ABSTRACT

The present study shows the petrological and mineralogical features and the ages of fracture fillings in sedimentary rock at coastal outcrops of Yakushima Island, Japan. Four samples of fracture fillings were collected from a single fracture in the sedimentary rock. Microscopic observations showed that the fracture fillings are composed of cementing materials and various kinds of fragments including mainly bioclasts and lithic fragments from host rock. It was also observed that the fracture fillings contain layered structures parallel to the fracture surface as a whole. The structures indicate that the fracture fillings were precipitated by multiple stages. XRD analysis showed that the cementing materials are mainly Mg-calcite. In addition, AMS 14C dating revealed that the ages of the fracture fillings range from 2,460 to 5,130 yrBP that are remarkably younger than the ages of hydrothermal and low-temperature fillings in rock fractures reported by previous studies. Furthermore, it was considered that the approximately 2,700 years variations might be caused by layered structures of fracture fillings.

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