Middle- and late-Holocene dune reactivation the Nebraska Sand Hills, USA

A combination of optical dating of aeolian sand, and radiocarbon dating of palaeosols and interdune sediments, has allowed some refinements to the chronostratigraphy of the Nebraska Sand Hills. Our results directly confirm previous inferences that multiple phases of aeolian deposition, including megabarchan dune reactivation, occurred within the Sand Hills during the middle and late Holocene. Optical dates on stratified aeolian (barchan dune) sediments from two localities provide ages ranging from c. 6 ka to <300 years ago. Weakly developed palaeosols intercalated within the dune sediments and other forms of post-depositional modification indicate periods of relative stability and reduced dune mobilization. Optical dates on the upper 12-15 m of two dune exposures indicate repeated, possibly regionally correlative, reactivations which occurred between c. 400-500 and 200-300 years ago. Comparison of late-Holocene aeolian activity with local and regional palaeoclimatic proxy records suggests that dune reactivation may have occurred frequently, possibly in response to periods of extended (>20 yr) drought.