Home – Home – Jornals – Russian Geology and Geophysics 2003 number 7

The paper presents new biogenic silica (BiSi) and total organic carbon (TOC) data for the past 130 kyr from BDP-98 and BDP-96-2 cores, respectively, showing a distinct climate periodicity correlated with Late Pleistocene rhythms. The high-resolution sedimentary records from Lake Baikal allow approaching the problem of the length of the last interglacial and stability of its climate in the Northern Hemisphere. The Siberian archives for the interval of 70 to 130 kyr contain brief sub-Milankovitch millenial-scale excursions correlated with events in the high-resolution records of North Atlantic ice cores and European continental pollen sequences. The correlation of the mid-Eemian cooling about 122 kyr BP and the cold Montaigu event about 103 kyr BP with low production signals in the Baikal cores evidence for a climatic connection between the geographically distant North Atlantic, continental Europe, and continental Siberia regions. This connection was well pronounced during interglacials and interstadials and weak during the later glaciation: The 5a/4 transition at 70-74 kyr BP is recorded as an abrupt irreversible cooling at Baikal but as two notable warm episodes in European and North Atlantic data.
Rapid warm/cold transitions in the Baikal record, especially the Kazantsevo/Early Zyrjanka transition, indicate that glaciation in Siberia began at 115-116 kyr BP, or 5-8 kyr earlier than in Europe and in the North Atlantic, as inferred from independent age models.
The continuous climate record from Lake Baikal provides a solid stratigraphic background for detailed correlation of Siberian continental sections.

Rock-magnetic studies of the Belovo key loess-paleosol section (52.4

Outlines and parameters of glaciers formed during the Pleistocene Last Glacial maximum (MIS 2) have been reconstructed based on remote sensing and field investigation of the glaciology and geomorphology of a 3293 km² key site in the Barguzin Range. The studies included (i) deciphering aerial photographs and satellite imagery, (ii) detection of glacier traces along 100 km of the Baikal shoreline and on divides, and (iii) data processing using GIS tools. The results indicate discontinuous mesh-type glaciation with local ice caps on mountain divides and dendritic valley glaciers. The largest lobes were 60-70 km long and spread outside their valleys into the North Baikal basin. Almost a half of the study area (46%, 1528 km²) was covered with ~174 km³ of ice. The maximum ice thickness attained 800 m in ponded depressions. Glaciology, lithology, and seismic stratigraphy indicate that for the Last Glacial (MIS 2-4), glaciers delivered about 30.6 x 10¹² kg of terrigenous load into the lake from the Tompuda, Shiril'dy, and Frolikha drainage basins, and the mean annual rate of glacial erosion was about 0.16 mm.

Paleobiogeographical zonation is usually based on a biochorological, or biogeographical, method, which is reduced to mapping of ranges of individual taxa (families, genera, and species), followed by their analysis. No unified nomenclature of biochores is available, because there are no approved rules for paleobiogeographical zonation. The problem of relationship between the rank of biochore and the rank of its indicator taxon has not been solved yet. A common rule is that the rank of a biochore depends on the rank of taxonomic distinctions. The rank Realm corresponds to the ranks Family and Superfamily of endemic taxa in Russian systematics; the criterion for recognizing Subrealms is mainly distinctions of generic level. Realms may be subdivided into Provinces, spatially separated communities whose specific character is determined by species (subgeneric, generic) distinctions. To solve the problem of the rank of biochores, it is necessary to analyze the history of the biota for a long time. It seems reasonable to submit the following hierarchical series of the main biogeographical categories: Superrealm, Realm, Province, with intermediate categories: Subrealm and Subprovince; the term region is for informal use.
The largest biogeographical unit is Superrealm. Only synthesis of areal data on nektonic, benthic, and planktonic groups permits recognition of general biogeographical regularities and, therefore, makes the paleobiogeographical division more objective. First of all, this is true for Superrealms and Realms. Recognition of a biochore should rely first of all on a certain chorotype. Chorotype can be that part of a biochore where its taxonomic originality is highlighted. The time of existence of the chorotype (chronotype) must also be provided. The rule of priority name is required.
Biochores are to be accompanied with certain information. The chorotype designation should be supplemented by the name of the first author(s) who proposed the biochore, initial time for which it was established, its territory; paleontological description; additions introduced into these attributes in subsequent publications. The present paper reports examples of description of some chorotypes.

Specific porphyraceous biotite-amphibole granites whose texture and rock and mineral compositions are like those of rapakivi have been distinguished among granitoids in the eastern Hovsgol region. The granites are close in geochemistry to the A-2 subtype of A-granites. According to structure and geochemical characteristics, in the absence of superposed structural and metamorphic alterations, the rapakivi-like granites are classified as postorogenic. Rb-Sr isochron dating of five bulk-rock samples yields an age of 423.4 20.3 Ma (MWSD = 0.217) at (⁸⁷Sr/⁸⁶Sr)₀ = 0.7069. Mineral isochron yields an age of 402.6 4.5 Ma (MWSD = 2.31) at Sr₀ = 0.7067, which coincides within the experimental error with the date obtained from the bulk-rock isochron. These dates correspond to the time of closure of Rb-Sr systems during the cooling of the granite massif, which crystallized (intruded) somewhat earlier. The data obtained indicate that folding and metamorphic processes in the eastern Hovsgol region terminated by the early-middle Silurian. Given a time gap between the intrusion of postcollision granites and collision processes, regional metamorphism in the eastern Hovsgol region might have occurred synchronously with high-grade metamorphism in the southern Baikal area (480-490 Ma). This supports the correct recognition of the Khamar-Daban metamorphic terrane comprising zonal metamorphic complexes of the eastern Hovsgol and central and western Khamar-Daban regions and the Slyudyanka granulite complex in the southern Baikal area.

We have studied Mn-carbonates revealed earlier by G.S. Yasovich, I.N. Ushatinsky, and O.G. Zaripov in the Upper Jurassic deposits of the Georgievka Horizon in the western part of the West Siberian Plate at depths of 1600-1800 m. The carbonates are similar in Mn content, thickness of ore beds, and area of occurrence to Mn-carbonate ores of the Chiaturskoe deposit and Nikopol' basin and abound in massive, stromatolite, oncolite, microstromatolite, and microoncolite varieties. The slackening Mn mineralization is traceable for 750 km to the east.

Regional regular variations in resin and asphaltene contents in Eurasian oils were studied using a petroleum chemistry database. Oils with high contents of resins and asphaltenes occur in western Eurasia, and oils with their low contents, in eastern Eurasia. We studied oil distribution by resin and asphaltene contents over 24 stratigraphic units and have established a cyclic character of changes in these contents depending on the age of reservoir rocks. The cycling is hypothesized to be related to the geotectonic cycles in the Earth's geologic history.

Seismic wave propagation in dry friable sands is described on the basis of a new approach by equations including grain interaction rather than the standard equation of state. If grains interact according to the Hertz law, one-dimensional propagation of shear waves in a channel with stiff walls is accompanied by secondary orthogonal motion described by a system of two related equations.
The theoretical results were tested by experiments in which physical parameters of sand were estimated from seismic data, P and S velocities were analyzed as a function of microstructure, and strain propagation in friable sand was measured for grains of different sizes.
The theoretical and experimental elastic constants of the medium showed good agreement.

Multistage evolution of strike-slip faults and relationship between their displacement and length are investigated through physical modeling of elastic-viscoplastic lithosphere. The evolution of a strike-slip fault includes several stages distinguished from structural criteria and fractal analysis and marked by specific displacement-length correlation. The experimentally observed changes in this correlation are interpreted in terms of synergetics.

Excitation of the Earth's magnetic field is explained in terms of the common magnetohydrodynamic (MHD) mechanism in the conducting fluid core. The proposed scheme of motion implies hydromagnetic induction of azimuthal currents, according to the left-hand rule, and their distribution is the same as that obtained by simulating the source of the axisymmetrical part of the geomagnetic field. The fluid core material, with conductivity typical ofimpurity-bearing iron, was estimated to flow at 5 x 10^-6 m/s. The scheme is consistent with the outstripping rotation of the inner core and the westward drift of small-scale field heterogeneities. This approach accounts for jerks and their relationship with irregularity in the Earth's rotation. Reversals and excursions of magnetic poles may be caused by changes in correlation between the meridional and azimuthal flows or by plumes in the fluid core.

The history of the term suite has been traced, from an optional to the fundamental stratigraphic unit. In the absence of certain rules for recognizing suites as lithostratigraphic units, the basin (local, regional) stratigraphy came to a crisis. The overwhelming majority of the suites established in the Mesozoic section of West Siberia cannot fulfill the main, correlating, function of stratigraphic unit. Suites cross other stratal bodies, even themselves.
The number of suites snowballs to become information noise. A possible way out of this situation is the use of a system approach, based on the suite as a system, with the resulting principles, requirements, rules, and consequences.
The system approach to recognition of suites drastically reduces their number and provides a safe tool for their unambiguous recognition and tracing (correlation) in the basin section. Any system, including the rock-layered one, is subject to classification, minimization, hierarchic arrangement, etc. according to certain properties.