Home – Home – Jornals – Russian Geology and Geophysics 2005 number 1

The values δ¹⁸O obtained from belemnite rostra of Subpolar Urals show extremely high paleotemperatures (20

The paper presents results of complex studies of lacustrine and palustrine deposits from three boreholes drilled on the eastern and southern shores of Lake Baikal: data of palynological study and seeds and fruits analyses, botanic composition of peat, and AMS ¹⁴C age. The radiocarbon age is brought to conformity with the actual age by a calibration scale. The general features as well as the specifics of the vegetative-cover structure and climate at separate localities of the lake shore are considered for a period of >13 kyr, with a minuteness of 50-250 years. It is shown that from 13 to 9.3(8.5) kyr ago, the climate and vegetation underwent a series of short-term (200-1000 years) changes. In the first three periods of changes (13-10.3(9.5) kyr ago), the climate remained continental cold-temperature and insufficiently humid, and the vegetation was dominated by forest-tundra and tundra landscapes (mainly spruce, larch, and birch insular forests). In the next three periods (10.3-9.3(8.5) kyr ago), the continental climate became milder, and cedar pine and fir forests appeared. Later on, from 9.3(8.5) to ~6.9(5.5) kyr ago, the climate was continental humid-temperate, and the vegetation was dominated by dark-coniferous cedar pine and fir forests. The decrease in cyclone activity ~5.5 kyr ago might have been responsible for the reduction in the natural geographical range of dark-coniferous fir taiga. At the last stage of the vegetation evolution ~6.9(5.5)-0 kyr ago), the forests were dominated by cedar pine, larch, and pine. Analysis of the climatic and ecologo-edaphic factors determining forest plant spreading on different Baikal shores suggests the existence of two long-term optimal periods in the Holocene: humid (9.3(8.9)-6.9(5.5) kyr ago) and thermal (recent 5.5 kyr).

Contributions of various diatom species to deposition were investigated in surface sediments (0-1 cm) sampled at eighty two geographically dispersed stations in the three subbasins of Lake Baikal. The species composition shows the highest contribution of planktonic diatoms, especially the endemic species of Aulacoseira baicalensis , Cyclotella minuta and Cyclotella baicalensis , in pelagic regions. The contribution of pennate benthic algae that are delivered by the Selenga and live near the delta is restricted to shallow waters along the shore. Aulacoseira baicalensis amount to 87% of the diatom and cyst total in northern North Baikal and to 60% in Central Baikal. Spores of Aulacoseira skvortzowii have rather high percentages in the Selenga delta region (about 30%) and in South Baikal (up to 20%) but are within 5% in the Northern and Central subbasins. Thick-wall frustules of Aulacoseira baicalensis reach the highest weight percent, up to 0.4 g per 1 g of dry sediment. The density of diatoms simulated in a 3D model on the basis of mean sedimentation rates and mean cell sizes correlates with mean annual particle fluxes to the three Baikal subbasins and the Selenga delta region.

Determination of the soil weathering rate plays an important role in estimation of the stability of terrestrial ecosystems because weathering is the major source of matter in ecosystem. This work was aimed at elaborating a technique for comparative evaluation of the rates of weathering in small areas making up a single landscape-geochemical system. The studies were carried out in the basin of the Pereemnaya River. The present-day and the average historical weathering rates were estimated. Data on the ion runoff show that the contributions of different areas of the water catchment basin are unequal. For the total content of Ca²⁺, Mg²⁺, K⁺, and Na⁺, the weathering rates calculated using the balance method vary from 1.1 to 5.4 keq·ha^-1·yr^-1. The weathering rates calculated from the isotopic composition of Sr are nearly the same (1.6-5.2 keq

This paper reports new data on geological structure, palynostratigraphy, and paleomagnetism obtained from key BH-9 as well as from BH-2, BH-6, and BH-13 drilled in the south of the Novosibirsk Region. The rock lithology has been described to follow the stratigraphic sequence. The question on recognition of the Upper Cretaceous is discussed. Zonal complexes of dinocysts, spores, and pollen are characterized. The marine deposits date from the Paleocene and Miocene, and the continental ones, from the Oligocene and Miocene. The data on microphytofossils confirm the recurrent character of development of the Tavda sea basin in the late Middle-Late Eocene. Cysts of dinoflagellates of the genus Pseudokomewuia were established for the first time in the Upper Oligocene sediments (Turtas lake-sea), which suggested a connection of the Turtas basin with southern seas through the Turgai strait at the beginning of Zhuravka time. The range of occurrence of dinocysts is bordered south of 55

Results of petro- and geochemical study of traps in the basin of the Morkoka-Markharata River are reported. The traps are compared with Permo-Triassic basites from other regions of the Siberian Platform. Permo-Triassic trap intrusions in the eastern Tunguska syneclise are made up of three petrochemically different types of basic melts. They successively intruded during the same tectonomagmatic cycle. Each of the intrusive groups has its proper geochemical specifics originated during the magma generation and preserved throughout evolutionary transformations up to the emplacement of magma in a modern chamber. This specifics does not depend on the volume of intruded melt, scale of intrachamber differentiation in the intrusions, character of transformation of magma during its deep-level fractionation on the path to a modern chamber, and position of the intrusions relative to magma control zones within the Tunguska syneclise.

Choice of observation sites is of key importance for understanding geodynamic processes and related phenomena, especially earthquakes, as it has been found out through three decades of investigation into preseismic, coseismic, and postseismic dynamic and nonlinear effects. Junctions of trans-lithospheric active faults are extremely heterogeneous zones in the multiphase polydisperse system of the lithosphere. These zones, marked by specific nonlinear and dynamic properties, build up the greatest elastic strain and are thus the least stable thermodynamic elements highly sensitive to external physical effects, mainly associated with regional stress variations. The sensitive local lithospheric zones with their ability to accumulate, redistribute, and release various types of energy were called sensitive energy active points (SEAP). Monitoring at the Kajaran SEAP station in an active seismic region of southern Armenia showed compression effects related to all earthquakes within the Arabia/Eurasia collision zone, irrespective of their epicentral distances.

The relationship between layer and apparent reflection velocities obtained for a layer much thinner than the overlying in a 2D transversely isotropic medium can be used to plot offset dependence of effective ray velocity indicative of anisotropy type. This approach, called point inversion, is based on the properties of two rays which are reflected from the layer top and bottom and connect a single source-receiver pair. Point inversion is applied, after constraining the layer thickness, to obtain the indicator function of ray velocity and then to find the horizontal velocity and anisotropy in each layer. Processing of seismoacoustic radio buoy data acquired in marine sediments and numerical modeling show up to 16 percent anisotropy of type 2.