Abstract: Structure of Continental Shelf, Eastern Gulf of Alaska

Terry R. Bruns, George Plafker

U.S. Geological Survey marine geophysical data indicate that structural style in the eastern Gulf of Alaska increases in complexity from east to west and reflects the change from predominantly strike-slip through oblique slip to dip-slip motion along the boundary between the North American and Pacific plates during the late Cenozoic.

The eastern part between Cross Sound and Icy Bay is characterized by a basin filled with as much as 9 km of relatively undeformed upper Cenozoic sediment unconformably overlying an irregular basement surface. The axis of the basin is near and generally parallel with the coast. The seaward flank of the basin is formed by an uplifted shelf edge. Maximum uplift occurs at Fair-weather Ground where probable Cretaceous to lower Tertiary highly deformed rocks are present at the seafloor; the amount of uplift diminishes westward. A central segment, beginning roughly at a line between Icy Bay and Pamplona Ridge and extending to Kayak Island, has an upper Cenozoic section, at least 7 km thick, that is folded and faulted and contains multiple angular unconformities indicating penecontemporaneous active deformation. Many large northeast-trending gently dipping, asymmetric and faulted folds are present in this segment, primarily in the east half near the Pamplona Ridge-Icy Bay trend. Some of these structures are concealed by 1 km or more of undeformed sediment, much of which may be Pleistocene or younger. Broad eastwest-trending folds are present at the shelf edge and inner shelf in the west half of the area. The western area, between Kayak and Montague Islands, is characterized by complex, tightly folded and intensely faulted structures, and locally shallow acoustic basement. The thickness of upper Cenozoic sediment is extremely variable. Faults and folds with divergent trends probably reflect multiple periods of deformation in this region.

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