Late Holocene Shorelines and Sea Level in Miyako Island, the .yukyus, Japan

Abstract

The present sea level in Miyako Island is the highest recorded during the Holocene, determined by systematic investigation of marine notches and beachrocks occurring along the coast. The elevations of the retreat points of the notches are consistent with the present tidal range and exposure. All beachrocks which are known to be due solely to tidal conditions are situated at an intertidal or almost intertidal zone. Near-intertidal beachrocks have been dated 425±70 and 1520±60 y. B. P. (Loc. 13), and 2120± 75 y. B. P. (Loc. 31), showing a relative stability of sea level during at least the past 2100 years. This situation clearly differs from the Late Holocene emergence prevailing in most of the major axial islands in the Ryukyu Frontal Arc. Such a difference can be ascribed to recent crustal movements.