The Eocene/Oligocene boundary has attracted the attention of many researchers from the viewpoint that it may represent a climatic threshold from the early Paleogene greenhouse earth to the late Neogene icehouse environment. Recently, Ocean Drilling Program (ODP) research cruises in the Southern Ocean have collected and documented microfossil faunal and floral changes in Eocene–Oligocene sediment sequences and correlated these with magnetostratigraphy. Eocene–Oligocene radiolarian faunal change in this region has been discussed by Caulet (1991), Takemura (1992), and Takemura and Ling (1997).
Many Paleogene radiolarians were reported during the Deep Sea Drilling Project (DSDP) from the equatorial Pacific. Riedel and Sanfilippo (1971), Moore (1971), and Johnson (1976) studied late Paleogene radiolarians from the Central Pacific in samples collected during DSDP Legs 7, 8, and 33, respectively. Goll (1972), Dinkelman (1973), and Nigrini (1985) examined Eocene–Quaternary radiolarians in samples collected during DSDP Legs 9, 16, and 85, respectively, from the eastern equatorial Pacific. The many common radiolarian events found among these sites have contributed to establishing a standard low-latitude radiolarian biostratigraphy (Sanfilippo and Riedel in Saunders et al., 1985; Sanfilippo et al., 1985; Sanfilippo and Nigrini, 1998). The time resolution of these events, however, was still uncertain because no chronologic control such as correlative magnetostratigraphy existed in the previous sequences. This research is the first attempt to examine late Paleogene radiolarian faunal change and tie it to a chronologic framework for the Central Pacific region.
Holes 1218A, 1219A, and 1220A were cored during ODP Leg 199 in the Central Pacific (Fig. F1). Radiolarian counts, 77 radiolarian events, and ages are presented here.