Lower Ordovician Sequences of the Ebeta Antiform, the Southern Urals

Abstract

Lower Ordovician sequences of the Ebeta antiform, a southern extension of the Uraltau zone, were deposited at the conjugation of paleocontinental and paleoceanic sectors of the southern Urals. Four types of sections were formed on opposite sides of cordillera that existed at the margin of the East European paleocontinent on the Preordovician volcanic belt. Sections of the first three types made up the western apron on the uplift that served as a provenance. Lateral and vertical relationships of various sedimentary associations, as well as their variable (in space and time) facies patterns and sedimentation conditions are considered. An important role of redeposition, slumping, and faulting in the apron development has been revealed. The apron fringed the eastern wall of the Sakmara marginal riftogenic basin that arose at the Cambrian-Ordovician boundary. On another side of the marginal uplift in the east, a slightly modified perioceanic environment existed in the Early Ordovician. Sections of another type formed here at the periphery of Uralian paleocean. These sections are characterized by the universal occurrence of ophiolithoclastic olistostrome with fragments of an older oceanic crust.