Pleistocene periglacial eolian deposits in southwestern Alaska: sedimentary facies and depositional processes

P. D. Lea, Bowdoin College


Pleistocene periglacial eolian sediments are widespread in the Nushagak, Holitna, and Upper Kuskokwim lowlands of southwestern Alaska. These sediments comprise mainly sand-sheet deposits and sand-loess intergrades, with subordinate sand-dune deposits and loess. Sand-sheet deposits range from 1) sharply defined, parallel, low-angle laminae by migrating wind ripples to 2) irregular subhorizontal strata which reflect migration of poorly segregated wind ripples, accumulation on a sparsely vegetated surface, adhesion on a quasi-planar bed, and/or niveo-eolian deposition. Sand-loess intergrades represent alternating bed-load and suspension deposition related mainly to the stochastic and seasonal variability of former wind systems. The dominance of sand-sheet deposits over deposits of well-formed dunes in the Pleistocene eolian record of southwestern Alaska reflects the limited availability of loose, dry sand in this former periglacial environment. Immobilization of sand after deposition as low-relief sheets resulted from a seasonally variable combination of ice cementation, sparse vegetation, high water tables, and snow cover. -Author