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No 3 (2025)
Articles
Geochemical peculiarities of the Pacific Pleistocene sediments
Abstract
In the geochemical review based on records from cruises of International project of Deep-Sea Drilling and other literature data concerning main lithologic types of the Pacific Pleistocene sediments we presented tables of average arithmetic chemical composition, meanweighted chemical composition, accumulation rates, and mass accumulation rates of chemical components. These tables can be used for comparative analysis with sediments of the same or other stratons in different oceanic basins and also with paleooceanic sediments on the continents. Terrigenous matrix dominates within lithogenic matter. We discovered a close resemblance between chemical composition of hemipelagic clays and volcanic sediments. Peculiarities of hydrothermal sediments are described. Using methods of mathematical statistics, we revealed main geochemical associations and principal factors determinating the chemical composition of studied sediments. Masses of oxides of petrogenic elements and a number of trace elements have been calculated for Pleistocene sediments. We managed to take an idea about average chemical composition of the Pacific Pleistocene.
Litologiâ i poleznye iskopaemye. 2025;(3):245-272
245-272
Vendian mudrocks chemical composition and some paleoclimate quantitative features in the Middle Urals
Abstract
It is shown that the lithogeochemical features of the Vendian non-glacial mudrocks in the Middle Urals (Serebryanka and Sylvitsa groups) give reason to believe that the average annual temperatures in paleo-catchments during their accumulation varied from 4 to 21°C. Such temperatures mainly comply to temperate and warmly temperate less often warm climates. Calculated RW-index values also suggest that the paleoclimate in the Vendian catchment areas was generally temperate. At the same time, some mudrock samples of the Garevka, Kernos, and Perevalok formations, as well as the Kobylii Ostrov Member of the Chernyi Kamen Formation, have RW-index values comparable to those of modern continental or subarctic climate. Variations in RW-index values and reconstructed MAP values demonstrate similar cooling/warming trends for clay rocks of non-glacial intervals of the Vendian in the Middle Urals.
Litologiâ i poleznye iskopaemye. 2025;(3):273-295
273-295
The Ozerninskaya strata of the Uda-Vitim zone (Western Transbaikalia, Russia): composition, age, and formation environment
Abstract
The results of the lithological and biostratigraphic study of the Ozerninskaya strata, the accumulation of which is associated with the beginning of the early Hercynian stage in the development of the Uda-Vitim structural-formational zone of the Baikal-Vitim folded system and the formation of gold-pyrite-polymetallic ore deposits of the Ozerninsky ore cluster, are considered. The strata is isolated from the Lower Cambrian Oldynda Formation. It is composed predominantly of greywacke arkose and quartz greywacke and includes two substrata. The lower substrata is represented by quartz-feldspar sandstone and siltstone with interlayers and lenses of polymictic conglomerate and gritstone, while the upper substrata is composed of interbedded polymictic sandstone and siltstone, calcareous siltstone and limestone with interlayers of clayey, clayey-siliceous, coal-clayey siltstone and mudstone. The paleontological characteristics of the Ozerninskaya strata determines its stratigraphic belonging to the Lower (Emsian Stage) – Upper (Lower Frasnian Substage) Devonian. The composition, structure, and paleo-biota indicate that the sediments formed in the open shelf sea environment with a significant input of terrigenous component. The lower substrata deposited in the shelf shallow water conditions, with active hydrodynamics, while the upper substrata accumulated in the most submerged parts of the shelf, in areas with stagnant hydrogeological regime.
Litologiâ i poleznye iskopaemye. 2025;(3):296-315
296-315
Age of detritic zircon and composition of Cambrian-Ordovician terrigenous-carbonate deposits in the middle reach of the Vilyui River (south of the Siberian platform)
Abstract
The article presents result of lithological and mineralogical studies of Upper Cambrian and Lower Ordovician terrigenous-carbonate deposits within the Vilyui syneclise (the middle reaches of the Vilyui River, south of the Siberian platform). The composition of detritic zircon, garnet, tourmaline and chromium spinels were carried out in a sample from the Upper Cambrian Kholomolokh Formation and two samples from the Balyktakh Formation (Upper Cambrian–Lower Ordovician). Predominant sources of the detritic minerals were igneous and metamorphic rocks of the Archean–Paleoproterozoic basement of the Siberian platform: rocks of acidic and intermediate compositions, amphibolite-facies metasediments and granulite- and amphibolite-facies mafic-ultramafic complexes. Results of U-Th-Pb dating of zircon from the Kholomolokh and Balyktakh Formations of the middle reaches of the Vilyui River showed a noticeable difference in the demolition sources of terrigenous matter in the Late Cambrian and Ordovician times. The sample from the Upper Cambrian Kholomolokh Formation contains the youngest zircon with a predominance of Neoproterozoic ages (peak ages of 550 and 845 Ma) indicating the main source of demolition in the Late Cambrian time were Neoproterozoic terranes rocks which are widespread along the southern margin of the Siberian craton. The Early Ordovician rocks of the Balyktakh Formation contain the main zircon population (~70%) f Paleoproterozoic (1880–1890 Ma) age. The Early Ordovician the most probable source of matter for the Vilyui syneclise was an uplift of the Archean-Paleoproterozoic basement in the Siberian platform central part that represented an eroded land during the Ordovician. The almost complete absence of younger zircon (~500–900 million years) in the Balyktakh deposits indicates a weak influence of the demolition source from the southeastern margin of the Siberian platform in the Ordovician time.
Litologiâ i poleznye iskopaemye. 2025;(3):316-345
316-345
First mineralogical and geochemical data on placer nephrite of the Vitim Highlands, Republic of Buryatia
Abstract
The material composition of placer (alluvial) dolomite-related nephrite from the Tsipa River in the nephrite-bearing region of the Vitim Highlands has been examined. Initial data on the mineral composition of both the inner and outer zones of alluvial dolomite-related nephrite pebbles have been obtained. Placer nephrite is characterized by a developed staining rim, a small amount of accessory minerals, fine-grained texture, randomly fibrous structure, and elevated alkali content. Chemical composition features of the staining rim formed under exogenous conditions include the development of manganese and iron hydroxides, with a significant increase in Fe3+ content and elevated levels of Co and Ba. A genetic relationship has been established between the placer nephrite and its primary source, the nephrite from the Kavoktinskoe deposit. A comparison between primary and placer dolomite-type nephrite has led to the identification of diagnostic characteristics for conducting expert assessments.
Litologiâ i poleznye iskopaemye. 2025;(3):346-360
346-360