1. Department of Geological Sciences; University of Florida; 241 Williamson Hall,; Gainesville; Florida; 32611-2120; USA
2. Centro de Geociencias; Universidad Nacional Autónoma de México, Campus Juriquilla; Querétaro; 76230; Mexico
3. Department of Geological Sciences and Geological Engineering; Queen's University; Kingston, Ontario; Canada; K7L 3N6