Range-front structure and lithostratigraphy of the Atigun Gorge area, northcentral Brooks Range, Alaska

Abstract

Allochthonous sedimentary rocks of the Brooks Range orogen and overlying foredeep deposits are well exposed in the Atigun Gorge area, at the northern mountain front of the Brooks Range. A stepwise northward decrease in structural relief occurs in this area, exposing progressively younger stratigraphic units. Present exposures reveal three structural levels: an antiformal imbricate stack and an overlying roof zone, composed of allochthonous Devonian to Cretaceous rocks, and a higher level of broad open structures in the overlying foredeep deposits.

The structures of the area formed either by two distinct deformational events, involving the emplacement and subsequent deformation of the antiformal stack and overlying foredeep deposits, or by a single event, involving emplacement and simultaneous backthrusting at the base of the structurally overlying foredeep deposits. Timing of the earliest deformation is indicated by Lower Cretaceous (Neocomian) synthrust deposits.