Samples of the Middle Ordovician Trenton Limestone were collected from 8 sites in Quebec, Ontario, and New York State for paleomagnetic study. Stepwise thermal demagnetization reveals a very well defined characteristic magnetization that has a corresponding paleomagnetic pole at 53.0¿ N, 126.90¿ E (K=97.7, A-95=2.7¿). This pole is not at all close to other Ordovician poles from cratonic North America but is near Lake Carboniferous and Early Permian ones, indicating that the Trenton was remagnetized in the Late Paleozoic. An earlier paleomagnetic investigation of the Trenton gave a pole that did ont appear to be Late Paleozoic in age. However, we demonstrate that this earlier study failed to isolate the ancient characteristic magnetization.

Rock magnetic experiments and analyses of magnetic extracts show that the carrier of magnetization is Fe3O4 that does not contain Ti or other elements in other solid solution that would indicate a detrital source. The magnetite and its associated remanence appear to have a diagenetic origin.