| 词条 | Bullhead Group |
| 释义 |
| name = Bullhead Group | image = | caption = | type = Geological formation | age = {{Fossil range|Barremian|Albian}} | period = Early Cretaceous | prilithology = Conglomerate, sandstone, siltstone and mudstone | otherlithology = Coal | namedfor = | namedby = F.H. McLearn[1] | region = {{flag|British Columbia}} {{flag|Alberta}} | country = {{flag|Canada}} | coordinates = {{coord|56.01|-122.14|name=Bullhead Group|display=inline,title}} | unitof = | subunits = Gething Formation Cadomin Formation | underlies = Fort St. John Group | overlies = Nikanassin Formation, Fernie Group, Minnes Group, Kootenay Group | thickness = up to {{convert|900|m|ft|-1}}[2] | extent = | area = | map = | map_caption = }}Bullhead Group is a stratigraphic unit of Lower Cretaceous age in the Western Canada Sedimentary Basin of northeastern British Columbia and western Alberta.[2] It was first defined by F.H. McLearn in 1918 as the Bullhead Mountain Formation,[1] 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.[3] LithologyBullhead 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.[3] DistributionThe 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 {{convert|900|m|ft|sp=us}} in the western foothills of northeastern British Columbia to about {{convert|100|m|ft|sp=us}} 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.[4] Relationship to other unitsThe Bullhead Group overlies a major regional unconformity caused by pre-Bullhead erosion.[3] 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.[4] References1. ^1 McLearn, F.H., 1923. Peace River Canyon Coal Area, British Columbia; Geological Survey of Canada, Summary Report 1922, Part B, pp. 1-46. {{WCSB|Northwest_Plains=yes}}2. ^{{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 19: Cretaceous Mannville Group of the Western Canada Sedimentary Basin|others=Compiled by Mossop, G.D. and Shetsen, I.|author= Canadian Society of Petroleum Geologists and Alberta Geological Survey|year=1994|accessdate=2016-06-20}} 3. ^1 2 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}}. 4. ^1 2 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}}. 7 : Geologic formations of Canada|Western Canadian Sedimentary Basin|Cretaceous British Columbia|Stratigraphy of British Columbia|Barremian Stage|Aptian Stage|Albian Stage |
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