Twitya Formation
Stratigraphic Unit in Northwest Territories, Canada
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The Twitya Formation is a geologic formation in Canada’s Northwest Territories. It preserves fossils dating back to the Cryogenian period.
| Twitya Formation | |
|---|---|
| Stratigraphic range: Cryogenian | |
| Type | Formation |
| Unit of | Hay Creek Group[1] |
| Underlies | Keele Formation |
| Overlies | Shezal Formation |
| Thickness | 900 m (2,952 ft)[2] |
| Lithology | |
| Primary | Limestone |
| Other | Mudstone, Siltstone, Shale, Sandstone |
| Location | |
| Coordinates | 64.043°N 128.833°W |
| Region | Northwest Territories |
| Country | Canada |
| Type section | |
| Named for | Twitya River |
  Twitya Formation (Northwest Territories) | |
Geology
At the base of the Twitya Formation, it is primarily composed of thin-bedded limestone rocks,[2] which contains finely laminated mudstone and siltstone. Above this, it then turns into pyritic black shale, and then into grayish-green siltstone and sandstone turbidites.[1]
It is overlain by the siliciclastic and carbonate Keele Formation, and is underlain by the Shezal Formation of the Rapitan Group.[1]
Dating
The Twitya Formation was previously considered to be Ediacaran in age,[3] although a later studies found this to not be the case,[4] with one study using a combination of combination of Re-Os geochronology and Os-Sr isotope dating at the base of the Twitya Formation, and recovering a date of 662±3 Ma, placing the formation within the late Cryogenian, and near the end of the Sturtian glaciation.[1]
Paleobiota
The Twitya Formation contains a small selection of discoidal and annunli forms, namely tentative records of Irridinitus and Vendella.[3] For a long time, these fossils were considered to be the oldest know probable animals, although many studies done since have recovered older probable remains.[5] Nimbia was previously recorded from this formation, although later studies discounted these records, instead noting the fossils may be simple microbial colonies.[6]
Color key
|
Notes Uncertain or tentative taxa are in small text; |
incertae sedis
| Genus | Species | Notes | Images |
|---|---|---|---|
|
Discoid organism. Later discounted as simple microbial colonies.[6] | ||
| Irridinitus (?)[3] |
|
Discoid organism, tentative assignment. | |
| Vendella (?)[3] |
|
Discoid organism, tentative assignment. It is noted that it may be a junior synonym of Beltanelliformis. | |
Flora
Microorganisms
| Genus | Species | Notes | Images |
|---|---|---|---|
| Leiosphaeridia[3] |
|
Acritarch. | |
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