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Eocene clocks agree: Coeval 40Ar/39Ar, U-Pb, and astronomical ages from the Green River Formation

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Smith, M Elliot, Chamberlain, K R, Singer, Bradley S, and Carroll, Alan R, Eocene clocks agree: Coeval 40Ar/39Ar, U-Pb, and astronomical ages from the Green River Formation: .

Summary

U-Pb ages of zircon from the Firehole and Analcite ash beds in the Eocene Green River Formation (Wyoming, United States) are indistinguishable from 40Ar/39Ar ages of sanidine after adjusting the latter to the astronomically calibrated age of 28.201 Ma for the Fish Canyon sanidine standard. Six of nine zircon analyses from the Firehole ash yield concordant ages in an overlapping cluster and give a weighted mean 238U-206Pb age of 51.66 {+/-} 0.20 Ma (full external 2{sigma} uncertainty), indistinguishable from the recalibrated 40Ar/39Ar age of 51.40 {+/-} 0.25 Ma (full external 2{sigma} uncertainty), which is adjusted to eliminate samples with low radiogenic 40Ar*. Significant 238U-206Pb age scatter likely reflects some combination of [...]

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From Source - Mendeley RIS Export <br> On - Wed Sep 19 08:08:31 MDT 2012

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Title Citation Eocene clocks agree: Coeval 40Ar/39Ar, U-Pb, and astronomical ages from the Green River Formation

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