Abstract: Cenozoic Sedimentation and Tectonics of Hope Basin, Southern Chukchi Sea

Stephen L. Eittreim, Arthur Grantz, O. T. Whitney

More than 3,000 m of young (Tertiary and possibly some Cretaceous) sedimentary material is present in elongate troughs of the Hope basin in the southern Chukchi Sea. Sediment distribution was controlled by east-west trending ridges, some of which appear to be offshore continuations of major topographic features of western Alaska. For example, Kotzebue Ridge, which is the most prominent of these basement ridges, extends westward across the southern Chukchi Sea as an apparent continuation of the Alaskan Baird Mountains. North of and parallel with Kotzebue Ridge is a series of ridges, some with thrust-faulted cores. The ridges divide Hope basin into many elongate subbasins. Hope basin contains one especially strong and coherent regional acoustic reflector estimated to be of iddle Tertiary age. Variations in the depth of the marker reflector reveal a significant change in position from earlier to later sediment depocenters. In late Tertiary time an elongate, wedge-shaped piece of crust subsided 2,500 m in a part of eastern Hope basin that was previously a platform. On the northeast the subsidence occurred at normal faults parallel with the Alaskan coast, on the south by antithetic and normal faulting on the north flank of Kotzebue Ridge, and on the northwest by a gentler series of up-to-the-north steps and ridges in the older sedimentary deposits and basement. Thickening of stratigraphic units and small-scale internal onlapping in the sediments on the north flank of Kotzebue Ridge indicate that the basin subsided relative to the ridge after deposition of the middle Tertiary reflector. Active uplift of the ridge in latest Tertiary time is indicated by erosional truncation of the uppermost several hundred meters of sediment over it.

AAPG Search and Discovery Article #90966©1977 Alaska Geological Society 1977 Symposium, Anchorage, Alaska