SEISMIC INTERPRETATION AND STRUCTURAL EVALUATION OF THE HOPE BASIN, ALASKA

The Hope Basin is a 700-km long, predominantly early Tertiary extensional basin located on the Chukchi shelf off the northwestern coast of Alaska and northeastern Russia. It is bound to the northeast by the Herald Arch, a basement uplift cored by northeast vergent thrust faults of Cretaceous age. The origin of the basin was attributed to transtensional deformation associated with the left-lateral Kobuk fault by Tolson (1987). We carried out a new seismic interpretation of the structural development of the Hope Basin using 2473 km of multi-channel seismic lines shot in 1977-80 by the USGS and reprocessed in 2000, and 1994 km of proprietary Western-Geco data acquired between 1980 and 1984.

Previous workers recognized four unconformity-bounded seismic sequences. The oldest unit is interpreted to be Eocene-age volcaniclastic rocks based on an indirect correlation to SOCAL wells located within the Selawik Basin, a sub-basin on the southeastern side of the Kotzebue Arch. The three younger units are interpreted from the SOCAL wells to range from marine to non-marine and progress in age from Neogene to late Pleistocene.

Our interpretation reveals a series of NW-SE and E-W trending faults, most of which dip to the southwest. The units vary in depth and thickness throughout the study area and in places are truncated by overlying unconformities. Isopach maps reveal a depocenter located roughly in the center of the study area. The depocenter of Unit III migrated to the SE, illustrating a classic characteristic of strike-slip basins. However, the geometry of individual structures in the basin suggests it was formed by extension. Further support of a non-strike-slip origin of the basin is based on its large size. According to Hempton and Dunne (1984), a strike-slip basin as large as the Hope Basin should have a sediment depth of over 50 km, much more than the 10 km thickness of sediment inferred from the Hope Basin seismic data.

We suggest that the Hope Basin developed in response to orogenic collapse of the Herald Arch. During the Albian, the Arch was a topographic high within the Brooks Range. Eventually, its high topography and weakened structure caused it to collapse, which could have lead to the development of the Hope Basin in its hinterland. This could account for the lack of strike-slip basin features within the study area.