Dating of Soils on the Raised Coral Reef Terraces of Kikai Island in the Ryukyus, Southwest Japan: With Special Reference to the Age of Red-Yellow Soils.

Abstract

Absolute ages of soils developed on the raised coral reef terraces in Kikai Island were estimated by using the mean rate of tectonic uplift and glacio-eustatic curve during late Quaternary. The results obtained are as follows: State of bare rock outcrop continues for ca. 1.5ka after the emergence, and it takes ca. 3.0ka to develop Lithosols. Initial Rendzina-like soils (Rendzic Leptosols, Lithic Rendolls) begin to develop 3.5-3.9ka after the emergence, and the soils of 35-40ka of age are Rendzina-like soils (Rendzic Leptosols, Lithic Rendolls). The soils of 50-55ka of age have changed into Brown Rendzina-like soils (Mollic Leptosols, Eutropeptic Rendolls). At the point of time 70-80ka from the emergence, free calcium carbonate has already been leached out from solum, humus decomposition and clay migration have started, and Terra fusca-like soils (Haplic Luvisols, Typic Hapludalfs) are formed. After 95-100ka from the emergence, rubefaction (reddening) proceeds and the soils become to Terra rossa-like soils (Chromic Luvisols, Typic Hapludalfs). The soils of 120-125ka of age have an intermediate properties between Terra rossa-like soils and Red-Yellow soils (Haplic Lixisols, Typic Hapludalfs), although the degree of base saturation is in the proximity of Red-Yellow soils. Therefore, it is concluded that it will take ca. 125ka for Red-Yellow soils (Acrisols, Hapludults) to develop on coral limestone in the humid subtropical rain forest climate region.