Home – Home – Jornals – Advanced Search

Seismic wave propagation in dry friable sands is described on the basis of a new approach by equations including grain interaction rather than the standard equation of state. If grains interact according to the Hertz law, one-dimensional propagation of shear waves in a channel with stiff walls is accompanied by secondary orthogonal motion described by a system of two related equations.
The theoretical results were tested by experiments in which physical parameters of sand were estimated from seismic data, P and S velocities were analyzed as a function of microstructure, and strain propagation in friable sand was measured for grains of different sizes.
The theoretical and experimental elastic constants of the medium showed good agreement.

Multistage evolution of strike-slip faults and relationship between their displacement and length are investigated through physical modeling of elastic-viscoplastic lithosphere. The evolution of a strike-slip fault includes several stages distinguished from structural criteria and fractal analysis and marked by specific displacement-length correlation. The experimentally observed changes in this correlation are interpreted in terms of synergetics.

Excitation of the Earth's magnetic field is explained in terms of the common magnetohydrodynamic (MHD) mechanism in the conducting fluid core. The proposed scheme of motion implies hydromagnetic induction of azimuthal currents, according to the left-hand rule, and their distribution is the same as that obtained by simulating the source of the axisymmetrical part of the geomagnetic field. The fluid core material, with conductivity typical ofimpurity-bearing iron, was estimated to flow at 5 x 10^-6 m/s. The scheme is consistent with the outstripping rotation of the inner core and the westward drift of small-scale field heterogeneities. This approach accounts for jerks and their relationship with irregularity in the Earth's rotation. Reversals and excursions of magnetic poles may be caused by changes in correlation between the meridional and azimuthal flows or by plumes in the fluid core.

The history of the term suite has been traced, from an optional to the fundamental stratigraphic unit. In the absence of certain rules for recognizing suites as lithostratigraphic units, the basin (local, regional) stratigraphy came to a crisis. The overwhelming majority of the suites established in the Mesozoic section of West Siberia cannot fulfill the main, correlating, function of stratigraphic unit. Suites cross other stratal bodies, even themselves.
The number of suites snowballs to become information noise. A possible way out of this situation is the use of a system approach, based on the suite as a system, with the resulting principles, requirements, rules, and consequences.
The system approach to recognition of suites drastically reduces their number and provides a safe tool for their unambiguous recognition and tracing (correlation) in the basin section. Any system, including the rock-layered one, is subject to classification, minimization, hierarchic arrangement, etc. according to certain properties.

The sections existing in the Permian-Triassic effusive traps of the Siberian Platform (SP) are of three types: (1) monotonous, with slightly altered composition of tholeiites within several successive formations in the same section; (2) with lava composition regularly changed from trachybasalts to picritoids, with a certain petrochemical trend in particular

Many fractures and lithophysae in rhyolite tuffs making up Yucca Mountain in Southern Nevada, USA, are lined with epigenetic minerals (calcite, quartz, chalcedony, opal, fluorite, zeolites, and strontianite) indicative of the migration of mineralized waters within the mountain vadose zone in the geologic past. To evaluate the possibility of formation of these minerals as a result of meteoric water-rhyolite interaction, we performed a thermodynamic modeling of the system rhyolite-carbonate-aqueous solution-gas (CO₂, O₂) open to oxygen (p_O2 = 0.2 bar) and carbon dioxide (p_CO2 = 0.0003 bar). The compositions of produced ground waters and equilibrated mineral associations were calculated using the

The Oceanic Anoxic Event that occurred at the transition from Cenomanian to Turonian (OAE2) is a bright episode in the Cretaceous history. The section of the Cenomanian-Turonian terrigene deposits on the Nizhnyaya Agapa River (Ust'-Yenisei region) with vestiges of OAE2 has been analyzed in sedimentology and palynology. Textural features of deposits as well as their facies interactions in the section have been studied in detail. Stagnation and normal-marine settings alternate, which is typical of black-shale facies. This is well expressed in the replacement of shallow-marine sand rocks containing benthic fauna by black and brownish-gray leaf clays with signs of pyritization, without macrofauna, reflecting settings of stagnation. Qualitative and quantitative changes in the composition of organic-wall microphytoplankton have been established, and the facies-dependent dynamics of taxonomic variety of dinocysts has been traced. Comparative analysis of distribution of palynomorphs has been performed in deposits related to the Cenomanian-Turonian Oceanic Anoxic Event in different regions.

The architecture of the sedimentary cover of the West Siberian plate is analyzed within the limits of a kinematic model implying cyclicity of deposition controlled by tectonic subsidence and uplift. The model accounts for the formation mechanism of large- and smaller-scale lithostratigraphic units (formations, members, sand beds). The vertical distribution of sedimentary units and markers in the section is controlled by the dominant 18 myr periodicity of tectonism. The paleogeography of the region is reconstructed for different periods in the context of an oscillatory process. Correlation of the theoretical lithostratigraphic units with the actual sedimentary section shows that the proposed kinematic model may provide a basis for detailed stratigraphic division of the platform cover of the West Siberian plate.

The structure, composition, and deposition environments of Callovian-Oxfordian strata in the Nadym-Taz interfluve are analyzed on the basis of deep drilling data from the Tyumen' SDB-6. Depositional and sequence stratigraphy modeling reconstructs coastal and shelf conditions of the Vasyugan deposition that records sea-level fluctuations. The Vasyugan sequence revealed by sequence stratigraphy analysis of the Callovian-Oxfordian section is bounded by unconformities and includes a transgressive and a highstand systems tracts separated by a maximum flooding surface. The highstand systems tract is divided into a lower (early HST) and an upper (late HST) units corresponding to progradation-aggradational and progradational deposition, respectively.

On the basis of 53 radiocarbon data from the range 15-9.7 Ka, we have reconstructed the dynamics of mammoth populations in Northern Asia in the Late Glacial and early Holocene. The latest data (12-9.7 Ka) have been calibrated. Within continental Asia, the last mammoths died out on Taimyr around 11,000 cal. yr BP (9.7 kyr BCE). Using paleogeographic data, we tentatively reconstructed the natural habitat of mammoths in Siberia in the Late Glacial. The Volch'ya Griva occurrence in southern West Siberia, for which a radiocarbon date of around 11.1 Ka was obtained, could play a key role in the revision of the dynamics of mammoth distribution after 12 Ka.