The Belt Basin (Rocky Mountains): Composition of Sedimentary Complexes and Some Features of Its Sedimentary Filling

The article overviews concepts of the formation of sedimentary sequences of the Belt-Purcell Supergroup, a classical Upper Precambrian section of the Rocky Mountains (North America). Analysis of data on the bulk chemical composition of mudstones of the Belt-Purcell Supergroup (González-Álvarez, 2005; González-Álvarez and Kerrich, 2010) suggests that the overwhelming part of the fine-grained aluminosiliciclastic filling in the Belt Basin was delivered from complexes with non-Archean geochemical characteristics. During almost the entire period of sedimentary filling in the Belt Basin, the fine-grained aluminosiliciclastic material was delivered by large river arteries similar to modern rivers of category 1, i.e., major rivers draining large (>100 000 km 2 ) continental areas (Bayon et al., 2015), and category 2 (rivers draining the “mixed/sedimentary” rocks). This fact confirms the concept of the formation of sedimentary sequences of the Belt-Purcell Supergroup inferred from both traditional geological methods and analysis of data on the U–Pb isotopic ages of detrital zircons and monazites from sandstones of various lithostratigraphic units.