Home – Home – Jornals – Russian Geology and Geophysics 2005 number 10

Support is given to the division of the Lower Kimmeridgian into the Pictonia involuta and Rasenia evoluta Zones adopted for West Siberia. It is shown that the Upper Kimmeridgian is recognizable in boreholes, still without zonation. Specific taxonomic differentiation of the Kimmeridgian families and genera of ammonites in the Northern Hemisphere permits recognition of two zoogeographic realms, circumpolar Arctic and Boreal-Atlantic, which taken together form the Panboreal Superrealm. A wide ecotone existed between them, treated as the Greenlandian-Uralian Province. In the Early Kimmeridgian, this province was part of the Arctic Realm, whereas in the Late Kimmeridgian it belonged to the Boreal-Atlantic Realm. The province is subdivided into subprovinces: nominal North Siberian and two West Siberian, western and eastern.

Study was given to the isotopic compositions of carbonate and organic carbons in the deposits of the Baikal Group in western Cisbaikalia. The section of this rock group is considered as a stratotype for the Baikalian, the upper subunit (younger than 850 Ma) of the Upper Riphean series. Results of petrographic, geochemical, and isotope studies show that relatively pure limestones and dolomites, in contrast to mixed carbonate-siliciclastic rocks, might have preserved a near-primary carbon isotope composition despite their strong recrystallization. The studied deposits have high δ¹³C

This paper is concerned with lamproites of the Tomtor massif, which we discovered in borehole cores. The lamproites are of two varieties, olivine and leucitic. Their mineral composition, petrochemistry, and geochemistry are discussed. A technique for restoration of carbonatized lamproites through chemical dissolution of superposed carbonates is proposed. The chemical composition of the insoluble residue gives insight into the composition of intact lamproite varieties. The REE patterns of the Tomtor lamproites are identical to those of Australian olivine lamproites. Taking into account the proximity of the Ebelyakh diamond placer to the Tomtor massif and the discovery of lamproitic magmatism in the latter, we suggest that the Tomtor lamproitic tuffs were the source of the Ebelyakh diamonds.

On September 25, 2002, a brilliant meteor was observed over the Mama-Chuya and Bodaibo Districts of the Irkutsk Region. Its flight was accompanied by significant light, sound, and electrophone phenomena as well as by an air shock wave. A U.S. satellite has recorded the coordinates of two observation points, and many eye-witnesses have testified to this natural phenomenon. On the basis of this information, the path of the meteorite fall has been reconstructed. In 2002-03, three expeditions explored the area where the meteorite had supposedly fallen. The main results of their complex research are reported in this paper.
In addition to the expeditions of the Irkutsk Scientific Center, experts from the Meteorite Agency of the RAS as well as teams of research workers and students from Ekaterinburg and Krasnoyarsk were engaged in the search for the meteorite matter. Neither of these groups succeeded in finding craters, or traces of fall, or fragments of this meteorite.
Examining the snow samples taken along the path of the meteorite flight, we have found mineral particles and spherules, whose origin might be linked to the cosmogenic matter precipitated from the smoke-dust ablation track of the meteorite, and analyzed them using an electron microprobe. Of the greatest interest for study are polymineral spherules and a particle of Ni-bearing pyrites and nickel-iron, whose Fe and Ni proportions correspond to those of kamacite and taenite, typical minerals of meteorites. Analysis of these mineral formations shows that they are not typical of the bedrock and weathering crust of the study area but are, in particular, similar to the spherules (micrometeorites) from the Antarctic ice discovered in the purposeful search for meteorite matter. An important argument for the meteorite origin of the found particles is the fact that the localities where they were found during the expeditions coincide with the areas of damaged and fallen forest along the projected path of the meteor.

We report reprocessed aftershock data from the

The three-dimensional velocity structure of upper crust in the epicentral area of the Chuya earthquake was imaged using traveltimes of P and S waves from aftershocks. The northeastern part of the area including the territory of the Chagan-Uzun block and the Kurai and Chuya intermontane basins corresponds to a zone of high S velocities and Poisson's ratios. The southwestern part is a zone of relatively low P velocities and Poisson's ratios within the North Chuya ridge. S velocities are rather uniformly distributed over the area and show no significant anomalies. The main shock and the aftershocks, which are aligned in the northwestern direction, originated at the edge of the revealed anomalous P velocity zone.

The stress field in the upper crust of the Baikal rift produced by the system of large faults, active in the Cenozoic, has been simulated in laboratory optical models and compared to the seismicity pattern. Different loading regimes in three sets of models provided extension strain in the central part of the rift and corresponded to impacts from different external forces. Stress distributions in the three model sets correlated to the superposed fault pattern showed features of similarity and difference. The distribution of large earthquakes in the Baikal rift can be accounted for in terms of the interplay of passive and active rifting mechanisms.

The geologic structure of shungite deposits in Karelia and the composition of shungites are considered. Modern models for the genesis of these rocks are presented. The specific features of the rocks are analyzed in terms of a recently proposed model for the genesis and evolution of shungites, implying the formation of soot during the combustion of deep-seated methane under oxygen deficiency conditions. It is concluded that the model is constructive and does not contradict factual data.