EVALUATING PALEOENVIRONMENT AND PALEOCLIMATE IN THE CENTRAL GREAT PLAINS, NORTH AMERICA DURING MARINE ISOTOPE STAGE 3 (CA. 59-27 KA)

Throughout the central Great Plains packages of alluvium and colluvium preserve paleosols that represent deposition and landscape evolution during MIS 3. These paleosols record important signals that can be used to evaluate paleoenvironment and paleoclimate during an interval that is characterized by frequent and rapid climatic fluctuations within the last Glacial period. Furthermore, these paleosols can be used to evaluate previous research suggesting that periods of landscape stability and soil development were likely the result of atmospheric circulation patterns that inhibited incursions of moist air from the Gulf of Mexico, minimizing high magnitude flooding events. Here we combine a variety of methods including numerical dating (radiocarbon and optically stimulated luminescence) and stable carbon, oxygen, and hydrogen isotope techniques to improve our understanding of late-Pleistocene climatic changes and landscape response in the Central Plains of North America.

Two stratigraphic sections were investigated in western and eastern Kansas. Paleosols in these sections date to late MIS 3 (ca. 40–27 ka) Estimated MAT produced from hydrogen and oxygen isotopes of pedogenic phyllosilicate minerals ranged from 6–9°C ± 3 °C, approximately 4–7 °C lower than modern MAT. Estimated δ¹⁸O values of soil water from phyllosilicates ranged from -10.6‰ to -9.6‰ VSMOW, which are lower (¹⁸O-depleted) by about 1.5–3‰ relative to modern measurements of meteoric precipitation δ¹⁸O values. However, given that soil water δ¹⁸O values are typically 3–5‰ higher than precipitation δ¹⁸O values, the δ¹⁸O of precipitation during MIS 3 was likely ¹⁸O-depleted by up to 8.5‰ relative to modern values. This could be explained by 1) cooler temperatures, 2) precipitation being sourced primarily from Pacific/Arctic air masses, 3) seasonal changes in precipitation patterns (i.e. predominantly winter precipitation), or 4) a combination of the above. Furthermore, the estimated δ¹⁸O values of soil water generated from pedogenic carbonate range from -8.4‰ to -9.2‰ VSMOW and are ¹⁸O-enriched by approximately 1–1.5‰ compared to the soil water δ¹⁸O values generated from phyllosilicates. The difference is likely due to seasonal bias in carbonate formation and suggests δ¹⁸O values obtained from pedogenic phyllosilicates may provide data more reflective of average conditions.