Sedimentologic and Taphonomic Interpretations of the Dinosaur-Bearing Upper Cretaceous Prince Creek Formation, Alaska: Insights from An Ancient High-Latitude Terrestrial Ecosystem

The Upper Cretaceous Prince Creek Formation of northern Alaska contains the densest concentrations of dinosaur bones of any high latitude rock unit in either hemisphere. Conditions unique to high latitudes may have contributed to forming this rich polar dinosaur record.

Sediments of the Prince Creek Formation were deposited in an extensive, low-energy alluvial/coastal plain. Paleosols developed primarily in floodplain claystones and siltstones, although many sandstones also display evidence of rooting. Floodplain paleosols are cumulative and relatively weakly-developed. Micromorphological features, including bioturbation, Fe-oxide coatings, depletion coatings, and illuvial clay coatings suggest periods of wetting and drying on the coastal plain, despite the predominance of drab colors and abundance of organics. The absence of any thick, well-developed paleosols strongly suggests that the floodplains were sedimentologically active. These features are consistent with climate models suggesting increased moisture in higher latitudes during the Cretaceous. Another possibility is that the seasonal darkness that must have been present in high latitudes decreased the overall evapotranspiration rates and, therefore, led to wetter and weaker soil development than that expressed in lower latitude Cretaceous locations.

Bonebeds on the North Slope are characterized by extreme specimen density (N=100s/m3) over large aerial extent (100s/m2) and an abundance of juvenile to subadult dinosaurs. Arctic bonebeds were formed under unique conditions. The Brooks Range formed the southern edge of the Colville Basin in the Cretaceous. A conservative estimate for the elevation of the Brooks Range at that time is 1500m. In contrast to estimates of mild temperatures on the coastal plain, estimates of mean annual temperature in the Brooks Range are below 00 and thus capable of supporting icefields and associated permafrost. Stream dynamics in permafrost dominated-watersheds are known for periods of intense seasonal runoff. This mechanism may be responsible for the bonebeds of the Prince Creek Formation during the Cretaceous.