METHANE-DERIVED CARBONATES AND CHEMOSYMBIOTIC COMMUNITIES OF PIEDMONT(MIOCENE, NORTHERN ITALY) - AN UPDATE

Stable carbon isotope values of authigenic carbonate rocks in the Mioc ene terrigenous sediments of Piedmont indicate a methane-related origi n. Some of these methane-derived carbonates (Lucina limestone) are cha racterized by the presence of abundant lucinid remains. Carbonate diss olution/precipitation and development of lucinid communities were rela ted to bacterial methane oxidation, both aerobic and anaerobic. Anaero bic oxidation led to carbonate precipitation and production of sulfide , which sustained lucinid communities through chemosynthetic symbiotic bacteria. Aerobic oxidation of methane likely resulted in dissolution of carbonate skeletal grains. Several phases of carbonate precipitati on, characterized by slightly different isotopic compositions, are rec ognizable in the limestones.