Organic geochemistry of recent marine sediments from the Nansha Sea, China

Recent marine sediments from two cores, collected on the continental slope of the Nansha Sea, China, have been analyzed for organic matter content, n-alkane and isoprenoid hydrocarbons, fatty acids, n-alkanols and sterols. The organic carbon contents of the two sediment cores average 0.7 and 0.53%, respectively, and are higher than those of other sedimentary environments in this region. The distributions of various lipid compounds indicate that most of the sedimentary organic matter in the two cores is derived from marine plankton and bacteria, with land-derived organic matter present in relatively small amounts. The decrease in relative abundances of shorter chain lipids (n-alkanes, n-fatty acids and n-alkanols) with depth is evident, as is the biochemical conversion of stenols to stanols in some samples. The low pristane/phytane ratios may result primarily from microbial activity, and reflect the occurrence of significant diagenetic alteration of organic matter in the two cores.