The Quaternary coral reef tracts of Hateruma, Ryukyu Islands, Japan
The island of Hateruma is located at the southwestern end of the Ryukyu Island chain and covers an area of about 15 km2 with its highest point at 59.5 m.a.s.l. The morphology of Hateruma is characterized by an eight-step staircase (I to VIII after Ota et al., 1982) most of which eroded into the previously formed coral reefs (II and IV to VIII). This study presents 100 age estimations on 43 coral samples using electron spin resonance (ESR), alpha- and mass spectrometric U-series methods. The dating results imply that the Ryukyu Limestone was predominantly formed during oxygen isotope stages 7 and 5e. Two age estimates of around 300 ka suggest an earlier reef-building period. The main problem for establishing the Quaternary history of Hateruma lies in the fact that the coral ages and the staircase morphology do not correlate. Additionally, it is difficult to distinguish autochthonous from allochthonous samples, the latter having possibly been relocated by tsunamis. Corals relating to substages 5a and 5c (around 75 and 105 ka, respectively) are found in the immediate vicinity of much older samples. The results of this study prove the disappointing fact that Hateruma cannot yet be used as a tool for reconstructing palaeo sea levels.
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