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No 3 (2025)

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THE MEDITERRANEAN SALT-TECTONIC SUPERGIANT: SALT DISTRIBUTION AND ITS TECTONO-KINEMATIC HISTORY

Belenitskaya G.A.

Abstract

The subject of our research is the Mediterranean salt-tectonic supergiant. Its geological history includes two peaks of salt accumulation of different ages: the most famous late Miocene Messinian and the preceding Triassic. Both peaks are associated with the main tectonic events in the history of the Neo-Tethys and its margins. The Triassic peak is associated with the riftogenic foundation and disclosure of the Neo-Tethys, and the Messinian peak is associated with the final phases of its collisional closure. It was made an attempt to substantiate the presence in the substrate and in the margins of the Messinian salt accumulation basins of more ancient buried salt strata, the processes of intensive crumpling of which during the collision of paleocontinents and paleomicrocontinents were accompanied by the removal of salts from their original locations and could contribute to the accumulation of salts at the Messinian level. The work is based on the results of long-term complex lithological and tectonic studies performed by the author, of salt-bearing sedimentary basins in Russia and the World and on a broad generalization of the data on the Mediterranean. The article summarizes and analyzes geological and tectonic material covering the modern distribution and relationship of the Miocene and Triassic salts in the Mediterranean, reveals the presence of spatial relationships between them, considers the main morpho-kinetic types of salt bodies and characterizes their features in different areas of the Mediterranean. For the Triassic salts, currently largely residual, a mode of their original distribution has been reconstructed, the most important feature of which was the maximum development of salts along riftogenic passive margins of paleo-continents and paleo-microcontinents. Possible changes in salt bodies during the tectonic and kinematic history of the region and the mode of their distribution by the beginning of the Messinian time are considered. It has been concluded that the basins of accumulation of Messinian salts were located mainly within the areas of pre-Messinian distribution of Triassic salts. The processes of collision of paleo-continents and paleo-microcontinents, which reached the greatest intensity at the end of the Miocene, led to a sharp increase in the intensity of the processes of compression, crumpling, and disruption of salt-bearing sedimentary complexes, widely developed along their passive paleo-margins, and was accompanied by large-scale tectono-kinematic removal of the Triassic brine-salt masses from these complexes. All this created material prerequisites for the participation of these masses in the allochthonous and neo-autochthonous accumulation of salts at the Messinian level and served as one of the probable causes of the Messinian salt crisis.
Geotektonika. 2025;(3):3-28
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THE MAIN STAGES OF THE FRAM STRAIT FORMATION IN THE NEOGENE: ANALYSIS OF GEOLOGICAL AND GEOPHYSICAL DATA

Zayonchek A.V., Sokolov S.Y., Soloviev A.V., Vasilieva E.G., Shkarubo S.I.

Abstract

The opening of the Fram Strait began in the Early Miocene (~19.5 Ma) as a result of movements of the North American and Eurasian lithospheric plates, which resulted in the formation of the narrowest segment of the strait, the Lena Trough. In the Miocene (~19.5–9.8 Ma), the opening of the central part of the Fram Strait led to formation of the central and northwestern parts of the Molloy Basin, which had an extended basement consisting of blocks of the West Spitsbergen fold-and-thrust belt. In the Late Miocene (~9.8 Ma), in the central part of the Fram Strait, a jump in the axis of its opening to the east occurred in the segments between the Molloy and Spitsbergen transform faults, and spreading began in the northernmost segment of the Knipovich Ridge. In the Late Miocene (~9.8 Ma), the deep-sea exchange of waters between the North Atlantic and the Arctic Ocean took place west of the Barents Sea continental “fragments” – the Hovgaard Ridge and Mount Hovgaard. In the Late Miocene (~6.7 Ma), the Molloy Basin began to open, which coincides with the beginning of the continuous subsidence of the Hovgaard Ridge, which was in subaerial conditions, and with a three-fold increase in the sedimentation rate in the central part of the Molloy Basin. In the Late Miocene‒Early Pleistocene (~9.8‒1.8 Ma), a warm current from the North Atlantic could have passed along the eastern continental margin of Greenland and, at the peak of its maximum intensity, ensured the existence of biological diversity in the conditions of the “polar desert” and “polar night” in the north‒northeast of Greenland and the shallow sea areas adjacent to the coast. The modern direction of the cold and warm currents in the Fram Strait could have formed in the Early Pleistocene (~1.8 Ma) and be associated with the opening of the northernmost segment of the Knipovich Ridge.

Geotektonika. 2025;(3):29-48
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STRUCTURAL PARAGENESIS AND GEOLOGICAL CONDITIONS OF FORMATION OF THE FRONTAL ALLOCHTHON OF THE SOUTHERN CIS-URALS

Przhiyalgovskii E.S., Lavrushina E.V., Kuznetsov A.B., Zhuravleva N.D.

Abstract

The article presents the results of structural and geological study of the Ik–Sakmara segment of the western zone of frontal deformations of the Urals. Within this tectonic zone, at the late stages of the evolution of the Hercynian structure of the Urals, a thick complex of Upper Paleozoic sedimentary rocks composing the eastern slope of the Pre-Ural Trough was deformed. The studies carried out, including field study of structures, detailed structural mapping and construction of principal cross-sections, made it possible to clarify the ideas about the tectonic structure of the Southern Urals in this region – the most controversial in terms of structure. Based on the results of the work, multi-rank tectonic structures were demonstrated on the compiled maps and in cross-sections, the morphological interconnection of which makes it possible to combine them into a single folded-fault paragenesis formed in the regional horizontal compression. The formation of tectonic structures began immediately after the deposition of the evaporite strata of the Kungur stage, accompanied by an orogenic rise during the deformation area up to 6–8 km. Calculations and graphical constructions performed in accordance with the basic provisions of the methods of structural reconstructions of folds-and-thrust belts and the concept of balanced sections made it possible to substantiate the allochthon structure of the zone of frontal deformations, to estimate the thickness of the allochthonous plate (7–8 km), to determine the amplitudes of displacement (decreasing from east to west) along the subhorizontal detachment, as well as the value of the horizontal deformation of layers in the allochthon (up to 40%).
Geotektonika. 2025;(3):49-71
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TECTONIC LAYERING OF THE PLATFORM COVER AND PRE-PLATE COMPLEX OF THE SCYTHIA‒TURANIAN PLATE IN THE CASPIAN SEA

Popkov V.I., Popkov I.V.

Abstract

Tectonic dislocations of the pre-plate Permian‒Triassic complex and in the overlapping platform cover of the northern part of the Caspian Sea have been studied. The tectonic stratification of the pre-plate complex has been established due to the development of gentle thrusts and disruptions in its section. Their formation is associated with the collisional processes that accompanied the closure of the residual basins of the Paleo-Tethys Ocean. In its subsequent development, the young platform periodically experienced horizontal compression, which led to the resumption of movement along the buried thrusts. As a result, asymmetric anticlines were formed in the sediments of the cover in the frontal parts of the thrusts. In addition to this type of structure, numerous layered tectonic faults and rootless anticlines have been identified in the sediments of the plate complex. The largest of the faults, experiencing the transformation of horizontal displacements into vertical ones in the head parts of the plates, penetrated into the overlying sediments, tearing the sedimentary cover to its full capacity. The reason for their formation is the transpressive effect of tangential stresses transmitted to the platform from the area of the Alpine orogeny of the Caucasus. The important role of tectonic deformations in the formation of oil and gas accumulations in the pre-plate complex and platform sediments is shown.
Geotektonika. 2025;(3):72-87
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AGE AND GEOLOGICAL POSITION OF CARBONATE ROCKS OF THE MISHIKHA FORMATION (SE SALAIR): ANALYSIS OF GEOCHEMICAL DATA, ISOTOPE CHEMOSTRATIGRAPHY AND ZIRCON U‒Pb DATING

Vetrova N.I., Vetrov E.V., Proshenkin A.I., Bychkova N.A.

Abstract

The Salair Terrane, located in the northwestern part of the Central Asian Folded Belt, is presented mainly by Cambrian volcanic, terrigenous and carbonate rocks. The Salair Terrane is a fragment of the juvenile Early Paleozoic crust formed as a result of the subduction process, accompanied by carbonate and terrigenous sedimentation. However, a series of Precambrian tectonic blocks of ambiguous origin are revealed in the structure of the Salair Terrane. In order to reconstruct the history of the geological development of the Paleo-Asian Ocean in the Late Proterozoic‒Early Paleozoic on the southwestern edge of the Siberian continent, we aimed to determine the age and tectonic conditions of the formation of sedimentary rocks of the Mishikha Formation of the Southeastern Salair, which formed the main part of the Precambrian tectonic blocks. The limestones of the Mishikha Formation are characterized by high contents of rare earth elements, Ce/Ce* (0.72 ± 0.04), Eu/Eu* (1.88 ± 0.70) and 87Sr/86Sr ratios of 0.70857–0.70860, normal δ18OSMOW values from 20.9 to 27.1‰ and positive δ13C values (from 0.5‰ to +4.1‰). Based on the analysis of geochemical and isotope-geochemical (Sr, C, O) data, it was established that the limestones of the Mishikha Formation were formed in an open ocean basin far from the passive margin of the Siberian continent in a sub-oxygen environment. Using the methods of Sr and C isotope chemostratigraphy and U‒Pb dating of zircons, age constraints (555–545 Ma) were obtained for the formation of carbonate deposits of the Mishikha Formation.

Geotektonika. 2025;(3):88-108
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