Biotic events and positive delta C-carb anomaly at 2.3-2.06 Ga

A comprehensive analysis of taxonomic composition of pre-Riphean silicified and organic-walled microfossils described in publications is performed and dynamics of stromatolite abundance during the Archean and Paleoproterozoic is reconstructed based on a calculation of a number of stromatolite-bearin g formations in seven time periods 300-400 m.y. long for the Archean and 20 0-300 m.y. long for the Paleoproterozoic. It is shown that the Jatulian pos itive delta(13)C(carb) anomaly, the largest one in the Earth's history that occurred 2.3-2.06 Ga ago was not related to evolutionary innovations in th e ancient microbiota but was synchronous with the sharpest, in geological h istory, increase in the global stromatolite abundance. This event was contr olled by a favorable combination of climatic, paleogeographic, and geodynam ic factors and occurred under condition of the prevalence of the mantle flu x into the World ocean over the continental runoff. Simultaneously, the tra nsition to "normal marine" delta(13)C(carb) values that marked the terminat ion of the Jatulian anomaly was accompanied by a slight increase in abundan ce of Paleoproterozoic stromatolites, which was reduced again only 1.8-1.6 Ga ago. It is concluded that the Jatulian anomaly was mainly related to the unique-scale expansion of cyanobacterial ecosystems that is recorded in st romatolite succession and occurred against the background of increasing oxy genation of atmosphere and surficial part of hydrosphere. Peculiarities of the C-isotope and paleontological records of the second half of the Paleopr oterozoic are briefly discussed with consideration of probable factors resp onsible for the disappearance of the anomaly in question.