The relation of two well-known ancient carbonate deposits to hydrocarbon seepage was confirmed by this study. Archaea are found to be associated with the formation of Oxfordian seep carbonates from Beauvoisin and with a Miocene limestone from Marmorito ("tube-worm limestone"). Carbonates formed due to a mediation by archaea exhibit extremely positive or extremely negative d 13 C carbonate values, respectively. Highly positive values (c15‰) reflect the use of 13 C-enriched CO 2 produced by methanogenesis. Low d 13 C values of the Marmorito carbonates (-30‰) indicate the oxidation of seepagederived hydrocarbons. Likewise, the d 13

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During the fi rst stage of the Late Miocene Messinian salinity crisis (5.97-5.60 Ma), deposition of sulfates (the Primary Lower Gypsum) occurred in shallow silled peripheral subbasins of the Mediterranean undergoing restricted water exchange with the Atlantic Ocean. Fluid inclusions in Messinian selenite crystals from the Piedmont Basin (northwest Italy) have surprisingly low salinities (average of 1.6 wt% NaCl equivalent), suggesting that parent waters were depleted in Na+ and Cl- compared to modern seawater. Modern gypsum from a Mediterranean salt work, in contrast, contains fl uid inclusions with elevated salinities that match the normal evaporation trend expected for seawater. The salinity data indicate that the Messinian sulfate deposits from the Piedmont Basin formed from hybrid parent waters. seawater mixed with Ca2+ and SO4 2- enriched freshwaters that dissolved coeval marginal marine gypsum. Such mixed parent waters and complex recycling processes should be taken into account when explaining the genesis of other Messinian gypsum deposits across the Mediterranean Basin

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