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Book Chapter

Biostratigraphy of Cambrian and Lower Ordovician Strata in the Llano Uplift, Central Texas

By
James F. Miller
James F. Miller
Department of Geography, Geology, and Planning, Missouri State University, Springfield, Missouri, U.S.A.
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James D. Loch
James D. Loch
Department of Biology and Earth Sciences, University of Central Missouri, Warrensburg, Missouri, U.S.A.
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John F. Taylor
John F. Taylor
Geoscience Department, Indiana University of Pennsylvania, Indiana, Pennsylvania, U.S.A.
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Published:
January 01, 2012

Abstract

Decimeter-scale sampling of the Cambrian and the lowermost Ordovician (Sauk megasequence) rocks of the Llano uplift, Texas, has produced a finely resolved biostratigraphic framework based primarily on trilobites and conodonts. Systematically collected trilobites of the Llano Uplift allow recognition of 13 biozones that extend from the Bolaspidella Biozone (Cambrian System, Marjuman Stage) through the Symphysurina Zone (Ordovician System, upper Skullrockian Stage). Systematic collection of conodonts has produced specimens assignable to 13 zones that range from the Proconodontus tenuiserratus Zone (Cambrian System, Sunwaptan Stage) through the Rossodus manitouensis Zone (Ordovician System, upper Skullrockian Stage). The base of the Ordovician System in the Llano uplift, as elsewhere, has been identified by the lowest occurrence of the conodont Iapetognathus fluctivagus and is closely approximated by the lowest occurrences of the cosmopolitan trilobite Juyjuyaspis and the Laurentian trilobite Symphysurina “bulbosa.” Although the overlying Ordovician strata of the Ellenburger Group have not been systematically sampled, scattered trilobite collections do establish the approximate positions of the base of the Stairsian Stage (based on Paraplethopeltis) and the base of the Jeffersonian Stage (based on Rananasus and Jeffersonia) in the Tanyard and Honeycut Formations, respectively.

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Contents

Memoir

Great American Carbonate Bank: The Geology and Economic Resources of the Cambrian—Ordovician Sauk Megasequence of Laurentia

James Derby
James Derby
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Richard Fritz
Richard Fritz
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Susan Longacre
Susan Longacre
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William Morgan
William Morgan
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Charles Sternbach
Charles Sternbach
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American Association of Petroleum Geologists
Volume
98
ISBN electronic:
9781629810201
Publication date:
January 01, 2012

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