Accuracy and precision of the late eocene-early oligocene geomagnetic polarity time scale

Diana Sahy*, Joe Hiess, Anne U. Fischer, Daniel J. Condon, Dennis O. Terry, Hemmo A. Abels, Silja K. Hüsing, Klaudia F. Kuiper

*Corresponding author for this work

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An accurate and precise geomagnetic polarity time scale is crucial to the development of a chronologic framework in which to test paleoclimatic and paleoenvironmental interpretations of marine and terrestrial records of the Eocene-Oligocene transition (EOT). The magnetic polarity patterns of relatively continuous marine and terrestrial records of the EOT have been dated using both radioisotopic techniques and astronomical tuning, both of which can achieve a precision approaching ±30 k.y. for much of the Paleogene. However, the age of magnetic reversals between chrons C12n and C16n.2n has proved difficult to calibrate, with discrepancies of up to 250 k.y. between radio-isotopically dated and astronomically tuned marine successions, rising to 600 k.y. for comparisons with the 206Pb/238U-dated terrestrial record of the White River Group in North America. In this study, we reevaluate the magnetic polarity pattern of the Flagstaff Rim and Toadstool Geologic Park records of the White River Group (C12n-C16n.2n). Our interpretation of the Flagstaff Rim polarity record differs significantly from earlier studies, identifying a previously unreported normal polarity zone correlated to C15n, which eliminates discrepancies between the WRG and the 206Pb/238-dated marine record of the Rupelian Global Stratotype Section and Point in the Italian Umbria-Marche basin. However, residual discrepancies persist between U-Pb- dated and astronomically tuned records of the EOT even when stratigraphic and systematic uncertainties associated with each locality and dating method are taken into account, which suggests that the uncertainties associated with astronomically tuned records of the EOT may have been underestimated.

Original languageEnglish
Pages (from-to)373-388
Number of pages16
JournalBulletin of the Geological Society of America
Issue number1-2
Early online date13 Jun 2019
Publication statusPublished - 1 Jan 2020


This work was funded through the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement no. [215458]. The authors thank Brent Breithaupt (Bureau of Land Management, Cheyenne, Wyoming), Carla Loop, and Barbara Beasley (Nebraska National Forest, U.S. Forest Service) for providing permits to collect samples at Flagstaff Rim and TGP, Bill Lukens for help during field work, and the staff of the Fort Hoofddijk Paleomagnetic Laboratory for access to their facilities and assistance with paleomagnetic measurements. The authors thank Courtney Sprain and an anonymous reviewer for their constructive comments.

FundersFunder number
Brent Breithaupt
Carla Loop, and Barbara Beasley
Nebraska National Forest
U.S. Forest Service
U.S. Bureau of Land Management
Seventh Framework Programme215458
Seventh Framework Programme


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