On the relationship between α^Al indices and the ratios of a number of trace elements – indicators of rock composition in paleo-catchments (on the example of the Riphean and Vendian clay rocks of the Southern and Middle Urals and the Shkapovo-Shikhan depression)

Research subject. Clay rocks (clay siltstones, shales and mudstones) of a number of Riphean stratigraphic units of the Bashkir megaanticlinorium, as well as the Vendian Shkapovo-Shikhan depression and the Kvarkush-Kamennogorsk megaanticlinorium. Methods. Calculation of αAl values based on the data on the bulk chemical composition of clay rocks and the analysis of their correlation links with the ratios (e.g., Th/Sc, (La/Yb)N, etc.) of a number of trace elements that are indicators of rock composition in paleo-catchments. In this case, any statistically significant correlation between the alpha index values and the indicator ratios was considered to be a consequence of the control of the α index values by the rock composition in paleo-catchments, and vice versa. Results. For both relatively small (7–8 analyses) and medium (22 or more analyses) analytical datasets, quite different relationships were established between the αAl indices and the ratios of the elements – indicators of the composition of rocks that make up the paleo-catchments. Conclusions. Similar to many other exospheric lithogeochemical indicators, the use of α indices without analyzing the influence of various factors thereon does not provide correct information on the intensity of weathering