Paleomagnetic study of thrust sheet rotation during foreland impingement in the Wyoming‐Idaho overthrust belt

Abstract

Upper Jurassic and Lower Cretaceous strata in the Darby and Absaroka thrust sheets were sampled in order to paleomagnetically evaluate thrust sheet rotation in the Wyoming‐Idaho overthrust belt. No significant rotations were found. Lack of rotation in these thrust sheets suggests that previously reported rotation of the Prospect thrust sheet was not transmitted to the older Darby and Absaroka thrust sheets, indicating that the Prospect thrust sheet only experienced local rotations in response to collision with the Teton‐Gros Ventre uplift. The Upper Jurassic Stump Formation possesses a magnetization that passes the fold test and gives a paleomagnetic pole at 64°N, 170°E ( K = 18, A95 = 15°), in good agreement with other published Upper Jurassic poles for cratonic North America. Samples from all Lower Cretaceous sites are believed to possess a synfolding remagnetization of chemical origin.