Crowsnest Formation

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Coordinates: 49°38′51″N 114°31′48″W / 49.64750°N 114.53000°W / 49.64750; -114.53000 (Crowsnest Formation)
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Crowsnest Formation
Stratigraphic range: Mid to Upper Albian
Blackstone Formation
OverliesMa Butte Formation
ThicknessUp to 488 metres (1,600 ft)[2]
Lithology
PrimaryVolcanic rocks, pyroclastic breccia
OtherSandstone
Location
Coordinates49°38′51″N 114°31′48″W / 49.64750°N 114.53000°W / 49.64750; -114.53000 (Crowsnest Formation)
Region Alberta
Country Canada
ExtentWestern Canadian Sedimentary Basin
Type section
Named forCrowsnest Pass
Named byG.M. Dawson[3]
Crowsnest Formation is located in Canada
Crowsnest Formation

The Crowsnest Formation, also called the Crowsnest Volcanics, is a geological formation in southwestern Alberta, Canada, on the southwestern margin of the Western Canada Sedimentary Basin.[4] It was named for the Crowsnest Pass near Coleman, Alberta. The formation consists mostly of pyroclastic rocks that were laid down in a series of explosive eruptions about 100 million years ago during the Albian stage of the Early Cretaceous epoch. It contains unusual minerals such as melanite (a variety of andradite garnet) and analcime (a variety of zeolite).[2]

Lithology and mineralogy

aegerine-augite and chlorite.[5][6] Blairmorite, a rare analcime-rich rock-type named for the town of Blairmore, Alberta, is known only from the Crowsnest Formation and a locality in Mozambique.[6]

Stratigraphy

The Crowsnest Formation is the uppermost unit of the

Blackstone Formation that were deposited during a marine transgression in the Late Cretaceous.[2][5]

Deposition

The volcanics were laid down on an inland floodplain that is represented by the underlying Ma Butte Formation. The eruptions probably occurred to the west near what is now

thrust faulting during the Laramide orogeny. It's estimated that the volcanics originally covered an area of about 1,800 km2 (690 sq mi), and their volume is estimated at 209 km3 (50 cu mi).[2]

Thickness and distribution

The Crowsnest Volcanics are exposed along a series of folded, west-dipping fault plates in the Front Ranges and foothills of the southern Canadian Rockies. They reach maximum thicknesses of 426 to 488 metres (1,400 to 1,600 ft) along a trend that extends northward from Coleman along McGillivray Ridge to Ma Butte.[2]

See also

References

  1. ISBN 0-920230-23-7
    .
  2. ^ a b c d e f g Leckie, D. and Burden, E.T. 2001. Stratigraphy, sedimentology, and palynology of the Cretaceous (Albian) Beaver Mines, Mill Creek, and Crowsnest Formations (Blairmore Group) of southwestern Alberta. Geological Survey of Canada, Bulletin 563, 103 p.
  3. ^ Dawson, G.M. 1886a. Preliminary report on the physical and geological features of that portion of the Rocky Mountains, between latitudes 49 and 51 30'. Geological and Natural History Survey of Canada, Annual Report, v. 1, p. 1B-169B.
  4. ^ 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 19: Cretaceous Mannville Group of the Western Canada Sedimentary Basin". Archived from the original on 2016-07-01. Retrieved 2016-06-20.{{cite web}}: CS1 maint: multiple names: authors list (link)
  5. ^
    doi:10.1139/e06-037. Retrieved 2013-11-03.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  6. ^ a b c Pearce, T.H. "Analcime phenocrysts in igneous rocks: Primary or secondary? – Discussion" (PDF). American Mineralogist 78: 225–229, 1993. Retrieved 2013-10-31.
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