Exshaw Formation
The Exshaw Formation is a stratigraphic unit in the Western Canada Sedimentary Basin. It takes the name from the hamlet of Exshaw, Alberta in the Canadian Rockies, and was first described from outcrops on the banks of Jura Creek north of Exshaw by P.S. Warren in 1937. The formation is of Late Devonian (late Famennian) to Early Mississippian (middle Tournaisian) age as determined by conodont biostratigraphy, and it straddles the Devonian-Carboniferous boundary.
| Exshaw Formation | |
|---|---|
| Stratigraphic range: | |
| Type | Geological formation |
| Sub-units | Lower and Upper Exshaw |
| Underlies | Banff Formation |
| Overlies | Wabamun Formation, Kotcho Formation, Palliser Formation |
| Thickness | up to 50 metres (160 ft) |
| Lithology | |
| Primary | Shale |
| Other | Siltstone, limestone |
| Location | |
| Coordinates | 51°05′29″N 115°09′29″W |
| Region | Alberta |
| Country | Canada |
| Type section | |
| Named for | Exshaw, Alberta |
| Named by | P.S. Warren, 1937 |
The Exshaw strata were deposited in a marine setting during the Hangenberg event, an oceanic anoxic event associated with the Late Devonian extinction. The black shales of the Exshaw Formation are rich in organic matter and are one of the most important petroleum source rocks of the Western Canada Sedimentary Basin.