Solid Bitumen at Atigun Gorge, Central Brooks Range Front: Implications for Oil Exploration in the North Slope Fold and Thrust Belt

Abstract

The Atigun Gorge area of the north-central Brooks range is a structurally complex region in which a sequence of north-verging duplex structures involving Paleozoic and Mesozoic Ellesmerian continental margin deposits are structurally overlain by a south-verging thrust of Brookian foreland basin deposits of Albian age. The resulting structural triangle zone is marked by numerous small-scale thrusts involving Permian and Triassic strata in which solid bitumen, occupying fissures up to 10 cm wide and several meters in length, has been found. The presence of aromatics in the odorless, black material was confirmed by ultraviolet fluorescence following extraction in dichloromethane. The occurrence of solid bitumen at Atigun Gorge adds to a growing inventory of hydrocarbon-filled fractures found mostly in Cretaceous rocks in the Brooks Range foothills. These occurrences are consistent with a model of hydrocarbon generation beneath the northern margin of the Brooks Range. The regional distribution of vitrinite reflectance isograds suggests that the northern margin of the Brooks Range and the adjoining foreland basin deposits of the North Slope have experienced similar thermal histories. The 0.6% vitrinite reflectance isograd intersects the land surface along the southern margin of the foreland and the 2.0% isograd lies within the northern part of themore » range. Although these relations suggest the possibility of petroleum resources at shallow depths beneath the Brooks Range foothills, they also indicate that a considerable amount of differential uplift has occurred, probably resulting in redistribution and some leakage of any oil and gas accumulations.« less