A strong acoustic reflection that parallels the sea floor has been observed in seismic profiles collected over the Blake Ridge region, off the southeastern United States. This anomalous reflection occurs at a subbottom depth of 400 to 700 m in water depths of 750 to 3,750 m and has been mapped over an area of at least 80,000 km². The reflection probably is due to the contrast between an upper high-velocity zone of sediment cemented by gas hydrates and an underlying low-velocity zone that does not contain gas hydrates.

Coring by the Deep Sea Drilling Project (DSDP) has shown that gas hydrates are present in this region. During DSDP Leg 11, high concentrations of gas were observed; gas was composed mainly of methane of light carbon isotopic composition (< -70 per mil relative to PDB standard) accompanied by minor amounts of heavier hydrocarbons and carbon dioxide. DSDP Leg 76 confirmed that high concentrations of methane are present in sediment from this region. Conclusive evidence for gas hydrates was obtained when a vigorously outgassing sediment sample with a matlike layer of white crystals was recovered. The volume of gas released from this sample was about 20 times the volume of pore fluid, a result clearly indicating gas hydrate. Results obtained by using a pressure core barrel also indicate that gas hydrate is present. The molecular composition of the hydrocarbon gases and the isotopic composition of the methane suggest that the methane is of biologic origin. This methane, if trapped beneath the gas hydrate in reservoir rocks, could represent a significant resource.

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