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Lower Paleozoic stratigraphy and structure of central Nevada: Comparisons and contrasts between the lower and upper plates of the Roberts Mountains thrust

By
Stanley C. Finney
Stanley C. Finney
Department of Geological Sciences, California State University, Long Beach, California 90840 USA
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Paula Noble
Paula Noble
Department of Geological Sciences, Mackay School of Mines, University of Nevada, Reno, Nevada 89557 USA
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J. Kelly Cluer
J. Kelly Cluer
Cameco (U.S.) Inc., Reno, Nevada 89502 USA
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Published:
January 01, 2000

Abstract

The Roberts Mountains of north-central Nevada is a classic area in which to examine the Roberts Mountains thrust, the thick Cambrian-Devonian section of carbonate-platform rocks of the lower plate, and the structurally complex basinal stratigraphic succession of the Roberts Mountains allochthon (RMA). The highest carbonate unit of the lower plate, the Middle Devonian Devils Gate Limestone, is overlain by the parautochthonous Misisisippian Webb Formation. It accumulated in a foreland basin as the carbonate platform subsided in front of the advancing allochthon, and locally it was incorporated into the basal RMA and translated a relatively short distance relative to overlying thrust nappes. Unnamed Devonian shale/ chert/limestone, variably developed, occupies the next higher nappe. These rocks were incorporated in the allochthon and transported from a deep-water basinal depositional location beyond the shelf margin. Higher nappes are composed of the Upper Cambrian-Ordovician Vinini Formation and the Silurian Elder Sandstone, although structural complexity higher in the allochthon repeats and imbricates lower and upper nappes.The Vinini Formation includes two prominent quartz sandstone intervals that can be recognized throughout much of the allochthon and provide direct sedimentological ties to the carbonate platform succession. An older, lower Whiterockian unit, which correlates with the uppermost Ninemile Shale and lower Antelope Valley Limestone of the platform, records a great sea-level lowstand that produced the unconformity between the Sauk and Tippecanoe cratonic sequences. The younger, upper Whiterockian unit is composed of the same quartz sands as the Eureka Quartzite. A facies succession in the uppermost Vinini Formation and the disconformable contact between the Vinini and Elder Formations are distinct records of Late Ordovician glacioeustatic sea-level fall and subsequent rise that are also represented in the carbonate platform succession. This is another precise sedimentological tie between platform and basin successions.The close stratigraphic ties between the Vinini Formation and correlative strata of the platform succession are strong evidence that rocks of RMA were deposited in a basin directly adjacent to, and along, the Cordilleran margin of Laurentia and that the RMA is not a far-traveled exotic terrain.

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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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