The Oldman Formation is a stratigraphic unit 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 ...

stage) age that underlies much of southern

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 ...

Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...

. It consists primarily of

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 that were deposited in fluvial channel and

floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river. Floodplains stretch from the banks of a river channel to the base of the enclosing valley, and experience flooding during periods of high Discharge (hydrolog ...

environments. It was named for exposures along the

Oldman River The Oldman River is a river in southern Alberta, Canada. It flows roughly west to east from the Rocky Mountains, through the communities of Fort Macleod, Lethbridge, and on to Grassy Lake, where it joins the Bow River to form the South Sa ...

between its confluence with the St. Mary River and the city of

Lethbridge Lethbridge ( ) is a city in the province of Alberta, Canada. With a population of 106,550 in the 2023 Alberta municipal censuses, 2023 municipal census, Lethbridge became the fourth Alberta city to surpass 100,000 people. The nearby Canadian ...

, and it is known primarily for its

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 and other fossils.Eberth, D.A. and Hamblin A.P. 1993. Tectonic, stratigraphic, and sedimentologic significance of a regional discontinuity in the upper Judith River Group (Belly River wedge) of southern Alberta, Saskatchewan, and northern Montana. Canadian Journal of Earth Sciences 30: 174-200.

Lithology

The Oldman Formation is composed primarily of light-colored, fine-grained sandstones. They are upward-fining, lenticular to sheet-like bodies that are yellowish, steep-faced and blocky in

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 ...

. The formation also includes lesser amounts of siltstone and mudstone.Eberth, D.A. 2005. The geology. In: Currie, P.J., and Koppelhus, E.B. (eds), Dinosaur Provincial Park: A Spectacular Ancient Ecosystem Revealed. Indiana University Press: Bloomington and Indianapolis, p. 54-82. .

Depositional environments

The sediments of the Oldman Formation were deposited in fluvial channels (the sandstones) and a variety of channel margin, overbank and

environments (the siltstones and mudstones). The formation is about thick at Dinosaur Provincial Park in southeastern Alberta. It thickens toward the southwest, and northwestern

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 ...

appears to have been the primary source of the sediments.

Relationship to other units

The Oldman Formation is a member of the Belly River Group (also known as the Judith River Group). It conformably overlies the Foremost Formation, and is separated from the overlying Dinosaur Park Formation by a regional disconformity. The sediments of the Oldman are superficially similar to those of the Dinosaur Park, which was included in the Oldman Formation prior to the recognition of the disconformity. The two formations can also be distinguished by petrographic and sedimentologic differences.

Age

The Oldman Formation was deposited during the middle

, between about 77.5 and 76.5 million years ago. It lies fully within magnetic polarity Chron 33n.Lerbekmo, J.F. 1989. The position of the 33-33r (Campanian) polarity chron boundary in southeastern Alberta. Bulletin of Canadian Petroleum Geology 37: 43-47.

Fossil content

List of dinosaurs found in the formation:Weishampel, D.B., Barrett, P.M., Coria, R.A., Le Loueff, J., Xu X., Zhao X., Sahni, A., Gomani, E.M.P., & Noto, C.N. 2004. Dinosaur distribution. In: Weishampel, D.B., Dodson, P., & Osmólska, H. (Eds.). ''The Dinosauria'' (2nd Edition). Berkeley: University of California Press. Pp. 517-606.

Theropods

Ornithischians

References

Bibliography

* D.A. Eberth. 1996. Origin and significance of mud-filled incised valleys (Upper Cretaceous) in southern Alberta, Canada. Sedimentology 43:459–477 * Ryan, M. J., and Russell, A. P., 2001. Dinosaurs of Alberta (exclusive of Aves): In: Mesozoic Vertebrate Life, edited by Tanke, D. H., and Carpenter, K., Indiana University Press, pp. 279–297 {{Western Canadian Sedimentary Basin, South AB=yes Upper Cretaceous Series of North America Cretaceous Alberta Campanian Stage Sandstone formations of Canada Fluvial deposits Ooliferous formations Western Canadian Sedimentary Basin