## 1 Introduction  
The Zarafshon River originates at the Zarafshon glacier, at an altitude of 2775 m, at the junction of the Turkestan and Zarafshon ranges, both of them belonging to the western sector of the Pamir-Alay system [1]. The initial part of the river, about 300 km long, lies in a narrow, deep valley. On the southern left bank, flowing between the Turkestan and Zarafshon ranges, it receives the Yagnob, Arthuch and Mogiyon rivers, as well as many small tributaries (Figure 1) [1; 2; 3]. After the city of Panaikent, the river follows a flat region, crosses the Tajikistan-Uzbekistan border, passes Samarkand and Bukhara, to finally disappear in the desert in the vicinity of the city of Karakul, without reaching the Amu Darya River [3; 4]. Its catchment basin, with an area of 17,700 km\({}^{2}\), covers diverse geological formations spread from the alpine zone, 3200-3500 m above sea level, to less than 150 m elevation westward towards the city of Karakul. In the Zarafshon mountain gorges, below 1500 m there are small areas of semi-savannahs as well as mountain forests. Here, regosols are prevalent [5], while in the western sector of Zarafshon Valley luvisols formed on loess deposits are common. Moreover, in mountain gorges, terraces of alluvial  
The \"Zarafshon\" name, which in Farsi means \"spreader of gold\", reflects the existence of ore fields along the river valley which, together with other outcrops of nonferrous ores makes it a mineral rich province requiring a detailed investigation. Although the total population of Zarafshon valley does not exceed 400,000 inhabitants, mainly populating small villages, the existence of non-ferrous ore outcrops could represent the main source of down-stream contamination, previously analyzed in [6]. For this reason, the distribution of major and rock-forming elements as well as of incompatible lithophile elements such as Sc, Ti, V, Cr, Zr, lanthanides (LN) Th or more soluble U together with siderophile Co and Ni were chosen for this study. All of them play a significant role in geochemistry and pedology as tracers of the origin of natural material which, disintegrated during weathering and erosion, represents the main constituents of sediments and soils [7; 8; 9; 10]. Besides them, there are other trace elements such as V, Cr, Co, Ni, Zn, As, Sb, or Hg, intensively used in diverse industrial processes, and, the presence of which, at levels significantly exceeding the natural ones, are related to an anthropogenic contamination which could be industrial [11; 12] or due to urban as well as rural agglomerations [13]. According to [14], soil is a result of the combined action of weather, geographic relief, organisms and human activity on the parent mineral substrate, all of them continuously interacting. The actual soil is no older than Pleistocene, i.e., 2.59 Ma almost coincident with the onset of Northern hemisphere glaciation. In turn, sediments represent a fragmented mineral substrate under the action of weathering and erosion and which is transported at long distances by the action of water, wind or ice and finally deposited. With respect to soil, sediments consist of unconsolidated clastic material with a reduced amount of organic matter. When consolidated by natural cementation processes, sediments turn into sedimentary rocks such as siltstone, sandstone, shale, etc. Both sediments and soils preserve the fingerprint of the parental mineral substrate, which, under the action of external factors, evolve in a different manner. Collected from the same places and investigated in tandem, these sedimentary materials could bring a bonus of information concerning the local geochemistry as well as their interrelationship. In this regard, in the period of spring-autumn, between 2015 and 2018, the Institute of Water Problems, Hydropower and Ecology of the Academy of Science of Tajikistan organized a field expedition to collect the most representative samples of sediments and soils from the Tajik sector of Zarafshon catching basin.