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Russian Geology and Geophysics

2004 year, number 8

1.
SILURIAN STRATIGRAPHY OF EAST SIBERIA

Yu.I. Tesakov
Institute of Petroleum Geology, Siberian Branch of the RAS,
3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: Formations, sedimentary basin, Silurian, East Siberia
Pages: 887-904

Abstract >>
Fauna-based formation units distinguished for the first time in the Silurian stratigraphy of East Siberia (Siberian Platform, Taimyr peninsula) have been correlated to the chronostratigraphic units. The Silurian section includes eleven formations (deep shelf mudstone, lower shallow shelf marl, shallow shelf limestone, half-restricted shelf dolostone, inner half-restricted shelf and restricted shelf marl dolostone, restricted shelf siltstone, tidal sandstone, tidal and trough conglomerate, tidal and trough brachiopod-coral marl, and shelly sapropel of coastal troughs) and thirty one subformations. The correlation of diachronic (formations and subformations) and isochronic (stages, horizons, and subhorizons) stratigraphic units is shown in five transects along and across the Silurian East Siberian sedimentary basin.
																								



2.
SPECIFIC GEOGRAPHIC DIFFERENTIATION OF BOREAL CEPHALOPODS OF CARNIAN AGE

A.G. Konstantinov and E.S. Sobolev
Institute of Petroleum Geology, Siberian Branch of RAS,
3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: Paleobiogeography, ammonoids, nautiloids, Late Triassic, Carnian Age, Boreal Realm
Pages: 905-912

Abstract >>
Comparative analysis of complexes of Boreal nautiloids and ammonoids has been made for the first time for some phases of the Carnian Age, and the rules that control their geographic differentiation have been unraveled. The distinctions between Carnian cephalopods of the western (Svalbard, Arctic Canada) and eastern (northeastern Asia) Boreal Realm allowed us to distinguish the Canadian and Siberian Provinces. Ammonoid-based provinces are possible for the late Early Carnian and Late Carnian, when ammonoid fauna in the Boreal Realm was distinguished by genera and families. The best-pronounced distinctions between these provinces by nautiloids (presence of specific genera) have been found in the Early Carnian (tenuis phase).
																								



3.
EVOLUTION OF SULFUR ISOTOPES IN PORPHYRY Cu-Mo ORE-MAGMATIC SYSTEMS OF SIBERIA AND MONGOLIA

V.I. Sotnikov, V.A. Ponomarchuk, A.P. Pertseva, A.P. Berzina, A.N. Berzina, and V.O. Gimon
United Institute of Geology, Geophysics and Mineralogy, Siberian Branch of the RAS,
3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: Porphyry Cu-Mo deposits, S and Sr isotopes, sulfide-sulfate system, sources of matter, Siberia, Mongolia
Pages: 913-923

Abstract >>
Paleozoic-Mesozoic (D-J3) porphyry Cu-Mo deposits in Siberia and Mongolia are characterized by a narrow range of 34S values of sulfides (pyrite, chalcopyrite, molybdenite), -2.0...10.2
																								



4.
THE Sm-Nd AGE OF WOLLASTONITE SKARNS IN THE SOUTHERN BAIKAL REGION

S.I. Shkol'nik, V.P. Kovach*, L.Z. Reznitsky, and N.Yu. Zagornaya*
Institute of the Earth's Crust, Siberian Branch of the RAS, 128 ul. Lermontova, Irkutsk, 664033, Russia
* Institute of Geology and Geochronology of the Precambrian, 2 nab. Makarova, St. Petersburg, 199034, Russia
Keywords: Wollastonite, skarns, Sm-Nd age, southern Baikal region
Pages: 924-927

Abstract >>
The age of wollastonite skarns from the Andreevskoe deposit (Slyudyanka crystalline complex, southern Baikal region) has been determined by the Sm-Nd method. A Sm-Nd isochron was constructed by five points: garnet, clinopyroxene, wollastonite, K-feldspar, and bulk rock (T = 419 19 Ma, MSWD = 1.8, Nd = -6.5). Formation of wollastonite skarns marks the final stage of orogeny and rise of the complex to a hypabyssal level.
																								



5.
PECULIARITIES OF THE FORMATION OF DIVERSE VEINLET BERYLLIUM MINERALIZATION AT THE ERMAKOVSKOE DEPOSIT (western Transbaikalia)

L.B. Damdinova and F.G. Reyf
Geological Institute, Siberian Branch of the RAS, 6a ul. Sakh'yanovoi, Ulan Ude, 670047, Russia
Keywords: Mineralization, beryllium, fluid inclusions, thermometry, microanalysis, role of CO2, Ermakovskoe deposit
Pages: 928-941

Abstract >>
Based on geological, mineralogical, and petrographic data and results of thermometric and microanalytical (electron probe microanalysis and atomic-emission spectroscopy) studies of fluid inclusions (FI), the major factors have been established which determined the composition and Be content of various types of veinlet mineralization at the Ermakovskoe F-Be deposit. Despite a great difference in the composition of vein filling (ores of types I and II), the parageneses in all near-fracture metasomatites are the same. In limestones, they form diffusion-metasomatic fringes composed of predominant fluorite, subordinate K-feldspar, calcite, quartz, apatite, spodiophyllite, and phenakite (up to 4%). In aluminosilicate schists, the veinlet fringes are 0.6 cm thick; they are dominated by K-feldspar, albite, and, to a lesser extent, dolomite and calcite, bear minor fluorite, and lack phenakite. These schists bear nearly barren veinlet mineralization of type II, which is due to the effect of the wallrock lithology on the composition of near-fracture metasomatites. Beryllium mineralization of type II occurs only in carbonates, though it is also poorer in Be than the ores of type I because of the low content of phenakite in the vein filling.
As the composition of veinlets does not depend on the lithology of the host rocks (in contrast to the composition of near-fracture metasomatites), the minerals seem to have deposited in fractures as a result of cooling of hydrothermal solutions. But the ores of types I and II are characterized by close temperature ranges of formation ( ~ 300-150 and 360-90
																								



6.
SPECIFIC STRUCTURE OF THE LOWERMOST EARTH'S CRUST AT THE ZAGADOCHNAYA KIMBERLITE PIPE, YAKUTIA

L.V. Buzlukova, V.S. Shatsky, and N.V. Sobolev
Institute of Mineralogy and Petrography, Siberian Branch of RAS,
3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: Lower crustal xenoliths, garnet granulites, compressional wave velocities
Pages: 942-959

Abstract >>
Study has addressed xenoliths of the crustal rocks from the Zagadochnaya kimberlite pipe, in the Daldyn-Alakit diamondiferous district of the Yakutian kimberlite province. Most xenoliths are represented by garnet granulites (60% of the bulk of xenoliths, of which paraganeses with amphibole amount to 20%), by plagiogneisses (30%) and garnet-biotite schists (10%).
P-T conditions of metamorphism for garnet granulites are 700-780
																								



7.
THE NATURE OF VERTICAL HYDROGEOCHEMICAL ZONING OF PETROLEUM DEPOSITS (exemplified by the Nadym-Taz interfluve, West Siberia)

S.L. Shvartsev and D.A. Novikov
Tomsk Affiliate of Institute of Petroleum Geology, Siberian Branch of RAS,
3 prosp. Akademichesky, Tomsk, 634021, Russia
Keywords: Underground waters, chemical composition, oil hydrogeology, vertical hydrogeochemical zoning, water genesis, composition formation, hydrogeochemistry
Pages: 960-972

Abstract >>
Geochemistry of underground waters of petroliferous deposits was studied in a vast region with different types of vertical hydrogeochemical zoning. It has been shown that the zoning nature is governed by two main factors: the genetic type of underground waters and character of water interaction with rocks and organic matter, which are, in turn, the products of the geologic history of the region. According to genesis, the groundwaters are divided into four types: (1) connate Jurassic, (2) connate from the Paleozoic basement, (3) ancient infiltrated, and (4) condensation-related. The chemical composition of each of these types of water is considerably modified by water interaction with rocks, gases, and organic matter, as well as by mixing with waters of other genetic types. Different successions of genetic types of waters subjected to different grade metamorphism and mixing at depth are responsible for the character of direct, inverse, or more intricate hydrogeochemical zoning in the region.
																								



8.
PREDICTION OF IN-FIELD OIL AND GAS RESERVES IN UNDEREXPLORED PETROLEUM PROVINCES

V.R. Livshits
Institute of Petroleum Geology, Siberian Branch of RAS,
3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: Petroleum province, hydrocarbon reserves, in-field reserves, Bayesian estimator, Monte-Carlo imitation, statistical performances
Pages: 973-984

Abstract >>
A new algorithm is suggested to assess in-field oil and gas reserves based on the size distribution of discoveries. The statistical performances of the estimators are tested through the Monte-Carlo imitation.
																								



9.
EVOLUTION OF INVADED ZONE INFERRED FROM ELECTROMAGNETIC LOGGING AND HYDRODYNAMIC MODELING

M.I. Epov, I.N. Yeltsov, A.A. Kashevarov*, A.Yu. Sobolev, and V.N. Ul'yanov
Institute of Geophysics, Siberian Branch of the RAS,
3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
* Lavrentiev Institute of Hydrodynamics, Siberian Branch of the RAS,
15 prosp. Akad. Lavrentieva, Novosibirsk, 630090, Russia
Keywords: Electromagnetic soundings, hydrodynamic modeling, reservoirs
Pages: 985-995

Abstract >>
The geoelectrical and hydrodynamic parameters of the near-hole space bear much useful information on the physical properties of hydrocarbon reservoirs. Time-dependent changes in the zone where wellbore fluids leak off into permeable formation make it difficult to estimate the electrical resistivity of the undisturbed portion of the reservoir. However, the invaded zone itself can be a target of studies.
The available advanced multiprobe logging tools yield high-resolution images of resistivity near a well. These data, integrated with the available advanced theoretical background and computing facilities for hydrodynamic modeling of porous media with a two-component fluid fill, provide a clue to reliable interpretation of electromagnetic logs.
The suggested 2D models of drilling mud circulation near the bore face take into account the real size of drill, growth and erosion of mud cake, filtration of water and oil (two immiscible fluids), salt transport, rock compressibility, and fluid viscosity.
Results of 2D simulation of the process in which drilling mud displaces oil and formation water from the invaded zone are reported for different drilling conditions and hydrophysical parameters of reservoirs. The parameters of the invaded zone show different distributions classified on the basis of numerical experiments and porosity and water content dependences of resistivity.
Problems related to inversion of EM logs in vertical and horizontal wells are discussed for specific field examples.
																								



10.
PHASE-AMPLITUDE MODULATION OF A SEISMOACOUSTIC WAVE UNDER DIURNAL TIDES

B.N. Bogolyubov, V.N. Lobanov, V.E. Nazarov, V.I. Rylov, A.A. Stromkov, and V.I. Talanov
Institute of Applied Physics, Russian Academy of Sciences,
46 ul. Ul'yanova, Nizhniy Novgorod, 603600, Russia
Keywords: Rocks, dissipative and reactive nonlinearity, diurnal tide, phase-amplitude modulation
Pages: 996-1000

Abstract >>
The effect of diurnal tides observed during a field experiment investigating the phase-amplitude modulation of a seismoacoustic P wave that propagated in porous oil- and gas-saturated sandstone is explained in terms of dissipative and reactive nonlinearity of rocks. The parameters of this nonlinearity at the observation site are predicted from comparison of theoretical and field estimates.
																								



11.
ASSESSMENT OF MINERAL RESOURCES IN TERMS OF THE ESTIMATION THEORY

Yu.A. Voronin
Institute of Computing Mathematics and Mathematical Geophysics, Siberian Branch of RAS,
6 prosp. Akad. Lavrentieva, Novosibirsk, 630090, Russia
Keywords: Theory of estimation and pattern recognition, mineral resources, calculation, formula expertise, normative recovery
Pages: 1001-1003

Abstract >>
The assessment of mineral resources is a formula expertise, and its results are applicable only to plausible arguments. A new approach is suggested to update the method using the theory of estimation and pattern recognition.