LATE PALEOGENE-EARLY NEOGENE DINOFLAGELLATE CYST BIOSTRATIGRAPHY IN ODP HOLE 959A, WEST AFRICA

Dinoflagellates are one of the most important unicellular phytoplankton groups that are mainly marine but can also be found in fresh water. Fossil dinoflagellate cysts have been used for Late Paleogene-Early Neogene biostratigraphic correlation in many parts of the world and they have proved extremely useful in age dating. Palynological analysis of 30 samples yields five dinoflagellate cyst zones (zone 1-zone 5) for the Late Eocene? to Early Miocene interval of ODP Hole 959A. These zones are defined by using the first occurrence or last occurrence of some marker bioevents and calibrated with published calcareous nannoplankton data. Zone 1 has a Late Eocene?-Early Oligocene age and is characterized by the presence of Hystrichokolpoma pusillum, Homotryblium vallum, and Schematophora speciosa. A Late Oligocene age is assigned to zone 2, which consists of Kallosphaeridium capulatum Membranophoridium aspinatum, and Tuberculodinium vancampoae. Zone 3 spans the Oligocene-Miocene boundary, and contains Ectosphaeropsis burdigalensis and Membranilarnacia? picena. Zone 4 has an earliest Early Miocene to latest Early Miocene age and mainly includes the following taxa: Exochosphaeridium insigne, Operculodinium piaseckii, and Pyxidinopsis fairhavenensis. Finally, zone 5 is latest Early Miocene and is characterized by Chiropteridium galea and Cribroperidinium spp. One notable outcome of this study is that the stratigraphic ranges of some of these taxa are different from those recorded in mid and high latitudes. This disparity may be due to the deep offshore depositional environment of the ODP Hole 959A sequence, or latitudinal differences.