Vol 472, No 2 (2017)

Radiolarians of Leugeonidae Yang et Wang, 1990, which represent a morphologically distinctive group of spherical radiolarians of the Spumellaria order, were found for the first time in Crimea and reliably confirm the Jurassic age of the finding. The nodules, which host the Jurassic radiolarians, were collected by A.S. Alekseev in 1983 in the terrigenous sequence of the Lozovskaya tectonic zone. The radiolarian assemblage in the nodules includes Levileugeo ordinarius Yang et Wang, Triactoma jonesi Pessagno, Pseudocrucella aff. prava Blome, Paronella kotura Baumgartner, P. ex gr. mulleri Pessagno, and Praeconocaryomma sp. The Levileugeo genus is easily identified due to its unique hexagonal element, which is typical only of the Jurassic, in particular, Upper Bajocian–Lower Tithonian radiolarians.

Analyses of trace elements and Lu/Hf isotopes have been carried out in already U–Pb dated detrital zircons from the Upper Ordovician sandstones of the southern part of the Bashkir Uplift. The concentrations of trace elements in the zircons suggest that they were derived from rocks of intermediate (62%), basic (24%), and felsic (9%) compositions as well as alkaline rocks (2%). The Lu/Hf systematics of the zircons demonstrated a wide variation of both ε_Hf (from +9.5 to–8.7) and model ages of the parental rocks (1.60 Ga < T_DM^C < 3.28 Ga). Comparison of the isotopic–geochemical characteristics of the detrital zircons from different levels of the Riphean–Paleozoic sequence of the Bashkir Uplift against those from the Early Cambrian Brusov Formation of the Mezen Basin and Early Neoproterozoic Dzhezhim sandstones of Timan Ridge suggests that at the end of the Late Precambrian near the Uralian margin of Baltica a large block of Late Mesoproterozoic–Early Neoproterozoic crust existed, comprising a significant proportion of melanocratic rocks.

It has been established that terrigenous units of mainly carbonate deposits of the Yudoma Group in the Uchur–Maya Region of the Siberian Platform contain an assemblage of Late Vendian Ediacaran-type macrofossils. The assemblage contains species such as Aspidella terranovica, Beltanelliformis brunsae, Nenoxites curvus, and Palaeopascichnus sp., which had widespread geographic distribution. Finds of Ediacaran fossils in fossil-rich deposits of the Yudoma Group have expanded the possibilities of using the classic biostratigraphic approach applied for subdivision and global correlation of carbonate deposits in Late Precambrian paleobasins.

The western Baikal region (Ol’khon region, Nutgei zone, Kharikta area) is characterized by the development of packets of thrust-type folds and synkinematic granites corresponding to the stage of thrust deformations (overthrust-type granites). Two stages in the formation of thrust-type folds separated by episodes of granite emplacement are definable. The data obtained make it possible to estimate both the time of transition from thrust to strike-slip deformations and the duration of accretionary‒collisional events that resulted in regional strike-slip deformations, which terminated in the western Baikal region 460‒455 Ma ago.

U–Pb dating of tonalite of the Shaytantas Pluton located within the Ulutau sialic Massif (Central Kazakhstan) has been carried out. Their crystallization age of 521 ± 2 Ma corresponds to the Early Cambrian (boundary of Stages 2 and 3). The obtained geochronological data allow us to identify the Early Cambrian stage of the intraplate magmatic activity in the history of formation of the sialic massifs in the western part of the Central Asian fold belt.

This work presents the geological structure and a description of gold-ore manifestations and gold placers in the Un’ya–Bom ore-placer cluster of the Amur gold-bearing province. The host rocks are Late Paleozoic and Mesozoic black-shale formations. Intrusive formations are rare. The sublatitudinal Un’ya thrust fault, along which Paleozoic sandstones overlap Mesozoic flyschoid deposits, is regarded as an orecontrolling structure. Gold–quartz and low-sulfide ores are confined to quartz-vein zones. Ore minerals are arsenopyrite, scheelite, ferberite, galena, and native gold. Gold-ore manifestations and placers contain high-Hg native gold. The high Hg content in native gold is explained by the occurrence of the eroded frontal part of the gold-ore pipe in the ore cluster, a source of native gold.

The geochemical features and conditions of formation of the Paleozoic epithermal Au–Ag mineralization in the pre-accretion Kedon (D_2–3) volcanoplutonic belt located within the Omolon craton terrain are described. The new data on the composition and contents of trace and rare-earth elements (REEs) in igneous ores of epithermal deposits is provided. The elevated grades of a wide range of trace elements as compared to the average values of the upper crust have been identified.

New types of geochemical barriers on which chemical elements are immobilized as a result of combined complex formation and precipitation of barely soluble mineral phases are examined. A significant concentration of major components (Fe, Al) forming more stable complexes than an immobilized component X in the material is a necessary condition for this type of geochemical barriers. Filtration of the solution through a geochemical barrier is accompanied by substitution of X in the complex with a major component. As a result, the activity of X in the free state increases, and one barely soluble mineral phase or another of the component X precipitates when the state of saturation is achieved.

The problem of the Daly Gap is considered for the example of bimodal basalt–trachyte series and their intrusive analogs (layered syenite–gabbro intrusions). It is shown that the gap is not controlled by the processes of crystallization differentiation or liquid immiscibility in intermediate chambers of igneous systems (intrusive chambers) and has a primary nature. We interpret its origin as from the existence of two independent types of melts from the materials of head parts of the same mantle plumes. These are mid-alkali Fe–Ti basalt, products of its adiabatic melting, and trachyte, which is the result of incongruent melting of the material of the upper cool rims of plumes under the influence of fluids percolating from the underlying zone of adiabatic melting.

Analysis of smoke blanketing of European Russia (ER) in summer 2016 is presented. The results of the analysis indicate that the cause of the smoky atmosphere over ER was long-range transport of smoke from wildfires in Siberia. The aerosol optical thickness at a wavelength of 550 nm over ER in late July reached 3. The features of circulation in the troposphere over northern Eurasia in July 2016, with an anomalous east transfer of combustion products in the troposphere over thousands of kilometers, which is opposite to the westerly transfer prevailing in the mid-latitudes, are discussed. A comparison of variations in the probability distribution functions of the aerosol optical thickness is performed for ER and Siberia for the summer periods in different years with massive wildfires.

A long-term endogenous nanomicroseismic event was registered instrumentally for the first time on Valaam Island (Lake Ladoga) in the winter of 2012. In the past, similar events in the form of acoustic emissions of separate phases have occurred from time to time and were heard by many residents and visitors to the island. This emission has long been known as barantida. The identification of the signal was based on a comprehensive analysis of the obtained seismograms and the subjective descriptions of this rare phenomenon by witnesses. It is proposed to continue instrumental observations in the mode of continuous high resolution seismoacoustic monitoring.

In 2013, simultaneous observations of acoustic and electromagnetic emissions ranging from 200 Hz to 11 kHz were carried out in Kamchatka; as a result, abnormal surges of the emissions were registered 1–2 days before seismic events with magnitudes M_LH ≥ 5 at a hypocentral distance up to 200 km. The most likely cause of the occurrence of the abnormal emissions in inherently different fields was activation of deformation processes preceding the earthquakes.

The aim of this work is to obtain the vertical isotopic profile of the thick Pestsovoe pingo ice core in the southern part of the Tazovsky Peninsula, to determine the oxygen and hydrogen isotopic composition of the ice, and to reveal its formation conditions. Two trends were identified for the isotopic profile of the pingo ice: an insignificant increase of the δ¹⁸O (~1.5‰) and δD (~9‰) values at depths of 12–15 m and a gradual decrease of isotopic values by 3.8 and 23‰ for δ¹⁸O and δD, respectively, at a depth of 15–26 m. The formation of the pingo ice core in the semiclosed system resulted in fractionation of the isotopic composition of oxygen and hydrogen by more than 4 and 20‰, respectively.

According to radiochemical and biostratigraphic studies of the buried peat layer in the Cheremoshnik key section on the East European plain, the first age dating of this peat was obtained and its assignment to the Mikulino interglacial was confirmed. The Th/U isotope age data obtained for the peat horizon allow us to state with confidence that it was formed during the MIS5e. It was found that a variety of signs, including the lithological characteristics of dated layers and climatic indexes, is evidence that the Cheremoshnik site and Borisoglebsk upland occurred in the periglacial zone during MIS3–MIS2.

The data on the ice distribution in the Franz Josef Land Archipelago area during the 2010/2011 and 2014/2015 ice seasons depending on climate oscillations are presented with consideration of the dynamics of the annual and seasonal variations in the main parameters of the ice regime (ice coverage area, position of the ice edge, duration of the ice period). Using the data on the ice coverage in the Barents Sea from the electronic database, a comparative analysis of changes in the average seasonal parameters of the ice regime is performed for the Franz Josef Land Archipelago and the entire Barents Sea.

We analyze autocorrelations and power spectra of the time series of monthly mean data characterizing sea surface temperature anomalies in the equatorial Pacific in the years 1920–2013 and show that the rhythms of El Niño–Southern Oscillation can be interpreted as the responses of the climate system to the external quasi-periodic forcing generated by the motions of the Earth’s pole. We conclude that the ENSO phenomenon has no prediction limits.