Near-Surface Temperature and Climate 1750–600 Ma Ago by the Example of Clay Rocks of the Riphean Stratotype (the Southern Urals)

The results of calculating the near-surface mean annual temperatures (MAT) and the mean annual precipitation (“simple” and “more rational” variants) for source areas using the bulk chemical composition of clay rocks of the Riphean stratotype (the western slope of the Southern Urals, Bashkirian meganticlinorium) are presented. It is found that during most of the time interval 1750–600 Ma, the climate was comparable to the climate which, according to the classification by L. Zhang et al. [1], is considered temperate (9°C ≤ MAT < 23°C) and less often tropical (MAT > 23°C) or dry cold (MAT < 18°C). The opinions are stated about the relationship of the Riphean paleoclimate both with the sublatitudinal drift of crustal blocks and with various subglobal and local events. For example, at the beginning of the Middle Riphean, MATavg decreased from more than 22°C (Mashak age) to ~13°C (Zigaza-Komarovo age). This was due to sequentially (1) an increase in the concentrations of CO2 and other volcanic gases in the atmosphere during the activity of the Mashak large igneous province; (2) a decrease in the CO2 content as a result of intensive weathering of the mafic igneous rocks of the same province. At the end of the Riphean, the MATavg values could have been affected by the drift of Baltica to middle (30°–60° S) latitudes, which was reconstructed from paleomagnetic data.