Lithology and foraminiferal fauna of allochthonous limestones (Changhsingian) in the upper part of the Toyoma Formation in the South Kitakami Belt, Northeast Japan

Abstract

Allochthonous limestones less than 3m thick are intercalated lenticularly within sandstones and mudstones of the upper part of the Upper Permian Toyoma Formation in the South Kitakami Belt. They are bedded and laminated, and have many thin interbeds of sandstone and mudstone. These limestones are narrowly distributed exclusively in the Kesennuma area, and largely differ from platform limestones of the Lower Permian Sakamotozawa and Middle Permian Kanokura formations, both widely distributed in the South Kitakami Belt, in their occurrence and extent. Thirty-two species of foraminifers, some of which are restricted to the Changhsingian, are discriminated in limestones, limestone conglomerates, and calcareous sandstones of the upper part of the Toyoma Formation. This foraminiferal fauna evidently belongs to the Tethyan province paleobiogeographically, and is characterized by dominant Colaniella parva, subordinate Nanlingella cf. meridionalis, and accessory Palaeofusulina sp. These three species are described herein.