Bearpaw Formation

Bearpaw Formation Stratigraphic range: Campanian-Maastrichtian, 75–72 Ma PreЄ Є O S D C P T J K Pg N ↓
Contact (red arrow) between the underlying marine shales of the Bearpaw Formation and the coastal Horseshoe Canyon Formation.
Type	Geological formation
Unit of	Montana Group
Underlies	Horseshoe Canyon Formation, St. Mary River Formation, Eastend Formation, and others
Overlies	Dinosaur Park Formation, Judith River Formation
Thickness	Up to 350 meters (1,150 ft)^[1]
Lithology
Primary	Shale, claystone
Other	Siltstone, sandstone, concretionary beds
Location
Coordinates	48°15′0″N 109°30′0″W / 48.25000°N 109.50000°W / 48.25000; -109.50000 (Bearpaw Formation)Coordinates: 48°15′0″N 109°30′0″W / 48.25000°N 109.50000°W / 48.25000; -109.50000 (Bearpaw Formation)
Region	Alberta, Saskatchewan, Montana
Country	Canada United States
Extent	Northern Montana to central Alberta and southern Saskatchewan
Type section
Named for	Bear Paw Mountains, Montana
Named by	Hatcher and Stanton, 1903^[2]

The Bearpaw Formation, also called the Bearpaw Shale, is a geologic formation of Late Cretaceous (Campanian) age. It outcrops in the U.S. state of Montana, as well as the Canadian provinces of Alberta and Saskatchewan, and was named for the Bear Paw Mountains in Montana.^[2] It includes a wide range of marine fossils, as well as the remains of a few dinosaurs. It is known for its fossil ammonites, some of which are mined in Alberta to produce the organic gemstone ammolite.^[3]

Lithology and depositional environment

Bearpaw shale being excavated to recover ammonites for ammolite production.

The formation was deposited in the Bearpaw Sea, which was part of the Western Interior Seaway that advanced and then retreated across the region during Campanian time.^[4] It is composed primarily of dark grey shales, claystones, silty claystones and siltstones, with subordinate silty sandstones. It also includes bedded and nodular concretions (both calcareous and ironstone concretions) and thin beds of bentonite. As the seaway retreated toward the southwest, the marine sediments of the Bearpaw became covered by the deltaic and coastal plain sediments of the overlying formations.^[1]^[5]^[6]

Relationship to other units

The Bearpaw Formation conformably overlies the Dinosaur Park Formation of the Belly River Group in central Alberta, and the Judith River Formation in the plains to the east and Montana. It is overlain by the Horseshoe Canyon Formation in central Alberta; by the Blood Reserve Formation and the St. Mary River Formation in southern Alberta; by the Eastend Formation in southern Saskatchewan; and by the Fox Hills Formation in Montana. To the east, it merges into the Pierre Shale.^[1]

Fauna

A specimen of Placenticeras ammolite from the Bearpaw Formation.

The Bearpaw Formation is famous for its well-preserved ammonite fossils. These include Placenticeras meeki and Placenticeras intercalare, and the baculite Baculites compressus, some of which are mined south-central Alberta to produce the organic gemstone ammolite.^[3]

Other fossils found in this formation include many types of shellfish, bony fish, sharks, rays, birds, and marine reptiles like mosasaurs, plesiosaurs and sea turtles. Dinosaur remains have occasionally been discovered, presumably from carcasses that washed out to sea.^[7]^[8]

Dinosaurs

Dinosaurs reported from the Bearpaw Formation
Genus	Species	Location	Stratigraphic position	Material	Description	Images
Brachylophosaurus^[7]	Indeterminate^[7]					Brachylophosaurus
Edmontonia^[7]	Indeterminate^[7]
cf. Kritosaurus				"Nearly complete skull and postcranium."^[9]	A hadrosaurid
Prosaurolophus^[7]	Indeterminate^[7]
Stegoceras^[7]	Indeterminate^[7]

References

1 2 3 Glass, D.J. (editor) 1997. Lexicon of Canadian Stratigraphy, vol. 4, Western Canada including eastern British Columbia, Alberta, Saskatchewan and southern Manitoba. Canadian Society of Petroleum Geologists, Calgary, 1423 p. on CD-ROM. ISBN 0-920230-23-7.
1 2 Hatcher, J.B. and Stanton, T.W., 1903. The stratigraphic position of the Judith River beds and their correlation with the Belly River beds. Science, no. 5, v. 18, p. 211-212.
1 2 Mychaluk, K.A.; Levinson, A.A. & Hall, R.H. "Ammolite: Iridescent fossil ammonite from southern Alberta, Canada." (PDF). Gems & Gemology. 37 (1): 4–25. Retrieved 2015-01-11.
↑ Latest Cretaceous Western Interior Seaway
↑ Canadian Society of Petroleum Geologists (1994). "The Geological Atlas of the Western Canada Sedimentary Basin, Chapter 24: Upper Cretaceous and Tertiary strata of the Western Canada Sedimentary Basin". Compiled by Mossop, G.D. and Shetsen, I. Retrieved 2016-06-20.
↑ Wall, J.H., Sweet, A.R. and Hills, L.V. 1971. Paleoecology of the Bearpaw and contiguous Upper Cretaceous formations in the C.P.O.G. Strathmore well, southern Alberta. Bulletin of Canadian Petroleum Geology, vol. 19, no. 3, p. 691-702.
1 2 3 4 5 6 7 8 9 Weishampel, David B; et al. (2004). "Dinosaur distribution (Late Cretaceous, North America)." In: Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. Pp. 574-588. ISBN 0-520-24209-2.
↑ Bearpaw fauna in Alberta
↑ "Table 20.1," in Weishampel, et al. (2004). Page 441.

Western Canadian Sedimentary Basin
Hydrocarbon history	Oil sands and heavy oil Frontier exploration and development Natural gas liquids Natural gas
Depositional regions	Southern Alberta Central Alberta Northwestern Alberta Plains South-central Canadian Rockies foothills North-east Plains North-central foothills Liard River Fort Nelson Northern Rocky Mountains Fort St. John Saskatchewan Western Manitoba
Northeastern plains	Bearpaw FM Belly River GRP Lea Park FM La Biche GRP Viking FM Joli Fou FM Colony SS Mannville GRP McLaren MBR Grand Rapids FM Waseca SS Sparky SS Gen. Petr. SS Clearwater FM Rex SS Lloydminster SS Wabiskaw MBR Cummings MBR McMurray FM Dina MBR Banff FM Exshaw FM Wabamun FM Winterburn FM Woodbend GRP Grosmont FM Irteton FM Cooking Lake FM Beaverhill Lake GRP Elk Point GRP Canadian Shield
Central Alberta	Paskapoo FM Scollard FM Edmonton GRP Battle FM Whitemud MBR Horseshoe Canyon FM Bearpaw FM Belly River GRP Ribstone Creek MBR Victoria MBR Brosseau MBR Lea Park FM Colorado GRP Cardium FM Mannville GRP Glauconitic Sandstone Ostracod Beds Sunburst Member Taber Member Detrital Beds Fernie GRP Rock Creek MBR Nordegg MBR Rundle GRP Mount Head FM Elkton MBR Shunda FM Pekisko FM Banff FM Exshaw FM Canadian Shield
Saskatchewan	Cypress Hills FM Ravenscrag FM Frenchman FM Whitemud FM Eastend FM Bearpaw FM Judith River GRP Belly River FM Oldman FM Foremost FM Lea Park FM Pakowki FM Milk River FM Colorado GRP Viking FM Mannville GRP Pense FM Cantuar FM Success FM Vanguard FM Ellis GRP Swift FM Rierdon FM Sawtooth FM Shaunavon FM Piper FM Gravelbourg FM Gypsum Springs FM Watrous FM Big Snowy GRP Madison GRP Charles FM Poplar Ratcliffe Midale Mission Canyon FM Kisbey SS Alida Tilston Lodgepole FM Souris Valley Three Forks GRP Bakken FM Big Valley FM Torquay FM Saskatchewan GRP Birdbear FM Duperow FM Manitoba GRP Souris River FM Elk Point GRP Davson Bay FM Prairie FM Winnipegosis FM Ashern FM Interlake FM Stonewall FM Stony Mountain FM Herald FM Yeoman FM Winnipeg FM Deadwood FM Canadian Shield

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