Plate boundaries in the Far East region of Russia (from GPS measurement,seismic-prospecting,and seismological data)

The recent geodynamics of the Far East region of Russia is considered, where three large tectonic plates converge—Eurasian, North American, and Pacific, as well as several microplates—Okhotsk, Bering, and Amurian—have been hypothesized to exist. The available data on the position of the plate boundaries, the relative plate rotation poles, and the regional seismicity were analyzed, and parameters of plate motion models for northeastern Russia were determined in this study. The regional deep structure was investigated, using data obtained by different geophysical methods. The results of observations of the Magadan–Vrangel Island profile by deep seismic sounding (DSS), common-depth point (CDP) method, and correlation refraction method (CRM) are presented.     

Assessment of Planetary Indices of Geomagnetic Activity Based on Data from Individual Magnetic Observatories in the Russian Sector

Geomagnetism and Aeronomy - The relationships between local indices at stations in the Russian sector and the planetary Ap and Kp indices and the potential to evaluate planetary indices based on...     

Meridian observations of solar system bodies with the struveertel instruments of the Pulkovo Observatory

Two Struve-Ertel instruments were used for the daytime observations of the Sun, Mercury, Venus and Mars at Pulkovo from 1956 to 1976. The FK4 equinox and equator corrections were derived. Both the instruments were installed in 1983–1986 at the Kislovodsk Station of the Pulkovo Observatory. The atmospheric dispersion and lateral refraction have been estimated at the Station.     

Magnetic fronts in galaxies

Magnetic-field reversals observed in the Milky Way at one or more Galactocentric radii are interpreted as long-lived transient structures containing memory of the seed magnetic fields. These magnetic fronts can be described using the so-called no-z approximation for the nonlinear, mean-field dynamo equations, which are the topic of the paper. We obtain asymptotic estimates for the speed of propagation of discontinuities in the solution (internal fronts). These estimates agree well with numerical solutions of the no-z equations, and support support our interpretation of the magnetic-field reversals as long-lived transients.     

Microbial Mats As a Source of Carbonate Sediments in the Late Precambrian: Evidence from the Linok Formation, the Middle Riphean of the Turukhansk Uplift, Siberia

The Linok Formation is made up of clayey and carbonate strata, 180–300 m thick, formed at the terminal Middle Riphean on the northwestern margin of the Siberian Platform. In the modern structure, it is exposed in the lower part of the Turukhansk Uplift section. The sediments accumulated in the distal part of the epiplatformal basin as a symmetrical transgressive–regressive cycle. Its lower part represents a deep-water basin environment with the mixed carbonate–clayey sedimentation, whereas the upper part reflects the origination and evolution of a carbonate platform. Microstructures discussed in this work suggest not only the ancient existence of benthic microbial assemblages (mats) but their active influence upon the facies pattern of sediments as well. The influence was determined by the ability of mat-forming communities to produce carbonate sediments under certain environmental conditions. The analysis of the facies succession suggested the absence of an appreciable influx of carbonate material to the basin from other sources. Based on the carbonate generation ability, one can distinguish three (carbonate-free, low-productive, and high-productive) groups of microbial communities. Groups 1 and 2 represent deep-water basin mats, whereas group 3 represents relatively shallow-water platformal microbial–mineral systems. The carbonate productivity of communities is inversely proportional to the depth of their dwelling and the relative rate of clayey sedimentation. The morphological reconstruction of microbiolite structures showed that the structures in basins and platforms greatly differed in terms of the size of elements. The ability of microbial communities to generate carbonate could be realized only within large ecosystems.     

Microbial Mats and Terrigenous Sedimentation Settings in the Precambrian: The Middle Riphean Bezymyannyi Formation of the Turukhansk Uplift

The Bezymyannyi Formation is a thick (up to 900 m) terrigenous rock complex that formed in the distal part of the ciliciclastic shelf with the storm-influenced sedimentation settings. The barrier belt of coarse-grained sandy sediments divided different-depth zones of the outer and inner shelf that included spacious areas populated by mat-forming communities. Development peculiarities of these communities and their relationship with erosion–flow structures are considered in detail. Microbial mat domains represented transient zones that both determined the internal sedimentation patterns and influenced sediment flows in the entire basin. The model explaining peculiarities of the Precambrian terrigenous sedimentation by the influence of intrabasin factor (wide development of matground microbial communities) is proposed.     

Tectonodynamics of fluid-conducting structural elements and migration of radionuclides in massifs of crystalline rocks

The principal aspects of reconstruction of conditions and paths of fluid migration in massifs of crystalline rocks are considered. The spatiotemporal relationships between stress fields, brittle failure, and migration of radionuclides are discussed. The main attention is focused on the staged character of tectonic events, fluid circulation conditions, and the sequence of uranium mineral formation as determined with structural, geological, tectonophysical, petrophysical, petrographic, mineralogical and geochemical, microstructural, microthermometric, and radiographic methods. As is exemplified in uranium deposits and massifs of silicic igneous rocks, the comprehensive consideration of the tectonodynamics of fluid-conducting structural elements and radionuclide migration is necessary for providing insights into the localization and redistribution of uranium, the PT conditions of uranium ore formation, and the forecast for long-term safety of disposal of radioactive wastes in crystalline rocks.     

Considerations concerning the non-rigid Earth nutation theory

This paper presents the reflections of the Working Group of which the tasks were to examine the non-rigid Earth nutation theory. To this aim, six different levels have been identified: Level 1 concerns the input model (giving profiles of the Earth's density and theological properties) for the calculation of the Earth's transfer function of Level 2; Level 2 concerns the integration inside the Earth in order to obtain the Earth's transfer function for the nutations at different frequencies; Level 3 concerns the rigid Earth nutations; Level 4 examines the convolution (products in the frequency domain) between the Earth's nutation transfer function obtained in Level 2, and the rigid Earth nutation (obtained in Level 3). This is for an Earth without ocean and atmosphere; Level 5 concerns the effects of the atmosphere and the oceans on the precession, obliquity rate, and nutations; Level 6 concerns the comparison with the VLBI observations, of the theoretical results obtained in Level 4, corrected for the effects obtained in Level 5.Each level is discussed at the state of the art of the developments.     

A Vendian-Cambrian boundary succession from the northwestern margin of the Siberian Platform: stratigraphy, palaeontology, chemostratigraphy and correlation

Siberia contains several key reference sections for studies of biological and environmental evolution across the Proterozoic-Phanerozoic transition. The Platonovskaya Formation, exposed in the Turukhansk region of western Siberia, is an uppermost Proterozoic to Cambrian succession whose trace and body fossils place broad limits on the age of deposition, but do not permit detailed correlation with boundary successions elsewhere. In contrast, a striking negative carbon isotopic excursion in the lower part of the Platonovskaya Formation permits precise chemostratigraphic correlation with upper-most Yudomian successions in Siberia, and possibly worldwide. In addition to providing a tool for correlation, the isotopic excursion preserved in the Platonovskaya and contemporaneous successions documents a major biogeochemical event, likely involving the world ocean. The excursion coincides with the palaeontological breakpoint between Ediacaran- and Cambrian-style assemblages, suggesting a role for biogeochemical change in evolutionary events near the Proterozoic Cambrian boundary.