The results from the geological and geophysical investigations of the Siljan Ring impact structure (central Sweden) have shown that the Paleozoic sedimentary succession and the Precambrian basement were strongly affected by complex deformational processes. Studies of a new drill core from the C-C-1 well provide valuable additional information necessary for the reconstruction of the geological setting in the southwestern part of the Siljan Ring. It was found that the contact between the basement and the sedimentary cover is tectonic, not normal sedimentary, in origin. The basement interval comprises Precambrian metavolcanic and metasedimentary rocks with a single mafic intrusion (gabbro-dolerite) in the upper part. The rocks have only been partially metamorphosed. The intercalation of calcareous mudstones, skeletal wackstones, and black shales in the sedimentary cover interval is not consistent with the regional lithostratigraphy scheme. Thus, more likely that the sedimentary sequence is not complete as a result of tectonic displacements, and a significant part of the Lower and Middle Ordovician succession is missing. The Post-Proterozoic tectonic reactivation and impact event also caused the formation of four types of fracture. The third type of fracture is accompanied by cataclastic zones and probably have an impact-related nature. In the highly fractured basement rocks, a dissolution along the second type of fracture has resulted in the development of open vugs. Open vugs and microporosity in cataclastic zones have been considered to be an effective storage space for hydrocarbons.

The article presents lithological studies of reservoir rocks of terrigenous deposits of the Lower Cretaceous of the Krasnoleninsky arch of Western Siberia. A distinctive feature of these deposits is the high variability of lithotypes, which is expressed in a wide range of textural features of thedeposits that determine the nature of oil saturation. According to the results of textural analysis, it was revealed that the studied sediments were formed in various zones of underwater channels of the delta complex and lagoons. To assess the total number of oil-saturated reservoir rocks and the degree oftheir stratification, 10 models were selected that allow us to characterize the distribution of oil-saturated reservoir rocks in different facies complexes. The methodology developed at Gubkin University at the Department of Lithology made it possible to quantify the heterogeneity of the distribution of oil saturation in the multifacial deposits of the Lower Cretaceous of the Krasnoleninsky arch.