{{Short description|Stratigraphic unit in central Alberta, Canada}} {{Infobox rockunit | name = Edmonton Group | image = Horseshoe Canyon Alberta Nov 1988.jpg | caption = Horseshoe Canyon Formation of the Edmonton Group | type = Geological group | age = {{Fossil range|Campanian|Danian|Late Cretaceous to Early Paleocene}} | period = Danian | prilithology = Sandstone, shale | otherlithology = Bentonite, coal | namedfor = Edmonton | namedby = Joseph Tyrrell, 1887 | region = Alberta | country = Canada | coordinates = | unitof = | subunits = Scollard Formation, Battle Formation, Whitemud Formation, Horseshoe Canyon Formation | underlies = Paskapoo Formation | overlies = Bearpaw Formation, Belly River Group | thickness = {{convert|328|m|ft|}} to {{convert|763|m|ft|}}<ref name="CSPG_Lexicon" /> | extent = | area = | map = | map_caption = }} Within the earth science of geology, the '''Edmonton Group''' is a Late Cretaceous (Campanian stage) to early Paleocene stratigraphic unit of the Western Canada Sedimentary Basin in the central Alberta plains.<ref name=Mossop24 /> It was first described as the Edmonton Formation by Joseph Burr Tyrrell in 1887 based on outcrops along the North Saskatchewan River in and near the city of Edmonton.<ref>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.</ref> E.J.W. Irish later elevated the formation to group status and it was subdivided into four separate formations.<ref name=Irish>Irish, E.J.W. 1970. The Edmonton Group of south-central Alberta. Bulletin of Canadian Petroleum Geology, vol. 18, p. 125-155.</ref> In ascending order, they are the Horseshoe Canyon, Whitemud, Battle and Scollard Formations.<ref name=Mossop24>{{Cite web|url=http://ags.aer.ca/reports/atlas-of-the-western-canada-sedimentary-basin.htm|title=The Geological Atlas of the Western Canada Sedimentary Basin, Chapter 24: Upper Cretaceous and Tertiary strata of the Western Canada Sedimentary Basin|author=Mossop, G.D. and Shetsen, I. (compilers), Canadian Society of Petroleum Geologists|year=1994|access-date=2016-06-20|archive-date=2016-07-01|archive-url=https://web.archive.org/web/20160701131122/http://ags.aer.ca/reports/atlas-of-the-western-canada-sedimentary-basin.htm|url-status=dead}}</ref><ref name="CSPG_Lexicon" /> The Cretaceous-Paleogene boundary occurs within the Scollard Formation, based on dinosaurian and microfloral evidence,<ref>Lerbekmo, J.F., Singh, C., Jarzen, D.M., and Russel, D.A. 1979. The Cretaceous-Tertiary boundary in south-central Alberta - a revision based on dinosaurian and microfloral evidence. Canadian Journal of Earth Science, 16: 325-330.</ref> as well as the presence of the terminal Cretaceous iridium anomaly.<ref>Lerbekmo, J.F. and St. Louis, R.M. 1985. The terminal Cretaceous iridium anomaly in the Red Deer Valley, Alberta. Canadian Journal of Earth Science, 23: 120-124.</ref>
== Distribution and thickness == The Edmonton Group is present in the central plains of Alberta. It consists of sedimentary rocks that were deposited in nonmarine to brackish water environments between the Canadian Rockies in the west and the Western Interior Seaway to the east.<ref name=Mossop24 /> Its reaches a maximum thickness of {{convert|763|m|ft}} near the foothills of the Rockies in the west, and thins eastward to zero at its erosional edge east of Edmonton.<ref name="CSPG_Lexicon" />
== Lithology == The Edmonton Group consists of fine-grained sandstones, calcareous sandstones, siltstones, sandy shales and mudstones, bentonitic sandstones and shales, bentonite beds, ironstone concretions, carbonaceous shales and coal seams. Hard sandstones commonly cap mesas, buttes and plateaus where erosion has formed badlands topography, as is the case for much of the Horseshoe Canyon Formation and the Scollard Formation. Coarse-grained sediments are rare in the Edmonton Group.<ref name="CSPG_Lexicon" />
== Paleontology == Plant fossils are common in both the Late Cretaceous and early Paleocene portions of the Edmonton Group.<ref>Bell, W.A. 1949. Uppermost Cretaceous and Paleocene floras of western Canada. Geological Survey of Canada, Bulletin 13, 231 p.</ref> Remains of Triceratops and other dinosaurs are found in the Late Cretaceous portion, especially the Horseshoe Canyon Formation and the lower part of the Scollard Formation. Molluscs such as Ostrea and Unio are found in both portions.<ref name="CSPG_Lexicon">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}}.</ref>
== Relationship to other units == The Edmonton Group is disconformably overlain by the Paskapoo Formation and conformably overlies the Bearpaw Formation or, where the Bearpaw is absent, the Belly River Formation.<ref name="CSPG_Lexicon" />
The Edmonton Group grades into the sequence of the Blood Reserve Formation, St. Mary River Formation and Willow Creek Formation in the southern Alberta plains; into the upper part of the Wapiti Group in the northern Alberta and northeastern British Columbia; and into the upper part of the Brazeau Formation and the Coalspur Formation in the foothills of the Canadian Rockies. It is equivalent to, but not contiguous with, the Eastend Formation, Whitemud Formation, Battle Formation and Frenchman Formation in the Cypress Hills of southeastern Alberta and southwestern Saskatchewan; and with the Fox Hills Formation in Saskatchewan.<ref name=Mossop24 /><ref name="CSPG_Lexicon" />
Formations that are stratigraphically equivalent in the western United States are the Horsethief Formation in Montana; the Fox Hills Formation and Lance Formation in Montana; and the Lennup Formation and Muteetse Formation in Wyoming.<ref name="CSPG_Lexicon" />
=== Subdivisions === The formations of the Edmonton Group are: {|class="wikitable" |- ! Formation !! Age !! Lithology !! Maximum<br />Thickness !! Reference |- | Scollard || Maastrichtian-Paleocene || sandstone, siltstone, mudstone, coal || {{convert|400|m|ft|-1|abbr=on}} |<ref name="CSPG_Lexicon" /> |- | Battle Formation || Maastrichtian || bentonitic silty shale, montmorillonitic clay || {{convert|14|m|ft|-1|abbr=on}} |<ref name="CSPG_Lexicon" /> |- | Whitemud|| Maastrichtian || kaolinitic sandstone, clay, shale || {{convert|23|m|ft|-1|abbr=on}} |<ref name="CSPG_Lexicon" /> |- | Horseshoe Canyon || Campanian-Maastrichtian || sandstone, siltstone, mudstone, coal || {{convert|227|m|ft|-1|abbr=on}} |<ref name="CSPG_Lexicon" /> |- |}
== See also == {{Portal|Geology|Canada|Paleontology}} * List of fossiliferous stratigraphic units in Alberta * Coalspur Formation
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== References == {{reflist}}
{{Western Canadian Sedimentary Basin| Central_Plains=yes| South AB=yes}}
Category:Geologic groups of Alberta Category:Western Canadian Sedimentary Basin Category:Cretaceous Alberta Category:Paleogene Alberta Category:Paleocene North America Category:Cretaceous–Paleogene boundary Category:Sandstone groups of Canada Category:Coal groups Category:Shale groups of Canada