Four drilling cores are observed from a high-latitude coral reef at the northwestern Mage Island (N30゜45' 40").
The thickness of the Holocene reef is around 2.5m in the reef edge and 4m in back reef. The Holocene thickness is relatively thin comparing to the modern reefs in the middle or the southern Ryukyu Islands. The reef structure Acropora facies, reworked coral rubble facies. This zonal structure conforms to the ecological coral-zonation corresponding to the wave-energy gradient
