Alaska714

Alaska Onshore

Gonkagut Offshore

It is admitted by most geoscientists who have worked in this area that the rifting (formation of rift-type basin filled by pre-Brookian sediments) and the onset of the Brookian orogeny formed three major tectonic features of the northern Alaska margin : the Hinge Line, the Barrow Arch, and the Colville geographic basin. The hinge line, which, often, appears on seismic data as a zone of down-to-the-north normal faulting system, marks the point at which the seaward slope of the basement surface increases markedly into the Canada geographic basin Basin (Grantz and May, 1983). The divergent Atlantic-type margin (Brookian strata) developed northward of the rift-shoulder over a basement and/or the oceanic crust, since the breakup of the Laurentia continental crust, which seems to have occurred at Lower Cretaceous. Rift-type basins were created during the lengthening of the Franklinian sequence and filled by pre-Brookian sediments. The transgressive phase of the Atlantic-type margin is mainly of Cretaceous age, while the regressive phase last since Paleocene.

On this Canvas autotrace of a seismic line of the northern offshore Alaska, located near the USA/Canada frontier and, mainly, seaward of the Alaska rift shoulder (Barrow Arch) the Brookian sequence (Atlantic-type divergent margin) shows is maximum development. The Alaska rift shoulder is a broad structural high trending along the Arctic coast of Alaska created during Jurassic and Cretaceous time from a combination of various geologic events. The northern flank of the arch formed from post-rifting subsidence of the northern part of the Arctic Platform in Middle Cretaceous time. The Brookian clastic wedge prograded northward and eastward from Late Cretaceous through Tertiary time, filling the basins formed by post-rift subsidence on the north side of the Barrow Arch.