Tag: Samantha Hopkins

A Lithostratigraphic Analysis of the Crooked River Mascall Formation

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.

The Evolution of Camelids in the Pacific Northwest in Response to the Grassland Expansion

Presenter(s): Eleanor Froehlich—Earth Sciences

Faculty Mentor(s): Samantha Hopkins, Dana Reuter

Session 6: The Earth, Sky & Everything In Between

Camelids, the artiodactyl group including camels, llamas, and alpacas, evolved in North America during the Eocene . The first camelids were smaller than a goat; however, some extinct genera were giraffe sized . Most studies of North American camelids focus on fossils found in the Great Plains and as a result little is known about how camelid diversity responded to climate and vegetation changes in the Pacific Northwest. Horses are a well-studied example of ungulate responses to climactic changes and grassland expansion . They show a general increase in body size that is concurrent with their switch from browsing to mixed feeding and eventually to the grazing we see in modern examples . I suspect that as the environment in the Pacific Northwest dried out, camelids also increased in size due to the grassland expansion . I also believe that camelids incorporated more grasses into their diet . I tested this by documenting camelid diversity in the Pacific Northwest, specifically the states of Idaho, Oregon, and Washington, using the published fossil occurrences on the Paleobiology Database . Body size data was estimated using tooth measurements collected on the Fossilworks database . Camelid species were categorized according to two ecological parameters, body size and diet . I used these to track camelid evolution through time . I found that although body mass does increase there were still small browsing lineages late into the Miocene . This study provides a broader biogeographical picture of how grassland expansion influenced camelid evolution and ecology .

New specimen of Monosaulax typicus (Mammalia, Castoridae) from the Mascall Formation of Twin Buttes in the Crooked River Basin, Oregon

Presenter(s): Shyla Davison—Earth Science

Faculty Mentor(s): Samantha Hopkins

Session 6: The Earth, Sky & Everything In Between

The Mascall formation of Central Oregon is a rock unit that was formed during the middle Miocene (~15 million years ago) . The Mascall formation was first described from North Central Oregon, but also outcrops to the south in the Crooked River Basin, where it is much older . While these southern outcrops of the Mascall Formation have been known for some time, recent research shows that they are about a million years older than the outcrops of the same formation in the John Day Basin . This particular formation is known for producing many Barstovian-age mammals . Recent collections by University of Oregon field crews have yielded new material from the Crooked River region . I have diagnosed two new specimens recovered from the Mascall formation from Twin Buttes near Paulina, OR, as Monosaulax typicus from the family Castoridae . One specimen is a fragment of a lower right jaw that contains the p4-m2, while the other is a left jaw fragment . These are the most complete remains of M . typicus from the Mascall formation; other known specimens are isolated teeth . The teeth have all the diagnostic characteristic of other previously identified specimens of M . typicus that were found in Southeast Oregon rocks of similar age (Shotwell, 1968) . The information of this new specimen will add to the limited knowledge of this species and the environment of the Crooked River Basin .