Alaska1783

Alaska Offshore

NW Point Barrow 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 the location map of this tentative geological interpretation, we recognize : (i) The oceanic Canada geographic basins ; (ii) The North Chukchi geographic basin ; (iii) The hinge-fault zone (rift-shoulder) ; (iv) The Barrow arch ; (v) the Arctic platform ; (vi) The Hanna trough ; (vii) The Chukchi platform ; (viii) The Colville foreland basin and the Brooks Range orogenic belt. Some of this geological feature are easily highlighted on the tentative interpretation of a Canvas autotrace of an old seismic line of the area. From North to South and above the northern Alaska Franklinian sequence, which includes includes Devonian and older rocks representing diverse origins and a complex geologic history, we can identify ; a) The divergent continental margin, in which the Nuwuk geographic basin developed ; (ii) The hinge-line fault zone (rift-shoulder) bordering the north flank of the Barrow arch that marks the northward expansion of Cretaceous and Tertiary depocenters ; (iii) The Barrow Arch, which is a remnant of a late Paleozoic to early Mesozoic south-facing continental margin and (iv) the Arctic platform, which encompasses Arctic Platform The Arctic Platform comprises a thick sequence of Proterozoic to Paleogene sedimentary rocks that have not been folded or thrust-faulted on a regional scale (Thorsteinsson and Tozer 1970; Douglas 1970). Geoscientists consider the Barrow arch and adjacent hinge-line fault zone as geological features developed during a Jurassic - Early Cretaceous episode of rifting that is at the origin of the oceanic Canada geographic basin and the flanking divergent margin.