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Magnetostratigraphy of the Ludlow Member of the Fort Union Formation (lower Paleocene) in the Williston Basin, North Dakota

Daniel J. Peppe, D. A. D. Evans and A. V. Smirnov
Magnetostratigraphy of the Ludlow Member of the Fort Union Formation (lower Paleocene) in the Williston Basin, North Dakota
Geological Society of America Bulletin (January 2009) 121 (1-2): 65-79

Abstract

To determine the geomagnetic polarity stratigraphy and the duration and age of the Ludlow Member of the Fort Union Formation (Lower Paleocene), we constructed a 325 m composite lithostratigraphic section of the Upper Cretaceous Hell Creek Formation and the Lower Paleocene Ludlow and Tongue River Members of the Fort Union Formation in the Little Missouri River valley of North Dakota, USA. We analyzed paleomagnetic samples from nine of the logged sections. The principal magnetic carrier in the Ludlow Member sediments is likely titanomaghemite, as indicated by predominantly irreversible thermomagnetic curves measured from sandstone, siltstone, and carbonaceous shale samples. The analyzed paleomagnetic samples document a series of polarity zones that can be correlated from C29n to C27r on the geomagnetic polarity time scale (GPTS). We infer that the magnetization of the samples is primary because the characteristic directions are consistent with those of the Paleocene of North America, and the reversal stratigraphy from this section corresponds to the GPTS with reasonable sediment accumulation rates. By extrapolating the measured sediment accumulation rate from the Cretaceous-Tertiary (K-T) boundary to the top of C28n and then to the top of the Ludlow Member, we estimate the duration of the member to range from 2.31 to 2.61 m.y. This is the first estimate for the duration and age of the Ludlow Member, and it can be used as an important tool for interpreting rates of biotic recovery after the K-T extinction.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 121
Serial Issue: 1-2
Title: Magnetostratigraphy of the Ludlow Member of the Fort Union Formation (lower Paleocene) in the Williston Basin, North Dakota
Affiliation: Yale University, Department of Geology and Geophysics, New Haven, CT, United States
Pages: 65-79
Published: 200901
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 70
Accession Number: 2009-017704
Categories: Stratigraphy
Document Type: Serial
Bibliographic Level: Analytic
Annotation: With GSA Data Repository Item 2008172
Illustration Description: illus. incl. sects., 2 tables, geol. sketch map
N46°00'00" - N47°30'00", W104°00'00" - W103°00'00"
Secondary Affiliation: Michigan Technological University, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 200911
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