The Bearpaw Formation, also called the Bearpaw Shale, is a
geologic formation of
Late Cretaceous
The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...
(
Campanian
The Campanian is the fifth of six ages of the Late Cretaceous epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campa ...
) age. It
outcrop
An outcrop or rocky outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth and other terrestrial planets.
Features
Outcrops do not cover the majority of the Earth's land surface because in most p ...
s in the U.S. state of
Montana
Montana ( ) is a landlocked U.S. state, state in the Mountain states, Mountain West subregion of the Western United States. It is bordered by Idaho to the west, North Dakota to the east, South Dakota to the southeast, Wyoming to the south, an ...
, as well as the
Canadian
Canadians () are people identified with the country of Canada. This connection may be residential, legal, historical or cultural. For most Canadians, many (or all) of these connections exist and are collectively the source of their being ''C ...
provinces of
Alberta
Alberta is a Provinces and territories of Canada, province in Canada. It is a part of Western Canada and is one of the three Canadian Prairies, prairie provinces. Alberta is bordered by British Columbia to its west, Saskatchewan to its east, t ...
and
Saskatchewan
Saskatchewan is a Provinces and territories of Canada, province in Western Canada. It is bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, to the northeast by Nunavut, and to the south by the ...
, and was named for the
Bear Paw Mountains in Montana.
It includes a wide range of marine
fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...
s, as well as the remains of a few
dinosaur
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...
s. It is known for its fossil
ammonite
Ammonoids are extinct, (typically) coiled-shelled cephalopods comprising the subclass Ammonoidea. They are more closely related to living octopuses, squid, and cuttlefish (which comprise the clade Coleoidea) than they are to nautiluses (family N ...
s, 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
The Western Interior Seaway (also called the Cretaceous Seaway, the Niobraran Sea, the North American Inland Sea, or the Western Interior Sea) was a large inland sea (geology), inland sea that existed roughly over the present-day Great Plains of ...
that advanced and then retreated across the region during Campanian time. It is composed primarily of dark grey
shale
Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of Clay mineral, clay minerals (hydrous aluminium phyllosilicates, e.g., Kaolinite, kaolin, aluminium, Al2Silicon, Si2Oxygen, O5(hydroxide, OH)4) and tiny f ...
s,
claystones, silty claystones and
siltstones, with subordinate silty
sandstone
Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...
s. It also includes bedded and
nodular concretions (both
calcareous
Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime (mineral), lime or being chalky. The term is used in a wide variety of Science, scientific disciplines.
In zoology
''Calcare ...
and
ironstone concretions) and thin beds of
bentonite
Bentonite ( ) is an Absorption (chemistry), absorbent swelling clay consisting mostly of montmorillonite (a type of smectite) which can either be Na-montmorillonite or Ca-montmorillonite. Na-montmorillonite has a considerably greater swelli ...
. 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. .]
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
Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class (biology), class of aquatic animal, aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed b ...
''
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
Osteichthyes ( ; ), also known as osteichthyans or commonly referred to as the bony fish, is a Biodiversity, diverse clade of vertebrate animals that have endoskeletons primarily composed of bone tissue. They can be contrasted with the Chondricht ...
,
shark
Sharks are a group of elasmobranch cartilaginous fish characterized by a ribless endoskeleton, dermal denticles, five to seven gill slits on each side, and pectoral fins that are not fused to the head. Modern sharks are classified within the ...
s,
rays, birds, and marine reptiles like
mosasaur
Mosasaurs (from Latin ''Mosa'' meaning the 'Meuse', and Ancient Greek, Greek ' meaning 'lizard') are an extinct group of large aquatic reptiles within the family Mosasauridae that lived during the Late Cretaceous. Their first fossil remains wer ...
s such as ''
Prognathodon overtoni'' and ''
Plioplatecarpus peckensis'',
plesiosaur
The Plesiosauria or plesiosaurs are an Order (biology), order or clade of extinct Mesozoic marine reptiles, belonging to the Sauropterygia.
Plesiosaurs first appeared in the latest Triassic Period (geology), Period, possibly in the Rhaetian st ...
s such as ''
Dolichorhynchops herschelensis
''Dolichorhynchops'' is an extinct genus of polycotylid plesiosaur from the Late Cretaceous of North America, containing the species ''D. osborni'' and ''D. herschelensis'', with two previous species having been assigned to new genera. Definitive ...
'', ''
Albertonectes
''Albertonectes'' is an extinct genus of elasmosaurid plesiosaur known from the Late Cretaceous (middle upper Campanian stage) Bearpaw Formation of Alberta, Canada. It contains a type species, single species, ''Albertonectes vanderveldei''. ''Alb ...
'' and ''
Nakonanectes'', and
sea turtle
Sea turtles (superfamily Chelonioidea), sometimes called marine turtles, are reptiles of the order Testudines and of the suborder Cryptodira. The seven existing species of sea turtles are the flatback, green, hawksbill, leatherback, loggerh ...
s.
Dinosaur
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...
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
Plesiosaurs
Mosasaurs
Turtles
Bony fish
Cartilaginous fish
Flora
References
{{Western Canadian Sedimentary Basin, Northeast_Plains=yes, Central_Plains=yes, Saskatchewan=yes
Geologic formations of Saskatchewan
Cretaceous Alberta
Cretaceous Montana
Cretaceous Saskatchewan
Western Canadian Sedimentary Basin
Campanian Stage
Geologic formations of Alberta
Geologic formations of Montana
Upper Cretaceous Series of North America