Wapiti Formation
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| Wapiti Formation | |
|---|---|
| Stratigraphic range: | |
| Type | Geological formation |
| Lithology | |
| Primary | Sandstone, siltstone, mudstone |
| Other | conglomerate, coal |
| Location | |
| Region | Alberta |
| Country | Canada |
| Type section | |
| Named for | Lower part of Wapiti River |
| Named by | G.M. Dawson, 1881.[1] |
The Wapiti Formation is a geological formation of the Western Canada Sedimentary Basin in northwestern Alberta, and northeastern British Columbia, Canada. Its deposition spanned the time interval from the upper Campanian through to the lower Maastrichtian, between approximately 80 and 68 Ma.[2][3] It was named by G.M. Dawson in 1881,[1] presumably for exposures along the lower part of the Wapiti River and downstream along the Smoky River in Alberta.[4]
Dinosaur remains are among the fossils that have been recovered from the Cretaceous portion of the formation.[5][6] The Wapiti Formation does not produce many fossils due to its limited surface exposure and accessibility, although two Pachyrhinosaurus bone beds have been productive.[7] Plant fossils and trace fossils have been unearthed here too.[8][9][10]
The Wapiti Formation consists of interbedded sandstones, siltstones, shales and mudstones, with thin conglomerates, coal seams and bentonite beds. The sandstones are typically thick, pale grey, crossbedded and bentonitic. The middle part contains less sandstones, more mudstones, and fewer and thinner coals. The upper part contains thicker lenticular sandstones and more coals.[4]
Depositional environment
The Wapiti Formation was deposited in inland fluvial and floodplain environments, with local areas of lacustrine sediments.[11] The sandstones were deposited mainly in fluvial channel environments, with siltstones, carbonaceous shales and coals accumulating in overbank settings.
Thickness and Distribution
The Wapiti Formation rests conformably on the marine shales of the Smoky Group. It is more than 1,300 m (4,300 ft) thick in the foothills of the Canadian Rockies in the west,[11] and it thins eastward to its erosional edge.[12] It is correlative with the entire sequence of the Belly River Group, Bearpaw Formation, Edmonton Group and Scollard Formation in south-central Alberta.[11] In most areas it is unconformably overlain by glacial and post-glacial sediments of Quaternary age, or exposed at surface. In a few upland areas it is unconformably overlain by Paleogene gravel deposits.[4]
