Radiocarbon Measurements of Samples Collected from Conglomeratic Beachrock Developing at Higashihama-cho, Sasebo, Nagasaki Prefecture

A total of four muddy-fine sand deposits attached to the undersides of cobles and boulders and three Claudiconcha japonica fossils were collected to determine the formation age of con-glomeratic beachrock developing at Sasebo, Nagasaki prefecture. The geology of the surveyed coast consists of non-limestone rocks. Radiocarbon dating using Accelerator Mass Spectrometry (AMS14C dating) for the collected samples was conducted to determine the formation age of the beachrock. It was not possible to determine the age of four muddy -fine sand deposits because of their low CaCO3 concentrations (1.4%); however, the Claudiconcha japonica fossils yielded an age of Modern (102.5 +/- 0.3 pMC-101.6 +/- 0.3 pMC). The elemental composition of the cement samples analyzed with ICP-MS showed Al and Fe concentrations of 6.9% and 4.9%, respectively; however, the Ca concentration was low at 0.6%. The analytical results lead to the conclusion that the formation age of conglomeratic beachrock at Sasebo could not be determined with AMS14C dating, and that cobles and boulders, including mud and fine sand deposits, were cemented with Al2O3 and Fe2O3, or probably with SiO2, and formed conglomeratic beachrock.