Organic geochemistry of ODP Hole 162-985A sediments

Dark, organic-rich sediments were recovered from the lower Miocene section (~16.6 Ma) in Hole 985A in the Norway Basin during Ocean Drilling Program Leg 162. Organic carbon and total sulfur contents of the dark sediments showed a maximum concentration of 5.6 and 26.1 wt%, respectively. Sulfur enrichment in the sediments indicates that these dark layers were formed under anoxic conditions in bottom water. Four dark and eight greenish gray sediment samples, ranging in age from early Miocene to Pleistocene, were analyzed for lipid-class compounds (aliphatic hydrocarbons, fatty alcohols, and sterols) using gas chromatography (GC) and GC/mass spectrometry to better understand the formation processes of the organic-rich dark layers and to reconstruct the paleoenvironmental changes. The molecular distributions of n-alkanes and fatty alcohols indicate that terrigenous organic matter largely contributed to both types of sediments. Significant amounts of hopanoid hydrocarbons, such as diploptene and hop-17(21)-ene, however, were detected characteristically in the dark sediments, which suggests that prokaryotes such as methane-oxidizing bacteria or cyanobacteria may have significantly contributed to the formation of these organic-rich, dark sediments. These results indicate that the bottom waters of the Norway Basin had been subjected to anoxic conditions during the early Miocene.

TOC, CaCO3, n-alkane and alkenone concentrations of ODP Sites 202-1237 and 202-1239

We generated preliminary downcore records of total organic carbon content, calcium carbonate, long-chain n-alkane concentration, total alkenone concentration, and alkenone-based sea-surface temperature for samples from the easternmost flank of Nazca Ridge (Site 1237) and the eastern crest of Carnegie Ridge (Site 1239). Total organic carbon and long-chain n-alkane concentrations will be used to evaluate terrestrial sediment sources. Downcore records of alkenone sea-surface temperature will benefit studies of paleoceanography of the southeastern Pacific. Since these sites are located under the influence of major tectonic events, such as the uplift of the Andes Mountains and the closure of the Isthmus of Panama, the records will help us to examine the effects of the tectonic events on the oceanic environment.