Description of Wrench Tectonics in Chukchi Sea, Alaska

Dennis K. Thurston

Analysis of proprietary, multichannel seismic reflection profiles acquired by Western Geophysical Company in the Chukchi Sea planning area (Alaska Outer Continental Shelf Lease Sale No. 109) has revealed wrench-fault structures of Late Cretaceous(?) to Tertiary age. These structures and related features occur along numerous discrete north to northeast-trending faults, which we term the Hanna wrench-fault zone.

The eastern margin of the zone is approximately 60 mi offshore of Icy Cape, located on the western boundary of the National Petroleum Reserve in Alaska, and the zone extends over 100 mi westward to the U.S.-USSR boundary (Convention Line of 1867). The northern extent of the wrench-fault zone is obscured by a thick (over 40,000 ft) Early Cretaceous to Tertiary clastic wedge which occupies the North Chukchi basin and by the highly deformed strata in the North Chukchi high. The southern extent of the Hanna wrench-fault zone is obscured by northwest-trending folds in thick (over 20,000 ft) Early Cretaceous strata of the Colville basin. The wrench-fault zone apparently intersects the Herald arch overthrust farther to the south.

Characteristic structural features in the Hanna wrench-fault zone include broad uplift and local subsidence of strata adjacent to master faults, and the formation of flower structures in strata above master faults. Flower structures, expressed on seismic reflection profiles as antiforms and synforms that are rooted in a master fault, are characterized by multiple upward-diverging splay faults that exhibit complex offsets. Regional mapping suggests that some of these master faults may be reactivated basement faults.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.