NEOPROTEROZOIC STRATIGRAPHY OF THE ALTAI-SAYAN FOLDED AREA

Abstract

New paleontological findings, analysis of section structure, and literature data on the Neoproterozoic stratigraphy of the Altai-Sayan Folded Area, ASFA, provide support to the recognition of three heterochronous polyfacies complexes of deposits: Vendian, Baikalian, and Mayaian (pre-Baikalian Late Riphean). The Vendian-Cambrian boundary is recommended to be drawn according to the change of complexes (associations) of calcareous algae and small shelly fossils at the base of Member 4 of the Anastas'ino Formation, the main phosphorite-bearing horizon of Member 2 of the Zabit Formation in the East Sayans and its analogs in the Kuznetsk Alatau. The lower Vendian boundary is related to tectonic restructuring expressed in an interruption in sedimentation. The sedimentary bodies between the Vendian-Cambrian boundary and the regional gap are characterized by Ediacaran fauna, small shelly fossils, and Vendian calcareous algae. The Late Riphean complexes are distinguished on the basis of data on geochronology and evolution of geodynamic settings in the region. The reported materials considerably change our ideas of the age and lateral persistence of composition of the earlier recognized ancient regional horizons: Kabyrza (R2), West Siberian (R3), Belka (V), and their analogs on the adjacent territories. It is shown that the geodynamic development of the Altai-Sayan Folded Area is principally similar to the development of the Baikal-Patom Folded Area.