Dinoflagellate Taxonomy and Biostratigraphy at the Cretaceous-Tertiary Boundary, Round Bay, Maryland

Don G. Benson, Jr.


Dinoflagellate assemblages from the Monmouth (Cretaceous) and Brightseat (Paleocene) formations are described. The dinoflagellate assemblages support the placement of the Monmouth Formation by previous workers in the Maestrichtian Stage, and the assignment of the Brightseat Formation to the Paleocene series. The Cretaceous-Tertiary boundary is characterized by a sudden change in the content of the dinoflagellate assemblage. Based on this sudden change the boundary is interpreted as a paraconformity. Changes in the dinoflagellate assemblage within the Monmouth Formation of this area form the basis for the establishment of three provision al zones which may serve as a framework for future work in this region. The dinoflagellate assemblages contain 35 genera and 66 species of which two genera and eight species are described for the first time. The new genera are Cyclapophysis and Diversispina.

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