Abstract: Structural Elements of Offshore Gulf of Alaska Tertiary Province

Terry R. Bruns, George Plafker

Preliminary interpretation of recently acquired U.S. Geological Survey geophysical data indicates that the offshore Gulf of Alaska Tertiary province consists of at least three areas with markedly differing tectonic styles and histories. In general, structural development becomes more intense from east to west.

The first area, between Cross Sound and Icy Bay, is characterized by a basin filled with as much as 9 km of relatively undeformed sediment presumed to be of late Cenozoic age. The seaward flank of the basin is formed in part by a shelf-edge arch at Fairweather Ground; the axis of the basin is near the coast and generally parallels it. The next area, which begins roughly at a line between Pamplona Ridge and Icy Bay and extends to Kayak Island, has a late Cenozoic section at least 7 km thick that is characterized by multiple angular unconformities indicating active deformation during deposition. Many large folds are present in the region of the Pamplona-Icy Bay boundary; some of these structures are covered by 1 km or more of relatively undisturbed sediment. A broad shelf-edge arch is p esent in the west half of the area. The third area, which is between Kayak Island and Montague Island, is characterized by complex tightly folded structures, severe deformation, and continuing active tectonism. The late Cenozoic sediment thickness is extremely variable. Faults and folds have divergent trends that may indicate multiple periods of deformation.

The structural development of the Gulf of Alaska Tertiary province appears to be due to a combination of wrenching and compression reflecting late Cenozoic interactions between the North American and the Pacific Ocean plates. The Pamplona-Icy Bay and Kayak Island boundaries may be major compressional tectonic zones related to this interaction.

AAPG Search and Discovery Article #90976©1976 AAPG-SEPM-SEG Pacific Section Meeting, San Francisco, California