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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°42′N 81°54′W / 78.7°N 81.9°W / 78.7; -81.9
Approximate paleocoordinates76°06′N 30°42′W / 76.1°N 30.7°W / 76.1; -30.7
RegionEllesmere Island, Northwest Territories, Nunavut
Country Canada
ExtentSverdrup Basin
Margaret Formation is located in Canada
Margaret Formation
Margaret Formation (Canada)
Margaret Formation is located in Nunavut
Margaret Formation
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

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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

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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

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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

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Palaeosinopa
 
Coryphodon
 
Presbyornis
 
Gastornis
 
Allognathosuchus

The formation has provided the following fossils:[1]

Mammals

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

Birds

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Anseriformes
Gastornithiformes

Reptiles

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Turtles
Crocodiles
Lizards
Snakes

Amphibians

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Caudata

Fish

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Teleostei
Amiiformes
Lepisosteiformes

Correlations

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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
Formation Wasatch DeBeque Claron Indian Meadows Pass Peak Tatman Willwood Golden Valley Coldwater Allenby Kamloops Ootsa Lake Margaret Nanjemoy Hatchetigbee Tetas de Cabra Hannold Hill Coalmont Cuchara Galisteo San Jose Ypresian (IUCS) • Itaboraian (SALMA)
Bumbanian (ALMA) • Mangaorapan (NZ)
Basin Powder River
Uinta
Piceance
Colorado Plateau
Wind River
Green River
Bighorn		 Piceance
Colorado Plateau


Wind River



Green River





Bighorn		 Williston Okanagan Princeton Buck Creek Nechako Sverdrup Potomac GoM Laguna Salada Rio Grande North Park Raton Galisteo San 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                  
Environments Alluvial-fluvio-lacustrine Fluvial Fluvial Fluvio-lacustrine Fluvial Lacustrine Fluvio-lacustrine Deltaic-paludal Shallow marine Fluvial Shallow marine Fluvial Fluvial
  Wasatchian volcanoclastics

  Wasatchian fauna

  Wasatchian flora
Volcanic Yes No Yes No Yes No Yes No Yes No

See also

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References

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  1. ^ a b Margaret Formation at Fossilworks.org
  2. ^ a b 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. ^ a b Stidham & Eberle, 2016, p.5
  9. ^ a b c West et al., 1977
  10. ^ a b c d Eberle & McKenna, 2002
  11. ^ a b c Eberle, 2001
  12. ^ Rose et al., 2004
  13. ^ McKenna, 1980
  14. ^ a b c d e Dawson, 2001
  15. ^ Dawson, 1990
  16. ^ a b Beard & Dawson, 2014
  17. ^ a b Alroy, 2002
  18. ^ Dawson, 2012
  19. ^ Eberle, 2005
  20. ^ a b Stidham & Eberle, 2016, p.3
  21. ^ a b c d e f g h i j k l 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

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Geology and climate
  • West, Christopher K.; Greenwood, David R.; Reichgelt, Tammo; Lowe, Alexander J.; Vachon, Janelle M.; Basinger, James F. (2020), "Paleobotanical proxies for early Eocene climates and ecosystems in northern North America from middle to high latitudes", Climate of the Past, 16 (4): 1387–1410, Bibcode:2020CliPa..16.1387W, doi:10.5194/cp-16-1387-2020, retrieved 2020-09-05
  • Sudermann, Markus; Galloway, Jennifer; Greenwood, David Robert; West, Christopher K.; Reinhardt, Lutz (2017), A palynological investigation of the Arctic late Paleocene–early Eocene Margaret Formation at Stenkul Fiord, Ellesmere Island, NU, Canada, Climate and Biotic Events of the Paleogene (CBEP 2017), p. 1, retrieved 2020-09-05
  • Eberle, Jaelyn J.; Greenwood, David R. (2012), "Life at the top of the greenhouse Eocene world — A review of the Eocene flora and vertebrate fauna from Canada's High Arctic", GSA Bulletin, 124 (1–2): 3–23, Bibcode:2012GSAB..124....3E, doi:10.1130/B30571.1
  • Schubert, Brian A.; Jahren, A. Hope; Eberle, Jaelyn J.; Sternberg, Leonel S.L.; Eberth, David A. (2012), "A summertime rainy season in the Arctic forests of the Eocene", Geology, 40 (6): 523–526, Bibcode:2012Geo....40..523S, doi:10.1130/G32856.1
  • Reinhardt, Lutz; Andruleit, Harald; Estrada, Solveig; Henjes Kunst, Friedhelm; Piepjohn, Karsten (2010), Altered volcanic ashes in Paleocene/Eocene Eureka Sound Group sediments (Ellesmere Island, Arctic Canada) – new stratigraphic tie-points?, GeoCanada 2010 – Working with the Earth, pp. 1–2
Paleontology
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