- Usage in publication:
-
- Cedar Bluff Rhyolite
- Modifications:
-
- Named
- Dominant lithology:
-
- Rhyolite
- Tuff
- AAPG geologic province:
-
- Midcontinent region
Summary:
Cedar Bluff 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 southern slopes of Shepherd Mountain; along Highway M, 2 mi west of Ironton; on Pond Ridge; and on northerly extension of Russell Mountain. Consists of brownish-maroon to grayish ash-flow tuff containing 25 to 50 percent white plagioclase phenocrysts. Thickness 580 m. Overlies Shepherd Mountain Rhyolite (new); underlies Pond Ridge Rhyolite (new). Age is Precambrian. Report includes geologic map. Unit named and described on stratigraphic column (table 1).
Cedar Bluff Rhyolite replaces: Middlebrook Group (near Cedar Bluff School), Pilot Knob Felsite (Shepherd Mountain), and Stouts Creek Rhyolite (Pond Ridge and southwestern edge of Shepherd Mountain) as mapped by Tolman and Robertson (1969, Missouri Geol. Survey Rpt. Inv., no. 44); upper part of undifferentiated felsite of Anderson (1970, Missouri Geol. Survey Rpt. Inv., no. 46); and Unit 710 of Berry and Bickford (1972, Bull. Volcanology, v. 36, p. 303-318).
Type section: in NE/4 NW/4 sec. 3, T. 33 N., R. 3 E., Ironton quadrangle, Iron Co., MO. Origin of name not stated by author, but probably named from Cedar Bluff School located about 2 mi west of Ironton, Iron Co., MO.
[Name preempted by Cedar Bluff Group of Swann (1963) in IL, KY.]
Source: Modified from GNU records (USGS DDS-6; Denver GNULEX).
- Usage in publication:
-
- Cedar Bluff Rhyolite
- Modifications:
-
- Revised
- AAPG geologic province:
-
- Midcontinent region
Summary:
/Cedar Bluff Rhyolite, 2nd 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 Shepherd Mountain Rhyolite (revised) of Taum Sauk; underlies Pond Ridge Rhyolite (revised) of Taum Sauk. Age is Precambrian Y. Nomenclature listed in table 1.
[Conflicts with nomenclature guidelines (ACSN, 1970; NACSN, 1983, 2005, 2021): preempted by Cedar Bluff Group of Swann (1963) in IL, KY; 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 ([ ]).