Paleomagnetism of the upper Keweenawan sediments: the Nonesuch Shale and Freda Sandstone
The natural remanent magnetization of the upper Keweenawan Nonesuch Shale and Freda Sandstone has been analyzed with thermal, alternating field, and chemical demagnetization techniques. The results of this study are in good agreement with previously published works by DuBois and by Vincenz and Yaskawa, but place a tighter constraint on the North American apparent polar wander path. Fifty-eight samples, representing nearly 900 m of section, have been collected from the flanks of the Porcupine Mountain uplift. From principally thermal demagnetization analyses, a mean direction of primary magnetization has been calculated for the Nonesuch Shale, with declination 279.8°, inclination +9.8°, yielding a virtual geomagnetic pole position at 176.5° E, 10.3° N, and for the Freda Sandstone, with declination 271.3° inclination + 0.7°, yielding a virtual geomagnetic pole at 179.5° E, 1.2° N. A group of intermediate (secondary) components of magnetization is removed between temperatures of 350 °C and 550 °C, yielding w...