Stratigraphy and OSL chronology of lunette deposits indicates that Nebraska’s rainwater basins formed by aeolian deflation between 39 and 25 ka

Abstract The rainwater basins are northeast-southwest oriented deflation basins on an aeolian sediment–mantled remnant alluvial plain south of the Platte River in central Nebraska. Many of them hold runoff, at least seasonally. Most basins are ovoid, with long axes ranging from 1 to 2.5 km in length, and lunettes are commonly found along their southeastern and/or southern margins that stand 8 to 12 m above basin floors. Core stratigraphy indicates that the basins were eroded from Pleistocene alluvium and aeolian sand and later mantled with loess. Lunettes consist of very fine to medium sand capped by Peoria Loess. We collected 22 optically stimulated luminescence (OSL) samples from lunettes around seven basins and four additional samples from the loess-mantled dunes and sandy alluvium that underlies the Rainwater Basin Plains. OSL dating shows the lunettes were deposited approximately 51 to 20 ka, although most ages lie between 39 and 25 ka. Our chronology shows that the basins and lunettes formed primarily during Marine Isotope Stage 3 (MIS 3) when a combination of aridity and intermittent wetter climates facilitated basin deflation and subsequent remodeling by wave activity when the basins held water. The basins and lunettes were subsequently stabilized and mantled by Peoria Loess during MIS 2.