A combination of the nannofossil zonal schemes of Martini (1971), Martini and Muller (1986), and Okada and Bukry (1980) is used for Leg 149 sediments (Table 1). Most zonal markers of Martini (1971) and Okada and Bukry (1980) can be recognized, although some zonal boundaries cannot be located owing to the absence or rare occurrence of some zonal markers.
The Paleocene/Eocene boundary is defined in this study by the first occurrence (FO) of Tribrachiatus bramlettei, which marks the NP9/10 boundary of Martini's (1971) zonal scheme. Discoaster diastypus, used by Okada and Bukry (1980) to define this boundary, is not present in Leg 149 cores.
The Eocene/Oligocene boundary is determined in this study by the extinction of rosette-shaped discoasters such as Discoaster barbadiensis and Discoaster saipanensis. The boundary so determined could be slightly higher than its true position owing to problems from reworking.
The lower/middle Eocene boundary (NP13/14) is defined by the FO of Discoaster sublodoensis. The middle/upper Eocene boundary (NP17/18) is more difficult to determine, because the zonal markers (Chiasmolithus oamaruensis and Isthmolithus recurvus) are generally rare.
Some difficulties exist for the middle Eocene zonation (Zones NP14 to NP17, or CP12 to CP14). According to Martini (1971), Zone NP15 (Nannotetrina fulgens Zone) is defined as the interval from the FO of N. fulgens to the last occurrence (LO) of Rhabdosphaera gladius. However, R. gladius is very rare in the sediments retrieved on Leg 149; only one specimen was found (Sample 149-900A-65R-2, 48-49 cm; Pl. 2, Fig. 20). Therefore, R. gladius cannot be used here as a zonal marker. Bukry (1973) used the first appearance of Reticulofenestra umbilicus and Discoaster bifax to mark the top of Zone NP15. Although there is some controversy about using the FO of Reticulofenestra umbilicus to mark the boundary between Zones NP15/16 (Martini and Muller, 1986), I still use specimens greater than 14 µm to define the NP15/16 boundary as suggested by Wise and Mostajo(1983).