Comparisons of age determinations and correlations derived from calcareous plankton with those derived from benthic foraminifers in a number of sections in California show significant overlap in time of the Ynezian through the Ulatisian Stages. Thus interbasin time correlations deduced from these stage assignments must be treated with caution.
Calcareous plankton occasionally associated with benthic foraminifers diagnostic of the Narizian through the Zemorrian Stages indicate that the Narizian-Refugian boundary is within the upper Eocene of international usage and that the Refugian is entirely upper Eocene. Overlap of the Narizian and the Refugian appears to be minimal. The Zemorrian correlates, mostly, with the Oligocene, although the upper limit of the Zemorrian might be in the lower Miocene.
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USGS Numbered Series
Age and correlation of California Paleogene benthic foraminiferal stages