Molecular and isotopic composition of free hydrocarbon gases from Sicily, Italy
Article first published online: 19 MAR 2004
Copyright 2004 by the American Geophysical Union.
Geophysical Research Letters
Volume 31, Issue 6, March 2004
How to Cite
2004), Molecular and isotopic composition of free hydrocarbon gases from Sicily, Italy, Geophys. Res. Lett., 31, L06607, doi:10.1029/2003GL019362., , , , , and (
- Issue published online: 19 MAR 2004
- Article first published online: 19 MAR 2004
- Manuscript Accepted: 24 FEB 2004
- Manuscript Revised: 29 JAN 2004
- Manuscript Received: 23 DEC 2003
 Chemical and isotopic data have been used as geochemical tracers for a genetic characterization of hydrocarbon gases from a total of eleven manifestations located in Eastern and Central-Southern Sicily (Italy). The molecular analysis shows that almost all the samples are enriched in methane (up to 93.2% Vol.), with the exception of four gas samples collected around Mt. Etna showing high mantle-derived CO2 content. Methane isotope signatures suggest that these are thermogenic gases or a mixture between thermogenic gases and microbial gases. Although samples from some mud volcanoes in Southern Sicily (Macalube di Aragona) show isotope signatures consistent with a mixing model between thermogenic and microbial, by combining the molecular compositions (C1/(C2 + C3)) and the methane isotope ratios (δ13C1), such a process seems to be excluded. Therefore, the occurrence of secondary post-genetic processes should be invoked. Two main hypotheses have been considered: the first hypothesis includes that the gas is produced by microbial activity and altered post-genetically by microbial oxidation of methane, while according to the second hypothesis thermogenic gas have modified their molecular ratios due to vertical migration.