The Margaret Formation is a

geologic formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

of the Eureka Sound Group in the Sverdrup Basin in

Northwest Territories The Northwest Territories (abbreviated ''NT'' or ''NWT''; french: Territoires du Nord-Ouest, formerly ''North-Western Territory'' and ''North-West Territories'' and namely shortened as ''Northwest Territory'') is a federal territory of Canada. ...

and

Nunavut Nunavut ( , ; iu, ᓄᓇᕗᑦ , ; ) is the largest and northernmost territory of Canada. It was separated officially from the Northwest Territories on April 1, 1999, via the '' Nunavut Act'' and the '' Nunavut Land Claims Agreement Act'' ...

, Canada. The unit belonging to the Eureka Sound Group which crops out at

Ellesmere Island Ellesmere Island ( iu, script=Latn, Umingmak Nuna, lit=land of muskoxen; french: île d'Ellesmere) is Canada's northernmost and third largest island, and the tenth largest in the world. It comprises an area of , slightly smaller than Great Bri ...

preserves

fossils A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

dating back to the

Early Eocene In the geologic timescale the Ypresian is the oldest age (geology), age or lowest stage (stratigraphy), stratigraphic stage of the Eocene. It spans the time between , is preceded by the Thanetian Age (part of the Paleocene) and is followed by th ...

period, or

Wasatchian The Wasatchian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 55,400,000 to 50,300,000 years BP lasting . It is usually c ...

in the NALMA classification.Margaret Formation
at

Fossilworks Fossilworks is a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database, a large relational database assembled by hundreds of paleontologists from around the world. History Fossilworks was cre ...

.org The Margaret Formation comprises

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

s, sandy

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, ...

s, clay-rich sandstones, coal seams and clay-rich

coal Coal is a combustible black or brownish-black sedimentary rock, formed as stratum, rock strata called coal seams. Coal is mostly carbon with variable amounts of other Chemical element, elements, chiefly hydrogen, sulfur, oxygen, and nitrogen ...

seams and volcanic ash beds. The thickness of the formation, which overlies the Mount Moore Formation, reaches about . 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 and warmest month mean temperatures from . The deltaic to swamp environment of the Margaret Formation has provided a diverse fauna of various groups of mammals, birds (''

Presbyornis ''Presbyornis'' is an extinct genus of anseriform bird. It contains two unequivocally accepted species; the well-known ''P. pervetus'' and the much lesser-known ''P. isoni''. ''P. pervetus'' was approximately the size and shape of a goose, but w ...

'' and ''

Gastornis ''Gastornis'' is an extinct genus of large flightless birds that lived during the mid Paleocene to mid Eocene epochs of the Paleogene period. Fossils have been found in Europe, Asia and North America, with the remains from North America origina ...

''), reptiles (turtles, snakes, lizards and crocodiles) and fish.

Description

The Margaret Formation comprises

s, sandy

s, clay-rich sandstones, coal seams and clay-rich

seams and volcanic ash beds. The thickness of the formation, which overlies the Mount Moore Formation, reaches about . The formation was probably deposited in a lush proximal delta front to delta plain

environment Environment most often refers to: __NOTOC__ * Natural environment, all living and non-living things occurring naturally * Biophysical environment, the physical and biological factors along with their chemical interactions that affect an organism or ...

, with abundant channels and coal swamps.Bay Fiord
at

.org

Dating

A volcanic ash layer containing

crandallite Crandallite is a calcium aluminium basic phosphate mineral. It has ideal formula . Crandallite was named after Milan L. Crandall, Jr, who worked for Knight Syndicate. This mineral is found in laterite and in alteration products of phosphate rich ...

in the middle of the formation was dated using U-Pb radiometric dating in 2017 to 53.7 ± 0.6 Ma.Sudermann, 2017 In 2010, ashes of the formation were dated to 52.6 ± 1.9 Ma.Reinhardt et al., 2010, p.2

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 , mean annual precipitation (MAP) of , mild frost-free winters (coldest month mean temperature >), and climatic conditions that supported extensive temperate forest ecosystems.West et al., 2020, p.1387 Ensemble estimates of mean annual temperatures for the high-latitude fossil localities in Arctic Canada ranged from , with the range of coldest month mean temperature from and warmest month mean temperatures from . Mean annual precipitation estimates for the Margaret Formation ranged between .West et al., 2020, p.1394 The mean summer precipitation has been estimated at and mean winter precipitation at .Schubert et al., 2012, p.525 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 or higher. These temperatures are a far cry from today's High Arctic, where central Ellesmere Island experiences a mean annual temperature of , a warm month mean temperature of about and a cold month mean temperature of or colder.Stidham & Eberle, 2016, p.5 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 ''Coryphodon'' (from Greek κορῦφὴ, "point", and ὀδοὺς, "tooth", meaning ''peaked tooth'', referring to "the development of the angles of the ridges into points n the molars") is an extinct genus of pantodonts of the family Coryph ...

'', were year-round residents in the High Arctic. Given that ''

'' was large (approaching ) and flightless, it likely also was a year-round resident of the Arctic. In contrast, the volant ''

'' might have been a seasonal migrant to the Arctic.

Fossil content

The formation has provided the following fossils:

Mammals

;Primates * Paromomyidae indet.West et al., 1977 ;Acreodi * '' Pachyaena sp.'' ;Carnivora * '' Miacis sp.'' * '' cf. Vulpavus sp.'' ;Dermoptera * '' Plagiomene sp.'' ;Eutheria * '' Palaeosinopa nunavutensis''Eberle & McKenna, 2002 * '' Anacodon sp.'' ;Ferae * '' Arcticanodon dawsonae''Rose et al., 2004 * '' Palaeonictis sp.'' * '' Viverravus sp.''McKenna, 1980 ;Glires * '' Microparamys bayi'' * '' Paramys hunti''Dawson, 2001 * '' Strathcona major'' * '' S. minor'' * ?Paramyinae indet. ;Hyaenodonta * '' Prolimnocyon sp.''Dawson, 1990 ;Leptictida * '' Prodiacodon sp.''Eberle, 2001 ;Multituberculata * '' Ectypodus arctos''Beard & Dawson, 2014 * Neoplagiaulacidae indet. ;Pantodonta * '' Coryphodon pisuqti''Dawson, 2012 ;Perissodactyla * '' Lambdotherium sp.'' * '' Thuliadanta mayri''Eberle, 2005 * Equidae indet.Alroy, 2002

Birds

;Anseriformes * '' Presbyornis cf. pervetus''Stidham & Eberle, 2016, p.3 ;Gastornithiformes * '' Gastornis sp.''

Reptiles

;Turtles * '' Geochelone sp.''Estes & Hutchison, 1980 * Cryptodira indet. * Emydinae indet. * Kinosterninae indet. * Trionychidae indet.Alroy, 2006 ;Crocodiles * '' Allognathosuchus sp.'' ;Lizards * Anguidae indet. * Varanidae indet. ;Snakes * Erycidae indet.

Amphibians

;Caudata * '' Piceoerpeton willwoodense''Gardner, 2012

Fish

;Teleostei * '' Esox sp.'' ;Amiiformes * '' Amia fragosa'' * '' Amia cf. uintaensis'' ;Lepisosteiformes * '' ?Lepisosteus sp.''

Correlations

The formation has been correlated with the

Allenby Formation The Allenby formation is a sedimentary rock formation in British Columbia which was deposited during the Ypresian stage of the Early Eocene. It consists of conglomerates, sandstones with interbedded shales and coal. The shales contain an abund ...

and

Kamloops Group Kamloops ( ) is a city in south-central British Columbia, Canada, at the confluence of the South flowing North Thompson River and the West flowing Thompson River, east of Kamloops Lake. It is located in the Thompson-Nicola Regional District, w ...

British Columbia British Columbia (commonly abbreviated as BC) is the westernmost Provinces and territories of Canada, province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include ...

, the

Chickaloon Formation The Chickaloon Formation is a geologic formation in Alaska. It preserves fossils dating back to the Paleogene The Paleogene ( ; British English, also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic ...

of Alaska,West et al., 2020, p.1390 and with the Wishbone, Chuckanut and Iceberg Bay Formations.West et al., 2020, p.1391 The upper Margaret Formation also has been correlated with the Buchanan Lake Formation of the Eastern Arctic Archipelago.Eberle & Greenwood, 2012, p.6

References

Bibliography

;Geology and climate * * * * * ;Paleontology * * * * * * * * * * * * * * {{cite LSA , last=West , first=R. M. , first2=M. R. , last2=Dawson , first3=J. H. , last3=Hutchison , year=1977 , title=Fossils from the Paleogene Eureka Sound Formation, N.W.T., Canada; occurrence, climatic and paleogeographic implications. In West, R. M. (ed), Paleontology and plate tectonics with special reference to the history of the Atlantic Ocean , journal= Milwaukee Public Museum Contributions in Biology and Geology , volume=2 , pages=77–93 Geologic formations of Canada Eocene Series of North America Paleogene Northwest Territories Paleogene Nunavut Ypresian Stage Wasatchian Sandstone formations of Canada Siltstone formations Coal formations Coal in Canada Tuff formations Deltaic deposits Paludal deposits Fossiliferous stratigraphic units of North America Paleontology in the Northwest Territories Paleontology in Nunavut Formations