- Usage in publication:
-
- Kogruk formation*
- Modifications:
-
- Named
- Biostratigraphic dating
- Dominant lithology:
-
- Limestone
- Chert
- AAPG geologic province:
-
- Alaska Northern region
Summary:
Named as middle formation (of 3) of Lisburne group in DeLong Mountains for Kogruk Creek, west-flowing tributary of Utukok River. Type section designated on Tupik Mountain in mountain-top outcrops adjoining and south of Utukok formation type section, DeLong Mountains, northern AK. Composed of thick-bedded fine- to coarse-grained gray limestone with minor beds and lenses of chert. Thickness at type is about 520 ft; other sections up to 1500 ft thick. Conformably overlies Utukok formation (new) of Lisburne group. Contact with overlying Tupik formation (new) of Lisburne group may be faulted. Fossil assemblages indicate Early and Late Mississippian age.
Source: GNU records (USGS DDS-6; Menlo GNULEX).
- Usage in publication:
-
- Kogruk Formation*
- Modifications:
-
- Age modified
- Biostratigraphic dating
- AAPG geologic province:
-
- Alaska Northern region
Summary:
Age is Early and Late Mississippian and, locally, Early Pennsylvanian based on revised megafossil zonations. Assemblages (mollusks, gastropods, and corals) in DeLong Mountains, western Brooks Range, range from Meramecian to Chesterian in age. Assemblages (mollusks, gastropods, corals, and brachiopods) in Lisburne Peninsula range from Meramecian to Morrowan in age.
Source: GNU records (USGS DDS-6; Menlo 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 ([ ]).