Abstract: Complex Ridge and Trough Topography on Shallow, Current-Dominated Shelf, Northwest Alaska

C. Hans Nelson, David A. Cacchione, Michael E. Field

Linear sand shoals, 15 to 30 km long, 3 to 7 km wide, and 5 to 15 m high, are present near Bering Straits, Alaska. All these sand bodies are constructional, but they apparently represent an interplay of sedimentary processes related to past transgressive shoreline history and present strong, northward-flowing currents. Ridge crests coincide with depths of ancient submerged beaches elsewhere in northern Bering Sea. However, sand waves and current and oscillation ripples demonstrate active modification by the present current regime. Other sand bodies, as much as 50 km long, 10 km wide, and 10 to 20 m high, appear to have been caused by secondary (leeside) circulation systems induced by King Island and the Cape Prince of Wales promontory.

Current measurements and observations of the shoal crests with underwater television demonstrate active bedload movement in oscillation-sand ripples; current speeds measured 20 to 30 cm/sec. Water samples taken 2 m over the shoal contained abundant terrigenous coarse silt and locally very fine sand. Asymmetric sand waves (^eegr~2 m and ^lgr~ 15 m) superimposed on the linear shoals generally are aligned normal to the mean (northward) bottom currents, but these bed forms probably are active only during periods of intensified flow caused by storms.

Our studies suggest that these larger linear sand ridges have been generated by three major processes: deposition from interrupted current flow leeward of islands and peninsulas; initial formation as spits at shoreline stillstands during transgressions; and accumulations mainly as modern sand-wave fields modifying ancient construction features.

AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC