Abstract

The Oligocene/Miocene boundary interval at Ocean Drilling Program (ODP) Site 959 on the Cote d'Ivoire-Ghana Transform Margin is characterized by cyclical variations in siliceous and mixed calcareous-siliceous deposits. This cyclical pattern is reflected in the distribution of dispersed organic matter in the deposits, which shows an alternation between dominantly marine organic matter and mixed marine-terrestrial matter. There is some correlation between the composition and abundance of dispersed organic matter, dinoflagellate cysts (dinocysts), and calcareous and siliceous microfossils in the deposits. A study of the dinocysts revealed (1) an abundance of inner neritic forms in a deep marine (bathyal) setting, and (2) a pattern of cyclical alternation of the dominant dinocysts between gonyaulacalean and peridinialean forms. Spiniferites spp., and to a much lesser extent Hystrichokolpoma rigaudiae, are the most common gonyaulacoid dinocysts. One sample contains a noticeable proportion (6%) of the outer neritic to oceanic dinocyst Nematosphaeropsis labyrinthus. Peridinioid dominated sections are characterized by large numbers of protoperidinioid cysts. The cyclical patterns of dispersed organic matter, dinocysts, and calcareous and siliceous microfossils are probably indicative of transportation by current systems, climatic changes, and paleoproductivity.

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