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. 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.
Lithology and depositional environment
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. 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.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. .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.
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.
Fauna
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.
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.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. .
Dinosaurs Dinosaurs from the Bearpaw Formation Genus Species Location Member Material Notes Images Brachylophosaurus Indeterminate Daspletosaurus Edmontonia Indeterminate cf. Kritosaurus "Nearly complete skull and postcranium""Table 20.1," in Weishampel, et al. (2004). Page 441. A hadrosaurid Prosaurolophus P. maximus Three juvenile specimens A Saurolophinae hadrosaurid, also known from the Dinosaur Park and Two Medicine Formations Stegoceras Indeterminate
Plesiosaurs Plesiosaurs from the Bearpaw Formation Genus Species Location Member Material Notes Images Albertonectes 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. Nakonanectes N. bradti Montana A nearly complete skeleton including the skull A small elasmosaurid plesiosaur with an unusually short neck Terminonatator T. ponteixensis Saskatchewan A partially articulated incomplete skeleton, including a skull An elasmosaurid plesiosaur Dolichorhynchops 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 M. missouriensis Alberta and Montana Several specimens, including a near complete skeleton with stomach contents A large mosasaurine mosasaur M. conodon Saskatchewan A large mosasaurine mosasaur Prognathodon P. overtoni Alberta Several exceptionally preserved specimens A large mosasaurine mosasaur Plioplatecarpus P. primaevus Saskatchewan A widespread genus of plioplatecarpine mosasaur P. peckensis Montana Tylosaurus T. saskatchewanensis Saskatchewan A single semi-complete skeleton A large tylosaurine mosasaur
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
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 UrsichthysU. longiparietalisAlbertaPartial skeleton, recovered within a Mosasaurus specimenAn ichthyotringoid aulopiform Cartilaginous fish Cartilaginous fish from the Bearpaw Formation Genus Species Location Member Material Notes ImagesSqualicoraxS. spAlbertaSharkMeristodonoides M. montanensis AlbertaParaorthacodus P. andersoniAlbertaSqualus S. worlandensisAlbertaCarchariasC. cf samhammeriAlbertaOdontaspisO. aculeatusAlbertaCretoxyrhina C. mantelli Alberta Flora Plants from the Bearpaw Formation Genus Species Location Member Material Notes ImagesAquilapollenitesA.quadrilobusSaskatchewanPollen from a flowering plantA.attenuatusSequoiaS.spMontanaRedwood conifer
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