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

January 1, 1992

A discontinuous record of late Eocene-Oligocene geomagnetic polarity has been determined using high-precision (±<0.15 m.y.) 40Ar/39Ar 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.

Publication Year 1992
Title Calibration of the latest Eocene-Oligocene geomagnetic polarity time scale using 40 Ar/ 39 Ar dated ignimbrites
DOI 10.1130/0091-7613(1992)020<0459:COTLEO>2.3.CO;2
Authors W. C. McIntosh, J. W. Geissman, C.E. Chapin, Michael J. Kunk, Christopher D. Henry
Publication Type Article
Publication Subtype Journal Article
Series Title Geology
Index ID 70207641
Record Source USGS Publications Warehouse
USGS Organization Eastern Geology and Paleoclimate Science Center; Florence Bascom Geoscience Center