In the framework of the hydrological survey of the Mont Terri anticline (Mont Terri rock Laboratory in the Folded Jura, Switzerland), a 58 m-deep borehole (BHS-1) was drilled through the Jurassic low permeability shale sequence. Dedicated sampling was carried out to characterize gases within a 13 m-thick unit of organic matter-rich Early Jurassic Rietheim black shales and adjacent units, including the underlying Beggingen aquifer. A cone-in-cone calcite, observed at the bottom of the black shale, as identified as an indicator of oil-window conditions and records a maximal burial temperature of similar to 80-90 degrees C. Two fracture zones within the black shales, marked by calcite infillings, provide evidence for at least two episodes of water paleocirculations: (1) an early circulation between fractures at the top of black shales and the Main Fault, and (2) a later circulation between fracture zones within the black shales and the lower Beggingen aquifer. Gas migration was investigated within the complex geological context of regional uplift, Jura folding and thrusting, and associated water flows. Alkane data reveal a partial carbon isotope reversal of thermogenic gases within the black shales between the two fracture zones, strongly suggesting alkane migration linked to the second water paleocirculation episode.

The Parentis sub-Basin, located southwest of Bordeaux (France), has been known since the 1950s as a prolific oil reservoir. It lies at the eastern end of the Bay of Biscay. Several fields are exploited in the onshore part of the basin, the largest being at Parentis-en-Born, discovered by ESSOREP in 1954 and exploited by VERMILION REP since 2006. The field is an east-west anticlinal structure, formed during various geodynamic episodes in connection with halokinesis of the Triassic and Hettangian series. One of the reservoirs exploited is a limestone/dolomite dating from the Barremian to the Upper Jurassic characterized by a matrix porosity of 14% and a permeability of 100 mD over an average thickness of 200 metres. Numerous studies and acquisitions (3D seismic, 122 boreholes) have been carried out by ESSOREP and VERMILION REP exploration geologists to characterise the limestone/dolomite reservoir, particularly regarding the origin of the dolomitization and porosity. Models of emplacement suggest post-sedimentary dolomitization by reflux and epigenic karstification linked to early tectonic bulges. Our study aims to use modern methods and concepts to gain a better understanding of the major stages in the development of this reservoir in relation to the geodynamic events. It is based on a detailed study of cores and thin sections. A total of 160 samples were taken from 7 boreholes to conduct a diagenetic study (petrography, cathodoluminescence and initial results on strontium isotopes). The macroscopic study of the cores showed the presence of numerous mud losses (no-recovery zones), often correlated with faults (striations observed), which were previously interpreted as epigenic karstification. Numerous veins were observed in the fracture zones, composed of calcite, saddle dolomite and anhydrite. Microscopically, the paragenesis shows primary dolomitization prior to burial (euhedral to subhedral dolomite), followed by phases of circulation of magnesium-rich hydrothermal fluids (saddle dolomite - ‘non-planar’) and sulphates (anhydrite). Initial interpretations suggest that the void zones encountered in the boreholes are linked to the upwelling of deep-seated fluids sourced by Triassic/Lower Jurassic evaporites and dolomites, resulting in hypogenic karstification. These episodes would be linked to the resumption of the anticline during the Pyrenean phase.

Water transfers and processes governing the chemistry of groundwaters and clay pore waters were investigated in the critical zone developed in Te ' gulines Clay in the area of Brienne-Le-chateau, at east of the Aube alluvium plain (France). A pit-digging campaign along two-stepped west-facing hillslopes along the Brevonne valley and the Aube/Brevonne paleo-valley gives evidence of a thin Quaternary clay silty and carbonate-free loams over-lying Te ' gulines Clay, mobile regolith along the slopes and the presence of a carbonate alluvium layer in pits of the Brevonne valley. Groundwaters at the first ridgetop attest of a temporary perched water table, while groundwaters at top of Te ' gulines Clay along the first west-facing steep slope toward the Brevonne River provide evidence of lateral groundwater transfers and runoff of waters toward the valley which is a discharge zone belonging to the present-day Aube alluvium plain. Groundwaters have low concentrations of Total Dissolved Solids (TDS < 600 mg/L) and are calcic-carbonate waters. Their delta 18O and delta D of groundwaters are consistent with local meteoric values. An 18O and D enrichment in groundwaters at the bottom of the second hillslope and in waters from reservoirs indicates evaporation processes. The delta 13CCO2 of dissolved inorganic carbone in ground-waters is essentially due to degradation of organic matter. The composition of the pore waters from Te ' gulines Clay in boreholes are chemically heterogeneous and different from groundwaters. They are Ca-Mg-SO4-rich and show a large range of TDS concentrations (592-6457 mg/L). The highest values are measured in the most intensely weathered clay developed in the first 10-15 m under the first ridge top and the low east-facing slope of the Aube/Brevonne paleo-valley. This latter seems to represent a large intermediate discharge zone between the coarse ridgetops (recharge zones) and the current Aube alluvium plain. The delta 18O and delta D of pore waters are alined along the local meteoric water line, indicating that meteoric waters have diffused through the clay for-mation during post-depositional history and replaced original connate seawater. On contrary the 87Sr/86Sr ratios of pore waters remain almost similar to that of Lower Cretaceous seawater, suggesting a limited diffusion of Sr since the formation deposition. Toward the top of the formation in the Aube/Brevonne paleovalley, major cation and anion concentrations, 18O and D enrichment and a slight increase of the 87Sr/86Sr ratios suggest the diffusion of evaporated waters. The delta 13C, delta 18O, 87Sr/86Sr ratios and 14C activity of concretions at top of Te ' gulines Clay show that they precipitated from evaporated old groundwaters, the oldest one at -34 ky in the TPH2-1 pit at the ridgetop of the second hillslope and a younger age of -8 ky in the TV4-1 pit.

There is evidence that the emission of 14C –free CO2 during volcanic emissions creates a bias for radiocarbon dating of volcanic events (Holdaway et al., 2018), showing that integration of “dead” carbon by vegetation can serve as indicator of geogenic gas emissions. We tested 14C activities and stable carbon isotope ratios of tree rings and herbal vegetation in the proximity of a natural gas seep in the French Subalpine chains where both methane (<90% in the main vent) and CO2 (<11%) are present (Gal et al., 2018). Wood samples were taken from two alder trees, at different distances and directions from the main gas vent. Grass leaves and roots (Carex sp.) were analysed for two spots with contrasting soil methane concentrations and fluxes within the zone of diffuse gas emanation around the main vent (Gal et al., 2019). Grass and wood samples show contrasting isotope compositions depending on their species, age, and position with respect to the gas seep, some with 14C activities significantly lower than present day values. This offers perspectives of using vegetation carbon isotopes as proxies for present and past gas emanations, including man-induced gas leaks, e.g. from gas storage or natural gas exploitation facilities. This research was co-funded by the EU H2020 Programme (grant 764531 – SECURe “Subsurface Evaluation of Carbon Capture and Storage and Unconventional Risk”) Gal F., Kloppmann W., Proust E., Humez P. (2018) Gas concentration and flow rate measurements as part of methane baseline assessment: Case of the Fontaine Ardente gas seep, Isère, France. Applied Geochemistry, 95, 158-171. Gal F., Proust E., Kloppmann W. (2019) Towards a Better Knowledge of Natural Methane Releases in the French Alps: A Field Approach. Geofluids, 2019, 1-16. Holdaway R. N., Duffy B., Kennedy B. (2018) Evidence for magmatic carbon bias in 14C dating of the Taupo and other major eruptions. Nature Communications, 9, 4110.

(MgCl 2 :6H 2 O) are two highly soluble salts that are difficult to study considering their high power of deliquescence upon exposure to moist atmosphere. They may represent extreme evaporation stage of seawater or evolved brines but could also have a pure hydrothermal origin. To unravel their complex origin, an isotopic characterization ( (cid:71) 37 Cl and (cid:71) 18 O/ (cid:3)(cid:71) D (cid:12)(cid:3) is highly desirable. In order to better interpret the data obtained by isotopic analysis on natural samples, an artificial synthesis of the two minerals have been realized. Fractionation is studied during the evaporation of the mother-solution before and during the precipitation of the salts. The method of precipitation consists in the dissolution of one or two hydroxides MgOH 2 and CaOH 2 in a titrated solution of HCl (6M). When the dissolution of the hydroxides neutralizes exactly the acid, the stoichiometry of the minerals is perfectly verified. The solutions are finally evaporated a 0.5%. The precipitation of the salts have been obtained a period of 2 weeks at 25°C without any heating of the brines. The mineralogical nature of the salts have been verified by XRD spectroscopy using a moisture control chamber. The brines and the salts have been analysed for (cid:71) 18 O/ (cid:3)(cid:71) D after an adapted extraction of H 2 O molecules using lyophilisation techniques.

The early Eocene experienced a series of short-lived global warming events, known as hyperthermals, associated with negative carbon isotope excursions (CIE). The Paleocene-Eocene Thermal Maximum (PETM or ETM-1) and Eocene Thermal Maximum 2 (ETM-2) are the two main events of this Epoch, both marked by massive sea-floor carbonate dissolution. Their timing, amplitude and impacts are rather well documented, but CIEs with lower amplitudes also associated with carbonate dissolution are still poorly studied ( e.g. events E1 to H1), especially in the terrestrial realm where hiatus/disconformities and various sedimentary rates in a single succession may complicate the assignation to global isotopic events. Here we present a new high-resolution multi-proxy study on the terrestrial, lagoonal and shallow marine late Paleocene-early Eocene succession from two sites of the Cap d’Ailly area in the Dieppe-Hampshire Basin (Normandy, France). Carbon isotope data (δ 13 C) on bulk organic matter and higher-plant derived n -alkanes, and K-Ar ages on authigenic glauconite were determined to provide a stratigraphic framework. Palynofacies, distribution and hydrogen isotope values (δ 2 H) of higher-plant derived n -alkanes allowed us to unravel paleoenvironmental and paleoclimatic changes. In coastal sediments of the Cap d’Ailly area, δ 13 C values revealed two main negative CIEs, from base to top CIE1 and CIE2, and 3 less pronounced negative excursions older than the NP11 nannofossil biozone. While the CIE1 is clearly linked with the PETM initiation, the CIE2 could either correspond to 1) a second excursion within the PETM interval caused by strong local environmental changes or 2) a global carbon isotopic event that occurred between the PETM and ETM-2. Paleoenvironmental data indicated that both main CIEs were associated with dramatic changes such as eutrophication, algal and/or dinoflagellate blooms along with paleohydrological variations and an increase in seasonality. They revealed that the intervals immediately below these CIEs are also marked by environmental and climatic changes. Thus, this study shows either 1) a PETM marked by at least two distinct intervals of strong environmental and climatic changes or 2) at least one “minor” CIE: E1, E2, F or G, was associated with strong environmental and climatic changes similar to those that occurred during the PETM.

The oxidation profile of a surficial clay aquitard was studied on a 35-meter borecore from the Albian Tégulines Clay near Brienne-le-Château (Paris Basin, France). Mineralogical, geochemical, and petrophysical data showed evidences of gradual oxidation taking place down to a depth of 20 m. Below 20 m, the clay material was nonplastic and nonfractured, and it inherited reduced redox conditions from bacterial sulfate reduction that occurred after sediment deposition. Above 20 m, the clay material was plastic. Up to a depth of 10-11 m, only rare yellowish aggregates of glauconite attested to limited oxidation, and pore water chemistry was unmodified. The 5–11 m depth interval was characterized by intensive pyrite oxidation, calcite dissolution, and formation of sulfate and iron hydroxide minerals. The upper 2-3 m was ochrous and entirely oxidized. These mineralogical changes were mirrored with pore water chemistry modifications such as an increase of alkalinity and sulfate concentration in the upper part of the profile. The presence of siderite at ~11 m evinced the reactivity of Fe(II) in the structure of clay minerals with dioxygen from meteoric waters that infiltrated into the Tégulines Clay through vertical fractures.

"Man-made" or unconventional freshwater, like desalinated seawater or reclaimed effluents, is increasingly introduced into regional water cycles in arid or semi-arid countries. We show that the breakthrough of reverse osmosis-derived freshwater in the largely engineered water cycle of the greater Tel Aviv region (Dan Region) has profoundly changed previous isotope fingerprints. This new component can be traced throughout the system, from the drinking water supply, through sewage, treated effluents, and artificially recharged groundwater at the largest Soil-Aquifer Treatment system in the Middle East (Shafdan) collecting all the Dan region sewage. The arrival of the new water type (desalinated seawater) in 2007 and its predominance since 2010 constitutes an unplanned, large-scale, long-term tracer test and the monitoring of the breakthrough of desalination-specific fingerprints in the aquifer system of Shafdan allowed to get new insights on the water and solute flow and behavior in engineered groundwater systems. Our approach provides an investigation tool for the urban water cycle, allowing estimating the contribution of diverse freshwater sources, and an environmental tracing method for better constraining the long-term behavior and confinement of aquifer systems with managed recharge.

The Roussillon sedimentary Basin (South France) is a complex multi-layered aquifer, close to the Mediterranean Sea facing seasonally increases of water abstraction and salinization issues. We report geochemical and isotopic vertical variability in this aquifer using groundwater sampled with a Westbay System® at two coastal monitoring sites: Barcarès and Canet. The Westbay sampling allows pointing out and explaining the variation of water quality along vertical profiles, both in productive layers and in the less permeable ones where most of the chemical processes are susceptible to take place. The aquifer layers are not equally impacted by salinization, with electrical conductivity ranging from 460 to 43,000μS·cm(-1). The δ(2)H-δ(18)O signatures show mixing between seawater and freshwater components with long water residence time as evidenced by the lack of contribution from modern water using (3)H, (14)C and CFCs/SF6. S(SO4) isotopes also evidence seawater contribution but some signatures can be related to oxidation of pyrite and/or organically bounded S. In the upper layers (87)Sr/(86)Sr ratios are close to that of seawater and then increase with depth, reflecting water-rock interaction with argillaceous formations while punctual low values reflect interaction with carbonate. Boron isotopes highlight secondary processes such as adsorption/desorption onto clays in addition to mixings. At the Barcarès site (120m deep), the high salinity in some layers appear to be related neither to present day seawater intrusion, nor to Salses-Leucate lagoonwater intrusion. Groundwater chemical composition thus highlights binary mixing between fresh groundwater and inherited salty water together with cation exchange processes, water-rock interactions and, locally, sedimentary organic matter mineralisation probably enhanced by pyrite oxidation. Finally, combining the results of this study and those of Caballero and Ladouche (2015), we discuss the possible future evolution of this aquifer system under global change, as well as the potential management strategies needed to preserve quantitatively and qualitatively this water resource.

The identification of the sources of contaminants present in groundwater at industrial sites is primordial to address environmental and industrial issues. However, available tools are often inadequate or expensive. Here, we present the data of stable isotopes (δ18O and δ2H) of the water molecule at an industrial site where electrochemistry plant occurs impacting the groundwater quality. High ClO3 and ClO4 contents and 2H enrichment have been measured in groundwater. Recharge of aquifer relates to infiltration of rainwater and by subsurface inflow. On-site, industrial products are generated by electrolysis. We show that the electrolysis process leads to a large 2H enrichment (+425‰) in solutions. In the absence of hydrothermal water input containing H2S, we demonstrate that the relationship between δ18O and δ2H can be easily used in a way to trace the origin of the ClO3 and ClO4 in groundwater. Isotopes evidenced first a leakage from end-product storage tanks or during the production process itself. Then, an accumulation and release of ClO3 and ClO4 from soil is demonstrated. Our study successfully shows that stable isotopes are a powerful and low cost tool for tracing pollutant plumes in an industrial context using electrolysis process.

The Centenario and Ratones salars are located in the SE part of the Argentina Puna, on the SW part of Altiplano-Puna region covering Chili, Bolivia and Argentina. They host all together the richest Li brine resources in the world. The northern Centenario salar has a halite core surrounded by fine grained clastic sediments, while the Ratones salar to the south comprises lesser evaporites and coarser grained volcanoclastics. Two aquifers occur at subsurface down to 250 m depth. They are classified as CI-Na (SO4) brine types containing several hundred mg/I of Lithium. The surface waters are generally characterized by Li < 7 mg/I, delta Li-7 of approximate to 9.5 parts per thousand, delta D: -66 parts per thousand and delta O-18(SMOW):-7.8 parts per thousand. The stable isotopic composition differs slightly from the upper aquifer (delta Li-7 approximate to 9.2 parts per thousand, delta D-47.2 parts per thousand and delta O-18(SMOW): -0.8 parts per thousand) to the lower aquifer (delta Li-7: 9.7 parts per thousand, delta D: -51.6 parts per thousand and delta O-18(SMOW): -1.7 parts per thousand, respectively). The dominant source of Li is attributed to leaching of andesites and pegmatites by metoric waters and to the interaction of brines with the pyroclastic material of the host aquifer. On the basis of the present results, hot hydrothermal waters can be excluded as a supplement Li source.

The aim of this study was to develop an easy-to-use, reliable method for measuring the isotopic composition of individual alkanes present in natural gases at concentrations below 1000 ppmv without the need of expensive or complex pre-concentration devices. The proposed method combines pre-concentration of the gaseous compounds (C1 to C5) in a cooled, programmable temperature injector equipped with a Carbosieve-packed liner followed by compound-specific isotope analysis (CSIA) by gas chromatography – isotope ratio mass spectrometry (GC-IRMS). This method requires only small sample volumes of up to 10mL and allows reliable isotopic measurements at low concentrations (< 100 ppmv) within the typical precision of GC-IRMS: ≤ 0.5‰ for carbon and ≤ 5‰ and hydrogen isotope analysis, respectively. The proposed injection techniques have been developed and validated using gaseous hydrocarbon samples of different origins.

Characterization of dissolved CO2 and alkane gas in clayrocks may help assessing the confinement properties of geological barriers considered as potential host rocks for a deep geological disposal as well as for caprocks of gas storages.A monitoring of alkanes with CO2, combined with carbon isotopes was performed on core samples coming from Underground ResearchLaboratories (Bure, Mont Terri, Tournemire) and the Schlattingen borehole in France and Switzerland. Compositionof hydrocarbon gas and δ13Cof methane strongly suggest a dominant thermogenic origin of methane which ismixed with a bacterial origin for the Toarcian shales, Pliensbachien and Callovian-Oxfordian clayrocks. Results also evidence the contrasted behavior of CO2, which is controlled by chemical equilibrium between pore water and carbonate mineralogy, compared to the alkanes which are present in the porosity as a stock of dissolved gases which can be depleted during degassing experiments.

Future improving of the innovative technology of Lithium air batteries correlates with an increased demand for Li-resources. We analyzed and compared stable isotopic compositions from 4 Argentinean Li rich salars. The Pozuelos (PS), Centenario (CN), Ratones (RT) and Hombre Muerte (HM) belong to the world class brine resources of the Atacama triangle. CN has a halite core surrounded by fine grained clastic sediments, while RT comprises lesser evaporates, but coarser grained volcanoclastics. Two Cl-Na SO4 brine aquifers (down to 250 m depth) host several hundreds of mg/l of Li. The surface waters are characterized by Li < 7 mg/l, delta Li-7 of approximate to 9.5, delta D: -66 parts per thousand and delta O-18(SMOW): -7.8 parts per thousand. The stable isotopic composition differs slightly from the upper aquifer (delta Li-7 approximate to 9.2 parts per thousand, delta D -47.2 parts per thousand and delta O-18(SMOW) -0.8 parts per thousand) to the lower aquifer (delta Li-7: 9.7 parts per thousand, delta D: -51.6 parts per thousand and delta(OSMOW)-O-18 : -1.7 parts per thousand). The dominant source of Li is related to water-rock interactions (surface, saline waters with andesites, pegmatites, pyroclastics). The comparison of our RT and CN data to those of the close-by PS and HM, shows that each salars has its own geological, hydrological and climate history which can be defined by crossing isotope tracers. However, the development of pertinent isotopic regional and local exploration proxies, needs identical data sets on systematically defined samples of the same aquifer type, on country rocks and minerals. (C) 2015 Published by Elsevier B.V.

A shallow CO2 injection experiment was performed at the CO2FieldLab site near Svelvik, Norway in Sept. 2011. The gas was injected through a 45° inclined well to a target depth of 20 m. Its aim was to test various geophysical and geochemical monitoring tools for integrated near-surface leakage monitoring. A total of 1.67 t of CO2 was injected over a period of six days. Groundwater level was at 60 cm-depth and a complex salinity stratification with brackish water overlying fresh- and saltwater was observed at the beginning of the experiment. Four water sampling boreholes were located at each corner of a square configuration of 8 m with the nominal injection at the center. From baseline conditions to the post-CO2 injection phase, pH, temperature and electrical conductivity of the groundwater were measured, collecting water samples at three different depths (5, 10 and 15 m) for analyses of major, minor, and trace elements (Ca, Na, SO4, Cl, Mg, Al, Ba, Mn, Ni, Co, B, Li), and isotopes (δ11B, δ7Li, δ34SSO4, δ18OSO4, 87Sr/86Sr, δ18OH2O, δ2HH2O). Significant changes in chemical and isotope signatures of water over the duration of the experiment indicated two processes: 1) Binary mixing with seawater and rainwater as the possible end-members due to a near-seashore location, and 2) CO2–water–rock interactions enhanced by dissolved CO2 causing acid conditions and favoring rock dissolution. The relative contribution of those processes was quantified by a mass balance model and equilibrium calculations. This comprehensive geochemical and isotope approach allowed discriminating reactive mechanisms from non-reactive (mixing) processes associated with CO2 leaks, within an aquifer with a strong conductivity stratification and heterogeneous mineralogy and this approach seems promising for investigating CO2 leaks at field scale.