AGE TRANSFORMATIONS IN THE FACIES-ECOLOGI CAL STRUCTURE OF PRECAMBRIAN BIOTAS AND STRATIGRAPHY OF THE RIPHEAN

The representative regional sequences of the Riphean Siberian and Ural ian microfossils are characterized by extremely rare new morphotypes. The most representative units in sections follow large regional breaks and/or thick units of sediments of specific shallow genesis. This per mits one to consider biota transformations to be the result of the per iodic critical states of the paleoenvironment, which were caused by th e cyclic evolution of Riphean basins. Most biotic transformations, pro bably, led to the minimization of the consequences of the abiotic stre ss during the most intense regressions and to the restoration of the d isturbed area of biota distribution after the end of unfavorable condi tions. In Proterozoic basins a complex lateral biotic structure formed , which had a spatially limited optimal zone with organisms of the mos t complex structures. This was a compromise between the biota tendency to provide its long stable existence and its progressing biological d ifferentiation.