1. ^†Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90024, USA
2. ^‡Marine Physical Laboratory, Scripps Institution of Oceanography, University of California at San Diego, La Jolla, California 92093, USA
3. ^*Present address: School of Oceanography, Oregon State University, Corvallis, Oregon 97331, USA.

Abstract

Petroleum has been dredged from an active hydrothermal mound area in the southern rift of Guaymas Basin, Gulf of California. This organic matter is composed of gasoline-range aliphatic and aromatic hydrocarbons and predominantly residual polar asphaltic material. The aliphatic hydrocarbons of two bitumen samples have very different boiling range and composition. Both samples contain polynuclear aromatic hydrocarbons and olefins, which indicate formation at pyrolytic temperatures. The overall compositional data indicate an origin from biological detritus by thermal alteration and rapid quenching by hydrothermal removal, followed by condensation at the seabed.