The Lower-Middle Riphean Boundary in the Southern Urals: New Isotopic U-Pb (SHRIMP II) Constraints

摘要

In the general Precambrian stratigraphic scale of the former USSR approved at the 2nd All-Russia meeting on general problems of Precambrian stratigraphy (Ufa, 1990), the Riphean representing the largest Upper Pro-terozoic subdivision comprises three chronostrati-graphic units—the Lower Riphean (Burzyanian), Middle Riphean (Yurmatinian), and Upper Riphean (Kara-tavian)—with the lower isotopic boundaries at 1650 ± 50, 1350 ± 20, and 1000 ± 50 Ma, respectively . The Riphean-Vendian boundary is placed at 650 ± 20 Ma.