To the question of local stratigraphic subdivisions of Cretaceous sediments of the Ukrainian sector of the northwestern shelf of the Black Sea. Article 1. Lower Cretaceous

Abstract

Introduction. One of the tasks of the modern stratigraphy of the closed basins of Ukraine is to clarify and detail the existing stratigraphic schemes of Cretaceous sediments of the north-western shelf of the Black Sea, which are oil and gas bearing. The aim of the study. To revise the local stratigraphic units of the Cretaceous sediments of the Ukrainian sector of the northwestern Black Sea shelf proposed by the team of authors in 2013, as well as to revise our own proposals for the stratigraphy of this region, which were not included in the stratigraphic schemes of 2013, using a set of geological methods. Object of study. Cretaceous sediments of the Ukrainian sector of the north-western shelf of the Black Sea. Subject of the study. The stratigraphy of these deposits.

Materials and methods. The article analyses the drilling materials of 10 deep wells that uncovered Lower Cretaceous sediments of the northwestern shelf of the Black Sea and 10 wells of the adjacent land, the latest seismic data and results of previous geological and geophysical studies in the region, own developments and generalisations, as well as information on the geological structure of the study area obtained from reports on the implementation of research works on geological study of the subsoil.

Results. A revision of local stratigraphic subdivisions of the Lower Cretaceous sediments of the Ukrainian sector of the northwestern Black Sea shelf was carried out using a set of geophysically based methods (logging), taking into account the results of regional seismic studies, paleontological determinations of the relative geological age of rocks, literary and stock materials. According to the results of the research, the Albian sediments are distinguished as part of the Tendrivska (for the first time) and Yevpatoriyska Formation. The Tendrivska Formation is named after the Tendrivska Spit on the north-western shelf of the Black Sea. It is identified for the first time. The stratotype is a section of the Tendrivska-19 well in the depth interval 2626-2500 m. It is distributed within the South Ukrainian monocline. It is represented by light grey limestones with yellowish tinge, organogenic detrital, coarse-grained, strong, dense. It occurs with a stratigraphic break in the Lower Aptian formations and overlies erosion contact or transgressively Cenomanian deposits. Deposits are up to 230 m thick. The Yevpatoriyska Formation is named after a structure on the Kalamitsky Rise on the north-western shelf of the Black Sea. Formerly known as the Kalamitska Formation. The name was changed due to pre-occupation. The stratotype is a section of the Yevpatoriyska-2 well in the depth interval 560-1060 m. It is distributed in the waters of the north-western Black Sea shelf within the Scythian plate. It is composed mainly of silicate rocks. It is divided into three sub-sections. Sediments are 500 m thick.

Conclusions. Based on the results of the research, it is proposed to distinguish the Albian sediments as part of the Tendrivska Formation (for the first time) and the Yevpatoriyska Formation. The sections of the formations offered for consideration are accompanied by geological and geophysical plates.