- Usage in publication:
-
- Loco Ridge gypsum bed
- Modifications:
-
- Named
- Dominant lithology:
-
- Gypsum
- Limestone
- Dolomite
- AAPG geologic province:
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- Central Montana uplift
Summary:
Named as an informal bed in "Forestgrove member" (informal, new) of Heath Formation for Loco Ridge, 6 mi south of Forestgrove, Fergus Co, MT on Central Montana uplift. No type locality designated. Ranges from 18 to 24 ft thick. Overlies unnamed interbedded shale and limestone unit of Heath. Underlies upper part of Heath. Distinguished on geologic map of Fergus Co south of Lewistown and on correlation diagram. Consists of white to grayish black, massive to laminated gypsum, gray limestone, black dolomite, and gray siltstone. Upper part has nodular gypsum. Lower part has contorted interbeds of laminated limestone and massive crystalline gypsum. Thin limestone and dolomite flat-pebble conglomerates mark upper and lower contacts. Extends several mi northwest of study area. Of Mississippian age. Measured sections.
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 ([ ]).