## 4 Discussion  
In this section we discuss the corrected thickness and density maps for major sedimentary deposits within the study area. Very principal changes have been obtained for the Black Sea and adjacent basins. The sedimentary basins in the western and eastern parts of the Black Sea are already different in the initial model; the eastern basin is much shallow than the western one (Figure 3a). In the corrected model we found also a strong difference between the northern and southern parts of the East Black Sea (Figure 7). The deepest part of the western Black Sea basin is now shifted to the north and joined to the Indolo-Kuban basin. The upper part of the sedimentary cover of the Black Sea was extensively studied by seismic methods (CDP), which results have been summarized in [24; 57; 58]. The sedimentary map, presented in these papers, is characterized by a completely opposite pattern; the northeastern part of the basin is much shallow than the southeastern part. However, the deepest boundary shown in these studies is represented by the top of Cretaceous sediments, which is considered as basement. The density of these sediments might be relatively low even if the seismic velocities are normal, e.g., [59]. Therefore, we have to conclude that the effect of the Cretaceous and possibly even older layers is also significant and may not be ignored in a complete model. The density changes, obtained for the Black Sea basins are not significant because the total sedimentary thickness is quite large (Figure 8). North of the Black Sea, some gradual density changes from north to south have been revealed for the Black Sea depression. These changes are mainly due to the differences in sedimentary types and their age. The density gradient (1.8 to 2.25 g/cm\({}^{3}\), approximately) agrees with the presence of more dense Eocene, Jurassic, and even Paleozoic rocks underlying the upper Neogenic layer represented by carbonate, sandy-clayey and coarse-dettrial Miocene and Pliocene deposits in the southern and southwestern parts of the basin. It is clear that the Northwestern Black Sea shelf combines the structures of three tectonic regions: The EEP, the Scythian plate and the Mountain Crimea folded belt. In the new model, the Karkinit depression basin appears to be more isolated from the rest of the Western Black Sea basin, although its depth remains the same. The new model proves that the Karkinit depression developed on a previously existing deep fault. The eastern part of the Indolo-Kuban basin continues in the Pre-Caucasus in latitudinal direction and is characterized by nearly constant density (about 2.4-2.45 g/cm\({}^{3}\)), joining the western part of the similar Terek-Caspian basin. The Kuma-Manych depression is also clearly revealed as a sublatitudinal zone with the density about 2.4 g/cm\({}^{3}\). However, both models for this structure (the initial and the new ones) show similar thickness with its slight increase to the southeast while approaching the Caspian. The Greater Caucasus is  
Figure 8: (a) Corrections for the initial (vertically averaged) density of sediments; (b) final model of the average density of sediments. clearly divided into two parts, which are characterized by remarkably different structure of the lithosphere, e.g., [60]. For the West Greater Caucas we did not obtain any significant correction, which demonstrates that the initial model without sediments works well. Contrary to the western part, the East Greater Caucas is characterized by extensive sedimentary layers with the total thickness reaching 2.5 km in the initial model (Figure 3a). However, their density was previously reported as rather high. According to the density model summarized in [61], the average density of the Paleogenic rocks is 2.23 g/cm\({}^{3}\), of the Cretaceous--2.48 g/cm\({}^{3}\) and of the Jurassic and older--2.62 to 2.72 g/cm\({}^{3}\). Therefore, the top of the Cretaceous was already considered as a basement since the density of the lower layers is not much different from the crystalline crust.