## 2 Hypothesis and Research Objectives  
As presented before, the Zarafshon catchment basin covers a diversity of geological formations of which the origin dates back to Oligocene. This was when, as mentioned in [22], a Jurassic basin filled with continental sediments, under the pressure exerted by the Hindustan continental plate, and generated the Pamir-Alay system. Therefore, it is to be expected that the materials of which the Zarafshon valley is made up to contain a significant proportion of crustal matter. In time, due to weathering, this tends to be transported by the river and its tributaries as suspended load and deposited on river beds and river banks, as the mineral constituents of soils. Accordingly, the main goals of this study consist of:  
(i) to verify to what extent the geochemistry of depositional material, i.e., sediments and soils, can be related to crustal material, better approximated by UCC [17] \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Element** & **Sediment** & **CSU** & **Soils** & **CSU** & **UCC** & **NASC** & **PAAS** & **SMWR** & **AWSS** \\ \hline SiO\({}_{2}\) & 62.75 & 12.65 & 59.39 & 9.7 & 66.62 & 64.48 & 62.8 & 54.76 & 54.34 \\ TiO\({}_{2}\) & 0.62 & 0.22 & 0.83 & 1.06 & 0.64 & 0.72 & 1 & 0.65 & 0.73 \\ Al\({}_{2}\)O\({}_{3}\) & 9.9 & 3.52 & 12.92 & 4.07 & 15.4 & 16.9 & 2.2 & 16.31 & 16.48 \\ FeO & 3.79 & 2.5 & 5.78 & 2.01 & 5.04 & 5.7 & 18.9 & 6.47 & 7.47 \\ MnO\({}_{2}\) & 0.07 & 0.07 & 0.09 & 0.03 & 0.1 & 0.06 & 0.11 & 0.15 & 0.22 \\ MgO & 6.32 & 3.42 & 5.8 & 2.72 & 2.48 & 2.85 & — & 2.39 & 2.09 \\ CaO & 10.59 & 10.71 & 9.46 & 9.06 & 3.59 & 3.56 & 1.3 & 3.64 & 3.62 \\ K\({}_{2}\)O & 2.4 & 0.99 & 2.83 & 0.79 & 2.8 & 3.99 & 3.7 & 2.59 & 2.04 \\ Na\({}_{2}\)O & 1.4 & 0.79 & 0.9 & 0.41 & 3.27 & 1.15 & 1.2 & 1.11 & 0.96 \\ Sc & 9.6 & 4 & 11 & 5 & 14 & 15 & 16 & 14 & 18 \\ V & 101 & 56 & 254 & 1500 & 97 & — & — & 120 & 129 \\ Cr & 71 & 40 & 90 & 57 & 92 & 124 & 110 & 85 & 130 \\ Co & 11.5 & 6.4 & 14.5 & 7.1 & 17.3 & — & — & 19 & 22.5 \\ Ni & 46 & 32 & 65 & 31 & 47 & 58 & 55 & 50 & 74 \\ Zn & 102 & 57 & 119 & 54 & 67 & — & — & 130 & 208 \\ As & 63 & 254 & 84 & 600 & 4.8 & 28.4 & — & 14 & 36.3 \\ Br & 2.6 & 4.3 & 1.9 & 1.6 & 1.6 & 0.9 & — & 9 & 21.5 \\ Rb & 92 & 41 & 103 & 39 & 84 & 126 & 160 & 77.0 & 79 \\ Sr & 143 & 63 & 177 & 100 & 320 & 142 & 200 & 150.0 & 187 \\ Zr & 220 & 133 & 210 & 101 & 193 & 200 & 210 & 150.0 & 160 \\ Sb & 59 & 560 & 38 & 270 & 0.4 & — & — & 1.4 & 2.2 \\ Cs & 4.5 & 570 & 7.5 & 3.6 & 4.9 & 5.2 & 15 & 5.2 & 6.3 \\ Ba & 724 & 450 & 784 & 500 & 624 & 636 & 650 & 500 & 522 \\ La & 28 & 14 & 32 & 12 & 31 & 31 & 38.2 & 32 & 37 \\ Ce & 53 & 26 & 61 & 25 & 63 & 67 & 79.6 & 68 & 73.6 \\ Nd & 27 & 15 & 32 & 17 & 27 & 27 & 33.9 & 29 & 32.2 \\ Sm & 5 & 2.5 & 6.3 & 3.4 & 4.7 & 5.6 & 5.6 & 5.8 & 6.1 \\ Eu & 0.9 & 0.6 & 1.1 & 0.8 & 1 & 1.2 & 1.1 & 1.4 & 1.3 \\ Gd & 3.9 & 3.3 & 2.9 & 2.4 & 4 & — & 4.7 & 5.6 & 5.3 \\ Tb & 0.7 & 0.3 & 1 & 0.4 & 0.7 & 0.9 & 0.8 & 0.8 & 0.8 \\ Tm & 0.3 & 0.3 & 0.5 & 0.5 & 0.3 & — & 0.4 & 0.4 & 0.4 \\ Yb & 1.9 & 1.2 & 2.2 & 1.5 & 2 & 3.1 & 2.8 & 2.5 & 2.1 \\ Hf & 5.5 & 3 & 5.8 & 2.6 & 5.3 & 6.3 & — & 4.4 & 4 \\ Ta & 0.8 & 0.4 & 1 & 0.5 & 0.9 & 1.12 & 14.6 & 0.9 & 1.3 \\ W & 2.5 & 5.7 & 2.8 & 2.7 & 1.9 & 2.1 & — & 1.4 & 2 \\ Hg & 2.5 & 14.7 & 1.1 & 4.5 & 0.1 & — & — & 0.1 & — \\ Th & 8.9 & 4.3 & 10.9 & 3.5 & 10.5 & 12.3 & 3.2 & 10 & 12.1 \\ U & 3 & 1.5 & 3.9 & 1.7 & 2.7 & 2.7 & — & 2.4 & 3.3 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The mass fraction of investigated elements in sediments and soils as well as the main literature references: UCC [17]; North American Shale Composite NASC [18]; Post Archaean Australian Shale (PAAS) [8]; Suspended Matter of the World’s Rivers (SMWR) [19]; as well as Average World Suspended Sediments (AWSS) [20]. Oxides’ mass fraction expressed in wt.%, in mg/kg for other elements, excepting Hg of which the mass fraction is expressed in ug/kg. CSU represents the Combined Standard Uncertainty [21].