GHOST DUNE HOLLOWS: MID-LATE PLEISTOCENE TO HOLOCENE CLIMATE FLUCTUATIONS AND LANDSCAPE EVOLUTION ON THE EASTERN SNAKE RIVER PLAIN, IDAHO, USA

A group of ~30, basalt-rimmed and partially sediment-filled, 5-10 m-deep topographic depressions are distributed across ~40 km² of the eastern Snake River Plain, Idaho. These crescentic to elongate depressions, here termed ghost-dune hollows, are an unusual type of topographic inversion that developed after the ~62 ka basaltic Split Butte lava encased mid-late Pleistocene sand dunes. The hollows have comparable shapes and sizes to, but orientations that are ~10-15º more easterly than, NE-migrating barchan and barchanoid ridge dunes in the nearby modern St. Anthony dune field. Sedimentary, stratigraphic and pedologic evidence from hand-augered samples, Split Butte basalt ⁴⁰Ar/³⁹Ar ages and optically stimulated luminescence (OSL) ages suggest four stages of ghost-dune hollow development: 1) pre-62 ka, ancestral sand dunes encased by the Split Butte basalt, 2) post ~62 ka, water-table influenced deflation of well-sorted, cross-stratified to massive, basalt-lithic rich dune sand, 3) ~62-14 ka, hollow infilling by sandy loess, sand dune, paludal and colluvial sediment with weak to moderate pedogenesis, 4) ~14 ka, to present, moderate to strong pedogenesis of eolian, paludal, and colluvial sediment. Paleoclimates before and during ghost-dune hollow infilling fluctuated between persistent arid conditions that favored widespread eolian activity with limited pedogenesis and intermittently wetter conditions that favored localized eolian, paludal, and colluvial deposition with pervasive pedogenesis. Petrographic and U/Pb detrital zircon analyses reveal that the ancestral ghost dunes received sediment primarily from Henrys Fork alluvial and Yellowstone volcanic plateau sources whereas the St. Anthony dunes also received sediment from Snake River alluvial and glacial Lake Terreton sources. The ghost-dune hollow paleoclimatic record correlates broadly with climate-influenced episodes of glacial Lake Terreton (south-central Idaho) expansion and contraction as well as episodes of loess deposition and paleosol development in SE Idaho and southern Jackson Hole, Wyoming. Additional OSL ages and chronostratigraphic control will refine these correlations and improve understanding of interrelations between paleoclimate, eolian sediment dispersal, volcanism and landscape evolution in this region.