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Russian Geology and Geophysics

2007 year, number 4

1.
LATE QUATERNARY AND RECENT DEFORMATION IN THE WESTERN TUNKA SYSTEM OF BASINS: STRUCTURAL, GEOMORPHIC, AND SEISMOLOGICAL EVIDENCE

A.V. Arzhannikova, V.I. Mel'nikova, and N.A. Radziminovich
Keywords: Structural geomorphology, earthquake mechanisms, deformation style, southwestern flank of the Baikal Rift Zone
Pages: 305-341

Abstract >>
Integrated seismological, structural, and geomorphic studies of the western Tunka system of rift basins show that the historic seismicity reflects the general Late Quaternary evolution trend of structures. Crustal deformation occurs mainly as shear with compression. Compression follows the boundaries of blocks and the mountainous northern periphery of basins, whereas extension acts upon their inner parts, which remain in
																								



2.
RESULTS OF RESEARCH INTO HOLOCENE SEDIMENTS OF THE SOUTH AND CENTRAL BASINS OF LAKE BAIKAL (BDP-97 and short cores)

E.G. Vologina a , S.A. Kashik a , M. Sturm b , S.S. Vorob'eva c , T.K. Lomonosova a ,I.A. Kalashnikova a , T.I. Khramtsova a , S.Yu. Toshchakova
a Institute of the Earth's Crust, Siberian Branch of the RAS, 128 ul. Lermontova, Irkutsk, 664033, Russia
b EAWAG, CH-8600 Dubendorf, Switzerland
c Limnological Institute, Siberian Branch of the RAS, POB 4199, 3 ul. Ulanbatorskaya, Irkutsk, 664033, Russia
Keywords: Bottom sediments; turbidites; minerals; diatoms; grain size; magnetic susceptibility; Lake Baikal
Pages: 312-322

Abstract >>
Results of investigations of Baikal bottom sediments from a long core (BDP-97) and several short (0-1 m) cores are presented. It has been shown that the Holocene sediments in the Baikal basins consist of biogenic-terrigenous muds, accumulated under calm sedimentation conditions, and of turbidites, formed during catastrophic events. The turbidites can be distinguished from the host sediments by their enrichment in heavy minerals and thus their high magnetic susceptibility. Often, Pliocene and Pleistocene diatom species observed in the Holocene sediments (mainly in the turbidites) point to redeposition of ancient offshore sediments. Our results indicate that deltas, littoral zones, and continental slopes are the source areas of turbidites. The fact that the turbidites occur far from their sources confirms the existence of high-energy turbidity currents responsible for long-distance lateral-sediment transport to the deep basin planes of the lake.
																								



3.
NEW DATA ON KIMBERLITE MAGMATISM IN SOUTHWESTERN ANGOLA

K.N. Egorov a , E.F. Roman'ko b , V.T. Podvysotsky b , S.M. Sablukov c , V.K. Garanin d , D.B. D'yakonov b
a Institute of the Earth's Crust, Siberian Branch of the RAS, 128 ul. Lermontova, Irkutsk, 664033, Russia
b Zarubezhgeologiya Enterprise, 10 Kaloshin per., Moscow, 119002, Russia
c Central Research Geological Prospecting Institute of Nonferrous and Noble Metals, Russian Academy of Sciences,
129B Varshavskoe shosse, Moscow, 113545, Russia
d Moscow State University, Vorob'evy Gory, Moscow, 119992, Russia
Keywords: Kimberlites; diamonds; barophilic minerals; geochemical composition; rare-earth elements; Angola
Pages: 323-336

Abstract >>
First data on the geologic and geochemical compositions of kimberlites from nine kimberlite pipes of southwestern Angola are presented. In the north of the study area, there are the Chikolongo and Chicuatite kimberlite pipes; in the south, a bunch of four Galange pipes (I-IV); and in the central part, the Ochinjau, Palue, and Viniaty pipes. By geochemical parameters, these rocks are referred to as classical kimberlites: They bear mantle inclusions of ultrabasites, eclogites, various barophilic minerals (including ones of diamond facies), and diamonds. The kimberlite pipes are composed of petrographically diverse rocks: tuffstones, tuff breccias, kimberlite breccias, autolithic kimberlite breccias, and massive porphyritic kimberlites. In mineralogical, petrographic, and geochemical compositions the studied kimberlites are most similar to group I kimberlites of South Africa and Fe-Ti-kimberlites of the Arkhangel'sk diamondiferous province. Comparison of the mineralogical compositions of kimberlites from southwestern Angola showed that the portion of mantle (including diamondiferous) material of depth facies in kimberlite pipes regularly increases in the S-N direction. The northern diamond-bearing kimberlite pipes are localized in large destructive zones of NE strike, and the central and southern diamond-free pipes, in faults of N-S strike.
																								



4.
LATE CENOZOIC PALEOMAGNETISM OF WEST SIBERIAN PLATE

Z.N. Gnibidenko
Institute of Petroleum Geology and Geophysics, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: Paleomagnetic scale; geomagnetic field; magnetic minerals; orthozone; fauna; seed assemblages; palynoflora; Neogene; West Siberian Plate
Pages: 337-348

Abstract >>
On the basis of combined (paleomagnetic, lithological, and paleontological) data, a scale of Neogene geomagnetic polarity is proposed for the West Siberian Plate (WSP). It comprises 17 large orthozones of normal and reversed polarity. The scale was compiled by comparing and correlating the Neogene key sections of the Kulunda and Baraba plains, Irtysh regions between Omsk and Pavlodar and near Tara, and Ob' region near Tomsk. The reliability of paleomagnetic data is confirmed by component analysis of natural remanent magnetization and by a possibility of determining its primary component. In the studied Neogene rocks this is a high-temperature component related to magnetite, hematite, and maghemite, which decays at 420-675
																								



5.
APPLICATION OF GEOLOGICAL AND PETROMAGNETIC METHODS TO FACIES-GENETIC DIVISION OF SUBAERIAL DEPOSITS IN THE OB' REGION NEAR NOVOSIBIRSK ( Ogurtsovo key section )

A.I. Zhdanova a , A.Yu. Kazansky a , I.D. Zol'nikov a , G.G. Matasova a , S.A. Gus'kov b
a Institute of Geology and Mineralogy, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
b Institute of Petroleum Geology and Geophysics, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: Quaternary deposits; granulometry; petromagnetism; Ob' region near Novosibirsk
Pages: 349-360

Abstract >>
The Ogurtsovo section, one of the key sections of the Ob' region near Novosibirsk, has been comprehensively studied using a detailed geological description of deposits, granulometric and petromagnetic analyses. The combined methods allowed us not only to interpret the geologic structure of the Ogurtsovo section in terms of its facies and genesis but also to refine and supplement the Pleistocene geologic history of the region. Emphasis was placed upon relationships between granulometric and petromagnetic parameters. As a result, we have revealed regularities in the behavior of magnetic characteristics and their relationships as a function of granulometry in different lithogenetic types of deposits. On the example of this key section, criteria are proposed for distinguishing facies of the subaerial complex by analytical methods.
																								



6.
BIOSTRATIGRAPHY AND DEPOSITION ENVIRONMENTS OF THE MIDDLE-LATE MIOCENE VOLCANOSEDIMENTARY SECTION IN THE DZHILINDA BASIN, WESTERN TRANSBAIKALIA

G.P. Chernyaeva a , N.A. Lyamina b , S.V. Rasskazov a , I.N. Rezanov c , V.V. Savinova c
a Institute of the Earth's Crust, Siberian Branch of the RAS, 128 ul. Lermontova, Irkutsk, 664033, Russia
b East Siberian Research Institute of Geology, Geophysics, and Mineral Resources, 29 ul. Dekabr'skikh Sobytii, Irkutsk, 664007, Russia
c Institute of Geology, Buryatian Science Center, Siberian Branch of the RAS, 6a ul. Sakhyanovoi, Ulan Ude, 670047, Russia
Keywords: Dzhilinda Formation; Miocene; diatom; spore and pollen; K-Ar dating; western Transbaikalia
Pages: 361-370

Abstract >>
We report results of an integrated study of volcanosedimentary rocks of the Middle-Late Miocene Dzhilinda Formation consisting of the prevolcanic sedimentary Lower Dzhilinda and volcanosedimentary Upper Dzhilinda subformations. The section was studied in three wells drilled near Lake Mukhal (Khoigot paleovalley, Vitim upland). The Dzhilinda sediments contain ubiquitous Alveolophora jouseana (Moiss.) Moiss. typical of Miocene environments. Deposition occurred in two main stages represented by different water (diatoms) and land (spores and pollen) plant communities. The upsection successive changes in diatom species are attendant with changes in pollen and spore assemblages. The K-Ar ages of lavas indicate that the mostly sedimentary lower section of the Dzhilinda Formation deposited between 12 and 14 Ma and the more volcanic upper section, with a lacustrine lens at base, formed at about 10.8-9.5 Ma. The isotope dating of volcanic rocks agrees with the ages inferred from the diatom and spore-pollen analyses. The prevolcanic Lower Dzhilinda subformation deposited during the Middle Miocene climate optimum. The stratigraphy, lithology and facies of sediments suggest that the Dzhilinda deposition was associated with the development of a deep freshwater lake in the conditions of active tectonism and volcanism.
																								



7.
BOTTOM TEMPERATURE MONITORING IN LAKE BAIKAL

A.D. Duchkov, S.A. Kazantsev, A.A. Duchkov
Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: Submarine methane vents; bottom temperature monitoring; autonomous temperature recorder; mathematical modeling of heat transfer; South Baikal basin; Lake Baikal
Pages: 371-377

Abstract >>
We report results of bottom temperature monitoring of 2003-2004 in the deepwater South Baikal basin (Lake Baikal) near active gas-fluid methane vents at lake depths of 1020 and 1350 m. Sediments and water temperatures were measured using an autonomous temperature recorder designed at the Institute of Geophysics (Novosibirsk). Experiments implied short-duration recording and pioneering continuous 350 day-long monitoring near the Staryi vent. Measurements within a 1 m thick layer above and below the bottom showed notable variations in water (up to 0.07
																								



8.
A MORPHOTECTONIC STUDY OF THE CENTRAL SYSTEM, IBERIAN PENINSULA

M.O. Cotilla, D. Cordoba, M. Herraiz
Departamento de Fisica de la Tierra, Astronomia y Astrofisica I. Facultad de Ciencias Fisicas,
Universidad Complutense de Madrid, Ciudad Universitaria, s/n. 28040 Madrid
Keywords: Morphotectonics; Iberian Peninsula; Central System
Pages: 378-387

Abstract >>
The Central System (CS) or Spanish Central System forms part of two of the five morphotectonic mesoblocks that make up the Intermediate macroblock (number 6) of the Iberian plate. The combination of geological, geophysical and geomorphological data, used in accordance with the Rantsman methodology (1979), served as the basis for obtaining a regional analysis. The cartography obtained shows territorial units (4 macroblocks, 4 mesoblocks, 35 blocks, 85 microblocks and 162 nanoblocks), morphotectonic alignments (quantity/order: 3/2, 4/3, 5/23, 6/48, 7/93 and 8/164) and morphotectonic knots (quantity/order: 1/2, 5/3, 35/4, 85/5, 162/6, 324/7, 816/8). The number of delimited morphostructures increases from the central part towards the east. At the block level, one may distinguish a transverse differentiation of the territorial units and alignments, which is interpreted as an expression of the region's lithospheric heterogeneity. There is a close relationship between the morphostructures and seismicity, indicating that greater activity occurs in the blocks of the eastern and northeastern sectors.