Structural Evolution of Bering Continental Margin: Cretaceous to Holocene: ABSTRACT

Abstract

Spreading in a broad arc from Kamchatka to the tip of the Alaska Peninsula, the Bering continental margin separates the deep Bering Sea from its fringing shelf. Rock dredgings and geophysical data indicate that beneath a veneer of Cenozoic deposits the central sector of the margin (between Alaska and Siberia) is in part underlain by folded sedimentary strata of Late Cretaceous (Campanian) age. These rocks can be traced seaward beneath the deep basin of the Bering Sea, as well as landward to coastal exposures of Mesozoic rocks in Siberia and western Alaska. The deeply submerged Cretaceous rocks appear to be the eroded remnants of a continental margin that was uplifted and deformed in latest Cretaceous or earliest Tertiary time. We speculate that tectonism of the continental margin may be linked with the convergence of a North Pacific lithospheric plate and an American-Eurasian plate in the late Mesozoic; normal or direct convergence off southe n Alaska and the Kamchatka-Koryak region where coastal mountain building was intense, and oblique convergence along the less deformed central sector of the Bering margin. By Oligocene time the seaward fringes of the coastal mountains were beveled to low relief and submerged to form the foundation of the Neogene shelf and continental margin. Submergence was very extensive along its central sector. There narrow grabens parallel with the margin formed in response to extensional rifting and filled with as much as 2,600 m of neritic and upper bathyal deposits. Faults bordering outer-shelf basins and flanking structural highs in the central sector may connect on the west with major fractures offsetting Cretaceous rocks underlying the Koryak Mountains (Cape Navarin area). Eastward from the central sector outer-shelf structural trends appear to turn inside or north of the Alaska Peninsula rather than merge with Pacific marginal structures. During the Neogene, 500 m or more of pelagic and terrigenous sediment accumulated over the collapsing margin. These deposits were deformed by slumping and basement faulting and, in the late Cenozoic, largely stripped from some areas by an episode of intense canyon cutting. End_of_Article - Last_Page 2503------------