No 5 (2024)

The article provides an overview of more than 80 of all known locations of Mesozoic reptiles in eastern Russia, discovered over the last hundred-plus years. Since the beginning of the new millennium, the increase in new data and finds of dinosaurs in the regions of the Krasnoyarsk Territory, Transbaikal Territory, Buryatia, Amur Region and ichthyosaurs in the north of Siberia, Chukotka and Southern Primorye has increased significantly. Further searches in these and newly discovered locations will allow paleontologists to form a more detailed picture of the organic world of the ancient Mesozoic eras and give more accurate systematic definitions of representatives of the class Reptilia.

The article presents an interpretation of data for stable isotope composition of sulfur-34 and -33 from sulfide minerals of the Early Paleoproterozoic (~2.5 Ga) Monchegorsk pluton, located in the central part of the Kola Peninsula, Russia. Available data indicate that the sulphide sulfur has both a mantle source and an atmospheric sulfur source with an isotopic anomaly. We believe that atmospheric sulfur (a product of photochemical reactions in the oxygen-free atmosphere of Archean) was transferred from the atmosphere into the deep layers of the mantle due to the processes of subduction of the oceanic crust along with sediments and their subsequent melting. The homogeneous sulfur isotopic composition of sulfur-34 and -33 for sulfide mineralization of the Monchegorsk pluton indicates fairly intense mixing of sulfur from different sources. Thus, the sulfur isotope anomaly archived in the magmatic sulfides of the Monchegorsk pluton provides an opportunity to trace the global circulation of terrestrial matter in the ancient history of the Earth.

A group of gold deposits with bismuth mineralization, potentially promising for industrial gold mineralization within the southern and western Sikhote-Alin, is considered. Ore bodies are represented by veins, stockworks, and ore zones. The ores are characterized by a close association of early-generation native gold with Ni, Co sulfoarsenides and bismuth sulfotellurides and tellurides, and late-generation native gold with sulfosalts of Pb-Bi, Pb-Bi-S, Pb-Cu-Sb composition. In the studied deposits, a significant variation in the size of native gold grains was revealed – from coarse and medium to dusty. Native gold of the early generation is characterized by a fineness of 775–900‰, rarely 990‰, and in the late generation – 600–850‰. Geological and mineralogical-geochemical data indicate a genetic connection in one case (Bolotistoe deposit) with bodies of Eocene dacites and granodiorites, as well as with an intrusion of Eocene gabbroids and monzonitoids. In other cases, deposits (Krinichnoye, Malinovskoye, Namovskoye and Pasechnoye) are characterized by a genetic connection with Early-Late Cretaceous granitoid magmatism.

The results of studying various mineral systems of spherical and globular morphology using analytical scanning electron microscopy are presented. Their microstructure and chemical composition have been studied. Several genetic types of spheroids have been established: cosmogenic iron-oxide microspherules from the fall sites of the Sikhote-Alin meteorite; similar in composition, but nickel-free iron-oxide spherules from the Late Permian mafic rocks of Popov Island and from the Late Oligocene acidic explosive deposits of Southern Primorye; spheroid formations from continental Fe-Mn microcrusts – spherical aluminosilicate and ferro-manganese condensate globulites on the surface of gas channels and cavities in basalts, silica microspheroids in segregation centers of acidic volcanic glass; nanosphere formations in the structure of noble opal from the Raduzhnoe deposit (Primorye). The composition of the spheroids, presumably of meteorite origin, is predominantly magnetite with Ni impurities. Only a few of them have a wüstite composition (FeO). Spheroids from pyroclastic rocks are also characterized by a similar composition, but they lack nickel. Spheroids identified in rhyolite glasses have a quartz composition and consist of a core and a shell. Spheroids found in ore crusts are characterized by hydroaluminosilicate and Fe-Mn compositions. The latter often contain high concentrations of Co, Ba, Ce, and sometimes Pb, which are typical elements of oceanic ore genesis. Monocerianite (CeO₂) and phosphate-rare earth spherical formations are also common. The ideal beads in noble opal are composed of pure silica and water molecules. With all the variety of conditions and environments for the formation of spherical forms of matter, the controlling mechanisms are surface tension forces (in conditions of liquid heterogeneous media), the gravitational factor and condensation phenomena in closed chambers. The cooperativity of the process determines the unified state of the substance and its morphology.

The structure of benthic foraminifera shells was studied by X-ray microtomography as a clarifying step in the study of secondary authigenic carbonate formation on foraminifera shells at methane vent sites. Without destroying the specimens, images of the outer surface and sections of benthic foraminifera shells were obtained, and the percentages of shell volumes, solid inclusions, and voids within the shells of the specimens were calculated. Shells of the species Nonionellina labradorica, sampled from sediment horizons corresponding to intense and prolonged methane events, compared to shells of the same species from horizons without methane events, show a 26.9% increase in the mean shell fraction, a nearly twofold increase in the mean solid inclusion fraction, and a 10.4% decrease in the mean shell void fraction. For shells of the species Uvigerina parvocostata, a similar comparison showed the following results: an increase in the mean value of the shell fraction by 6.5%, a 4-fold decrease in the mean value of the fraction of solid inclusions, and a 6.3% decrease in the mean value of the void fraction.