TAPHONOMY OF THE ANDREW'S SITE QUARRIES, LOWER CRETACEOUS CEDAR MOUNTAIN FORMATION, GRAND COUNTY, EAST-CENTRAL UTAH

The Andrew's Site Quarries are located in the upper part of the Yellow Cat Member of the Cedar Mountain Formation. Two superimposed bone horizons are separated by about a three meter interval that includes a sandstone splay around 25 cm thick, which laterally preserves a track assemblage. In the lower bone horizon, scattered bone can be observed over a distance of more than 100 meters. Roughly four square meters of the lower bone horizon was excavated. The lower site predominantly preserves isolated scutes and spines of an ankylosaur, most likely Gastonia, in a purplish mudstone matrix. The upper bone horizon is much more restricted laterally than the lower horizon, and the approximate eleven square meters of the upper bone horizon that was excavated may represent the entire extent of the site. Fossils collected from the upper site include partially articulated and isolated bones. A large adult iguanodontid skeleton, cut by a drainage, was excavated. Modern root systems caused much damage to the fossil bone, and many of the bones were distorted by compaction. The skeleton was preserved in a well sorted, very fine grained, subrounded, light greenish grey sandstone lens with a number of large clasts and smaller bones. No sedimentary structures were apparent. After some months of preparation, the blocks collected from the upper site yielded remains of a juvenile iguanodontid (skull), a terrestrial crocodile (skull and skeleton), and a third skull, to be described in a later publication. The Yellow Cat Member has been interpreted as representing a semi-arid monsoonal climate. The local depositional environment is interpreted as a low-energy stream setting. The Andrew's Site Quarries are located at approximately the same stratigraphic level as the Gaston Quarry, which produced the type specimens of Gastonia and Utahraptor. The Andrew's Site Quarries represent an important fossil location and warrant further study.