Abstract The well-calibrated mid- to late Eocene sediment record of ODP Leg 171B (Site 1053A, Blake Nose) allows a detailed stratigraphic and palaeoenvironmental analysis of the dinoflagellate cyst (dinocyst) content. 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 milieu, with possibly some shallowing of water depth towards the top of the section. This trend is also indicated by a corresponding increase of inner neritic dinocysts. The close agreement in the abundance peaks of inner neritic dinocysts and terrestrial palynomorphs indicats 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 late Eocene time, are Diphyes colligerum and Thalassiphora delicata . The presence of these, and other lower-latitude species, confirms that warmer-water conditions persisted during mid- to early late Eocene time in the vicinity of Site 1053. Eighteen new taxa are described, two of them formally: Charlesdowniea proserpina sp. nov. and Oligosphaeridium anapetum sp. nov.