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Geochemical Journal
Geochemical Journal An open access journal for geochemistry
Published for geochemistry community from Geochemical Society of Japan.

Growth rate of terrestrial ferro-manganese nodules in the limestone area of the Ryukyu Islands

Hatsuo Taira, Yasushi Kitano, Kiyoshi Kaneshima
Geochemical Journal, Vol. 13, No. 6, P. 301-305, 1979


The growth rate of terrestrial ferro-manganese nodules formed in limestone areas of the Ryukyu Islands has been determined by a radiochemical method. The ionium-thorium ratios exponentially decrease with depth from the surface of the manganese nodule, and the growth rate has been evaluated as (61 ± 9)mm per 106 years for samples collected from a reddish soil accumulated on the stratum of Naha Limestone at Nakijin-son, the northern part of Okinawa-jima. The growth rate will lead to the age of (16 ± 2) × 104 years for a manganese nodule about 2.0cm in diameter, which is of the largest size in the area. This may give an estimation of the upper limit age for the Riukiu (Naha) Limestone formation.

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