Geochemical indicators in Western Mediterranean Messinian evaporites: Implications for the salinity crisis

Abstract

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.