Pleistocene glacial tectonism and sedimentation on a macrotidal piedmont coast, Ekuk Bluffs, southwestern Alaska

P. D. Lea, Bowdoin College


Extensive wave-cut exposures at Ekuk Bluffs in the Nushagak lowland of southwestern Alaska provide a 7-km longitudinal section through deposits related to advance of Pleistocene glaciers from the Ahklun Mountains onto the adjoining piedmont. Facies analysis of the proglacial sediments reveals the following successive depositional environments: 1) lower sandy tidal flats, 2) upper muddy tidal flats, 3) upper foreshore/beach face, and 4) braided sandur. Horizontal compression at the toe of the advancing glacier induced large-scale imbricate thrusting and folding of the proglacial sediments, producing a distally accreting wedge of deformed sediment beyond the ice margin. The presence of this topographic wedge subsequently dictated the overall pattern of sediment dispersal, forward during ice advance and rearward during retreat, and led to extensive gravity-driven resedimentation. -from Author