Natural sources of carbon dioxide and methane from the fluvio-lacustrine sediments of the Fucino Plain (Central Italy): evidence from stable carbon isotopes

Francesca Giustini (*) & Mauro Brilli (*)
(*) Istituto di Geologia Ambientale e Geoingegneria, CNR, Area della Ricerca di Roma1, Via Salaria Km 29,300 - 00015 Monterotondo Staz., Roma. Corresponding author (Phone: ++39 06 90672645; Fax: ++39 06 90672733; E-mail: francesca.giustini@igag.cnr.it).

The present investigation focused on the origin of CO2 and CH4 in the soil gas and two gas vents present in the Fucino plain, a tectonically active intramontane depression of central Italy. The soil gases have concentrations of CO2 ranging from 1 to 10% and CH4 in the order of a few parts per million. Using carbon isotopes, it was possible to identify two different sources of CO2 in the soil gas: biogenic CO2 (d13CCO2~ –20‰) produced in the fluvio-lacustrine sediments of the plain and CO2 produced from CH4 oxidation in soil (d13CCO2 –34/–38‰). The two gas vents yield CO2 contents of 2.63 and 15.33% and CH4 of 94.7 and 8.5%. In the CH4-dominated gas vent, the carbon isotopes of methane (d13CCH4 = –64‰) point to a gas of microbial origin. The other gas vent, with a d13CCH4 of –52.8‰, may be affected by a microbial oxidation process.

Soil gas, carbon dioxide, methane, isotopes, Fucino plain (Italy).