Margaret Formation

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]

Margaret Formation
Stratigraphic range: Wasatchian
54.3–50.7 Ma
TypeFormation
Unit ofEureka Sound Group
OverliesMount Moore Formation
Thickness140 m (460 ft)
Lithology
PrimarySandstone
OtherSiltstone, coal, tuff
Location
Coordinates78.7°N 81.9°W / 78.7; -81.9
Approximate paleocoordinates76.1°N 30.7°W / 76.1; -30.7
RegionEllesmere Island, Northwest Territories, Nunavut
Country Canada
ExtentSverdrup Basin
Margaret Formation (Canada)
Margaret Formation (Nunavut)

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 140 metres (460 ft). 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 7.6 to 12.9 °C (45.7 to 55.2 °F) and warmest month mean temperatures from 18.2 to 22.2 °C (64.8 to 72.0 °F). 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 140 metres (460 ft).[2]

The formation was probably deposited in a lush proximal delta front to delta plain environment, with abundant channels and coal swamps.[3]

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.[2] In 2010, ashes of the formation were dated to 52.6 ± 1.9 Ma.[4]

Arctic climate of the Early Eocene

Early Eocene proxy ensemble data from fossil localities showing (a) MAT and (b) MAP estimates with the Margaret Formation indicated with (3)

During the Early Eocene, the climate of much of northern North America was warm and wet, with mean annual temperatures (MAT) as high as 20 °C (68 °F), mean annual precipitation (MAP) of 100 to 150 centimetres (39 to 59 in), mild frost-free winters (coldest month mean temperature >5 °C (41 °F)), 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 7.6 to 12.9 °C (45.7 to 55.2 °F), with the range of coldest month mean temperature from 1.3 to 4.2 °C (34.3 to 39.6 °F) and warmest month mean temperatures from 18.2 to 22.2 °C (64.8 to 72.0 °F). Mean annual precipitation estimates for the Margaret Formation ranged between 131 and 180 centimetres (52 and 71 in).[6] The mean summer precipitation has been estimated at 1,134 millimetres (44.6 in) and mean winter precipitation at 366 millimetres (14.4 in).[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 vertebrate bones 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 20 °C (68 °F) or higher. These temperatures are a far cry from today's High Arctic, where central Ellesmere Island experiences a mean annual temperature of −19 °C (−2 °F), a warm month mean temperature of about 6 °C (43 °F) and a cold month mean temperature of −38 °C (−36 °F) 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 (approaching 2 metres (6.6 ft)) 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

Palaeosinopa
Coryphodon
Presbyornis
Gastornis
Allognathosuchus

The formation has provided the following fossils:[1]

Mammals

Primates
Acreodi
Carnivora
Dermoptera
Eutheria
Ferae
Glires
Hyaenodonta
Leptictida
Multituberculata
Pantodonta
Perissodactyla

Birds

Anseriformes
Gastornithiformes

Reptiles

Turtles
Crocodiles
Lizards
Snakes

Amphibians

Caudata

Fish

Teleostei
Amiiformes
Lepisosteiformes

Correlations

Correlation of the Margaret Formation with other Early Eocene formations in northern North America

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
FormationWasatchDeBequeClaronIndian MeadowsPass PeakTatmanWillwoodGolden ValleyColdwaterAllenbyKamloopsOotsa LakeMargaretNanjemoyHatchetigbeeTetas de CabraHannold HillCoalmontCucharaGalisteoSan JoseYpresian (IUCS) • Itaboraian (SALMA)
Bumbanian (ALMA) • Mangaorapan (NZ)
BasinPowder River
Uinta
Piceance
Colorado Plateau
Wind River
Green River
Bighorn
Piceance




Colorado Plateau





Wind River





Green River






Bighorn
WillistonOkanaganPrincetonBuck CreekNechakoSverdrupPotomacGoMLaguna SaladaRio GrandeNorth ParkRatonGalisteoSan Juan
Margaret Formation (North America)
Country United States Canada United States Mexico United States
Copelemur
Coryphodon
Diacodexis
Homogalax
Oxyaena
Paramys
Primates
Birds
Reptiles
Fish
Insects
Flora
EnvironmentsAlluvial-fluvio-lacustrineFluvialFluvialFluvio-lacustrineFluvialLacustrineFluvio-lacustrineDeltaic-paludalShallow marineFluvialShallow marineFluvialFluvial
Wasatchian volcanoclastics

Wasatchian fauna

Wasatchian flora
VolcanicYesNoYesNoYesNoYesNoYesNo

See also

References

  1. Margaret Formation at Fossilworks.org
  2. Sudermann, 2017
  3. Bay Fiord at Fossilworks.org
  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. Eberle, 2001
  12. Rose et al., 2004
  13. McKenna, 1980
  14. Dawson, 2001
  15. Dawson, 1990
  16. Beard & Dawson, 2014
  17. Alroy, 2002
  18. Dawson, 2012
  19. Eberle, 2005
  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

Bibliography

Geology and climate
Paleontology
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