Clarks of concentration of some trace elements in Upper Riphean clay rocks OF Bashkirian meganticlinorium (South Urals)

Abstract

The clarke of concentration of a number of rare and trace elements in clay rocks of the Karatau Group of the Upper Riphean of the Bashkirian meganticlinorium (South Urals) was analyzed. For this purpose, from the lithostratigraphic units of the Karatau Group, in which clay rocks are present, about 90 samples of shales and mudstones with no visible signs of secondary changes (the so-called “background rocks or deposits”) were randomly selected in a number of representative sections. Determination of the contents of rare and trace elements in them is performed by the ICP-MS method. Two “geochemical standards” were used for the calculation and analysis of clarke of concentration: the average composition of the upper continental crust, UCC, and the average post-Achaean Australian shale, PAAS. In the first case, the distribution of Sc, V, Cr, Co, Ni, Cu, Zn, Ga, Rb, Sr, Y, Zr, Nb, Mo, Cs, Ba, La, Ce, Nd, Sm, Eu, Gd, Yb , Hf, Pb, Bi, Th and U, in the se­cond - Li, Sc, V, Cr, Co, Ni, Cu, Zn, Ga, Rb, Sr, Y, Zr, Nb, Mo, Cs, Ba, La, Ce, Nd, Sm, Eu, Gd, Yb, Lu, Hf, Pb, Bi, Th and U is considered. It was established that the background fine-grained clastic rocks of the Upper Riphean Karatau Group do not possess any anomalous contents of trace elements and they are comparable in their geoche­mical features with clayey rocks of different levels of the Burzyan and Jurmatau groups of Lower and Middle Riphean. From the bottom to up the section of the “diversity” of the distribution of rare and trace elements in individual samples decreases, which, on the whole, correlates with the transgressive tendency of the development of the Late Riphean sedimentary basin. Sour­ces of fine aluminosilicoclastic for the Upper Riphean deposits of the Bashkirian meganticlinorium were catchment areas, in which both acidic and basic magmatic formations were present.