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]
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]
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
Eberle, J. J (2001), "Early Eocene Leptictida, Pantolesta, Creodonta, Carnivora, and Cete from Ellesmere Island--Arctic Links to Europe and Asia", Journal of Vertebrate Paleontology, 21: 46A
West, R. M.; Dawson, M. R.; Hutchison, J. H. (1977), "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", Milwaukee Public Museum Contributions in Biology and Geology, 2: 77–93
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