Home – Home – Jornals – Russian Geology and Geophysics 2001 number 5

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.

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 C_org), and is depleted in ¹³C (_av =

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.

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

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 [BeF₄]²

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 12

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.

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.

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.

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.