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.Margaret Formation at Fossilworks.org

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 . 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 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 .

The formation was probably deposited in a lush proximal delta front to delta plain environment, with abundant channels and coal swamps.Bay Fiord at Fossilworks.org

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.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, were year-round residents in the High Arctic. Given that Gastornis was large (approaching ) 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.

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 nunavutensisEberle & McKenna, 2002 Anacodon sp.

Ferae

Arcticanodon dawsonaeRose et al., 2004 Palaeonictis sp. Viverravus sp.McKenna, 1980

Glires

Microparamys bayi Paramys huntiDawson, 2001 Strathcona major S. minor ?Paramyinae indet.

Hyaenodonta Prolimnocyon sp.Dawson, 1990 Leptictida Prodiacodon sp.Eberle, 2001 Multituberculata

Ectypodus arctosBeard & Dawson, 2014 Neoplagiaulacidae indet.

Pantodonta Coryphodon pisuqtiDawson, 2012 Perissodactyla

Lambdotherium sp. Thuliadanta mayriEberle, 2005 Equidae indet.Alroy, 2002

Birds Anseriformes Presbyornis cf. pervetusStidham & 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 willwoodenseGardner, 2012

Fish Teleostei Esox sp. Amiiformes

Amia fragosa Amia cf. uintaensis

Lepisosteiformes ?Lepisosteus sp.

Correlations

The formation has been correlated with the Allenby Formation and Kamloops Group of British Columbia, the Chickaloon Formation 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

+ Wasatchian correlations in North America Formation 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 RiverUintaPiceanceColorado PlateauWind RiverGreen RiverBighorn 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 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 Volcanic Yes No Yes No Yes No Yes No Yes No

Margaret Formation

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