Riphean stratotype mudrocks composition and some paleoclimate quantitative characteristics

The object of research is Lower, Middle and Upper Riphean mudrocks in the stratotype area – southern Urals western slope Bashkirian megaanticlinorium. We analyzed major element oxides composition of the 154 samples selected from shales and mudstones.Research method. Mean annual temperature (MAT) and precipitation (MAP), also as Köppen aridity index (AIKöppen) was calculated by using different modern approach for ancient catchments. Such computations became possible thanks to CIA values corrected via Al2O3–(CaO* + Na2O)–K2O diagram and granites actual (not predicted) weathering trend in humid temperate climate. In addition, we apply not only strata but RW-index value clusterization for our data base.Results. According to estimated paleotemperature values different Riphean catchment areas may be considered as the they existed in humid temperate or cold arid climate. However calculated MAP and AIKöppen are more likely to be invalid through positive correlation between MAP and MAT variables. That is why we also present few examples of MAP estimation for Upper Riphean era by using AIKöppen boundary values and MAT values.Conclusions. We think that such reconstruction tactics as paleotemperature evaluation in complex with subsequent applying of Köppen aridity index and the paleoclimate mineral proxies are the best for the quantitative paleoclimate characteristics estimation for Precambrian and, more than likely, beyond. This approach makes possible computation of the MAP lower limit for humid climates and MAP upper limit for arid climates.

Riphean, Bashkirian meganticlinorium, mudrocks, major element oxides, paleoclimate, mean annual temperature, mean annul precipitation