## 5 Results and Discussion
### Trace Elements  
More data concerning the origin of investigated sedimentary materials can be inferred analyzing the distribution of trace elements and especially, as mentioned in the Introduction, of those considered incompatible and insoluble such as Sc, Zr, La, Ce, Nd, Sm, Eu, Gd, Tm, Yb, Th as well as U and, to a lower extent, Cr and Ni [6, 7, 40]. Notably, the felsic rocks are richer in Th and light REE, whereas mafic rocks contain more Sc, Cr, Co, Ni and an increased fraction of heavy REE [41]. In this regard, Sc of average mass fraction is less than 20 mg/kg in felsic rocks but increases to 20-40 mg/kg in mafic rocks, showing it to be one of the most appropriate discriminating elements [42]. In the case of investigated sediments and soils, Sc mass fractions were 9.56 \(\pm\) 4 and 11.4 \(\pm\) 4.6 mg/kg, respectively, confirming the previous inference concerning the felsic origin of Zarafshon valley sedimentary material. The same finding was confirmed by discriminating Th/Co vs. La/Sc bi-plot [43] (Figure 5a) and ternary Sc-La-Th [7, 44] diagram (Figure 5b). On both diagrams, the majority of Zarafshon experimental data regarding either sediments or soils are distributed around UCC [17] and NASC [18]. Moreover, on the Th/Co vs. La/Sc bi-plot [43], all Zarafshon data are closely grouped on the felsic sector of discriminating bi-plot reproduced in Figure 5a. Two relatively closer bi-plots La/Th vs. Hf (Figure 6a) [45] and Th/Sc vs. Zr/Sc (Figure 6b) [8, 46, 47] provide a new type of information concerning not only the source material, but also the past processes that have been shaping the current position. Indeed, Hf has an increasing tendency to be enriched during the erosion of ancient (meta) sedimentary rocks. The mineral zircon, in turn, showed to be extremely resilient during recycling, so that the higher the Zr mass fraction, the larger the sedimentary material sorting and recycling [48]. In this regard, both bi-plots confirm previous inferences concerning the felsic nature of investigated sediments and soils, as well as reducing the cycle of erosion and recycling, i.e., a relatively young material. Only sediments and soils collected around the Fondarya tributary, the Kumargi Poyon, Yangob and Chore estuaries, showed a mixed felsic/basic source characterized by a higher La/Th ratio simul  
Figure 5: Discriminating bi-plots La/Th vs Hf (**a**) and Th/Sc vs. Zr/Sc; (**b**) confirming the felsic origin of Zarafshon sediments and soils as well as the absence of a significant recycling of sedimentary material. Hf mass fraction. On contrary, the increased mass fraction of Hf together with reduced values of La/Th ratio suggest the presence of old sediment sources in the Mastchohi kuhi, Shahriston and some regions of Panjekent [38]. Rare Earth Elements (REE) represent a group of 17 elements, including 15 LN, Sc and Y, all of them playing a significant role in provenance studies. Traditionally, LN are classified in light LN or light REE (LREE)--La to Sm and heavy REE (HREE)--from Eu to Lu. Since REE are not easily fractionated during sedimentation, they keep the \"fingerprints\" of the mother rocks making them helpful in establishing their origin [48; 49]. Moreover, the Eu, which can exist in two valence states (Eu\({}^{2+}\) and Eu\({}^{3+}\)) in its bivalent state due to a smaller ionic radius, can be substituted by Sr\({}^{2+}\) ions in plagioclase feldspars. As this process takes place only in reducing conditions which can be found only in the superior mantle or lower crust, this leads to a distinctly negative anomaly in rocks coming from the upper crust [49; 50]. Another distinctive characteristic of LN, useful in evidencing the rock origin, is related to the asymmetry of LREE and HREE in felsic rocks being enriched in LREE with respect to mafic ones, depleted in this category of REE.