Geologicheskii Vestnik

The results of a comparison of various indicator ratios of trace elements-indicators of the composition of provenances for clay rocks of the Middle Riphean Avzyan Formation and the Upper Riphean Biryan Subformation of the Zilmerdak Formation (Bashkirian meganticlinorium, Southern Urals) are analyzed. The formation of these two objects is separated by a hiatus, the maximum duration of which can reach 250 Ma. The study is based on data on the content of trace elements in 28 and 16 samples of clay / fine-grained clastic rocks, respectively, of the Avzyan Formation and the Biryan Subformation from the collections of E.Z. Gareev and the author, obtained by the ICP-MS method at the IGG Ural Branch of the Russian Academy of Sciences (Yekaterinburg). Distribution of individual and average data points of clay rocks of named objects on diagrams La / Sc — Th / Co, Sc — Th / Sc, Eu / Eu* — Th / Sc, Ni — V — 10*Th, Th — La — Sc, Y / Ni — Cr / V, Cr / Th — Th / Sc, and Hf — La / Th are largely comparable. The spectra of rare earth elements normalized to chondrite are also comparable. Only on the Th — Th / U diagram the distribution of the data points has a slightly different form. This either indicates the invariance of the composition of the provenances for almost 250 Ma, or suggests that the duration of the pre-Upper Riphean hiatus was not so long, or the author’s analytics is “lame”, or there are other reasons.

Southern Urals, Bashkirian meganticlinorium, Middle and Upper Riphean boundary, provenances, fine-grained clastic rocks, geochemistry

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