Figure F24. Digital photograph of the record of the OligoceneMiocene transition and Mi-1 glacial step at ODP Site 1218. Lithology and magnetic susceptibility records show the distinct cyclicity in carbonate content and physical properties observed around the O/M boundary. Together with unambiguous magnetostratigraphy and biostratigraphy, the cycle record contributes to the first high-resolution astronomical-calibrated chronology for the O/M boundary in the Pacific. Bioevents such as the first and last appearance datums of the clacareous nannofossil, Sphenolithus delphix, and the appearance datum of the foraminifer Paragloboroatlia kugleri are identical within current resolution to these same events in the Atlantic Ocean. Hence, we have no doubt that the Site 1218 record will become a standard reference section for the OligoceneMiocene interval in the Pacific that can be correlated precisely to Atlantic sites that typically lack unambiguous magnetochronologies.
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