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Normal polarity magnetosubchrons in 24r and the age of the Paleocene-Eocene boundary

J. F. Lerbekmo, L. M. Heaman, H. Baadsgaard, Karlis Muehlenbachs, M. E. Evans and A. R. Sweet
Normal polarity magnetosubchrons in 24r and the age of the Paleocene-Eocene boundary
Canadian Journal of Earth Sciences = Revue Canadienne des Sciences de la Terre (July 2008) 45 (7): 781-793

Abstract

A late Paleocene to early Eocene sequence of flat-lying continental strata occurs in an area known as Obed Mountain, west-central Alberta. The upper 110 m consist of interbedded fluvial channel sandstones and overbank mudrocks containing five back swamp coal seams. Two coreholes, 3.5 km apart, that extend through the entire coal zone were sampled for magnetostratigraphy and (super 13) C isotope analysis. Bentonites in the No. 1 (lowest) and No. 5 coal seams and a tuff in the No. 3 coal seam were sampled for U-Pb and (or) Rb-Sr dating of zircon and biotite, respectively. Magnetostratigraphic analysis of 520 samples identified the younger part of chron 25r, the whole of chron 25n and the older half of chron 24r. We find six normal polarity subzones in this part of chron 24r, which we correlate to tiny wiggles 6 to11 in marine magnetic profiles. Carbon isotope analysis of 14 samples from two cores revealed a negative shift of about 2% peaking near the base of 24r.8r. We interpret this as the carbon isotope excursion (CIE), the base of which is now accepted as defining the Paleocene-Eocene boundary. The thickness of the CIE in the Obed Mountain section implies that it lasted between 210 000 and 254 000 years. Radiometric dates of 58.4+ or -0.2, 57.7+ or -0.3, and 56.9+ or -0.8 Ma are obtained for the No. 1, No. 3, and No. 5 coals, respectively. Combining these with magnetostratigraphy and cyclostratigraphy yields an age of 57.1+ or -0.1 Ma for the Paleocene-Eocene boundary.


ISSN: 0008-4077
EISSN: 1480-3313
Coden: CJESAP
Serial Title: Canadian Journal of Earth Sciences = Revue Canadienne des Sciences de la Terre
Serial Volume: 45
Serial Issue: 7
Title: Normal polarity magnetosubchrons in 24r and the age of the Paleocene-Eocene boundary
Affiliation: University of Alberta, Department of Earth and Atmospheric Sciences, Edmonton, AB, Canada
Pages: 781-793
Published: 200807
Text Language: English
Summary Language: French
Publisher: National Research Council of Canada, Ottawa, ON, Canada
References: 47
Accession Number: 2008-130472
Categories: StratigraphyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. strat. cols., 3 tables, sketch map
N53°19'60" - N54°00'00", W118°00'00" - W117°00'00"
Secondary Affiliation: Geological Survey of Canada, CAN, Canada
Country of Publication: Canada
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 200851
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