@article{oai:soar-ir.repo.nii.ac.jp:00011862,
 author = {木村,  克己 and 別所,  孝範 and 坂本,  隆彦 and 公文,  富士夫 and 鈴木,  博之},
 issue = {2},
 journal = {地質学雑誌},
 month = {Feb},
 note = {Fission-track ages of zircon were determined with the grain-by-grain external detector (ED1) method for two samples of coarse acidic tuff (CH-1 and CH-2), which were collected from the Chibiki-yama acidic tuff unit in the lower Ryujin Formation of the Cretaceous Shimanto Supergroup, Kii Peninsula. The formation is of Late Campanian to Maastrichtian age based on the radiolarian fossil zone. CH-1 is a coarse pumiceous crystal tuff, and CH-2 is a coarse vitric crystal tuff. These specimens include three types of zircons; A group is characterized by euhedral form without abrasion, B group is euhedral but less abraded, and C group is much abraded and purplish. These characteristics of zircons indicate that A group is essential, while the others are detrital. A and B groups are major constituents and were selected for fission-track dating. The results demonstrate no significant difference in frequency distribution of grain age between both groups. Fission-track dating for essential zircons gave ages of 69.8±3.7 Ma (CH-1), and 67.5±3.4 Ma (CH-2). The FT ages of the tuff are within the age range of the radiolarian fossil zone of the Ryujin Formation, and indicate that the lower Ryujin Formation is of Late Maastrichtian age. The age constraint, in addition to previous geologic data, suggests that the coarse acidic tuff was derived from the simultaneous rhyolite pyroclastic rocks such as the Nohi Rhyolite and Suyama Pyroclastic Rocks distributed in the Chubu District of Southwest Japan., Article, 地質学雑誌. 102(2):116-124 (1996)},
 pages = {116--124},
 title = {紀伊半島四万十累層群の上部白亜系竜神累層に挟まれる酸性凝灰岩のフィッション・トラック年代とその意義},
 volume = {102},
 year = {1996}
}