FLUVIAL RESPONSE TO LATE QUATERNARY CLIMATIC FLUCTUATIONS, CENTRAL KOBUK VALLEY, NORTHWESTERN ALASKA

Much of northwestern Alaska remained unglaciated during the Pleistocen e and thus offers a favorable setting for examining long-term records of high-latitude geological and biological change. Epiguruk, a large c ut bank 3.5 km long and up to 36 m high on the Kobuk River south of th e Brooks Range in eastern Beringia, exposes complex sedimentary succes sions representing cycles of upper Quaternary alluviation and eolian s edimentation, downcutting, and soil formation. A rich record of plants and mammals is also preserved in the section. Deposits of fluvial cha nnels and flood plains, eolian dunes, sand sheets, loess, and ponds, a s well as organic soils (Histosols) are represented. Parallel-bedded f ine sand and coarse silt couplets that commonly contain root structure s, ripple cross-lamination, and silt drapes are flood-plain sediments apparently deposited at the interface of fluvial and eolian environmen ts. Multiple fluvial-to-eolian depositional sequences were caused by i nflux of eolian sediment to the river from intermittently active dune fields south of the Kobuk River. Alluviation in the Kobuk Valley was c oeval with glaciation in the Brooks Range, whereas downcutting occurre d during interstadials when dune stabilization limited sediment supply . The depositional model developed at Epiguruk may be useful in interp reting some of the widespread subhorizontally stratified late-glacial deposits of Europe and North America.