二枚貝フォーナからみた東北日本と西南日本の白亜系の関連について
1989 年 43 巻 3 号 p. 129-139
詳細
1989 年 43 巻 3 号 p. 129-139
In Northeast Japan, the Lower Cretaceous strata, i. e., the Ofunato, Oshima and Miyako Groups and several strata which were correlated with the groups, are distributed sporadically in Kitakami and Abukuma Mountains. The Ofunato Group is undoubtedly correlated with the Monobegawa Group which is distributed at the northern Chichibu Belt in southwest Japan, because of the nearly same bivalve fauna and close resemblance of rock facies between them. This probably ranged the Monobegawa Group as a same Lower Cretaceous sedimental basin. The Oshima Group and the uppermost part of the Soma Group are also certainly correlated with the uppermost part of the Torinosu Group and basal part of the Nankai Group which were sporadically croping out at the Middle Chichibu Belt (Kurosegawa Tectonic Belt) in southwest Japan, by their very similar faunas and litho-facies. The Miyako Group is akin to the Yatsushiro and Kesado Formations of the Pre-Sotoizumi Group at Central Kyusyu and the upper part of the Nankai Group, e. g., the Ikuna Formation of Tokushima in Shikoku or the Ochiai Formation of Oita in Kyusyu, in the occurrence of many common species of bivalves. The faunal evidence is shown the relationship among Miyako, Oshima and Soma Groups. And in Early Cretaceous, the basin of the groups was probably located at lower paleogeographical latitude than that of the Ofunato Group. Some bivalve species from the Miyako Group are probably concerned with those from the Middle Yezo Group and the Goshonoura Group of the Upper Cretaceous of Japan as the species on same lineages or the derivatives from the former. The Upper Cretaceous System of northeast Japan are distributed at southern Pacific coast of Fukushima and Ibaraki Prefectures, and northern Pacific coast and Kitakami Mountains of Iwate Prefecture. The Kuji and Futaba Groups, and the several strata which were able to correlate with the groups, are known. They are composed of the shallow shelf sediments which were overflowed the Pre-Cretaceous basements by the Urakawan Transgression.
