Sedimentology, paleoclimatology, and geomorphology of a late Pleistocene-Holocene paired eolian system, Columbia Plateau

The study of eolian sediments is key to understanding continental paleoclimate. Previously, these studies have focused either on sand dunes or loess. This research aims to integrate eolian studies by demonstrating that sand dunes and downwind loess accumulations derived from the same source are genetically related in a 'paired' eolian system. Qualitative models presented here describe the interactions between eolian sand and loess via bioclimate and topography, overridden by atmospheric circulation patterns.; Eureka Flat in south-central Washington is a deflational zone aligned with prevailing winds. An abundant sediment supply derived from periodic glacial outburst flooding has contributed to the formation of sand dunes, sand sheets, and loess. Stratigraphy within Eureka Flat documents the bioclimatic shift from sand sheet development to loess accumulation with changes in soil moisture and vegetation density, accompanied by changing pedologic and sedimentologic properties. Thus, bioclimatic conditions have controlled where loess and sand have accumulated through time.; Incised stream valleys such as Juniper Canyon at the southern margin of the Palouse separate upwind eolian sand from downwind loess. Juniper Canyon acts as a topographic trap for saltating sand particles. Post-last glacial maximum (LGM) loess derived from deflation of the Umatilla Basin reaches thicknesses of 8 m downwind of the topographic traps. Bracketed tephra ages within the loess document high mass accumulation rates from 15,500--13,200 yr B.P., followed by relative landscape stability and soil formation during the Younger Dryas cold interval at the close of the Pleistocene. Research at Juniper Canyon suggests that loess accumulation is punctuated rather than gradual.; While bioclimatic and topographic effects clearly influence the distribution of eolian sediments, atmospheric circulation patterns ultimately control the large-scale generation of dust. General circulation models simulate a glacial anticyclone generated by the Laurentide Ice Sheet during the LGM. This anticyclone weakened westerly air flow in the Pacific Northwest, enhancing aridity. Luminescence ages, paleoecologic evidence and paleosol properties from the loess suggest weakened prevailing winds suppressed dust formation, resulting in thin loess and strong soil development across the Columbia Plateau. This is the first study to demonstrate the role of the glacial anticyclone in LGM eolian deposits.