Home – Home – Jornals – Russian Geology and Geophysics 2001 number 3

Three major stages of the evolution of sedimentation settings have been refined by lithofacies, geochemical, and microphytological studies. They correspond to the sequential changes of paleobasins: taphrogenic passive margin of the continent, back-arc basin, and foreland. Peculiarities of the paleogeographic zonation of each paleobasin have been determined according to facies analysis of transverse sections. The volume of stagnant conditions tends to increase up the section, reaching its maximum in the pre-Vendian time. On the basis of the reconstructions and actuopaleontological comparison, an ecobiological interpretation of some morphotypes of organic-walled microfossils (OM) has been proposed. Green and brown algae and bacterial associations characteristic of paleobasin zones of various depths have been identified. It has been proven that the appearance of new traits in some OM occurred at the Riphean-Vendian boundary, against the background of a change in the sedimentation pattern. The newly appearing species belong mainly to OM considered to be ancestors of green algae. It is suggested that the formation of the carbon component of the Precambrian aleuropelites was considerably contributed by benthic bacterial associations.