| 研究実績の概要 |
During FY 2023 research activities related to Grant-in-Aid for Scientific Research (B) project number 21H01169 have been focused on the description and sampling of core sections from seven new boreholes drilled into the Minatogawa Formation in southern Okinawa Island. The new boreholes (8-23 m in length) were drilled in this geological formation in August and September 2022. The total cored length is 98 m. These new cores, together with cores from five boreholes previously drilled in December 2021 and January 2022, are stored at the Kochi Core Center on the Monobe Campus of Kochi university. The cores from the seven new boreholes were split lengthwise at the Kochi Core Center in July 2023 to enable the description of their lithological and biological content. The description and sampling of the new core sections were completed in December 2023. A total of 146 samples were collected for sedimentological and geochemical analyses, as well as for the taxonomic identification of scleractinian corals, coralline algae, and foraminifers. This brings the total number of samples for the twelve boreholes drilled so far to 306. Eight coral samples were analyzed by XRD to evaluate their suitability for radiometric dating. However, all eight samples showed aragonite to calcite recrystallization. During FY 2023 time was also dedicated to the production of thin sections and polished sections for the sedimentological analysis of the limestones of the Minatogawa Formation. A total of 41 thin sections were produced, and 49 polished sections were scanned at high resolution.
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