The Nemuro Belt (根室帯, Nemuro-tai) is the easternmost tectonic unit or terrane[1]: 178 of Hokkaidō, Japan.[2]: 202 The boundary with the Tokoro Belt to the west is marked by the Abashiri Tectonic Line (網走構造線),[3]: 1114 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 (浦幌断層).[4]: 96 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".[5]: 1377 As dated by potassium–argon geochronology and radiolarians, the oldest sequences are Campanian‐Maastrichtian.[5]: 1377 The belt has rotated counterclockwise some 15–25° since the Late Cretaceous.[5]: 1389
Running roughly east to west,[5]: 1377 the primary rock strata of the Nemuro Belt are the Late Cretaceous (Campanian) to early Palaeogene (Palaeocene and, in places, Eocene) deposits of the Nemuro Group (根室層群),[2]: 210 which occur in the Shiranuka Hills and extend along the south coast from Kushiro and the Nemuro Peninsula into the South Kurils, to Zelyony (Shibotsu) and Shikotan,[6]: 607 and perhaps as far as the submarine Vityaz Ridge.[5]: 1377 The Nemuro Group is in part overlain by the Middle Eocene Urahoro Group (浦幌層群), which is in turn overlain by the Upper Eocene to Lower Oligocene Onbetsu Group (音別層群).[7]
The group includes the following formations, in ascending order:[6][8]
The group includes the following formations, in ascending order:[7][9]
At the western end, the Rushin Formation (留真層) correlates with the Beppo, Harutori, and Tenneru Formations.[7]