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Map showing publication footprint
  • Usage in publication:
    • Birdbear formation*
  • Modifications:
    • Original reference
  • Dominant lithology:
    • Anhydrite
    • Dolomite
    • Limestone
    • Shale
  • AAPG geologic province:
    • Central Montana uplift
    • Sweetgrass arch
    • Williston basin
Publication:

Sandberg, C.A., and Hammond, C.R., 1958, Devonian System in Williston basin and central Montana: American Association of Petroleum Geologists Bulletin, v. 42, no. 10, p. 2293-2334. [Available online, with subscription, from AAPG archives: http://www.aapg.org/datasystems or http://search.datapages.com]


Summary:

Pg. 2292 (fig. 2), 2302-2303 (fig. 4), 2318-2322. Birdbear formation of Jefferson group. Proposed for widespread beds of light-colored finely crystalline dolomite and limestone that overlie the Duperow and underlie the Three Forks in [subsurface of] Williston basin and central Montana. Thickness ranges from fraction of a foot to 125 feet; in type well 90 feet. Replaces term Nisku formation now restricted to type area in central Alberta. Age is Late Devonian.
Type section (subsurface): depth-interval 10,310 to 10,400 ft, Mobil Producing Company Birdbear No. 1 well, in sec. 22, T. 149 N., R. 91 W., Dunn Co., ND.
[Misprint (US geologic names lexicon, USGS Bull. 1200, p. 346): type well stated to be Birdwell; should be Birdbear.]

Source: US geologic names lexicon (USGS Bull. 1200, p. 346).


Map showing publication footprint
  • Usage in publication:
    • Birdbear Member*
  • Modifications:
    • Revised
  • AAPG geologic province:
    • Bighorn basin
    • Central Montana uplift
    • Montana folded belt
    • Sweetgrass arch
    • Williston basin
    • Yellowstone province
Publication:

Sandberg, C.A., 1965, Nomenclature and correlation of lithologic subdivisions of the Jefferson and Three Forks Formations of southern Montana and northern Wyoming, IN Contributions to stratigraphy: U.S. Geological Survey Bulletin, 1194-N, p. N1-N18.


Summary:

Pg. N6 (fig. 2), N7; 1962, Billings Geol. Soc. Gdbk., 13th Ann. Field Conf., p. 47-50. Birdbear Member of Jefferson Formation. Dolomite, partly pseudobrecciated. Thickness 70 feet at type section of Jefferson; generally ranges 50 to 80 feet. Is the upper member of Jefferson Formation. Overlies lower member of Jefferson; underlies Logan Gulch Member (new) of Three Forks Formation. Recognized in western Montana and northwestern Wyoming. Age is Late Devonian.

Source: Publication.


Map showing publication footprint
  • Usage in publication:
    • Birdbear Member*
  • Modifications:
    • Biostratigraphic dating
  • AAPG geologic province:
    • Snake River basin
    • Sweetgrass arch
Publication:

Sandberg, C.A., and Poole, F.G., 1977, Conodont biostratigraphy and depositional complexes of Upper Devonian cratonic-platform and continental-shelf rocks in the western United States, IN Murphy, M.A., and others, eds., Proceedings of the 1977 annual meeting of the Paleontological Society on Devonian of western North America: University of California-Riverside, Campus Museum Contributions, Paleontological Society, 1977 annual meeting, Riverside, CA, November, 1977, no. 4, p. 144-182.


Summary:

As the upper member of the Jefferson Formation, Birdbear is 10 m thick south and east of town of Monarch, Little Belt Mountains, Cascade Co, MT on Sweetgrass arch where it is of Frasnian?, Late Devonian age, 10 m thick, and in polygnathid biofacies. In Long Canyon, west side of Beaverhead Mountains, Clark Co, ID in Snake River basin, the Birdbear is 12 m thick and of Famennian, Late Devonian age. In Long Canyon, Birdbear is in the PALMATOLEPIS MARGINIFERA conodont zone. The Long Canyon section is the easternmost well-dated section in ID. A Famennian brachiopod SINETECTIROSTRUM also found at Long Canyon.

Source: GNU records (USGS DDS-6; Denver GNULEX).


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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 ([ ]).