GEOMORPHOLOGY AND ACTIVATION CHRONOLOGY OF THE ARKANSAS RIVER DUNE FIELD

Prehistoric megadroughts were geographically extensive droughts much more severe than historic droughts such as those of the 1930s and 1950s. Megadroughts have been previously documented in paleoclimatic records of Great Plains dune fields, but these events are not well understood, especially in the central Great Plains, where such research has been limited. Defining Holocene megadrought activity in the central Great Plains is essential for identifying regional drought patterns. This study explores the 250 km-long Arkansas River dune field (ARDF), a 3600 km² sand body that lies south of the Arkansas River, from eastern Colorado to central Kansas. The dune field is located on a late Pleistocene terrace (~13-14 ka) and is derived from sand transported by the river. The ARDF is geomorphically complex with southerly linear and parabolic dunes overprinted by younger northward trending parabolic dunes. The bimodal dune morphology suggests that at least two major episodes of activity were present since initial formation. A luminescence chronology supports multiple periods of dune activity with substantial activation during and at the termination of the Medieval Climatic Anomaly (~0.6-0.4 ka). Optical ages also record historic eolian sedimentation of the 1930s and 1950s dust bowl droughts. Ages of dune activity in the ARDF are in agreement with previously reported ARDF optical ages and with radiocarbon ages from the adjacent Great Bend Sand Prairie.