Remagnetization Overprints in the Upper Ordovician Kope Fm., Kentucky

The Upper Ordovician (Edenian) Kope Formation was sampled at 61 stratigraphic levels in four overlapping sections in northern Kentucky. Although the objective was to evaluate the usefulness of remanence for magnetostratigraphic correlations between these sections, the samples, mainly silty limestones and siltstones, are pervasively remagnetized. The NRM directions are well-grouped, slightly steeper than the expected present field direction. However, AF and thermal demagnetization, up to 100 mT a.f. peak field and 380ºC respectively, reveal remagnetization trends in vector orthogonal and stereographic plots. Endpoints and break-points in these remagnetization trends are consistent with the expected field directions calculated for this locality from Ordovician and Permian (Kiaman) reference poles for North America. The predominance of the overprints obviates the use of remanence for stratigraphic correlations of the Kope sections sampled. Poles computed from the remagnetized directions are compared with Ordovician and Permian poles for North America.