| Pleistocene calcareous nannofossils from 16 Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) holes (Holes 502, 504, 519A, 593, 607, 644A, 647B, 677A, 704A, 822A, 834A, 848D, 897A, 897C, 898A, and 900A) were investigated to refine Pleistocene nannofossil biostratigraphy and to correlate paleoclimate changes with nannofossil abundance variations. The objectives of this study were (1) to perform a high-resolution Pleistocene nannofossil biostratigraphic study of material from ODP Leg 149; (2) to clarify the species concept of R. asanoi and to find a more precise and reliable way to utilize its evolutionary biostratigraphic datums through ultrastructural and biometric analyses of Pleistocene Reticulofenestra; and (3) to demonstrate the potential of using nannofossil abundance variation patterns as paleoclimatic indicators. The results of these investigations are summarized as follows.; (1) The high-resolution Pleistocene nannofossil biostratigraphic results of ODP Leg 149 Holes 897C and 900A agree rather well with complementary paleomagnetic analysis of the same material. As a result, the combination of nannofossil biostratigraphic and paleomagnetic studies provides important information for determining the history of turbidite sedimentation in the Iberia Abyssal Plain.; (2) The mean size of R. asanoi increases globally through geological time as well as geographically from low to middle and high latitudes within the same geological interval. Three evolutionary stages (1, 2, and 3) of the R. asanoi lineage were recognized through biometric study. The boundaries between these stages and at the top of 3 (R. asanoi events A, B, and C) provide three nannofossil events or datums that can be used to establish a high-resolution Pleistocene nannofossil biostratigraphy.; (3) The abundance variations of Coccolithus pelagicus, Calcidiscus leptopora, Helicosphaera spp., small Gephyrocapsa ({dollar}<2.5 mu{dollar}m), large Gephyrocapsa ({dollar}>2.5mu{dollar}m), and total nannofossil abundances in Holes 607 and 647B provide further evidence that nannofossil abundance variation patterns can be used to indicate Pleistocene paleoclimatic change or glacial-interglacial events. The accuracy of this kind of application, however, depends on thorough understanding of the samples' geographic and oceanographic setting.; In addition to the above, a nannofossil biostratigraphic study was conducted on the single Eocene section cored during ODP Leg 149. This initial investigation will be complemented by future work on three similar sections drilled during a follow-up cruise to the Iberia Abyssal Plain (ODP Leg 173). This subsequent study, conducted by departmental colleagues, will provide a detailed history of early Cenozoic turbidite sedimentation in the study area. |
