α^AlE indices of Riphean clay rocks of the Southern Urals and weathering features (first attempt at analysis)

Research subject. The clay rocks (fine-grained clayey siltstones, shales and mudstones) of the Lower, Middle and Upper Riphean of the Bashkir megaanticlinorium of the Southern Urals (Riphean stratotype).Materials and Methods. The αAlE values are calculated for clay rocks based on the bulk chemical composition (major rock-forming oxides and some trace elements), which makes it possible to judge the intensity of weathering of source rocks in catchments. A comparison was made of the αAlE values characteristic of silts and particulate suspended matter of a number of modern rivers in South Africa, Northern Eurasia and North America, as well as clay rocks of a number of the Riphean formations of the Southern Urals.Results. The αAlE curves for clay rocks of the various Riphean formations of the Southern Urals are significantly similar to each other. They are characterized by moderate values of αAlNa, fairly high values of αAlСa and αAlSr, and predominantly low values of a number of other αAlЕs. For clay rocks of most stratigraphic levels of the Riphean stratotype, αAlNaaverage are close or comparable to those characteristic of suspensions in the rivers of temperate climate. The average αAlK values in shales are also comparable to those calculated for particulate suspended matter in the rivers of temperate climate, for example, the Lena or the Hudson. The silts of the rivers of South Africa, on the contrary, have slightly higher αAlK. At the same time, the shales of the Riphean stratotype have slightly higher αAlВaverage than the silts of the rivers of South Africa or the particulate suspended matter of the rivers of the temperate climatic zone of Northern Eurasia or North America.Conclusions. Based on “direct” comparison of αAlЕ for clayey rocks of the Riphean stratotype and those for silts and particulate suspended matter of a number of rivers in South Africa, Northern Eurasia and North America, we can conclude that the eras of accumulation of terrigenous deposits of the Riphean of the Southern Urals were characterized by a climate reminiscent of the modern temperate climate of the northern hemispheres.

Riphean, Southern Urals, clay rocks, αAlE indices, weathering