Molecular and isotopic composition of free hydrocarbon gases from Sicily, Italy

Mariano Valenza, Eckhard Faber, Giorgio Capasso, Fausto Grassa, Salvatore Inguaggiato, Rocco Favara

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Abstract

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 (C-1/(C-2 + C-3)) and the methane isotope ratios (delta(13)C(1)), 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.
Original languageEnglish
Pages (from-to)1-4
Number of pages4
JournalGeophysical Research Letters
Volume31
Publication statusPublished - 2004

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Earth and Planetary Sciences(all)

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    Valenza, M., Faber, E., Capasso, G., Grassa, F., Inguaggiato, S., & Favara, R. (2004). Molecular and isotopic composition of free hydrocarbon gases from Sicily, Italy. Geophysical Research Letters, 31, 1-4.