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Calibration of the latest Eocene-Oligocene geomagnetic polarity time scale using 40 Ar/ 39 Ar dated ignimbrites

W. C. McIntosh·J. W. Geissman·C.E. Chapin·Michael J. Kunk·Christopher D. Henry
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Abstract

A discontinuous record of late Eocene-Oligocene geomagnetic polarity has been determined using high-precision (±<0.15 m.y.) 40 Ar/ 39 Ar sanidine dating and a paleomagnetic study of 37-27 Ma ignimbrites in New Mexico, Colorado, and Texas. This record provides age control for several geomagnetic polarity reversals that occurred during three periods of intense ignimbrite volcanism: 36.8-33.5 Ma, 32.7-31.4 Ma, 29.1-26.9 Ma. The relative timing of these polarity reversals permits four possible correlations with the geomagnetic polarity time scale (GPTS). The preferred correlation yields calibration ages for Chron C10R (28.0-29.0 Ma) and Chron C13R (34.4-33.1 Ma) that indicate an Eocene-Oligocene boundary age near 33.4 Ma, some 0.3-0.6 m.y. younger than boundary ages indicated by other recently proposed GPTS calibrations based on terrestrial and marine sedimentary sequences.

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W. C. McIntosh, J. W. Geissman, C.E. Chapin, Michael J. Kunk, Christopher D. Henry. 1992. Calibration of the latest Eocene-Oligocene geomagnetic polarity time scale using 40 Ar/ 39 Ar dated ignimbrites. https://doi.org/10.1130/0091-7613(1992)020%3C0459%3Acotleo%3E2.3.co%3B2

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