Organic Geochemistry of Quaternary Sediments from Deep Sea Drilling Project Leg 72, South Atlantic Ocean

Abstract

Organic matter in sediments from Sites 515, 516, and 517 reflects a history of low marine productivity and of oxygenated bottom waters in the western South Atlantic since the Pliocene. Organic carbon contents are low, averaging 0.26% of sediment weight. Distributions of n-alkanes, /i-alkanols, and «-alkanoic acids show evidence of microbial reworking, and n-alkanes contain important terrigenous contributions, presumably of eolian origin.

Organic geochemistry of late Cenozoic sediments from the subtropical South Atlantic Ocean

“…Leg 72 samples contain relatively small contributions of long chainlength acids compared to other DSDP samples of similar ages (Meyers and Dunham, 1983). The low proportion of long chain-length acids can be attributed to extensive microbial reworking of organic matter in these sediments which were deposited under regions of low surface productivity in the western South Atlantic.…”

“…Sediments analyzed from these sites are of similar ages but differ in their compositions. Samples from Legs 72 and 74 represent low-productivity regions with relatively similar, low concentrations of organic carbon (Meyers and Dunham, 1983;Meyers and Keswani, 1984), whereas Leg 75 samples are from an area of high productivity associated with the Benguela upwelling system off South-West Africa (Hay et al, 1982;Meyers and Dunham, 1984).…”