Abstract
The Ryukyu Group, consisting of Pleistocene reef complex deposits that laterally pass into terrigenous sediments, crops out on Toku-no-shima, Ryukyu Islands, southwestern Japan. We propose a major revision of the previous stratigraphic scheme for the Ryukyu Group and provide a formal stratigraphic description. The Pleistocene sequences comprise the Tokunoshima and Metegu Formations, in ascending order, on this island. The Tokunoshima Formation reaches 140 m in thickness and is exposed extensively, covering peripheral areas of the island at elevations less than 210 m. It is divisible into two units, each consisting of proximal coral limestone and distal rhodolith, Cyclo-clypeus-Operculina, and detrital limestones. The Metegu Formation resting unconformably on the Tokunoshima Formation is composed mainly of thin (< 5 m) coral limestone. It is exposed at limited outcrops in southern parts of the island, ranging in elevation from 20 to 60 m. Stratigraphic position, known age-diagnostic nannofossils, and uranium-series and ESR dates indicates that the Tokunoshima Formation may be correlative to the main body of the Ryukyu Group on Okierabu-jima and Yoron-jima. An ESR date denotes that the Metegu Formation accumulated at > 146 ka.
