Application of cosmogenic 10Be to dating soils on the raised coral reef terraces of Kikai Island, southwest Japan

Abstract

10Be concentrations of six soils on the raised coral reef terraces of Kikai Island, southwest Japan range from 0.80 to 7.17×10 9 atoms g −1. The annual deposition rate of 10Be from the atmosphere to Kikai Island from 2000 to 2002 ranges from 2.0 to 3.5×10 6 atoms cm −2 year −1, with a mean of 2.8±0.7×10 6 atoms cm −2 year −1. Minimum absolute ages, calculated from the inventory of meteoric 10Be in the soils and the annual deposition rate of 10Be, are: Initial Rendzina-like soil, ≥8 ka; Rendzina-like soil, ≥18 ka; Brown Rendzina-like soil, ≥56 ka; Terra fusca-like soil, ≥127 ka; Terra rossa-like soil, ≥136 ka; and Intergrade between Terra rossa-like and Red-Yellow soil, ≥102 ka. Therefore, it was concluded that soil formation during the first ∼60,000 years would be as Rendzina-like soils and more than ∼100,000 years would be required for Red-Yellow soils to develop on raised coral reef terraces under subtropical humid climatic conditions.