Modern shallow-water graded sand layers from storm surges, Bering Shelf: a mimic of Bouma sequences and turbidite systems.

A sequence of graded sand layers, interbedded with mud, extends offshore over 100km from the Yukon Delta shoreline across the flat, shallow epicontinental shelf of the northern Bering Sea, Alaska. Proximal graded sand beds on the delta-front platform near the shoreline are coarser, thicker and contain more complete vertical sequences of sedimentary structures than distal beds. The sequence of graded sands appears to be related to the major storm surges that occur every several years. The major storms increase the average 10-m water depth in southern Norton Sound as much as 5m and cause fluctuations in pore pressure from wave cyclic loading that may liquefy the upper 2 to 3m of sediment. -from Author