Vol 487, No 2 (2019)

An attempt to provide a new explanation for the change in the geodynamic regime in the Early Cretaceous is presented below. It accounts for data on a number of global geodynamic characteristics in the range of 200–65 Ma reflecting processes both deep in the Earth and on the surface, and seemingly directly unrelated to the formation of a transform margin in Eastern Asia. It has been found that the geodynamic regime changed in the range of 115‒110 Ma.

Two new localities of Mesozoic mammals have been discovered: Bol’shoi Ilek and the Berezovaya River (Russia, Krasnoyarsk Territory, Lower Cretaceous, Ilek Formation). Bol’shoi Ilek locality has yielded an edentulous fragment of the maxillary of Docodonta indet. A fragment of dentary without teeth attributed to Mammalia indet. (presumably eutriconodontan or symmetrodontan) has been found at the Berezovaya River locality. These new localities fill the geographical gap between previously known mammalian sites of the Ilek Formation in the basins of the Kiya and Bol’shoi Kemchug rivers.

The relationship between radon and the tectonic activity of faults for two geodynamically active regions of Central Mongolia is shown with account for the influence of individual characteristics of the radon field. As a whole, the radon activity of the faults increases with an increasing contribution of extension to the dynamic environment of their formation, with increasing seismic activity, and near concentrated faults of the late stages of evolution in comparison with the wide zones of fractures at the early stages of the formation of the internal structure. The studied patterns should provide an increase in the efficiency of application of radon surveys in investigation of the seismic hazard of faults in the Earth’s crust.

Analysis of the data of seismoacoustic investigations and geotechnical drilling in the Eastern Barents Sea has shown the following. The cover of the Upper Weichselian glacial deposits spreads regionally. It represents a seismostratigraphic complex (SSC) SSC III, which occurs unconformably on the Mesozoic deposits and partly on the Lower Weichselian morain (SSC V) and is overlain unconformably by the Late Glacial glaciomarine (SSC II)–Holocene marine (SSC I) sediments. SSC III consists of two seismofacies (SF). The dominant SF III-C is represented almost entirely by ordinary moraine, and SF III-T is represented by M-moraine. The occurrence of these moraines almost totally determines the distribution of the SSC III thicknesses. The ordinary moraine thickness varies from <10 m to 10–25 m. The M-moraine forms positive accumulation bodies huge in plan with a thickness of >25 m, reaching 50–75 m. The Upper Weichselian deposit cover has also exhibited other immense structural morphological elements: end moraines (a giant form has been recorded) and powerful subglacial cuts representing a unique unburied analog of so-called tunnel valleys. The features of the structure, composition, and thicknesses of the SSC III deposit cover are determined by the specific character of the development of Last Glaciation in the region.

For the first time among Russian meteorites, refractory forsterite-rich inclusions are determined in the North Kolchim meteorite (H3). Forsterite-rich inclusions are found mainly in carbonaceous chondrites; they are extremely rare in ordinary chondrites. These inclusions are considered by most researchers as one of the earliest formations in the Solar System. The inclusions of the North Kolchim meteorite are composed of high-magnesia forsterite (FeO 0.4–2%), which contains higher CaO (0.5–1%) and Al₂O₃ contents (up to 0.4%) and is depleted in MnO. In some places, forsterite is found in intergrowths with high-magnesia enstatite (FeO of 0.5–2.5%) also containing CaO impurities of up to 0.5%, Al₂O₃ of up to 1.5%, and MnO below the detection limits. A characteristic feature of forsterite-rich inclusions is that, unlike chondrules, they are mostly represented by acute-angled fragments, and that is probably due to their relatively frequent collisions.

The early Mesozoic Baga-Khentei pluton is a part of the Daurian–Khentei batholite that was formed under the impact of the Mongolian plume on the lower horizons of the continental crust in the collision compression zone that appeared during closing of the Mongol–Okhotsk Ocean. Mantle and crustal melt sources were involved in the formation of the batholith and its margins. The Ikh-Narotin-Khid massif tends to the boundary of the rift region on the periphery of the Late Mesozoic area. The petro-geochemical similarity of its rocks to the composition of host gneisses suggests that the latter belong to the most likely substrate in the formation of palingenic granitoids of the calc-alkaline series. The differences in the rock compositions of large plutons are shown in minor differentiation of the Baga-Khentei massif, which is likely to be determined by the anatexis conditions and the subsequent formation of melts in the collision compression setting, while the granites of the Ikh-Narotin-Khid massif were formed under extension, which favored deep differentiation of magmatic melts.

A find of coesite in a kyanite graphite–diamond-bearing eclogite xenolith from the Udachnaya–Vostochnaya kimberlite pipe is described in this paper. The coesite relics were found in intensely fractured garnet indicating some influence of the kimberlite melt, which is supported by the typical secondary mineral assemblage around this inclusion. These data indicate that shallower diamond-free coesite-grade rocks (2.7 GPa) underwent metamorphism distinct from diamond-bearing coesite eclogites (≥4 GPa). The metasomatic alteration of rock as a result of the C–O–H fluid-rock interaction during diamond crystallization may be another possible reason for the absence of coesite in diamond-bearing xenoliths.

The sorption–desorption barium balance during interaction between silt–sand terrigenous material and salty seawater is determined experimentally. The mean value of barium desorption in the mixing zone of river waters and seawaters is 13 μg/g, making up an additional supply of 80 000 tons of Ba per year, or 8.6% of its runoff to the ocean, without runoff transformation at the river–sea geochemical barrier being taking into account. The obtained estimate of the role played by desorption in transformation of dissolved barium runoff agrees, in terms of the order of value, with the data of real observations for the majority of mouth zones of the world rivers.

The results of experimental synthesis of carbide Fe₇C₃ at 5.5 GPa are presented. It is found that carbide Fe₃C and several polytypes of carbide Fe₇C₃ are formed along with diamond during cooling of the system. It is considered that the Fe₇C₃ phase is a component of the Earth’s inner core. Our results indicate that polytypic carbide modifications could have been formed under natural conditions at relatively low pressures during differentiation of the Earth.

The first data on five primary molybdenite sources within the gabbro-dolerite complex of Pay-Khoy (Pay-Khoy Ridge, Yugra Peninsula, Russia) are presented. The mineral is extended areally in Devonian ore-bearing gabbro-dolerites, contact rocks, and quartz veins. This paper considers the mineralogical–geochemical features of molybdenite, its occurrence, the composition of host rocks, and spectroscopic studies.

Morphometric terrain parameters such as slope angles and altitudes make a considerable contribution to the features of mudflows. In order to assess the contribution of these factors, this study analyzes their characteristics in the Western, Central, and Eastern Caucasus on the basis of an original digital terrain model. The average slope angles in the Western Caucasus are higher by 0.5° than those in the Central and Eastern Caucasus, thus contributing to more active mudflow. On the other hand, the Western Caucasus is distinguished by lower altitude differences. From the standpoint of this factor, the Central Caucasus is the most mudflow hazardous. Hence, the absolute altitude distribution and high forestation neutralize the factor of more significant slope angles and ensure the less considerable mudflow danger in the Western Caucasus relative to the Central and Eastern Caucasus.

An integrated mathematical model of the Barents Sea and White Sea Large Marine Ecosystem proposed as a tool for assessing natural risks and efficient use of the biological resources is considered. The model includes the following main blocks (modules) of (а) oceanographic variation and biological productivity; (b) trophodynamics and fishery management; (c) environmental and biota pollution; (d) social and economic development; and (e) assessment of ecological risks from marine activities. The results of using the integrated model for assessing hydrological variability, long-term dynamics of ecosystem productivity, and assessment of fishing pressure on the most important fishery species of the Barents Sea are presented. A new scheme of zoning of the Barents Sea area performed under the supervision of Academician G.G. Matishov with respect to geomorphological and hydrological factors is proposed. A comparative scheme of distribution of the estimated gross primary production in the Barents Sea area in the second half of the twentieth century and in the 2010s is presented. The energy balance of the Barents Sea ecosystem in the late 1900s and early 2000s is calculated by the model of trophodynamics. The necessity of using mathematical models of the ecosystem instead of single-species models during the calculation of fishing pressure on the populations is suggested. To estimate fishing mortality, it is necessary to take into account not only spatial effects related to the features of a fish life cycle and distribution of fishing pressure, but also the impact of climate factors and ecosystem interactions. The use of recent information technologies both in the field of accumulation and analysis of the primary data and in the area of their subsequent generalization for the diagnosis of past changes makes it possible to understand better the possible consequences of the existing plans for developing and use of available natural resources for the Barents Sea and White Sea LME based on the experience (sometimes negative) of recent years and expected climate changes.

A new phenomenon, an increase in the winter and early spring streamflow of Siberian rivers, has been studied. Based on the assumption that the increased discharge may be due to permafrost degradation in the river basins, the rate of degradation of the different zones of permafrost distribution is estimated by modeling. A mathematical model that takes into account the typification of the permafrost zones and reflects the dependence of the streamflow on the cryological conditions of the drainage basins has shown rapid degradation of sporadic permafrost and expansion of discontinuous permafrost owing to the intense transition of continuous permafrost to this state.

The quantitative characteristics of the bottom sediment color of the Chukchi Sea is presented. The correlation relationships with the contents of grain-size fractions, chemical elements, and biogenic components are analyzed. The diagenetic factor influence is considered. The prospects of the colorimetric index such as saturation S is noted in the matter of lithostratigraphy.

There are contradictory opinions on the contribution of the near-surface layer of bubbles to the attenuation of low-frequency sound in the ocean. Taking into account the new experimental data on the distribution of bubbles in seawater, it is shown that the influence of the near-surface layer of bubbles on the structure of the spatial decay in sound propagation can be significant at rather typical concentrations of bubbles in the near-surface layers of the ocean. A possible explanation for the contradictions is the spatial restructuring of the field in which the main effect of the bubbles is focused on the near distance; sound attenuation at a great distance is not affected.

The junction zone between Lomonosov submarine ridge and the shelf of the East Siberian Sea was studied. The aim was to prove the absence of a strike-slip fault in the junction zone between Lomonosov Ridge and the East Siberian shelf. The problem of the existence of a fault zone in the region where the Lomonosov Ridge joins the East Siberian shelf is still currently debateable. The geological and geophysical data used to solve it are insufficient. To remove this ambiguity, seismological data obtained in neighboring areas were used. An analysis of the map of earthquake epicenters in the region showed that, if the fault zone mentioned existed, present-day intraplate seismic activity would certainly be observed within its limits. The absence of seismicity in the junction zone between Lomonosov Ridge and the adjacent shelf clearly indicates the genetic unity of these structures.