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. 471 Amon E.O. T he Middle and Late Cretaceous paleogeography of the Great Urals is considered.
Emphasis is placed on the sea basins existing in the region.
A nomenclature of the basins is proposed. The temporal variations in their outlines and areas are traced. The positions of straits and the directions of biota migration are outlined. 484 Kontorovich V.A. T he geologic structure and petroleum potential of the Bajocian-Bathonian deposits in southeastern West Siberia are considered. Such are the areas where the marine sediments of the Vasyugan Formation are replaced by the Naunak Formation, deposited under continental conditions, and the Paleozoic-Mesozoic boundary zone is made up of permeable rocks.