fluid flow.

International audience

International audience

Large volumes of borate resources exist in Bolivia, with the most important being the Rio Grande deposit, located close to the Salar of Uyuni. Here, borates occur in beds and lenses of variable thickness. A mineralogical and thermal characterization of borates from the Rio Grande was made using XRD, FTIR, SEM and DTA–TG. The deposit is mainly composed of B2O3, CaO and Na2O, with minor contents of MgO and K2O. Some outcrops are constituted by pure ulexite aggregates (NaCaB5O6(OH)6·5H2O) of fibrous morphology; in other cases, gypsum, calcite and halite also are present. The thermal decomposition of ulexite begins at 70 °C and proceeds up to ~550 °C; this decomposition is attributed to dehydration and dehydroxylation processes in three steps: at 115, 150–300 and 300–550 °C. The last mass loss of 1–5 % at 800 °C is due to the removal of Cl2 from the decomposition of halite. DTA shows two endothermic events related to the removal of water; in the first, NaCaB5O6(OH)6·5H2O evolved from NaCaB5O6(OH)6·3H2O, at 108–116 °C; in the second, NaCaB5O6(OH)6 is formed at 180–185 °C and NaCaB5O9 (amorphous) is formed at 300–550 °C. The exothermic peak (658–720 °C) is related to the crystallization of NaCaB5O9. A small endothermic peak appears due to the halite melting. Later, another endothermic event (821–877 °C) appears, which is related to the decomposition of NaCaB5O9 into a crystalline phase of CaB2O4 and amorphous NaB3O5. The XRD pattern evidences that, at 1050 °C, CaB2O4 still remains in the crystalline state.