LITHOSTRATIGRAPHY AND PALEOENVIRONMENTS OF PLAYA-LUNETTE SYSTEMS ON THE KANSAS HIGH PLAINS

Playa-lunette systems (PLSs) are geographically isolated, ephemeral wetlands with crescent-shaped dunes adjacent to the wetland. Two PLSs on the High Plains of central Kansas were investigated to reconstruct paleoenvironment throughout evolution and identify the primary processes and mechanisms of PLS formation and development. Soil cores were collected throughout both PLSs, and cores were analyzed for color, particle size distribution, magnetic susceptibility, and stable carbon isotopes.

PLS origin appears related to paleotopography, with a depression in the Ogallala Formation underlying playa fill and a ridge underlying lunette fill. Several stratigraphic units are preserved within PLSs (i.e. Sangamon Soil, Gilman Canyon Formation soils and loess, Peoria Loess, Brady Soil, Bignell Loess and Holocene-aged soils) spanning at least from MIS 3 and perhaps as far back as MIS 5. Stratigraphic investigations indicate Marine Isotope Stage (MIS) 3 was characterized by a climate similar to or slightly warmer than present. Effective precipitation was either relatively low or precipitation was more evenly distributed throughout the year, playa floors were exposed for prolonged periods throughout the year. During MIS 2, temperatures were cooler and effective precipitation greater, though precipitation varied cyclically at sub-millennial scales. Slightly wetter phases were associated with water storage in playas and pedogenesis surrounding playas, and drier phases were dominated by sediment remobilization from playa floors and burial of incipient soils on the lunette. The P-H transition was a period in which temperature and C₄ plant contributions increased, though multiple shifts of 3–5 °C in 5–10 cm intervals are preserved and correlate to the Bølling-Allerød/Younger Dryas chronosequence. Warming continued throughout the Holocene, and precipitation was highly variable, resulting in multiple Holocene-aged soils throughout PLSs. Thus, the dominant process of PLS evolution has likely varied over time, with dissolution more important during initial development and periods of high effective precipitation. Fluvial-eolian processes increased in importance as playa expansion proceeded and effective precipitation decreased.