A GLACIOGENIC ORIGIN FOR LATE QUATERNARY DUNE FIELDS IN THE UPPER TANANA RIVER VALLEY OF EASTERN ALASKA, USA

New evidence is presented on the origin of a 100-km-long chain of dune fields in east-central Alaska. The Tok, Tetlin, and Northway dune fields (informal names, northwest to southeast) all host parabolic dunes, stabilized by boreal forest vegetation. The Tok dune field consists of three small areas of dunes. The larger Tetlin dune field has parabolic dunes with arms pointing to the southwest and noses facing northeast, indicating southwesterly paleowinds, consistent with the northeast dip orientations of high-angle foreset beds. The largest dune field, the Northway dune field, hosts parabolic dunes with arms pointing to the northwest and noses facing southeast, indicating northwesterly paleowinds. Radiocarbon ages indicate that most eolian sand was deposited in the late Quaternary, well after ~45 ka, and dunes were stabilized well before deposition of the White River ash, ~1.9 ka. Other radiocarbon ages indicate that eolian sand deposition was still in progress at ~14.7 ka (cal yr) in the Tetlin dunes and at ~13 ka (cal yr) in the Northway dunes, dating to the late last-glacial period. All eolian sands are compositionally immature, containing minerals (mica, chlorite, calcite) that typically do not survive long in dune fields that experience repeated sand transport. Major element (SiO2 vs. Na2O+K2O, SiO2 vs. CaO+MgO, SiO2 vs. Fe2O3+TiO2+MnO) and major/trace element (K/Ba vs. K/Rb, Ca/Sr vs. K/Sr, Ti/Zr vs. Ti/Nb) data are used to evaluate possible source sediments, which include locally derived sands from granitic grus, Tok River alluvium, and Tanana River alluvium. The best compositional fit for all dune fields is with sands of the Tanana River. This river carried large amounts of outwash from tributary streams that drained late Pleistocene glaciers in the Alaska Range and the Wrangell Mountains. Thus, observations made here demonstrate that glaciogenic sediments provided an important source for dune building well beyond the glacial limits of nearby mountain ranges.