Ravenscrag Formation

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Ravenscrag Formation
Stratigraphic range: Paleocene
Type Geological formation
Sub-units Upper Ravenscrag
Lower Ravenscrag
Underlies Swift Current Formation
Overlies Frenchman Formation
Thickness up to 244 metres (800 ft)[1]
Lithology
Primary Claystone, mudstone, siltstone
Other Sandstone, coal
Location
Coordinates 49°30′07″N 108°58′33″W / 49.50182°N 108.97585°W / 49.50182; -108.97585 (Ravenscrag Formation)Coordinates: 49°30′07″N 108°58′33″W / 49.50182°N 108.97585°W / 49.50182; -108.97585 (Ravenscrag Formation)
Region Western Canada Sedimentary Basin
Country  Canada
Type section
Named for Ravenscrag, Saskatchewan
Named by N.B. Davis, 1918

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.[2]

Lithology[edit]

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.[1][3][4] These sediments were deposited in floodplain, overbank and swamp environments.[5]

Age[edit]

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.[6]

Distribution[edit]

The Ravenscrag Formation is exposed along the flanks of the Cypress Hills.

The Ravenscrag Formation reaches a maximum thickness of 244 metres (800 ft) and is present in southwestern Saskatchewan and the Cypress Hills area of southeastern Alberta.[1]

Relationship to other units[edit]

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 (the No. 1 or Ferris 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.[7] 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[edit]

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, Lyptophyla, Dermoptera, Primates, Carnivora, Condylartha 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.[8]

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.[5] The fossil pollen assemblage has also been described.[9]

Economic use[edit]

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.[4]

Clay has been produced from the Ravenscrag Formation and used primarily for the manufacture of various types of brick.[10]

References[edit]

  1. ^ a b c Lexicon of Canadian Geologic Units. "Ravenscrag Formation". Retrieved 2010-01-01. 
  2. ^ Davis, N.B., 1918. Report on the clay resources of southern Saskatchewan; Canada, Department of Mines, Mines Branch, Report 468, 93 p.
  3. ^ Glass, D.J., editor, 1997. Lexicon of Canadian Stratigraphy, vol. 4, Western Canada. Canadian Society of Petroleum Geologists, Calgary, Alberta, 1423 p. on CD-ROM, ISBN 0-920230-23-7.
  4. ^ a b Mossop, G.D. and Shetsen, I., (compilers), Canadian Society of Petroleum Geologists (1994). "The Geological Atlas of the Western Canada Sedimentary Basin, Chapter 33: Coal Resources of the Western Canada Sedimentary Basin". Retrieved 2013-08-01. 
  5. ^ a b 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.
  6. ^ 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.
  7. ^ Mossop, G.D. and Shetsen, I., (compilers), Canadian Society of Petroleum Geologists and Alberta Geological Survey (1994). "The Geological Atlas of the Western Canada Sedimentary Basin, Chapter 24: Upper Cretaceous and Tertiary strata of the Western Canada Sedimentary Basin". Retrieved 2013-08-01. 
  8. ^ Fox, R.C., 1990. The succession of Paleocene mammals in western Canada. Geological Society of America, Special Paper 243, pp. 51-70.
  9. ^ Sweet, A.R. 1978. Palynology of the Ravenscrag and Frenchman formations. In: Whitaker, S.H. et al. (eds), Coal resources of southern Saskatchewan: a model for evaluation methodology. Geological Survey of Canada, Economic Geology Report 30, p. 29-38.
  10. ^ Worcester, W.G. (1950). "Clay resources of Saskatchewan.". Province of Saskatchewan, Dept. of Natural Resources, Technical and Economic Series Report No. 2, 199 p. Retrieved 2013-11-04.