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Geologic Unit: Flathead
Map showing publication footprint
  • Usage in publication:
    • Flathead formation
    • Flathead shales
  • Modifications:
    • Original reference
  • Dominant lithology:
    • Shale
    • Sandstone
    • Limestone
  • AAPG geologic province:
    • Montana folded belt
Publication:

Peale, A.C., 1893, The Paleozoic section in the vicinity of Three Forks, Montana, with petrographic notes by G.P. Merrill: U.S. Geological Survey Bulletin, 110, 56 p.


Summary:

Flathead formation. Divided into Flathead shales above and Flathead quartzite below. The shales are soft, green, shaly beds interlaminated with thin beds of glauconitic limestone; toward base are beds of very dark reddish-brown and green sandstone. Thickness of the shales 290 feet. Overlain by Trilobite limestone, the basal member of Gallatin formation. Fossils. Age is Middle Cambrian. [For description of the quartzite see Flathead quartzite.]
Named from exposures in Flathead Pass, northeastern corner Threeforks [Three Forks] quadrangle, MT.

Source: US geologic names lexicon (USGS Bull. 896, p. 738).


Map showing publication footprint
  • Usage in publication:
    • Flathead shales†
    • Flathead formation†
    • Flathead quartzite
  • Modifications:
    • Overview
Publication:

Wilmarth, M.G., 1936, [Selected Geologic Names Committee remarks (ca. 1936) on Cambrian and Ordovician rocks of the U.S.], IN Wilmarth, M.G., 1938, Lexicon of geologic names of the United States (including Alaska): U.S. Geological Survey Bulletin, 896, pts. 1-2, 2396 p.


Summary:

The use of Flathead in 3 senses being objectionable, the name has for many years been restricted to the quartzite, and the so-called "Flathead shales" have been combined with the overlying trilobite-bearing limestones and OBOLELLA-bearing shales (originally included in Gallatin formation) into a formation named Gros Ventre formation.

Source: US geologic names lexicon (USGS Bull. 896, p. 738).


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 ([ ]).

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