Japan Geoscience Union Meeting 2016

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Symbol B (Biogeosciences) » B-PT Paleontology

[B-PT07] Biotic history and its relation to the Earth history

Wed. May 25, 2016 10:45 AM - 12:15 PM 303 (3F)

Convener:*Isao Motoyama(Department of Earth and Environmental Sciences, Yamagata University), Takao Ubukata(Division of Geology & Mineralogy, Department of Earth & Planetary Sciences, Kyoto University), Kazuyoshi Moriya(Department of Earth Sciences, Faculty of Education and Integrated Arts and Sciences, Waseda University), Chair:Isao Motoyama(Department of Earth and Environmental Sciences, Yamagata University), Takao Ubukata(Division of Geology & Mineralogy, Department of Earth & Planetary Sciences, Kyoto University), Kazuyoshi Moriya(Department of Earth Sciences, Faculty of Education and Integrated Arts and Sciences, Waseda University)

11:15 AM - 11:30 AM

[BPT07-09] Geologic age of the whale fossil-bearing calcareous float concretion from the Hae River, Hokkaido, Japan, based on radiolarian and diatom analyses

*Isao Motoyama1, Toshiaki Maruyama1, Tomohiro Nishimura2, Kazuhiko Sakurai2, Akane Kasukawa1, Kenji M. Matsuzaki3 (1.Department of Earth and Environmental Sciences, Yamagata University, 2.Hobetsu Museum, 3.Geological Survey of Japan, AIST)

Keywords:whale fossil, Radiolaria, Diatom

Radiolarian and diatom fossils have been used to constrain the age of calcareous concretion collected from the Hae River, Hidaka Town, southern central Hokkaido, Japan. The calcareous concretion contains whale fossils and was discovered as a float during the riparian works in 2005. Recovered radiolarian and diatom assemblages indicate the Lipmanella redondoensis Zone (9.0 to 7.4 Ma) and the Rouxia californica Zone (7.7 to 6.5 Ma), respectively. Thus the concretion can be dated as 7.7 to 7.4 Ma. This age is concordant with the age range of the Nina Formation which is distributed near the locality of the concretion and was previously dated as ca. 10.1 to 3.5 Ma based on the diatom stratigraphy in the surrounding area. We will examine some samples collected from the Nina Formation exposed along the Hae River to confirm the origin of the concretion.