The importance of Precambrian microfossils for modern biostratigraphy

A new model of the distribution of Proterozoic microorganisms is developed, based on studies of Riphean and Vendian silicified and organic-walled microfossils from the reference sections of northern Eurasia, and on their comparison with other known microfossil assemblages. Within the interval from 2.0 to 0.535 Ga, seven successive informal global microphytological units (referred to as proterohorizons) are determined: (1) Labradorian proterohorizon occupies the upper part of the Lower Proterozoic (Paleoproterozoic), 2.0–1.65 Ga; (2) Anabarian proterohorizon, Lower Riphean-lower Middle Riphean (lower and middle Mesoproterozoic), 1.65–1.2 Ga; (3) Turukhanian proterohorizon, upper Middle Riphean (upper Mesoproterozoic), 1.2–1.03 Ga; (4) Uchuromayan proterohorizon, lower Upper Riphean (lower Neoproterozoic), 1.03–0.85 Ga; (5) Yuzhnouralian proterohorizon, upper Upper Riphean (upper Neoproterozoic without Ediacaran); (6) Amadeusian proterohorizon, Lower Vendian (Ediacaran), 0.6–0.55 Ga; and (7) Belomoryan proterohorizon, Upper Vendian (Ediacaran), 0.55–0.535 Ga.