Abstract

Paleomagnetic determinations indicate that Upper Devonian and Mississippian sedimentary rocks in a large part of the Brooks Range were remagnetized following a major episode of thrusting and folding. After treatment in alternating fields, sandstone in the Devonian and Mississippian(?) Kanayut Conglomerate of the Endicott Group (Devonian and Mississippian) retains a magnetic overprint that corresponds to a paleomagnetic pole at 59°N, 197°E (alpha 95 = 12°). Similar overprints were determined from samples from several sites in Mississippian limestone of the Lisburne Group. The remagnetized zone extends at least 450 kilometers along the northern range front. Rapid uplift and cooling of the northern range front during the final stages of the Brooks Range orogeny may account for the simultaneous remagnetization of this immense region. A Cretaceous age for the remagnetization is supported by reset K-Ar ages in the southern Brooks Range and by the pole position obtained from the magnetic overprint. Hypotheses concerning counterclockwise rotation of Arctic Alaska cannot be tested in the areas of the Brooks Range that were sampled because the original magnetic signatures of the Paleozoic rocks have been lost.

Two oriented cores have been taken in the subsurface of the North Slope in order to avoid the remagnetization problem. Analysis of one core from the National Petroleum Reserve gives a pole that is consistent with large-scale counterclockwise rotation of Arctic Alaska. Acceptance of the rotation hypothesis requires confirmation from additional oriented cores because there are uncertainties in the age of magnetization and in the accuracy of the core orientation.