宮古島の石灰岩について

概要

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A field study was made on the distribution and thickness of the raised reef limestone of Miyako Island, the Ryukyu Islands. Thickness was mainly estimated from the depth measurements of more than 70 wells, most of which are proved to be sunkun through the limestone layer down to the surface of the foundation rock of the bluish gray marls.Terraces are developed on the western slopes of the ridges which run northwest to southeast and parallel to each other.Coastal benches are also observed along the coast lines. Terraces and coastal benches are tentatively classified into six altitude groups, namely; 1) 5-10 m., 2) 20-30 m., 3) 40-45 m., 4) 60-73 m., 5) 80-85 m., 6)95-107 m.Limestone covers the entire island, its thickness varying locally a few to 50 meters.Limestone is generally about 20 meters thick, and it exceeds 30 meters in some place.There is one region (Unatô plateau, see fig. 1) where its thickness attains 50 meters.Examination of the cross sections of the island and the other results of the field study reveal that the main topographic features were formed by the block movements which probably occured after the deposition of limestone. More field study is neededbefore making any further account on the history of the limestone formation.
琉球大学文理学部の論文