Carbon-isotope compositions of n-alkanes, pristane and phytane, and total organic carbon were measured and compared against isotopic trends of coeval alkadienones from Miocene sediments containing very low organic-carbon contents. Compound-specific isotope analysis ofn-alkanes and isoprenoid lipids, in conjunction with abundance distributions of n-alkanes reveal the influence of terrestrially derived organic carbon at all sites analyzed. In general, n-alkanes are derived from allochthonous sources with the exception of n-C37 from site 516, which appears genetically related to coeval alkadienones. Further, pristane and phytane from pelagic sites 608 and 516 apparently derive from terrestrial sources as well, although a marine origin cannot be excluded. dTOC values lack a coherent relationship to %TOC and d 13 C37:2. Differential alteration and mixing of diverse isotopic signals most likely contribute to temporal variation and spatial differences in dTOC. Therefore, when working with sediments from oligotrophic settings, we do not recommend dTOC as an indicator of phytoplankton d 13 C values. Copyright © 1999 Elsevier Science Ltd