CONCLUSIONS

1. The dinoflagellate biostratigraphic results of the present study are in agreement with the ship-based biostratigraphy, based on foraminifers and calcareous nannofossils, assigning an Oligocene age to Sections 184-1148B-56X-1 through 39X-CC and 184-1148A-76X-6 through 52X-CC and an early Miocene age to Sections 184-1148A-48X-2 through 40X-1. A barren interval above 473.1 mbsf indicates a great environmental shift during the transition from the latest Paleogene to earliest Neogene (Fig. F2). Some discrepancy exists among the data from dinoflagellate cysts, nannofossils, and foraminifers regarding the position of the boundary between early and late Oligocene.
2. In spite of the many factors that can influence the detailed character of dinoflagellate zones, our two assemblage zones and two subzones can be correlated, with various degrees of confidence, with coeval assemblage(s) or zone(s) from other regions on the basis of shared species. The most significant species include E. pectiniformis, D. ellipticum, M. aspinatum, and P. amoenum as key indicator species for an Oligocene age, and C. satchelliae, H. obscura, M. choanophorum, and M.? picena as key species indicating a Miocene age. These key species often are accompanied by other important species such as C. ancyreum, C. cantharellum, E. arcuata, H. plectilum, H. cinctum, P. laticinctum, and T. pelagica.