DECIPHERING FLUVIAL AND EOLIAN DEPOSITS WITHIN A HOLOCENE DUNE FIELD IN THE SOUTHERN GREAT PLAINS OF WESTERN OKLAHOMA

Eolian activity has provided one of the best records of drought from the Great Plains of North America. However, these records may be incomplete due to the possibility of older eolian sediments being reworked by more recent eolian activity. Fluvial successions within dune fields may provide a more complete record of drought than eolian deposits alone. The Little Sahara sand dunes of western Oklahoma in the southern Great Plains provide an excellent setting for studying the interactions between fluvial and eolian activity and the ability of fluvial successions to record periods of past eolian activity and therefore drought. A cutbank along a small creek near the western edge of the dune field at Little Sahara Sand Dunes State Park contains a series of stacked paleosols separated by 50 to 100cm thick aggradational units. Structure, grain-size, magnetic susceptibility, and optically stimulated luminescence dating are used to document the paleosols and interbedded sedimentary units and determine their age. We used grain-size characteristics of the sedimentary units to determine their origin by comparison with grain-size characteristics of neighboring modern dunes and fluvial deposits. Our data shows two to three distinct grain-size populations, and seems to support our proposed model of fluvial aggradation during times of dune mobility. A comparison is made between the timing of aggradational events and regional records of eolian activity which suggests that the aggradational events are reliable recorders of drought. We present a model for the landscape development of repeated aggradational and denudational events, in which the aggradational units record periods of dune activity and hence drought conditions.