The Biostratigraphical Studies of the Poronai Formation
Especially on the Zoning by Mega Fossils in the Oyubari area
1963 Volume 13 Issue 62 Pages 303-313
Details
1963 Volume 13 Issue 62 Pages 303-313
The Poronai Formation which is more than 1000 m thick and consists of massive, unstratified and extremely monotonous mudstone, covers a large area of the Yubari district, Ishikari Coal field. Therefore, to make clear the highly complex structure of the district, subdivision of the formation was of prime importance.
H. Onishi, who has been engaged in detailed mapping since 1947, succeeded in 1950 with his assistants to subdivide the poronai Formation into 7 biostratigraphical zones, statistically treating mega fossils, marl lenses, glauconite, etc.
Since the method of zoning was thus applied, the accuracy of zone-boundary was improved and finally 9 zones were established. This method is easily applied to the interpretation of drilling logs and tunnel geology and actually benefits the understanding of geologic structure of the district.
