(Table 1) Total and organic carbon in sediments at DSDP Holes 69-504 and 69-505

Sediments from Deep Sea Drilling Project Sites 504 and 505 near the Costa Rica Rift were examined by thermal methods. It was found that production index (P.I.) values, which measure the degree of thermal hydrocarbon generation in the sediment, were slightly different for the two sites when compared for sediments with similar types of organic matter. Highly burrowed sections of these immature sediments gave anomalously low values of pyrolyzable hydrocarbons, suggesting production of inert organic carbon by purely biological processes. Organic carbon levels correlate with pyrolyzable hydrocarbons at both sites and show that samples with less than 1 % organic carbon are inert to hydrocarbon generation under any conditions of time and temperature.