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Abstract:

The stable oxygen isotope record for the Cenozoic is characterized by a series of large third-order steps of +1 per mil superimposed on a long-term second-order trend. This second-order trend accounts for a δ18O change of nearly +4 per mil from the early Eocene into the Neogene. The second- and third-order changes in the δ18O signal are driven primarily by a combination of glacio-eustatic sea-level and ocean paleotemperature changes. These changes are global responses to evolving circulation and climate patterns. Timing of the δ18O events is in good agreement with the seismically defined changes in the coastal-onlap curve (Vail and others, 1977). Agreement in the timing of events supports a common mechanism, perhaps that glaciation is apparent throughout much of the record and certainly intensified beginning in the Neogene. Agreement is not good between the magnitudes of apparent changes in sea level using the EXXON onlap record and oceanic δ18O events. Consideration of the δ18O, ice volume, and sea-level relationships during the Pleistocene suggests that sinusoidal eustatics, i.e., the rise and fall of sea level being equal, is not a good assumption at fourth- and fifth-order sea-level events. Although interpretation of the δ18O record is not without its assumptions and limitations, it offers an independent geochemical check on seismically defined changes in stratal patterns.

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