秋吉帯高山石灰岩層群の褶曲構造

The fold structure of the Akiyoshi Belt was analyzed in Kawakami-cho, Okayama Prefecture, where the Lower Carboniferous to Middle Permian Ko-yama Limestone Group (Yokoyama et al., 1979), Permian Yoshii Group (Sano et al., 1987) and Triassic Nariwa Group (Teraoka, 1959) are distributed. The Nariwa Group unconformably covers the Paleozoic successions (Otoh, 1985). The Lower Carboniferous to Middle Permian Ko-yama Limestone Group, dated by foraminifers and fusulinids (Yokoyama et al., 1979), is mainly composed of massive limestone with basic volcanics, acidic tuff and chert. The Paleozoic successions of the Akiyoshi Belt were folded during the Middle to Late Permian (Suzuki et al., 1990). Strata of the Ko-yama Limestone Group generally strike E-W and dip to the north. The Hoya section about 300 m thick is composed of limestone, basic tuff, chert and acidic tuff, limestone, basic lava and tuff in ascending order. In this section, Ishida et al. (2012) recognized a nearly complete conodont faunal succession ranging from the upper Visean to the lower Moscovian. The faunal succession indicates younging southward, and the strata are overturned. A folded strucuture of tight overfold with north-dipping axial plane was reconstructed. Similar style of small scale overfolds of banded chert and turbidite were observed in the overlying Yoshii Group.