EOLIAN SAND EVIDENCE FOR LANDSCAPE INSTABILITY IN THE CENTRAL GREAT PLAINS DURING MIS 3

A high terrace extending intermittently along the entire length of the Kansas River valley in northeastern Kansas was recognized in the mid-nineteenth century and designated the Menoken Terrace. Our stratigraphic investigations indicate that the fill is comprised primarily of reworked till (glaciofluvial). The terrace fill likely correlates to the glaciation of northeastern Kansas 700-600 ka, which is corroborated by the occurrence of Lava Creek B volcanic ash (~640 ka). Eolian sand, expressed as low, broad-crested dunes, mantles the terrace tread at most locations. OSL dating of the sand was conducted on samples within the upper 2 m of both the dune crests and swales. Ages indicate that the dune crests were last active during the latter part of MIS 3, ~ 36 ka to 31 ka (36, 34.4, 31.1 ka), while ages from interdunal areas were mid-Holocene (6.04, 6.01, 4.81 ka). From the global perspective, these dunes were last active during a peak in mid-latitudinal summer insolation, within the Bond Cycle between Heinrich Events 4 and 3, and during times of high atmospheric dust loads, e.g., NGRIP. Regionally, the central and eastern Great Plains also experienced loess deposition (Gilman Canyon Formation loess: 36-30 ka) and instability in the Kansas, Arkansas and Cimarron river systems. Mid-Holocene deposition recorded within the interdunal areas likely reflects modest dune-slope instability, coincidental with stream system instability and deposition within playas in the Central Great Plains.