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Organic geochemical character of opal-rich sediments in light-dark cycles near the Pliocene-Pleistocene boundary in Deep-Sea Drilling Project Site 532, Walvis Ridge


  • Philip A. Meyers,

  • Keith W. Dunham,

  • Greg H. Rau


Geochemical studies have been done on organic matter from biogenic sediments from Deep-Sea Drilling Project site 532, which is under the seaward edge of the Benguela upwelling system and has light-dark color cycles resulting from variations in sediment properties. Cyclical fluctuations in opal, organic carbon, and calcium carbonate accompany the color changes. Examination of early Pleistocene sediments taken at 10-cm intervals from section 532B-17-2 reveals that high carbonate concentrations coincide with lower organic carbon percentages. Carbon and nitrogen isotope contents of organic matter remain essentially constant through the color cycles. Geolipid contents show somewhat better retention of original character in darker sediments than in lighter portions of this section and reflect variations in the degree of preservation of organic matter. The origin of the light-dark cycles may be fluctuations in the Benguela Current caused by variations in the earth's obliquity.

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