Geologic history of the continental margin of North America in the Bering Sea

The North American continental margin beneath the Bering Sea is nearly 1,300 km long and extends from Alaska to eastern Siberia. The margin is a canyon-scarred 3,200–3,400-m high escarpment separating one of the world's largest epicontinental seas (the shallow Bering Sea) and the Aleutian Basin (the deep-water Bering Sea), a marginal oceanic basin distinguished by having its southern boundary formed by the Aleutian Ridge.

Three geomorphic provinces can be recognized: a southeastern province characterized by a gentle continental slope (lacking V-shaped canyons) and an outlying continental borderland (formed by Umnak Plateau); a central province distinguished by a steep canyon-scarred slope, and a northwestern province having a gentler and, apparently, less eroded continental slope.

Continuous seismic reflection profiles show that the margin is constructed of three major structural-stratigraphic units: (1) an acoustic basement underlying the outer shelf and upper slope; (2) an overlying main layered sequence; and (3) a stratified rise unit underlying and forming the continental rise at the base of the slope.

The existing margin evolved with downbowing and faulting of the acoustic basement, an older margin probably of Late Mesozoic age, consisting in part of well-indurated siltstone and mudstone, in Early Tertiary time. Concomitant with subsidence as much as 1,500 m of main-layered-sequence strata were draped over the basement. Intense canyon cutting, presumed to have been caused by the rapid deposition of unstable masses of riverborn sediment over the outer shelf and upper slope, is thought to have begun in Late Tertiary and Quaternary time. Concurrent with canyon cutting, submarine fans, consisting of turbidites forming the rise unit, accrued at the base of the continental slope.

Subsidence of the continental margin during the Tertiary may be related to foundering (“oceanization”) of a continental block to form the Aleutian Basin, or to simple isostatic depression of a former segment of the North Pacific oceanic floor in response to sediment infilling north of the Aleutian Ridge.