GSA Connects 2021 in Portland, Oregon

Paper No. 75-9
Presentation Time: 10:35 AM


BUDD, Susannah, Pomona College, Geology, 185 E. Sixth Street, Claremont, CA 91711 and MCLAUGHLIN, Win, Geology, Pomona College, 185 E. Sixth Street, Claremont, CA 91711

The abrupt and dramatic spike in atmospheric CO2 levels associated with the Mid Miocene Climate Optimum makes it a compelling analogue for the similar spike seen today. However, this event is still not well-understood, with major questions remaining about how much of this global warming event was a response to changing ecosystems and how much this drove further ecosystem remodeling. Much of Northern Nevada contains paleosol deposits from the Miocene Epoch post-MMCO, making this region a promising location to further develop understanding surrounding the effects of this climatic event. Additionally this location addresses the role of topographic remodeling as an exacerbating factor for climate with the development of Basin and Range. Four stratigraphic columns from new fossiliferous vertebrate deposits just north of Wells, Nevada were measured and described to gain insight into the regionally evolving climate and ecosystem. The sequences described were laterally heterogenous and consistent with fluvial deposition on broad flood plains, with proximal areas of higher topography. The peds content in collected paleosol samples is consistent with alfisols and mollisols, and large, woody root traces were also present throughout much of the column, indicating that the ecosystem was supporting fairly large vegetation throughout much of the area, but also some of the early grasslands, which may have contributed to the changing climates as evidenced by the soils and grazers such as equids and camelids. Large amounts of reworked ash were also present suggesting a local source. Additionally, samples of carbonate nodules and enamel collected from the columns are currently being analyzed via XRF and stable oxygen and carbon isotope analyses to further develop estimates of climate proxies like precipitation and air temperature. This and further analysis of samples from this period offers insight into the climatic effects of this period, thus informing our understanding of how today’s climate may change alongside atmospheric CO2 levels. These new localities are important for understanding how global scale changes to climate shift local ecosystems and contribute to the high degree of ecological heterogeneity seen across the American West today, as well as how those ecosystems respond to anthropogenic climate change.