[B-PT07] 地球生命史

[BPT07-09] 北海道波恵川産含鯨類化石転石炭酸塩団塊の放散虫・珪藻化石年代

*本山 功¹、丸山 俊明¹、西村 智弘²、櫻井 和彦²、粕川 茜¹、松崎 賢史³ (1.山形大学理学部地球環境学科、2.むかわ町穂別博物館、3.産業技術総合研究所 地質情報研究部門)

キーワード：鯨類化石、放散虫、珪藻

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.