Molecular Composition and Diagenesis of Organic Matter (Geolipids) in Sediments from Sites 677 and 678, Leg 111

Abstract

The results of a preliminary organic analysis conducted on sediment samples from Sites 677 and 678, ODP Leg 111, indicate that the lipids are derived mainly from marine organisms, with bacterially-derived lipids. Terrestrial higher plant wax residues exist only in trace amounts. Diagenesis of organic matter by thermal stress is not extensive at either site. Sites 677 and 678 of Ocean Drilling Program (ODP) Leg 111 are about 200 km south of the spreading axis of the Costa Rica Rift, in the eastern equatorial Pacific. The remote sites are about 400 km from the terrigenous influence of the Ecuador coast. Because Site 677 is on a local minimum heatflow area and Site 678 is on a local maximum, sediments at the two sites were subject to different degrees of thermal stress resulting from vary­ ing geothermal heat flow. Therefore, it is of interest to examine whether the different regimes of geothermal heat flow at the two sites caused differences in the sedimentary organic matter. Whelan and Hunt (1983) characterized the sedimentary organic matter at nearby Deep Sea Drilling Project Sites 504 and 505 by a thermal analysis-gas chromatography technique, from which they recognized different degrees of thermal hydrocarbon gener­ ation resulting from the thermal differences between the two sites. No lipid analysis has been conducted on sediments in this area. As a preliminary study, we conducted lipid analysis on sedi­ ment samples from Sites 677 and 678 to determine the nature and source of the sedimentary organic matter and to examine maturation effects on the composition of the sedimentary or­ ganic matter.