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RADIOCARBON AGES AND ISOTOPE FRACTIONATIONS OF BEACHROCK SAMPLES COLLECTED FROM THE NANSEI ISLANDS, SOUTHWESTERN JAPAN

Kunio Omoto

Abstract


A total of 294 beachrock samples were collected from 116 sites on 15 islands in the Nansei Islands chain,southwestern Japan, and were radiocarbon dated. The beachrocks began to form at about 6900 BP and some are still under development in the islands. Values of isotope fractionations of different materials making up the beachrocks ranged between +9.4%0 and - 5.7%0. Isotope fractionations outside the range of 0 2%0 suggest that these beachrocks were strongly influenced by underground water and running freshwater when they were cemented. The sea level during the late Holocene has remained the same for at least the past 5000 yr, except for several uplifted coasts.

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