Isotopic evidence for biogenic precipitation as a principal mineralization process in coastal gasohydrothermal vents, Punta Mita, Mexico

In Punta Mita vents, almost all δ34S values measured in pyrite range from − 13.3‰ to − 4.9‰, and δ13C values in calcite vary from 0‰ to − 39‰. These results agree with the hypothesis that calcite and pyrite were deposited by mediation of microbial activity, caused by the coupled reactions of vent methane oxidation and marine sulphate reduction, and suggest that biomineralization prevails over abiotic precipitation processes in such coastal gasohydrothermal vents. The 14C ages obtained from carbonates, of approximately 40,000 years, may represent the minimum age for the methane that generates the carbonates in the vents.