No 1 (2024)

Based on lithogeochemical data for fine-grained clastic rocks of the Volyn, Valdai and Baltic series of the west of the East European Platform (Belarus and Volyn, partly Lithuania), categories of rivers that transported fine-grained aluminosiliciclastics to the sinks were reconstructed. It is concluded that the formation of Vendian and Lower Cambrian sedimentary sequences developed in this area was controlled mainly by river systems similar to modern large rivers (rivers with a catchment area > 100000 km²) and rivers draining sedimentary formations (rivers with a catchment area < 100000 km²). The fine-grained aluminosiliciclastics transported by them came mainly from areas composed of rocks of the crystalline basement of the platform and, in part, sedimentary formations. The distribution of data points of Vendian and Lower Cambrian clay rocks on the diagrams (La/Yb)_N–Eu/Eu^* and (La/Yb)_N–Th with fields of composition of pelitic and silty-pelitic sediments in the estuarine parts of modern rivers of different categories shows that mafic rocks of the Volyn-Brest large igneous province, apparently, were not suppliers of fine-grained aluminosiliciclastics in the indicated time intervals.

Data on the composition, age and formation conditions of the Ulzutui and Kydzhimit strata, which are combined as part of the Eravna Series of the Eravna Subzone of the Udino-Vitim Zone, are considered. The Eravna series, at least 2400 m thick, is composed of tephroturbidites with a significant amount of lavas and tuffs of felsic and intermediate compositions, with which tectonic-gravitational mixtites are spatially and genetically related. The features of the structure and composition of the Eravna series indicate the formation of sediments in an open deepening marine basin adjacent to the zone of active volcanism. For the first time, according to the Miospores, the time of formation of the Ulzutui sequence is limited to the Late Devonian – Early Carboniferous (Late Famennian – Early Tournaisian), the Kyjimite strata is limited to the Early Carboniferous (Visean) ages. At this time, the Kyjimit volcanic zone was formed. The suprasubduction nature of the zone is evidenced by the features of volcanites (predominance of acidic varieties, belonging of basalts to the tholeiitic, and dacites and rhyodacites to the calcareous-alkaline series, the presence of high-potassium rock varieties, their belonging to the K-Na type of alkalinity, very low MgO values, low and moderate TiO₂ contents, high Al₂O₃ and K₂O, enrichment of volcanogenic rocks in large-ionic lithophilic elements relatively to highly charged elements, minimum in Nb and negative values of εNd), their spatial association with monzonites (have suprasubduction features) and tephroturbidites, as well as metallogenic specialization (Cu and Zn) of the Eravna series. We believe that the ore-hosting strata for both pyrite-polymetallic Ulzutui and Ozernoe deposits is the Upper Devonian–Lower Carboniferous Eravna series.

New results of lithological structural and textural observations and petrographic study of rocks of the Uryuk formation exposed in the basin of the Maly Tolpar River in the Bashkir meganticlinory are presented. For the first time, a wide development of consedimentary underwater landslide folds in the Uryuk deposits has been established, the sizes of which vary from the first tens of centimeters to the first meters. In sandstones, the presence of oblique, wavy, flasery and horizontal, with a dual character of thin clay layers, layering, as well as structureless layers with a massive texture, is recorded. Signs of shallow wave ripples have been established. Mechanoglyphs and textures similar to Arumberia banksi have been found, which presumably represent the lithified structures of bacterial mats that existed under certain conditions – shallow-sea environments and conditions of sandy-clay sedimentation. It is concluded that the Uryuk deposits, despite the absence of direct lithological signs of diamictites in them, form a single sedimentary sequence with the underlying Tolparov-Suirovsky marine glacial deposits, in which a shallow-sea sedimentation regime is established by the end of the Uryuk time. It is shown that the presence of ferruginous minerals in sandstone cement is secondary in nature and is associated with their epigenetic transformations. It is concluded that the red-colored color of the rocks of the Uryuk formation cannot be used for stratification of its sections and reconstruction of sedimentation conditions in the Uryuk time.

The study presents the results of studying the material composition of terrigenous rocks from the Early – Middle Permian deposits of the Reshetnikovka formation of the Laoeling-Grodekovo terrane of South-Western Primorye. Studies were carried out in order to reconstruct paleogeodynamic environments for the accumulation of studied deposits, as well as to determine the tectonic type and composition of source rocks of sources areas. It has been established that in terms of mineral and geochemical parameters, the sandstones of the formation are petrogenic or “first cycle” rocks, correspond to arcoses and, only partially, subarcoses and lithite arenites, are characterized by a fairly high degree of maturity of clastic material, and their formation was due to the destruction of largely weathered parent rocks of sources areas. Paleogeodynamic interpretation of the obtained data indicates that in the Early and Middle Permian sedimentation occurred in the basins of the passive continental margin, which are intra-and intercontinental rifts and aulacogens. The main influence on sedimentation processes was exerted by continental sources areas: cratons and uplifted basement blocks, which were projections of the crystalline basement framed by rift zones. Mainly acidic igneous and metamorphic rocks were eroded with the participation of ancient sedimentary formations. U–Pb isotopic dating of detrital zircons made it possible to establish the age and possible location of magmatic complexes, due to the destruction of which formation deposits were formed.