MINERALOGY AND SEDIMENTOLOGY OF THE NORTHWESTERN NEBRASKAN BRULE FORMATION AND IMPLICATIONS REGARDING BIOSTRATIGRAPHY

In northwestern Nebraska, the badlands section along the flanks of the “Mesohippus” Valley, informally named by Augustana College students, belongs to the Oligocene-aged Brule Formation. The complete Brule Formation of Nebraska is made up of the Orellan, Whitney and “Brown Siltstone” Members; however, it is uncertain which part of Brule section is represented by the exposures along "Mesohippus" Valley. The Orellan is a fluvial deposit dominated by paleosols and unconformities. The overlying Whitney Member consists of pink siltstones, claystones and loess, and the end Member of the “Brown Siltstone” includes volcaniclastic unconformities. By analyzing sediment taken from various stratigraphic levels and correlating data with published material on the Brule, the portion of the Brule section found in this valley will be determined. In addition to working out the stratigraphy of "Mesohippus" Valley, samples taken throughout this section are being analyzed for mineralogical content. According to previous studies, quartz, calcite, and clays are abundant in this formation. These minerals, including montmorillonite, kaolinite and halloysite are being analyzed in an X-Ray Diffractometer to examine the fluctuation of common clays and minerals throughout the "Mesohippus" Valley section. This mineralogical data, combined with other sedimentological data, will help give a better understanding of the distribution of fossils among the various facies.