Anatomy of the Early to Middle Miocene SW Japan Arc: Opening up the frontier of the sedimentology and palaeoecology in the active plate margin

2022 Fiscal Year Final Research Report

• Project/Area Number: 16K05591
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Stratigraphy/Paleontology
• Research Institution: Kochi University
• Principal Investigator: Nara Masakazu 高知大学, 教育研究部自然科学系理工学部門, 教授 (90314947)
• Project Period (FY): 2016-04-01 – 2023-03-31
• Keywords: 古生態 / 古環境 / 古生物 / 生痕化石 / 堆積地質学

Outline of Final Research Achievements

The most important finding is that the sediment mass-production and over-sedimentation that affected the Miocene shallow marine benthic communities in the Misaki Group was probably caused by the active extension tectonics, forced subduction of the young and hot Shikoku Basin, and regional uplifting in and around the Kuma Basin by volcanism that later deposited the overlying Ishizuchi Group. Along with this, I, with the help of other workers, reported several additional things, such as a very thickly bedded sandy tsunamiite probably formed by powerful tsunami backwash in the Tanabe Group, probable tidal flat and estuarine deposits in the Misaki Group, and new ichnospecies characteristically found in the tidal flat deposits of the SW Japan Miocene strata. Moreover, based on the international joint research, co-authors and I described giant fossil burrows belonging to a new ichnogenus and ichnospecies in the Miocene of Taiwan and interpreted them as a dwelling structure of the eunicids.

Free Research Field

古生態学

Academic Significance and Societal Importance of the Research Achievements

この研究は，従来，その一般的変動速度の小ささからほとんど考慮されてこなかった固体地球の変動が，日本海拡大の様に急速な場合には十分に生態系に影響を与えることを示した画期的なものである．その成果は，地球温暖化をはじめとした諸問題を抱える地球システムの今後を考える上で小さくない影響をもたらすだろう．また，主な対象の一つである生痕化石は，地層群の堆積環境解析に活用可能であり，ボーリングコアの堆積環境復元や炭化水素ポテンシャルの判定を通じて，資源地質学的にも有用である．さらに，津波堆積相モデルの確立は津波防災にも寄与するものとなろう．本研究は，こうしたさまざまな側面から社会に大きく貢献するものである．