Impact of methane seeps on the local carbon-isotope record: a case study from a Late Jurassic hemipelagic section

• Published in: Terra Nova
• Main Authors: Louis-Schmid, Beat, Rais, Pauline, Logvinovich, Dmitry, Bernasconi, Stefano M., Weissert, Helmut
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2007
• Subjects: Methane hydrate
• Online Access: https://doi.org/10.1111/j.1365-3121.2007.00744.x

An Oxfordian (Late Jurassic) hemipelagic succession from Beauvoisin (SE France) contains a pronounced, short-lived negative excursion in the bulk-carbonate carbon-isotope record, with an amplitude of 4‰. It was shown previously that the Beauvoisin paleoenvironment was impacted by hydrocarbon seepage. New isotopic data corroborate that methane was a significant constituent of these hydrocarbons. The negative excursion was caused by transient enhanced precipitation of 13 C- depleted carbonate, mediated by anaerobic oxidation of methane. Despite its local diagenetic origin, the Beauvoisin excursion is similar in shape and duration to globally recognized negative C-isotope excursions that have been related to catastrophic, massive dissociation of methane hydrate. Shape and duration of negative excursions therefore cannot be used as an argument when determining their origin if they have not been shown to represent a global perturbation of the carbon cycle.