抄録
The Middle Miocene marine strata was found to occur in the northern part of the Hidaka belt, the Kitami-Takinoue region, northern Hokkaido. In this area the Miocene sediments can be divided into three formations, as follows; [table] The following molluscan fossils were found in the basal part of the Kamishiyubetsu Formation; Acila sp., Yoldia haborensis, Serripes notabilis, Mercenaria chitanina, Peronidia cf. t-matsumotoi, Neptunea sp., Natica sp.. This molluscan fauna is correlative with the Chikubetsu fauna (KANNO et al., 1960) in the Haboro coal field, Northern Hokkaido. Foraminifera fossils such as Cyclammina japonica and Cyclammina incisa were also found in the upper mudstone member of the Kamishiyubetsu Formation. Molluscan fossils such as Portlandia hayasakai and Malletia sp. were found in the Oshiraneppu-gawa Formation. These fossils are similar to those found in the Tokomuro Formation in the Kushiro coal field and the Nupinai Formation in the Tokachi region. The molluscan fossils above-mentioned suggests that the Kamishiyubetsu Formation and Oshiraneppu-gawa Formation were accumulated in middle Miocene age.
