大分県秩父帯（小坂亜帯）白亜系の衝上ナップ

概要

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The Mesozoic strata of the Osaka area, Oita Prefecture, Kyushu, are distributed in several narrow regions within Chichibu Terrain. On the basis of stratigraphic and paleontological studies, they are classified into the following formations: the Koshigoe {Hauterivian-Lower Barremian}, Haidate (emend.) {Barremian}, Osaka {Barremian} and Shiibaru {Cenomanian} Formations. Among them the Koshigoe and Haidate Formations are combined under the name Haidateyama Group. The Koshigoe Formation unconformably overlies the basement rocks with a conglomerate. On the other hand, the Osaka Formation belongs to one of the “Pre-Sotoizumi Group”. Therefore the “Pre-Sotoizumi Group” which was regarded as a member of the Ryoke Belt, is cropping out as the thrust sheets on the Hidateyama Group, in the Osaka and Takaya areas.In this paper, the Stratigraphy is described in some detail, with remarks on correlation, and the features of the bivalve faunas are made clear. The faunal composition with other areas of Southwest Japan, together with the faunal change in time and space, are also discussed.
2012-12-12