Stephen Formation
Geologic formation in Canada
title: "Stephen Formation" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["cambrian-alberta", "cambrian-british-columbia", "cambrian-system-of-north-america", "cambrian-southern-paleotropical-deposits", "cambrian-northern-paleotropical-deposits", "geologic-formations-of-alberta", "geologic-formations-of-british-columbia", "limestone-formations-of-canada", "shale-formations-of-canada", "siltstone-formations-of-canada", "burgess-shale"] description: "Geologic formation in Canada" topic_path: "philosophy" source: "https://en.wikipedia.org/wiki/Stephen_Formation" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0
::summary Geologic formation in Canada ::
::data[format=table title="Infobox Rockunit"]
| Field | Value |
|---|---|
| name | Stephen Formation |
| image | WalcottQuarry080509.jpg |
| caption | The Walcott Quarry in the Stephen Formation shales |
| type | Geological formation |
| period | Middle Cambrian |
| prilithology | Shale, limestone |
| otherlithology | Siltstone |
| namedfor | Mount Stephen (from George Stephen) |
| namedby | Charles Doolittle Walcott, 1908 |
| region | Canadian Rockies |
| country | Canada |
| coordinates | |
| underlies | Eldon Formation |
| overlies | Cathedral Formation |
| thickness | "Thin" Stephen: |
| "Thick" Stephen: up to <ref name | lexicon |
| :: |
| name = Stephen Formation | image = WalcottQuarry080509.jpg | caption = The Walcott Quarry in the Stephen Formation shales | type = Geological formation | period = Middle Cambrian | prilithology = Shale, limestone | otherlithology = Siltstone | namedfor = Mount Stephen (from George Stephen) | namedby = Charles Doolittle Walcott, 1908 | region = Canadian Rockies | country = Canada | coordinates = | unitof = | subunits = | underlies = Eldon Formation | overlies = Cathedral Formation | thickness = "Thin" Stephen: "Thick" Stephen: up to 335 m | extent = | area = | map = | map_caption = The Stephen Formation is a geologic formation exposed in the Canadian Rockies of British Columbia and Alberta, on the western edge of the Western Canada Sedimentary Basin. It consists of shale, thin-bedded limestone, and siltstone that was deposited during Middle Cambrian time (513 to 497 million years ago). It is famous for the exceptional preservation of soft-bodied fossils: the Burgess Shale biota. The formation overlies the Cathedral escarpment, a submarine cliff; consequently it is divided into two quite separate parts, the 'thin' sequence deposited in the shallower waters atop the escarpment, and the 'thick' sequence deposited in the deeper waters beyond the cliff. Because the 'thick' Stephen Formation represents a distinct lithofacies, some authors suggest it warrants its own name, and dub it the Burgess Shale Formation. The stratigraphy of the Thin Stephen Formation has not been subject to extensive study, so except where explicitly mentioned this article applies mainly to the Thick Stephen Formation.
Sedimentary setting
::figure[src="https://upload.wikimedia.org/wikipedia/commons/9/9d/Burgess_Shale,_Yoho_National_Park_of_Canada.jpg" caption="[[Satellite]] image of the area."] ::
The Stephen Formation formed at a low-latitude miogeoclinic continental margin, at the western limit of a continental craton. Detrital sediments were washed in by rivers from the continent, over the limestone reefs which formed the shallow sea floor. At the top of sequence-stratigraphic cycles, oncoids were sometimes washed in to the Thin Stephen formation from the shallower waters closer to the shore.
The fossiliferous deposits of the Stephen Formation are a sequence of slightly calcareous dark mudstones, about old. The beds were deposited on top of and at the base of a cliff about 160 m tall, below the depth agitated by waves during storms,{{Cite journal | last1 = Gabbott | first1 = S.E. | last2 = Zalasiewicz | first2 = J. | last3 = Collins | first3 = D. | year = 2008 | title = Sedimentation of the Phyllopod Bed within the Cambrian Burgess Shale Formation of British Columbia | journal = Journal of the Geological Society | volume = 165 | issue = 1 | pages = 307 | url = http://jgs.lyellcollection.org/cgi/content/abstract/165/1/307 | doi = 10.1144/0016-76492007-023| bibcode = 2008JGSoc.165..307G| url-access = subscription
It was originally thought that the Burgess Shale was deposited in anoxic conditions, but mounting research shows that oxygen was continually present in the sediment. The anoxic setting had been thought to not only protect the newly dead organisms from decay, but it also created chemical conditions allowing the preservation of the soft parts of the organisms. Further, it reduced the abundance of burrowing organisms — burrows and trackways are found in beds containing soft-bodied organisms, but they are rare and generally of limited vertical extent.
Subdivisions
The formation is made up of the Kicking Horse member, which includes the Alalcomenaeus–Sanctacaris beds; this underlies and interdigitates with the unfossiliferous Yoho River member. These two are truncated by an unconformity and covered by the Campsite Cliff member, which contains the Ogygopsis beds. The Wash member, which contains many shelly but no soft-bodied fossils, interrupts this sequence in places, and directly underlies the Phyllopod beds, which mark the base of the Walcott Quarry member. This underlies the Wapta member, which is unconformably overlain by 'Tokumm'.
The Wapta member has been redefined into the Raymond Quarry member, Emerald Lake member, Odaray member, Paradox member and Marpole member. The thin Stephen grades conformably into the overlying Eldon formation.
Fossiliferous collection sites
Of the dozen-plus fossiliferous sites in the Stephen formation, while the Collins Quarry (containing the Sanctacaris beds) is situated in the Kicking Horse member. The S7 locality on Mount Stephen has been attributed both to the Campsite Cliff member mark the southerly extent of fossiliferous exposure on Mount Stephen, although many more sites exist on the inaccessible northeasterly flank of the mountain. The Lower Trilobite Beds, although lower on the mountainside, are in fact stratigraphically higher than the Upper Trilobite Beds.
Fossils have also been collected from the 'thin' Stephen Formation, in the vicinity of the Stanley Glacier, some 40 km from the main collecting sites on Fossil Ridge and Mount Stephen. They have been recorded around Odaray Mountain, Park Mountain, Curtis Peak, Natalko Lake and Monarch Cirque, although no major collection at these localities has yet been performed.
References
References
- Walcott, C.D., 1908a. Nomenclature of some Cambrian Cordilleran formations; Smithsonian Miscellaneous Collections, vol. 35, no. 1.
- Walcott, C.D., 1908b. Cambrian geology and paleontology: Cambrian sections of the Condilleran area. Smithsonian Miscellaneous Collections, vol. 53, no. 5, pp. 204-208.
- [[Lexicon of Canadian Geologic Units]]. "Stephen Formation".
- "Lithological Unit Search". [[Natural Resources Canada]].
- (2009). "Reinterpretation of 'Middle' Cambrian stratigraphy of the rifted western Laurentian margin: Burgess Shale Formation and contiguous units (Sauk II Megasequence); Rocky Mountains, Canada". Palaeogeography, Palaeoclimatology, Palaeoecology.
- Slind, O.L., Andrews, G.D., Murray, D.L., Norford, B.S., Paterson, D.F., Salas, C.J., and Tawadros, E.E., Canadian Society of Petroleum Geologists and Alberta Geological Survey. (1994). "The Geological Atlas of the Western Canada Sedimentary Basin (Mossop, G.D. and Shetsen, I., compilers), Chapter 8: Middle Cambrian and Early Ordovician Strata of the Western Canada Sedimentary Basin".
- (1998). "The Middle Cambrian Burgess Shale and its relationship to the Stephen Formation in the southern Canadian Rocky Mountains". Canadian Journal of Earth Sciences.
- {{Burgess Shale Primer. 2
- (1972). "Sediments of the Middle Cambrian Burgess Shale, Canada". Lethaia.
- (2009). "Comparison of Geochemical and Distinctive Mineralogical Features Associated with the Kinzers and Burgess Shale Formations and their Associated Units". Palaeogeography, Palaeoclimatology, Palaeoecology.
- (2006). "A soft-bodied mollusc with radula from the Middle Cambrian Burgess Shale". Nature.
- 1
- (2010). "A new Burgess Shale-type assemblage from the "thin" Stephen Formation of the southern Canadian Rockies". Geology.
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