An examination of the calcareous nannoplankton and planktonic foraminifera of the lectostratotype Castle Hayne Formation, New Hanover County, North Carolina, has shown that it is of late middle Eocene (latest Lutetian or earliest Bartonian) age (upper zone NP16 to lower NP17 and P12–13, respectively), rather than latest Eocene (Zone NP19–20) as has been reported recently. Dinoflagellate biostratigraphy supports this age assignment.

A Rb-Sr glauconite isochron date of 34.8 ± 1 Ma reported from the lectostratotype in support of an age estimate of about 33 Ma for the Eocene-Oligocene boundary is shown to be irrelevant to the boundary age problem, anomalously young, and, indeed, about 8 to 10 rn.y. younger than the age estimated on the basis of magnetobiochronology.

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