BIOSTRATIGRAPHY OF THE CRETACEOUS (MAASTRICHTIAN) NORTH HORN FORMATION, PRICE CANYON, CARBON COUNTY, UTAH

The North Horn Formation type locality at North Horn Mountain has long been known for its Late Cretaceous dinosaur fossils. Reported here are the first dinosaur bones from correlative strata in Price Canyon, Carbon County, Utah.

The basal unit of the North Horn Formation in Price Canyon is approximately 50 m thick. It consists of thin lacustrine shales and lime wackestones overlain by variegated floodbasin mudstones and fine-grained fluvial sandstone lenses with thin granule horizons. The lithology and fossils at this locality are similar to those that occur 80 km to the southwest in the Maastrichtian part of the formation (especially in the lower part of the middle unit) at the North Horn Mountain type locality.

In Price Canyon, dinosaur fossils occur as bone, eggshell fragments and track beds. Eggshells and track beds are observed up to the upper middle part of the unit while bone occurs from the middle to the uppermost part of the unit. Some of the eggshells and track beds here were reported in earlier phases of this study.

Dinosaur bone, representing fragments of ribs and limb bones and, tentatively, an incomplete hadrosaurid humerus, occurs in the upper middle and the uppermost parts of the unit. Eggshell fragments include dinosauroid-prismatic, dinosauroid-spherulitic and ornithoid basic (parataxonomic) types. An unnamed type of eggshell is commonly observed in the lacustrine limestone with turtle shell (Adocus), gar scales, gastropods, bivalves and charophytes (Platychara compressa, Retusochara). Track beds in cross-sectional outcrop view are more extensive than was previously reported. Shallow tracks representing large and small dinosaurs appear on the soles of sandstone beds at several levels in lacustrine and fluvial portions of the unit. Some tracks are heavily bioturbated by Planolites trace fossils.

Crocodile scutes, turtle shell (Adocus, Trionychidae), small tetrapod trace fossils and fossil logs and plant fragments occur in the upper middle of this unit near the same levels as dinosaur fossils.