INTERPRETATION OF THE DEPOSITIONAL ENVIRONMENT OF DINOSAUR SITES, BRUSHY BASIN MEMBER OF THE JURASSIC MORRISON FORMATION, EAST-CENTRAL UTAH

The 2 km² area surrounding the John Oliver Dinosaur Site, Aaron Scott Dinosaur Site, and the West Virginia University at Parkersburg 2002 Dinosaur Site in east-central Utah has produced at least 11 dinosaur specimens, hundreds of Allosaurus teeth, thousands of individual bones and dinosaur trace fossils such as tracks and coprolites. These sites are located within the Brushy Basin Member of the Jurassic Morrison Formation near Ferron, Utah. This study measured nine detailed stratigraphic sections across the surrounding area of the John Oliver Dinosaur Site, Aaron Scott Dinosaur Site, and the West Virginia University at Parkersburg 2002 Dinosaur Site, including seven localities of appreciable dinosaur bone accumulations and many individual bones. The depositional environment is interpreted as meandering stream deposits, consisting of single-story channel sequences flowing to the south-east encased in extensive overbank deposits that are tens of meters thick. Channel deposits, which range in thickness from 1 to 3 meters, demonstrate lateral accretion surfaces (LAS), basal scour and gutter casts, and are infilled by cross-bedded sandstone (lithofacies St and Sp), mud intraclasts (Se), coarse-grained massive sandstones (Smc), and ripple-laminated sandstone (Sr). Abraded dinosaur bones are common in basal channel sequences. The overbank deposits include laminated and massive siltstone-mudstone (lithofacies Fl and Fm), coal and bivalve-bearing carbonaceous mudstone (Fc), thin freshwater limestone or tufa (Lm), and carbonate paleosols. Paleosols demonstrate stage I-III calcretes, with mottling, drab-halo rootcasts, and blocky ped structures. Several lines of evidence suggest seasonal aridity. The dinosaur specimens apparently accumulated in or near floodplain ponds or wetlands, and subsequent bank erosion may have introduced individual bones to the channels.