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

No abstract

No abstract

No abstract

No abstract