Home – Home – Jornals – Russian Geology and Geophysics 2011 number 9

We have studied for the first time the organic geochemistry of the Vendian thick section stripped by the parametric well Vostok-3 in the depth range 5002-3870 m in southeastern West Siberia. The results point to the aquagene-plankton-derived and bacterial nature of the buried organic matter (OM). At some depth levels, the deposits are enriched in OM (up to 0.7-9.6%). The study of kerogens has shown that the OM is transformed to the apocatagenesis stage. The composition of biomarker hydrocarbons in bitumens has been studied, and the geochemical criteria for the petroleum presence prediction are considered.

The Oxfordian-Lower Hauterivian section of the Nordvik Peninsula (northern Central Siberia) is a reference for developing zonal scales for various fossil groups and improving the Boreal zonal standard. In the middle 1950s-late 1980s, it was studied extensively by geologists, stratigraphers, lithologists, and experts on various fossil groups. These studies yielded rich fossil and microfossil collections and a set of parallel zonal scales for various faunal groups. Recently, a new detailed ammonite zoning of the Oxfordian and Kimmeridgian units of this section has been proposed. These results contradict the previous biostratigraphic data on ammonites, foraminifers, and palynomorphs. In the present paper, all the biostratigraphic data on the Oxfordian and Kimmeridgian units of the Nordvik Peninsula (Cape Urdyuk-Khaya) and northern Central Siberia undergo a comprehensive analysis and comparison with those on the Boreal Realm. The ammonite-constrained stratigraphic position of the lower Upper Jurassic in the Cape Urdyuk-Khaya section is interpreted as Upper Oxfordian or Middle Oxfordian. In our view, this difference in the understanding is due to the misidentification of some Oxfordian ammonite forms. The zones based on other fossil groups (foraminifers, dinocysts) which were distinguished in the Upper Oxfordian and Kimmeridgian sections of the Nordvik Peninsula are well traceable circumarctically. Their stratigraphic position in various regions of the Northern Hemisphere is constrained by ammonites and bivalves. However, if we use the last alternative ammonite zoning of this part of the section, hardly explicable contradictions will appear in interregional foraminifer and dinocyst correlations.

The structure of the Lower-Middle Ordovician Tuloi and Karasinka Formations, which occur widely in northeastern Gornyi Altai, has been studied. A bed-by-bed description of a new section of the boundary sediments between these stratigraphic units has been given. The graptolite, trilobite, and brachiopod assemblages typical of the Tuloi and Karasinka Formations have been analyzed. Graptolite zones and subzones have been recognized, which permit correlating the stratotype and key sections of these local stratigraphic units with the stages of the International Stratigraphic Chart (ISC). The Karasa Formation occupies a considerably larger stratigraphic volume than presumed: It spans the late Arenig and the entire Llanvirn (including the Llandeilo) of the British standard, which is used in Russia (= Upper Dapingian-Darriwilian of the new Ordovician standard in the ISC). Finally, the paper discusses the suggested changes in the names of regional units (horizons) in the Ordovician stratigraphic chart of the western Altai-Sayan fold belt.

Based on the new petrological and thermochronological data, analysis of the metamorphism conditions and tectonic evolution of the Bodonchin zonal complex in Mongolian Altay was performed. Using mineral geothermometers and geobarometers, the parameters of the thermal state of the Mongolian Altay crust site during the collision of terranes were estimated, and the paleogeotherm at the peak of syncollisional metamorphism was reconstructed. The thermal state of the crust was characterized by either a high content of radioactive heat sources or a high mantle heat flow. The estimated metamorphism temperatures and pressures of rocks in two zones (staurolite-kyanite schists and migmatites) of the Bodonchin complex correspond to the paleogeotherms with average temperature gradients δT/δz = 25.5 and 27.2?C/km. The results of isotope dating of zircons and metamorphic minerals were used to construct a thermochronological model for the regressive stage of evolution of the polymetamorphic complex. The rates of the ascent of metamorphic rocks to the surface as a result of thrusts in the Bulgan Fault zone were estimated at 0.3-1 mm/year.

The northern Tien Shan is the northern front of the Himalayan mountain belt, which resulted fr om the collision between the Indian and Eurasian Plates. This region encompasses the most active seismic zones of the orogen, which generated the strongest ( M > 8) earthquakes. Since there are scarcely any written accounts, the only way to trace back strong earthquakes is the paleoseismological method. Since 1984 we have been studying the northwestern Issyk Kul' basin, wh ere there are differently directed anticlines, which constitute the Kungei megaanticline. Here, several active tectonic structures (faults, folds) are located, whose development was accompanied by strong earthquakes. Our field studies in 2008 in the Iiri-Taldybulak River valley, along the adyrs (foothills) of the Kungei-Ala-Too Range, revealed two unknown historical earthquakes. The first one, which occurred along the southern rupture in the late 7th century, gave rise to a seismic scarp; the latter broke through the river floodplain and a tash-koro (ancient settlement). The second one, which occurred along the northern rupture in the late 9th century, increased the height of the seismic scarp existing on the Early Holocene and older terraces. Note that this region already records a strong seismic event at ~500 A.D. Archeologic data have revealed one more strong earthquake, which took place in the 14th century. Note that the above-mentioned strong seismic events are coeval with the decline of the nomadic civilizatious (Wusun, Turkic, Mogul) in the northern Tien Shan and Zhetysu (Semirech'e).

Deep seismic investigation carried out in Russia in long-range profiles with peaceful nuclear explosions allowed clarifying in detail the structure of the upper mantle and the transition zone down to a depth of 700 km within the vast area of old and young platforms in Northern Eurasia. The variability of horizontal heterogeneity of the upper mantle with depth serves for the qualitative estimation of its rheologic properties. The upper part of the mantle (down to a depth of 80-100 km) is characterized by a block structure with significant velocity steps of seismic waves at the blocks often divided by deep faults. This is the most rigid part of lithosphere. Below 100 km, horizontal heterogeneity is insignificant, i.e., at these depths the substance is more plastic and not capable to retain block structure. On the lithosphere bottom at a depth of 200-250 km, a plasticity increase is observed as well but the zone of the lower velocities that might have been related to the area of partial melting (asthenosphere) has not been found. These three layers with different rheologic properties are divided by seismic boundaries presented by thin layering zones with alternating higher and lower velocities. At the specified depths, no phase boundaries have been distinguished.  These thin layering zones are assumed to form owing to high concentrations of mantle fluids at some depths where the mechanical properties and permeability of substance change. A minor quantity of fluids might result in streaks with partial or film melting at relatively low temperature, i.e., the appearance of weakened zones where subhorizontal shifts are possible. According to seismic data, seismic boundaries are observed at a depth of about 100 and 200 km in many world regions; they can be globally spread. There are signs that areas of xenolith formation and earthquake concentration, i.e., zones of high deformations, are confined to these depths.

The dielectric properties of the bentonite-oil-salt solution mixtures with different water and oil saturation were experimentally studied in the frequency range of 10 kHz to 4 GHz at 25-60?C. It has been established that besides the region of the Debye water relaxation, there are two more relaxation regions resulting from the interfacial interaction of the mixture components in this frequency range. To describe the dielectric permittivity and equivalent conductivity of the mixture, a spectroscopic model taking into account the multifrequency relaxation is proposed. The dependence of the model parameters on the water saturation and temperatures of the samples has been determined. The experimental data are compared with the modeling results, and the error of prediction for the dielectric permittivity and conductivity of mixture is estimated using the proposed model.

A spectral method for modeling high-frequency electromagnetic waves in axisymmetric geometry is proposed.The method is based on the expansion of the solutions of Maxwell's equations in Laguerre functions in the time region.
The spectral method is used to solve Maxwell's equations for both 2D media and stratified media. In the case of stratified media, a Fourier-Bessel expansion in the radial variable is used. The effectiveness of the spectral and finite-difference methods is compared. Harmonic solutions and solitary solutions by the Laguerre method are considered, and the dynamics of monochromatic and broadband electromagnetic pulses are examined.