This paper documents the Eocene to Miocene dinoflagellate cyst assemblages found at Site 94 in the southern part of the Gulf of Mexico. Four unique dinoflagellate cyst assemblages representing depositional periods from the Early Eocene to the Early Miocene are defined in this study. The Early to Middle Eocene assemblage presents the highest average concentrations of dinoflagellate cysts, is dominated by Operculodinium, and contains few heterotrophic taxa. The Early Oligocene assemblage has medium concentration and is dominated by Deflandrea. The Late Oligocene also has high average concentrations of dinoflagellate cysts, is dominated by Homotryblium, and contains few heterotrophic taxa. The Early Miocene assemblage has lower average concentrations of dinoflagellate cysts, is dominated by Pyxidinopsis, and lacks heterotrophic taxa. Our palynological data is related to significant regional paleogeographic and paleoceanographic changes. Namely, the Early to Middle Eocene free flow of tropical water masses from the south and the Late Eocene restriction of this flow by a land bridge connecting northern South America to Cuba in the north. The Oligocene gradual return of the tropical water masses and finally, the Early Miocene emergence of the Florida Platform when the Gulf of Mexico reached modern oceanographic conditions. The stratigraphic ranges of selected dinoflagellate cysts fit in age with previous microfossil data from the site and allowed us to define the Early Oligocene - Late Oligocene transition. The presence of well-preserved dinoflagellate cysts allowed the identification of 60 species and the discovery of three new species: Achomosphaera psilata sp. nov., Carpatella reticulata sp. nov., and Hystrichosphaeropsis gulficum sp. nov.
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