The proposed Eocene-Oligocene stratotype, SW Alabama: not ideal due to magnetostratigraphic inconsistencies ( USA).

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In the magnetic polarity time scale, the Eocene-Oligocene boundary is within a reversed polarity interval (Chron 13 R) with normal polarity intervals 500 000-750 000 years below and above the boundary. This sequence, however, is not observed at St. Stephens Quarry, where paleomagnetic samples for the entire uppermost Eocene-lowermost Oligocene record normal polarity or are magnetically unstable. The samples contain glauconite and abundant authigenic pyrite, and in places both minerals show considerable late-stage alteration to hematite. The authigenic hematite is present throughout the section and dominates the magnetization, obscuring primary magnetization polarity boundaries and preventing correlation with the standard polarity time scale. Since magnetic polarity data may provide globally synchronous correlations, we recommend that the magnetic characteristics be evaluated in the recognition of stratotype sections. Therefore, because of remagnetization, the St. Stephens Quarry section is not an ideal stratotype for th Eocene-Oligocene boundary.-from Authors

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