Changes in holocene ostracode faunas and depositional environments in the Kitan Strait, southwestern Japan

Abstract

At least 106 species were identified from 36 samples obtained from two cores (T1 and T2), which were recovered from the Kitan Strait off Wakayama City, southwestern Japan. Q-mode cluster analysis of cores T1 and T2 revealed three biofacies (PL, PT and LS). Changes in depositional environments based on the observed distribution of ostracodes were analysed, and the following sequence is proposed. Before ca. 7,000 cal yr BP, the T1 site was a sandy coast, ranging from an outer bay to the open sea, close to a river mouth, at water depths of more than 15-20 m, while the T2 site ranged from a bay coast to an outer bay, close to a river mouth, at water depths of less than 15-20 m. During ca. 7,000-2,000 cal yr BP, the position of the sites fell within ranging an outer bay to the open sea at water depths of 30-40 m influenced by residual and/or tidal currents from the straits. After ca. 2,000 cal yr BP, the sites were situated on a sandy coast, ranging from an outer bay to the open sea, close to a river mouth, at water depths of more than 15-20 m. Two new species, Trachyleberis ishizakii and Cytheropteron kumaii, are also described.