Figure 1: Secular variations in δ¹³C of Late Proterozoic marine carbonates from different stratigraphic groups. Ages of stratigraphic groups were estimated from the best geochronologic information presently available. Figure is taken from Derry et al. (1992). Negative excursion in the δ¹³C curve, according to the model (Ivlev, 2016), correspond to the onset of “greenhouse” period.