LATE CAMBRIAN – EARLY ORDOVICIAN AGE OF BASALT-SILICEOUS-TERRIGENOUS ZASUR’YA FORMATION (northwestern Gorny Altai) Available to Purchase

This paper considers the structural position of the Zasur’ya Formation and reports the first data on its paleontology in a section of the Gorno-Altai Series in NW Gorny Altai. Conodonts and Radiolaria have been found in the siliceous rocks of this formation after chemical treatment. Assemblages of Conodont taxa correlatable with complexes of three Upper Cambrian conodont zones (Muellerodus? erectus, Westergaardodina matsushitai, Proconodontus) have been found in some localities in the Charysh River basin (Krasnoshchekovo Village, upper reaches of the Talitsa and Maralushka Rivers). Two localities (Krasnoshchekovo Village and the upper reaches of the Talitsa River) contain conodont complexes, such as Paracordylodus gracilis Lindstrom, Oistodus gracilis Lindstrom, Acontiodus reclinatus Lindstrom, and Oepikodus evae Lindstrom, allowing the host siliceous rocks to be dated at the Early Ordovician (Upper Tremadoc-Lower Arenig). The problem under discussion is correlation of the Zasur’ya Formation with the strata from the western Altai-Sayan folded area, which occupy the same stratigraphic position and are similar in composition. The new paleontological data prove the Late Cambrian-Early Ordovician active-margin stage in the evolution of the Paleoasian ocean.