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.
16-458: 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
32-519: A central nucleus, such as a shell fragment, and a calcium carbonate structure is deposited by encrusting microbes . Oncolites are indicators of warm waters in the photic zone , but are also known in contemporary freshwater environments. These structures rarely exceed 10 cm in diameter. Oncolites may have either a porostromate or spongiostromate texture. Most oncolites are spongiostromate, having no recognisable cellular texture or microstructure. Porostromate oncolites are mostly unknown during
48-669: Is a stub . You can help Misplaced Pages by expanding it . Odaray Mountain Odaray Mountain is a 3,137-metre (10,292-foot) summit located west of Lake O'Hara in the Bow Range of Yoho National Park , in the Canadian Rockies of British Columbia , Canada . Its nearest higher peak is Mount Huber , 3.86 km (2.40 mi) to the east. The standard climbing route follows the southeast glacier and ridge starting from Elizabeth Parker hut . Pronunciation sounds like
64-683: 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
80-608: Is southeast of the true summit. The mountain's current name became official in 1952 when the Geographical Names Board of Canada rescinded the name Mount Odaray . Odaray Mountain is composed of sedimentary rock laid down during the Precambrian to Jurassic periods. Formed in shallow seas, this sedimentary rock was pushed east and over the top of younger rock during the Laramide orogeny . Based on
96-603: The Cathedral Formation , which probably formed shortly before the deposition of the Burgess shale. The precise formation mechanism is not known for certain, but the most widely accepted hypothesis suggests that the edge of the Cathedral formation reef became detached from the rest of the reef, slumping and being transported some distance — perhaps kilometres — away from the reef edge. Later reactivation of faults at
112-657: The Ogygopsis -bearing Mount Stephen trilobite beds (both on Mount Stephen ), 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 and the Kicking Horse member. The Trilobite Beds, the first Burgess Shale locality to be discovered, mark the southerly extent of fossiliferous exposure on Mount Stephen, although many more sites exist on
128-928: The Precambrian ; since the Eocene they have mostly been confined to freshwater environments. The appearance of recent or near-recent freshwater oncoids has been documented in two rivers in Bavaria : the Alz , whose source is the Chiemsee , and the Moosach , near Freising . Modern oncoids also grow in some springs in Atacama Desert in South America. In one particular case a system of oncoids have been observed interface between Salar de Antofalla and an adjacent wetland. This trace fossil -related article
144-697: 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. Of the dozen-plus fossiliferous sites in
160-577: The Stephen formation, the Walcott Quarry is the most famous, bearing the Phyllopod beds . This lies at the base of the Walcott Quarry member, and three other quarries – the Raymond, UE and EZ – lie above it. The UE and EZ quarries herald from the U pper E hmaniella Zone and E hmaniella Z one, respectively, and belong to the Emerald Lake member. The Campsite Cliff member contains
176-410: The base of the formation led to its disintegration from about 509 million years ago . This would have left a steep cliff, the bottom of which would be protected, because the limestone of the Cathedral formation is difficult to compress, from tectonic decompression. This protection explains why fossils preserved further from the Cathedral formation are impossible to work with — tectonic squeezing of
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#1732780886293192-535: The beds produced a vertical cleavage that fractures the rocks, so they split perpendicular to the fossils. The Walcott quarry produced such spectacular fossils because it was so close the Stephen formation — indeed the quarry has now been excavated to the very edge of the Cambrian cliff. Both the thick and thin Stephen formation were deposited below wave base. It was originally thought that the Burgess Shale
208-1003: 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. Oncoid Oncolites are sedimentary structures composed of oncoids , which are layered structures formed by cyanobacterial growth. Oncolites are very similar to stromatolites , but, instead of forming columns, they form approximately spherical structures. The oncoids often form around
224-474: The shore. The fossiliferous deposits of the Stephen Formation are a sequence of slightly calcareous dark mudstones, about 508 million years old. The beds were deposited on top of and at the base of a cliff about 160 meters (520 ft) tall, below the depth agitated by waves during storms, and thus at a water depth of around 200 m. This vertical cliff was composed of the calcareous reefs of
240-572: The two words "ode array" (/ōd/ /əˈrā/). The first ascent of the mountain was made in 1887 by James J. McArthur , and he named it Odaray which is the expression for "many waterfalls" in the Stoney language . Other reports have it being named in 1894 by Samuel Evans Stokes Allen for the Stoney Indian word for "cone". However, it is possible that McArthur only ascended the lesser secondary summit cone (2965 m) now known as Little Odaray which
256-522: 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. The formation
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