Paleogene sporomorph biostratigraphy, Northeastern Virginia

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Abstract
This paper discusses the morphology, taxonomy, and stratigraphic occurrences of 62 forms of spores and pollen grains and four forms of freshwater(?) microplankton, in the Paleogene part of the Oak Grove core from northeastern Virginia. The known geologic ranges of these taxa in southeastern United States are also given. Seven new species are proposed: Lusatisporis indistincta, Momipites flexus, Nuxpollenites psilatus, Piolencipollis endocuspoides, Porocolpopollenites virginiensis, Triatriopollenites triangulus, and Tricolpites crassus. Sporomorph occurrences in seven samples from the upper Sabinian (lower Eocene) and lower Claibornian (lower part of the middle Eocene) of the Gulf Coast are also listed; these samples were analyzed to provide additional control for correlating the assemblages from Virginia with those in southeastern United States. Several sporomorph taxa, including Carya and Kyandopollenites anneratus, appear to range lower in the section (into probable Midwayan rocks) in Virginia than they do farther to the south. On the basis of sporomorphs and other fossils, the Oak Grove core includes the following sequence in ascending order: Aquia(?) Formation, probably Midwayan (lower Paleocene), 12.5 m thick; Aquia Formation, lower Sabinian (upper Paleocene), 22.3 m thick; Marlboro Clay, lower Sabinian, perhaps the upper part of the formation being upper Sabinian (lower Eocene), 5.4 m thick; and Nanjemoy Formation, upper Sabinian, 37.4 m thick. The position of the boundary between the lower and upper Sabinian (that is, the Paleocene‐Eocene boundary) could not be precisely determined by means of sporomorphs because of a lack of data on sporomorph assemblages from near this boundary in southeastern United States. The sequence in the Oak Grove core appears to represent more or less continuous deposition across the boundary between the lower and upper Sabinian; such a sequence rarely if ever occurs in southeastern United States.