The Ordovician Period in Earth history (505 to 438 million years ago) appears to have been a time of rapid rotation of North America. The most important evidence for this rotation is paleomagnetic; the magnetic signal recorded in Ordovician rocks. Unfortunately, the original magnetic record in many Ordovician rocks has been overwritten by a wide-spread hydrothermal alteration during the late Paleozoic. This late Paleozoic remagnetization obscures our view of the Ordovician motions of North America and has made it very difficult to develop a consistent record of reversals of the magnetic field (magnetostratigraphy) in the Ordovician. Reversals are very useful as time markers in the rock record because they occur simultaneously over the entire Earth. The late Paleozoic overprinting is so widespread that it is of significant interest in itself: What is the cause of the overprinting event? Why are some rocks strongly affected and others hardly at all? To detail the Ordovician motions of North America and develop an Ordovician magnetostratigraphy, and at the same time examine the nature of the late Paleozoic event, we need a set of Ordovician rocks which are only partially affected by that event. We can then use the magnetic signal of the unaltered rocks to address the issue of Ordovician polar wander and magnetostratigraphy, and use the relationship between the unaltered and altered rocks to determine the controls on the late Paleozoic alterations. This study will focus on such a set of rocks from northern Arkansas. The results of such a study will provide valuable insight into the dynamic history of the Earth and its magnetic field, as well as information regarding the dynamics of the hydrothermal system responsible for the remagnetization of Paleozoic rocks in North America.
