The Pliocene-Pleistocene calcareous nannofossils of Leg 149 are abundant and well preserved in most of the samples examined. Holes 897C and 898A yielded significant Pliocene-Pleistocene sediments, which provided a high-resolution nannofossil biostratigraphy essential for locating paleomagnetic polarity events and interpreting the age and frequency of turbidite sedimentation in the Iberia Abyssal Plain (as discussed by Zhao et al., this volume, and Milkert et al., this volume).
The Pleistocene nannofossil zonal scheme in this paper is a modification of the schemes proposed by Gartner (1977), Pujos (1985), Takayama and Sato (1987), Matsuoka and Okada (1989, 1990), Sato and Takayama (1992), and Wei (1993). The Pliocene/Pleistocene boundary was defined by the FO of Gephyrocapsa oceanica s.l. (>4 µm). The LO of Helicosphaera sellii and the LO of large Gephyrocapsa cannot be clearly distinguished in the Leg 149 sediments. The FO of Emiliania huxleyi, LO of Pseudoemiliania lacunosa, LO of Reticulofenestra asanoi, reoccurrence of Gephyrocapsa oceanica (>3 µm), and FO and LO of large Gephyrocapsa (>5.5 µm) are useful and reliable Pliocene-Pleistocene nannofossil events for subdividing Zone NN19 and thus improve considerably the resolution of the Pleistocene nannofossil biostratigraphy.
The standard zonation of Martini (1971) was followed in this study for the Pliocene biostratigraphy; the definition of Zone MNN19a by Rio et al. (1990a) was followed in the uppermost Pliocene. In the lower Pliocene Zones NN14 and NN15 were combined, as suggested by Raffi and Rio (1979) and Rio et al. (1990b); but the FO of Discoaster asymmetricus was replaced by the FO of Pseudoemiliania lacunosa. The lowermost Pliocene was not always recorded at these sites, and an unconformity may be suggested between the Miocene and the lower Pliocene sediments in Holes 897C, 899A, and 900A; a more evident break in the sedimentary record occurs in Hole 898A, where all the lower Pliocene and part of upper Pliocene are absent.
Pliocene-Pleistocene nannofossil events reveal that the sedimentation rates along the transition from the Iberian Peninsula to Iberia Abyssal Plain increase from the continental margin to the deep sea along with increasing of water depth.
Pliocene-Pleistocene nannofossil biostratigraphic results for Holes 897C and 900A coincide rather well with the magnetostratigraphy. The combination of nannofossil biostratigraphic and paleomagnetic studies can provide important information for fulfilling the second objective of this leg: to determine the history of turbidite sedimentation in the Iberia Abyssal Plain.