Peculiarities of Stratigraphic Distribution and Paleoecology of Jurassic Bivalve Mollusks of the Pre-Сarpathian Foredeep

Abstract

Pre-Carpathian region is one of the oldest oil and gas producing regions of our country, which is attracting more and more attention of scientists. In the Outer zone of the Pre-Carpathian Foredeep, Jurassic deposits occur at considerable depths (up to 3,000 m), so we obtain almost all geological information about them exclusively during the study of core material selected during drilling. A comprehensive and detailed study of the Jurassic deposits of this zone during exploration drilling in the 1950s contributed to the discovery of the Kokhanivske and Sudovovyshnianske oil deposits and Rudkivske gas deposit, as well as a number of oil and gas manifestations. After that, the interest in the conditions of formation and stratification of Jurassic deposits increased. Researchers have begun to treat them as the promising objects for oil and gas exploration. Jurassic deposits in the Pre-Сarpathian Foredeep fill a single depression – the Stryi Jurassic deflection, covered by a thick layer of Cretaceous and Neogene rocks. The study of their geology and stratigraphy has acquired important applied and scientific significance, because stratigraphic research serves as a basis for clarifying the history of geological development of the region, performing tectonic constructions, reconstruction of paleogeographic and paleoecological conditions, comparison of productive horizons and specification of their stratigraphic position, search for new objects promising for hydrocarbons. Extremely rare finds of paleontological remains (which are not always well preserved) do not allow to unambiguously determining the age of the host rocks. It is still not always possible to clearly stratigraphically distinguish and correlate these rocks due to weak paleontological study and partial uncertainty in the interpretation of the geological structure of these strata. Despite the significant amount of research we have done, there are some debatable issues regarding the completeness of the section of these rocks and the presence of separate stratigraphic units in them. For many years, we have studied in detail and comprehensively bivalve mollusks found in the core of wells drilled in the Outer zone of the Pre-Carpathian Foredeep. As a result, the age of the host strata was specified and confirmed, as well as the thickness of individual stratigraphic units.