Home – Home – Jornals – Russian Geology and Geophysics 2006 number 6

Impact tuffisites of the Popigai astrobleme are described. This class of rocks has first been discovered in terrestrial astroblemes. Their dikes in the target gneisses are made up of a mixture of glass (10-90 vol.%), gneiss fragments, and cryptograin matrix. Most of the glass particles are porous; they are

The dispersed organic matter of the Bazhenov Formation and Togur Member was correlated with the Bazhenov- and Togur-type oils in the southern Nyurol'ka megadepression, the Tomsk Region. On the basis of lithostratigraphic columns, data of testing and sampling of nineteen prospecting-exploratory boreholes, and vitrinite reflectance, the Mesozoic-Cenozoic sedimentary section was mathematically simulated in the form of a 3D-2D thermal model. According to the temperature zoning of oil and gas formation in the Bazhenov and Tyumen' Formations, loci of oil generation were established and the time of their joining the major zone of oil formation was determined. The locus of generation of the Bazhenov-type oils appeared at 32-24 Ma. In plan, it coincides with local folds in the Upper Jurassic sediments of the Igol'sk-Talovaya uplift, Karai-Aisaz trough, and northwestern Aisaz bank. The locus of generation of the Togur-type oils originated at 24 Ma and is associated with the Karai fold and local uplifts of the Karai-Aisaz trough. The possible effect of nonstationary deep heat flow, Pleistocene-Holocene cryogenic processes, and Miocene erosion on the forecast model for oil generation loci has been quantitatively estimated.

Sections of the Bazhenov and Georgiev Formations in the northern Ob'-Irtysh interfluve were studied. Four lithologic types of sections of the Bazhenov Formation and three types of sections of the Georgiev Formation have been recognized, and their relationship with the petroleum potential of the Jurassic-Cretaceous deposits has been established. It is shown that the settings in which sediments accumulated on positive structures at the bottom of the Georgiev paleosea were more favorable for the formation of phosphorite concretions and intense concentration of glauconite grains than the settings in syneclises. The conditions of accumulation of both formations have been refined.

In the course of regional geological surveys of the Central Urals guide conodonts were found. On the basis of these findings, we dated the volcanosedimentary deposits of the western slope formed under the conditions of continental rifting (leading ultimately to the rupture of the continental plate and to the birth of an ocean) and the volcanic complexes developed on the eastern slope of the Urals at the base of an island arc, whose origin suggests the existence of a mature oceanic structure. Thus, a sufficiently narrow age interval has been established to time the ocean opening. According to the data obtained, the rift-related tholeiitic volcanic rocks of the western slope were formed immediately before the continental crust had broken and the continental rift had transformed into oceanic, as late as the Middle Ordovician. The island-arc volcanic complexes of the eastern slope began to form in the Late Ordovician. This implies that the paleo-ocean in the Central Urals opened about the time of Middle-Late Ordovician transition.

A complex of paleomagnetic, geologo-lithological, and paleontological data served as a base for a geomagnetic polarity scale that existed on the West Siberian Plate (WSP) in the Paleogene. The scale comprises 31 large magnetic zones (orthozones) of normal and reversed polarity. To compile the scale, we compared and correlated the Paleogene reference sections of the Kulunda, Baraba, and Tomsk lithologo-facies zones. The reliability of paleomagnetic data is controlled by the possibility to distinguish the primary component of natural remanent magnetization and structural similarity of the WSP paleomagnetic scale with the global magnetochronological scale and paleomagnetic scales of other regions. During a 34.5 Myr period, from Upper Paleocene to Lower Miocene, the Early Cenozoic geomagnetic field reconstructed from NRM vectors of the WSP Paleogene rocks experienced 31 reversals (at the rank of orthozone boundaries), with 16 and 15 regimes of normal and reversed polarity, respectively.
Comparison of the Paleogene WSP scale with the Berggren scale permitted us to demarcate Early Cenozoic series in the regional WSP stratigraphic scale in absolute chronology. The Paleocene-Eocene boundary, approximately at 55 Ma (Chron C24r), is recorded in the regional scale near the roof of the Lower Lyulin-Vor Subformation (inside Orthochron R₂E₁t). The Eocene-Oligocene boundary at 33.8 Ma (Chron C13r) runs in sediments near the sole of the Atlym Formation in Orthochron R_8-1E_2-3pr. The Oligocene-Miocene boundary at 23.8 Ma runs above the Zhuravka Formation.
The WSP Paleogene geomagnetic polarity scale is of interregional importance. Being the only Paleogene scale for northern Asia, it is a crucial link between the continental-type scale and oceanic scale compiled from bottom cores of deep-sea drilling and sea magnetic anomalies.

The problem of paleoclimatic reconstructions in Central Asia is intimately related to study of the material composition of bottom sediments of Lakes Baikal and Hövsgöl. We report results of a quantitative IR spectroscopic analysis of non-clay components from these lacustrine sediments, such as quartz, plagioclase, carbonate minerals, and biogenic silica. The analyses were carried out using calibration curves (optical density at the absorption peak of component vs. its concentration in the sample). The calibration curves were constructed using synthetic mixtures of known composition. A method has been developed for a quantitative estimation of biogenic silica from the high-frequency shoulder of its absorption band 800 cm^-1. The obtained results are in agreement with chemical data. Estimation of the total content of non-clay components made it possible to determine the portion of layered minerals in the sediments and determine its dependence on paleoclimatic conditions. The relative error of most analyses is much lower than 10%. The maximum concentration of kaolinite in the sediments is 5%.

The paper presents an energy model of an earthquake source as a basis for estimating quantitative source parameters. Stress drop (Δσ), slip ( D ), and the source length ( L ) and width ( W ) are found using the integral source parameter p as
p = 2( 4 / π ) V_S / C_L ) ³ √ E _c / M ₀
where E_sis the seismic energy, M₀ is the seismic moment, f₀ is the angular frequency, C_L is the velocity of dislocation front in the source, V_S is the shear wave velocity, Δ ε is the strain drop.
In terms of physics the parameter p is an integral parameter of a seismogenic medium which characterizes its response to propagating dislocation. Its true values, as well as the values of other dynamic parameters, are impossible to estimate, the solution of the inverse source problem being ambiguous. Yet, there is no need in true values as the necessary information comes from space-time variations of p and other source parameters. This approach may allow more efficient solutions to the problems of earthquake prediction and seismic zoning.
Results of mass measurements of the p arameter show that it varies in earthquakes of the same energy class as a function of energy flux to the source area (e.g., the water level rise of the Nurek water reservoir). Space-time variations in the p parameter can be used as diagnostic for the location and time of pending events.

Satellite measurements cannot provide the appropriate monitoring of space and time geomagnetic secular variations as data from magnetic observatories are not properly taken into account. With the rare regional network of magnetic observatories in Siberia and the Russian Far East, it is essential to resume systematic monitoring of the geomagnetic field at repeat stations (RS). We suggest a method of vector magnetic measurements at repeat stations using fluxgate theodolite-proton magnetometer sets. The method was developed on the basis of analysis of uncertainty in vector magnetic measurements and imitation modeling of data from five observatories around Novosibirsk. We chose an efficient way for reducing the RS diurnal values of field components to their annual values by interpolation of differences between these values at the neighbor observatories. The new method can be used for resuming geomagnetic monitoring at repeat stations.

Chromato-mass-spectrometric studies of fractions of saturated and aromatic hydrocarbons from oils and oil shows of the Nepa-Botuobiyan and Aldan anteclises as well as chloroform extracts from mudstones of the Lower Cambrian Sinyaya Oil Shale Formation have revealed a series of new biomarker molecules. In oils from the Nepa-Botuobiyan anteclise, 3-alkyl steranes with 32 carbon atoms in the molecule were identified. Biological precursors of these alkyl steranes are still unknown. Such structures might have been produced from Δ²-sterenes as a result of bacterial methylation. The Cambrian oil shales and oil shows of the Aldan syneclise have abnormally high concentrations of triaromatic steroids C₂₈. In addition, new triaromatic steroids with an alkyl chain substituent in the ring A have been identified. The identical distribution of biomarkers in the oils and oil shales casts no doubt on their genetic relationship.