Analyses of Cemented and Un-cemented Sand Layers and Spring Water, Collected from Yoshino Coast, Southeast of Miyako Island, Okinawa

Abstract

　　　Along the Yoshino coast, southeast of Miyako Island, several spring waters gush out from the lower part of the marine terrace cliff. Several stratified and cemented sand layers are observed at 1.5～2.0 m a.s.l. along the small streams of spring water.

　　　To obtain basic data related to the formation mechanism of cemented sand layer, hydrological analysis of spring water and measurements of radiocarbon concentration and δ¹³C value of cemented and un-cemented sand layers were carried out. The results are summarized as followings:

1） Spring water is classified into Ca-HCO₃ type, which indicates characteristic in other limestone area.

2） DIC (Dissolved Inorganic Carbon) of two spring water samples gave yielded values of 89.8±0.3 pMC and 89.3±0.3 pMC respectively. While DIC of cemented and stratified sand layer, and un-cemented lower sand layer indicated 84.1±0.3 pMC and 77.5±0.2 pMC.

3） The δ¹³C values of two spring water samples were －9.8‰ and －9.9‰, while those of the cemented sand layer, and lower un-cemented sand layer were －0.9‰ and +0.4‰, respectively.

4） The stratified and cemented sand layers were formed under the cementation of sand and CaCO₃ precipitated in the reverse reactions of the resolved limestone solution. The area of distribution, slope, hardness, superposition form, sedimentary facies and ¹⁴C age of the cemented sand layers differ from beachrock, eolianite and tufa.