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Nº 6 (2025)
Articles
Genetic Types of Ore-Bearing Sediments of the Northern Near-Equatorial Zone of the Mid-Atlantic Ridge
Resumo
Two genetic types of metal-bearing and ore-bearing sediments formed under the influence of different pro- cesses have been identified based on the results of the study of the bottom sediments of hydrothermal fields of the Russian Atlantic exploration area. The 1st type was formed as a result of ore minerals precipitation from the hydrothermal plume, the 2nd type ‒ under the influence of diffuse hydrothermal flows entering the sediments from the substrate rocks. The distinctive features of the two identified genetic types of ore-bearing and metal-bearing sediments formed in different conditions were established: the character of distribution in the section and over the area, mineral and geochemical composition and textural and structural features.
Litologiâ i poleznye iskopaemye. 2025;(6):581-599
581-599
The Formation Conditions of the Lower Maeotic Oolites Сarbonates (Cape Kazantip, Crimea)
Resumo
The genesis of oolitic carbonates among the sulfate-carbonate-clayey deposits of the Lower Maeotian in the sections of Cape Kazantip was investigated through detailed analysis. Laboratory studies were conducted utilizing a range of analytical techniques, including carbonate chemical analysis, optical polarisation with computer support for photography and scanning electron microscopy (SEM), energy dispersive spectros- copy (EDS), isotopy, gas chromatography (GCM), electron paramagnetic resonance (EPR), infrared (IR) spectroscopy, and X-ray diffractometry. The chemical composition of the oolitic carbonates was found to be characterizing by the constant presence of dolomite (11.93–40.98%) and clay (2.42‒19.40%) compo- nents, as well as the most isotopically heavy values of carbonate carbon (2.74–5.40‰) among the enclos- ing carbonates. This indicates the oolites formation in saltwater of an extremely shallow coastal lagoon. The presence of gypsum in oolite cores and as cement in oolitic carbonates and oolitic conglogravelites has been established, and it has been determined that gypsumification of the sediments occurred at the stage of oolite formation. This process took place during a sharp fall in sea level and could be associated with the participation of sulphate ions from meteoric waters in the removal of sediments into the zone of meteoric-vadose conditions, possibly together with gas-fluid seepage. The occurrence of bottom gas-fluid seeps is corroborated by the detection of mineralized extracellular polymeric substance (EPS) in oolites, as well as the presence of bacterially induced halite, barite and high-Mn kutnogorite from the dolomite group. Among the carbonate minerals found in oolites, low and high-Mg calcites and Ca-dolomite have been identified; the distribution of the latter indicates the primary sedimentary genesis of dolomite micro- crystals in the oolite structure.
Litologiâ i poleznye iskopaemye. 2025;(6):600-626
600-626
Sources of Clastic Material for the Cretaceous‒Paleogene Boundary Deposits of Klementyev Mountain, Eastern Crimea (Results of U‒Th‒Pb Dating of Detrital Zircon Grains and Their Significance for Regional Paleogeographic Reconstructions)
Resumo
The paper presents the results of U–Pb isotope dating (LA-ICP-MS, Collective Use Center of the Geological Institute of the Russian Academy of Sciences) of detrital zircons from sandstones of the Upper Cretaceous (Maastrichtian) – Lower Paleogene (Danian) boundary level sections of the Klementyev Mountain section of the Uzyn-Syrt Upland (eastern Crimean Mountains). The obtained data set from the Upper Maastrichtian Klementyev Fm. (sample K22-001) contains 5 Jurassic dates, 22 Triassic dates, 55 Paleozoic dates (including 10 Permian and 7 Carboniferous ones), 18 Neoproterozoic dates, 13 Mesoproterozoic (1014–1511 Ma) dates, 27 Paleoproterozoic dates, 10 Archean (including 1 Paleoarchean one) dates; from the Lower Danian Feodosiya Fm. (sample K22-002) ‒ 2 Jurassic dates, 4 Triassic dates, 55 Paleozoic dates (including 11 Permian and 16 Carboniferous ones), 24 Neoproterozoic dates, 25 Mesoproterozoic (1008‒1525 Ma) dates, 42 Paleoproterozoic dates, 13 Archean dates. Such a very wide range of ages from Jurassic to Paleoarchean indicates a variety of primary provenances, including Archean, Paleoproterozoic, Mesoproterozoic, Neoproterozoic and Paleozoic crystalline complexes. Such a provenance signal cannot be obtained by accumulating erosion products from a nearby local source. Thus, the traditional paleogeographic schemes of Crimea for the Maastrichtian and Danian are not confirmed, in which at that time in place of Mountainous Crimea there is shown land that supplied detrital material to the sedimentary basin adjacent to it from the north, including that part of it where the UzynSyrt plateau area with the dominant peak of Mount Klementyev is now located. The most probable sources of demolition for the studied strata were the Epi-Hercynian Scythian and ancient East European platforms. The recorded decrease in the share of Triassic zircon in the Danish strata and the increase in the contribution of Neoproterozoic zircon in the Maastricht strata was recorded in the Mount Klementyeva section.
Litologiâ i poleznye iskopaemye. 2025;(6):627-656
627-656
U–Th–Pb Isotopic Dating of Detrital Zircons and Garnet and Tourmaline Indicators from Molassic Deposits of the Belorechenskaya Formation (Western Pre-Caucasus): Geological Implications
Resumo
In order to determine the provenance areas and to solve paleotectonic and paleogeographic problems related to the stage of orogenic molasse formation in the Western Pre-Caucasia, sands and sandstones from Quaternary strata sections corresponding to two stratigraphic levels were studied: (i) the lower part of the Belorechenskaya Fm section (Gelazian) (sample MK-29) and (ii) the strata forming a series of contiguous terraces (Upper Neopleistocene) in the area of the southwestern outskirts of Maikop town (sample MK-30). U‒Th‒Pb isotope dating and morphological study of detrital zircons (dZr), as well as mineralogical analysis of garnet and tourmaline grains extracted from the heavy fraction of the samples have been performed. Density probability curves (DPC) characterizing the distribution of dZr ages from the studied samples were obtained. Together with previously published similar data for the Eo-Pleistocene sands of the middle part of succession of the Belorechenskaya Fm (sample K23-073) and the Holocene sands of the modern alluvium of the Belaya River (sample K22-032), this made it possible to obtain a summary characteristic for four successive stratigraphic levels of Quaternary deposits, demonstrating the change over time in the provenance signal in the orogenic molasse of the western Pre-Caucasia.The studied complex of clastic rocks participating in the Quaternary orogenic molasse contains well-defined signs of the “southern” (Caucasian) provenance signal, presented in the sets of U‒Pb isotope ages of dZr grains. In the case under consideration, the “southern” signal is represented by components characteristic only of it, associated with the erosion of: 1) Lower and Middle Jurassic volcanogenic-sedimentary, volcanogenic, subvolcanic and intrusive rocks of the Cimmerian structural level (Cimmerian provenance signal); 2) Early Paleozoic and Late Neoproterozoic igneous and metamorphic formations of the Cadomian complex (Cadomian provenance signal) as part of the Hercynian basement. A tendency of gradual decrease in the intensity of the Cimmerian and increase in the intensity of the Hercynian provenance signals in the sequence of stratigraphic units of the Quaternary age from the lower to the upper levels of the section has been established. This regularity characterizes the process of successive deepening of erosion of the Greater Caucasus orogen. In the beginning, at the early stages of formation of the western segment of the orogen in Gelasian, erosion affected rock complexes mainly of the Cimmerian structural stage. Later, starting from the Eo-Pleistocene and upto the present time, the main source of detrital material became the complexes of the Hercynian basement exposed on the surface.
Litologiâ i poleznye iskopaemye. 2025;(6):657-681
657-681
Coarse clastic rocks of North-Eastern Kamchatka: morphology, material composition, formation settings
Resumo
The results of studying the conditions of occurrence, morphological features and material composition of coarse-grained rocks of the Cenozoic molasse of the Olyutorsky terrane of North-Eastern Kamchatka are considered. Consideration of the obtained data allows usto draw conclusions about the paleogeological conditions of their formation. Morphological studies have shown that conglomerates are usually medium-sized, fairly well sorted and rounded, however, during the transition from marine to continental deposits, their dimension increases slightly, and the sorting and roughness deteriorate. Gravelites range from medium gravel in marine deposits to large gravel in continental ones. Sorting and rounding of fragments is good. Analysis of the obtained data shows that the accumulation of rocks of the Alugin and Pakhacha formations occurred in narrow intermountain troughs covered by a shallow sea, and the Korf formation in continental environments. The area of demolition was the mining structures that bordered the basins and supplied them with a huge amount of coarse grained material transported by temporary and permanent watercourses. The material composition of the psephite fragments indicates that mainly local sources of demolition were eroded, composed of a complex of volcanogenic-siliceous and terrigenous formations underlying the molasse. A secondary sources that supplied the basin with fragments of feldspar-quartz sandstones, ancient siliceous and granite-metamorphic rocks were the Cretaceous-Paleocene turbidites of the Ukelayat terrane and the Late Paleozoic-Early Mesozoic formations of the Koryak folded region located to the north.
Litologiâ i poleznye iskopaemye. 2025;(6):682-697
682-697
RTH MINERALIZATION IN RIFT FORMATIONS OF THE ISHLYA GRABEN (WESTERN SLOPE OF THE SOUTHERN URALS)
Resumo
Rift formations of the Ishlya graben, widespread on the western slope of the Southern Urals, are represented by alternating terrigenous rocks (carbonaceous shales, siltstones, siltstones) with a volcano-plutonic association (gabbrodolerites, basic effusives with a small amount of pyroclastic material). In the rocks of the Ishlya graben, complex rare earth mineralization was discovered, represented by allanite-(Ce), REE-containing epidote, monazite-(Ce), xenotime-(Y), chevkinite-(Ce), fergusonite-(Nb), rare earth fluorocarbonates (bastnaesite-(Ce), hydroxylbastnaesite-(Ce), parisite-(Ce), synchysite-(Ce)), which is characterized by a wide variety of morphological types of mineralization and the presence of complex associations. Based on the analysis of the chemical composition of metamorphic minerals, the P–T parameters of rock metamorphism were established (T = 250–600°C, P = 2–10 kbar), the chemical composition of the fluid phase and its temperature (CaCl2 + NaCl; T = 180–408°C, for primary inclusions and FeCl2; T = 121–248°C for secondary ones), as well as the hematization temperature (465–593°C) andre-equilibration of the ilmenite-titanomagnetite association (T = 501–576°C at oxygen fugacity from –23.15 to –21.25) were determined. It is shown that in the natural environment, the processes of rare earth mineral formation are diverse and multifactorial, with the chemistry of the local-scale mineral formation environment being of great importance. Based on the comparative analysis of the chemical composition of monazite and xenotime, it was established that neither the configuration of the normalized graphs nor the chemical composition of the minerals found in the rocks of the Ishlya graben and the Shatak complex correspond to analogs from alluvial deposits. Thus, it can be stated that the primary source of rare-earth phosphates from channel and alluvial deposits are the Riphean-Vendian metamorphosed rocks of the eastern subzone of the Bashkir meganticlinorium.
Litologiâ i poleznye iskopaemye. 2025;(6):698-714
698-714
On the formation and transformation of siliceous sequences. Brief analysis of some publications
Resumo
The article analyzes the influence of endogenous processes – volcanism during the sedimentation stage and hydrothermal impact on rocks during catagenesis – using the example of siliceous and clayey-siliceous deposits of Western Siberia, which are described in a series of publications. Arguments against such interpretation are presented, and alternative concepts regarding the formation of such sequences through biogenic sedimentation are outlined. The sharp intensification of biochemical weathering during the Cretaceous period led to the transport of dissolved silica masses into the World Ocean, ultimately triggering the development of organisms with siliceous function and, consequently, silica accumulation.
Litologiâ i poleznye iskopaemye. 2025;(6):715-719
715-719
ВСЕРОССИЙСКОЕ ЛИТОЛОГИЧЕСКОЕ СОВЕЩАНИЕ С МЕЖДУНАРОДНЫМ УЧАСТИЕМ “ГЕОЛОГИЯ РИФОВ – 2025”
Litologiâ i poleznye iskopaemye. 2025;(6):720-722
720-722