(Table 1) Oxygen and carbon isotopic values for mixed species of Cibicidoides at DSDP Hole 85-574

Oxygen and carbon isotopic data from mixed species of the benthic foraminifer Cibicidoides at Site 574 in the equatorial Pacific are compared with benthic foraminiferal isotopic data from equatorial Pacific Site 77 (Keigwin and Keller, 1984) and western North Atlantic Site 563 (Miller and Fairbanks, 1983, in press). Cibicidoides within the age range of about 33 to 35 Ma (within the early Oligocene) at the Pacific sites were lower in d13C than those of the same age from the North Atlantic site. For those from about 26 to 33 Ma (late early to late Oligocene), the equatorial Pacific and western North Atlantic d13C values were similar, whereas for those from about 26 to 12 Ma (latest Oligocene to Miocene) (see Miller and Fairbanks, 1983), Pacific values were lower. We suggest that this reflects bottom-water production analogous to modern North Atlantic Deep Water (NADW) in the early Oligocene and latest Oligocene to Miocene and reduced production of "NADW" in the late early to late Oligocene. High d18O values (approximately 2.0 per mil) were recorded at Site 574 for Cibicidoides at 36 Ma (earliest Oligocene); high, oscillating d18O values occurred from 30 to 29 Ma (near the early/late Oligocene boundary). These intervals of high d18O values apparently represent either bottom waters colder than at present or the presence of significant continental ice sheets. We suggest that major periods of continental glaciation occurred at approximately 36 and from 29 to 30 Ma