Edmonton Group

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Edmonton Group
Stratigraphic range: Late Cretaceous
Horseshoe Canyon.jpg
Horseshoe Canyon Formation of the Edmonton Group
Type Geological formation
Sub-units Battle Formation, Whitemud Member, Horseshoe Canyon Formation
Underlies Paskapoo Formation
Overlies Bearpaw Formation, Belly River Group
Thickness 328 metres (1,080 ft) to 763 metres (2,500 ft)[1]
Lithology
Primary Sandstone, shale
Other Bentonite, coal
Location
Region WCSB
Country  Canada
Type section
Named for Edmonton
Named by Joseph Tyrrell, 1887

The Edmonton Group is a stratigraphical unit of Late Cretaceous age in the Western Canadian Sedimentary Basin.

It takes the name from the city of Edmonton, and was first described in outcrops on the banks of the North Saskatchewan River near the city by Joseph Burr Tyrrell in 1887.[2]

Lithology[edit]

The Edmonton Group is composed fine grained calcareous sandstone and sandy shale with bentonite, ironstone concretions and coal. The sediments were deposited in fresh and brackish water environments. [1]

Paleontology[edit]

Vertebrate fossils are found in the formation, including Triceratops remains. Molluscs such as Ostrea and Unio can also be retrieved from the Edmonton Group.

Distribution[edit]

The Edmonton Group reaches a maximum thickness of 763 metres (2,500 ft) in the Canadian Rockies foothills, and is typically 350 metres (1,150 ft) thick in the plains.[1] It forms the erosional surface in Central Alberta and often forms badlands topography.

Relationship to other units[edit]

The Edmonton Group is disconformably overlain by the Paskapoo Formation and conformably overlays the Bearpaw Formation or Belly River Formation.[1]

It is equivalent to Fox Hills Formation in Saskatchewan and is not differentiated in the upper Montana Group. It can be correlated with the Horsethief Formation in Montana, the Lennup Formation and Muteetse Formation in Wyoming, the Blood Reserve Formation and St. Mary River Formation in southern Alberta, with the Eastend Formation, Whitemud Formation, Battle Formation and Frenchman Formation in the Cypress Hills, with the Fox Hills Formation and Lace Formation in Montana, as well as with the Wapiti Group and Brazeau Group in the Canadian Rockies foothills.

Subdivisions[edit]

Subdivisions of the Edmonton Group include:

Sub-unit Age Lithology Max
Thickness
Reference
Battle Formation Maastrichtian bentonitic silty shale, montmorillonitic clay 14 m (50 ft) [3]
Whitemud Member Maastrichtian bentonitic shale, argillaceous sandstone 6 m (20 ft) [4]
Horseshoe Canyon Formation Maastrichtian sandstone, siltstone, shale 227 m (740 ft) [5]

References[edit]

  1. ^ a b c d Lexicon of Canadian Geologic Units. "Edmonton Group". Retrieved 2009-03-01. 
  2. ^ Tyrrell, J.B., 1887. Report on a part of northern Alberta and portions of adjacent Districts of Assiniboia and Saskatchewan. Geological Survey of Canada, Ann. Rept.1886, new ser., v.11, Part E, p.1-176.
  3. ^ Lexicon of Canadian Geologic Units. "Battle Formation". Retrieved 2010-01-03. 
  4. ^ Lexicon of Canadian Geologic Units. "Whitemud Member". Retrieved 2010-01-03. 
  5. ^ Lexicon of Canadian Geologic Units. "Horseshoe Canyon Formation". Retrieved 2010-01-03.