Description of the Drilling Cores through the Holocene Coral Reefs at the Gushichan Coast in the Southern Okinawa Island, the Ryukyus, Japan

Holocene emerged coral reefs develop at the Gushichan coast in the southern Okinawa Island, the Ryukyus. Drilling through the Holocene reefs at Gushichan was carried out to reach the basement rock of Tertiary mudstone named the Shimajiri Group with about 10 to 15 m depth, and has obtained five drilling cores. These cores suggest the following characteristics of Holocene reef development and sea-level changes: First, Holocene coral reefs at Gushichan commenced to have formed probably about 8000 years BP on the flat surface about 10 to 15 m below the present sea level ("Start up" phase). Second, during the period between about 8000 and 6000 years BP, coral reefs grew upward catching up with the rapid sea-level rise ("Catch up" phase). Third, coral reef proper formed about 6000 years BP keeping up with the sea-level rise ("Keep up" phase). Fourth, after about 6000 years BP, coral reefs formed laterally in correspondence with small fluctuation of sea level