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National Geologic Map Database
Geologic Unit: Dell
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Map showing publication footprint
  • Usage in publication:
    • Dell Tuff*
  • Modifications:
    • Original reference
  • Dominant lithology:
    • Tuff
  • AAPG geologic province:
    • Great Basin province
Publication:

Lindsey, D.A., 1979, Geologic map and cross sections of Tertiary rocks in the Thomas Range and northern Drum Mountains, Juab County, Utah: U.S. Geological Survey Miscellaneous Investigations Series Map, I-1176, 1 sheet, scale 1:62,500


Summary:

Dell Tuff. Gray to pink rhyolitic ash-flow tuff. Chiefly crystals of quartz, sanidine, biotite, and plagioclase in a poorly welded to unwelded matrix of devitrified shards and pumice. Thickness 180 m. Unconformably overlies Drum Mountains Rhyodacite, or locally overlies Oligocene(?) breccia at Spor Mountain or Paleozoic rocks; unconformably underlies Spor Mountain Formation. Age is Oligocene, based on average fission-track age of 32 Ma.
Type locality: The Dell, in secs. 23 and 24, T. 12 S., R. 12 W., Thomas Range, Juab Co., western UT. Named from The Dell.

Source: US geologic names lexicon (USGS Bull. 1564, p. 44-45).


Map showing publication footprint
  • Usage in publication:
    • Dell Tuff*
  • Modifications:
    • Areal extent
    • Geochronologic dating
  • AAPG geologic province:
    • Great Basin province
Publication:

Lindsey, D.A., 1982, Tertiary volcanic rocks and uranium in the Thomas Range and northern Drum Mountains, Juab County, Utah: U.S. Geological Survey Professional Paper, 1221, 71 p. [Available online from the USGS PubsWarehouse: http://pubs.er.usgs.gov/pubs/pp/pp1221]


Summary:

Is an Oligocene unit--a simple cooling unit--limited to Thomas Range and Key Mountains, in the Great Basin province. Has an average isotopic age of 32.0+/-0.6 Ma.

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 ([ ]).