Monach Formation

Monach Formation
Stratigraphic range: Valanginian
Monach Formation; Stratigraphic range: Valanginian
Type	Formation
Unit of	Minnes Group
Underlies	Bickford Formation
Overlies	Beattie Peaks Formation
Thickness	maximum 350 m (1,150 ft)
Lithology
Primary	Sandstone
Other	Siltstone, mudstone, coal
Location
Coordinates	55.8500°N 122.5°W
Region	British Columbia
Country	Canada
Extent	Western Canadian Sedimentary Basin
Type section
Named for	The Monach
Named by	W.H. Mathews, 1947[1]
	Monach Formation (Canada)

The Monach Formation is a geologic formation of Early Cretaceous (Valanginian) age in the Western Canada Sedimentary Basin that consists primarily of sandstone. It is present in the northern foothills of the Canadian Rockies and the adjacent plains in northeastern British Columbia.[2][3][4]

Lithology

The Monach Formation consists primarily of clean, white to light grey, well sorted, medium- to coarse-grained quartzose sandstone, and grey to brown, thin bedded to finely laminated argillaceous sandstone, with lesser interbeds of dark grey mudstone, thin coal seams, carbonaceous shale, and rare conglomerate.[2]

Environment of deposition

The Monach Formation was deposited in marine and nonmarine environments within and adjacent to the Western Interior Seaway. Depositional settings ranged from marine to shoreline, deltaic, river channel, floodplain, and swamp environments.[2]

Paleontology and age

The age of the Monach Formation has been determined from its fossil fauna, primarily species of the bivalve Buchia.[2]

Thickness and distribution

The Monach Formation is present in the foothills of the Canadian Rockies and the adjacent plains in northeastern British Columbia. It extends from the Chowade River in the north, to south of the Sukunka River where it grades into the Gorman Creek Formation. It attains a maximum thickness of 350 m (1,150 ft) in the foothills, and thins to zero about 80 km (50 mi) or less beyond the eastern edge of the foothills where it was removed by erosion prior to the deposition of the Cadomin Formation.[2][4]

Relationship to other units

The Monach Formation is part of the Minnes Group. It was deposited conformably on the Beattie Peaks Formation and is conformably overlain by the Bickford Formation, both of which also belong to the Minnes Group. To the east where it was removed by erosion, the Monach Formation is unconformably overlain by the Cadomin Formation. To the south it grades into the Gorman Creek Formation.[2][3][4]

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References

Mathews, W.H. 1947. Geology and coal resources of the Carbon Creek, Mount Bickford map area. British Columbia Department of Mines, Bulletin 24, 27 p.
Stott, D.F. 1998. Fernie Formation and Minnes Group (Jurassic and lowermost Cretaceous), northern Rocky Mountain foothills, Alberta and British Columbia. Geological Survey of Canada, Bulletin 516.
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 18: Jurassic and Lowermost Cretaceous strata of the Western Canada Sedimentary Basin". Retrieved 2016-06-20.CS1 maint: multiple names: authors list (link)
Glass, D.J. (editor) 1997. Lexicon of Canadian Stratigraphy, vol. 4, Western Canada including eastern British Columbia, Alberta, Saskatchewan and southern Manitoba. Canadian Society of Petroleum Geologists, Calgary, 1423 p. on CD-ROM. ISBN 0-920230-23-7.