News16.07.2018Publication of the article “Geochemical indicators in Western Mediterranean Messinian evaporites: Implications for the salinity crisis.” |
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PhD. Javier García Veigas, Head of the Technology of Scanning Electron Microscopy of the CCiTUB in the Diagonal Campus, has published the article: "Geochemical indicators in Western Mediterranean Messinian evaporites: Implications for the salinity crisis" in the Marine Geology(Elsevier) journal. The analysis also included the instrumentation and collaboration of the technical staff of the units of Isotopic ratio mass spectrometry and metal analysis of the CCiTUB. The work presents a geochemical study, mainly isotopic, of more than 400 samples of gypsum and salt from different evaporitic deposits of Spain (Alicante, Almeria and Mallorca) and Sicily, all of them assigned to the Messinian (Upper Miocene). These gypsum deposits, together with an uncertain volume of salt in the bottom of the Mediterranean (more than 1000m of power, over an area of more than 2,000,000 km2), were formed in less than 1 million years and constitute the base of the theory of the 'Salinity Crisis of the Messinian' that assumes that the Mediterranean drained due to a closure with the Atlantic. The work concludes that the theory of 'desiccation' is not correct, that the Mediterranean remained as a deep basin, with restricted oceanic connection, and with the development of a concentrated mass of water (brine), chemically stratified and isotopically modified by sulfate-reducing microorganisms. The abstract of the article is: "The Messinian Salinity Crisis (MSC) led to deposition of one of the youngest saline giant on Earth. The increasing restriction of the connections between the Mediterranean, the Atlantic Ocean and the freshwater Paratethyan basins resulted in the deposition of massive amounts of evaporites (gypsum, anhydrite, halite and potash salts) in shallow marginal basins as well as in deep Mediterranean basins. Here we show that each gypsum unit in the circum-Mediterranean marginal basins in Sicily and Spain is characterized by a narrow range of sulfate isotopic values (δ34S~23‰ and δ18O~14‰ in the Lower Gypsum; δ34S~23‰ and δ18O~17‰ in the Upper Gypsum). Sulfate isotope compositions found in MSC evaporites from a variety of circum-Mediterranean basins are homogenously high relative to expected Late Miocene marine evaporites (δ34S~22‰ and δ18O~12‰). This points to a stratified Mediterranean Sea with a high-salinity, dense, and anoxic bottom water mass. An intermediate depth gypsum-saturated brine flooded marginal basins from which selenite deposits formed during the MSC Stage 1 (Primary Lower Gypsum) and MSC Stage 3 (Upper Gypsum). Messinian brines were gradually affected by biogenic redox processes and isotopically differentiated from global seawater values. The homogeneity of isotopic signatures between distant synchronous gypsum deposits further supports the deep-basin deep-water model for the Mediterranean during the entire MSC event." More information at the following link: [+]. |
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