编号 2 (2023)

Phosphorite breccias compose a 6-m member in the Vendian terrigenous Kernos Formation in the basin of the Mezhevaya Utka and Sylvitsa rivers in the Middle Urals. Phosphorite pebbles and gravel are accumulations of fragments of redeposited crusts, originally formed in the early diagenesis near the surface of sandy-argillaceous deposits below the water-sediment boundary. Phosphorite is represented by fluorocarbonate apatite with unit cell parameter a from 0.9359 to 0.9363 nm, spectral mode parameters in Raman spectra (FWHM = 1–2 cm^–1 and position from 963 to 966 cm^–1), and a band at 1095 cm^–1 in IR spectra. The absorption bands at ~1430 and 1453 cm^–1 in the IR spectra correspond to the substitution of the orthophosphorus group by the carbonate ion (B-type). According to thermal analysis data, the CO₂ content in apatite varies in the range of 0.04–0.8%, and the admixture of dispersed organic matter in the form of aliphatic compounds is 0.3–0.8%. Apatite is represented by two generations: primary in the form of basal structureless fine-crystalline cement and secondary in the composition of euhedral crystals up to 10 µm in size. Both generations corrode detrital quartz grains. Secondary apatite is enriched in P₂O₅, CaO, and F and contains less SiO₂, FeO, Al₂O₃, MgO, and K₂O than primary apatite. The PAAS-normalized REE distribution has a smoothed profile with a La/Yb ratio of about 2 and positive Ce- and Eu anomalies in enrichment phosphorites. The average value of F/P₂O₅ is 0.09 and corresponds to that in typical fluorocarbonate apatites that have undergone catagenesis. The high values of ⁸⁷Sr/⁸⁶Sr (from 0.7130 to 0.7253) in detrital phosphorites of the Kernos Formation suggest their deposition in a desalinated wave-dominated shallow-marine paleobasin near a significant inflow of continental waters or catagenetic recrystallization.

New data on the mineral composition of Lower Triassic terrigenous deposits in the north of the Pechora oil and gas bearing basin are presented. The relevance of the study is due to the fact that terrigenous natural reservoirs confined to this part of the section have a heterogeneous structure both in area and in section. The purpose of the article was to identify the features of the formation and distribution of minerals that fill the void space of reservoirs. As a result of studying by the methods of optical microscopy, X-ray phase analysis, electron microscopy, signs of mineralogenesis processes, post-sedimentary transformations of sandy reservoirs were revealed. It is shown that the most widespread are quartz regeneration, transformation of minerals of the mica group, formation of calcite of various generations, formation of authigenic clay minerals, etc. Diagenetic changes in terrigenous rocks play a significant role in the formation of reservoir properties and lead to heterogeneity of reservoirs. It is shown that a large amount of calcite in sandstone cement leads to a significant decrease in porosity and permeability parameters. Pore cement of chlorite-smectite composition in fine-grained sandstones also leads to a decrease in the quality of reservoirs. Coarse and medium-grained sandstones with a low content of cement, predominantly of kaolinite or chlorite composition, are characterized by higher reservoir properties. Crustification cement of chlorite composition, pore-filling cement of kaolinite composition contribute to the formation of reservoirs with higher rates.

The article discusses the main directions of lithological research in the field of oil and gas geology, continuing and developing the ideas and research of  L.V. Pustovalov. A number of such areas are closely coordinated with other branches of geology – tectonics, stratigraphy, etc. A wide range of such studies includes the analysis of the structure and development of sedimentary basins, the elucidation of the structure of the internal structure of sedimentary complexes, the forecast and search for non-structural traps of oil and gas, the study of natural reservoirs of oil and gas at different hierarchical levels.