Margaret Formation Explained

The Margaret Formation is a geologic formation of the Eureka Sound Group in the Sverdrup Basin in Northwest Territories and Nunavut, Canada. The unit belonging to the Eureka Sound Group which crops out at Ellesmere Island preserves fossils dating back to the Early Eocene period, or Wasatchian in the NALMA classification.^[1]

The Margaret Formation comprises sandstones, sandy siltstones, clay-rich sandstones, coal seams and clay-rich coal seams and volcanic ash beds. The thickness of the formation, which overlies the Mount Moore Formation, reaches about 140m (460feet). Radiometric dating of the formation provided ages of 52.6 ± 1.9 Ma (2010) and 53.7 ± 0.6 Ma (2017).

The area where the formation was deposited in the Early Eocene experienced a much warmer climate than the High Arctic today, with mean annual temperatures ranging from 7.6C12.9C and warmest month mean temperatures from 18.2C22.2C. The deltaic to swamp environment of the Margaret Formation has provided a diverse fauna of various groups of mammals, birds (Presbyornis and Gastornis), reptiles (turtles, snakes, lizards and crocodiles) and fish.

Description

The Margaret Formation comprises sandstones, sandy siltstones, clay-rich sandstones, coal seams and clay-rich coal seams and volcanic ash beds. The thickness of the formation, which overlies the Mount Moore Formation, reaches about 140m (460feet).

The formation was probably deposited in a lush proximal delta front to delta plain environment, with abundant channels and coal swamps.^[2]

Dating

A volcanic ash layer containing crandallite in the middle of the formation was dated using U-Pb radiometric dating in 2017 to 53.7 ± 0.6 Ma.^[3] In 2010, ashes of the formation were dated to 52.6 ± 1.9 Ma.^[4]

Arctic climate of the Early Eocene

During the Early Eocene, the climate of much of northern North America was warm and wet, with mean annual temperatures (MAT) as high as 20C, mean annual precipitation (MAP) of 100cmto150cmcm (00inchesto60inchescm), mild frost-free winters (coldest month mean temperature >5C), and climatic conditions that supported extensive temperate forest ecosystems.^[5]

Ensemble estimates of mean annual temperatures for the high-latitude fossil localities in Arctic Canada ranged from 7.6C12.9C, with the range of coldest month mean temperature from 1.3C4.2C and warmest month mean temperatures from 18.2C22.2C. Mean annual precipitation estimates for the Margaret Formation ranged between 131cmand180cmcm (52inchesand70inchescm).^[6] The mean summer precipitation has been estimated at 1134mm and mean winter precipitation at 366mm.^[7]

The fossils and sedimentology indicate a lush, rain forest community on a coastal delta plain. Multiple palaeoclimate proxies, ranging from oxygen isotope analysis of vertebratebones and teeth to palaeofloral analyses, estimate a mild temperate climate for the Eocene High Arctic, where winters remained at or just above freezing and summer temperatures extended to 20C or higher. These temperatures are a far cry from today's High Arctic, where central Ellesmere Island experiences a mean annual temperature of -19C, a warm month mean temperature of about 6C and a cold month mean temperature of -38C or colder.^[8]

Despite the mild Eocene Arctic climate, the vertebrate fauna would have experienced months of total darkness and cooler temperatures during the winter. Recent isotopic work suggests that some mammals, including the hippo-like Coryphodon, were year-round residents in the High Arctic. Given that Gastornis was large (approaching2m (07feet)) and flightless, it likely also was a year-round resident of the Arctic. In contrast, the volant Presbyornis might have been a seasonal migrant to the Arctic.^[8]

Fossil content

The formation has provided the following fossils:^[1]

Mammals

Primates

• Paromomyidae indet.^[9]

Acreodi

• Pachyaena sp.

Carnivora

• Miacis sp.
• cf. Vulpavus sp.

Dermoptera

• Plagiomene sp.^[9]

Eutheria

• Palaeosinopa nunavutensis^[10]
• Anacodon sp.^[10]

Ferae

• Arcticanodon dawsonae^[11]
• Palaeonictis sp.^[10]
• Viverravus sp.^[12]

Glires

• Microparamys bayi
• Paramys hunti^[13]
• Strathcona major^[13]
• S. minor^[13]
• ?Paramyinae indet.^[13]

Hyaenodonta

• Prolimnocyon sp.^[14]

Leptictida

• Prodiacodon sp.^[15]

Multituberculata

• Ectypodus arctos^[16]
• Neoplagiaulacidae indet.

Pantodonta

• Coryphodon pisuqti^[17]

Perissodactyla

• Lambdotherium sp.^[9]
• Thuliadanta mayri^[18]
• Equidae indet.^[19]

Birds

Anseriformes

• Presbyornis cf. pervetus^[20]

Gastornithiformes

• Gastornis sp.^{[16] [20]}

Reptiles

Turtles

• Geochelone sp.^[21]
• Cryptodira indet.^[21]
• Emydinae indet.^[21]
• Kinosterninae indet.^[21]
• Trionychidae indet.^[22]

Crocodiles

• Allognathosuchus sp.^[21]

Lizards

• Anguidae indet.^[21]
• Varanidae indet.^[21]

Snakes

• Erycidae indet.^[21]

Amphibians

Caudata

• Piceoerpeton willwoodense^[23]

Fish

Teleostei

• Esox sp.^[21]

Amiiformes

• Amia fragosa^[21]
• Amia cf. uintaensis^[21]

Lepisosteiformes

• ?Lepisosteus sp.^[21]

Correlations

The formation has been correlated with the Allenby Formation and Kamloops Group of British Columbia, the Chickaloon Formation of Alaska,^[24] and with the Wishbone, Chuckanut and Iceberg Bay Formations.^[25] The upper Margaret Formation also has been correlated with the Buchanan Lake Formation of the Eastern Arctic Archipelago.^[26]

Wasatchian correlations in North America

Formation													Margaret									Ypresian (IUCS) • Itaboraian (SALMA) Bumbanian (ALMA) • Mangaorapan (NZ)
Basin		Piceance	Colorado Plateau	Wind River	Green River																	align=center rowspan=14
Copelemur	align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center
Coryphodon	align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center
Diacodexis	align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center
Homogalax	align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center
Oxyaena	align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center
Paramys	align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center
Primates	align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center
Birds	align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center
Reptiles	align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center
	align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center
Insects	align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center
	align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center		align=center
	Alluvial-fluvio-lacustrine	Fluvial				Fluvial	Fluvio-lacustrine	Fluvial	Lacustrine		Fluvio-lacustrine		Deltaic-paludal	Shallow marine		Fluvial	Shallow marine	Fluvial		Fluvial
Volcanic	Yes	No							Yes	No	Yes	No	Yes	No						Yes	No

See also

• List of fossiliferous stratigraphic units in Northwest Territories
• List of fossiliferous stratigraphic units in Nunavut

References

Bibliography

Geology and climate

Paleontology

Notes and References

1. https://paleobiodb.org/classic/displayStrata?geological_group=Eureka%20Sound&formation=Margaret&group_formation_member=Margaret Margaret Formation
2. https://paleobiodb.org/classic/displayCollResults?collection_no=15583 Bay Fiord
3. Sudermann, 2017
4. Reinhardt et al., 2010, p.2
5. West et al., 2020, p.1387
6. West et al., 2020, p.1394
7. Schubert et al., 2012, p.525
8. Stidham & Eberle, 2016, p.5
9. West et al., 1977
10. Eberle & McKenna, 2002
11. Rose et al., 2004
12. McKenna, 1980
13. Dawson, 2001
14. Dawson, 1990
15. Eberle, 2001
16. Beard & Dawson, 2014
17. Dawson, 2012
18. Eberle, 2005
19. Alroy, 2002
20. Stidham & Eberle, 2016, p.3
21. Estes & Hutchison, 1980
22. Alroy, 2006
23. Gardner, 2012
24. West et al., 2020, p.1390
25. West et al., 2020, p.1391
26. Eberle & Greenwood, 2012, p.6