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Diatom Biostratigraphy of Miocene Pungo River Formation, Onslow Bay, North Carolina Continental Shelf

Eric R. Powers

Diatom floras in the Miocene Pungo River Formation of the North Carolina continental margin indicate deposition from the late Burdigalian to middle Serravallian stages. Assemblages from 15 vibracores from the continental shelf in Onslow Bay, North Carolina, and one stratigraphic section from the phosphate mine at Aurora, North Carolina, provide the basis for biostratigraphic interpretations. High-resolution seismic profiling in Onslow Bay has delineated at least 20 fourth-order seismic sequences, each bounded by unconformities, which can be grouped into third-order sequences named FPF, AF, and BBF from oldest to youngest. Biostratigraphic age assignments are based on indicator species of Abbott's 1978 Atlantic Miocene diatom zonation, in which Actinoptychus heliopelta and Delphineis ovata do not co-occur. The A. heliopelta zone spans the Burdigalian, and the D. ovata zone is early Langhian. Their co-occurrence in the lowermost third order sequence (FPF) in Onslow Bay indicates a late Burdigalian age. The overlying AF sequence contains species common to the D. ovata/D. penelliptica zone. The concurrent range zone of these species indicates the Langhian stage. The uppermost BBF third-order sequence contains definitive species of the Coscinodiscus plicatus zone of the middle Serravallian stage. The intervening D. penelliptica and D. penelliptica/C. plicatus zones have not yet been observed in the BBF sequence. Samples from the lower Pungo River Formation at Aurora contain abundant specimens of A. heliopelta and other species characteristic of the Burdigalian suggesting correlation with the FPF sequence of Onslow Bay. Upper Pungo River sediments at Aurora yielded no diatoms.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.