Bearpaw Formation

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Template:Short description Script error: No such module "Infobox".Script error: No such module "check for unknown parameters". 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.[1] 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.[2]

Lithology and depositional environment

File:Ammolite mining.jpg
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.[3] 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.[4][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.[4]

Fauna

Color key
Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon
Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.
File:Ammolite from Placenticeras fossil ammonite, Alberta.jpg
A specimen of Placenticeras ammolite from the Bearpaw Formation.

The Bearpaw Formation is famous for its well-preserved ammonite fossils. These include Placenticeras meeki, Placenticeras intercalare, Hoploscaphites, and Sphenodiscus, the baculite Baculites compressus and the bivalve Inoceramus, some of which are mined south-central Alberta to produce the organic gemstone ammolite.[2]

Other fossils found in this formation include many types of shellfish, bony fish, sharks, rays, birds, and marine reptiles like mosasaurs such as Prognathodon overtoni and Plioplatecarpus peckensis, plesiosaurs such as Dolichorhynchops herschelensis, Albertonectes and Nakonanectes, and sea turtles. Dinosaur remains have occasionally been discovered, presumably from carcasses that washed out to sea.[7][8]

Dinosaurs

Dinosaurs from the Bearpaw Formation
Genus Species Location Member Material Notes Images
Brachylophosaurus[7] Indeterminate[7]
File:Brachylophosaurus NT.png
Brachylophosaurus
Daspletosaurus
File:Daspletosaurus torosus steveoc.jpg
Daspletosaurus
Edmontonia[7] Indeterminate[7]
File:Edmontonia dinosaur.png
Edmontonia
cf. Kritosaurus "Nearly complete skull and postcranium."[9] A hadrosaurid
File:Kritosaurus BW.jpg
Kritosaurus
Prosaurolophus[7][10] P. maximus[10] Three juvenile specimens[10] A Saurolophinae hadrosaurid, also known from the Dinosaur Park and Two Medicine Formations
File:Prosaurolophus Maximus.jpg
Prosaurolophus
Stegoceras[7] Indeterminate[7]
File:Stegoceras validum.jpg
Stegoceras

Plesiosaurs

Plesiosaurs from the Bearpaw Formation
Genus Species Location Member Material Notes Images
Albertonectes[11] A. vanderveldei Alberta A complete, well-preserved postcranial specimen, missing only the skull. An elasmosaurid plesiosaur. Albertonectes has the longest neck of any known plesiosaur.
File:Fossil vertebrae.jpg
Albertonectes
Nakonanectes[12] N. bradti Montana A nearly complete skeleton including the skull. A small elasmosaurid plesiosaur with an unusually short neck.
Terminonatator[13] T. ponteixensis Saskatchewan A partially articulated incomplete skeleton, including a skull. An elasmosaurid plesiosaur.
Dolichorhynchops[14] D. herschelensis Saskatchewan An incomplete skeleton One of the latest known polycotylids.

Mosasaurs

Mosasaurs from the Bearpaw Formation
Genus Species Location Member Material Notes Images
Mosasaurus[15] M. missouriensis Alberta and Montana Several specimens, including a near complete skeleton with stomach contents A large mosasaurine mosasaur.
File:TMP 2008.036.0001.jpg
Mosasaurus missouriensis
M. conodon Saskatchewan A large mosasaurine mosasaur.
File:MOR 006 (1).jpg
Mosasaurus conodon
Prognathodon[16] P. overtoni Alberta Several exceptionally preserved specimens A large mosasaurine mosasaur.
File:Tyrrell mosasaur.jpg
Prognathodon overtoni
Plioplatecarpus[17] P. primaevus Saskatchewan A widespread genus of plioplatecarpine mosasaur.
File:PlioplatecarpusDB.jpg
Plioplatecarpus
P. peckensis Montana
Tylosaurus[18] T. saskatchewanensis Saskatchewan A single semi-complete skeleton A large tylosaurine mosasaur.
File:Tylosaurus (side angle).jpg
Tylosaurus

Turtles

Turtles from the Bearpaw Formation
Genus Species Location Member Material Notes Images
Nichollsemys N. baieri Alberta Known from skulls A basal chelonioid sea turtle.
File:Turtle skull fossil.jpg
Nichollsemys

Bony fish

Bony fish from the Bearpaw Formation
Genus Species Location Member Material Notes Images
Dercetis D. magnificus Alberta 2 articulated specimens A dercetid aulopiform.[19]
File:Dercetis sp.jpg
Dercetis
Ursichthys U. longiparietalis Alberta Partial skeleton, recovered within a Mosasaurus specimen. An ichthyotringoid aulopiform.[20]

Cartilaginous fish

Cartilaginous fish from the Bearpaw Formation
Genus Species Location Member Material Notes Images
Squalicorax S. sp Alberta Shark

Flora

Plants from the Bearpaw Formation
Genus Species Location Member Material Notes Images
Aquilapollenites[13] A.quadrilobus Saskatchewan[13] Pollen from a flowering plant
A.attenuatus
Sequoia[21] S.sp[22] Montana[22] Redwood conifer

References

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  1. ↑ Cite error: Script error: No such module "Namespace detect".Script error: No such module "Namespace detect".
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  4. ↑ a b 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. Template:ISBN.
  5. ↑ Script error: No such module "citation/CS1".
  6. ↑ 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.
  7. ↑ a b c d e f g h 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. Template:ISBN.
  8. ↑ Script error: No such module "citation/CS1".
  9. ↑ "Table 20.1," in Weishampel, et al. (2004). Page 441.
  10. ↑ a b c Script error: No such module "Citation/CS1".
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  20. ↑ Script error: No such module "Citation/CS1".
  21. ↑ Script error: No such module "Citation/CS1".
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