S. B. Chernov

Problems and methods of dating low-activity samples by liquid scintillation counting

The important problem of contamination of old samples by younger 14C necessitates treatment of organic and carbonate samples to ensure more complete removal of contaminating carbon. Here we present studies of chemical procedures for the liquid scintillation method of 14C dating undertaken since 1960 in the former USSR. We discuss new procedures such as lithium carbide synthesis from charred organic samples and benzene synthesis on a catalyst, as well as memory effect in the carbide synthesis procedure and characteristics of two homemade counters.

New data on chronology of landscape-paleoclimatic stages in northwestern Russia during the late glacial and Holocene.

Two lake and bog sediments have been thoroughly studied using palynological and radiocarbon dating methods. These are the Lembolovskoye Lake section located in the southern part of the Karelian Ithmus and the Mshinskoye bog section located in the southwestern part of the Leningrad province. The data obtained allow us to reconstruct the main features of the vegetation cover evolution, the chronology for the appearance and a real distribution of the main arboreal species from the south of the Leningrad province to the north, and to construct curves of the paleoclimate parameter changes for the area under study. Thirty-six (super 14) C dates were obtained for the Lembolovskoye Lake section (7 m thick). According to those dates, the organic gyttja formation in the lake began 9870+ or -170 BP. Spore-pollen spectra with high percentage of herbs, arborescent, and shrub-birch dated back to the Younger Dryas were found out in clay layers at a depth of 6.5 m. An appearance of spruce and alder pollen is dated at 6860+ or -120 and 7510+ or -150 BP, respectively. The maximal percentage of broad-leaved species falls on the first half of the Atlantic (AT-1). Thirty-two dates were obtained for the Mshinskoye bog section (6 m thick): from 60+ or -70 to 9520+ or -170 BP (the last date fixed the beginning of peat formation); 12 palinozones from the Preboreal to the Subatlantic were recognized there. The spruce and alder pollen began to appear 7520+ or -110 and 7670+ or -130 BP, respectively. The maximal amount of broad-leaved species is observed at 4690+ or -80 BP. The detailed reconstruction of changes in vegetation communities during the Late Glacial and Holocene was correlated with paleoclimatic characteristics, which have been reconstructed for the section under study by using the information from a statistical method of spore-pollen data processing.

Deposits of historical and paleotsunamis on the coast of eastern Primorye

Deposits left by tsunamis from earthquakes in the Sea of Japan floor were identified for the first time on the coast of eastern Primorye. Data are presented on the definite coastal zones from Plastun Bay to Peschanaya Bay, Ol’ga Bay, and from Valentin Bay to Proselochnaya Bay. Historical and Late Holocene paleotsunamis, the traces of which were found in the sections, were presumably the larger scale events than known tsunamis of the 20th century. The grain-size composition of the tsunamigenic deposits was analyzed, their similarity with and difference from the other coastal-marine facies were established, and the source areas of the material were determined. The age of the events, the height of the wave runups, and the length of the flood zones on the coastal areas with different geomorphology were determined. The obtained data may serve as the first step for compiling a geological record of tsunamis for the northwestern Sea of Japan.

Geochronology of vegetation stages of south-east Baltic coast (Kaliningrad region) during the middle and Late Holocene

The raised bog sediments that have been continuously accumulated over time represent the most suitable natural object which enables us to reconstruct Late Glacial and Holocene vegetation and palaeoclimates. Bog peat consists of organic carbon formed in situ. It contains moss, plant fragments and microfossils that are necessary for the study of palaeovegetation and palaeoclimate. However, a successful study of palaeoenvironment can be carried out on the basis of investigation of a great quantity of samples along the whole peatbog thickness. In the present paper, the authors present the results of palynological, botanical investigations and radiocarbon dating of 31 peat samples taken from the raised bog Velikoye, located in the eastern part of Kaliningrad Region. The data obtained have enabled us to reconstruct the palaeovegetation, reveal the evolution of the bog and determine rate of peat formation at different evolutional stages over the last 7500 cal BP.

Chronology of Tsunamis Documented in Sections of the Coastal Lowlands in East Primorye

One of the fields in the study of how catastrophic events are manifested is investigation of sediments produced by historical and paleotsunamis. This infor� mation allows researchers to define the age, scale, and frequency of these events in the past. These studies are especially topical for the coasts of the Russian Far East where chronicles have provided almost no evidence and instrumental observations have been carried out only since the second half of the 20th century (1, 2). The longterm works on studying paleotsunamis have been being carried out in the Kuril-Kamchatka Region (3-5), but there are no data on the sediments of the historical and paleotsunamis for the continental coast of the Sea of Japan until the recent time. The Primorye is located in the rare seismoactive zones of Russia, and although most earthquakes in this region are deep focus ones, some strong shallow earthquakes of 5-7 in magnitude have been reported (6). Large tsu� namis in the region are related to the earthquakes whose epicenters are clustered along the narrow band of the shelf and submarine slope of the island of Japan, stretching to Moneron Island (2). Four large tsunamis were reported here during the 20th century: in 1907, 1940, 1983, and 1993; the effects of the last two events were investigated on the coasts of Primorye immedi� ately after the tsunami struck (1, 7, 8). The effects of these tsunamis on the natural and economic objects located in the coastal zone were also assessed, and the zonation of coasts in terms of tsunami hazard was car�

The first uranium-thorium dating of the Middle Neopleistocene peat in West Siberia

For a sample from the roof of peat (0–2 cm) located in a reference section for the Middle Neopleistocene in West Siberia near the village of Krivosheino, we obtained an exorbitant value of 14C date ≥53.9 ka B.P. (LU-6024). In the peat proper, the 230Th/U dates obtained by the isochronous method are 195.2 ± 10.8/9.1 ka B.P. for the L/L model and 204.1 ± 17/13 ka B.P. for the TSD model. The palynospectra of the peat characterize, from the bottom up, birch forests with fir and spruce participation; then spruce forests with fir; next spruce-cedar forests, similar to the middle taiga subzone. In the clay, the following palynospectra have been examined: forb-gramineous grasslands and light forests with spruce and Betula fruticosa. In the upper part of clays, the palynospectra reflect the evolution of swampy, birch, light forests with spruce participation. The conclusion is made that the studied part of the section formed at the end of the Samarovo Ice Age and in the last third of the Taz Ice Age. The break in sedimentation related to the erosion contact covers a part of the Samarovo Ice Age and the first two-thirds of the Taz Ice Age.

The origin and evolution of relict larch stands on Shikotan Island (Lesser Kuril Ridge) in the Holocene

Palynological and geochronological data have been used to ascertain the time history of a unique natural-territorial complex — the relict larch stands that have persisted in the southeastern part of Shikotan Island since the Late Pleistocene. The study revealed the development stages of landscapes. Factors favoring vegetation conservation in the refugium are discussed.

Some features of dynamics of ensemble of the technogenic microparticles instantaneous injected in a near-earth space by the point source moving on the elongated elliptic orbit with a low perigee

The computer program modeling the evolution of an ensemble of certain number of noninteracting spherical man-made microparticles is developed. In this case, we assumed that all particles have certain radius and are injected instantly by point source, which is moving on given trajectory in the NES. Particle initial velocities is defined by casual selection realized computer with correspond to given initial velocity distribution of injected particles. We suppose that injection is isotropic and injection velocities are uniformly distributed in given interval in the reference system of injector. The ensemble current state is determined by calculation of ensemble particles locations with the help of numerical solving of the single particle motion equations. These equations take into account that microparticle is influenced by the central gravitational field of the Earth and its perturbation caused by the polar compression of the Earth; force of the solar pressure; the upper atmosphere resistance force and electrodynamics forces.