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ABSTRACT

Samples from Onslow Bay vibracores containing siliceous microfossils were obtained for biostratigraphic and paleoenvironmental studies of radiolarians. Three early to middle Miocene radiolarian zones were recognized: Stichocorys wolffii Zone (Frying Pan Section), Calocycletta costata Zone (Onslow Bay Section) and Dorcadospyris alata Zone (Bogue Banks Section) on the basis of 22 age-diagnostic species.

An average of 16 taxa (of approximately generic level) per sample were observed in the Frying Pan and Onslow Bay sections, with subequal representation by spumellarians and nassellarians. Seven taxa were predominant (consistently >5% of the assemblage) in the Frying Pan Section, six in the Onslow Bay Section. Radiolarians were too sparse in samples of the Bogue Banks Section for quantitative studies.

The assemblages generally consist of shallow-dwelling groups, although a few specimens of deep-dwelling taxa occur in one core from the Bogue Banks Section, perhaps suggesting strong upwelling or intrusions from deep levels of the Gulf Stream. Abundance and diversity of radiolarians are lower in the Onslow Bay sections than in correlative units of the mid-Atlantic Miocene, suggesting that different paleoenvironmental factors prevailed in each region.

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