Geological Survey of Canada, Canada

Fossil organic-walled dinoflagellate cysts (dinocysts) are useful for biostratigraphic correlation and as a proxy for palaeoecological surface water conditions. The stratigraphic ranges for Paleogene dinocysts are available from many regions around the Atlantic Ocean, but no information from the subtropical western Atlantic Ocean was available. However, recent drilling of the Blake Nose Ridge, provided well-calibrated middle to late Eocene sediments. From ODP Site 1053A, 46 samples have been palynologically analysed, emphasising dinocyst distribution and palaeoecology. Most of the investigated samples contain well preserved palynomorph assemblages. In all palynologically productive samples, the aquatic palynomorph fraction is more abundant than terrestrial components. Within all encountered dinocyst assemblages, the Spiniferites group is dominant. The recovered assemblages are a mixture of inner neritic, outer neritic and oceanic species. The autochthonous dinoflagellates, principally those of the Impagidinium group, indicate an oceanic environment. The close agreement in the abundance peaks of inner neritic dinocysts and terrestrial palynomorphs indicated that both are allochthonous. This is confirmed by the much higher number of neritic species found in JOIDES Holes 1 and 2, on the continental shelf of eastern Florida, immediately to the west of the Blake Nose. Lower latitude species found in Hole 1053A, but not occurring at higher latitudes during the late Eocene, are Diphyes colligerum and Thalassiphora delicata. The presence of these, and other lower latitude species confirms that warmer water conditions persisted during the middle to early late Eocene in the vicinity of Site 1053. Eighteen new taxa are described, of which two formally: Charlesdowniea proserpina sp. nov. and Oligosphaeridium anapetum sp. nov. (van Mourik et al., in press)