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Vol 53, No 3 (2018)
- Year: 2018
- Articles: 5
- URL: https://journals.rcsi.science/0024-4902/issue/view/9874
Article
Structure and Formation Conditions of the Bazhenovo Horizon in the Pal’yanovo Area, West Siberia
Abstract
Comprehensive studies of cores from 7 boreholes drilled in the Pal’yanovo area provided insight into the Bazhenovo Horizon in southwestern Siberia represented by the lower subformation of the Tutleim Formation. The work presents a typification of organic-rich biogenic-terrigenous rocks. The Bazhenovo Horizon is divided into 11 lithotypes grouped into 5 large members. Members I‒IV correspond to the lower subformation of the Tutleim Formation; member V, to the upper subformation. The identified members are traced explicitly over the Pal’yanovo area, making it possible to examine the whole vertical succession of the Tutleim Formation and reconstruct its evolution based on the proposed sedimentation model.
179-189
Ocean Redox State at 2500‒500 Ma: Modern Concepts
Abstract
Modern concepts on variations of the redox conditions of Proterozoic ocean and atmosphere are reviewed. Generalized data indicate a non-linear evolution of the О2 content in atmosphere and ocean for almost 2 Ga of the geological history. Contrasting distribution of minimum and maximum values of diverse proxies of the ocean redox state was found for the Great Oxygenation Event, Early–Late Proterozoic transition stage, and the Late Precambrian–beginning of Cambrian. The last interval is marked by a wide scatter of Mo, V, and Used concentrations and values of Мо/TOC, δ98Mo, δ53Cr, and δ82Se in different geological objects. This time interval also coincided with one more large-scale oxygenation event, Neoproterozoic. Thus, according to the modern concepts, the О2 contents near the Earth’s surface and in ocean significantly varied during the entire Proterozoic. These concepts are consistent with the assumption by Frolov and many other researchers concerning the heterogeneous distribution of рН and Eh in ancient hydrosphere and the existence of diverse, sufficiently contrasting “gas” facies. They also agree with conclusions by Sochava that the periodical variations of О2 content in atmosphere and hydrosphere, especially at the Precambrian–Phanerozoic boundary, are related to the mass extinctions, emergence of adaptive response of animals (appearance of exoskeletons, food search strategy change, and others) and heavy taxonomic radiation of the latters.
190-211
Sources and Typomorphism of Platinum in Carbonaceous Rocks in Far East Russia
Abstract
Results of the study of carbonaceous metasedimentary rocks in the northern part of the Khanka and eastern part of the Bureya massifs (Primorye and Khabarovsk territories, JAR) and associated platinum mineralization are presented. It is shown that platinum minerals are represented by microparticle dispersion in shales of the greenschist-facies metamorphism (Sutyr and Kimkan sequences, Mitrofanovo Formation) and by Pt and PtO2 nanoparticles associated closely with graphite in shales of the amphibolite facies (Turgenev and Soyuznoe graphite deposits). The studied carbonaceous sequences were likely formed in the hemipelagic setting in a suprasubduction trench during the intense input of terrigenous material into basin. Carbon was derived from the marine biogenic material and superimposed graphitization related to a lower crustal material. Iron ores in the carbonaceous shales are hydrothermal formations. Platinum mineralization was likely related to two sources: (i) sedimentary-chemogenic source that made up the protolith of graphite–sericite–quartz shales of the Sutyr and Kimkan sequences (Mitrofanovo Formation); (ii) graphitizing fluid generated in deep magma chambers. Mineralization produced from these sources is transformed during the hydrothermal activity (coarsening of microparticles) and/or regional metamorphism (disintegration of microparticles and remobilization of Pt into graphite).
212-235
Reef Formations in the West Canada Basin and Their Oil and Gas Potential
Abstract
Devonian reefs are widespread in the West Canada Basin in three regions: lower Givetian in the north (Elk Point subbasin), upper Givetian and middle Frasnian in the central part (framing of the Peace River Arch), and middle Frasnian (southern end of the basin). Each stage of reef formation ended with regression, and the last reefs terminated long before the Frasnian/Famennian biotic crisis and mass extinction. Reefs of this basin are petroliferous. Moreover, the structure of reservoirs is determined by the reef type, and the highest reservoir properties are related to bioherm varieties in reefs.
236-251
Geochemistry of Brines in the Tunguska and Olenek Artesian Basins (Siberian Platform)
Abstract
A comparative analysis of the chemical composition of underground brines in sections of the Tunguska and Olenek artesian basins is accomplished. The paper examines the equilibrium degree of brines with host rock minerals: carbonate (dolomite, calcite, magnesite, strontianite), sulfate (gypsum and celestine), chloride (halite, sylvite) and some aluminosilicates (anorthite, albite, illite, montmorillonites, kaolinite, muscovite, and others). Origin of brines is discussed based on results of the calculation of genetic coefficients. The paper presents a schematic generalization of data on the chemical composition, mineral concentration, genesis, and abundance of brines in the studied subjects.
252-262