## 2 Materials and Methods  
### Sedimentary Basins in the Study Area: Origin and Structure  
The study area includes the southern part of the EEP, Scythian plate and part of the Alpine-Mediterranean fold belt (the Caucas and East Carpathians). The tectonic history of this area represents a long period from the pre-Riphean (more than 1600 MA), when the ancient crystalline basement of the East European Platform was formed, to the Miocene with the formation of the Greater Caucas and the Black Sea depression (as a part of the Alpine Mediterranean fold belt). Most of the Scythian plate, except of its northwestern, southwestern and southeastern margins, was located within the Sarmatian shield divided by the Riphean and partially Late Devonian rafts. The Scythian plate represents a vast region of the modern Pre-Caucasus area, where the orogenic processes in the Carboniferous formed the Paleozoic (Hercynian) basement. Further development of this area, associated with the Arabia-Eurasia plate collision, resulted in formation of the extensive depressions that later evolved into sedimentary basins. Here we provide a description of the main sedimentary basins in the study area (Figure 1). For convenience, we use the abbreviations from this figure. The Dnieper-Donets basin was initially formed as an ancient rift. Recent paleotectonic reconstructions [15] indicate that the development of the Dnieper-Donets depression included different stages. Initially, the riftogenesis was induced by mantle activity in the Late Devonian with simultaneous sedimentation under the conditions of marine transgression and subsequent regression. The next sedimentation stage was related to another marine transgression in the Middle Carboniferous. The deep depression in the southeastern part of the Dnieper-Donets basin was also developed in the Late Devonian--Early Carboniferous. The Pripyat depression (PD) evolved almost simultaneously with the Dnieper-Donets basin on its west end in the Late Hercynian [16]. At that time, the terrigenous and carbonate rocks accumulated during the Devonian and Carboniferous with total thickness of 425 m above the existing Late Proterozoic (Riphean and Vendian) terrigenous deposits. Next, during the Early and Middle Carboniferous, the carbonate-terrigenous and coal-bearing deposits were accumulated with the total thickness 170-400 m. In the Late Carboniferous, the regional rise of the territory occurred completing the rifting process [17]. The Caspian basin is one of the largest sedimentary basins in the study area. The northern part of the basin is a part of the Scythian plate, and the southern one is associated with the Alpine-Mediterranean Cenozoic fold belt region. The sea basin within the present Caspian Sea appeared in Paleozoic, its shoreline has changed many times since then as a result of repeating transgressions and regressions which continue to this day due to climate changes [18]. Five main crustal blocks are defined within this region [19]: The North Caspian Basin (that is a part of the Pre-Caspian depression), the Middle Caspian Basin, the Apsheron Sill (separating the northern and middle Caspian basins), the Mangyshak Sill (separating the middle and south Caspian basins) and the South Caspian Basin. Recent studies have shown that the rapid accumulation of sediments occurred within the South Caspian happened during the Mesozoic-Paleogene time. According to the existing maps, the thickness of sediments in the South Caspian increases from the north to the south, although this conclusion is not verified by seismic data. The Pre-Caspian basin (PCB), sometimes referred as the North Caspian basin, is one of the deepest basins in the world, having more than 20 km sediments in the central part. Being a part of the East European Platform, the basin is bordered by the Uralides and the Northern Ustyurt Block in the east and by the Karpinsky rift in the southwest. The underlying basement represents either oceanic or thinned continental crust likely affected by several rifting processes between the Riphean and the Triassic.