High-precision 40Ar/39Ar age spectrum dating of sanidine from the Middle Pennsylvanian Fire Clay tonstein of the Appalachian basin

GSA Special Papers
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Abstract

40Ar/39Ar plateau age spectra of seven sanidine samples from the Fire Clay tonstein (Middle Pennsylvanian), collected along a 300-km traverse in the Appalachian basin, range from 310.3 to 311.4 Ma. All plateau ages agree, within the limits of analytical precision, with their respective total gas ages. This agreement, together with the reproducibility between samples, suggests the analyzed samples did not contain any significant contaminant feldspar. The mean of these seven plateau ages, 310.9 ± 0.8 Ma, is interpreted to represent a precise numerical estimate of time of eruption and deposition of this tonstein and the coal bed in which it is found. The lack of any discernible difference between the age of two samples of the Fire Clay tonstein collected from east of the Pine Mountain thrust fault, along with the age of five samples from west of this fault, suggests that the Fire Clay tonstein has been reliably correlated with a tonstein on the Cumberland overthrust sheet. This correlation, together with the age data presented in this paper, indicates that the Pine Mountain thrust fault must be younger than the 310.9-Ma age obtained for the Fire Clay tonstein.

The Fire Clay tonstein is biostratigraphically correlated with the Trace Creek Shale Member of the Atoka Formation in the Midcontinent of North America and with a position near the Westphalian B-C boundary in Western Europe. Our age of 310.9 ± 0.8 Ma for the Westphalian B-C boundary represents a well-constrained point, useful for the numerical refinement of the geologic time scale.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title High-precision 40Ar/39Ar age spectrum dating of sanidine from the Middle Pennsylvanian Fire Clay tonstein of the Appalachian basin
Series title GSA Special Papers
DOI 10.1130/SPE294-p105
Volume 294
Year Published 1994
Language English
Publisher GSA
Contributing office(s) Eastern Geology and Paleoclimate Science Center
Description 9 p.
First page 105
Last page 112
Country United States
State Kentucky, West Virginia
Other Geospatial Middle Pennsylvanian Fire Clay tonstein of the Appalachian basin
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