Geotechnical characteristics of bottom sediment in the northeastern Bering Sea

Abstract

Sediment of Holocene age derived from the Yukon River, consisting dominantly of silty fine sand and sandy silt, covers the bottom of central and western Norton Sound, which is a high energy environment involving extensive ice loading, high waves, and strong bottom currents. The sediment contains significant amounts of sand in some areas and a generally minor amount of clay-size material ranging from 0 to 20 percent. Moreover, the sediment is generally dense, although loose and weak zones occur at the surface and also at depth between relatively dense layers. These characteristics, evidence of storm sand layers and scour depressions, and the results of preliminary analytical studies indicate that this sediment is susceptible to liquefaction during major storms. Substantially finer grained, weak, and highly compressible sediment of Holocene age, derived from the Yukon River and from local rivers and streams, covers eastern Norton Sound and the Port Clarence embayment, which are low energy environments with negligible ice loading, low waves, and weak bottom currents. Transgressive deposits of late Pleistocene age that cover the bottom of Chirikov Basin include an inner-shelf fine sand underlain by a basal transgressive medium sand that is exposed on the north and east flanks of the basin. Geotechnical data in the latter, obtained in the sand waves fields near Port Clarence, show that the material is loose near the surface but becomes firm rapidly with depth and could not be penetrated more than about 3 m with the Alpine vibratory corer. Pleistocene peaty deposits underlie the Holocene and late Pleistocene deposits in both Norton Sound and Chirikov Basin and are somewhat overconsolidated, probably because of subaerial desiccation during low sea level stands in the late Pleistocene. These materials have a higher clay content than the overlying deposits and they contain substantial amounts of organic carbon and gas. The presence of gas suggests that in situ pore pressure may be high. If so, the strength of the material could be low even though the material is generally overconsolidated.