An apparently complete 150-m Oligocene sequence of pelagic sediment at equatorial Pacific Deep Sea Drilling Project Site 77B has been analyzed for stable-isotope and quantitative planktonic foraminiferal studies. Lower abundance of inferred warm-water species and enrichment of 18O and 12C in foraminiferal tests during the interval 29 to 32 m.y. ago suggest cooler climate, lowered sea level, and significant volume of continental ice compared to earlier and later times in the Oligocene.

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