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Russian Geology and Geophysics

2009 year, number 6

1.
The Nui Chua layered peridotite-gabbro complex as manifestation of Permo-Triassic mantle plume in northern Vietnam

G.V. Polyakova, R.A. Shelepaeva, Tran Trong Hoab, A.E. Izokha, P.A. Balykina, Ngo Thi Phuongb, Tran Quoc Hungb, Bui An Nien b
a Sobolev Institute of Geology and Mineralogy, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
b Geological Institute of the Vietnamese Academy of Sciences and Technologies, Hanoi, Vietnam
Keywords: layered peridotite-gabbro complex; Permo-Triassic mantle plume; layered and pegmatoid series; parental melts; ore-geochemical specialization; Vietnam
Pages: 493-508

Abstract >>
New data on the age, composition, formation conditions, and ore-geochemical specialization of the Nui Chua layered peridotite-gabbro complex are reported. They evidence that the complex resulted from the Permo-Triassic mantle plume activity in northern Vietnam (southern framing of the Yangtze Platform). Two series of mafic and ultramafic rocks differing in ore productivity-layered (PGE-Cu-Ni) and pegmatoid (Fe-Ti-V)-have been recognized within the complex. The first estimates of the composition of their parental melts have been obtained.



2.
Provenance of Miocene sandstones in northern Iraq: constraints from framework petrography, bulk-rock geochemistry and mineral chemistry

A.I. Al-Jubourya, T. McCannb, M.M. Ghazalc
a Research Center for Dams and Water Resources, Mosul University, Iraq
b Geological Institute, Bonn University, Nussallee 8, 53115 Bonn, Germany
c Geology Department, Mosul University, Iraq
Keywords: provenance; heavy minerals; mineral chemistry; modal analysis; Miocene; Iraq
Pages: 509-526

Abstract >>
Modal analysis, bulk-rock geochemistry and phase chemistry of sandstones of the Miocene Fat'ha and Injana formations, northern Iraq, show that the clastics were derived from heterogeneous sources that include basic igneous and metamorphic rocks as well as older sedimentary rocks. The sandstones are generally carbonate-rich lithic arenites. Their geochemistry supports the petrographic results and indicates that they are all Fe-rich, lithic or quartz arkosic sandstones. According to geochemical data, garnets are derived from metamorphic sources, hornblende is of igneous origin, and clinopyroxenes, are produced by basic igneous rocks. Epidote is most probably to be a product of disintegration of metamorphic rocks, essentially, metamorphosed igneous rocks. Rutile geochemistry implies low-grade metamorphic and basic to ultrabasic igneous sources. Chemical composition of chromian spinels indicates that they are derived from Alpine-type peridotite. The ophiolitic-radiolarite belts of Taurus-Zagros as well as the uplifted Cretaceous and Paleocene strata of north and northeastern Iraq are likely to be the major source of clastics to the Fat'ha-Injana basin, a foreland basin formed as a result of the continental Arabian and Turkish/Iranian plates collision.



3.
The conditions of existence and typomorphism of native gold in ores of the Degdekanskoe deposit (northeastern Russia) in black-shale strata

I.S. Litvinenko
Northeastern Complex Research Institute, Far Eastern Branch of the RAS, 16 ul. Portovaya, Magadan, 685000, Russia
Keywords: deposit; ore; gold; northeastern Russia
Pages: 527-532

Abstract >>
We studied the typomorphic features of native gold in orebodies with veinlet-disseminated quartz-sulfide mineralization at the Degdekanskoe deposit localized in Permian black-shale strata of the Ayan-Yuryakh anticlinorium in the upper-Yana-Chukchi folded area. With a successive HF and HNO3 dissolution of samples, the abundance of native gold intimately intergrown with sulfides (on the average, 42.1%) and carbonaceous substance was revealed. It is shown that most of its grains are small and fine (the <0.25 mm fraction averages 90.2%) and are accumulated mainly in interstices. Two gold generations have been revealed: low-medium-grade (751-840 ‰) (main) and high-grade (885-931 ‰). The zonal structure of mineralization has been established. The upper, most enriched horizons bear coarser-grained gold of the two generations, which are localized in both sulfide and silicate minerals. With depth, the total content of gold decreases, the share of sulfide gold increases, and the grain size and grade also diminish, with the low-medium-grade generation prevailing.



4.
New homologous series of biomarker molecules from Vendian deposits of the Sayan-adjacent Biryusa area

V.A. Kashirtsev, Yu.K. Sovetov, E.A. Kostyreva, V.M. Melenevskii, A.Yu. Kuchkina
Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: mudstones; hydrocarbons; 2,7-dimethyl alkanes; Vendian
Pages: 533-537

Abstract >>
We studied the organochemical distribution of saturated hydrocarbons in organic matter of mudstones of the Vendian Marna Formation in the Sayan-adjacent Biryusa area. The formation is composed of glacial, glacio-alluvial, and lacustrine deposits.
In the fraction of saturated hydrocarbons in chloroform extracts (bitumoids), a homologous series of earlier unknown 2,7-dimethyl alkanes has been identified, with molecules having the even number of carbon atoms prevailing. The possible sources of such abundant biomarkers are considered.



5.
Seismites in Quaternary sediments of southeastern Altai

E.V. Deev a , I.D. Zolnikov b , S.A. Gus'kov a
a Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
b Sobolev Institute of Geology and Mineralogy, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: seismite; Quaternary deposits; seismicity; southeastern Altai
Pages: 538-553

Abstract >>
We study earthquake-induced soft-sediment deformation (seismites) in reference Quaternary sections of southeastern Altai. Sediments in the sections bear signature of liquefaction and fluidization and deformation is localized in thin (few centimeters to 0.5-1.0 m) continuously striking and frequently repeated layers sandwiched between undeformed sediments. The soft-sediment deformation records coseismic motion of different slip geometries. Seismic origin is also inferred for layers and lenses of coarse colluvium slid into the lake bottom from the slopes, which intrude plane-bedded silt and sand and vary in thickness from a few centimeters to one meter. The occurrence of seismic soft-sediment deformation at different stratigraphic levels of the Quaternary and in the Upper Pliocene Beken Formation confirms the high seismicity of southeastern Altai in Quaternary time.



6.
Callovian foraminiferal assemblages in West Siberia

L.K. Levchuk
Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: Callovian; biostratigraphy; zones; assemblages; foraminifers; Shaim oil and gas district; Mykhpai field; West Siberia
Pages: 554-563

Abstract >>
The paper presents data on Callovian foraminiferal assemblages from several wells in two localities of the West Siberian plain (Shaim oil and gas district, northwestern West Siberia, and Mykhpai field, central West Siberia). The assemblages are compared and studied in terms of space and time changes of their stratigraphy, which can make basis for a more detailed zonal subdivision as more data become available. The taxonomic compositions of the assemblages are summarized in tables for specific wells to highlight their geographic variations.



7.
An electromagnetoacoustic method of measuring electric conductivity and ξ-potential

V.N. Dorovsky, S.V. Dorovsky
BAKER HUGHES, 2001, Rankin Road, P.O. Box 1407 (77251-1407), Houston, TX 77073-5100, USA
Keywords: Key words: magnetoacoustics; conductivity; ξ-potential
Pages: 564-570

Abstract >>
A nonsteady filtration theory combined with electromagnetism by means of common physical principles of hydrodynamic description of condensed media is constructed. Based on the linear version of the theory, an electromagnetic method for measuring ξ-potential is suggested.



8.
Temperature monitoring in Bakchar bog (West Siberia)

E.A. Dyukarev a , E.A. Golovatskaya a , A.D. Duchkov b , S.A. Kazantsev b
a Institute of Monitoring of Climatic and Ecological Systems, Siberian Branch of the RAS, 10/3 prosp. Akademicheskii, 634055, Tomsk, Russia
b Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: soil temperature patterns; autonomous digital temperature recorder; peatland soil; seasonal frozen layer; rainwater percolation; Bakchar bog
Pages: 571-578

Abstract >>
We report the results of continuous temperature monitoring (812 days, from 28 June 2005 to 26 September 2007) in a 80 cm layer of peat soil in Bakchar bog (West Siberia), at sampling rates of 60 min in wintertime and 15 min in summertime. Both annual and daily temperature patterns are controlled by water table position and weather conditions. Wintertime soil temperature patterns are disturbed by the formation of a seasonal frozen layer with its thickness (freezing depth) depending on the time when steady snow cover sets up and on soil moisture. During the period of frozen layer thawing, the temperature of peat becomes sensitive to peat moisture and water table position as well as to the air and peat surface temperature. The warm-season soil temperature patterns bear effects of peat warming by rainwater percolation, both in night- and daytime. The patterns with soil warming during rainfall and phase change during seasonal freezing-thawing cycles record disturbances to conductive heat transfer.