Belt Series

(named after the Little Belt Range in Montana, USA), a local subdivision of the Upper Precambrian era in the USA. It is a layer of colorful shale and black clay schists and sandstones, as well as limestone and dolomites with stromatolites (up to 6,000 m thick) overlying and eroding metamorphic rock and granite (about 1.6 billion years old). The belt is divided into four strata. The age of the uppermost stratum is calculated at 1.04–1.05 billion years according to the argonpotassium and rubidium-strontium methods of measuring the age of glauconite. The age of the uranium mineralization in the third stratum from the bottom is 1.1–1.2 billion years. On this basis the Belt Series may be compared with the Lower and Middle Riphaeic series of the USSR.