PERIODICITY OF DEPOSITION IN THE SILURIAN AND RELATIONSHIPS OF GLOBAL GEOLOGICAL EVENTS IN THE MIDDLE PALEOZOIC OF THE SOUTHWESTERN MARGIN OF THE SIBERIAN CONTINENT Available to Purchase

Alignments of the Altai Silurian stratigraphic scale, which is the reference one for the entire south of West Siberia, and standard scale for this system are clarified. The cyclic structure of the succession is analyzed, and four transgressive-regressive cycles combined by pairs in two depositional phases A and B are recognized. It is shown that these cycles are connected with eustatic sea level changes. “Deepenings” of the basin at starts of the first three cycles are estimated at no less than 60–100 m. Anoxia appeared at these eustatic rises. They are marked by sedimentary and simultaneously biological events: Chineta (persculptus), Syrovatiy (sedgwicki), and Chesnokovka (Cyrtograptus). General preliminary analysis is given to a single Silurian–Devonian succession of eustatic cycles established in shallow shelf facies in the south of West Siberia. Cycles of three orders and periodicity in a combination of first-order (lowest magnitude) cycles are revealed. It is established that the regular pattern of eustatic fluctuations of sea level, fixed in sedimentation, completely agree with the regular pattern in the evolution of dechenelloid trilobites, being their mirror reflection. The conclusion is made that the factors determining the parallel character of processes of deposition and evolution of benthic organisms, like trilobites, are the same.