- Usage in publication:
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- East Gulch Tuff*
- Modifications:
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- Named
- Dominant lithology:
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- Tuff
- AAPG geologic province:
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- Denver basin
Summary:
Named for East Gulch in secs 2, 3, and 11, T49N, R12E, Fremont Co., CO in the Denver basin. Is a tuff--a simple-cooling unit, with well developed zonation and conspicuous eutaxitic fabric. A black vitrophyre zone as much as 15 ft thick is common in lower third. Zone grades into a piperno zone in which lenses of black glass are interspersed in a gray vitroclastic matrix. Is rhyolitic. Contains sanidine, plagioclase, quartz, and biotite as important phenocrystic minerals. Is 70 ft thick at type; averages 50 ft thick. Overlies Antero Formation; underlies Thorn Ranch Tuff. Has reverse polarity. Is of Oligocene age. Source is unknown, but probably is west of present outcrops.
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 ([ ]).