Cenozoic silicoflagellates and ebridians from ODP Leg 113

Silicoflagellates are present at ODP 113 Sites 689, 690, 693, 695, 696, and 697. These are generally Neogene in age except for Oligocene and Eocene silicoflagellates and ebridians at Sites 689, 690, and 693, and Lower Cretaceous (Albian) silicoflagellates at Site 693 (the latter are described in McCartney, et al., this volume). The uppermost Miocenelowermost Pliocene of most sites contains an interesting assemblage of Distephanus speculum speculum that lack apical rings (the "pseudofibula plexus"). These co-occur with the youngest ice-rafted sediments deposited during the late Miocene-early Pliocene West Antarctic glaciations and are discussed in detail to show the variability within this group. We believe that these variations resulted from environmental stress, the precise nature of which is still undetermined. The "pseudofibulid" condition has developed at several different times during the Cenozoic within the Distephanus speculum lineage to produce such ecophenotypes. One new form from the "pseudofibula plexus," D. s. speculum f. pseudopentagonus, is described.