The article gives a comparative description of the hydrochemical situation of two adjacent deposits (Dzhiginskoye and Blagoveshchenskoye) located in the junction zone of the northwestern end of the meganticlinorium of the Greater Caucasus, the Kerch–Taman and West Kuban troughs. Despite more than a century and a half-century of study, to date, there is no common opinion on the boundaries, the nature of the ongoing geological processes, as well as the conditions for the formation of oil and gas deposits in the territory under consideration. As a result of the comparison of hydrochemical situation, two tendencies are revealed that are characteristic of the Miocene deposits of Blagoveshchenskaya and Dzhiginskaya areas: 1) an increase in the mineralization of stratal waters along a section from Pontus to Sarmatians, and then its decrease from Sarmatians to Chokrakians; 2) a change in the type of waters from chloride-magnesium in the section of Pontus to bicarbonate sodium in the section of Chokrak. Desalination of the waters of the lower Sarmatian, Karagan and Chokrak, accompanied by a change in the type of water, is associated with the introduction of epigenetic Maikop waters squeezed from clay, which has an impulse character. The similarity of the hydrochemical situation of Miocene sediments over comparable areas indicates the unity of paleogeographical conditions and the generality of the geological processes that influence its formation. An essential difference between the hydrochemical situation of the Miocene complex of the Dzhiginskaya area in comparison with Blagoveshchenskaya is that regardless of the amount of mineralization, the water of the first one is hydrocarbonate–sodium.