MULTIPLE GENERATIONS OF LATE HOLOCENE LINEAR DUNES, NEBRASKA SAND HILLS, USA

Extending over 58,000 sq km and presently stabilized by native grassland, the Nebraska Sand Hills have mobilized several times in the Holocene. Limited optically stimulated luminescence dates, mostly from the large-scale transverse dunes, indicate these dunes were actively migrating during one or more periods of aridity between 3-9 ka. Recent optical dating of small-scale dunes, and upland paleosols, combined with radiocarbon dating of aeolian sand beds in interdune peatlands, indicates there were several periods of aridity and dune activity within the last 3 ka. In the central and eastern Sand Hills, these late Holocene aeolian bedforms are primarily linear dunes, 1-3km long and 15m high, occurring either in discrete dune fields or superimposed on larger transverse dunes. Preliminary optical dates of aeolian sand collected from the superimposed linear dunes suggest that they were formed between 950 and 750 a. This episode of dune activity is coeval with the “megadrought” preserved in aeolian sand sheets in interdune wetlands within the central Sand Hills. However, OSL dates from linear dunes near the southeastern and eastern edge of the Sand Hills, indicate dune activity between 2.5 and 2 ka and 500-600 a. It appears that much of the eastern half of the Sand Hills have seen linear dune mobilization during drought episodes of the past 2.5 ka, however different areas were active at different times and associated wind regimes may not have been the same.