Eocene calibration of geomagnetic polarity time scale reevaluated: Evidence from the Green River Formation of Wyoming
- 1Department of Earth and Environmental Sciences and Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York 10964, USA
Abstract
We reevaluate the Eocene geomagnetic polarity time scale on the basis of single-crystal 40Ar/39Ar ages for air-fall tuffs from the Wilkins Peak Member of the Green River Formation of Wyoming. Tuff 6 is dated as 49.1 ± 0.2 Ma, and tuff 3 is dated as 50.4 ± 0.3 Ma (maximum estimate). When combined with published magnetostratigraphic constraints, these age determinations suggest that the currently accepted age of chron C22r is 1.5–2.5 m.y. too old, which supports a significantly longer duration for the early Eocene, for the early Eocene climatic optimum, and the Wasatchian North American Land Mammal Age.
Footnotes
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↵GSA Data Repository item 2004018, analytical methods and details of stratigraphy, Figure DR1 (cumulative age-probability curves), Table DR1 (Ar isotope data), Table DR2 (inverse isochron ages), and Table DR3 (GPTS calibration data), is available online at www.geosociety.org/pubs/ft2004.htm, or on request from editinggeosociety.org or Documents Secretary, GSA, P.O. Box 9140, Boulder, CO 80301-9140, USA.
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- Accepted October 21, 2003.
- Received August 4, 2003.
- Revision received October 17, 2003.
- Geological Society of America
