JpGU-AGU Joint Meeting 2017

講演情報

[JJ]Eveningポスター発表

セッション記号 B (地球生命科学) » B-PT 古生物学・古生態学

[B-PT06] [JJ] 地球生命史

2017年5月20日(土) 17:15 〜 18:30 ポスター会場 (国際展示場 7ホール)

[BPT06-P04] 北海道日高地方波恵川クジラ化石産出地点周辺の中新統の地質と珪質微化石層序

*本山 功1丸山 俊明1粕川 茜1松崎 賢史2西村 智弘3櫻井 和彦3 (1.山形大学理学部地球環境学科、2.東京大学、3.むかわ町穂別博物館)

キーワード:珪藻、放散虫、鯨類化石

A calcareous concretion containing whale bones was discovered as a float during the riparian works on the Hae River, Hidaka Town in 2005. Radiolarian and diatom assemblages recovered from the concretion indicate the Lipmanella redondoensis Zone and the Rouxia californica Zone, respectively, suggesting an age of 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. However, because of very few biostratigraphic data for the sedimentary rocks exposing along the Hae River, the location of the original home of the concretion is unknown. In order to detect the home locality, we surveyed geology along the river and analyzed diatom and radiolarian biostratigraphy for the sedimentary sequence. The Nina Formation exposing along the Hae River mainly consists of diatomaceous mudstone, sandy mudstone and sandstone. Many of the studied samples yielded common to abundant fossil diatoms that include various index species, Denticulopsis praedimorpha, Denticulopsis dimorpha, Denticulopsis katayamae, Thalassionema schraderi and Neodenticula kamtschatica. The occurrences of these species indicate that the Nina Formation encompasses the Middle Miocene through the Pliocene. However, we have not found diatom assemblages indicative of the Rouxia californica Zone from the studied samples, and, thus, the home locality of the whale fossil is still an unsolved question.