Several calcareous nannofossil zonal schemes have been proposed for the subdivision of Cenozoic strata (e.g., Martini, 1971; Okada and Bukry, 1980). We chose the calcareous nannofossil zonal scheme of Bukry (1973, 1975) and Okada and Bukry (1980) to subdivide the Neogene and Quaternary sections of Holes 998A, 999A, and 1000A because this zonation was established largely on the basis of Caribbean sequences. Studies by Raffi and Flores (1995), Takayama et al. (1995), and Backman and Raffi (1997) of continuous sections in the eastern equatorial Pacific (ODP Leg 138), the Ontong Java Plateau (ODP Leg 130), and the Ceara Rise in the equatorial Atlantic (ODP Leg 154), respectively, have provided additional datums. The ages of most datums of Bukry (1973, 1975) and Okada and Bukry (1980) and other useful biohorizons were estimated using an orbitally tuned time scale (Backman and Raffi, 1997).
In this study, the ages of nannofossil datums and bioevents were taken from Raffi and Flores (1995) for the Miocene to lower Pliocene and Takayama et al. (1995) for the upper Pliocene and Pleistocene (Table 2).