During Ocean Drilling Program (ODP) Leg 149, five sites were drilled on the Iberia Abyssal Plain (Fig. 1). The principal objective was to sample the acoustic basement within the ocean/continent transition in order to establish its petrologic and physical nature. Another important goal was to discover the history of late Cenozoic turbidite sedimentation and determine to what extent the age and frequency of turbidites relate to past climatic change.
Of the eight holes drilled at five sites during Leg 149, Holes 897 A, 897C, 898A, 899A, and 900A yielded Pliocene-Pleistocene sediments that consist mainly of terrigenous turbidites, hemipelagites, and pelagites. The hemipelagic and pelagic layers situated at the top of most turbidite sequences provided abundant and well-preserved Pliocene-Pleistocene nannofossil assemblages. This study describes primarily the calcareous nannofossil assemblages and discusses the Pliocene-Pleistocene nannofossil biostratigraphy of Leg 149 (Table 1, Fig. 1).
In this study, in addition to most of the Pleistocene zonal boundaries of Gartner (1977) and the Pliocene standard zonal boundaries of Martini (1971), several other nannofossil events proposed by Rio et al. (1990a, 1990b), Sato and Takayama (1992), and Raffi et al. (1993) were recognized. This enabled us to provide a high-resolution nannofossil biostratigraphy, and thus to contribute essential age assignments to fulfill the second objective of this leg. In addition, this study provided important information for locating paleomagnetic events (see Zhao et al., this volume).