Home – Home – Jornals – Russian Geology and Geophysics 2008 number 6

Sedimentological and geochemical studies of a Triassic volcanosedimentary section of the Tura Group on the southern margin of the Koltogory-Urengoi Rift have shown a wide occurrence of fine- and very fine-clastic turbidites with admixtures of glauconite and basic and acid pyroclastic material. According to petrographic and geochemical data, the section sandstones are mainly graywackes and partly litharenites, and the mudstones are montmorillonite clayey rocks with admixtures of chlorite, hydromica, and kaolinite. The sourcelands of the peneplaned plateau abound in basic volcanics, which suggests (by analogy with the Triassic strata of the Siberian Platform) a wider occurrence of flood basalts in the past. Most of these basalts were, most likely, eroded, which resulted in a predominance of rift basalts on the pre-Jurassic weathering surface. Along with tephra and volcanoclastics, the clastic rocks are dominated by products of chemical weathering developed after basic volcanics. Marine deposits revealed in the Koltogory-Urengoi Rift section suggest the inflow of sea waters from the northern (in the modern frame of reference) ocean basin localized north of the modern Severnaya Zemlya Archipelago. The sedimentation basin of the rift was a narrow but extended bay of the Red Sea type, where the formation of marine deposits was accompanied by the eruption of basalts in the area of Nikol'skaya BH-1 lasting up to the late Middle Triassic.

nsoluble carbonaceous substance (ICS) at the Sukhoi Log gold deposit has been studied following the scheme: source shales - concentrates - residual substance of rocks. Examination by electron microscopy, transmission electron microscopy with electron microdiffraction, thermography, and mass spectrometry revealed several morphogenetic ICS varieties: dot-drop-like, honeycomb, single graphite crystals, and spherical graphite crystals.
Study of source shales and concentrates has shown their similar carbon isotope compositions (δ¹³C _av = 18.03-17.54 ‰). Residual carbonaceous substance is characterized by a heavy carbon isotope composition (δ¹³C _av = 10 ‰). Its enrichment with heavy carbon isotope, as compared with the source rocks, calls for special geochemical studies. The ICS heterogeneity in the Sukhoi Log shales points to variations in the physicochemical settings of ore formation at the deposit.

Cenozoic combustion metamorphic (CM) complexes produced by fossil natural coal fires are widespread at range-basin junctions worldwide. Large-scale fires accompany the initial orogenic phases as fresh coal-bearing strata become drawn into the aeration zone as a result of crustal deformation. In combustion metamorphism, the protolith melts to different degrees either into ferrous basic paralava or in glassy clinker. The melt rocks have a phase composition favorable for ⁴⁰Ar/³⁹Ar dating of ignition coeval with the onset of each episode in Late Cenozoic orogenic events. We suggest an algorithm providing correct ⁴⁰Ar/³⁹Ar age determination of CM rocks followed by well-grounded geological interpretation and test the new approach on melt rocks from the Kuznetsk Coal Basin.
Paralava samples were dated by ⁴⁰Ar/³⁹Ar incremental heating and the isotope ratios were corrected for Ca-, Cl-, and K-derived Ar isotopic interferences. The interpretation of age-spectrum results was checked against internal and external criteria. The former were plateau and isochrone ages and the latter included the so-called

Distribution of hydrogen and carbon isotopes (D/H and ¹³C/¹²C) in the microbial systems CH₄-H₂O and CH₄-CO₂ was studied in different world's regions. According to the distribution of these isotopes in the above systems, two types of microbial methane are recognized in the Earth's crust: (1) resulting from CO₂ reduction and (2) produced through acetate fermentation. In the case of methane 1, the biologic distribution of hydrogen and carbon isotopes in the above systems corresponds to the thermodynamic isotope exchange equilibrium at a given temperature of the methane genesis medium. In the case of methane 2, the same systems show mainly a nonequilibrium distribution of these isotopes. We have revealed a linear relationship between the isotopic compositions of CH₄, H₂O, and CO₂: δD - CH₄ = α _D ^b δD - H₂ O + b and δ¹³ C - CH₄ = α _C ^b δ¹³ C - CO₂ + d, where α _D ^b

In 1996 the Volgian Stage was divided into the Jurassic and Cretaceous units, removed from the Geological Time Scale, and substituted by the Tithonian Stage according to the guidelines of the Interdepartmental Stratigraphic Committee of the Russian Federation (ISC RF). Consequently, the Upper Volgian Substage including three zones (five subzones) was placed into the Berriasian Stage (the Cretaceous) proceeding from ammonite fauna, and the Cretaceous lower boundary was defined by the base of the Kachpurites fulgens Zone. Some stratigraphers, however, contested that decision and suggested to restore the former status of the Volgian Stage. Their idea has been validated by magnetostratigraphic studies carried out in 2003 in Jurassic-Cretaceous boundary strata in the Nordvik Peninsula (the Laptev Sea), which bear the most complete record of Boreal deposition and biostratigraphy. The new data prove that the Volgian Stage, in its nearly full stratigraphic volume, rather belongs to the Jurassic period.

We report new radiocarbon ages, pollen stratigraphy, and botanical composition of an organic sediment sequence from mountains along the northwestern side of Lake Baikal. The calendar age of the peat is ca. 9.5 kyr BP. The pollen spectra between 9.5 and 8.5 kyr ago show vegetation consisting mostly of open larch and spruce-larch forests with minor birch. The interval from 7.5 to 6.8 kyr BP is marked by broad fir spread confirmed also by the peat botanical composition. The climate inferred for the period of fir dominance combines mild winters, cool summers, thick snow cover, and abundant moisture, apparently due to more intense North Atlantic air transport. Fir percentages decrease dramatically after 6.8 kyr BP, when pines begin to spread in the Baikal watershed. The peat record bears imprint of North Atlantic cooling events identified as intervals of ice-rafted detritus deposition and low surface water temperatures. The new data allow a better insight into the regional climate and landscapes, and the reliable age model provides regional and inter-regional correlations of global change events.

The problem of an elastic stress field in a rotating medium is formulated and solved analytically within the limits of the classical theory of elasticity with a symmetrical stress tensor. This is a rotation elastic field of action at a distance. There are two specific types of elastic waves with a moment in rotating media: solitons and excitons, or rotation waves. The soliton solutions to the wave equation represent waves of global earthquake migration (slow tectonic waves) which are no faster than ~1 cm/s, i.e., approach the migration velocity of large and great earthquakes (M > 7.5). The exciton solutions correspond to waves of local migration of foreshocks and aftershocks in earthquake sources (fast tectonic waves) and have their maximum velocity comparable to faulting rate and/or to S-wave velocities.

We have designed a frequency-domain electromagnetic induction sensor for imaging the distribution of electrical conductivity of soils in civil engineering applications. The device implements the ultimate technical feasibility of measuring harmonic signals on the ground surface. Digital recording and narrow bandpass filtering of synchronous detection allows a sufficient measurement accuracy for ~1 μV signals and suppression of power-line noise of more than 100 dB. We suggest practical methods for investigating the characteristics of the sensor and estimating its measurement accuracy.