No abstract

Until now, there has been no consensus over the stratigraphic correlation between the western and eastern parts of the Hinagu Belt in the Yatsushiro Mountains, Kyushu. Therefore, we examined the stratigraphy and structure of the Pre-Sotoizumi Group in the central part of the Hinagu Belt, with a particular emphasis on clarifying the stratigraphy and distribution of the Hachiryuzan, Kesado and Imaizumigawa formations. The Kawaguchi Formation was identified as the oldest formation in the study area, followed by the Hachiryuzan, Kesado and Imaizumigawa formations. The distribution of the Kesado and Imaizumigawa formations was confirmed in the eastern part of the study area, but the distribution of the former could not be recognized in the western part. The relationships between the Hachiryuzan and Kesado formations, and between the Hachiryuzan and Imaizumigawa formations were confirmed as being conformable and disconformable, respectively, as identified in previous reports. In contrast to previous reports, however, field evidence shows that the Kesado and Imaizumigawa formations are separated by a clino-unconformity. It is concluded that these two formations were folded during the Barremian-Aptian, prior to the deposition of the Imaizumigawa Formation.