722. INOCERAMIDS DISCOVERED FROM THE UWAJIMA GROUP IN THE CHIKANAGA DISTRICT, WESTERN SHIKOKU, JAPAN

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  • 722. 愛媛県南部, 近永地域の宇和島層群から発見したイノセラムス化石
  • 愛媛県南部,近永地域の宇和島層群から発見したイノセラムス化石〔英文〕
  • エヒメケン ナンブ キン エイ チイキ ノ ウワジマソウグン カラ ハッケンシ

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A number of pelecypod fossils belonging to Inoceramus yabei, I. teshioensis, and I. uwajimensis were discovered from the Shimanto Terrain in the Chikanaga district to the east of Uwajima, western Shikoku. This paper is concerned with their brief descriptions and with their significances on the stratigraphy of the Shimanto Supergroup. These inoceramids indicate Gyliakian to Urakawan ages and the existence of strata in the Chikanaga district which are synchronous with the Uwajima Group in the type area. In addition to the occurrence of an early Miyakoan ammonoid Cheloniceras (NAKAI and HADA, 1966), these fossils suggest that the shelf-facies Uwajima Group conformably overlies the geosynclinal facies Shimanto Group. It is confirmed not only from the biostratigraphical standpoint of view, but also from the lithostratigraphy, geologic structures and field observations. Taking the recently published report on the presence of the shallow sea strata within the geosynclinal ones in the Yukawa district of Western Kii Peninsula (NAKAZAWA et al., 1979) into consideration, the above-mentioned features give a clue to elucidate the tectonic development of the northern marginal part of the Shimanto Geosyncline.

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