Geology and Paleontology of Yonaguni-jima

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Yonaguni-jima is one of the southern islands of the Ryukyu-retto. extending from southern Japan southwestward nearly to Taiwan. About a half of the island's area is hilly, and most of the remainder consists of slightly tilted lowlands. The oldest rocks, Miocene in age, are Yayeyama coal-bearing beds, which consist principally of greenish to brown sandstone and black shale. The Yayeyama coalbearing beds have an exposed thickness of about a hundred meters at Arakawabana. It is overlain unconformably by the Ryukyu Limestone. The Ryukyu Limestone is a fringing reef limestone that crops out mostly north and southwest of the island and is at altitudes of sea level to about eighty meters. It consists of foraminiferous, coralliferous, and algal limestones. The maximum exposed thickness is about twenty meters. Recent deposits include sand and gravel of the present day beaches, sand dunes, and alluvium. Most of the f au1ts that cut the Yayeyama coal-bearing beds and Ryukyu Limestone are of high angle and east-west trending faults which make northward facing escarpments. Seven types of ichnofossils and two species of fossil plants are reported for the first time from the Yayeyama coal-bearing beds. At least 9 species of corals and 34 species of molluscs are reported for the first time from the Ryukyu Limestone. One species of corals and 12 species of molluscs from the Ryukyu Limestone of Tobaru more or less keep their natural color.
琉球大学理工学部の論文
1971-04-01

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野原朝秀
琉球大学教育学部

Geology and Paleontology of Yonaguni-jima

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