Brenna Curtis / Earth & Environmental Sciences / Faculty Mentor: Majie Fan
The analysis of loess deposits is critical in the reconstruction of paleoclimate as the mean grain size and grain-size distribution are specific to various transport mechanisms. Therefore, changes in mean grain size and distribution can indicate shifts in climate. While loess deposits of the late Eocene-Oligocene age have been identified in western North America, there have been few detailed studies. This project aims to examine the Oligocene loess deposits in northeastern Colorado. A total of 156 samples were collected from two sites near Pawnee Buttes (labeled PB and PBE) and analyzed using a Mastersizer Laser Diffraction analyzer. Samples from both the PB and PBE sites are consistently poorly sorted, showing very finely skewed and leptokurtic distributions. Most samples from the PB site show a bimodal distribution, however, samples from the PBE site are mostly unimodal. PBE samples have consistent U-ratios near 1.5. Although PB samples shows some fluctuations between 3.15 to 0.74 U-ratios, they generally remain around 1.5. The stable ratios indicate that the depositional environment remained largely consistent during deposition​.
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