Ordovician Continental Paleogeography and Paleoenvironment for the Michigan Basin from Paleomagnetic Analysis
Abstract
This study investigates the paleomagnetic record of Paleozoic rocks from two Michigan basin localities in southwestern Ontario to help close the 40 myr gap in Paleozoic paleomagnetic data. Paleomagnetic data from the Queenston (Upper Ordovician) formation consistently exhibits easily removed viscous remanence, an intermediate and a high temperature component consistent with the unblocking temperatures of magnetite and hematite respectively. Alternating-field and thermal demagnetization in 16–20 steps up to 670º C typically reveal a southeastern, shallow up direction removed from magnetite, and a southwestern, steep up direction removed from hematite. A Late Paleozoic overprint was preserved in the magnetite and a possible Cretaceous aged overprint was recorded in the hematite. Overprints are interpreted to be the result of chemical remanent magnetism, likely resulting from alteration and increased surface weathering. Magnetite from two sites seem to have preserved Early Paleozoic magnetism, which may be used as target areas in future studies to potentially deliver primary Ordovician remanence.