Volume 25, 2, 2006
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Volume 25, 2, 2006 |
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V.
P. Utkin, A. I. Khanchuk, E. V. Mikhailik, L. B. Khershberg
Structural dynamic conditions of the formation of guyots of the
Magellan Seamounts (Pacific Ocean)
The tectonic infrastructure of the Magellan Seamounts and the role of structural
dynamic factors for guyots’ formation are recognized by the method of
morphogenetic analogies between deformations of the continental and oceanic
crust. The following features are established: (1) the formation of both
individual guyots, their groups, and the entire system was mainly governed by
different-rank hierarchic strike-slip deformations manifested in plicative (folds)
and disjunctive (strike-slip faults, tension duplexes) forms; (2) the entire
ensemble of strike-slip deformations developed at different hierarchic levels
under meridional compression of the oceanic lithosphere. The assumption is made
that the Pacific intra-oceanic volcanic belts stretching for thousands of
kilometers were formed just like the Magellan Seamounts under the same
strike-slip geodynamical regime.
I.V. Buchko, Ye.B. Sal’nikova,
A.A. Sorokin, A.B. Kotov, A.M. Larin, S.Z. Yakovleva
Primary data on the age and geochemistry of rocks from the Kengurak-Sergachi
gabbro-anorthosite massif (south-eastern framing of the Siberian craton)
The geochemical and geochronological data (U-Pb method on zircon) for the
Kengurak-Sergachi gabbro-anorthosite massif of the Mogocha terrane of the
Selenga-Stanovoy superterrane are cited. The rocks of the massif under
consideration are characterized by moderate enrichment in large-ion lithophile
elements (LILE) and, on the contrary, by depletion with regard to some HFSE
elements and ferrum group elements, which is characteristic of the rocks of
anorthosite-rapakivi-granitic associations. Age estimation obtained for the
Kengurak-Sergachi massif, 1866±6 Ma, is the first evidence of occurrence of
Early Proterozoic gabbro-anorthosite magmatism within the eastern part of the
Selenga-Stanovoy superterrane.
I.L.
Zhulanova, L.P. Karsakov, V.K.
Kuz’min New regional stratigraphic scheme of the Early Precambrian assemblages,
Verkhoyansk-Chukotka region
The new regional stratigraphic scheme of the Early Precambrian assemblages of
the Verkhoyansk-Chukotka region is offered which was presented by the authors at
the 3rd Interdepartmental regional stratigrafic conference (IRSC) of
Northeastern Russia (Saint Petersburg, 2002). The method basis for its
development is characterized. New data on geology and geochronology of the Early
Precambrian in the region obtained after the latest IRSC (Magadan, 1974) are
outlined. The scheme is correlated with the General Early Precambrian
stratigraphic scale of Russia. The scheme was accepted by the above conference
and approved by the Interdepartmental stratigraphic committee of Russia.
L.G. Bondarenko, I.V. Kemkin
Presumed migration ways of
tumulus archaeocyatheans of Siberia and the Far East (in the light of plate
tectonics evidence)
The paper presents data obtained from a comparative study of tumulus
archaeocyathean complexes. A new scheme of their migration is proposed. Two
rather isolated paleobasins are suggested to occur in Cambrian time on each side
of the Siberian craton. They were surrounded by the continental margins of the
blocks that had been separated from ancient Pangaea and moved relative to each
other. These movements contributed to dispersal of archaeocyatheans from the
place of their origin (Siberian paleobasin) to the nearby continental margins,
which are currently wide apart from each other.
Sh. Suzuki, A.R. Ashraf, H. Okada
Sedimentary facies of Maastrichtian to Danian deposits in Amur River area,
Russian Far East
Sedimentary facies of the Tsagayan Formation distributed in the eastern
Zeya-Bureya Basin has been analyzed. The formation of the Maastrichtian to
Danian deposits is characterized by the cyclicily of the fining-upwards
successions. Analysis of environmental changes during the K/T boundary is the
focus of this study. Five facies have been identified: Facies A, thick and
laterally extensive coarse-grained to medium-grained sandstone units,
interpreted as channelfill deposits; Facies B, parallel-laminated to massive
mudstone units interpreted as interchannel lakes and flood plain deposits;
Facies C, sheet-like medium-grained to fine-grained sandstones interpreted as
crevasse splay deposits; Facies D, coal to coaly mudstone beds interpreted as
deposits of peatlands; Facies E, very poorly sorted sandy mudstone beds
interpreted as debris flow deposits. Fluvial environments with the low-relief
flat topography was inferred, A channel transported large volumes of clasts, and
a flood basin with interchannel lakes and peatlands was deciphered. Any distinct
change of sedimentary environments has not been identified throughout the
Tsagayan Formation (including the K/T boundary). However, two beds of debris
flow deposits were identified. The one occurs at the uppermost part of the lower
Tsagayan Subformation and contains dinosaur fossils. The other is intercalated
in the upper Tsagayan Subformation.
A.M. Korotky,
T.A. Grebennikova, L.P. Karaulova, L.M. Mokhova
Late Quaternary marine deposits of Eastern Primorye (Japan Sea)
Marine terraces (6-8, 8-10 and 12-15 m high) have been studied in the Japan Sea
northwestern sector. Their formation is compared with three phases of Riss- (Sangamon)
transgression when the sea level exceeded the modern sea level by 8-10 ì.
Thermoluminescent dates, spore-and-pollen and diatomic assemblages from the
deposits of these marine terraces allow us to compare the transgression with
stage 5å and the last episode of stage 5ñ. The wide distribution of coastal
deposits with warm, moderate-cold and cold assemblages proves the long-term
development of transgression with insignificant sea level fluctuations. For each
terrace its age is substantiated. Climatic and landscape conditions of
transgression development are recognized. Lithological and facial
characteristics of the deposits of marine terraces are determined. Various
deformations corresponding to the third phase of transgression are established
in the sections of the 6-8m marine terrace. These deformations are related to
long-term or thick seasonal frozen ground.
S. P. Pletnev, L. A. Izosov, M.G. Gorovaya
New data on the geology of the Kunsan depression sedimentary cover (East Korean
Bay, Japan Sea)
New evidence on biostratigraphy and lithology of Cenozoic sediments of the
Kunsan depression (East Korean Bay) is offered. The biostratigraphic analysis (foraminifera,
spore and pollen) of the core of hole D-1 at 50 m and thickness 2840 m made it
possible to distinguish the following layers: Upper Pleistocene-Holocene (0-40
m), Upper Pliocene-Lower Pleistocene (41-796 m), (?) Lower Pliocene (797-1250
m), Upper Miocene (1250-1880 m), and Middle Miocene (1880-2840 m). Hiatuses are
established in the Early Pliocene and Middle Pleistocene. A characteristic is
given to sedimentation conditions in the Miocene-Pleistocene.
S.S. Zimin, V.P. Molchanov, V.Ye.
Tupyakov, P.G.
KorostelevAccessory elements genetically related to precious metals, and their
implications for mineral resources evaluation of ore zones and belts
The paper reports that geochemical investigations can be more effective when
mineral resources in different geological structures are evaluated using
accessory elements genetically related to precious metals.