三重県に分布する中新統一志層群上部の浮遊性有孔虫・珪藻化石層序

• Published in: The Journal of the Geological Society of Japan
• Main Authors: 大信田 彦磨, 林 広樹, 柳沢 幸夫, 栗原 行人, 星 博幸
• Format: Article in Journal/Newspaper
• Language: Japanese
• Published: 日本地質学会 2018
• Subjects: biostratigraphy; diatom; Ichishi Group; microfossils; Miocene; N.7/N.8 zona lboundary; planktonic foraminifera; Chaya; Planktonic foraminifera
• Online Access: http://hdl.handle.net/10424/00008496; https://aue.repo.nii.ac.jp/?action=repository_uri&item_id=7375; https://aue.repo.nii.ac.jp/?action=repository_action_common_download&item_id=7375&item_no=1&attribute_id=15&file_no=1

筆者らは三重県に分布する中新統一志層群の上部について浮遊性有孔虫・珪藻化石層序を検討した．大井層三ヶ野部層上部と片田層茶屋部層から得られた浮遊性有孔虫化石群集は亜熱帯的な性質を持ち，それらは今回調査した堆積岩セクションが浮遊性有孔虫化石層序のN.7帯～N.8帯下部に対比されることを示す．今回調査したセクションにおいて，N.7帯/N.8帯境界は大井層/片田層境界の約19m下位に位置することが判明した．N.7帯/N.8帯境界より下位の三ヶ野部層上部は珪藻化石層序のCrucidenticula sawamurae帯（NPD2B帯）に対比可能である．今後，N.7帯/N.8帯境界と磁気極性層序との対応関係およびその境界年代を今回調査したセクションで解明できる可能性があり，それが解明されれば17～15Maの古地磁気-微化石年代尺度の精度と確度が向上すると期待される． We present new biostratigraphic data from an exposed Miocene sedimentary section of the upper part of the Ichishi Group in Mie Prefecture, central Honshu. Mudstone samples were collected from outcrop exposures, mainly found along a river, where we mapped lithologies and structures. Planktonic foraminiferal assemblages consisting mainly of warm water species were obtained from 21 samples above and below the lithostratigraphic boundary between the Mitsugano Member (upper part of the Oi Formation) and the overlying Chaya Member (lower part of the Katada Formation). The sedimentary sequence is correlated to zones N.7 and N.8 of the planktonic foraminiferal zonal scheme. Importantly, our results from high-resolution sampling show that the N.7/N.8 zonal boundary is located within a horizon ～19 m below the Oi/Katada formation boundary. Diatom fossils of the Crucidenticula sawamurae Zone (NPD2B; 18.1-17.0 Ma) were found in calcareous concretions within the Mitsugano Member below the N.7/N.8 zonal boundary. Our results suggest that the section is a suitable candidate for assessing the validity of early-middle Miocene planktonic foraminiferal biochronology.