No 7 (2024)

The search for hydrocarbon deposits in the sediments of the Lower Paleozoic complex of the Timan-Pechora oil and gas province, which are associated with the main prospects for increasing reserves, is a relevant topic for research. It is necessary to understand the formation processes of carbonate reservoirs within the complex under consideration to develop a strategy for predicting the structure of the complex reservoirs.

Obtaining data on the parameters of the fluid regime of the formation of secondary dolomites in the Paleozoic carbonate reservoirs of the Khasyrey field (Gamburtsev swell) was the aim of the study. We studied primary fluid inclusions in dolomite and anhydrite cements filling vuggy voids in reservoir rocks.

We showed that the inclusions contained up to 10 vol. % of the gas phase, which was represented by methane and water vapor. The liquid phase was characterized by a substantially chloride-calcium composition, the salinity is 13.5–23.5 wt. % NaCl-eq. These data might indicate the formation of cavities and cements of secondary dolomites from moderate-temperature solutions of high salinity, which were formed as a result of mixing sedimentation (primary marine) waters and brines of hydrothermal vents. The products of evaporite dissolution in the presence of hydrocarbons and sulfate reduction processes were the most likely source and supplier of the fluids, both the formation of leaching caverns in the rock and the cements performing them. Fluids could enter the upper floors of the section from hydrothermal sources in the basement zones and lower horizons of the sedimentary cover through a system of faults and cracks during tectonic activation.

The chemical composition was studied; spectroscopic (FTIR, EPR) and X-ray diffraction analyses of serpentines from the host rocks of gem garnet andradite-demantoid occurrences of their melange zone in the northern part of the Ray-Iz massif were carried out. The quantitative species composition of the serpentinites was determined by the method of synchronous thermal analysis. We found that serpentines were represented by three varieties of lizardite-1T and chrysotile-2M_cl in sample PTM-1 and chrysotile-Or_cl in sample PTM-2. The complex of conducted studies allowed specifying the mineral composition of the studied serpentinite samples and greenschist (chrysotile) facies of progressive contact metamorphism.

The article is timed to the 2000th anniversary of the birth of Pliny the Elder (23–79 A.D.), the author of «Natural History», in which two last volumes are devoted to rocks and minerals. Attention is drawn to the fact that he was the first to fix polyhedron attributes (faces, edges, vertices) on perfect natural crystals. It was not until 16 centuries later that their measurements led to the empirical laws of N. Steno (1638–1686) and R. J. Haüy (1743–1822). Translations from «Natural History» are given according to V. M. Severgin, descriptions of the eruption of Vesuvius in 79 are taken from the XVI letter to Tacitus by Pliny Jr. The purpose of the article is to accurately set the stage for the history of mineralogy and crystallography. It is aimed at historians of science, as well as teachers, graduate students and students of geological faculties of universities. The citation of old and ancient authors in the article is important to prove the main thesis — the priority of Pliny the Elder, and also aims to attract young researchers to read primary sources.