GEOLOGY & GEOPHYSICS, 2001, V 42, N 5, May.
High-resolution stratigraphy of the lower and middle jurassic petroliferous
deposits of northern west Siberia
Shemin G. G., Nekhaev A. Yu., Ryabkova L. V., Shurygin B. N., Beizel' A. L.,
Levchuk M. A., Brekhuntsov A. M., Bochkarev V. S., and Deshchenya N. P.
749
The Lower-Middle Jurassic petroleum-promising deposits of northern West Siberia
have a complicated structure and are poorly investigated by drilling.
Correlation of these deposits, in particular, petroleum-producing and promising
sand beds, is often disputable. We present results of a detailed correlation of
the deposits by bio- and lithostrigraphy at the level of zonal cyclites (ZC).
Twenty-two ZC have been recognized and traced in various structure-facies areas.
The stratigraphic positions and volumes of sand beds and their notation have
been refined. Nineteen regional beds at the bottom of ZC and thirty local beds
occurring at various stratigraphic levels of the middle and upper predominantly
clayey part of ZC have been recognized. A version of sand bed notation is
proposed in which numerals are assigned only to beds of regional occurrence.
Local beds are marked with the number of the main bed and a letter. In this
case, the indices of beds more precisely reflect their stratigraphic position.
A regional gap has been found at the bottom of the Dzhangodskoe Horizon. The
facies zonation of the Lower Jurassic deposits is refined. Lower Jurassic and
Middle Jurassic deposits, horizon, formation, subformation, zonal cyclite, bed,
correlation, facies zonation.
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Kerogen of the togur formation (west siberia) as an example of the organic
matter of petroleum-generating rocks of lacustrine formations
Bogorodskaya L. I., Melenevskii V. N., and Fomichev A. S.
766
Kerogen of the dispersed organic matter (DOM) of the Lower Toarcian Togur
Formation of the West Siberian Plate has been investigated by various methods:
elemental analysis, analysis of the isotopic composition of organic carbon, and
pyrolysis. It is shown that the kerogen composition depends of the facies
settings of sedimentation. Two groups of DOM kerogen samples have been
recognized. One of them formed under coastal conditions, and the other, in
fresh-water basins with a considerable inwash of terrigenous matter. The kerogen
of the first group is more aliphatic, yields more volatile compounds, has an
elevated hydrogen index (HI 250 mg HC/g Corg), and is depleted in 13C
(<$Edelta>13Cav = -28%), whereas the kerogen of the second group has a lower
pyrolysis potential (HI 120 mg HC/g Corg) and contains more
13C(<$Edelta>13Cav = -25.2%).The elemental composition of catagenetically
transformed kerogen of the two groups is compared with that of kerogen from
the world's facies analogs according to the Van Krevelen model, the facies
subdivision being performed according to B. Tissot and D. Welte. Togur
Formation, kerogen, oil, pyrolysis, isotopic composition of organic carbon,
West Siberian Basin
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Palynological and diatom analyses of sediments from the late cenozoic paleo-
amalat valley (Western Transbaikalia)
Rasskazov S. V., Logachev N. A., Ivanov A. V., Misharina V. A., Chernyaeva G.
P., Brandt I. S., Brandt S. B., Skoblo V. M., and Lyamina N. A.
773
Sections of interlayered sediments and basaltic lavas have been studied in drill
cores from the eroded valley of the paleo-Amalat River and its tributaries.
Deposition in the valley started in the Middle Miocene about 14 Ma ago and
ceased in mid-Quaternary time about 0.6 Ma ago. Palynologic and diatom age
constraints of the sediments are in line with K-Ar dating of volcanics. The
composition of diatoms attests to repeated appearance and drying of deep lakes
between 14 and 9 Ma ago. A factor analysis of spore and pollen spectra in the
sediments shows a two-stage evolution of vegetation on the Vitim plateau in the
Late Cenozoic: (1) progressive changes of Miocene Turgai-type flora in a warm
humid climate between 14 and 9 Ma ago and (2) transition to Boreal flora under
sharp cooling and aridization since 9-5 Ma ago. The two stages generally
correspond to similar evolution stages of the flora in southeastern East Sayan.
The Miocene flora in the territory between Northern Baikal and southeastern East
Sayan differed from that on the Vitim plateau. These differences gradually
disappeared since the Late Miocene, whereas the flora of southeastern East Sayan
still preserved its specific features. Central Asia, Late Cenozoic,
sediments, basalts, spore, pollen, diatoms
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40Ar/39Ar Geochronology of magmatic and metasomatic events in the sora
porphyry cu-mo ore cluster (Kuznetsk Alatau).
Sotnikov V. I., Ponomarchuk V. A., Shevchenko D. O., Berzina A. P., and Berzina
A. N.
786
40Ar/39Ar dating (23 determinations) has been carried out for magmatic and ore-
metasomatic processes in the Sora copper-molybdenum ore region. Formation of the
large Sora porphyry Cu-Mo deposit related to the evolution of an ore-bearing
porphyry complex was preceded by long formation of multipulse granitoid
magmatism, separate pulses of which were accompanied by the occurrence of
Cu-Mo-skarn mineralization and K-feldspathic metasomatites with dispersed
halcopyrite and molybdenite. The total age range of endogenic events in the
regions is 481-356 Ma. The evolution of the ore-bearing porphyry complex and
related ore-metasomatic processes proceeded in several stages. The major
industrial porphyry Cu-Mo mineralization of the Sora deposit is related to the
first porphyry stage (389-388 Ma BP). The occurrence of ore-bearing porphyries
and ore-metasomatic formations was preceded by intrusion of pre-ore dikes
(405-402 Ma BP). The development of multipulse magmatism and accompanying ore
mineralization of various ages but of the same geochemical profile (Cu, Mo),
with regard for and petrogeochemical similarity of magmatites, is related to the
general depth of magma formation. The same geochemical profile (Cu, Mo) of ore
mineralizations formed at different stages of multipulse magmatism and the
similar petrogeochemical compositions and low (87Sr/86Sr)0 values of magmatites
evidence their genesis in the same zone of magma formation. Porphyry Cu-Mo
mineralization, 40Ar/39Ar dating, granitoid magmatism, Kuznetsk Alatau
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Metal content of ore-forming solutions of the ermakovka beryllium deposit
(Western Transbaikalia)
Stel'machonok K. Z. and Ishkov Yu. M.
802
Thermometry and atomic-emission spectroscopy of individual fluid inclusions (FI)
unsealed by laser pulse were used to study the salt and metal contents of
solutions responsible for the formation of rich phenacite-bertrandite-fluorite
ores and K-feldspar-fluorite rocks with poor Be mineralization. These rocks form
vein zones in aluminosilicate rocks and metasomatic zones in limestones. Results
of study of fluid inclusions in fluorite from hydrothermalites enriched in
phenacite and/or bertrandite allow the following conclusions. At the contact
with aluminosilicate rocks and earlier deposited hydrothermal minerals,
ore-forming solutions were enriched in Be (to 2 g/kg solution), F (to 4.5 wt.%),
and B (6-0.9 g/kg), had elevated contents of Na and K (to 2.5 and 9 wt.%,
respectively), traces of Ca, Cl, and S, and a varying amount of Cu (2-0.02 g/kg
solution). The concentration of Be under these conditions was, as a rule, within
2-0.3 g/kg and could remain at this high level mainly at the cost of complexes
<$E roman BeF sub 4 sup 2- > and <$E roman BeF sub 3 sup - >, stable at high
activity of <$Eroman F sup -> and <$Eroman K sup +>. Under the conditions of
intense interaction with limestones accompanied by the formation of fluorite and
release of CO2, the solutions became enriched in Ca and CO2 (in places, up to
saturation). The activity of their F, obviously, decreased below the level
ensuring stability of the most soluble fluorine complexes of Be. This led to
crystallization of phenacite and/or bertrandide and a decrease in Be
concentration in the solution below 0.3 g/kg (down to 0.03 g/kg). At least part
of microcline-fluorite deposits and veins with poor Be mineralization was formed
by such "nonmetaliferous" solutions. The reaction of fluorine-bearing solutions
with limestones played a more important role in the formation of rich F-Be ores
than a decrease in temperature. Fluid inclusions, metal contents of fluid,
beryllium, ore formation, Ermakovka F-Be deposit
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Geochemistry of granulites of the sharyzhalgai protrusion of the siberian
platform (Arban Massif)
Turkina O. M.
815
The composition of minerals and rocks of the Arban granulite massif has been
studied. The massif is a tectonic block among stratified volcanometasedimentary
deposits of the Onot greenstone belt (Sharyzhalgai protrusion of the Siberian
Platform). According to mineral and chemical compositions two types of basic
granulites are recognized: leucocratic, close in contents of major and trace
elements to low-titanium tholeiitic basalts, and melanocratic, depleted in SiO2,
Na2O, Rb, Ba, Sr, and LREE and enriched in Fe2O3, Ti, Nb, HREE, Y, and Sc
(compared with the leucocratic granulites) and compositionally similar to
restite equilibrated with tonalite melt. Acid plagiogranulites are
compositionally close to high-alumina tonalite-trondjemites forming
from a metabasic source at P<$E>>=>10-15 kbar in equilibrium with garnet-
granulite restite. We determined the parameters of granulite metamorphism
(T = 690-830-C, P = 8.0-9.5 kbar) and proposed a model for the formation of
rocks of the Arban Massif through melting of a mafic substratum in the lower
crust and partial segregation of the acid melt and restite phases.
Granulites, tonalites, geochemistry, petrology, lower crust, Sharyzhalgai
protrusion
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Absorption, luminescence, and internal morphology of diamonds from placers of
the tungusskaya area (Lower Tunguska basin)
Mironov V. P. and Mityukhin S. I.
830
Luminescence, absorption, and internal morphology of diamonds from alluvium of
tributaries of the Lower Tunguska River have been studied and compared with the
same characteristics of diamonds from the Malaya Botuobiya and Daldyn-Alakit
kimberlite fields, closest to the Tungusskaya area. The color of diamond from
the Tungusskaya area is determined by the high concentration of N3 centers, by
plastic deformations, as well as by the fact that some crystals contain
radiation defects with different degrees of thermal transformation. Band N3 as
well as H3 and H4 dominate in photoluminescence spectra. Multistage growth,
specific for diamonds from highly diamondiferous sources, is not typical of the
investigated diamonds. Nevertheless, though most diamonds have a homogeneous
internal structure, which is characteristic of lowly diamondiferous primary
sources, the investigated collection contains individual diamonds of complicated
multizonal anatomy with the internal structure typical of
highly diamondiferous kimberlites. The obtained data suggest that the diamonds
from the Tungusskaya area have no genetic relation to the known primary sources
of the Yakutian kimberlite subprovince. The fact that the collection of diamonds
from the Tungusskaya area contains crystal groups with contrasting and sometimes
mutually excluding characteristics suggests their origin from several sources. A
conclusion is made that unknown kimberlite bodies exist either within the
platform or within its southern folded frame. Diamonds, photoluminescence and
absorption spectra, laser tomography, Tungusskaya area
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(??) New data on the time of collision of island arc with the continent on
kamchatka
Shapiro M. N., Solov'ev A. V., Shcherbinina E. A., Kravchenko-Berezhnoi I. R.,
and Harver G. I.
840
It is established that the upper part of the Lesnovsky terrigenous series on
Northern Kamchatka, which is the autochthon of the Lesnovsky thrust, contains
nanoplankton assemblages pertaining to the Lower Paleogene through the Middle
Eocene. According to track dating, the youngest population of zircon particles
in the sandstones of this series also belongs to the Lower Paleogene
(uppermost Paleocene-Middle Eocene). Since the lower part of the neoautochthon
of this thrust dates from the Lutetian Stage, the thrusting, as a result of the
collision of the Cretaceous-Paleocene island arc with Northeastern Asia,
occurred in the middle Lutetian, about 45 Ma ago.
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Low-frequency deconvolution of digital records of a short-period seismometer
Yushin V. I.
851
The classical problem of conversion of seismograms into the true displacement of
seismometer case is considered in view of the modern opportunities of digital
record and processing of data. Two methods are considered: (1) complete
deconvolution that provides reconstitution of residual displacement within a
limited time interval and (2) long-period deconvolution that allows
conversion of a continuous record of a short-period seismometer into a long-
period record in an unlimited time interval. The use of the methods is
illustrated by examples in which records of real teleseismic events by a
2-second velocimeter are inverted to seismometers with the own periods tens of
times longer. Deconvolution, inverse filtration, true movement,
seismometer, digital record of seismograms
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U-Pb age of hypersthene granites (kuzeevites) of the angara-kan protrusion
(Yenisei Range)
Bibikova E. V., Gracheva T. V., Kozakov I. K., and Plotkina Yu. V.
863
We report the first U-Pb dates for allochthone hypersthene granites - kuzeevites
-from the Angara-Kan protrusion of the Yenisei Range. The obtained age 1734..
4 Ma marks the termination of folding and metamorphism under the PT-conditions
of granulite facies which determined the internal structure of the Kan
crystalline rocks. Geochronology, zircons, charnokites, kuzeevites,
granulites, Early Proterozoic, Yenisei Range