抄録
On the basis of geological, magnetostratigraphical and fission track age data, IIDA recently expressed his opinion that an unconformity, a time-gap of which ranges from 2.0 to 1.1 m.y. ago, exists in the Osaka Group along the River Tsuda. This paper represents the results of our investigation on the above-mentioned "Shiba Unconformity" in the drainage of the River Tsuda. The results are as follows, 1) Field evidence shows that no unconformity is observable in the Osaka Group. 2) Magnetostratigraphical study shows that Olduvai normal polarity zone exists in the Osaka Group. 3) Fission track ages of tuff layers of the Osaka Group are consistent with magnetostratigraphical subdivisions of it. The authors also state that Olduvai normal polarity zone is traceable in the Osaka Group of Keihanna Hills and in the Kobiwako Group of Konan Hills, south of Lake Biwa. From these facts it is revealed that so-called "Shiba Unconformity" does not exist in the Osaka Group.
