Organic geochemistry of sediments at DSDP Leg 63 Holes

Selected core samples from the California Continental Borderland (Sites 467-469) were analyzed to evaluate the nature and composition of the lipids and kerogens in terms of their genetic origin and geological maturity. The lipids were of a multiple origin. On the basis of the homolog distributions of the n-alkanes and n-fatty acids, with the shape and magnitude of the unresolved branched and cyclic hydrocarbons, and the structural and stereochemical compositions of the molecular markers, these lipids were derived from primary autochthonous marine (microbial), from allochthonous terrigenous (higher plant wax), and from recycled (geologically mature organic matter) sources. The kerogens were composed of principally marine microbial detritus with a minor input of allochthonous terrestrial material. For the most part, the samples had undergone a thermal maturation according to a normal geothermal gradient, except in the proximity of intrusives. Such additional thermal stress was evident for the samples from Site 469 and to some extent for Site 467 at about a sub-bottom depth of 700 to 800 meters.

(Table 1) Carbon and lipids at DSDP Hole 61-462

The lipids of a Pliocene and a Cretaceous sample from Site 462 were analyzed to assess their source and diagenetic history. Judging from the distributions of the n-alkanes, n-fatty acids, n-alkylcyclohexanes and molecular markers, they are autochthonous, of marine origin, and deposited under oxic paleoenvironmental conditions of sedimentation. The stereochemistry of the various molecular markers (e.g., triterpanes and steranes) of the Pliocene sample indicates that the lipids are geologically mature. This supports the hypothesis of sediment recycling from older formations by turbidite redistribution into the Nauru Basin