Bearpaw Formation Explained

Bearpaw Formation
Type:Geological formation
Age:Campanian-Maastrichtian,
Period:Campanian
Prilithology:Shale, claystone
Otherlithology:Siltstone, sandstone, concretionary beds
Namedfor:Bear Paw Mountains, Montana
Namedby:Hatcher and Stanton, 1903[1]
Region:Alberta, Saskatchewan, Montana
Country:Canada, United States
Coordinates:48.25°N -109.5°W
Unitof:Montana Group
Underlies:Horseshoe Canyon Formation, St. Mary River Formation, Eastend Formation, and others
Overlies:Dinosaur Park Formation,
Judith River Formation
Thickness:Up to 350m (1,150feet)
Extent:Northern Montana to central Alberta and southern Saskatchewan

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.[2]

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.[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.

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.[7] [8]

Dinosaurs

Dinosaurs from the Bearpaw Formation
Genus Species Location Member Material Notes Images
BrachylophosaurusIndeterminate
Daspletosaurus
EdmontoniaIndeterminate
cf. Kritosaurus"Nearly complete skull and postcranium."[9] A hadrosaurid
Prosaurolophus[10] P. maximusThree juvenile specimensA Saurolophinae hadrosaurid, also known from the Dinosaur Park and Two Medicine Formations
StegocerasIndeterminate

Plesiosaurs

Plesiosaurs from the Bearpaw Formation
Genus Species Location Member Material Notes Images
Albertonectes[11] A. vanderveldeiAlbertaA complete, well-preserved postcranial specimen, missing only the skull.An elasmosaurid plesiosaur. Albertonectes has the longest neck of any known plesiosaur.
Nakonanectes[12] N. bradtiMontanaA nearly complete skeleton including the skull.A small elasmosaurid plesiosaur with an unusually short neck.
Terminonatator[13] T. ponteixensisSaskatchewanA partially articulated incomplete skeleton, including a skull.An elasmosaurid plesiosaur.
Dolichorhynchops[14] D. herschelensisSaskatchewanAn incomplete skeletonOne of the latest known polycotylids.

Mosasaurs

Mosasaurs from the Bearpaw Formation
Genus Species Location Member Material Notes Images
Mosasaurus[15] M. missouriensisAlberta and MontanaSeveral specimens, including a near complete skeleton with stomach contentsA large mosasaurine mosasaur.
M. conodonSaskatchewanA large mosasaurine mosasaur.
Prognathodon[16] P. overtoniAlbertaSeveral exceptionally preserved specimensA large mosasaurine mosasaur.
Plioplatecarpus[17] P. primaevusSaskatchewanA widespread genus of plioplatecarpine mosasaur.
P. peckensisMontana
Tylosaurus[18] T. saskatchewanensisSaskatchewanA single semi-complete skeletonA large tylosaurine mosasaur.

Turtles

Notes and References

  1. 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.
  2. Ammolite: Iridescent fossil ammonite from southern Alberta, Canada.. Mychaluk, K.A.. Levinson, A.A.. Hall, R.H.. amp. Gems & Gemology. 37. 1. 4–25. 10.5741/GEMS.37.1.4. 2015-01-11. 2016-10-05. https://web.archive.org/web/20161005004044/http://freeshipping.www.canadianammolite.com/SP01.pdf#page=5. dead.
  3. Web site: Latest Cretaceous Western Interior Seaway . 2007-06-22 . https://web.archive.org/web/20110927041935/http://www.scn.org/~bh162/maas.html . 2011-09-27 . dead .
  4. 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. .
  5. Web site: 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.. Canadian Society of Petroleum Geologists. 1994. 2016-06-20. https://web.archive.org/web/20160701131122/http://ags.aer.ca/reports/atlas-of-the-western-canada-sedimentary-basin.htm. 2016-07-01. dead.
  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. 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. .
  8. Web site: Bearpaw fauna in Alberta . 2007-06-22 . 2007-08-21 . https://web.archive.org/web/20070821233955/http://www.digitaldreammachine.com/sadrg/formation_bearpaw.html . dead .
  9. "Table 20.1," in Weishampel, et al. (2004). Page 441.
  10. Eamon T. Drysdale . François Therrien . Darla K. Zelenitsky . David B. Weishampel . David C. Evans . 2019 . Description of juvenile specimens of Prosaurolophus maximus (Hadrosauridae: Saurolophinae) from the Upper Cretaceous Bearpaw Formation of southern Alberta, Canada, reveals ontogenetic changes in crest morphology . Journal of Vertebrate Paleontology . 38 . 6 . e1547310 . 10.1080/02724634.2018.1547310 . 109440173 .
  11. Kubo . T. . Mitchell . M. T. . Henderson . D. M. . 10.1080/02724634.2012.658124 . Albertonectes vanderveldei, a new elasmosaur (Reptilia, Sauropterygia) from the Upper Cretaceous of Alberta . Journal of Vertebrate Paleontology . 32 . 3 . 557–572. 2012 . 129500470 .
  12. 10.1080/02724634.2017.1278608 . Serratos . Danielle J. . Druckenmiller . Patrick . Benson . Roger B.J. . A new elasmosaurid (Sauropterygia, Plesiosauria) from the Bearpaw Shale (Late Cretaceous, Maastrichtian) of Montana demonstrates multiple evolutionary reductions of neck length within Elasmosauridae . Journal of Vertebrate Paleontology . 2017 . 37 . 2 . e1278608. 132717607 .
  13. Sato . Tamaki . 2003 . Terminonatator ponteixensis, a new elasmosaur (Reptilia:Sauropterygia) from the Upper Cretaceous of Saskatchewan . Journal of Vertebrate Paleontology . 23 . 1 . 89–103 . 10.1671/0272-4634(2003)23[89:TPANES]2.0.CO;2 . 130373116 . 0272-4634.
  14. Sato . Tamaki . https://bioone.org/journals/journal-of-paleontology/volume-79/issue-5/0022-3360(2005)079%5b0969%3aANPPRS%5d2.0.CO%3b2/A-NEW-POLYCOTYLID-PLESIOSAUR-REPTILIA--SAUROPTERYGIA-FROM-THE-UPPER/10.1666/0022-3360(2005)079[0969:ANPPRS2.0.CO;2.short A new Polycotylid Plesiosaur (Reptilia: Sauropterygia) from the Upper Cretaceous Bearpaw Formation in Saskatchewan, Canada ]. Journal of Paleontology . 1 September 2005 . 79 . 5 . 969 . 10.1666/0022-3360(2005)079[0969:ANPPRS]2.0.CO;2 . 131128997 .
  15. Takuya Konishi. Michael Newbrey. Michael Caldwell. 86325001. A small, exquisitely preserved specimen of Mosasaurus missouriensis (Squamata, Mosasauridae) from the upper Campanian of the Bearpaw Formation, western Canada, and the first stomach contents for the genus. 2014. Journal of Vertebrate Paleontology. 34. 4. 802–819. 10.1080/02724634.2014.838573.
  16. Konishi. Takuya. Brinkman. Donald. Massare. Judy A.. Caldwell. Michael W.. 2011-09-01. New exceptional specimens of Prognathodon overtoni (Squamata, Mosasauridae) from the upper Campanian of Alberta, Canada, and the systematics and ecology of the genus. Journal of Vertebrate Paleontology. 31. 5. 1026–1046. 10.1080/02724634.2011.601714. 129001212. 0272-4634.
  17. Cuthbertson . Robin S. . Holmes . Robert B. . A new species of Plioplatecarpus (Mosasauridae, Plioplatecarpinae) from the Bearpaw Formation (Campanian, Upper Cretaceous) of Montana, U.S.A. . Journal of Vertebrate Paleontology . 22 April 2015 . 35 . 3 . e922980 . 10.1080/02724634.2014.922980 . 129311001 .
  18. Jiménez-Huidobro, P.. Caldwell, M.W.. Paparella, I.. Bullard, T.S.. 2018. A new species of tylosaurine mosasaur from the upper Campanian Bearpaw Formation of Saskatchewan, Canada. Journal of Systematic Palaeontology. 17. 10. 1–16. 10.1080/14772019.2018.1471744. 90533033.

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