Author	De Verteuil, L. and Norris, G.
Year	1996a
Journal	Micropaleontology, volume 42, supplement, 1996Micropaleontology, volume 42, supplement, 1996
Title	Miocene dinoflagellate stratigraphy and systematics of Maryland and Virginia

Abstract De Verteuil, L. and Norris, G., 1996; Miocene dinoflagellate stratigraphy and systematics of Maryland and Virginia. Micropaleontology Volume 42 supplement 1996. Part I - Dinoflagellate cyst zonation and allostratigraphy of the Chesapeake Group Ten dinoflagellate cyst interval zones are erected for the Miocene of the Salisbury Embayment, Atlantic Margin, U.S.A., based on analyses of classic Miocene outcrops in Calvert County, Maryland, plus outcrop and subsurface sections from New Jersey, Delaware, Maryland and Virginia. The zonation provides continuous coverage from the uppermost Oligocene to the uppermost Miocene, utilizing 62 dinocyst horizons, with average zonal durations of ca. 1.8 My. The zonation refines earlier biostratigraphies based on diatoms, radiolarians and mollusks and is integrated with calcareous nannofossil and planktonic foraminiferal stratigraphies from ODP Leg 150 sites offshore New Jersey. Comparisons with Miocene dinocyst assemblages indicate that the lowest occurrences of Labyrinthodinium truncatum and Unipontidinium aquaeductum, and the highest occurrences of Distatodinium biffii and Hystrichosphaeropsis obscura, are important dinocyst horizons across the North Atlantic and Mediterranean. Regional endemism and paleoenvironmental parameters are responsible for significant differences in overall composition, as well as some species ranges, between Miocene assemblages from the Mediterranean and western North Atlantic. Although high latitude dinocyst assemblages from the Norwegian Sea and Baffin Bay are distinctive, there is reasonable correlation with mid-latitude assemblages from the Salisbury Embayment. Twelve informal allostratigraphic units are defined from outcrops that yielded dinocysts, in relation to Chesapeake Group lithostratigraphy and earlier statigraphic work in the Calvert Cliffs ourcrop belt. Dinocyst stratigraphy facilitates the extention of these units into the subsurface of eastern Virginia, Maryland, Delaware and New Jersey. The distribution of Miocene allostratigraphic units in the Salisbury Embayment is related to 2nd order eustasy and basin structure. Fifteen potential 3rd order depositional sequences are identified in the Salisbury Embayment and dated by dinocyst stratigraphy; 3 in the lower Miocene, 5 in the middle Miocene and 7 in the upper Miocene. These show excellent agreement with the 2nd order eustatic curve of the Exxon Cycle Chart but chronostratigraphic resolution does not permit detailed comparisons of the 3rd order cyclicity. Part II - Homology and structure in dinoflagellate cyst terminology Research over the past three decades has produced a rich vocabulary for describing dinoflagellate cysts. Ideas about homology have exerted a strong influence on the development of this terminology. From wall structure to tabulation, some of these ideas are inconsistent with homology concepts in contemporary evolutionary biology. In this selective review of the descriptive terminology for fossil dinoflagellates, a practical and theoretically consistent terminology is proposed from among the present plurality of terms. We perceive tabulation as the number, distribution and topology of thecal plates and cyst fields because the expression of these characters is the same for both the motile planozygote and the non-motile cyst. The Kofoid system of labeling tabulation elements is favored over the Taylor-Evitt approach, where specific homologies must be assumed present between naturally occurring tabulations and the model. We apply the results of our analysis in descriptions of 12 morphologically diverse new taxa from the Miocene of Maryland and Virginia. The new genus Cousteaudinium is erected with Cousteaudinium aubryae as the type. The taxon Labyrinthodinium truncatum Piasecki 1980 is emended and a new subspecies, Labyrinthodinum truncatum subsp. modicum, is described. The other new species are: Cannosphaeropsis passio, Cerebrocysta poulsenii, Cerebrocysta satchelliae, Exochosphaeridium insigne, lmpagidinium antecarcerem, Impagidinium arachnion, Lingulodinium multivirgatum, Pyxidiniopsis fairhavenensis, Spiniferites solidago and Sumatradinium hamulatum.