Blairmore Group
| Blairmore Group Stratigraphic range: Early Cretaceous | |
|---|---|
| Type | Group |
| Sub-units | Cadomin Formation, Gladstone Formation, Beaver Mines Formation, Ma Butte Formation |
| Underlies | Crowsnest Formation, Alberta Group |
| Overlies | Kootenay Group |
| Thickness | up to 2,000 m (6,560 ft)[1] |
| Lithology | |
| Primary | Sandstone, siltstone, mudstone |
| Other | Conglomerate, limestone |
| Location | |
| Region |
 Alberta  British Columbia |
| Country |
 Canada |
| Type section | |
| Named for | Blairmore, Alberta |
| Named by | W.W. Leach, 1914[2] |
The Blairmore Group, originally named the Blairmore Formation, is a geologic unit of Early Cretaceous age in the Western Canada Sedimentary Basin that is present in southwestern Alberta and southeastern British Columbia.[1][3] It is subdivided into a series of formations, most of which contain plant fossils. In some areas it contains significant reservoirs of natural gas.
Lithology
The Blairmore group includes the conglomerate and quartzose sandstones of the Cadomin Formation at the base, and grades to sandstone, siltstone, mudstone, and limestone in the overlying formations. The Beaver Mines and Ma Butte Formations in the upper part of the group also include minor beds of bentonite and tuff.[1]
Stratigraphy
The Blairmore Group is subdivided into the following formations from top to base:
| Formation | Age | Lithology | Max Thickness | Reference |
|---|---|---|---|---|
| Ma Butte Formation | Early Cretaceous | mudstone, siltstone, very fine-grained sandstone, bentonite and tuff | 120 m (390 ft) | [1] |
| Beaver Mines Formation | Early Cretaceous | greenish grey sandstone and mudstone; minor conglomerate, bentonite and tuff | 455 m (1,490 ft) | [1] |
| Gladstone Formation | Early Cretaceous | argillaceous limestone and calcareous shale | 180 m (590 ft) | [1] |
| Cadomin Formation | Early Cretaceous | conglomerate, sandstone | 170 m (560 ft) | [1] |
Some early workers included the Crowsnest Formation, which overlies the Ma Butte Formation, at the top of the Blairmore Group, but that practice has been abandoned.[1]
Distribution and Thickness
The name Blairmore Group is applicable in the foothills and mountains of southwestern Alberta and southeastern British Columbia, from the Canada–United States border northward to the Clearwater River. The equivalent strata north of the Clearwater River, which were originally assigned to the Blairmore Group, differ in that they contain major coal deposits and they have therefore been reassigned to the Luscar Group.[4]
The Blairmore Group has a maximum thickness of about 2,000 m (6,560 ft) and thins from west to east.[1]
Relationship to other units
The Blairmore Group unconformably overlies the Kootenay Group and is gradationally overlain by the Crowsnest Formation or, where the Crowsnest Formation is absent, is disconformably overlain by the Alberta Group. It is equivalent to the Luscar Group north of the Clearwater River[4] and to the Mannville Group in the plains to the east.[1]
Environment of deposition and paleontology
The Blairmore Group is an eastward-thinning wedge of clastic sediments derived from the erosion of newly uplifted mountains to the west. The sediments were transported eastward by river systems and deposited in a variety of braided stream, river channel, floodplain, and coastal plain environments along the western edge of the Western Interior Seaway. Its formations include a variety of plant fossils, trace fossils, bivalves, and mircofossils.
See also
- Various Contributors to the Paleobiology Database. "Fossilworks: Gateway to the Paleobiology Database". Retrieved 8 July 2014.
- List of fossiliferous stratigraphic units in Alberta
References
- 1 2 3 4 5 6 7 8 9 10 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.
- ↑ Leach, W.E. 1914. Blairmore map-area, Alberta. Geological Survey of Canada, Summary Report 1912, Map 107A.
- ↑ 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. Retrieved 2016-06-20.
- 1 2 Langenberg, W.C. and McMechan, M.E. 1985. Lower Cretaceous Luscar Group (revised) of the northern and north-central foothills of Alberta. Bulletin of Canadian Petroleum Geology, v. 33, p. 1-11.