AMS 14C ages and petrological features for solidified fractures with carbonates at coastal outcrops of Yakushima Island, Japan

This paper describes the petrological features and the ages of rock fractures filled mainly with carbonates at coastal outcrops of Yakushima Island, Japan. Microscopic observation and geochemical analysis were used to investigate the petrological features and the compositions of the fracture fillings. In addition, AMS 14C dating was also performed to estimate the ages of them. Microscopic study indicated that the fracture fillings contain not only cementing materials but also lithic fragments from host rock and bioclasts. SEM observation showed that the cements exhibit the characteristic textures of beachrocks. The cements were identified as Mg-calcite from XRD analysis. It was also observed from geochemical analysis that there were at least two stages of precipitation within the fractures. In addition, AMS 14C dating for seventeen samples of fracture fillings showed that the ages range from 2,460 to 5,130 years BP which is found to be younger than that of the uplifted coral at Yakushima Island (approximately 5,300–5,600 years BP). The results suggest that the fractures were solidified after the coral was uplifted.