Alexo Formation
The Alexo Formation a stratigraphic unit of Late Devonian (late Frasnian to early Famennian) age. It is present on the western edge of the Western Canada Sedimentary Basin in the central Rocky Mountains and foothills of Alberta. The formation consists primarily of dolomite. It is locally fossiliferous and includes remains of marine animals such as brachiopods[2] and conodonts.[3][4]
| Alexo Formation Stratigraphic range: late Frasnian to early Famennian | |
|---|---|
| Type | Formation |
| Underlies | Palliser Formation |
| Overlies | Southesk Formation, Mount Hawk Formation |
| Thickness | Up to about 100 metres (330 ft)[1] |
| Lithology | |
| Primary | Dolomite |
| Other | Siltstone |
| Location | |
| Coordinates | 52°26′00″N 115°54′00″W |
| Region |  |
| Country | .svg.png.webp){kind=small} |
| Type section | |
| Named for | Alexo, Alberta |
| Named by | R. de Wit and D.J. McLaren, 1950.[2] |
Lithology and thickness
The Alexo Formation was deposited in a marine setting and consists of dolomite, silty and argillaceous dolomite, dolomitic siltstone, and vuggy dolomite. It has a maximum thickness of about 100 metres (330 ft), and is thinner in areas where it covers carbonate buildups (reefs) in the underlying formations.[1]
Distribution and relationship to other units
The Alexo Formation is present in the central Rocky Mountains of Alberta and the adjacent foothills, extending from the Crows Nest Pass area in the south to the North Saskatchewan River in the north. It overlies the Southesk or Mount Hawk Formation, depending on the location. It is overlain by the Palliser Formation.[1][5]
The Alexo was originally considered to extend as far north as Jasper but was revised by McLaren and Mountjoy in 1962. In the area between the North Saskatchewan River and Jasper, they designated the upper beds of the Alexo as the Sassenach Formation, and the lower beds as part of the upper Southesk Formation.[6]
References
- 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.
- de Wit, R. and McLaren, D.J. 1950. Devonian sections in the Rocky Mountains between Crows Nest Pass and Jasper, Alberta. Geological Survey of Canada, Paper 50-23, 66 p.
- Clark, D.L. and Ethington, R.L. 1965. Conodont biostratigraphy of part of the Devonian of the Alberta Rocky Mountains. Bulletin of Canadian Petroleum Geology, vol. 13, no. 3, p. 382-388.
- McLean, R.A. and Klapper, G. 1998. Biostratigraphy of Frasnian (Upper Devonian) strata in western Canada, based on conodonts and rugose corals. Bulletin of Canadian Petroleum Geology, vol. 46, no. 4, p. 515-563.
- Alberta Geological Survey. "Alberta Table of Formations, May 2019" (PDF). Alberta Energy Regulator. Retrieved 24 March 2020.
- McLaren, D.J. and Mountjoy, E.W. 1962. Alexo equivalents in the Jasper region. Geological Survey of Canada, Paper 62-23.
- Various Contributors to the Paleobiology Database. "Fossilworks: Gateway to the Paleobiology Database". Archived from the original on 2014-07-31. Retrieved 8 July 2014.