To the question of local stratigraphic subdivisions of Cretaceous sediments of the Ukrainian sector of the northwestern shelf of the Black Sea. Article 2. Upper cretaceous

Introduction. Upper Cretaceous deposits are widespread on the northwestern shelf of the Black Sea. They were discovered by drilling 35 wells on 18 areas and are considered promising for hydrocarbons. In these deposits, the Shmidtivske (Maastrichtian) gas field was discovered, and non-industrial gas inflows were observed in the Golitsynske and Odeska fields, in the Karkinitska, Flangova and Shtileva areas, as well as numerous oil and gas shows. The success of further geological prospecting and exploration works depends on a reliable stratigraphic framework of sedimentary strata promising for hydrocarbons. Materials and methods. We analyzed the drilling materials of 35 deep wells that exposed Upper Cretaceous sediments of the northwestern shelf of the Black Sea and 14 wells of the adjacent land, the latest seismic data and the results of previous geological and geophysical studies in the region, our own developments and generalizations, as well as information on the geological structure of the study area obtained from the reports on the implementation of research work on geological study of the subsoil, which are stored in the State Research and Production Enterprise “Geoinform of Ukraine”. The reference wells were selected as those whose sections were the most informative for stratigraphic constructions based on a set of geological factors (paleontological determinations of fossil fauna groups to establish the relative geological age of rocks, lithological description of stone material, geophysical surveys of wells, etc. To distinguish local stratigraphic units in the Cenomanian, Turonian, Coniacian and Santonian sediments, we used the sections of wells located on the adjacent land, namely: well Myrnivska-1, well Krasnoperekopska-2, well Henicheska-5 and well Borysivska-3. They characterize the same conditions of sedimentation of the marine basin, respectively, during each of the listed ages within the South Ukrainian monocline. Main research methods: bio-lithostratigraphic, lithological and geophysical. Results. For this purpose, a revision of the local stratigraphic units of the Upper Cretaceous deposits of the Ukrainian sector of the northwestern shelf of the Black Sea was carried out using a set of methods on a geophysical basis (logging), taking into account the results of regional seismic studies, paleontological determinations of the geological age of rocks, literary and stock materials in the Cretaceous section of the northwestern shelf Black Sea. These stratons were included in the stratigraphic scheme of 2013, as well as those highlighted by the authors of the article in 2015. Based on the results of the research, local stratigraphic subdivisions of Formations rank were distinguished: Semyhatkivska, Partizanska, Ryftova, Hamburtsevska, Bezimenna and Kornilovska for Cenomanian deposits; Myrnivska, Borysivska – Turonian-Coniacian deposits; Selskogo, Borysivska, Fedorovska, Nyzhnodniprovska and Pivnichnoarabatska – Santonian deposits; Selskogo and Zmiina – Campanian deposits; Selskogo – Maastrichtian deposits. Turonian-Santonian sediments, represented by andesite and diabase porphyrites with layers of sandstones and found in the well Illichivska-2 well in the depth interval of 1200-1745 m, are distinguished as part of a layer of sandstones, diabase porphyrites and limestones according to [2]. Сonclusions. The proposed stratons will be included in the new stratigraphic scheme of the Cretaceous deposits of the northwestern shelf of the Black Sea.