Variations in the content of hydrogenic elements in Riphean clay rocks of the Southern Urals
DOI:
https://doi.org/10.17308/geology/1609-0691/2026/1/33-42Keywords:
bulk chemical composition, clay rocks, hydrogenic elements, Riphean, Southern UralsAbstract
Introduction: the content of hydrogenic elements (Mg, Na and Sr) in clay rocks (mudstones, shales, fine-grained siltstones) of the Riphean stratotype (Bashkir meganticlinorium, Southern Urals) was analyzed. The formation of sedimentary sequences of this section covers an interval from ~1750 to 600 million years.
Methodology: data on the contents of a number of rock-forming oxides (~200 samples) and Sr (~100 samples) in clay rocks obtained by X-ray fluorescence analysis and ICP-MS were used. The Mg/Al, Na/Al, and Sr/Al values were calculated for individual samples and their average values for formations and subformations of the Riphean stratotype. An analysis of the distribution of average Element/Al values was carried out in the time interval from ~1750 to 600 Ma. The obtained curves were compared with the distribution in the same time interval of continental and oceanic large igneous provinces, orogenic granitoids, and dolerite dikes.
Conclusion: the Mg and Sr contents in Riphean clay rocks of the Southern Urals are comparable to those in the post-Archean average shale (PAAS), while Na is significantly lower. Variations in Mg and Na contents are symbatic throughout the Riphean. For Sr, Mg, and Na, this is only true for the Late Riphean. There is generally no visible correlation between the epochs of significant basalt formation in the upper levels of the continental crust and on its surface and the epochs of decreasing Mg content in clay rocks of the Riphean stratotype, although one can be assumed for a number of intervals.
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