1. Department of Earth Sciences; Carleton University; 1125 Colonel By Drive Ottawa Ontario K1S 5B6 Canada
2. Faculty of Geology and Geography; Tomsk State University; 36 Lenin Ave Tomsk 634050 Russia
3. Western Paleomagnetic and Petrophysical Laboratory; Western University; 1151 Richmond St. London Ontario N6A 5B7 Canada
4. Department of Physics; University of Toronto; 60 St George St Toronto Ontario M5S 1A7 Canada