Beringia--northeastern Siberia, western Alaska, and the separating shallow Bering Sea--is dominated by an M-shaped structure comprising the Alaskan and Chukotkan oroclines, and a broader intervening flexure that is submerged on the continental shelf. The Beringian flexures were evidently initiated during the Jurassic Period, possibly in conjunction with early rifting in the Atlantic. In Beringia curvilinear basins developed and filled with terrigenous and volcanic sediment. Near the end of the Cretaceous new stresses crumpled and uplifted these basins. The great transcurrent faults of Alaska and Beringia were initiated at this time. We also speculate that the Aleutian-Komandorsky Ridge (and adjacent trench?) formed at this time, signifying a southward shift (from continen al margin to ridge) in the site of ocean-continental crust interaction.

Beringia stood high during the Paleogene; sediment accumulated only in subsiding parts of the Bering continental margin and in rather restricted basins at the apices of the Alaskan and Chukotkan oroclines.

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In the early Tertiary, possibly in response to the extension of Atlantic rifting into the Arctic basin, a new stress field developed that produced subsidence and basin formation. Neogene subsidence allowed the sea to invade progressively linked subshelf basins, creating the first sinuous shallow water connection between the Pacific and Arctic Oceans late in Miocene time. This seaway was severed about 5 m.y. ago, probably in response to uplift of the Bering Strait horst. Subsidence resumed, and the Bering and Chukchi Seas assumed their present form about 3.5 m.y. ago during the late Pliocene Beringian transgression.

Local basin formation combined with general subsidence of the Bering shelf continues to the present. However, movement along the western submerged extensions of the major transcurrent faults of Alaska appears to be slow or absent.

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