STRATIGRAPHY AND PALEOENVIRONMENTS OF PLEISTOCENE NONGLACIAL DEPOSITS IN THE SOUTHERN NUSHAGAK LOWLAND, SOUTHWESTERN ALASKA, USA

Two Pleistocene nonglacial units underlie eolian deposits of the last glaciation in the southern part of the Nushagak lowland, a major Quaternary basin in southwestern Alaska. The Flounder Flat complex, the lower of the two units, consists mainly of deposits of tundra lakes. Pollen and beetle data suggest a somewhat mesic graminoid tundra without significant birch and ericaceous shrubs and a climate colder than present. The overlying Etolin complex includes organic silt, nonwoody peat, and associated inorganic sediments that accumulated in swales and on lower slopes, Lowermost peaty silt of the Etolin complex locally contains pollen spectra indicative of birch-shrub tundra and beetle assemblages characteristic of mesic-to-wet habitats broadly similar to those of the Holocene tundra. Evidence for full-interglacial climates, however, is ambiguous. Stratigraphically higher samples from the Etolin complex suggest a colder-than-modern graminoid tundra with local mesic-to-wet habitats but restricted shrub cover. Radiocarbon and paleoecological data suggest at least partial correlation of the Etolin complex with the middle Wisconsin (Boutellier) nonglacial interval, mostly > 38,000 yr BP.