GEOLOGY & GEOPHYSICS, 2003, V 44, N 6.
STRATIGRAPHY AND PALEONTOLOGY
MAJOR CAMBRIAN BIOTIC BOUNDARIES IN THE NORTHERN SIBERIAN PLATFORM
I. V. Korovnikov, A. V. Fedoseev, and D. P. Sipin
489
We have characterized complexes of the guide faunal groups
(small-shelled fauna, archaeocyathids, trilobites, and brachiopods)
and followed their stratigraphic and lateral distribution in the
Cambrian deposits of the northern Siberian platform. Eleven boundaries,
where these complexes undergo major biotic transformations,
have been established. The boundaries are compared with those
characterized in other studies, as well as with the carbon isotope
datings from different sections of the Siberian Platform.
Some of the boundaries established in this study correlate well
with global biotic events and with the extrema of carbon isotop
e ratio curves. The examples include Boundary 1, the lower boundary
of the Tommotian stage; Boundary 3, the lower boundary of the
Atdabanian stage; Boundary 5, the lower boundary of the Botomian stage;
and Boundaries 7 and 8 marking the transition from the Lower to
Middle Cambrian in the Siberian Platform. Additionally, Boundary 9
is an almost universally present lower boundary of the
Triplagnostus gibbus Zone of the Amgan stage.
Cambrian, trilobites, brachiopods, archaeocyathids,
small-shelled fauna, biotic boundaries, northern Siberian Platform
ORDOVICIAN SILICEOUS AND SILICEOUS-BASALT FORMATIONS OF KAZAKHSTAN
I. F. Nikitin
508
Data on the stratigraphy of siliceous-basalt deposits of Ordovician
age from Central Kazakhstan have been summarized. The age, succession,
and correlation between these deposits are refined. Geological dating
and correlation are based chiefly on conodonts and, to a lesser extent,
graptolites. It is established that the age of these formations
in the west and east of Central Kazakhstan is constrained by the Early
to Middle Ordovician and in the interior structures (Zhungaria-Balkhash zone)
it spans the entire Ordovician and, possibly, early Silurian.
The siliceous and siliceous-terrigene deposits of Ordovician age
are the water-deepest hemipelagic and pelagic sediments,
and their accumulation corresponds to the maximum of Arenigian-to-Llanvirnian
transgression. The reported paleogeographic and paleotectonic data
are in agreement with the existing paleotectonic reconstructions according
to which Central Kazakhstan was a marginal basin of the
West Pacific type during the Ordovician.
Ordovician, stratigraphy, conodonts, siliceous sediments, basalts, Kazakhstan
PETROLOGY, GEOCHEMISTRY, AND MINERALOGY
GEODYNAMICS OF MESO-CENOZOIC VOLCANIC COMPLEXES OF VALAGA RIDGE, KAMCHATKA
(evolution from spreading to within-plate and island-arc magmatism
or accretion of exotic terranes?)
Yu. M. Puzankov
524
The paper addresses a comparative geochemical study of volcanic complexes
that evolved in the Asia/Pacific transition zone from the Late Cenonian to Present.
Chemical compositions were analyzed in 111 representative samples of Cenozoic rocks
from the eastern side of the Valaga Ridge (Eastern Kamchatka) on continuation
of the Emperor's Ridge axis, in the region of hotspot volcanism; the dataset also
includes 39 additional precise analyses published earlier by Puzankov et al.
Trace elements were determined by INAA, XRF, AAS, LL methods and gamma spectrometry
developed in UIGGM, Novosibirsk.
The magmatic complexes of Eastern Kamchatka and the surrounding regions
were interpreted on the basis of rock chemistry as formed in spreading,
island-arc, and transitional geodynamic environments. Broad occurrence of
transitional igneous complexes brings together the Meso-Cenozoic volcanic
system including magmatic chambers at different depths. Accretion postdates
the magmatic evolution. According to paleontological and K-Ar age constraints,
the Eastern Kamchatka hotspot has not moved much for 40 Ma
(from the Eocene to the Pleistocene), though the total extent of alkaline
and subalkaline rocks attains 200-300 km.
Geochemistry, igneous rocks, Meso-Cenozoic, Eastern Kamchatka
Ar AND He ISOTOPES IN THE DOVYRA MAFIC-ULTRAMAFIC INTRUSION
E. G. Konnikov, E. M. Prasolov, I. V. Tokarev, E. V. Kislov, and D. A. Orsoev
539
The paper presents results of Ar and He isotopic studies in rocks and
sulfide ores of the Late Precambrian Dovyra dunite-troctolite layered
intrusion (Northern Baikal region). The intrusion shows 3He/4He
and 40Ar/36Ar ratios similar to other basic intrusions
in the continental crust, and the gases in fluid inclusions contain a
significant crustal component. The lowest 3He/4He
and 40Ar/36Ar ratios, similar to those typical of fluids
in the continental crust, were found in sulfide ores of the intrusion,
which indicates involvement of crustal fluids in magmatic mineralization
of the intrusion.
Isotopes, helium, argon, fluids, contamination, layered intrusions
GEOLOGY OF OIL AND GAS
STRUCTURALLY CONTROLLED OCCURRENCES OF BATHOMIAN RESERVOIR
RICKS WITHIN THE TAZ-NADYM INTERFLUVE
A. A. Kartashov
549
Analysis of borehole testing data shows that the large areas where
reservoir rocks exist within the Bathonian permeable complex gravitate
to certain structural features. These features have been analyzed
with respect to inflow of hydrocarbons. According to petroleum potential,
the structural settings were classified as highly promising, promising,
and nonpromising.
Reservoir zones, structural setting, Bathonian reservoir,
petroleum potential, West Siberia, Taz-Nadym interfluve
GEOPHYSICS
ONGOING VERTICAL MOVEMENTS IN THE ALTAI-SAYAN PROVINCE
AND THEIR RELATIONSHIP TO NEOTECTONICS AND SEISMICITY
P. P. Kolmogorova and V. G. Kolmogorov
563
Geodetic surveys, especially repeated leveling carried out for
the first time in the territory of the Altai-Sayan province
through the recent decades, have yielded a cartographic model
of ongoing vertical movements of the Earth's surface. The numerical
parameters of the model were obtained from the equation of leveling
network consisting of closed polygons and isolated lines,
about 10,000 km of total length.
The model reflects regional-scale regular distribution of the rates
of vertical movements. According to this regularity, the Biya-Katun',
Barnaul, and Mras blocks are stable, while the background ongoing
vertical movements in the province are regional-scale doming south
of the Barnaul-Biya-Katun' stable block and subsidence of the
province's northwestern part north of the stable zone.
Doming is accompanied by local but often considerable subsidence
which provides further deepening of intermontane depressions.
Analysis of the relationship between active and neotectonic
structures revealed regions in which the ongoing movements are
conformal to the evolution trends of the earlier neotectonic
stage and those in which they are different. The obtained model
of ongoing vertical movements of the Earth's surface was also
used to detect zones of active faulting.
Ongoing vertical movements, neotectonic movements,
correlation analysis, Altai-Sayan folded area