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

Research Article| June 01, 2010 Eocene clocks agree: Coeval 40Ar/39Ar, U-Pb, and astronomical ages from the Green River Formation M. Elliot Smith; M. Elliot Smith * 1Department of Geology, Sonoma State University, 1801 E. Cotati Avenue, Rohnert Park, California 94928, USA *E-mail: msmith@sonoma.edu. Search for other works by this author on: GSW Google Scholar K.R. Chamberlain; K.R. Chamberlain 2Department of Geology and Geophysics, University of Wyoming, 1000 University Avenue, Laramie, Wyoming 82071, USA Search for other works by this author on: GSW Google Scholar B.S. Singer; B.S. Singer 3Department of Geoscience, University of Wisconsin, 1215 W. Dayton Street, Madison, Wisconsin 53706, USA Search for other works by this author on: GSW Google Scholar A.R. Carroll A.R. Carroll 3Department of Geoscience, University of Wisconsin, 1215 W. Dayton Street, Madison, Wisconsin 53706, USA Search for other works by this author on: GSW Google Scholar Author and Article Information M. Elliot Smith * 1Department of Geology, Sonoma State University, 1801 E. Cotati Avenue, Rohnert Park, California 94928, USA K.R. Chamberlain 2Department of Geology and Geophysics, University of Wyoming, 1000 University Avenue, Laramie, Wyoming 82071, USA B.S. Singer 3Department of Geoscience, University of Wisconsin, 1215 W. Dayton Street, Madison, Wisconsin 53706, USA A.R. Carroll 3Department of Geoscience, University of Wisconsin, 1215 W. Dayton Street, Madison, Wisconsin 53706, USA *E-mail: msmith@sonoma.edu. Publisher: Geological Society of America Received: 22 Aug 2009 Revision Received: 12 Jan 2010 Accepted: 13 Jan 2010 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2010 Geological Society of America Geology (2010) 38 (6): 527–530. https://doi.org/10.1130/G30630.1 Article history Received: 22 Aug 2009 Revision Received: 12 Jan 2010 Accepted: 13 Jan 2010 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation M. Elliot Smith, K.R. Chamberlain, B.S. Singer, A.R. Carroll; Eocene clocks agree: Coeval 40Ar/39Ar, U-Pb, and astronomical ages from the Green River Formation. Geology 2010;; 38 (6): 527–530. doi: https://doi.org/10.1130/G30630.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract 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 2σ uncertainty), indistinguishable from the recalibrated 40Ar/39Ar age of 51.40 ± 0.25 Ma (full external 2σ uncertainty), which is adjusted to eliminate samples with low radiogenic 40Ar*. Significant 238U-206Pb age scatter likely reflects some combination of minor inheritance, Pb loss, and possibly magma chamber residence. Seven of eight analyses of Analcite ash zircon yield a weighted mean 238U-206Pb age of 49.23 ± 0.13 Ma (full external 2σ uncertainty), whereas the sanidine 40Ar/39Ar age is 49.24 ± 0.18 Ma (full external 2σ uncertainty). Calibrating Green River Formation 40Ar/39Ar ages to the 28.201 Ma age for Fish Canyon sanidine permits the first direct comparison of specific Green River Formation strata to the astronomical solution for Early Eocene insolation. This comparison supports the hypothesis that periods of fluvial deposition coincided with minima in long and short eccentricity, and that periods of lake expansion and evaporite deposition correspond to eccentricity maxima. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.