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Precise age of C33N-C32R magnetic-polarity reversal, San Juan Basin, New Mexico and Colorado

Mesozoic geology and paleontology of the Four Corners Region: New Mexico Geological Society, Forty-eighth Annual Field Conference, October 1-4, 1997

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Abstract

Polarity-chron boundary C33n-C32r has been identified in the Upper Cretaceous continental Farmington Sandstone Member of the Kirtland Shale in Hunter Wash in the southwest part of the San Juan Basin of New Mexico, and in the marine Lewis Shale at Chimney Rock, Colorado, in the northeast part of the basin. Single- and multiple-crystal laser fusion 40Ar/39Ar ages of sanidine crystals from volcanic ash beds bracketing the C33n-C32r polarity reversal at Hunter Wash establish its age as 73.50 ± 0.18 Ma. The reversal apparently occurs within the Baculites compressus Western Interior ammonite zone and within the Edmontonian land-vertebrate faunal zone. An 8 Ma hiatus separates Cretaceous and Tertiary rocks in the southern San Juan Basin. These findings provide a precise new interpolated Late Cretaceous tie point for geologic time scales, provide the basis for the direct correlation of Western Interior ammonite zones to European open-ocean faunal zones, and establish the first direct tie between continental and marine fossil zones within the Western Interior of North America.

Geospatial Extents

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Precise age of C33N-C32R magnetic-polarity reversal, San Juan Basin, New Mexico and Colorado
Series title:
Mesozoic geology and paleontology of the Four Corners Region: New Mexico Geological Society, Forty-eighth Annual Field Conference, October 1-4, 1997
Volume
48
Year Published:
1997
Language:
English
Publisher:
New Mexico Geological Society
Publisher location:
Socorro, NM
Description:
9 p.
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
First page:
239
Last page:
247
Number of Pages:
9
Country:
United States
State:
Colorado;New Mexico
Other Geospatial:
San Juan Basin