OVERVIEW OF THE GEOMORPHIC, SEDIMENTARY, STRATIGRAPHIC AND PALEOCLIMATIC HISTORY OF SAND-DOMINATED QUATERNARY EOLIAN DEPOSITS ON THE COLUMBIA PLATEAU, WA

The geomorphic, sedimentary and stratigraphic record of sand-dominated Quaternary eolian deposits on the Columbia Plateau of Washington is a paleoclimatically relevant part of the broader glacial outburst flood-dominated history of the Channeled Scabland. Textural and compositional analyses reveal that sand-dominated eolian deposits were largely derived from loosely consolidated accumulations of outburst flood slackwater sediment in the southern scabland. These deposits were mobilized to produce stabilized to active parabolic, blowout, barchanoid ridge and barchan dunes and sand sheets that are concentrated near their sources. The spatial distribution and morphologies of modern sand-dominated eolian deposits on the plateau provide a template for ancient eolian-influenced landscapes between previous glacial outburst-flood episodes.

The paleoclimatic history of these deposits complements that of the stratigraphically more complete loess record. The concentration of sand-rich eolian deposits in low-lying, source-proximal scabland positions has made them more susceptible to removal by subsequent outburst floods; hence, sand-rich eolian deposits have experienced a lower preservation potential and have tended to yield ages that are younger than the loess. The ages of sand dunes on the plateau are dominantly mid- to late-Holocene whereas the ages of sand-sheet deposits are Pleistocene. The sand dunes and sand sheets on the plateau developed in an arid to semi-arid climate that was subject to persistent and dominantly E- and NE-directed winds. Topographic irregularities and source-sediment placement contributed to development of a few prominent dune fields including one near Moses Lake and several (Hanford and Juniper dunes) near the confluence of the Snake and Columbia Rivers. Lenses and beds of Glacier Peak tephra contained in dunes on the northern scabland are evidence for late Pleistocene sand dune activity which is largely absent elsewhere on the plateau. Late Pleistocene sand dune mobilization accompanied the heightened sand sheet activity and clay/silt ejection responsible for thick post last glacial maximum loess deposition. Heightened episodes of Holocene sand dune mobilization, however, have not been clearly linked with similarly thick loess accumulations.