Three fundamental stages of the Cretaceous–Neogene tectonic evolution of the Odessa Shelf and Azov Sea (northern margins of western and eastern Black Sea basins, respectively) have been documented from the analysis of reinterpreted regional seismic profiling and one-dimensional (1-D) subsidence analysis of 49 wells, for which the stratigraphic interpretation was recently revised. (1) An initial active rifting stage began within the Early Cretaceous (not later than Aptian–Albian times) and continued until the end of the Santonian in the Late Cretaceous (c. 128–83 Ma). A system of half-grabens with mainly south-dipping normal faults developed on the Odessa Shelf at this time. The most profound faulting, accompanied by volcanic activity, occurred in the NE–SW orientated Karkinit-Gubkin rift basin at the boundary between the Eastern European and Scythian platforms. The footwalls of half-grabens were exposed above sea level and subject to erosion at this time. Active extensional processes affected the western part of Azov Sea and, while the onset and cessation of these cannot be tightly constrained, they are compatible with the well constrained results from the Odessa Shelf. (2) The second tectonic stage is one of passive post-rift thermal subsidence that lasted from the Campanian (Late Cretaceous) until the end of the Middle Eocene (83–38.6 Ma). (3) The third stage of basin evolution is one of inversion tectonics in a compressional setting. Discrete inversion events occurred at the end of the Middle Eocene, during the Late Eocene, during the Early Miocene and at Middle Miocene times (c. 38.6 Ma, c. 35.4 Ma, c. 16.3 Ma, c. 10.4 Ma, respectively) and typical inversion structures developed on the Odessa Shelf, some parts of which were uplifted and significantly eroded (down to the Lower Cretaceous succession). The southern part of the Azov Sea, opening into the northernmost eastern Black Sea basin, subsided rapidly during this time; thereafter, until the Quaternary, rapid subsidence was limited to its southeastern part, which was incorporated into the Indolo-Kuban foreland basin of the Greater Caucasus orogen.

Th is paper presents the author's integrated regional studies during the last decade. Th e main purpose is to present an overall understanding of the geological structure, sedimentary basins and hydrocarbon systems of the whole Western Black Sea Zone (WBSZ). Th is study is based on original data from boreholes, seismic and gravity-magnetic surveys and hydrocarbon accumulations.Many geophysical borehole data obtained for WBSZ during the last 3-4 decades were interpreted mostly at a national level using diff erent approaches, terminology and nomenclature for the same or similar lithostratigraphic and tectonic units. Th erefore, a unifi ed approach to interpretation of borehole-seismic data and correlation of stratigraphic, sedimentological and tectonic units has a key importance for overall clarifi cation of the deep geological structure and the hydrocarbon challenges.A set of regional geological cross-sections along good quality basic seismic lines and basic boreholes was constructed. A detailed tectonic map of the WBSZ has been compiled by integrated interpretation of seismic borehole and gravitymagnetic data. Th e defi nition of hydrocarbon systems and promising exploration trends is made by source rock assessment, Oil-Oil and Oil-Source rock correlations, analyses of the reservoir/seal pairs and the hydrocarbon migration and accumulation. Genetic correlations are based on many Rock-Eval, Gas Chromatography/Mass Spectrometry (GC-MS) and carbon isotope analyses.Th e complex geological structure of the WBSZ is defi ned by four groups of tectonic units: (1) Western Black Sea basin (WBSB) -its western zone with the Kamchia and the Histria westward wedging branches (sub-basins); (2) portions of the Moesian, Scythian and East European platforms; (3) fragments of the North Dobrogea, Eastern Balkan, Eastern Srednogorie and Strandzha orogens; (4) Burgas and Babadag basins.Four diff erent oil genetic types have been identifi ed. Th ree main hydrocarbon systems with economic potential are defi ned, they relate to: WBSB and its Histria and Kamchia branches, the East-Varna trough and the Bourgas basin. Conceptual models for hydrocarbon systems and their prospect exploration trends are constructed.

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The entire Ukrainian sector of the Black Sea, which occupies its northernmost part, was studied with the interpretation of the post-1990 seismic reflection data along seismic lines having a total length of some 30 000 km. In the northern Black Sea relatively low extension of the continental crust occurred in Albian-Cenomanian times and did not cause formation of deep (sub)-oceanic basins. Rift faults formed three major rift basins. One of the ENE-WSW oriented rift basins occupied areas of the present-day Karkinit Through, Krylov-Zmiiny Uplift, Gubkin Ridge and Sulina Depression within the Odessa Shelf. Another ENE-WSW oriented basin included areas of the present-day Tetyaev High, Sorokin Trough, Crimea Mountains and Marine Continuation of the Crimean Folds. The NW-SE oriented major rift basin occupied areas of the present-day Andrusov Ridge, Eastern Black Sea Basin, Shatskiy High and Euxinian Graben. Passive, thermal (post-rift) subsidence lasted in Turonian-Middle Eocene times and occurred in marine basins with a water depth that did not exceed a few hundred meters. A strong regional compression at the end of the Middle Eocene interrupted the post-rift (thermal) subsidence of rift basins, strongly deformed the sedimentary cover and formed a large NW-SE oriented landmass. This onshore terrain occupied the central and southern parts of the Odessa Shelf and the Crimean Peninsula, and deep-water area, including the Euxinian Graben, Marine Continuation of the Crimean Folds, Sorokin Trough, Tetyaev High, Andrusov Ridge, Shatskiy High and Eastern Black Sea Basin. Up to 5 km of sediments were eroded during the time of the existence of the emerged onshore terrain. Two subsequent S-N compressional events occurred at the end of the Late Miocene and invoked folding and thrusting of the sedimentary sequences in the originally ENE-WSW Cretaceous rift basins mainly. Anticlinal structures on the Odessa Shelf underwent additional growth and numerous new anticline folds were generated on the margins of the Western Black Sea Basin, including the Sorokin Trough and Marine Continuation of Crimean Folds. During both Late Miocene compressional events broad landmasses arose across the northern Black Sea region. These onshore terrains ran in a roughly E-W direction and occupied the present-day shallow shelves and northern part of the current deep water as well as almost the whole Crimea Peninsula. Like the Late Eocene landmass, the Late Miocene onshore terrains were evidently a source of sediments into marine basins that surrounded them. The first Late Miocene compression probably coincided in time with the Messinian Salinity Crisis and it was apparently accompanied by a sharp fall of the sea level. Prior to the second Late Miocene compressional event the sea level had risen sufficiently that a considerable part of the Odessa Shelf and other parts of the middle Pontian landmass were covered, at least periodically, by a shallow sea. The present-day deep-water part of the study area began to subside rapidly in the Pliocene. The mechanical...