Presenter(s): Alexandra Thompson
Faculty Mentor(s): Samantha Hopkins
Poster 72
Session: Sciences
This project presents a comprehensive lithological and biostratigraphic record of the Miocene Mascall Formation deposits of the Crooked River Basin in Central Oregon. The Columbia River Basalt Group (CRBG) covered the Crooked River Basin and much of the Pacific Northwest in the middle Miocene, altering the landscape and ecosystem. As a result of this event, an analysis of the depositional history of this region is worthwhile because it explores the impact of large scale basalt flows on subsequent basin evolution. University of Oregon geology students have measured stratigraphic sections in four different locations across the Crooked River basin in order to quantify the differences in depositional history across the basin. The sites are stratigraphically situated between the lower boundary CRBG and upper capping Rattlesnake Ash Flow Tuff (RAFT). For each region, we have created a representative stratigraphic column, and correlated rock units between the regions. The Mascall Formation in the Crooked River Basin is consistent with published descriptions of the Lower Mascall Formation: mostly fine siltstone and sandstone with diatomite, ash, and chert deposits and some tuff strata (Bestland, 1998). Each of the four sites share characteristics of the Lower Mascall which suggests similar depositional environments across the sites; however, the sections vary in the thickness and representation of individual identifiable strata, suggesting variation in where deposition was greatest through the half-million years of the section. This is the first comprehensive assessment of the stratigraphy of the Crooked River Basin, which has significant implications for understanding landscape reorganization following volcanism.