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Russian Geology and Geophysics

2005 year, number 8

1.
SHALLOW ELECTROMAGNETIC SOUNDING: NUMERICAL ANALYSIS OF RESPONSES FOR GEOECOLOGICAL AND ENGINEERING-GEOPHYSICAL APPLICATIONS

V.N. Glinskikh and M.I. Epov
Institute of Geophysics, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: Forward problem, approximate approaches, phase difference, relative amplitude, shallow EM sounding
Pages: 759-768

Abstract >>
New approximate solutions to forward 3D shallow EM problem and software for fast processing of electromagnetic responses are applicable to detection of geoelectric targets (underground pipelines, engineering structures, zones of flooding and petroleum leakage, near-surface cavities, etc.) by recording the high-frequency components of the magnetic field. The new algorithms were tested in complex 3D numerical models of real geoecological and engineering settings and showed practically suitable accuracy and high performance.
																								



2.
WAVELET ANALYSIS IN PROCESSING CONTROLLED-SOURCE THREE-COMPONENT SIMULTANEOUS SEISMIC DATA

O.A. Khachai, V.S. Druzhinin, G.I. Parygin, and O.Yu. Khachai*
Institute of Geophysics, Uralian Branch of the RAS,
100 ul. Amundsena, Ekaterinburg, 620016, Russia
* Uralian State University, 51 prosp. Lenina, Ekaterinburg, 620083, Russia
Keywords: Wavelet analysis, seismic inhomogeneity, controlled-source monitoring, quarry blasts
Pages: 769-774

Abstract >>
Three-component simultaneous seismic records of quarry blasts were processed using a new approach of wavelet representation of the inhomogeneity parameter. The results show that quarry blasts can be successfully used in controlled-source seismic monitoring.
																								



3.
HIGH-TEMPERATURE ELECTRICAL CONDUCTION OF CHROMITE ORE AND THE HOST ULTRAMAFICS

V.V. Bakhterev
Institute of Geophysics, Uralian Branch of the RAS,
100 ul. Amundsena, Ekaterinburg, 620016, Russia
Keywords: Electrical parameters, high temperature, ultramafics, chromite ore
Pages: 775-784

Abstract >>
Physical, physicochemical, and petrographic methods were applied to investigate temperature dependences of dc and ac electrical resistance and dielectric loss, as well as their correlation, in the range from 20 to 850
																								



4.
CAMBRIAN-ORDOVICIAN TECTONIC EVOLUTION OF THE KOKCHETAV METAMORPHIC BELT, NORTHERN KAZAKHSTAN

N.L. Dobretsov, M.M. Buslov, and F.I. Zhimulev
Institute of Geology, Siberian Branch of the RAS,
3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: Subduction, collision, diamond- and coesite-bearing gneisses, exhumation, olistostromes, overthrust, nappe, Kokchetav microcontinent
Pages: 785-795

Abstract >>
The Cambrian-Ordovician tectonic evolution of the Kokchetav metamorphic belt containing UHP-HP rocks proceeded through several stages. The subduction of the Paleoasian Ocean lithosphere, containing blocks of continental crust, and collision of the Kokchetav microcontinent with island arcs are responsible for the formation and exhumation of UHP-HP rocks. Initially, in the Early Cambrian (535-523 Ma), the microcontinent was subsided into the subduction zone to depths of 150-200 km, which led to metamorphism as well as to partial melting of rocks. In next substage (523-513 Ma), the produced acid melts including blocks of UHP-HP rocks were exhumated quickly, at a velocity of up to 100-10 cm/year, to depths of 90 km, which permitted the preservation of the high-pressure associations. Then, the UHP-HP rocks were exhumated at a velocity of 0.5 cm/year along faulting zones of the accretionary wedge to depths of 30 km. In the Middle and Late Cambrian (513-480 Ma), the continuing subduction of the Kokchetav microcontinent led to the outwedging of the subduction zone, extrusion of UHP-HP rocks along retro-overthrust zones, heaping and overthrust in the accretionary prism. The formation of a new zone of subduction and the Late Arenigian-Early Caradocian collisional processes (480-450 Ma) led to the thrusting of allochthones, made up of the rocks of the Kokchetav microcontinent, and accretionary prism over the fore-arc trough of the Stepnyak island arc. The formation of an imbricated structure was completed with granitoid magmatism and accumulation of molasses in the Late Ordovician.
																								



5.
EARLY PALEOZOIC GRANITOID MAGMATISM OF CALEDONIDES IN THE ALTAI-SAYAN FOLDED AREA: MANIFESTATION AND EVOLUTION

A.N. Distanova and A.E. Teleshev
Institute of Geology, Siberian Branch of the RAS,
3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: Early Paleozoic granitoid magmatism, lithology, magmatism evolution, accretion-collision and collision-shear zones, Altai-Sayan Folded Area
Pages: 796-809

Abstract >>
On the basis of the fundamental works of Academician Yu.A. Kuznetsov and later obtained research data, including ours, we have considered the geology, petrology, and petrochemistry of major types of Early Paleozoic granitoid associations of the Altai-Sayan area, as well as their role in the evolution of island-arc and collisional structures. Scarce early island-arc complexes are assigned to mantle tholeiitic plagiogranites. The superlarge areas of the mass occurrence of batholith granitoids formed at the accretion-collision stage have many geologo-lithologic peculiarities accounted for by their geodynamic settings. Study is given to early collisional K,Na-granitoid associations, Na-K-syenite-granite complexes of back-arc and continent-marginal zones, and Silurian collisional K-Na-granitoid complexes of the outer accretion zone, formed before magmatism took place on the Devonian active continental margin. The distribution of different types of associations is determined by the degree of maturity of the enclosing crust, which is expressed in the age and lateral compositional variations of granitoids. In general, the Early Paleozoic granitoid magmatism is specified by the existence of preceding basites of different types and repeated intense crushing of the enclosing rocks, which accompanied their metasomatism during the formation of granitoid plutons.
																								



6.
MINERALOGY OF CLAYS IN LOWER TOARCIAN TERRIGENOUS SEDIMENTS IN THE SOUTHEAST OF THE WEST SIBERIAN PLATE

P.A. Solotchin, E.P. Solotchina, and V.N. Stolpovskaya
United Institute of Geology, Geophysics and Mineralogy, Siberian Branch of the RAS,
3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: Clay minerals, X-ray diffraction, IR spectroscopy, simulation, Lower Toarcian, Lower Jurassic, West Siberia
Pages: 810-821

Abstract >>
Data on the lithology of Lower Toarcian (Lower Jurassic) terrigenous sediments in the southeast of the West Siberian Plate are presented. Using cores from three parametric boreholes (mudstone (I), mudstone-siltstone (II), and sand (III) sections), the petrography and mineralogy of the sediment clays have been studied. The mineral composition was determined by optical and electron microscopy, X-ray diffraction, and IR spectroscopy. A comparative analysis of the associations, crystal chemistry, and structure of clay minerals from the three sections was carried out by simulation of X-ray diffraction spectra. The clay matter from all sections is dominated by minerals of the kaolin group (kaolinite, dickite) and mica group (illite, muscovite). Chlorite minerals (chlorite, chlorite-smectite) are subordinate and occur in sections I and II only. It is shown that the degree of structural ordering of the kaolin group minerals varies depending on the grain size of rocks: from disordered kaolinites in the mudstones to more regular dickite in the sandstone and gravelstone cement.
																								



7.
FLORA, VEGETATION, AND CLIMATE OF THE MIDDLE CENOPHYTIC (PALEOCENE-EOCENE) OF SIBERIA: PALYNOLOGICAL DATA

V.S. Volkova and O.B. Kuz'mina
Institute of Petroleum Geology, Siberian Branch of the RAS,
3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: Palynology, Paleocene, Eocene, Oligocene, flora, vegetation, paleogeography, climate, Siberia
Pages: 822-833

Abstract >>
A host of palynological data on West Siberia obtained recently at the Institute of Petroleum Geology have been considered and generalized, with the literature data on central Siberia and northeastern Russia invoked. The main large stages of sedimentation, formation, and evolution of sea and lake basins, evolution of floras and climate on the territory of Siberia in the Cenozoic are recognized and described. The Paleocene and Eocene Siberian palynofloras are taxonomically described in detail. Quantitative characteristics (temperatures of January and July, precipitation) of the climatic conditions of the Middle (optimum) and Late Eocene of Siberia have been obtained by the method of climatograms. Floristic relationships of Paleogenic palynofloras of Siberia with those from other regions are considered, with emphasis placed on their role in estimating the effect of paleoclimate and zoning on the distribution of vegetation zones.
																								



8.
BIOHERMS OF THE LOWER CAMBRIAN OSA HORIZON IN THE TALAKAN-UPPER CHONA ZONE OF PETROLEUM ACCUMULATION, SIBERIAN PLATFORM

N.V. Mel'nikov, V.S. Sitnikov*, V.I. Vasil'ev, S.I. Doronina, and L.V. Kolotova
Siberian Research Institute of Geology, Geophysics and Mineral Resources,
67 Krasny prosp., Novosibirsk, 630091, Russia
* Goskomgeologii of Sakha Republic (Yakutia), 13 ul. Kirova, Yakutsk, Russia
** Department of Mineral Resources of Irkutsk Region, 34 ul. Lenina, Irkutsk, 664033, Russia
Keywords: Talakan-Upper Chona zone, Osa horizon, marginal reef, bioherm, geomorphology
Pages: 834-841

Abstract >>
The Talakan-Upper Chona zone of petroleum accumulation lies at the top of the Nepa arch. The largest Talakanskoe petroleum deposit has been discovered there, in carbonates of the Lower Cambrian Osa Horizon.
The structure of the Talakan petroleum field and data of prospecting drilling for oil and gas in the Irkutsk Region and in the Republic of Sakha (Yakutia) have shown that within the Talakan-Upper Chona zone a sublatitudinal Talakan-Ignyali marginal reef formed in Osa time. It extends along the southern margin of the Botuobiya-Talakan carbonate platform of Osa age. Also within the platform, there were bioherms and separating basins.
Analysis of the distribution and thicknesses of halite beds overlying the Osa Horizon shows that the lower beds of halites successively overlapped the surfaces of the Osa bioherms. Zones of thin deposits distinctly outline the Talakan-Ignyali marginal reef and bands of bioherms. The geomorphology of the Talakan-Upper Chona zone in late Osa-early Late Usol'ye time has been reconstructed from the distribution and thickness of the lower beds of halite. The sublatitudinal Talakan ridge no less than 20 m above sea level has been recognized there. North of the ridge lies the Upper Nyuya lowland flooded occasionally by sea waters. In the northeast and south of the Talakan-Upper Chona zone, there are margins of a halmeic sea basin. On the land, the most likely processes were karsting and destruction of carbonates of the Osa Horizon, which led to the formation of reservoirs of porous and cavernous types. The sublatitudinal position of the Talakan-Ignyali reef was not reflected in paleotectonic reconstructions of the zone.