Three terranes in northern Alaska have potential for petroleum: a Tertiary basin in the eastern Arctic Plain, a post-Neocomian Cretaceous basin in the Northern Foothills and western Arctic Plain, and a complex of thrust-faulted late Paleozoic and pre-Albian Mesozoic rocks in the Brooks Range and Southern Foothills. Recent re-analysis of these terranes suggests that the disposition of extensive thrust sheets may have controlled the distribution of petroleum reservoirs in much of the area. This interpretation has significant implications in evaluating the petroleum potential of northern Alaska.

The Tertiary basin contains interfingering marine and non-marine clastics. A few open folds are present and may provide structural traps. Stratigraphic traps may be expected along the tectonically active southern margin and along the stable basement rise under the present continental shelf. Elements of the Brooks Range may have been thrust over the southern margin of the basin in late Pliocene time. This basin awaits exploratory drilling. In the post-Neocomian Cretaceous basin, interfingering marine and non-marine terrigenous clastic sediments in open folds offer a host of structural and stratigraphic traps. Some of these have been drilled, and a few contain sizable reserves of high-quality oil and gas. Stratigraphic traps may be expected also in pre-Cretaceous rocks along the basemen rise that forms the northern margin of the basin. Buried detachment fault planes may underlie some of the southern folds, offering the possibility of different, and possibly equally interesting, structures and stratigraphic sections.

The Brooks Range and Southern Foothills terrane is the most complex and difficult to assess, but its geology and oil potential are the most intriguing. The distribution of formations and facies is the result of northward movement of extensive thrust sheets during at least two major episodes of thrusting in mid-Early Cretaceous (pre-Albian) and early Tertiary times. Tectonic movement may have been as much as 75 miles, thus telescoping facies trends in all formations. As a result, Upper Devonian through Lower Cretaceous (Neocomian) rocks of numerous facies are now exposed in a belt of imbricate thrust plates. Holes drilled in this terrane can test a variety of structures and numerous facies of several formations, but the geology is so complex that paleogeographical and palinspastic reco structions must precede the drilling. Similar terranes elsewhere have been very productive.

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