Oldman Formation
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| Oldman Formation | |
|---|---|
| Stratigraphic range: Campanian, | |
| Type | Geological formation |
| Unit of | Belly River Group |
| Underlies | Dinosaur Park Formation |
| Overlies | Foremost Formation |
| Thickness | up to 328 feet (100 m)[1] |
| Lithology | |
| Primary | Sandstone |
| Other | Mudstone and bentonite |
| Location | |
| Coordinates | 49°37′41″N 112°53′23″W / 49.62806°N 112.88972°W |
| Region | Western Canada Sedimentary Basin |
| Country |  Canada |
| Type section | |
| Named for | Oldman River |
| Named by | Russell, L.S. and Landes, R.W. |
| Year defined | 1940[2] |
  Oldman Formation (Canada)  Oldman Formation (Alberta) | |
The Oldman Formation is a stratigraphic unit of Late Cretaceous (Campanian stage) age that underlies much of southern Alberta, Canada. It consists primarily of sandstones that were deposited in fluvial channel and floodplain environments. It was named for exposures along the Oldman River between its confluence with the St. Mary River and the city of Lethbridge, and it is known primarily for its dinosaur remains and other fossils.[3]
Depositional environments
The sediments of the Oldman Formation were deposited in fluvial channels (the sandstones) and a variety of channel margin, overbank and floodplain environments (the siltstones and mudstones). The formation is about 40 metres (130 ft) thick at Dinosaur Provincial Park in southeastern Alberta. It thickens toward the southwest, and northwestern Montana appears to have been the primary source of the sediments.[4]
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.[3][4] In Central Montana, The Oldman Formation is equivalent to the upper part of the Mclelland Ferry Member, as well as the Woodhawk and Coal Ridge Members of the Judith River Formation.[5] It is also believed to be equivalent to parts of the Two Medicine Formation in Western Montana.[6]
