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

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Five boreholes (10-27 m in length) were drilled into late Middle Pleistocene limestone (Minatogawa Formation) along a transect perpendicular to shore in southern Okinawa Island in December 2022 and January 2022. The total cored length is 90 m. After shipping the cores to the Kochi Core Center for safe storage, each core was X-ray CT-scanned. The cores were then split in half, photographed, and their lithology, sedimentary structures, and major fossil biotic components, particularly corals, coralline algae, and foraminifers, were carefully described in September 2022. Seven additional boreholes (8-23 m in length) were drilled in the same geological formation in August and September 2022. The total cored length is 98 m. Five of these boreholes were drilled along a second transect perpendicular to shore situated 800 m to the south-west of the first transect. One borehole was drilled between the first and second transect, and another borehole was drilled along the first transect. The seven new cores were shipped to the Kochi Core Center for storage in January 2023. Sampling of the cores of the first transect was conducted at the Kochi Core Center in February 2023 for sedimentological analysis, radiometric dating, taxonomic identification of corals, crustose coralline algae, and foraminifers, as well as elemental and stable isotope geochemistry. In addition, the corals observed in the cores of the first transect were identified at the lower taxonomic level possible and their status (in situ vs. not in situ) duly noted. The thickness of coralline algal crust was also recorded.