Reconstruction of late Quaternary sea-level and reef growth history in the Ryukyu Islands

2023 Fiscal Year Final Research Report

• Project/Area Number: 21H01169
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 17030:Human geosciences-related
• Research Institution: Nagoya University
• Principal Investigator: Humblet Marc 名古屋大学, 環境学研究科, 准教授 (40623616)
• Co-Investigator(Kenkyū-buntansha): 井龍 康文 東北大学, 理学研究科, 教授 (00250671) ; 藤田 和彦 琉球大学, 理学部, 教授 (00343377) ; 横山 祐典 東京大学, 大気海洋研究所, 教授 (10359648)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: Coral reef / Sea level change / Climate change / Quaternary / Minatogawa Formation / Ryukyu Islands / Okinawa

Outline of Final Research Achievements

The Minatogawa Formation in Okinawa-jima represents a unique late Middle to Late Pleistocene record of carbonate sedimentation consisting of well-sorted foraminiferal grainstones and coral-rich limestones. This formation yields important information on Quaternary sea-level and reef growth history. In this study, we have recovered 188 m of core sections from twelve boreholes drilled into the Minatogawa Formation in southern Okinawa-jima. In order to record lateral variations in sedimentary facies, we have drilled along two transects about 1 km apart and perpendicular to the shoreline. Six boreholes (Hole 1-6) were drilled along the first transect and five (Hole 1b-5b) along the second. One borehole (Hole C) was drilled between the two transects. The older Pleistocene basement (Naha Formation) underlying the Minatogawa Formation was reached in all but one hole. The thickness of the Minatogawa Formation ranges from 0 m in the most inland holes to 24 m closer to the shoreline.

Free Research Field

Geology

Academic Significance and Societal Importance of the Research Achievements

The cores from the Minatogawa Formation provide a unique window into the late Middle to Late Pleistocene sea-level and reef growth history in the Northwest Pacific. This time window is particularly important to study rapid environmental changes and their impact on coral reef ecosystems.