宇和島地方の白亜系

Upper Cretaceous in Uwajima, Iyo Prov., Ehime Pref., Shikoku, Japan

NAKANO Mitsuo

廣島大學地學研究報告

Geological report of the Hiroshima University

The fossiliferous Upper Cretaceous rocks named under the Uwajima group are well developed in the neighbourhood of Uwajima-city, being separated from the so-called Shimantogawa complex by the thrust faults in the northern and southern wings.
Though litho-facies is fairly variable in horizontal distribution, the stratigraphy of the group is summarized as follows :
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"Shimantogawa Complex"... Alternation of sandstone and shale with siliceous red shale and limestone layers in some horizons.
Speaking generally, the Uwajima group forms a synclinorium structure and its axial direction is about E—W, although the complicated foldings are observable in some places.
From the lower half of the group, i. e. the Chiyoura and Narukawa formations, a number of Inoceramids, Ammonoids and others were collected. Among them, Inoceramus uwajimensis YEHARA is the most important for chronological determination and it is limited to occur in the lower Urakawan (Coniacian) age of Japan and her adjacent areas. Therefore, both formations are probably the lower Urakawan (Coniacian) in age.
It is an interesting fact that in this district Apiotrigonia minor (YABE and NAGAO) was collected from various horizons and localities of the group and that its associated forms are different in horizons. In the lower half of the group, i. e. the Chiyoura, Narukawa and Ishibiki formations, this species is collected from coarse-grained sandstone or conglomerate layers and it is associated with Ostrea sp. and Archaeozostera sp., the latter of which might inhabited in brackish water of the temperate zone. On the other hand, this form is obtained from sandy shale to medium-grained sandstone beds in the upper half of the group and it is accompanied with Echinoids, Acila (Truncacila), Chlamys and others in the neritic environment of the open sea. Judging from the above-mentioned facts, Apiotrigonia minor (YADE and NAOAO) might in-habited in the littoral environment of the brackish water in the temperate zone and also in the neritic condition of the open sea.

jpn

廣島大學理學部地學教室

[ISSN] 0073-2303

[NCID] AN00213676