The Navarin basin province, which lies beneath the northwestern Bering Sea shelf, is a large (45,000 sq km) frontier area for petroleum exploration. Our preliminary geochemical survey of this province measured hydrocarbon gases in near-surface sediments in search of evidence for the possible occurrence of petroleum. Hydrocarbons (methane through butanes) were analyzed from sediment samples taken at a depth of 1 m from cores collected during the summer of 1980 at 32 stations spaced approximately 50 km apart. In addition, samples at the same depth were analyzed from five stations spaced about 5 km apart over a shallow acoustic anomaly. All samples analyzed contained hydrocarbon gases, but none had significant amounts of hydrocarbons of obvious thermogenic (petroleum-related origin. At only two stations on the shelf and one on the slope were concentrations of methane and ethane significantly above background values, whereas those of propane and the butanes were not. Concentrations of methane and ethane were 5 to 9 and 10 to 20 times, respectively, higher than background values, and ratios of ethane to ethene of 6, 30, and 25 were unusually large relative to background values of about 1. The ratios of methane to ethane + propane of 100, 140, and 180, and the large ratios of ethane to ethene, suggest that some thermogenic hydrocarbons are present. Although petroleum is potentially present at depth in the Navarin basin province, our preliminary survey did not detect surface hydrocarbon-gas anomalies that would unequivocally signal its presence.

End_of_Article - Last_Page 1004------------