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The Pennsylvanian Fire Clay tonstein of the Appalachian basin—Its distribution, biostratigraphy, and mineralogy

By
Charles L. Rice
Charles L. Rice
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Harvey E. Belkin
Harvey E. Belkin
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Thomas W. Henry
Thomas W. Henry
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Robert E. Zartman
Robert E. Zartman
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Michael J. Kunk
Michael J. Kunk
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Published:
January 01, 1994

The Middle Pennsylvanian Fire Clay tonstein, mostly kaolinite and minor accessory minerals, is an altered and lithified volcanic ash preserved as a thin, isochronous layer associated with the Fire Clay coal bed. Seven samples of the tonstein, taken along a 300-km traverse of the central Appalachian basin, contain cogenetic phenocrysts and trapped silicate-melt inclusions of a rhyolitic magma. The phenocrysts include beta-form quartz, apatite, zircon, sanidine, pyroxene, amphibole, monazite, garnet, biotite, and various sulfides. An inherited component of the zircons (determined from U-Pb isotope analyses) provides evidence that the source of the Fire Clay ash was Middle Proterozoic (Grenvillian) continental crust inboard of the active North American margin. 40Ar/39Ar plateau ages of seven sanidine samples from the tonstein have a mean age of 310.9 ± 0.8 Ma, which suggests that it is the product of a single, large-volume, high-silica, rhyolitic eruption possibly associated with one of the Hercynian granitic plutons in the Piedmont. Biostratigraphic analyses correlate the Fire Clay coal bed with a position just below the top of the Trace Creek Member of the Atoka Formation in the North American Midcontinent and near the Westphalian B-C boundary in western Europe.

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Contents

GSA Special Papers

Elements of Pennsylvanian Stratigraphy, Central Appalachian Basin

Charles L. Rice
Charles L. Rice
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Geological Society of America
Volume
294
ISBN print:
9780813722948
Publication date:
January 01, 1994

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