Developing Rock Magnetic Techniques for Correlation Purposes: Principles and Case Studies

Maria T. Cioppa
University of Windsor, Windsor, ON

Correlation techniques typically aim at determining the time-equivalency of depositional events. Paleomagnetism should provide a method of doing so; however, the presence of tectonic overprints, such as that caused by Alleghanian fluid flow, often renders this technique unusable. Magnetic properties (e.g. susceptibility, saturation remanence, coercivity) are often used as a correlation tool and as magnetic tracers in Quaternary and present-day environments: the question is whether they can be used in Mesozoic and Paleozoic rocks.

In order to examine this possibility, the University of Windsor Magnetic Laboratories carry out, in addition to the standard paleomagnetic techniques, susceptibility, saturation remanence (SIRM), anhysteretic remanence (ARM) and various magnetic ratio (S-ratio, HIRM) measurements. These have been made on a variety of Paleozoic carbonates and clastics from the Western Canada, Williston and northern Appalachian basins. In the Western Canada Sedimentary Basins, magnetic properties are strongly dependent on lithology, which may be primary depositional or secondary diagenetic phases. In the eastern Williston Basin, central North America, paleomagnetic and rock magnetic studies of several Paleozoic formations, including the Ordovician Red River, Devonian Duperow and Birdbear, display a post-depositional hematite-carried magnetization that has strongly affected the original magnetic properties. The studies suggest that post-depositional processes may modify the magnetic signal extensively; however, they also suggest that magnetic properties may be useful as a tracer for specific geologic events in Paleozoic rocks.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005