Prince Creek Formation

Age

The PCF ranges from Late Cretaceous (Campanian) to Paleocene in age. Due to a slight structural dip, the unit becomes progressively younger downriver (northward). Biostratigraphic analyses from the upper, vertebrate-bearing portion of the unit near Ocean Point indicate a temporal range from as old as late Campanian to as young as late Maastrichtian. Although previous radiometric dating suggested an early Maastrichtian age, more recent work indicates the fossiliferous beds near Ocean Point to be late Campanian in age (Druckenmiller et al. 2023).

Habitat

During the time when the fossiliferous beds were deposited, Earth was going through a global cooling phase. The depositional environment included tidally influenced meandering rivers, anastomosed distributary channels, crevasse splays, levees, lakes, ponds, and mires. Large amounts of plants material are represented by peridonoid dinocysts, algae, fungal hyphae, fern and moss spores, projectates, Wodehouseia edmontonicola, bisaccate pollen, taxodiaceous pollen, and pollen from trees, shrubs, and herbs. Preserved woody trunks show trees did not exceed 20cm in diameter and canopy heights were estimated to have been around 5-6 meters tall. Frequent false rings observed in the dendrochronology of the stumps were deduced to have been caused by sudden drops in temperature during the growing season to between 6-10 C suggestive of more sub-arctic summer conditions. These trees were compared to the modern Picea mariana which is common throughout the modern North American Taiga. Another similarity to modern boreal forests is the presence of charcoal indicating frequent forest fires in the depositional environment. Emerging methodologies using oxygen-18 isotope values from fossil vertebrate remains to estimate average meteoric water temperature have yielded highly accurate results. When applied to the Prince Creek Formation it estimated a mean annual temperature near or just above 0 C. Mean annual precipitation was around 1300 mm.

North of Oceans Point, a section of non-marine deposits represent moderately to poorly consolidated conglomerate, sand, gravelly-sand as well as pebbly shale with thin coal beds and lignitised logs. Many gravel clasts are composed of rock types which do not occur in the nearby parts of the Brooks Range, arguing against the source of local bedrock fragmentation. These clasts are as large as 1.2 meters in diameter with some bearing faceted surfaces characteristic of glacial transportation, though not by iceberg transport, as indicated by the non-marine deposition. These deposits are later assigned a Maastrichtian to lowermost Tertiary age, though recent radiometric revisions in age of older strata could suggest a slightly older age. Palynological assemblages here are characterised by a depauperate assemblage of Betulaceae, Myricaceae, Ulmaceae, Ericales, Pinaceae, Taxodiaceae, various Tracheophytes and Sphagnum. The paleolatitude of the formation at the time of deposition was around 80°N, high in the Arctic Circle, and would have likely experienced 120 days of winter darkness.

Vertebrate paleofauna

Dinosaurs

Theropods

Indeterminate tyrannosaurid remains are present, mostly in the form of teeth. The teeth are from the Kikak-Tegoseak Quarry, Liscomb Quarry, and Byers Bed, totaling 8 teeth. Fossils of crown or near-crown birds as well as members of Hesperornithes and Ichthyornithes have been reported in 2025, providing the oldest evidence of birds nesting at polar latitudes reported to date.

Ornithischians

Mammals

Cartilaginous fish

Ray-finned fish

Plants

A Reinvestigation of the Parataxodium-type flora has revealed the assemblage was far more diverse than previously thought. However, this sedimentary block's stratigraphic origins are uncertain. No other in situ limestone blocks comparable to the Parataxodium-type flora have been located along the Colville River. Rivers upstream from the point of discovery cut through Upper Cretaceous deposits that range in age from Late Albian to Cenomanian. The diversity of flora present is more consistent with the Tuluvak Formation, which is dated to the Turonian-Coniacian.**

References

Bibliography

• Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. 861 pp. .

References

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