Vol 487, No 1 (2019)

This paper provides a brief tectonic and geological overview of the Ural– Novaya Zemlya Forebelt of Oil-and-Gas Accumulation and describes the conditions under which the hydrocarbon deposits were formed in the structures of high- and low-angle reverse faults (upthrust-and-thrust) on the eastern side of the belt. It is shown that the early stages of belt formation are associated with Paleozoic subduction and obduction processes that occurred in the transition zone between the Paleo-European continent and the Ural paleo-ocean located eastward (in modern coordinates) of the continent. The intensive cover-folded dislocations of the western vergency are fixed into the eastern side of the Ural–Novaya Zemlya Forebelt of Oil-and-Gas Accumulation. We associate these dislocations with the continental collision that occurred during the closure of the Ural paleo-ocean in the Late Paleozoic, and in the northern-most segments of the belt, probably in the Early Mesozoic. The structural paragenesis of the eastern side of the Ural–Novaya Zemlya Forebelt of Oil-and Gas-Accumulation includes upthrust–thrusts and thrusts, as well as structural units of different sizes, which were formed under the conditions of latitudinal compression.

Niobium metallogeny over the course of geological history has been considered on the basis of data from 45 largest deposits in the world belonging to any of three metallogenic types: alkaligranitic, foidic, and carbonatitic. The deposits were formed under variable intensity from the Middle Paleoproterozoic to the Cenozoic. The greatest resources of niobium are accumulated in the deposits formed during the Rodinian, Pangean, and Amasian supercontinent cycles. These cycles are characterized by the prevalence of deposits associated with carbonatite complexes.

New data on the composition of volcanic rocks of the Atlantis Rise (Central Atlantic) have been obtained. Incoherent element ratios suggest that those volcanics were formed at low degrees of partial melting within a garnet facies at depth. The isotopic ratios of Pb and Nd imply that their compositions cannot be unequivocally attributed to any of the nearby magmatic provinces (Madeira, Canary, or Cabo Verde). They are distinguished by high radiogenic Pb isotopes, indicating a significant addition of a HIMU component. No significant EM1 addition has been observed. It may be assumed that the Atlantis Rise volcanics were formed from an independent mantle source.

Based on study of the morphological features of a coal seam in a mine of the Eastern Donbas, the mineral and coal elements of the object studied were identified as a single sedimentary association of a pseudo-washout nature. Specific criteria for attributing coal-bearing structures to epigenetic or syngenetic washouts of a coal seam were elaborated.

Transverse petrogeochemical zoning in the location of volcaniс rocks of the Shadaronsii (J_2‒3) and Mulinskii (J_2‒3) groups typical of volcanic arcs has been revealed in Eastern Transbaikalia. Volcanic rocks of the tholeiitic and calc-alkaline series occur in the frontal zone of the volcanic arc and in the suture zone of the Mongol–Okhotsk Suture (MOS); volcanic rocks of the calc-alkaline series occur in the rear zone of the MOS. The volcanic rocks of the frontal and rear parts differ in their petrogeochemical composition, in the degree of iron oxidation, and in the distribution of REEs. These differences are typical of volcanic arcs in the zones of transition from the ocean to the continent. Vulcanoplutonic structures of the frontal zone of MOS produce gold mineralization; the rear zone of MOS produces polymetallic mineralization.

Semi-quantitative and qualitative analyses of the overlapping (postvolcanic) ore mineralization of the main volcanic rock types that compose submarine rises in the Sea of Japan (marginal continental, postrift, and alkaline) were performed for the first time. Special attention was given to the mineral forms of nonferrous, noble, and rare metal occurrence in these rocks. This mineralization is expressed most vividly in the rocks of the postrift type; this is attributable to the high fluid saturation of the parent magma and the long duration of volcanic and the associated postvolcanic processes.

The primary isotope–geochemical and geochemical characteristics (by the TerraneChrone® technique) are presented for detrital zircons dated previously (U/Pb, LA–ICP–MS dating) from Ordovician sandstones (the Ordovician-2 borehole of the Sol-Iletsk block). The characteristics of the treated zircons were compared to the corresponding parameters of the complexes constituting the possible sources provinces.

The results of expeditionary studies of the behavior of mercury in the water of small rivers in the basin of Onega Bay of the White Sea are presented. The priority forms of mercury migration are determined, and the forms of its occurrence along the main stem of the Kyanda River are estimated. The interrelations between the contents of various forms of mercury on the one hand and the salinity, pH, and Eh of waters on the other hand are analyzed. The influence of the hydrological phases on the transformation of inorganic forms of mercury is revealed. The differences in the levels of contents of dissolved mercury and its relation to salinity in the estuarine areas of marginal filters of the subarctic rivers under natural and anthropogenic conditions are established.

The information content of lake sediments in Western Siberia for reconstruction of the latest environmental and climatic changes was evaluated. The possibility of reliable registration of negative changes in the physicochemical parameters of lake waters was studied on the basis of classical and innovative methods of diatom analysis.

The results of study of primary melt inclusions in accessory Cr–spinelides from dunite have revealed features of the chemical compositions of high-magnesium picrite–basalt melts that formed ultramafic massifs of the Siberian Platform. Computational modeling (with the PETROLOG and PLUTON software) using the inclusion compositions allowed determination of the crystallization temperatures of olivines from dunites of the Guli (1520–1420°С), Konder (1545–1430°С), Inagli (1530–1430°С), and Chad (1460–1420°C) massifs. The Cr–spinellids from the same complexes crystallized at Guli (1410–1370°С), Konder (1420–1380°С), Inagli (up to 1430°С), and Chad (1430–1330°С). Overall, computational modeling has revealed two types of trends of high-Mg melt evolution on the Siberian Platform. The first type is characteristic of the Guli Pluton, with the following rock sequence: dunite–pyroxenite–alkalic rocks. The second type occurs in the Konder massif, with a different sequence: dunite–kosvite–pyroxenite and olivine–diopside rocks.

The isotope and geochemical characteristics of Eocene–Oligocene igneous rocks of Western Kamchatka were studied. It was shown that igneous rocks of the Eocene Kinkil complex of Western Kamchatka (45–53 Ma) were characterized by the geochemical features of subduction volcanism. The isotope composition of the rocks by Sr, Nd, and Pb along with the low concentrations of HFSEs and HREEs related to the MORB composition point to the formation of primary melts from depleted or slightly isotope-enriched sources of the mantle wedge contaminated to various degrees by quartz–feldspar sialic sediments. From the end of the Middle Eocene, under the conditions of intraformational activation in Western Kamchatka, the K–Na-alkali–basalt magmatism appeared (46–31 Ma) with similar geochemical characteristics to those of E-MORB, along with the ultra-potassic alkali–basalt magmatism developing right up to the Early Miocene (35–17 Ma). The geodynamic nature of the Late Paleogene alkaline magmatism implies the occurrence of processes of diffuse rifting.

The main aim of this work is to study the oxygen isotope composition of Late Pleistocene syngenetic repeated ice wedges and to obtain a high-resolution isotope diagram based on detailed sampling of the Seyakha yedoma section in the sequence of the Late Pleistocene third lagoonal-marine terrace near the mouth of the Seyakha (Zelenaya) River, on the shore of the Gulf of Ob. According to three new radiocarbon ages (25.2 to 23.3 ka BP) from absolute heights of +2 to +5 m and also ages obtained earlier (17.3 ka BP from +18.8 m; 11.6 ka BP from +21.2 m), the approximate age of this ice wedge ranges from 23 to 15–18 ka. The values of δ¹⁸О in the upper fragment of the ice wedge vary from –25.75 to –23.15‰. The amplitude of horizontal variations in δ¹⁸О at +15.2 m height is 1.49‰ (–23.41 to –24.9‰). The lower fragment of the ice wedge at +6 m height is characterized by a broader variation range of δ¹⁸О compared to the upper one: δ¹⁸О varies in the horizontal direction from –23.41 to –26.63‰. The detalization step of the oxygen isotope diagram obtained is 80–100 years. The mean January temperature in the period 23–15 (18) ka BP ranged from –35 to –39°C.

Rock freezing affects soil complexes with maximum temperature gradients and forms a set of the specific cryotrasologic features in a solid matrix of soils. Remaining unchanged, these features serve as direct and indirect indicators of the past cryogenic settings. Transformation of the soil mass at the macro- and micromorphological levels is related to the direct indicators. Soil gleyzation in the drained positions is conditioned by the occurrence of frozen aquicludes in past settings; it is related to indirect indicators. We revealed the complex of such features in paleosols to the north of the European and Western Siberian Loess Belt and used them to estimate the cryogenic settings of the Late Pleistocene.

An isotopic–geochemical study was carried out for waters of Tsivolkii and Sedov bays (southeastern coast of the Novaya Zemlya Archipelago). The waters of these bays can be freshened by several potential sources involving the river runoff from the continent, atmospheric precipitation of the region, and waters coming from the archipelago. The possibility to use the deuterium excess for identification of freshwater components in the waters entering the bays studied is shown. The calculations, which we made on material sampled in 2015, showed the presence of the estuarine waters of the Ob River in the surface waters of Sedov Bay. In the same period, the waters of the halocline of Tsivolkii Bay were freshened by local sources, namely runoff from the Novaya Zemlya Archipelago.

The first field data describing the dynamics of the carbonate system, the aragonite saturation state, and CO₂ fluxes between the ocean and the atmosphere in the Gulf of Anadyr in the late autumn season are presented. It was established that during this period the gulf waters absorbed carbon dioxide from the atmosphere at a rate of –22.5 mmol m^–2 day^–1, which determined the “classical” mechanism of seawater acidification due to uptake of excess atmospheric CO₂. In general, surface waters of the gulf were supersaturated with respect to aragonite. The exception was the highly dynamic region of Anadyr Strait, where the vertical distribution of the investigated parameters was homogeneous, the surface waters were close to equilibrium with respect to aragonite, and the CO₂ flux was directed to the atmosphere. The bottom waters of the gulf, in contrast, were characterized by significant seasonal corrosivity due to remineralization of organic matter. It was shown that, during the late fall, relatively salty and acidic, quasi-equilibrium with respect to aragonite, and oxygen-depleted waters with high concentrations of nutrients and CO₂ enter into the Chirikov Basin and further to the Arctic Ocean with Navarin Current.

Based on the data of experimental studies of wave disturbances in the Earth’s atmosphere before and after the earthquakes in Uzbekistan (May 26, 2013) and Kyrgyzstan (January 8, 2007), earlier unknown changes in the parameters of internal gravity waves are revealed. These changes were manifested during the period of five days before the earthquake and in certain cases can be used for short-term prediction of the time when seismic events are to occur.