Bitumen seepages from a trachyte flow on the Suswa volcano (East African Rift) are anomalously enriched in O and N heteroatomic organic compounds and depleted in aliphatics. Compositional and geologic data suggest that the biogenically derived bitumens were extracted and/or transported by liquid or supercritical CO2, rather than H2O, possibly from caldera-lake sediments. Compositionally atypical hydrocarbons and reduced carbon associated with other alkaline-peralkaline igneous complexes, as well as Hg and Au deposits, may also reflect CO2, fluids. Hydrocarbon extraction and migration in CO2-rich fluids are considered realistic mechanisms in certain geologic environments.

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