Paleomagnetic Lab. 'Fort Hoofddijk', Utrecht Univ., Budapestlaan 17, Utrecht, 3584 CD Netherlands ; Institute for Marine Resources and Environment, Geological Survey of Japan, AIST, Tsukuba Central 7 1-1-1 Higashi, Tsukuba, 305-8567 Japan
Graduate School of Environmental Earth Science, Hokkaido Univ., 5-chome Nishi 10-jo Kita-ku Kita, Sapporo, 060-0810 Japan
Graduate School of Environmental Earth Science, Hokkaido Univ., 5-chome Nishi 10-jo Kita-ku Kita, Sapporo, 060-0810 Japan
Graduate School of Environmental Earth Science, Hokkaido Univ., 5-chome Nishi 10-jo Kita-ku Kita, Sapporo, 060-0810 Japan