Quick
Search: 		  
advanced search
 GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help 
Geology Don't get GSW? Talk to your librarian.
JOURNAL HOME HELP CONTACT PUBLISHER SUBSCRIBE ARCHIVE SEARCH TABLE OF CONTENTS
Geology; May 2006; v. 34; no. 5; p. 393-396; DOI: 10.1130/G22265.1
© 2006 Geological Society of America
This Article
Right arrow Figures Only
Right arrow Full Text
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via ISI Web of Science (7)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Smith, M. E.
Right arrow Articles by Fournelle, J. H.
Right arrow Search for Related Content
GeoRef
Right arrow GeoRef Citation

High-resolution calibration of Eocene strata: 40Ar/39Ar geochronology of biotite in the Green River Formation

M. Elliot Smith*,1, Brad S. Singer1, Alan R. Carroll1 and John H. Fournelle1

1 University of Wisconsin-Madison, Department of Geology and Geophysics, 1215 W. Dayton St., Madison, Wisconsin 53706, USA

The Sixth tuff of the Wilkins Peak Member of the Green River Formation is an important potential calibration point for magnetic stratigraphy, mammalian evolution, and lacustrine processes. However, two recent 40Ar/39Ar ages based on laser fusion of biotite from this important bed are not in agreement with one other. Most large, euhedral biotite from the basal 1 cm give concordant age spectra when incrementally heated. However, some crystals yield discordant age spectra and have plateau and integrated ages that are scattered toward both older and younger apparent ages. Electron-probe microanalysis indicates that intergrown alteration phases occur in a small fraction of Sixth tuff biotite crystals, and likely contributed to open-system processes that led to the observed discordance and age scatter. A new age of 49.62 ± 0.10 Ma is obtained from 22 concordant incremental-heating experiments. This age agrees with a new 49.78 ± 0.08 Ma age for the sanidine from the Layered tuff, which is stratigraphically 24 m below the Sixth tuff.

Key Words: 40Ar-39Ar • Green River Formation • biotite • sanidine • geomagnetic polarity time scale




This article has been cited by other articles:


Home page
 Geol Soc Am BullHome page
S. Giorgis, W. McClelland, A. Fayon, B. S. Singer, and B. Tikoff
Timing of deformation and exhumation in the western Idaho shear zone, McCall, Idaho
GSA Bulletin, September 1, 2008; 120(9-10): 1119 - 1133.
[Abstract] [Full Text] [PDF]

Home page
 GeologyHome page
S. R. Meyers
Resolving Milankovitchian controversies: The Triassic Latemar Limestone and the Eocene Green River Formation
Geology, April 1, 2008; 36(4): 319 - 322.
[Abstract] [Full Text] [PDF]

Home page
 Geol Soc Am BullHome page
M. E. Smith, A. R. Carroll, and B. S. Singer
Synoptic reconstruction of a major ancient lake system: Eocene Green River Formation, western United States
GSA Bulletin, January 1, 2008; 120(1-2): 54 - 84.
[Abstract] [Full Text] [PDF]


JOURNAL HOME HELP CONTACT PUBLISHER SUBSCRIBE ARCHIVE SEARCH TABLE OF CONTENTS
Copyright © 2008 by Geological Society of America