Arctic Alaska Basin, Hanna Trough and Beaufortian Rifted Margin Composite Tectono-Sedimentary Elements

Abstract

Abstract The Arctic Alaska region includes three composite tectono-sedimentary elements (CTSEs): (1) the Arctic Alaska Basin (AAB), (2) the Hanna Trough (HT) and (3) the Beaufortian Rifted Margin (BRM) CTSEs. These CTSEs comprise Mississippian–Lower Cretaceous (Neocomian) strata beneath much of the Alaska North Slope, the Chukchi Sea and westernmost North Slope, and the Beaufort Sea, respectively. These sedimentary successions rest on Devonian and older sedimentary and metasedimentary rocks, considered economic basement, and are overlain by Cretaceous–Cenozoic syn- and post-tectonic strata deposited in the foreland of the Chukotka and Brooks Range orogens and in the Amerasia Basin. (1) The Mississippian–Neocomian AAB CTSE includes two TSEs: (a) the Ellesmerian Platform TSE, comprising mainly shelf strata of Mississippian–Middle Jurassic age, and including a relatively undeformed domain in the north and a fold-and-thrust domain in the south; and (b) the Beaufortian Rift-Shoulder TSE, which includes Middle Jurassic–Neocomian deposits related to rift-shoulder uplift. (2) The HT CTSE includes four TSEs: (a) the Ellesmerian Synrift TSE, which comprises Late Devonian(?)–Middle Mississippian growth strata deposited in graben and half-graben during intracontinental rifting; (b) the Ellesmerian–Beaufortian Sag-Basin TSE, which comprises Middle Mississippian–Upper Triassic strata deposited in a sag basin following cessation of rifting; (c) the Beaufortian Synrift TSE, comprising Jurassic–Neocomian graben-fill deposits related to rifting in the Amerasia and North Chukchi basins; and (d) the Beaufortian Rift-Shoulder TSE, which comprises Jurassic–Neocomian strata related to rifting and deposited outside rift basins. (3) The BRM CTSE includes two TSEs: (a) the Beaufortian Synrift TSE, comprising Middle Jurassic–Neocomian synrift strata deposited on attenuated continental crust associated with opening of the Amerasia Basin; and (b) the Ellesmerian Platform TSE, comprising mainly shelf strata of Mississippian–Middle Jurassic age that lie beneath Beaufortian synrift strata. The AAB, HT and BRM CTSEs contain oil-prone source rocks in Triassic, Jurassic and Cretaceous strata, and proven reservoir rocks spanning Mississippian–Lower Cretaceous strata. A structurally high-standing area in the northern AAB CTSE, northern HT CTSE and southernmost BRM CTSE lies in the oil window, whereas all other areas lie in the gas window. Known hydrocarbon accumulations in the three CTSEs total more than 30 Bboe, and yet-to-find estimates suggest that a similar volume remains to be discovered.