Identifying eroded Messinian deposits on the Maltese Islands by gypsum Sr isotopes

International audienceEvaporite sediments are known to have formed during the Messinian high salinity crisis that has been recognized in many Mediterranean areas. This event was however never identified on the Maltese Islands. In this study, a Sr isotopic characterization of gypsum, found as secondary minerals in the Oligocene-Miocene formations of Malta and Gozo is performed. The 87Sr/86Sr values are discussed on the basis of comparison with the surrounding rock Sr isotopic signature. The data outline two distinguishable 87Sr/86Sr ratios for gypsum according to their facies. Most of crack-infilling mineral data suggest a downward fluid circulation in the Miocene sediment associated with interaction in the currently outcropping limestones. Some gypsum crystals found as crystallized spherules show significantly lower 87Sr/86Sr ratios, close to those defined in the literature for Messinian evaporate sediments. Taken together, this may suggest that an evaporate formation of Messinian age had in the past covered the present-day sedimentary sequence in Malta and Gozo

Influence of Hyper-Alkaline pH Leachate on Mineral and Porosity Evolution in the Chemically Disturbed Zone Developed in the Near-Field Host Rock for a Nuclear Waste Repository

This paper evaluates the effect of hyper-alkaline (NaOH/KOH) leachate on the mineralogy and porosity of a generic quartzo-feldspathic host rock for intermediate- and low-level nuclear waste disposal following permeation of the cementitious repository barrier by groundwater. The analysis is made with reference to expected fluid compositions that may develop by contact of groundwater with the cementitious barrier to form a chemically disturbed zone (CDZ) in the adjacent host rock, as informed by relevant natural analogue sites. Theoretical analysis and numerical modelling is used to explore the influence of different host rock mineral assemblages on changes in pore fluid chemistry, multiple mineral dissolution and precipitation reactions and matrix porosity within the CDZ under these conditions. The numerical modelling accounts for kinetic and surface area effects on the mineral transformation and porosity development for periods of up to 10,000 years travel time from the repository and ambient temperature of 20∘C. The analysis shows that dissolution of quartz, feldspar and muscovite in the host rock, by the hyper-alkaline waste leachate, will create relatively high concentrations of dissolved Si and Al in the pore fluid, which migrates as chemical fronts within the CDZ. Precipitation of secondary mineral phases is predicted to occur under these conditions. The increase in matrix porosity that arises from dissolution of primary aluminosilicate minerals is compensated by a reduction in porosity due to precipitation of the secondary phases, but with a net overall increase in matrix porosity. These coupled physical and geochemical processes are most important for contaminant transport in the near-field zone of the CDZ and are eventually buffered by the host rock within 70 m of the repository for the 10,000 year travel time scenario. The predicted changes in matrix porosity may contribute to increased transport of radionuclides in the host rock, in the absence of attenuation by other mechanisms in the CDZ

Activation of Protein Kinase A and Exchange Protein Directly Activated by cAMP Promotes Adipocyte Differentiation of Human Mesenchymal Stem Cells

Human mesenchymal stem cells are primary multipotent cells capable of differentiating into several cell types including adipocytes when cultured under defined in vitro conditions. In the present study we investigated the role of cAMP signaling and its downstream effectors, protein kinase A (PKA) and exchange protein directly activated by cAMP (Epac) in adipocyte conversion of human mesenchymal stem cells derived from adipose tissue (hMADS). We show that cAMP signaling involving the simultaneous activation of both PKA- and Epac-dependent signaling is critical for this process even in the presence of the strong adipogenic inducers insulin, dexamethasone, and rosiglitazone, thereby clearly distinguishing the hMADS cells from murine preadipocytes cell lines, where rosiglitazone together with dexamethasone and insulin strongly promotes adipocyte differentiation. We further show that prostaglandin I2 (PGI2) may fully substitute for the cAMP-elevating agent isobutylmethylxanthine (IBMX). Moreover, selective activation of Epac-dependent signaling promoted adipocyte differentiation when the Rho-associated kinase (ROCK) was inhibited. Unlike the case for murine preadipocytes cell lines, long-chain fatty acids, like arachidonic acid, did not promote adipocyte differentiation of hMADS cells in the absence of a PPARγ agonist. However, prolonged treatment with the synthetic PPARδ agonist L165041 promoted adipocyte differentiation of hMADS cells in the presence of IBMX. Taken together our results emphasize the need for cAMP signaling in concert with treatment with a PPARγ or PPARδ agonist to secure efficient adipocyte differentiation of human hMADS mesenchymal stem cells

Modelling of multi-minerals kinetic evolution in hyper-alkaline leachate for a 15-year experiment

Cement has been widely used for low- to intermediate-level radioactive waste management; however, the long-term modelling of multiple mineral transfer between the cement leachate and the host rock of a geological disposal facility remains a challenge due to the strong physical-chemical interactions within the chemically disturbed zone. This paper presents a modelling study for a 15-year experiment simulating the reaction of crystalline basement rock with evolved near-field groundwater (pH = 10.8). A mixed kinetic equilibrium (MKE) modelling approach was employed to study the dolomite-rich fracture-filling assemblage reacting with intermediate cement leachate. The study found that the mineralogical and geochemical transformation of the system was driven by the kinetically controlled dissolution of the primary minerals (dolomite, calcite, quartz, k-feldspar and muscovite). The initial high concentration of calcium ions appeared to be the main driving force initiating the dedolomitization process, which played a significant role in the precipitation of secondary talc, brucite and Mg-aluminosilicate minerals. The modelling study also showed that most of the initially precipitated calcium silicon hydrate phases redissolved and formed more stable calcium silicon aluminium hydrate phases. The findings highlight the importance of a deep and insightful understanding of the geochemical transformations based on the type and characteristics of the host rock, where the system is under out of equilibrium conditions, and the rates of mineral reactions

Ageing effect on the mineral and chemical c 1 omposition of Opalinus Clays (Mont Terri, Switzerland) after excavation and surface storage

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Geochemical signature of paleofluids in microstructures from Main Fault in the Opalinus Clay of the Mont Terri rock laboratory, Switzerland

International audienceThe present study reports on elemental and Sr isotopic analyses of calcite and associated celestite infillings of various microtectonic features collected mostly in the Main Fault of the Opalinus Clay from Mont Terri rock laboratory. Based on a detailed microstructural description of veins, slickensides, scaly clay aggregates and gouges, the geochemical signatures of the infillings were compared to those of the leachates from undeformed Opalinus Clay, and to the calcite from veins crosscutting Hauptrogenstein, Passwang and Staffelegg Formations above and below the Opalinus Clay. Vein calcite and celestite from Main Fault yield identical 87Sr/86Sr ratios that are also close to those recorded in the Opalinus Claymatrix inside the Main Fault, but different from those of the diffuse Opalinus Clay calcite outside the fault. These varied 87Sr/86Sr ratios of the diffuse calcite evidence a lack of interaction among the associated connate waters and the flowing fluids characterized by a homogeneous Sr signature. The 87Sr/86Sr homogeneity at 0.70774 ± 0.00001 (2r) for the infillings of most microstructures in the Main Fault, as well as of veins from nearby limestonelayer and sediments around the Opalinus Clay, claims for an ‘‘infinite’’ homogeneous marine supply, whereas the gouge infillings apparently interacted with a fluid chemically more complex. According to the known regional paleogeographic evolution, two seawater supplies were inferred and documented in the Dele´mont Basin: either during the Priabonian (38–34 Ma ago) from western Bresse graben, and/or during the Rupelian (34–28 Ma ago) from northern Rhine Graben. The Rupelian seawater that yields a mean 87Sr/86Sr signature significantly higher than those of the microstructural infillings seems not to be the appropriate source. Alternatively, Priabonian seawater yields a mean 87Sr/86Sr ratio precisely matching that of the leachates from diffuse calcite of the Opalinus Clay inside the Main Fault, as well as that of its microstructures and the same features of the sediments above and below. To envision a Priabonian seawater supply, there is a need for its storage without a significant evolution in its Sr isotopic composition until the final deformation of the area. The paleo-hydrogeological context calls for a possible infiltration of the seawater into a limestone karst located above the Opalinus Clay that could have acted as the storage reservoir. The karstic nature of this reservoir also explains why the 87Sr/86Sr of the fluids was not modified significantly until expulsion. An alternative storage could have been provided by the regional faultingsystem that developed during the contemporary regional rifting of the Rhine Graben. The fluid expulsion started along these extensional faults during the further Upper Eocene–Lower Oligocene rifting phase. Later, the thin skinned deformation of the Jura Belt affected the Mont Terri region in the form of the Main Fault, probably between approximately 9 and 4 Ma on the basis of preliminary K–Ar ages of nanometer-sized authigenic illite crystals recovered from gouge samples

About Sr isotopes in coffee "Bourbon Pointu" of the Réunion Island

International audienceDemonstration of the regional source of a high-quality product is nowadays essential to protect it from commercial transactions and cheatings. In this study, Sr isotopes are proposed as a tool to identify the regional source of a vegetable, on the basis of a combined geochemical investigation on a Coffea Arabica var. Laurina cultivation plot located on th Réunion Island. The Sr isotopic composition (87Sr/86Sr) of the produced coffee beans (called Pointed Bourbon) and of their growing environment, including soils, parent rocks, waters and fertilizers are determined. Flux of Sr in coffee beans is mainly dominated by soil solutions that can be influenced by Sr-rich fertilizers. This influence is however low enough to detect the cultivation soils' Sr isotopic ratio in the vegetable product, even after roasting. It also allows discrimination of coffees produced on varied geological areas. Measurements performed on the same variety of coffee beans produced in New Caledonia strengthen the demonstration. (Résumé d'auteur