Piston core S68-24, collected in the central equatorial Pacific, contains a continuous sedimentary record that ranges from early middle Miocene to latest Oligocene and from earliest Oligocene to latest Eocene time. Paleomagnetic and radiolarian events observed in this core allow the extension of a proposed magnetic polarity time scale into Epoch 23 (ca. 27 m.y. B.P., latest Oligocene time). Correlation of this present data with planktonic foraminiferal and calcareous nannofossil events, primarily from Deep Sea Drilling Project results, shows that this time scale corroborates previous radiochronologies and biochronologies of deposits of early Neogene–latest Paleogene time. The Neogene-Paleogene boundary occurs within polarity Epoch 21 and the Lychnocanoma elongata Zone at about 23 to 24 m.y. B.P. The Oligocene-Eocene boundary (ca. 37.5 m.y. B.P.) falls within a long sequence of reversed magnetic polarities that may correlate with a similar sequence predicted between anomalies 12 and 13 by the sea-floor–spreading time scale.

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