pdf № 377, May

DOI: 10.19110/geov.2026.5.1

The article presents the results of long-term studies of Paleozoic organogenic structures in the Timan-northern Ural region. The article discusses the principles of defining reefs and other organogenic structures, which allow tracing the evolution and stages of the Upper Ordovician-Lower Permian reef formation in the region based on their temporal distribution. Three stages of reef formation have been identified in the Paleozoic of the region, differing in the geometry of organogenic structures, their growth rate, and paleogeographic position. (i) The Middle Katian-Early Emsian stage is characterized by local and barrier reefs of the outer margin of the carbonate shelf, reaching great thickness. (ii) The Middle Frasnian-Early Tournaisian stage is distinguished by the formation of large microbial mounds, both on the outer margin of the shelf and on the margins of shallow-water platforms within the dissected shelf, as well as the appearance of reefs in the coastal zone of the shelf. (iii) The Late Visean-Early Sakmarian stage is characterized by mud, microbial, and skeletal mounds arising on the slopes of depressions and uplifts in the degrading carbonate shelf. The distribution and geometry of organogenic structures were determined primarily by regional tectonic events and global geobiotic processes during this period of Earth's evolution. The uniqueness of this region allows it to be proposed as a model object for the study and understanding of Paleozoic reef formation.

Keywords: reefs, mounds, reef ecosystem, reef framework, reef formation, evolution, Timan-northern Ural region

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DOI: 10.19110/geov.2026.5.2

This study investigates the ontogenetic (growth-related) dietary shifts of the Frasnian conodont Mehlina gradata from the East European Platform localities. While the morphological shape of P1 elements of this species remained remarkably stable throughout its life, isotopic analysis revealed a significant correlation between the size of the element and its carbon isotope composition. As the P1 elements grew larger, they showed an increase in ¹³C enrichment. This suggests that while the feeding apparatus did not change shape, the trophic position did. Our results indicate that Mehlina gradata likely transitioned to higher trophic levels such as more active predation or scavenging as it matured, demonstrating that morphological stability does not necessarily imply ecological stasis.

Keywords: conodonts, ontogeny, C-isotopes, ecology

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DOI: 10.19110/geov.2026.5.3

Aluminum trifluoride is widely used in various industries (chemical, glass, ceramics, etc.). Industrial methods are based on the fluorination of aluminum hydroxide with hydrofluoric acid and hydrogen fluoride. The cost of raw materials and the environmental risks of AlF₃ production motivate the search for alternative processes based on the use of substandard aluminum ores and their processing waste.

Aluminum trifluoride synthesis technologies were developed using high-iron and low-iron bauxites (Middle Timan, Russia) and ammonium hydrofluoride. The sequence of phase transformations of boehmite and other mineral phases was identified, and their temperature ranges were determined. The size and morphostructural features of AlF₃ were determined. It was shown that fluoride processing technologies allow for the efficient recovery of mineral raw materials and the production of highly marketable products.

Keywords: aluminum trifluoride, aluminum raw materials, fluoride technologies, boehmite

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DOI: 10.19110/geov.2026.5.4

The article completes the consideration of the table of 27 species of symmetry (point groups, without cubic syngony). A hierarchy of 14 lines (families) of symmetry consistent with the hierarchy of 27 species of symmetry is given. The article is intended for teachers, postgraduate students, and students of natural sciences who are studying the basics of crystallography in a geometric context, without group theory or linear algebra. It is dedicated to the 85th anniversary of the publication of the textbook «Crystallography» by G. M. Popov and I. I. Shafranovsky.

Keywords: species (point groups), classes and lines (families) of symmetry, hierarchies of species, classes and lines; limiting symmetry groups

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