Twitya Formation

Twitya Formation
Twitya Formation
Stratigraphic range: Cryogenian
Type	Formation
Unit of	Hay Creek Group
Underlies	Keele Formation
Overlies	Shezal Formation
Thickness	900 m (2,952 ft)
Lithology
Primary	Limestone
Other	Mudstone, Siltstone, Shale, Sandstone
Location
Coordinates	64°02′35″N 128°49′59″W / 64.043°N 128.833°W / 64.043; -128.833
Region	Northwest Territories
Country	Canada
Type section
Named for	Twitya River
	Twitya Formation (Northwest Territories)

The Twitya Formation is a geologic formation in Canada’s Northwest Territories. It preserves fossils dating back to the Cryogenian period.

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

Taxon	Reclassified taxon	Taxon falsely reported as present	Dubious taxon or junior synonym	Ichnotaxon	Ootaxon	Morphotaxon

Notes
Uncertain or tentative taxa are in small text; ~~crossed out~~ taxa are discredited.

incertae sedis

Genus	Species	Notes
~~Nimbia~~³	~~N. occlusa~~	Discoid organism. Later discounted as simple microbial colonies.⁶
Irridinitus (?)³	Irridinitus (?) sp.	Discoid organism, tentative assignment.
Vendella (?)³	Vendella (?) sp.	Discoid organism, tentative assignment. It is noted that it may be a junior synonym of Beltanelliformis.

Flora

Genus	Species	Notes
Morania³	Morania sp.	Carbonaceous cyanobacteria.
Beltina³	Beltina sp.	Carbonaceous cyanobacteria.
Filamentous microfossils³	???	Too poorly preserved for taxonomic assignment.

Microorganisms

Genus	Species	Notes	Images
Leiosphaeridia³	Leiosphaeridia sp.	Acritarch.

References

Rooney, Alan D.; Macdonald, Francis A.; Strauss, Justin V.; Dudás, Francis Ö.; Hallmann, Christian; Selby, David (7 January 2014). "Re-Os geochronology and coupled Os-Sr isotope constraints on the Sturtian snowball Earth". Proceedings of the National Academy of Sciences. 111 (1): 51–56. doi:10.1073/pnas.1317266110. hdl:1721.1/89082. PMC 3890860.
Narbonne, G; Aitken, J (May 1995). "Neoproterozoic of the Mackenzie Mountains, northwestern Canada". Precambrian Research. 73 (1–4): 101–121. doi:10.1016/0301-9268(94)00073-Z.
Hofmann, H. J.; Narbonne, G. M.; Aitken, J. D. (1990). "Ediacaran remains from intertillite beds in northwestern Canada". Geology. 18 (12): 1199. doi:10.1130/0091-7613(1990)018<1199:ERFIBI>2.3.CO;2.
James, Noel P.; Narbonne, Guy M.; Dalrymple, Robert W.; Kyser, T. Kurtis (2005). "Glendonites in Neoproterozoic low-latitude, interglacial, sedimentary rocks, northwest Canada: Insights into the Cryogenian ocean and Precambrian cold-water carbonates". Geology. 33 (1): 9. doi:10.1130/G20938.1.
Grazhdankin, D. V.; Goy, Yu. Yu.; Maslov, A. V. (October 2012). "Late Riphean microbial colonies adapted to desiccating environments". Doklady Earth Sciences. 446 (2): 1157–1161. doi:10.1134/S1028334X12100157.
Grazhdankin, Dmitriy; Gerdes, Gisela (September 2007). "Ediacaran microbial colonies". Lethaia. 40 (3): 201–210. doi:10.1111/j.1502-3931.2007.00025.x.

Various Contributors to the Paleobiology Database. "Fossilworks: Gateway to the Paleobiology Database". Retrieved 17 December 2021.

[Rooney2014-1] Rooney, Alan D.; Macdonald, Francis A.; Strauss, Justin V.; Dudás, Francis Ö.; Hallmann, Christian; Selby, David (7 January 2014). "Re-Os geochronology and coupled Os-Sr isotope constraints on the Sturtian snowball Earth". Proceedings of the National Academy of Sciences. 111 (1): 51–56. doi:10.1073/pnas.1317266110. hdl:1721.1/89082. PMC 3890860.

[Narbonne1995-2] Narbonne, G; Aitken, J (May 1995). "Neoproterozoic of the Mackenzie Mountains, northwestern Canada". Precambrian Research. 73 (1–4): 101–121. doi:10.1016/0301-9268(94)00073-Z.

[Hofmann1990-3] Hofmann, H. J.; Narbonne, G. M.; Aitken, J. D. (1990). "Ediacaran remains from intertillite beds in northwestern Canada". Geology. 18 (12): 1199. doi:10.1130/0091-7613(1990)018<1199:ERFIBI>2.3.CO;2.

[4] James, Noel P.; Narbonne, Guy M.; Dalrymple, Robert W.; Kyser, T. Kurtis (2005). "Glendonites in Neoproterozoic low-latitude, interglacial, sedimentary rocks, northwest Canada: Insights into the Cryogenian ocean and Precambrian cold-water carbonates". Geology. 33 (1): 9. doi:10.1130/G20938.1.

[5] Grazhdankin, D. V.; Goy, Yu. Yu.; Maslov, A. V. (October 2012). "Late Riphean microbial colonies adapted to desiccating environments". Doklady Earth Sciences. 446 (2): 1157–1161. doi:10.1134/S1028334X12100157.

[Grazhdankin2007-6] Grazhdankin, Dmitriy; Gerdes, Gisela (September 2007). "Ediacaran microbial colonies". Lethaia. 40 (3): 201–210. doi:10.1111/j.1502-3931.2007.00025.x.

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