Radiocarbon ages of beach rocks and late Holocene sea-level changes in the southern part of the Nansei Islands, southwest of Japan.

Abstract

Beach rock is a good indicator of the past sea levels, as it is considered to have been formed within the range of intertidal zone. Radiocarbon dates of beach rocks collected from Iriomote Island, Ishigaki Island, and Miyako Island, in the southern part of the Nansei Islands, indicate that the beach rocks were formed between around 4000 BP and 400 BP. Late Holocene sea-level changes were revealed based on the elevations and (super 14) C dates of the beach rocks. The results indicate that the sea level was similar to the present one for at least the past 4000 BP. Isotopic fractionations (delta (super 13) C) of the beach rocks were between +9.4 per mil and -0.8 per mil, suggesting a different origin for calcium carbonate.