Leg 181 was the first ODP leg to drill the New Zealand margin. The margin had previously been drilled during two Deep Sea Drilling Project (DSDP) legs. During DSDP Leg 29, 10 sites around New Zealand and Australia were drilled. Sites 275, 276, and 277 were drilled on the southern edge of the Campbell Plateau. Oligocene and Eocene nannofossils were observed at Sites 276 and 277 (Edwards and Perch-Nielsen, 1975). At Site 277, a continuous upper Oligocene through Eocene sequence was recovered. Site 277 was reanalyzed to produce an integrated biostratigraphy (Hollis et al., 1997) between foraminifers, calcareous nannofossils, radiolarians, and palynomorphs. This analysis suggests that environmental deterioration in the southwest Pacific was episodic and began in the late Eocene to earliest Oligocene.
Eocene-Oligocene sections were recovered during DSDP Leg 90 at Sites 588C, 592, and 593, all located between Australia and New Zealand. Nannofossil biostratigraphy indicates a ~20-m.y. hiatus at Site 588C encompassing late Eocene-early Oligocene Zones NP17-NP23. Early Oligocene to early Miocene Zones NP22-NN2 encompassing ~16 m.y. are missing at Site 592. This early Oligocene to early Miocene hiatus is similar to that at Site 1123C. Biostratigraphic placement of the Eocene/Oligocene boundary could not be achieved at Site 593 because of volcanogenic input. No hiatus in the Oligocene to early Miocene was reported (Martini, 1986).