宮古島吉野海岸の固結砂層と湧水の分析結果.

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 SC value of cemented and uncemented 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 土 0.3 pMC and 89.3 土 0.3 pMC respectively. While DIC of cemented and stratified sand layer, and uncemented lower sand layer indicated 84.1 士 0.3 pMC and 77.5 士 0.2 pMC. 3) The S13C values of two spring water samples were -- 9.8%〇 and -- 9.9%〇, while those of the cemented sand layer, and lower un-cemented sand layer were -- 0.9%〇 and +0.4%〇, 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. [ABSTRACT FROM AUTHOR]

宮古島南東の吉野海岸では,湧水の流路に沿って板状に固結した複数の砂層がみ られる。湧水の水質が砂層の固結に関係している可能性が高いと推量し,因果関係 を解明する基礎試料を得るため,湧水,固結砂層およびその下方の非固結砂層を採 取して分析した。その結果,砂層の固結は石灰岩を溶解した湧水に含まれる CaCO3の析出による可能性が高いと考察した. [ABSTRACT FROM AUTHOR]