Geologiya i Geofizika, 2002, V 43, N 3, March.

OIL AND GAS GEOLOGY 

FLUCTUATIONS OF THE SEA LEVEL AND CARBON ISOTOPE COMPOSITION OF
CARBONATES IN A RIPHEAN PETROLIFEROUS BASIN ON THE WESTERN MARGIN 
OF THE SIBERIAN CRATON (Baikit uplift)
E. M. Khabarov, V. A. Ponomarchuk, I. P. Morozova, I. V. Varaksina, and S. 
V. Saraev
211

     The Riphean (1500-1450 to 1000-950 Ma, from 40Ar/39Ar and K/Ar age 
methods) section of petroliferous peritidal carbonates in the Baikit 
uplift in the western Siberian Platform contains five sequences, each 
divided into three to five subsequences, distinguished on the basis of 
sedimentology and isotope geochemistry. The five sequences deposited in 
the period from 80 to 100 Ma and reflect major fluctuations of the sea 
level. The stability of d13C estimates is confirmed by petrographical, 
geochemical, and isotope data (over 350 analyses), which show that early 
diagenic dolomites may retain primary d13C signal subject to only slight 
changes. The d13C values in the lowermost carbonates (1450-1350 Ma, from 
isotope data) are about zero (-0.2 to 0.5<194>). The overlying section 
contains long intervals with low positive d13C values of 0.5 to 2.0<194>, 
occasionally up to 3.0<194>, alternating with shorter intervals dominated 
by negative d13C values (to 2.2<194>). The negative shifts correspond to 
the deposition of lower Yurubchen (~1350 Ma), upper Yurubchen-Dolgokta 
(1270-250 Ma), Kopcher (1100-1080 Ma), and upper Yukta-lower Tokur (about 
1000 Ma) subsequences. The main trends in the sea level fluctuations 
correlate well with d13C variations: The negative isotopic shifts coincide 
with the boundaries of the five major sequences; the intervals with medium 
positive d13C record high sea stand and correspond to the periods of 
carbonate shelf aggradation; low d13C values often correlate with the 
boundaries and the lower segments of the subsequences. Isotope and 
geological data from other regions indicate that the low sea stand periods 
correlated with the boundaries of the sedimentary subsequences in the 
Baikit uplift are most likely associated with global geological events and 
reflect eustatic fluctuations.
     Sedimentology, carbon and oxygen isotopes, sea level fluctuations, 
stratigraphy, carbonate shelf, petroliferous basin, Riphean, Siberian 
Platform 

LITHOLOGICAL AND GEOCHEMICAL CLASSIFICATION AND A SEDIMENTATION MODEL
OF THE BAZHENOV FORMATION 
I. D. Polyakova, L. A. Krol', G. N. Perozio, and E. A. Predtechenskaya 
240

     Lithological and geochemical interpretation of standard log data for 
the Bazhenov Formation (southeastern and central West Siberian Plate), 
their classification and 1:500,000 mapping show an 
argillaceous-siliceous-sapropelic composition and high organic matter 
(colloalginite) content of the highly resistive and gamma-active parts of 
the sections. The Bazhenov deposition was controlled, among other factors, 
by the bottom topography and the depth of the ocean which transgressed to 
the southeastern West Siberian Plate in its early and, especially, 
intermediate evolution stages. The distribution of rock groups reflected 
in depth-dependent variations in apparent resistivity made a basis for 
distinguishing different types and classes of sections within the 
formation, including those promising for oil and gas.
     Bazhenov Formation, silica, organic matter, apparent resistivity, 
gamma-activity 

ADAPTIVE ESTIMATION OF OIL AND GAS RESOURCES 
V. F. Grishkevich
252
     Three conceptual fundamentals are proposed as a base for estimation 
of HC resources and simultaneously for analysis and planning of 
prospecting surveys. The first is the qualitative dynamic approach to 
recognition of objects for prediction of petroleum potential (reservoirs, 
cap rocks, traps, trapping areas, and volumes). The second is adaptive 
support for the oil-geological model of the region to be estimated on the 
basis of logged information technologies. The third is continuous 
refinement of HC balance of all kinds on the basis of constant comparison 
of current local estimates with current results of prospecting surveys. A 
method of geometrical parameterization is proposed for the Neocomian West 
Siberian clinoforms. Some implications of the proposed approach are 
discussed.
Estimation, resource, potential, oil, reservoir, cap rock, trap, oil 
trapping area, oil trapping volume, dynamic, balance, prospecting, model, 
technology, clinoform

PETROLOGY, GEOCHEMISTRY, AND MINERALOGY 

YERUDA AND CHIRIMBA GRANITOIDS (Yenisei Range) AS INDICATORS OF LATE
PROTEROZOIC COLLISIONS 
A. E. Vernikovskaya, V. A. Vernikovskii, E. B. Sal'nikova, V. M. Datsenko, 
V. P. Kovach,A. B. Kotov, A. V. Travin, and S. Z. Yakovleva
259
     Petrological, geochemical, and isotope (U-Pb, Sm-Nd, Sr-Sr, and 
Ar-Ar) studies of the Yeruda and Chirimba granitoids show that they belong 
to different magmatic complexes. The Yeruda low-K calc-alkalic granitoids 
(878±1.5 Ma, U-Pb dating from zircon) have a geochemistry corresponding to 
intermediate I-S-type granites. Their primary melts may have been derived 
from island-arc complexes, strongly contaminated with the material of old 
continental crust, which were molten as a result of a collision about 880 
Ma ago. The Chirimba high-K and high-F subalkalic granitoids (761±8 Ma, 
U-Pb dating from zircon) apparently formed by melting of Early Proterozoic 
(Sm-Nd model age) crustal substrate, including the lower crustal material. 
In geochemistry and isotope composition they are similar to A-type 
granites that formed in postcollisional or within-plate environments. The 
Chirimba granitoids are 120 Ma younger than the Yeruda rocks and thus 
cannot have been caused by the same event. Therefore, the region of the 
Yenisei Range may have experienced repeated accretionary and collisional 
events in Late Proterozoic time.
     Late Proterozoic, petrology and geochemistry of granitoids, isotope 
data, Yenisei Range

PLATINUM IN CARBONACEOUS SUBSTANCE IN ORES FROM THE SUKHOI LOG 
DEPOSIT (East Siberia) 
E. A. Razvozzhaeva, A. M. Spiridonov, V. D. Tsykhanskii, I. E. Vasil'eva, 
and S. I. Prokopchuk
273
     Insoluble carbonaceous substance (ICS) encountered in the Sukhoi Log 
gold deposit was extracted, using special techniques, from bitumen-free 
shales. Of two groups of ICS concentrators one is light and buoyant in 
water, platinum-free, and containing a sericite-carbonaceous component 
(carbon, silicon, aluminum, and magnesium); the other group of ICS 
concentrators contains carbon and platinum in the ranges of 42.2 to 91.78 
and 80 to 1500 ppm, respectively. The presence of platinum may attest to 
strong bonds between platinum and carbon and their compounds making the 
Sukhoi Log ores difficult to investigate. In experiments, carbonaceous 
substances increase their activity on thermal and acid treatment, which 
may be effectuated in nature as hydrothermal ore formation.
     Carbon, carbonaceous shale, ICS concentrator, platinum 

TYPOMORPHISM OF PARAMAGNETIC RADICALS CO2-, CO3-, AND CO33-  IN NATURAL CARBONATE-APATITES 
L. G. Gilinskaya, Yu. N. Zanin, and V. P. Naz'mov
286
     Exemplified by the carbonate-apatites from the phosphate-bearing 
regolith of the Magan and Yraas Massifs of the Maimecha-Kotui Province of 
ultrabasic-alkaline rocks and carbonatites, the EPR spectra of <$Eroman CO 
sub 2 sup ->, <$Eroman CO sub 3 sup ->, and <$E roman CO sub 3 sup 3- > 
radicals observed in them have been shown to be typomorphic and, thus, 
appropriate for separating endogenetic and supergene varieties.
     Analysis of experimental data shows that the spectra in endogenetic 
and supergene apatites are complicated superpositions owing to several 
individual centers. Computer simulation by means of the ESR1 program 
permitted us to recognize them and to identify and calculate proportions 
(weights) of components in complex spectra. It has also been documented 
that the form of absorption lines in endogenetic specimens is isotropic, 
and in supergene ones, anisotropic, i.e., isotropic and anisotropic EPR 
spectra of carbonate radicals with corresponding parameters are recorded.
     This signature reflects dynamic characteristics of radicals (rotating 
or fixed in the structure) and is due to molecular bound water, which is 
always present in supergene apatites and absent from endogenetic 
high-temperature varieties as inferred from data of chemical analysis, IR 
spectroscopy, and nuclear magnetic resonance.
     Apatite, ESR, radicals, typomorphic properties, Maimecha-Kotui 
Province

GEOPHYSICS 

FACTORS CONTROLLING ACCURACY OF ACOUSTIC LOGGING MEASUREMENTS 
M. G. Markov 
304
     The paper presents a solution to the forward acoustic logging problem 
for a multipole acoustic radiator located in a noncylindrical well off its 
axis. The modeling investigates how the noncylindrical well geometry and 
the displacement of the radiator from the well axis influence the 
parameters of the measured elastic waves.
     Acoustic logging, synthetic wave patterns, forward problem, acoustic 
multipole radiator