C1-C8 hydrocarbons at DSDP Site 93-603

Organiccarbon- lean sections contained only C1-C3 compounds believed to have migrated from organic-carbon-rich sections. Heavier (C4-C8) hydrocarbons were found only in organic-carbon-rich sections.

Restricted and sporadic distribution of C4-C6 compounds in 0-1100 m sub-bottom sediments suggest low-temperature (<20°C) biological/chemical generation processes. Increased C4-C8 concentrations and complexity, including unusually high levels of xylene, were detected in two deeper Cretaceous sections (603-34-2, 134 cm and 603-81-3, 120 cm). This behavior, which was not observed in 17 other samples from sub-bottom depths greater than 1100 m, is similar to that observed in immature surface sediments from the geothermally active Guaymas Basin (Gulf of California) area.