Global Ordovician Series boundaries and global event biohorizons, Monitor Range and Roberts Mountains, Nevada
Published:January 01, 2000
Stanley C. Finney, Raymond L. Ethington, 2000. "Global Ordovician Series boundaries and global event biohorizons, Monitor Range and Roberts Mountains, Nevada", Great Basin and Sierra Nevada, David R. Lageson, Stephen G. Peters, Mary M. Lahren
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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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Great Basin and Sierra Nevada, the second volume of the Geological Society of America Field Guide Series, focuses on the dynamic and spectacular geology of this region, providing the inspiring backdrop for the 2000 GSA Annual Meeting in Reno. This volume gives complete coverage of field trips held in conjunction with that meeting, and contains 20 chapters organized into three sections. The first section consists of 16 chapters arranged in geochronological order, beginning with the active tectonics of Lake Tahoe and the historical surface faulting and paleoseismicity of the central Nevada seismic belt, and ending with the Neoproterozoic glacial record of Death Valley. In between are chapters dealing with Basin and Range extension, Eocene magmatism, Mesozoic plutonism in the Sierra Nevada, Paleozoic subduction, and Ordovician stratigraphy, to name a few. The second section covers the geology of the Nevada Test Site and the nuclear-waste repository at Yucca Mountain. The last section is an invited field guide from the 1999 GSA Cordilleran Section meeting that covers the wines and geology of Napa Valley, California. Overall, Great Basin and Sierra Nevada is a comprehensive compilation of new and exciting research on this amazingly diverse region, with well-crafted guides to field localities of special interest. Full-color plates in some chapters make this guide an especially appealing and useful volume.