1. Department of Geoscience, Joetsu University of Education, 1 Yamayashiki, Joetsu 943-8512, Japan (e-mail: amano@juen.ac.jp)
2. Geochemical Research Center, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
3. Toyama Paleontological Research Club, 100 Nishitakagi, Imizu 939-0303, Japan