Paleomagnetism of the Wilberns Formation (Texas) and the Late Cambrian paleomagnetic field for North America

The natural remanent magnetizations of Late Cambrian siltstones of the Wilberns Formation have been analyzed with alternating field, thermal, and chemical demagnetization techniques. From mainly thermal demagnetization analyses a mean direction of magnetization has been calculated: declination D of 101.5°, inclination I of +13.5°, k = 171, and α95 = 4.6° for seven sites (55 samples), yielding a virtual pole position at 6.4°N, 158.8°E, dp = 2.4°, and dm = 4.7°. This polar error (dp, dm) represents the oval of 95% confidence about the pole position. Comparisons with previously published Late Cambrian data reveal good agreement between the thermally isolated directions of magnetization. The difference in the published results obtained through alternating field demagnetization can be explained by a late Paleozoic remagnetization or by a previously unexpected Cambrian shift or loop of the apparent polar wander path.