- Usage in publication:
-
- Ironton Rhyolite
- Modifications:
-
- Named
- Dominant lithology:
-
- Rhyolite
- Tuff
- AAPG geologic province:
-
- Midcontinent region
Summary:
Ironton Rhyolite. Unit is part of sequence of Precambrian volcanic rocks associated with Taum Sauk caldera in western part of St. Francois Mountains, southeast Missouri (Midcontinent region). Notable exposures on Buck, High Top, Lindsey, North Bell, and Russell Mountains, Iron and Reynolds Counties, Missouri. Consists of dark-maroon to black ash-flow tuff containing 5 to 15 percent phenocrysts of quartz and alkali feldspar; has conchoidal fractures. Thickness 340 m, though not all of unit exposed. Overlies Buck Mountain Shut-ins Formation (new); underlies Lindsey Mountain Rhyolite (new). Age is Precambrian. Report includes geologic map. Unit named and described on stratigraphic column (table 1).
Ironton Rhyolite replaces: Stouts Creek Rhyolite (Buck and Russell Mountains, and Pond Ridge) and Van East Group (High Top, Lindsey, and North Bell Mountains) as mapped by Tolman and Robertson (1969, Missouri Geol. Survey Rpt. Inv., no. 44); Unit A of tuff of Stouts Creek of Anderson (1970, Missouri Geol. Survey Rpt. Inv., no. 46); and Unit 740 of Berry and Bickford (1972, Bull. Volcanology, v. 36, p. 303-318).
Type section: in SW/4 sec. 33, T. 34 N., R. 3 E., Ironton quadrangle, Iron Co., MO. Origin of name not stated by author, but probably named from town of Ironton, Iron Co., MO.
[Technically, name Ironton is preempted by Ironton granite of Graves (1938), a poorly-defined, informal unit in same area.]
Source: Modified from GNU records (USGS DDS-6; Denver GNULEX).
- Usage in publication:
-
- Ironton Rhyolite
- Modifications:
-
- Revised
- AAPG geologic province:
-
- Midcontinent region
Summary:
Ironton Rhyolite, 5th formation from base (of 12) of /Taum Sauk Group (new) of /St. Francois Mountains Volcanic Supergroup (revised). Study area is St. Francois Mountains, southeast Missouri (Midcontinent region). Overlies Buck Mountain Shut-ins Formation (revised) of Taum Sauk; underlies Lindsey Mountain Rhyolite (revised) of Taum Sauk. Age is Precambrian Y. Nomenclature listed in table 1.
[Conflicts with nomenclature guidelines (ACSN, 1970; NACSN, 1983, 2005, 2021): name Taum Sauk used for both group and formation within it (Taum Sauk Rhyolite has priority); name St. Francois Mountains applied concurrently to two different units in same area; a [supergroup] name combines a geographic name with the term ["supergroup,"] and no lithic designation is included.]
Source: Modified from 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 ([ ]).