Paper No. 4
Presentation Time: 1:20 PM-5:20 PM
DESCRIPTION OF PALEOSOLS IN THE UPPER JURASSIC MORRISON AND LOWER CRETACEOUS CLOVERLY FORMATIONS NEAR A DINOSAUR SITE IN THE BIGHORN BASIN, WY
An extensive trenching and sediment sample collection effort was undertaken to develop a detailed physical and chemical description of the Morrison and Cloverly Formations at a dinosaur site north of Shell, WY, focusing on paleosols within the section. We examined lithology, color, carbonate content, and used Particle Induced X-Ray Emissions (PIXE) and X-Ray Fluorescence (XRF) analyses to determine major and minor element abundances and trends. The paleosols are made up of mostly mudstones and sandstones, and many of the mudstones are frequently intermixed with siltstones. Morrison Formation strata in the Bighorn basin are dominantly calcareous, except near the boundary with the overlying Cloverly Formation. Gypsum crystals and calcareous nodules occur frequently throughout the formation. Barite nodules are mainly found in a unit close to the upper boundary of the Morrison, denoted by a transition from coarse reddish brown sandstone to a much finer-grained white volcanic ash-rich unit. There were three basic color horizons in the paleosols which tended to repeat throughout the measured sections. The dominant colors are various shades of yellow, green, gray, and red, often intermixed (mottled) with each other within sections. 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. This is an ongoing study oriented toward determining the paleoenvironment and paleoclimate of this previously understudied exposure of the Morrison and Cloverly Formations to support interpretation of the paleontological information from the active dinosaur quarries.