Nemuro Belt
The Nemuro Belt is the easternmost tectonic unit or terrane of Hokkaidō, Japan. The boundary with the Tokoro Belt to the west is marked by the Abashiri Tectonic Line, which runs from the area of Abashiri on the north coast to that of Urahoro on the south coast, the southern portion coinciding with the Urahoro Fault. The belt is composed of volcanogenic sediments and volcanic rocks — for the most part, basalt and andesites; these may be remnants of an island arc that took shape over an "east or southeast dipping intraoceanic subduction zone". As dated by potassium–argon geochronology and radiolarians, the oldest sequences are Campanian‐Maastrichtian. The belt has rotated counterclockwise some 15–25° since the Late Cretaceous.
Running roughly east to west, the primary rock strata of the Nemuro Belt are the Late Cretaceous to early Palaeogene deposits of the Nemuro Group, which occur in the and extend along the south coast from Kushiro and the Nemuro Peninsula into the South Kurils, to Zelyony and Shikotan, and perhaps as far as the submarine Vityaz Ridge. The Nemuro Group is in part overlain by the Middle Eocene Urahoro Group, which is in turn overlain by the Upper Eocene to Lower Oligocene Onbetsu Group.
Nemuro Group
The group includes the following formations, in ascending order:- Nokkamappu Formation
- Ōtamura Formation
- Monshizu Formation
- Oborogawa Formation
- Hamanaka Formation
- Akkeshi Formation
- Tokotan Formation
- Kiritappu Formation
Urahoro Group
The group includes the following formations, in ascending order:- Beppo Formation
- Harutori Formation
- Tenneru Formation
- Yūbetsu Formation
- Shitakara Formation
- Shakubetsu Formation