MAJOR ELEMENT AND ISOTOPE GEOCHEMISTRY FROM LATE QUATERNARY PALEOSOLS IN SOUTHWESTERN KANSAS: ASSESSING CLIMATE AND PARENT MATERIAL CHANGE

Eolian stratigraphic sequences in the Great Plains provide important evidence of late-Quaternary paleoenvironmental change. Here we present data from two cores collected on the High Plains of southwestern Kansas that record eolian sedimentation, soil formation, and climate change in this understudied part of the Great Plains. Both cores contain eight eolian units with seven intercalated paleosols, spanning the period from late MIS 5 to present. Chronostratigraphic relationships indicate relatively rapid but episodic deposition of ~10 m of eolian sediments during late MIS 5 (ca. 84–75 ka), which stratigraphically correlate to the Loveland Loess. Relatively thin (2–3 m) eolian deposits record slow aggradation and pedogenesis during MIS 4 (ca. 70–54 ka). Up to 4 m of sediment representing the Gilman Canyon Formation was deposited and subsequently modified by pedogenesis during MIS 3 (ca. 52–35 ka), and surficial Peoria Loess deposits began to aggrade at the beginning of MIS 2 (ca. 29 ka).

Several indices derived from geochemical data were examined to assess the impact of climate and parent material on weathering. Preliminary data indicate that the most intense chemical weathering occurred during late MIS 5. Qualitative paleoclimatic conditions were inferred from stable C and O isotopes, which are supported by quantitative reconstructions of mean annual precipitation (MAP) and temperature (MAT) from major element geochemical data. Results suggest 1) relatively frequent shifts in temperature (5.3–9.1°C), precipitation (350–700 mm/yr) and potentially meteoric moisture sources during late MIS 5, 2) relatively cool (7.6°C) and dry (~550 mm/yr) conditions during MIS 4 with some evidence for fluctuations in temperature, seasonality, and/or meteoric water sources, 3) increased temperature (9.1°C) and aridity (~450 mm/yr) during MIS 3, 4) likely cool conditions during MIS 2 with sufficient effective precipitation to support C₄ plant communities, and 5) relatively warm and dry climatic conditions during MIS 1. A significant shift in the isotopic signal and abundance of immobile elements was observed at ~3 m depth in both cores. This shift is interpreted to represent a change in parent material from locally derived eolian sands to more distally derived eolian silts at ca. 29 ka.