Ravenscrag Formation


The Ravenscrag Formation is a stratigraphic unit of early Paleocene age in the Western Canada Sedimentary Basin. It takes the name from the settlement of Ravenscrag, Saskatchewan, and was first described in outcrop at Ravenscrag Butte near Frenchman River by N.B. Davis in 1918.

Lithology

The Ravenscrag Formation is an eastward-thickening wedge of sediments. It is composed primarily of buff, grey and white silty claystone, with mudstone, siltstone, sandstone, and it includes several significant coal seams. These sediments were deposited in floodplain, overbank and swamp environments.

Age

The Ravenscrag Formation is of early Paleocene age and the base of the formation coincides with the Cretaceous-Paleogene boundary, as evidenced by biostratigraphic changes and, in some places, the presence of the terminal Cretaceous iridium anomaly.

Distribution

The Ravenscrag Formation reaches a maximum thickness of and is present in southwestern Saskatchewan and the Cypress Hills area of southeastern Alberta.

Relationship to other units

Although some early workers included the underlying Frenchman Formation as the lower Ravenscrag, the two are separated by the Cretaceous-Paleogene boundary and are now treated separately. The contact is abrupt but conformable, and occurs at the base of the lowermost coal seam in the Ravenscrag Formation.
The Ravenscrag Formation is unconformably overlain by the Eocene age Swift Current Formation, and it is exposed at surface where younger formations have been removed by erosion. It is equivalent in age to the upper part of the Scollard Formation and the lower part of the Paskapoo Formation in southern Alberta, and to the Fort Union Formation in Montana and North Dakota.

Paleontology

The Ravenscrag Formation contains remains of vertebrates that provide important information about the dawn of the age of mammals after the Cretaceous-Paleogene extinction event. Material from the following groups of mammals has been reported: Multituberculata, Marsupicarnivora, Eulipotyphla, Dermoptera, Primates, Carnivora, Ungulata and Pantodonta. These occur as isolated teeth, fragments of jaws with teeth, and isolated skeletal parts. They are associated with the remains of fish such as Amia and Lepisosteus, small reptiles and amphibians, and crocodilians.
The formation also contains a wide variety of plant fossils. Ferns include species of Osmunda, Onoclea, Azolla and others. Gymnosperms are represented by remains of Ginkgo and cupressaceous conifers such as Metasequoia and Glyptostrobus, and there are numerous types of leaves, seeds, flowers and other structures from angiosperms. The fossil pollen assemblage has also been described.

Economic geology

The coal seams of the Ravenscrag Formation are of lignitic rank and have a low sulphur content. They are mined at several locations in southern Saskatchewan to fuel mine-mouth power stations.
Clay has been produced from the Ravenscrag Formation and used primarily for the manufacture of various types of brick.