- Usage in publication:
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- Upper Basin Member*
- Modifications:
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- Named
- Geochronologic dating
- Dominant lithology:
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- Rhyolite
- AAPG geologic province:
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- Yellowstone province
Summary:
Named as a member of Plateau Rhyolite (new) for exposures in Upper Geyser Basin (its type area), west-central Yellowstone National Park, WY in Yellowstone province. Includes early postcaldera rhyolitic lava flows and associated pyroclastic deposits that were erupted within the Yellowstone caldera after doming. Is characterized by abundant plagioclase phenocrysts, commonly oligoclase that is highly embayed. Is exposed only in upper Grand Canyon and area southeast to Fern Lake. Is younger than Mallard Lake Member (new) of Plateau Rhyolite. Is older than Central Plateau Member (new) of Plateau Rhyolite. K-Ar dating of sanidine, plagioclase, and nonhydrated glass from rhyolites shows most of the flows are younger than Lava Creek Tuff (new). Is part of the third volcanic cycle of Yellowstone Plateau. Cross sections; stratigraphic table.
Source: GNU records (USGS DDS-6; Denver GNULEX).
For more information, please contact Nancy Stamm, Geologic Names Committee Secretary.
Asterisk (*) indicates published by U.S. Geological Survey authors.
"No current usage" (†) implies that a name has been abandoned or has fallen into disuse. Former usage and, if known, replacement name given in parentheses ( ).
Slash (/) indicates name conflicts with nomenclatural guidelines (CSN, 1933; ACSN, 1961, 1970; NACSN, 1983, 2005, 2021). May be explained within brackets ([ ]).