EXPLORING THE PALEOENVIRONMENT OF THE MORRISON FORMATION IN THE BIGHORN BASIN

The Morrison Formation is one of the most prolific dinosaur-bearing formations in the world. Stretching from northern New Mexico throughout much of the western United States and into southern Canada, the units of this Formation have been explored, particularly for dinosaur fossils, since the 1800s. However, the vast majority of research has focused primarily on exposures in Colorado, Utah, and Wyoming, where many of the most famous Jurassic-aged dinosaurs were initially found. The northern areas of the Morrison, however, have not been thoroughly explored until much more recently, and have revealed a mix of unique and relatively common dinosaur species of the Jurassic. An exposure of the Morrison Formation located in the Bighorn Basin of Montana reveals an excellent site to explore and compare to other northern Morrison sites, as well as the longer-studied southern areas. In addition to more typical Morrison specimens of apatosaur, stegosaur, and allosaur material, a relatively unique specimen of the small sauropod Suuwassea was initially discovered at this site (Harris and Dodson, 2004). The geology of this site, however, has remained largely unstudied, and the question remains if Suuwassea is unique to the area due to rarity, temporal differences, or environmental differences restricting it to the northern areas.

This project focuses on the paleoenvironmental aspect of the exposure of the Morrison within the Bighorn Basin. I propose that the environment is different from exposures of the formation further south, with less sediment supply from the upper reaches of the fluvial complex, resulting in a generally wetter environment due to the soils largely being saturated by the higher water table. This will be accomplished though a variety of methods, including detailed sedimentology and stratigraphy, geologic mapping, paleosol analysis, thin section analysis, XRD and IC-PMS analysis. Initial observations, sedimentology and stratigraphy are explored here. These methods will be used to analyze the wetness of the environment, in combination with information from the fossil localities both within the Bighorn Basin and in comparison to other Morrison Formation sites, to determine how different the paleoenvironment was within this particular section of the Morrison Formation.