Fluvial Response to Late Quaternary Climatic Fluctuations, Central Kobuk Valley, Northwestern Alaska

Abstract

ABSTRACT Much of northwestern Alaska remained unglaciated during the Pleistocene and thus offers a favorable setting for examining long-term records of high-latitude geological and biological change. Epiguruk, a large cut bank 3.5 km long and up to 36 m high on the Kobuk River south of the Brooks Range in eastern Beringia, exposes complex sedimentary successions representing cycles of upper Quaternary alluviation and eolian sedimentation, downcutting, and soil formation. A rich record of plants and mammals is also preserved in the section. Deposits of fluvial channels and flood plains, eolian dunes, sand sheets, loess, and ponds, as well as organic soils (Histosols) are represented. Parallel-bedded fine sand and coarse silt couplets that commonly contain root structures, ripple cross-laminatio , and silt drapes are flood-plain sediments apparently deposited at the interface of fluvial and eolian environments. Multiple fluvial-to-eolian depositional sequences were caused by influx of eolian sediment to the river from intermittently active dune fields south of the Kobuk River. Alluviation in the Kobuk Valley was coeval with glaciation in the Brooks Range, whereas downcutting occurred during interstadials when dune stabilization limited sediment supply. The depositional model developed at Epiguruk may be useful in interpreting some of the widespread subhorizontally stratified late-glacial deposits of Europe and North America.