The Ravenscrag Formation is a

stratigraphic Stratigraphy is a branch of geology concerned with the study of rock layers ( strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithostr ...

unit of early

Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch that lasted from about 66 to 56 million years ago (mya). It is the first epoch of the Paleogene Period in the modern Cenozoic Era. The name is a combination of the Ancient Greek ''pal ...

age in the

Western Canada Sedimentary Basin The Western Canadian Sedimentary Basin (WCSB) underlies of Western Canada including southwestern Manitoba, southern Saskatchewan, Alberta, northeastern British Columbia and the southwest corner of the Northwest Territories. This vast sedimentary ...

. It was named for the settlement of Ravenscrag, Saskatchewan, and was first described from

outcrop An outcrop or rocky outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth. Features Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficia ...

s at Ravenscrag Butte near the

Frenchman River The Frenchman River, ( ats, níhʔɔɔtóóúníícááh, lit=white person river), also known locally as the Whitemud River, is a river in Saskatchewan, Canada and Montana, United States. It is a tributary of the Milk River, itself a tributary o ...

by N.B. Davis in 1918.Davis, N.B., 1918. Report on the clay resources of southern Saskatchewan; Canada, Department of Mines, Mines Branch, Report 468, 93 p. The Ravenscrag Formation includes a wide range of

vertebrate Vertebrates () comprise all animal taxon, taxa within the subphylum Vertebrata () (chordates with vertebral column, backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the ...

and plant

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 preserved ...

s, as well as economically significant

coal Coal is a combustible black or brownish-black sedimentary rock, formed as stratum, rock strata called coal seams. Coal is mostly carbon with variable amounts of other Chemical element, elements, chiefly hydrogen, sulfur, oxygen, and nitrogen ...

seams and

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay part ...

deposits.

Lithology

The Ravenscrag Formation is an eastward-thickening wedge of sediments. It is composed primarily of buff, grey and white silty

claystone Mudrocks are a class of fine-grained siliciclastic sedimentary rocks. The varying types of mudrocks include siltstone, claystone, mudstone, slate, and shale. Most of the particles of which the stone is composed are less than and are too sm ...

, with mudstone,

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, ...

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

, and several significant

seams. Glass, D.J., editor, 1997. Lexicon of Canadian Stratigraphy, vol. 4, Western Canada, p. 974. Canadian Society of Petroleum Geologists, Calgary, Alberta, 1423 p. on CD-ROM, . These sediments were deposited in

floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river which stretches from the banks of its channel to the base of the enclosing valley walls, and which experiences flooding during periods of high discharge.Goudi ...

, overbank and swamp environments.McIver, E.E. and Basinger, J.F. 1993. Flora of the Ravenscrag Formation (Paleocene), southwestern Saskatchewan, Canada. Palaeontographica Canadiana No. 10, 167 p. Geological Association of Canada and Canadian Society of Petroleum Geologists.

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 The term iridium anomaly commonly refers to an unusual abundance of the chemical element iridium in a layer of rock strata at the Cretaceous–Paleogene (K–Pg) boundary. The unusually high concentration of a rare metal like iridium is often take ...

.Lerbekmo, J.F., Sweet, A.R. and St. Louis, R.M. 1987. The relationship between the iridium anomaly and palynofloral events at three Cretaceous-Tertiary boundary localities in western Canada. Geological Society of America Bulletin, 99:25-330. Mammalian fossils from the formation indicate

North American land mammal age The North American land mammal ages (NALMA) establishes a geologic timescale for North American fauna beginning during the Late Cretaceous and continuing through to the present. These periods are referred to as ages or intervals (or stages when re ...

s of

Puercan The Puercan North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), spanning the interval from 66,000,000 to 63,300,000 years BP lasting . It is usua ...

Tiffanian The Tiffanian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 60,200,000 to 56,800,000 years BP lasting . It is usually co ...

Distribution

The Ravenscrag Formation reaches a maximum thickness of and is present in southwestern

Saskatchewan Saskatchewan ( ; ) is a province in western Canada, bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, to the northeast by Nunavut, and on the south by the U.S. states of Montana and North ...

and the Cypress Hills area of southeastern

Alberta Alberta ( ) is one of the thirteen provinces and territories of Canada. It is part of Western Canada and is one of the three prairie provinces. Alberta is bordered by British Columbia to the west, Saskatchewan to the east, the Northwest Ter ...

Relationship to other units

Although some early workers included the underlying

Frenchman Formation The Frenchman Formation is stratigraphic unit of Late Cretaceous (late Maastrichtian) age in the Western Canada Sedimentary Basin. It is present in southern Saskatchewan and the Cypress Hills of southeastern Alberta. The formation was defined by ...

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 (the No. 1 or Ferris coal seam) in the Ravenscrag Formation.Lerbekmo, J.F. 1985. Magnetostratigraphic and biostratigraphic correlations of Maastrichtian to early Paleocene strata between south-central Alberta and southwestern Saskatchewan. Bulletin of Canadian Petroleum Geology, vol. 33, p. 213-226. The Ravenscrag Formation is unconformably overlain by the

Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', " ...

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 The Scollard Formation is an Upper Cretaceous to lower Palaeocene stratigraphic unit of the Western Canada Sedimentary Basin in southwestern Alberta. Its deposition spanned the time interval from latest Cretaceous to early Paleocene, and it inclu ...

and the lower part of the

Paskapoo Formation The Paskapoo Formation is a stratigraphic unit of Middle to Late Paleocene age in the Western Canada Sedimentary Basin. The Paskapoo underlies much of southwestern Alberta, and takes the name from the Blindman River (''paskapoo'' means "blind ...

in southern Alberta, and to the

Fort Union Formation The Fort Union Formation is a geologic unit containing sandstones, shales, and coal beds in Wyoming, Montana, and parts of adjacent states. In the Powder River Basin, it contains important economic deposits of coal, uranium, and coalbed methane. ...

Montana Montana () is a U.S. state, state in the Mountain states, Mountain West List of regions of the United States#Census Bureau-designated regions and divisions, division of the Western United States. It is bordered by Idaho to the west, North ...

and

North Dakota North Dakota () is a U.S. state in the Upper Midwest, named after the indigenous Dakota Sioux. North Dakota is bordered by the Canadian provinces of Saskatchewan and Manitoba to the north and by the U.S. states of Minnesota to the east, S ...

Paleontology

The Ravenscrag Formation contains remains of

s 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 Multituberculata (commonly known as multituberculates, named for the multiple tubercles of their teeth) is an extinct order of rodent-like mammals with a fossil record spanning over 130 million years. They first appeared in the Middle Jurassic, ...

, Marsupicarnivora,

Eulipotyphla Eulipotyphla (, which means "truly fat and blind") is an order of mammals suggested by molecular methods of phylogenetic reconstruction, which includes the laurasiatherian members of the now-invalid polyphyletic order Lipotyphla, but not the afr ...

, Dermoptera,

Primate Primates are a diverse order (biology), order of mammals. They are divided into the Strepsirrhini, strepsirrhines, which include the lemurs, galagos, and lorisids, and the Haplorhini, haplorhines, which include the Tarsiiformes, tarsiers and ...

Carnivora Carnivora is a monophyletic order of placental mammals consisting of the most recent common ancestor of all cat-like and dog-like animals, and all descendants of that ancestor. Members of this group are formally referred to as carnivorans, ...

, Ungulata and Pantodonta. These occur primarily 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 ''Lepisosteus'' is a genus of gars in the family Lepisosteidae. Distribution While in the present day, ''Lepisosteus'' is only known across North America, fossil remains show it was much more widespread in the past, with specimens known from ...

'', small reptiles and amphibians, and

crocodilia Crocodilia (or Crocodylia, both ) is an order of mostly large, predatory, semiaquatic reptiles, known as crocodilians. They first appeared 95 million years ago in the Late Cretaceous period ( Cenomanian stage) and are the closest livi ...

nsFox, R.C., 1990. The succession of Paleocene mammals in western Canada. Geological Society of America, Special Paper 243, pp. 51-70. including '' Borealosuchus'' (originally ''Leidyosuchu''s) ''acutidentatus''. The formation also contains a wide variety of plant fossils.

Fern A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes except ...

s include species of '' Osmunda'', '' Onoclea'', ''

Azolla ''Azolla'' (mosquito fern, duckweed fern, fairy moss, water fern) is a genus of seven species of aquatic ferns in the family Salviniaceae. They are extremely reduced in form and specialized, looking nothing like other typical ferns but more res ...

'' and others.

Gymnosperm The gymnosperms ( lit. revealed seeds) are a group of seed-producing plants that includes conifers, cycads, '' Ginkgo'', and gnetophytes, forming the clade Gymnospermae. The term ''gymnosperm'' comes from the composite word in el, γυμν ...

s are represented by remains of ''

Ginkgo ''Ginkgo'' is a genus of non-flowering seed plants. The scientific name is also used as the English name. The order to which it belongs, Ginkgoales, first appeared in the Permian, 270 million years ago, and is now the only living genus withi ...

'' and cupressaceous

conifer Conifers are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up the division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single extant class, Pinopsida. All ex ...

s such as ''

Metasequoia ''Metasequoia'', or dawn redwoods, is a genus of fast-growing deciduous trees, one of three species of conifers known as redwoods. The living species ''Metasequoia glyptostroboides'' is native to Lichuan county in Hubei province, China. Altho ...

'' and '' Glyptostrobus'', and there are numerous types of leaves, seeds, flowers and other structures from

angiosperm Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. They include all forbs (flowering plants without a woody stem), grasses and grass-like plants, a vast majority of br ...

s. 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 Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...

content. They are mined at several locations in southern Saskatchewan to fuel mine-mouth electrical power stations. Clay has been produced from the Ravenscrag Formation and used primarily for the manufacture of various types of brick.Lindoe, L.O. 1965. Ceramic clays of the Cypress Hills. Alberta Society of Petroleum Geologists, 15th Annual Field Trip Guidebook, Part 1, Cypress Hills plateau, p. 210-225.

References

{{Western Canadian Sedimentary Basin, South AB=yes, Saskatchewan=yes Geologic formations of Alberta Geologic formations of Saskatchewan Western Canadian Sedimentary Basin Paleogene Alberta Paleogene Saskatchewan