PALEOSOL DESCRIPTION OF THE MORRISON FORMATION AT A DINOSAUR SITE IN THE BIGHORN BASIN NEAR SHELL, WYOMING

We engaged in extensive trenching and sediment sample collection to develop a detailed physical and chemical description of the Morrison Formation at a dinosaur site north of Shell, Wyoming, focusing on paleosols. We examined lithology, color, carbonate content, and elemental occurrences using field observations, color guides, Particle Induced X-Ray Emissions (PIXE) and X-Ray Fluorescence (XRF). The paleosols are made up of mostly shales and sandstones. Many of the shales are mudstones, frequently intermixed with siltstones. Morrison Formation sediments in the Bighorn Basin are calcareous, except near the boundary between the Morrison and Cloverly Formations. Gypsum crystals and calcareous nodules occur frequently throughout the formation. Barite nodules are mainly found in one layer near the upper boundary of the Morrison, which is denoted by a shift from coarse reddish brown sandstone to a much finer grained white deposit. There were three basic color horizons found to repeat throughout the measured section. The dominant colors are various shades of yellow, green/gray, and red, often intermixed with each other within sections, suggesting variation in oxidation and reduction within the soils. Random samples from throughout the Morrison tested by the PIXE and XRF had relatively high abundances of Ca, Fe, Mn, K and Ti. Trace amounts of Cu, Cr, Pb, Ni, Sr, Rb, V and Zr were also detected by these methods. This is an ongoing study oriented toward determining the paleoenvironment and paleoclimate of this previously understudied occurrence of the Morrison Formation.