RECONSTRUCTING REGIONAL PALEOENVIRONMENTS AND GEOMORPHIC HISTORY OF HIGH PLAINS PLAYA-LUNETTE SYSTEMS USING SOILS AND STRATIGRAPHIC RECORDS

Playas are ephemeral upland-embedded wetlands found in semiarid and arid regions worldwide. Lunettes are isolated dunes that form along the downwind margin of playas. The paleoclimatic and geomorphic history of High Plains playa-lunette systems (PLSs) are poorly understood. To address this, we characterize and interpret the stratigraphy of four PLSs in western Kansas, USA. Methods include: 1) collect soil-sediment cores from playa and lunettes; 2) describe cores using USDA techniques; 3) estimate age of stratigraphic units using radiocarbon (14C); and 4) reconstruct paleoenvironmental conditions and geomorphic processes using stable carbon isotopes (13C) and particle size data.

Playa stratigraphy is relatively simple and consists of well-developed surface soils underlain by gleyed clays. Playa 14C ages range from 6,280-23,600 cal yr BP. Lunette stratigraphy is complex; buried soils and thick units of light-dark bands are common. Lunette 14C ages range from 19,050-32,300 cal yr BP. 13C data indicate a warm-dry period dominated with C4 plants preceded ~30 ka, and was followed by a cool-moist, C3 plant dominated period before returning to warm-dry conditions throughout much of the Holocene.

Playa records extend from marine isotope stage (MIS) 3 (i.e., prior to the Last Glacial Maximum), and lunette records extend into MIS 3. Playa stratigraphy suggests they were dominated by alluvial-lacustrine processes during the late Pleistocene and early Holocene. Alternating light-dark bands in lunettes are hypothesized to represent incipient soils and aeolian sediment resulting from small-scale shifts in climate throughout much of the late Pleistocene and early Holocene, with geomorphic processes alternating between aeolian deposition and pedogenesis. Well-developed surface soils in playas and lunettes suggest stabilization and pedogenesis dominated the mid to late Holocene under a warming and drier climate. Thus, PLS development appears linked to both global-scale and regional climate processes.