C1-C8 HYDROCARBONS IN SEDIMENTS FROM GUAYMAS BASIN, GULF OF CALIFORNIA - COMPARISON TO PERU MARGIN, JAPAN TRENCH AND CALIFORNIA BORDERLANDS

Surface seafloor sediments, hydrothermal vent samples, and Deep Sea Drilling Project sediments (Hole 481A) from the Guaymas Basin were examined for C//1-C//8 hydrocarbons. The proportions of various classes of compounds were examined and compared to those from other geographic areas (Peru upwelling region and Japan Trench) to gain insight into the relative importance of thermal generation, migration and biodegradation. Alkene/alkane ratios of 0. 1 or greater were typical of both geothermally cold sediments and also of very hydrocarbon-rich Alvin samples recovered from the seafloor. Because little or no alkene was generally detected in buried sediments exposed to geothermal temperatures greater than 30 degree C, it is suggested that the alkenes are produced by biogenic processes. Similarities in compositions of branched and cyclic compounds were observed in some pairs of bitumen-rich Guaymas seafloor samples recovered from different areas, suggesting common mechanisms of light hydrocarbon generation and/or migration.