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Global Ordovician Series boundaries and global event biohorizons, Monitor Range and Roberts Mountains, Nevada

By
Stanley C. Finney
Stanley C. Finney
Department of Geological Sciences, California State University, Long Beach, California 90840 USA,
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Raymond L. Ethington
Raymond L. Ethington
Department of Geological Sciences, University of Missouri, Columbia, Missouri 65211 USA,
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Published:
January 01, 2000

Abstract

Stratigraphic sections in the Monitor Range and Roberts Mountains provide both shelf and basin depositional records for two prominent stratigraphic intervals in the Ordovician System. The Whiterock Narrows section in the Monitor Range is proposed as a candidate global stratotype section for the base of the Middle Ordovician Series. The boundary interval in the upper Ninemile Formation and lower Antelope Valley Limestone, deposited on the carbonate platform, contains excellent biostratigraphic records of conodonts, used to define the boundary, trilobites and brachiopods. The boundary level can be correlated into a deep basin facies at the Red Canyon section in the Roberts Mountains because conodonts that define the boundary co-occur with graptolites in calcareous sandstones of the Lower Member of the Vinini Formation.

The Vinini Creek section in the Roberts Mountains provides continuous exposure of the stratigraphic interval in the Upper Member of the Vinini Formation that includes the Late Ordovician mass extinction and was deposited in a deep basinal setting. The decline in diversity of the graptolite fauna coincides with the initiation of sea-level fall. However, conodont and chitinozoan faunas were unaffected. The Copenhagen Canyon section in the Hanson Creek Formation in the Monitor Range records the Late Ordovician events in a platform margin setting. There, faunas were affected by the sea-level fall much earlier than in the deep basinal setting, and the extinction of conodonts and chitinozoans occurred substantially later than that of graptolites.

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GSA Field Guide

Great Basin and Sierra Nevada

David R. Lageson
David R. Lageson
Department of Earth Sciences Montana State University Bozeman, MT 59717 USA
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Stephen G. Peters
Stephen G. Peters
Reno Field Office Mackay School of Mines, MS-176 University of Nevada Reno, Nevada 89557-0047 USA
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Mary M. Lahren
Mary M. Lahren
Department of Geological Sciences MS-l72 University of Nevada Reno, Nevada 89557 USA 2000
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Geological Society of America
Volume
2
ISBN electronic:
9780813756028
Publication date:
January 01, 2000

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