Bullhead Group is a stratigraphic unit of Lower Cretaceous age in the Western Canada Sedimentary Basin of northeastern British Columbia and western Alberta.[3] It was first defined by F.H. McLearn in 1918 as the Bullhead Mountain Formation,[2] but later was upgraded to group status. It consists of the Cadomin and Gething Formations, although some early workers included the Bluesky Formation and others in the group.[4]
| Bullhead Group | |
|---|---|
| Stratigraphic range: | |
| Type | Geological formation |
| Sub-units | Gething Formation Cadomin Formation |
| Underlies | Fort St. John Group |
| Overlies | Nikanassin Formation, Fernie Group, Minnes Group, Kootenay Group |
| Thickness | up to 900 metres (2,950 ft)[1] |
| Lithology | |
| Primary | Conglomerate, sandstone, siltstone and mudstone |
| Other | Coal |
| Location | |
| Coordinates | 56°01′N 122°08′W / 56.01°N 122.14°W |
| Region |  British Columbia Alberta |
| Country |  Canada |
| Type section | |
| Named by | F.H. McLearn[2] |
Lithology
editBullhead Group includes the conglomerate and quartzose sandstones of the Cadomin Formation at the base, and grades to sandstone, siltstone, mudstone, shale and coal seams of the overlying Gething Formation. Those sediments were deposited in alluvial fan, braided river, deltaic and coastal plain environments.[4]
Distribution
editThe Bullhead Group is present in the foothills of the Northern Rocky Mountains and the adjacent plains, extending from the Tuchodi River of British Columbia in the north to the Smoky River of Alberta in the south. It thins eastward from about 900 meters (3,000 ft) in the western foothills of northeastern British Columbia to about 100 meters (330 ft) in the Peace River plains, reaching zero near Fort St. John. The most complete section is found in the type locality of the Gething Formation in the Peace River Canyon immediately downstream from the W. A. C. Bennett Dam.[1]
Relationship to other units
editThe Bullhead Group overlies a major regional unconformity caused by pre-Bullhead erosion.[4] It rests unconformably on the Fernie Formation, the Nikanassin Formation, the Minnes Group or the Kootenay Group, depending on the location and the extent of the erosion. It is overlain conformably by the glauconitic sandstones and marine shales at the base of the Fort St. John Group.[1]
References
edit- ^ a b c 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.
- ^ a b McLearn, F.H., 1923. Peace River Canyon Coal Area, British Columbia; Geological Survey of Canada, Summary Report 1922, Part B, pp. 1-46.
- ^ 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". Compiled by Mossop, G.D. and Shetsen, I. Archived from the original on 2016-07-01. Retrieved 2016-06-20.
- ^ a b c Stott, D.F. 1965. Lower Cretaceous Bullhead and Fort St John Groups, between Smoky and Peace Rivers, Rocky Mountain foothills, Alberta and British Columbia. Geological Survey of Canada, Bulletin 152, 279 p. ISBN 0-660-10208-0.