| Sekwi Formation | |
|---|---|
| Stratigraphic range: ; Fallotaspis, Nevadella, and Bonnia-Olenellus trilobite zones [2] | |
| Type | Formation |
| Underlies | |
| Overlies |
|
| Thickness | 700 m [2] |
| Location | |
| Region | Northwest Territories |
| Country | Canada |
The Sekwi Formation is a geologic formation in Northwest Territories, Canada, which preserves fossils dating back to the Cambrian period.
The formation principally comprises shallow water carbonates, but deepens to include mid-shelf mudstones, both calcareous and siliciclastic. [2]
It dates from c. 525-510 Ma, the Nevadella / Bonnia-Olenellus trilobite zones. [3]
Nevadia is an extinct genus of redlichiid trilobites, with species of average size. It lived during the Atdabanian stage, which lasted from 530 to 524 million years ago, in what are today Western Canada, the Western United States, and Mexico.
The halkieriids are a group of fossil organisms from the Lower to Middle Cambrian. Their eponymous genus is Halkieria, which has been found on almost every continent in Lower to Mid Cambrian deposits, forming a large component of the small shelly fossil assemblages. The best known species is Halkieria evangelista, from the North Greenland Sirius Passet Lagerstätte, in which complete specimens were collected on an expedition in 1989. The fossils were described by Simon Conway Morris and John Peel in a short paper in 1990 in the journal Nature. Later a more thorough description was undertaken in 1995 in the journal Philosophical Transactions of the Royal Society of London and wider evolutionary implications were posed.
The Chancelloriids are an extinct family of superficially sponge-like animals common in sediments from the Early Cambrian to the early Late Cambrian. Many of these fossils consists only of spines and other fragments, and it is not certain that they belong to the same type of organism. Other specimens appear to be more complete and to represent sessile, radially symmetrical hollow bag-like organisms with a soft skin armored with star-shaped calcareous sclerites from which radiate sharp spines.
Elliptocephala is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It lived from the later part of the Tommotian to the upper Botomian. Elliptocephala can easily be confused with Ellipsocephalus, a trilobite genus of the Ptychopariida order.
Callavia is an extinct, monotypic genus of trilobite arthropods. C. broegeri lived during the late Atdabanian stage, which lasted from 530 to 524 million years ago during the early part of the Cambrian Period in what are today Canada and the United States.
Nevadella is an extinct genus of trilobites, fossil marine arthropods, with species of average size. It lived during the late Atdabanian stage, which lasted from 530 to 524 million years ago during the early part of the Cambrian Period.
The Wheeler Shale is a Cambrian (c. 507 Ma) fossil locality world-famous for prolific agnostid and Elrathia kingii trilobite remains and represents a Konzentrat-Lagerstätte. Varied soft bodied organisms are locally preserved, a fauna and preservation style normally associated with the more famous Burgess Shale. As such, the Wheeler Shale also represents a Konservat-Lagerstätten.
The Mount Cap Formation is a geologic formation exposed in the Mackenzie Mountains, northern Canada. It was deposited in a shallow shelf setting in the late Early Cambrian, and contains an array of Burgess Shale-type microfossils that have been recovered by acid maceration.
The Marjum Formation is a Cambrian geological formation that overlies the Wheeler Shale in the House Range, Utah. It is named after its type locality, Marjum Pass, and was defined in 1908. The formation is known for its occasional preservation of soft-bodied tissue, and is slightly younger than the Burgess Shale, falling in the Ptychagnostus praecurrens trilobite zone.
Achiasterella is a genus of scleritophoran known from the Burgess Shale and earlier (Branchian) deposits, and originally described as Chancelloria by Walcott. The species may represent form taxa rather than true species.
The Spence Shale is the middle member of the Langston Formation in southeastern Idaho and northeastern Utah. It is exposed in the Bear River Range, the Wasatch Range and the Wellsville Mountains. It is known for its abundant Cambrian trilobites and the preservation of Burgess Shale-type fossils.
The Carrara Formation is a geologic formation in Nevada. It preserves fossils dating back to the Cambrian period.
The Windfall Formation is a geologic formation in northeastern and southern Nevada.
The Brigus Formation is a fossiliferous upper lower Cambrian geologic formation in Newfoundland and Labrador.
The Blueflower Formation is a geologic formation in Northwest Territories. It preserves fossils dating back to the Ediacaran period.
The Rockslide Formation is a geologic formation in Northwest Territories. It preserves fossils dating back to the Drumian.
The Illtyd Formation is an up to 1000-m thick geologic formation in Yukon. It preserves fossils dating back to the Dyerian subdivision of the Cambrian period, which spans the Stage 3 / Stage 4 boundary; it's considered to belong to the mid-upper Bonnia-Olenellus trilobite Zone. Top of the unit corresponds, more or less, to the top of Stage 4. These fossils include Lower Cambrian trilobites'.
The Rabbitkettle Formation is a geologic formation in the Yukon, comprising thin bedded silty and occasionally siliciclastic limestones deposited in deep waters. It preserves fossils dating back to the Ordovician period.
The Ingta Formation is a geological unit containing green sandstones and shales; it crops out in the Canadian Mackenzie Mountains. Its age is poorly constrained, though it straddles the Precambrian/Cambrian boundary. Below the boundary its ichnofauna comprises subhorizontal Planolites burrows; above it, Phycodes burrows immediately appear, with Nemakit-Daldyn SSFs appearing soon after.
William Harold Fritz was a geologist who worked for the Geological Survey of Canada. He is known for his work in stratigraphy and on olenelloid trilobites.
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