Paleomagnetic investigation of the Cambrian Waynesboro and Rome Formations of the Valley and Ridge Province of the Appalachian Mountains

Abstract

The Lower to lower Middle Cambrian Waynesboro and Rome formations yield paleomagnetic directions with east‐southeast to southeast declinations and shallow positive inclinations; the corresponding pole positions fall at 28°N, 165°E (dp = 11°, dm = 22°) and 39°N, 142°E (dp = 6°, dm = 12°), respectively. The sampling concentrated on red sandstones and siltstones and crossed several styles of deformation and changes in structural trend in the central Appalachians. Thermal and alternating field demagnetizations were analyzed with the aid of vector diagrams and the combined results of the two formations yield a positive fold test at the 99% confidence level. Since the mean directions from these formations deviate substantially in a clockwise sense from directions predicted by previously published paleomagnetic poles obtained from Cambrian rocks, the possibility of local rotations of the sampling sites has been considered. Two arguments, however, can be raised against such rotations. First, there is no geological evidence for rotations of the Tennessee thrust sheets relative to one another or relative to the craton. Second, there are directions from Ordovician and late Precambrian‐Early Cambrian formations in the Tennessee thrust sheets that do not deviate in a clockwise sense from those predicted by results from the craton. Remagnetization and nondipole behavior of the Cambrian geomagnetic field have been suggested as alternative explanations for the North American Lower and Middle Cambrian paleomagnetic poles but are considered unlikely causes for some of the new results from this and a companion paper. Instead, Cambrian apparent polar wander is proposed to explain the distribution of the pole positions.