Possibilities of lithological and stratigraphic division of geological sections based on natural gamma ray spectrometry

Establishing the geological structure of complex sedimentary sections in oil- and gas-bearing areas of Ukraine, specifically their lithological and stratigraphic division, is quite challenging and often ambiguous when interpreting the sequence of sedimentary rock layers. The aim of the work was to study the possibility of lithological and stratigraphic division of a geological section based on the results of natural gamma-ray spectrometry in the interval of the boundaries between the Tournaisian and Visean deposits within the Plyskiv-Lysohorskyi outcrop of the crystalline basement of the Dnipro-Donets Basin. The methodology for studying the boundaries between the Tournaisian and Visean deposits was based on the results of the distribution of the concentration of radioactive isotopes of natural gamma radiation obtained directly during the drilling of exploration and prospecting wells. In addition, core material was taken from the Visean and Tournaisian stages of the Lower Carboniferous coal deposits, and its lithological and petrographic study was carried out by macroscopic description of core samples, preparation and description of thin sections, as well as X-ray structural and gamma-spectrometric analyses of the material composition of the sample collection. In general, the quantitative presence of natural radioactive elements was determined. Based on the results of these comprehensive geological and geophysical studies, it was established that the distribution of natural radioactive elements in the intervals of deposit occurrence depends on the lithological composition of the rocks and, accordingly, changes in the conditions of the sedimentation, which causes changes in the distribution of radioactive elements. Therefore, this particular feature of the structure can be used to trace the boundaries of lithotype distribution in horizons of different stratigraphic thicknesses. Considering that the radioactivity of polymictic rocks was characterised by a significant cumulative effect, and was caused by the increased radioactivity of the rock matrix skeleton and the clay material that fills the intergranular space. Therefore, it is advisable to determine clay content using gamma-ray spectrometry results based on the concentration of potassium-40 or gamma logging data. The introduction of such approaches not only facilitates the identification of boundaries between deposits but also enables the reconstruction of the physical and geological conditions under which the sedimentation of different lithotypes of rock was deposited