琉球列島の完新世サンゴ礁段丘上に形成されるカメニツァの成長速度

概要

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Solutional depressions, called kamenitzas, are frequently observed in the splay zone on limestone coasts. The present study examines the long diameter (A), short diameter (B) and depth (D) of kamenitzas on raised coral reef terraces of known ages at Kikai-jima and Okinawa-jima, in the Ryukyu Islands, Japan. Supposing that the formation of the kamenitzas started from the emerged time of the terraces, the growth rate of the kamenitzas can be estimated from the measurement of their plan diameters and depth on the several terraces. The result indicates that both long and short diameters (A and B) increase with time (T) and the plan shape, denoted by A/B, also increases with time. The former fact suggests that the kamenitzas extended in all directions with time, keeping elliptic outlines; and the latter fact suggests that they coalesced as they grew. More irregularity of the kamenitza outline of older terrace would be due to multiple coalescence. The relationship between the depth of kamenitza, D (cm), and the period of their formation, T (year), was found to be D=0.025T.
2009-10-25