## 2 Materials and Methods
### Sedimentary Basins in the Study Area: Origin and Structure
The thickness of the crust is still disputable and depends on interpretation of the high velocity layer at the base of the crust [20]. Despite being explored for about 100 years, the PCB's structure is still poorly studied. There are several hypotheses concerning the origin of the basin, with the predominant one suggesting that the basin originated as a pre-Late Devonian rift. The deepest sediments of the PCB can be of either Riphean or Devonian origin, butthe oldest rocks found in wells are of the Early and Middle Devonian age. According to existing seismic profiles, there exist three major layers constituting the basin: The subsalt, salt (Lower Permian) and upper layers. The sediments forming the subsalt layer differ in the central part of the basin and on its margins [21]. The Manych (Kuma-Manych) depression (KMD) is located at the border between the EEP and Scythian plate; it was formed within the fault zone that existed from the very beginning of the plate history. The KMD consists of a number of narrow en-echelon basins formed in compression environment during the continental plate collision. According to a long-standing hypothesis, the KMD is an ancient strait between the basins of the future Caspian and Black seas. Modern studies [22] confirm the existence of even four Pleistocene straits. The origin of the Black Sea basin, adjoined to the Alpine-Mediterranean belt in the south, is still a subject of discussions. Its central part, which is about 15 km thick, overlays a suboceanic crust (\(\sim\)25 km) and was formed during the Paleozoic-Cenozoic [23]. The structure of the eastern part is nearly symmetrical, while the Western Black Sea Basin is characterized by remarkable asymmetry. Both Western and Eastern Black Sea basins have an oceanic or highly extended continental crust; they are separated by the Andrusov and Arkhangelsky ridges with a continental crust. [PERSON] et al. [24] concluded that the Eastern Black Sea Basin was originated through rifting along an Early Cretaceous volcanic arc. The Karkinit depression (KD) is located at the Black Sea border on the western coast of the Crimea Peninsula. However, being a part of the northwestern shallow water area of the Black Sea, the Western Crimea shelf has its own history and is different from the northwestern shelf of the Black Sea. The depression was formed on an ancient (pre-Riphean) deep fault [25] and is characterized by large thickness of the Cretaceous and Paleocene deposits. The overall thickness of sediments is about 6-7 km. The Indolo-Kuban basin (IKB) was developed as a depression in the front of the plate collision belt. The depression extends from the Indol river to the east along the edge of the eastern part of the Mountainous Crimea, along the Kerch Peninsula to the Sea of Azov and then in the Pre-Caucasus towards the Kuban river delta. Geophysical data indicates that the depression, filled with thick sediments, is narrow and asymmetrical. In its western part (the Indol basin) the total strata thickness is about 4, 5 km; while in the central part (north of Kerch) the sediments are 10-13 km thick. In the eastern part of the basin the sedimentary thickness is approximately 3 km. The Indolo-Kuban basin is usually considered as a part of the large Azov-Kuban basin filled with Cretaceous to Cenozoic sediments [26]. The Terek-Caspian foredeep (TCF) is also related to the continental plate collision, being a foredeep of the East Greater Caucasus filled mainly with Meso-Cenozoic sediments with a Hercynian basement [27]. The southern part of the TCF experienced an intense subsidence due to the Stavropol uplift in Pliocene that separated the Indolo-Kuban (Azov-Kuban) and Terek-Caspian basins. The upper layer consists of the marine and continental Upper Pliocene and Quaternary deposits, mostly represented by ancient and modern alluvial river sediments. The Black Sea Depression (BSD), adjacent to the Black Sea basin and the southern part of the EEP, is located at the north border on the Ukrainian Shield.