Geology and Gepophysics, 2003, V 44, N 1-2, January-February.
Special issue
THEORETICAL PROBLEMS OF OIL AND GAS GEOLOGY
EVOLUTION OF STRUCTURES OF THE URALS, KAZAKHSTAN, TIEN SHAN, AND
ALTAI-SAYAN REGION WITHIN THE URAL-MONGOLIAN FOLD BELT (Paleo-Āsian ocean)
N. L. Dobretsov
On the basis of generalizations and analysis of new materials on regional
and thematic research, the main problems involved with the evolution of the
Paleo-Āsian ocean and structure of the huge Ural-Mongolian Fold Belt have been
considered.
Separate segments of the Ural-Mongolian Fold Belt resulting from the
evolution of the Paleo-Āsian ocean developed in a specific fashion. Hence,
Altaides, Kazakhstanides, Tien-Shanides, Uralides, Salairides, and Baikalides
may be recognized within its limits. At the same time, the main stages of
development of separate structures are well correlated with each other, and the
paleomagnetic data and palinspastic reconstructions confirm the common evolution
of the Paleo-Āsian ocean in the period 950-250 Ma.
The large stages of reconstruction and closure of the Paleo-Āsian ocean are
connected with superplumes, which appeared in the Permo-Triassic (Siberian), in
the Devonian (European), and, possibly, in the Early-Middle Ordovician. These
plumes also favored the synchronization of events in separate parts of the
Paleo-Asian ocean. The best synchronization is observed in the periods of
superplume appearance at about 485, 360, and 245 Ma ago, and about 120 Ma ago
in the Mesozoic, at intervals of 120 Ma. The presence of these superplumes is
hypothesized in the Late Precambrian as well, in a lapse of 120 Ma, thus
reaching the best synchronization at around 610, 730, and 850 Ma. In the periods
between these major plumes, smaller local plumes appear at an interval of about
30 Ma and, correspondingly, local synchronization of tectonic processes occurs
(restructuring of island arcs and related local collisional processes,
exhumation of eclogites and glaucophane schists, reflected in the maxima of
isotope ages.
Evolution, structure, Paleo-Asian ocean, Ural-Mongolian belt, superplume,
Periodicity
URALIDES AND TIMANIDES: THEIR STRUCTURAL RELATIONSHIP AND POSITION
IN THE GEOLOGIC HISTORY OF THE URAL-MONGOLIAN FOLD BELT
V. N. Puchkov
We substantiate theoretically the recognition of the Paleozoic-Early
Mesozoic Ural-Paikhoi-Novaya Zemlya fold belt as Uralides not analogous to
Hercynides (Variscides) and the preceding Late Vendian Timan folded structures
and Uralian lower structural units as Timanides not analogous to Baikalides.
Uralides and underlying Timanides are noticeably distinguished from the other
rocks of the Ural-Mongolian fold belt. The Ordovician rifting and subsequent
drift of continents, resulted in the Paleouralian ocean, seriously disturbed the
initially intimate relationship between Timanides and European Cadomides and
brought the former into a closer proximity to Baikalides, which formed at
different time. The subsequent evolution of Uralides also proceeded mainly in
antiphase with more eastern, initially quite remote parts of the Ural-Mongolian
belt. However, from Carboniferous to Middle Jurassic, during the formation of
Pangea, the Uralian, Kazakhstan, and Siberian continents underwent collision,
and new intimate structural relationships were established within the Ural-
Mongolian fold belt.
Rifting, continental drift, Uralides, Timanides, Ural-Mongolian fold belt
JUNCTION OF THE URAL FOLD BELT, PAI-KHOI, AND THE BASEMENT OF THE
WEST SIBERIAN PLATE
V.N. Voronov and V.K. Korkunov
Analysis of geological and geophysical evidence reveals a tectonic (rift-
related) origin of the junction of the Arctic Ural fold belt with the pre-
Jurassic basement of the West Siberian Plate. The available data allow an idea
of the relationship between the Urals and Pai-Khoi. The Hercynian structures of
the Urals are bounded by an arcuate deep fault at the termination of the
Baidartskaya Guba in the north and contact the Kimmeridgian (?) Pai-Khoi folded
complexes in the west. The study territory may store oil and gas in Permian
(Permian-Triassic) reservoirs.
Rift structure, fault, petroleum potential, Urals, Pai-Khoi, West
SiberianPplate, Shchuchy basin
ROLE OF STRIKE-SLIP FAULTS IN LATE PALEOZOIC-EARLY MESOZOIC TECTONICS AND
GEODYNAMICS OF THE ALTAI-SAYAN AND EAST KAZAKHSTAN FOLDED ZONE
M.M. Buslov, L.V. Smirnova, I. Fujiwara, K. Iwata, I. de Grave,
N.N. Semakov, A.V. Travin, A. P. Kir'yanova, and D. A. Kokh
Correlation and generalization of published and new structural,
paleomagnetic, geochronological, and paleogeographic data on the Altai-Sayan
Fold Belt and Eastern Kazakhstan show a crucial role of large-amplitude Late
Paleozoic-Early Mesozoic strike-slip movements having formed the final structure
of these regions.
The large-amplitude strike-slip faults form the Central Asian terrane
collage, which resulted from the collision of the Kazakhstan and Siberian
continents in the Late Devonian-Early Carboniferous and from the collision of
the East European, Kazakhstan, and Siberian continents in the Late
Carboniferous-Early Mesozoic. As a consequence of these collisions, the
accretion-collision margins of the continents were separated by strike-slip
faults and joint thrusts into some terranes, thus disturbing the primary
paleogeographic zoning.
In this paper, we characterize the kinematics and dynamics of the largest
faults of the Altai-Sayan and East Kazakhstan zone. We have shown that the
collision of the Altai-Sayan terrane from the Gondwana Group with the Siberian
continent during the Late Devonian-Early Carbonaceous was accompanied by the
formation of the Charysh-Terekta zone of dextral faults, followed by the Kurai
and Kuznetsk-Teletskoe-Bashkaus sinistral faults. The collision of the
Kazakhstan and Siberian continents in the Late Carboniferous-Permian was
accompanied by left-lateral movements along the Chara ophiolite zone and Irtysh
and Northeastern zones of folding. The age of deformations for each collision
step is increasingly younger toward the interior of the Siberian continent; the
amplitude of movements along the faults decrease in the same direction from
thousands of kilometers to a few hundred kilometers.
Collision, strike-slip fault, structure, terrane, continent,
geochronology, paleomagnetism, Altai, Central Asia
THE YENISEI RANGE AND ITS JUNCTION WITH THE SIBERIAN PLATFORM
AND WEST SIBERIAN PLATE
V.S. Starosel'tsev, A.V. Migurskii, and K.V. Starosel'tsev
Analysis of the earlier information and new geological and geophysical data
permitted us to improve the model for the structure of the Yenisei Range and its
multistep thrust over adjacent regional structures. Quantitative parameters of
the dislocation of the Riphean-Cambrian horizons, interpretation of
seismotomographic sections, and comparison of their geoelectric characteristics
to depths of 10-15 km show a principal difference between the areas of the West
Siberian Plate and Siberian Platform adjacent to the Yenisei Range, though the
former is very similar to the range.
Junction zones, index of dislocation, seismotomography, geoelectric section, overthrusts
GEOCHEMISTRY OF PERMO-TRIASSIC VOLCANIC ROCKS OF WEST SIBERIA
A. Ya. Medvedev, A. I. Al'mukhamedov, and N. P. Kirda
We consider the lithology of Permo-Triassic buried volcanic rocks of the
West Siberian Plate. By now, three types of volcanic rocks have been recognized:
basalts, rocks of shoshonite-latite series, and acid effusions (rhyolites and
rhyodacites). Basalts, amounting to >>80% of all effusions, are referred to
subalkaline and tholeiitic series and are enriched in mobile trace elements
relative to N-MORB. The rocks of shoshonite-latite series are subdivided into
moderate- and high-potassium. Their common feature is enrichment in easily
mobile elements (Rb, K, Ba, Sr, Nb, etc.). Acid effusions are referred to
typical rhyolites and rhyodacites of calc-alkaliņ series.
We have shown that all the studied rocks are the products of rifting
magmatism caused by the action of superplume beneath the Siberian craton. Though
the rock series differ significantly in minerals and chemical compositions, they
show a similar distribution of trace elements, which confirms the influence of
plume smoothing the compositions of volcanic rocks.
The available geochemical, including isotope, data evidence that the
parental magmas for the three series had different sources. Basalts and
moderate-potassium shoshonites formed from undepleted mantle; high-potassium
shoshonites, from enriched mantle; and acid effusions, from crustal substratum.
Basalts, shoshonites, superplume, West Siberian Plate
DEEP STRUCTURE OF THE CONSOLIDATED BASEMENT OF THE WEST SIBERIAN PLATFORM
AND ITS FOLDED SURROUNDINGS
A.S. Egorov and
The deep structure of the West Siberian Plate and its folded surroundings
has been imaged in geoscience transects based on geophysical surveys (DSS, CMP
profiling, seismic tomography, gravity, magnetic, geothermal, MT, and remote
sensing) along regional profiles. The resulting interpretative cross sections
obtained by original geological-geophysical and geodynamic modeling show the
contours of the Ural, Kazakhstan, Central West Siberian, Altai-Sayan, and
Yenisei fold systems beneath the sedimentary cover of the West Siberian Plate,
as well as the 3D distribution and the Phanerozoic geodynamic environments of
paleoplates, sutures, regional shear zones, and relict basins.
Geoscience transects, regional geophysical surveys, geodynamics, West
Siberian Platform
GEOLOGY OF OIL AND GAS
PALEOZOIC AND TRIASSIC EVOLUTION OF WEST SIBERIA
(data of comprehensive studies)
V.S. Bochkarev, A.M. Brekhuntsov, and N.P. Deshchenya
New geological and geophysical models of pre-Jurassic stages in West
Siberia based on log data, CMP reflection and refraction profiling, and DSS made
it possible to update the idea of the Paleozoic and Triassic evolution of the
region. The structure of Paleozoic and Triassic formations, reinterpreted on the
basis of new evidence, suggests their high petroleum potential.
Paleozoic, Triassic, structure-facies zone, rifts, ramps, West Siberia syncline
RINTRANTS AS ELEMENTS OF CRATONAL MARGINS AND THEIR RELATION
TO PETROLEUM POTENTIAL
A.K. Basharin and S.Yu. Belyaev
The paper considers the Neogean evolution of the North American and North
Asian cratons. Ophiolite zones and major faults on the western margin of North
Asia and southeastern margin of North America are interpreted as angular
outlines of Riphean-Paleozoic stable blocks that broke off the Rodinia
supercontinent and displaced along transform faults. The original boundaries of
the blocks were smoothed out by later tectonism and are poorly pronounced in the
present-day framework.
Folded rintrants, which protrude inward the cratons, and silents, the
outward protrusions, are suggested to be continent-marginal structures of high
petroleum potential.
North American craton, North Asian craton, rintrant, silent, petroleum potential
OCEANIC SEDIMENTATION SETTINGS AND FAUNA ASSOCIATIONS IN THE PALEOZOIC
ON THE SOUTHERN MARGIN OF THE WEST SIBERIAN PLATE
N. V. Sennikov, K. Iwata, V. D. Ermikova, O. T. Obut, and T. V. Khlebnikova
The geologic structure, geochemistry, lithology, and paleontology of the
Late Cambrian-Early Ordovician volcanosedimentary Zasur'ya Group in Gorny Altai
are considered. Its geochemical parameters, lithologic features, and biomarkers
are indicative of its oceanic genesis. The regularities of the spatial
distribution of various facies types of Zasur'ya Group sections are revealed.
Eight conodont zones are recognized there. They allow precise dating of the
unit. The Gorny Altai sector of the Paleoasian ocean has been proven to exist
for ca. 40 Ma. The stratigraphic position of the metamorphic and
volcanosedimentary deposits of Rudny Altai is considered. In the Chara sector of
the Paleoasian ocean, the age position of the volcanosedimentary units is
refined and the stratigraphic levels of oceanic sediments are outlined.
Paleoasian ocean, Upper Cambrian-Lower Ordovician Zasur'ya Group, Middle
Devonian Karakoitas Formation, Lower Carboniferous Vera-Char Formation,
conodonts, radiolarians, Gorny Altai, Rudny Altai, Chara zone
LATE DEVONIAN PALEOGEOGRAPHY OF THE WEST SIBERIAN PLAIN
AND ITS MOUNTAINOUS SURROUNDINGS
E.A. Elkin, N.K. Bakharev, N.G. Izokh, N.P. Kirda, A.G. Kirda, A.G. Klets,
V.A. Kontorovich, O.T. Obut, and I.G. Timokhina
A Late Devonian paleogeographic reconstruction for the territory of the
West Siberian Plate and the surrounding regions of the Altai-Sayan folded area
and the Siberian Platform has been obtained from lithology and facies of Upper
Devonian deposits. Zones of continental and shallow- and deep-water marine
deposition are interpreted as continental, shelf, and oceanic-type offshore
environments. Late Devonian Kuzbass is considered as a reference region for
Siberia, the West Siberian Plate, and the Siberian Platform on the basis of
correlation of updated regional scales. The reconstruction includes reliably
timed volcanism in the West Siberian Plate. The Kolyvan'-Tom' fold belt had not
formed yet by that time.
Paleogeography, facies, Late Devonian, West Siberia