(Lithosphere)
Published by The Institute of Geological Sciences of the National Academy of Sciences of Belarus & The Belarusian Geological Society, Minsk, Republic of Belarus
|
LITASFERA (Lithosphere) Published by The Institute of Geological Sciences of the National Academy of Sciences of Belarus & The Belarusian Geological Society, Minsk, Republic of Belarus |
Abstract: The evolution history of Lower Precambrian granite-greenstone terrains was considered in the context of the vertical age tectonic-material pattern of these specific lithosphere segments within the general framework of the primary accretional and subsequent thermal Earth's evolution in the Early Precambrian. The results obtained suggest mainly relaxation development of these lithosphere units now preserved in the continent structure as granite-greenstone terrains. The relaxation process acted as a part of the global different-age disturbances of in major energy-geodynamic Earth's region, which the authors attribute to a continuous and, perhaps, laterally differential subsidence of the core and lower mantle interface.
I.V. Naidenkov
Plate tectonics in the Early Precambrian in Belarus. pp. 20--27
Abstract: The paper discusses the current general ideas of the plate tectonics (PT) in the Early Precambrian and presents some information of PT evidences in the Early Precambrian in Belarus. The analysis of numerous data available from the literature suggests that though the moment of PT initiation is uncertain and data on geodynamics at the initial stages of the Earth's crust evolution in the Early Precambrian are lacking, some evidences of plate tectonics may be noted as early as 3.0--3.2 Ga B.P., when the lithosphere evolution had taken its plate-tectonic path, despite the absence of natural associations typical of the Phanerozoic PT indicates a specific character of geodynamic processes at this stage. PT processes were evidently absent in the Katarchean when gigantic meteoric bombardement had greatly influenced the crust structural aspect, and in the Early Archean when the lithosphere geodynamics had been determined by mantle plumes and intracontinental rifting (in the time interval from 3.9-4.2 to 3.0-3.2 Ga). It is remarkable that evidences of PT processes are almost absent on the terrestrial globe in the time interval from 1.65 to 1.0 Ga (Lower and Middle Riphean). The classical PT similar to that of the present-day is noted from the beginning of the Upper Riphean (since the time of 1.0--0.85 Ga). In the Early Precambrian PT evidences are noted in Belarus from the end of the Early Archean when the granulite facies migmatites were exstensively formed suggesting collision conditions. Some Archean-Early Proterozoic evidences of the Wilson cycle that, probably, occurred at least two times are supported by crustal collision of ultrametamorphic granitoids of the Polon migmatite-granite complex (dated at 3.0 and 2.6 Ga). By the middle of the Early Proterozoic one more Wilson cycle had been completed, when the ocean basin was closed, and the Smolevichy-Drogichin suture zone with basic-ultrabasic differentiates - analogues of formations being a part of the ophiolite associations replaced the subduction zone. Somewhat later (in the second half of the Early Proterozoic) granitoid rock masses of the Mikashevichy and Vygonov complexes formed under conditions of active continental margins or collision. The latest geodynamic events in the Precambrian of Belarus took place at the end of the Early -- beginning of the Late Proterozoic as processes of tectonic-magmatic activation, which the development of the Mazur-Mogilev and, probably, Polotsk fault zones and intrusion of subalkali basic granitoid rocks are associated with.
Abstract: The results of several years' studies of brachiopods from Lower Famennian (intersalt) deposits revealed from numerous boreholes near Rechitsa-Visha fault (the Shatilki Depression, Chervonaya Sloboda step of the Pripyat Trough within the Gomel region of Belarus) have been generalized. This territory is a narrow submeridional zone, where the main oil fields in the Pripyat Depression were investigated and most of boreholes were drilled. Brachiopods from the Lower Famennian have been studied there since the early sixties. Brachiopod assemblages of the Tonezh Beds of the Zadonsk Horizon, Turov and Drozdy Beds of the Yelets Horizon and Petrikov Horizon have been described within this territory. A not numerous brachiopod assemblage revealed in the Tonezh beds includes the following genera (in decreasing order) of decreasing abundance : Cyrtospirifer, Sinotectirostrum, Sphaeridiorhynchus, Iloerhynchus, Ptychomaletoechia, Donalosia. Each of the genera is represented by the only one species. The Turov and Drozdy beds contain more diverse brachiopod assemblages. Athyris, Schizophoria, Schuchertella, Cyrtospirifer, Ardiviscus, Sinotectirostrum, Ptychomaletoechia are dominant in shallow-water deposits. In more deep-water deposits rhynchonellids (Petasmaria, Paromoeopygma, Eoparaphorhynchus, Chapinella) and productids (Nigerinoplica, Ardiviscus) are dominant. The assemblage of the Drozdy beds is more diversified than that of the Turov beds and is characterized by the predominance of Eoparaphorhynchus and Nigerinoplica, which are absent in the Turov beds. The Petrikov horizon shows the most diverse and numerous brachiopod fauna: "Plectorhynchella", Eoparaphorhynchus, Paromoeopygma, Porostictya, Levipugnax, Nigerinoplica, Crurithyris, Longispina, Athyris and other genera. This original brachiopod assemblage revealed in the upper part of the Lower Famennian (rhomboidea zone) has not yet been discovered in the other regions of the East European Platform and West Europe. Brachiopod communities from the Tonezh beds and Petrikov horizon were described in detail for the first time and illustrated with biofacies models. The Cyrtospirifer community existed as early as in Tonezh time. This is not numerous community involving some dominant species, which are met together with oncolites of blue-green algae. In Petrikov time at least three brachiopod communities existed simultaneously within this territory (at different depths and in different parts of the bottom. A highly diverse community (more that 20 species) of Eoparaphorhynchus nikae inhabited a relatively shallow sea zone. Together with numerous representatives of Eoparaphorhynchus, Paromoeopygma, Porostictya, Nigerinoplica, Cyrtospirifer and Mucrospirifer there are abundant small nodules (not oncolites) of blue-green algae, more rarely - bactrites, goniatites, crinoids, gastropods, pelecypods, bryozoans. The not numerous "Plectorhynchella" community inhabited the more deep-water parts of the sea bottom. This communities is 95--100% shells of three unstudied species "Plectorhynchella" sp. nov. 1; "P." sp. nov. 2; "P." sp. nov. 3. Shells of the larger species of "P." sp. nov. 1 are sometimes covered by very thin crusts or films of blue-green algae. In Early Famennian time shells of "Plectorhynchella" apparently formed big (up to 0.5 m high) banks. The not abundant Crurithyris fecundus community inhabited bathymetrically the same sea zone, as the "Plectorhynchella" community did, but these communities never occurred together. Two species of Crurithyris fecundus Lyashenko (70--80%) and Longispina granulata (Lyashenko) (15--20%) are obvious dominants of the Crurithyris fecundus ßommunity. This community dwelled at the silt bottom in apparently calm water parts of small sea bottom depressions.
L.V. Piskun, A.G. Laptsevich, A.S. Makhnach, N.V. Veretennikov
Paleophytologic description of the Kotlin horizon of the Vendian of Belarus. pp. 38--46
Abstract: Vendian deposits of the Kotlin strata are widespread within a large territory in the northern and south-westernmost region of Belarus. The most complete sequences of these deposits are exposed in the northeast where they were sunk by the borehole Orsha 4 in the depth range of 570 to 792 m. The deposits are represented by one sedimentary cycle composed of the lower sandstone, middle clayey-siltstone and thick upper clayey members. A thickness of these deposits decrease from 130 to 62 m south of the above sequence. The amount of sandy rocks is increased in the sequence with decreasing clayey siltstones and clays. Sandy, sandy-gravel and sandy-silt rocks are dominant in sequences of the Kotlin deposits in the north-western area and especially on the slopes of the Belarussian Anteclise. This is mainly due to their facies belonging to marginal parts of the Kotlin sedimentary basin. Formations similar to the Kotlin deposits of northwestern Belarus occur in the west of the Belarussian part of the Podlasie-Brest Depression. Clayey-silt and clayey rocks of the Kotlin strata include abundant organic remains, among them Vendetenides, filamentous algae and acritarchs have been well studied. Their species composition and images are presented in four Tables. Complexes of acritarchs and filamentous algae have been recognized with account taken of their species composition and quantity. The study of microfossils all over the territory occupied by the Kotlin deposits in Belarus enabled the authors to distinguish the Kotlin horizon in the composition of the Vendian formations, to find out a relation between various facies sequences, as well as to correlate them with the same age Upper Vendian deposits found within adjacent territories of the East European Platform.
G.I. Simakova
Paleogeography of the Krivina mire (Belarussian Poozerie area) in the late glacial and Holocene. pp. 46--52
Abstract: Lithological peculiarities of deposits, as well as the palynological analysis of six sections were used to establish that the Krivina mire situated in the Belarusian Poozere area has its origin at the beginning of the Atlantic (~ 7 800 years BP) in the place of a paleolake formed in the middle of the Dryas (~ 12 100 years BP). Several regression levels have been recognized in the development of this lake. The first regression took place approximately at 11 500 years BP, when mud laminae appeared in lacustrine clay deposits. The next regression is reflected by a transition from lacustrine clay to carbonate gittja at the boundary between the Late Glacial and Early Holocene. At the beginning of the Atlantic the lake disappeared. Pollen data record the history of the vegetation development since the Middle Dryas (~ 12 100 years BP) until the present day. Special diagrams made for every section show 3 phases of human impact on the vegetation cover of the studied locality.The first phase (~6 600--5 000 years BP) is noted by an increase of ruderal weed pollen in spectra. The second phase (~5 000-3 000 years BP) is recorded by a rise of the pasture weed curve and by the appearance of single Triticum grains accompanied by the presence of arable land weeds. The third phase (~ 3 000 years BP - present time) the most significant anthropogenic impact. It is characterized by a rise of curves of all the anthropogenic indicators: cultural cereals, ruderal, pasture and arable weeds. The woods became more scattered and meadow spaces are more widespread. The presence of the human impact indicators in pollen spectra, as well as archeological evidences allow us to infer the type of economic activities of the native tribes in the Neolithic, Bronze and Early Iron Ages.
S.M. Obrovets, S.A. Kruchek, E.A. Vysotsky
The relief impact on the formation of non-anticlinal oil traps in the Devonian evaporite deposits of the Pripyat trough. pp. 53--58
Abstract: Searching for non-anticlinal traps is the determination of paleostructrures that had existed in the paleorelief and that are not necessarily manifested in the modern structural pattern. Paleogeo-morphological reconstructions may be used to forecast these traps. The relief of the northern part of the Upper-Devonian saliferous basin floor has been reconstructed. Negative and positive paleolandforms have been differentiated: islands, submarine slopes of islands, submarine uplands, hills, submarine plains and valleys. The types of traps occurring in the halite substrata have been distingished, some peculiarities of their morphology have been determined, and the main features of paleogeomorphological environments where reservoir rocks were deposited have been revealed. Paleogeomorphologically, the distribution of hydrocarbon traps in the halite subformation was dependent on the paleorelief of the sedimentary basin floor, i.e. these are usually confined to specific paleomorphological structures: submarine uplifts, hills, ridges, submarine island slopes, and to fan deltas - in the south of the Pripyat Trough.
S.D. Astapova, Ya.I. Anoshko, N.N. Khavryuk
Material composition of the Poozerie moraine along the Chudsky glacial stream way. pp. 59--64
Abstract: Morainic deposits formed and accumilated along the whole way of the Chudsky glacial stream movement from Finland to Belarus. The results obtained from the study of their material composition within Finland, the Otepya upland in southeastern estonia, the Latgal upland in Latvia, the Lepel site and Polotsk lowland in Belarus permitted a conclusion that the formation of the Poozerie moraine of the Chudsky glacial stream was mainly influenced by the crystalline massif rocks of Finland and Devonian rocks of the platform cover. It has been shown that in spite of transformation and differentiation of heavy minerals that occurred at the first stages of glacial lithogenesis (destruction and cryogenesis of aluminosilicates), fine sandy and silty fractions of moraines within the crystalline shield are more rich in heavy minerals as compared to those from the platform cover. Heavy minerals are mainly represented by amphiboles with hornlende predominant, biotite and pyroxene. The Poozerie moraine of the Chudsky glacial stream outside the crystalline shield typically shows the similar mineral composition. This is explained by the fact that all the way of the glacial stream movement the glacier did not come into immediate contact with bedrock and advanced mainly due to natural lows enriching the moraine with local carbonate minerals and phosphates. A transition mineral association (epidote - garnet - ilmenite) involved in the morain formation process along the glacier way suffered the most important quantitative transformation. Regional peculiarities associated with local distributive provinces observed in moraines of the more ancient glaciations have not been distinguished in the case of the Poozerie moraine.
V.I. Abramenko
Clay minerals of Cambrian deposits of Belarus as indicators of the paleogeographical conditions of sedimentation. pp. 65--73
Abstract: Deposits of the Cambrian of Belarus are represented by sandy and clayey rocks. The major attention has been given to the Pretrilobitian deposits (Baltic series), where clay constitutes 60--80% of strata. The major mineral association of Cambrian clays is the kaolinite-illite complex with a small admixture of chlorite. Montmorillonite associated with erosion of weathered effusive rocks of the Upper Proterozoic age was revealed in the northeast of the Brest Depression. Cambrian deposits of Belarus are differentiated both over the area of their occurrence and in the vertical sequence. The clay mineral distribution in the vertical sequence shows a well-defined pattern: kaolinite dominant over illite at the bottom of the horizon (that are often the basis of the transgressive rhythm) and almost illite composition of the upper parts. The correlation of the clay minerals over the lateral changes with respect to conditions that existed in the Cambrian paleobasin. The illite-kaolinite assotiation of clay minerals (often with a considerable prevalence of kaolinite) is typical of the marginal shallow water zone of the basin adjacent to uplifts of the Belarussian Anteckise. Illite is the main clay mineral in the relatively deep-water zones distant from washing areas. There are small amount of chlorite there.
V.P. Korzun
Devonian magmatism in the Pripyat trough in the context of oil and diamond occurrence problem. pp. 73--80
Abstract: Rocks of alkali-ultramafic-alkali-basaltoid magmatic formation represented as explosive, effusive, subvolcanic and volcanic facies are of widespread occurrence in the southeastern part of Belarus at the junction of the Pripyat and Dnieper-Donets Troughs. These rocks cover an area measuring 45x65 km and being a part of the Pripyat oil and gas field. The Alexandrovka, South-Alexandrovka, Borschev, Vetkhin, Krasnoye Selo and other oil pools and deposits discovered there are certain to be results of the volcanic activity. Investigations performed have revealed two aspects of the deep magmatism effect upon the hydrocarbon formation in the sedimentary cover. Firstly, these are nutrients (phosphorus, silicon, etc.) supplied to the sedimentation basin that increased the basin biological productivity and, consequently, the organic content of rocks. The second factor is the thermal effect of the magma intrusion into the sedimentary cover. The alkali-ultramafic-alkali-basaltoid formation distinguished in the zone of junction of the Pripyat and Dnieper-Donets Troughs is of practical interest, as diamondiferous kimberlites are usually associated with rocks of similar formations in the best studied diamon-bearing regions of the world. The more so as alkali basaltoids, alkali-ultramafic rocks and kimberlites undersaturated with silicon acid occur under similar structural-tectonic conditions. The investigations performed suggest that the formations of the crystalline basement and sedimentary cover located in the eastern part of Belarus within a territory bounded by the Dnieper valley from Rechitsa to Orsha are considered to be promising for kimberlites and other potentially diamondiferous magmas.
V.M. Artemenko, V.V. Yudin
Peculiar features of geodynamics and metallogeny of the Donets folded area. pp. 80--86
Abstract: The creation of structurally balanced sections using palinspastic reconstructions made it possible to develop a crucially new geodynamic structural model of the toughly studied Hercynian folded area located at the southeastern margin of the Dnieper-Donets Through. The principal constituents of the model are the Donets structure of south dip, a set of layer-by-layer detachments, thrusts, perithtrust folds and displicates in the Lower-Middle Carboniferous sedimentary complexes. These constituents are characteristic of complicated folded structures vormed under the tectonic regime of longitudinal compression. It is supposed that structures of the Dnieper-Donets Trough situated northwest of the studied region are of the similar structure. The interpretation of the results obtained explains perfectly the transverse metallogenic zoning of the folded Donbas area. So, a non-commercial mercury mineralization is confined to the "cold"(low temperature and low pressure) zone. This zone is mostly distant from the endogenous suture zone and is connected with it only by layer-by-layer impermeable detachments. Complex gold-polysulfide and mercury-antimony (with platinum) mineralizations are located farther south, nearer to the suture within the Main anticline in the higher temperature and pressure zone among black schist rock masses, and a mineralization of gold-mercury formation in carbonate rocks occur further southward. The proposed balanced model makes it possible to outline part of the region (less than a half of the territory) showing good prospects for geological search for mercury-antimony, gold-arsenic-sulfide and platinum-bearing gold-polysulfide, gold-palladium-platinum and gold-mercury deposits in the context of new metallogenic knowledge.
R.G. Garetsky, V.S. Konischev, A.M. Kovkhuto
Classification of salt structures of the Pripyat-Dnieper-Donets aulacogen. pp. 86--93
Abstract: Classification of local sinclinal and anticlinal salt structures of the Pripyat-Dnieper-Donets aulacogen as a single tectonic structure was created for the first time. A system of the coordination features revealed permits a differentiation of groups, subgroups, types, subtypes, classes, subclasses, kinds, sorts and varieties of positive salt structures. All uplifts may be of single salt and double salt types. Single salt uplifts are subdivided into two subtypes: anticlines and domes, among which two classes - inherited and superimposed uplifts, and three subclasses - diapiroids, cryptodiapirs and diapirs are differentiated. Cryptodiapirs may be of several kinds: Pre-Mid-Famennian, Pre-Upper-Famennian, Pre-Carboniferous, Pre-Upper-Visean, Pre-Upper-Serpukhovian, Pre-Moskovian, Pre-Triassic, Pre-Olenekian, Pre-Jurassic, Pre-Tertiary ones. All salt uplifts are subdivided into the inherited buried and degradation ones. In shape of salt stocks two varieties of cryptodiapirs and diapirs are distinguished: pillar- and mushroom-like ones. Negative structures are divided into three types: interdome structures, structures of compensation and structures of subsidence.
V.V. Kotsur
Hydrogeochemistry of the intensive water exchange zone within the Gomel chemical plant territory. pp. 93--100
Abstract: The peculiarities of technogenic metamorphization of the ground and underground water within the territory of the Gomel chemical plant that produces phosphorus fertilizers and sulfuric acid were determined from the data obtained over the 12 years, monitoring period. Shallow ground water shows a mosaic pollution pattern. A degree of pollution and local peculiarities of the ground water chemical composition changes are connected with the plant process characteristics, phosphogypsum location and industrial waste water. The distribution of the total salt content, acidic-alkaline properties, the sulfate, phosphate and fluorine content of groundwater were studied. Technogenic sulfates penetrated to a depth of 60 m and reached the Paleogene aguifer. The sulfate content of the paleogene water under phosphogypsum dumps is 30-50 times that within non-polluted areas. The transformation of the groundwater chemical composition in the Quaternary and Paleogene aquifers results in the substitution of hydrocarbonate ions with sulfate ions and formation of sulfate type groundwater.
Abstract: Geophysical indications and criteria used to reveal deep faults in the lithosphere of Belarus were summarized and described. It was shown that zones of joining crustal blocks of various deep structure types are deep mantle faults that are 150--700 and more kilometers long, up to 30-40 km wide and show a sharp bench at the Moho interface and important variations of thickness and material composition of the crust bottom ("basaltic" layer) in the blocks they separate. Deep faults penetrate as deep as 45-55 km. A map showing deep mantle faults (deep faults in the lithosphere, crust-penetrating faults) found within the territory of Belarus was compiled. Faults of similar class are considered not only as projections of fault fissure surfaces, but as three-dimensional geological bodies. In the potential fields deep faults of the studied class show mainly a band pattern. Some typical set patterns created by deep mantle faults in the gravity field are distinguished: 1. commensurable intense up to 10-15 mGal gravity minima running along the length of a zone or along its considerable part; 2. narrow relatively lowered linear zone between intense positive gravity anomalies, a chain of local gravity minima their intensity ranging from 5 to 15 mGal is observed against the background of this zone; 3. latitudinal gravity gradient zones, transition areas between high positive and negative fields which isolines run along the fault strike; 4. chains of local gravity minima of various, mainly low intensity with individual weak gravity highs; 5. a chain of alternating local gravity highs and lows of various intensity. In the magnetic field almost all the deep mantle faults show chains of local maxima and their associated minima, often linearly elongated, which suggests their intrusive nature. Zones of fault intersection (nodes) are associated in most cases with pronounced local gravity minima of different intensity and sizes corresponding to node dimensions. In the magnetotelluric fields deep faults are described by a sharp variation of a geoelectric pattern both in the upper Earth's crust and in the mantle.This is shown in discontinuites in conductive layers, as well as in lateral changes of electrical resistivity values. Their main indication are: an essential change of a shape of transversal curves of electrical resistivity with even small distances between MTS stations, decreased masking effect of crustal conductive layers by the poorly conductive layers in the lithosphere, some structural peculiarities of conductive layers in the lithosphere sequence, a pattern of lateral changes of electrical resistivity values. The DSS data indicate that in the deep crustal structure faults are associated with sharp benches in the Moho relief and essential differences in thickness and material composition of the lower crustal part ("basaltic" layer) in blocks separated by faults. Deep-seated development of deep faults are indirectly supported by the results of studying recent time variations of the gravity and magnetic fields within the Belarussian integrated geophysical testing ground. Repeated field measurements have shown that zones of jointing blocks with different types of deep crustal structure correlate with heavy gradients of the gravity and magnetic field variation in time. This may be explained by intense deep tectonophysical processes operating nowadays in the block jointing zones. Many deep faults zones are zones of tectomagmatic activation (ex. gr. Smolevichy-Drogichin, Mazury-Mogilev, Polotsk-Kurzem zones and others) that are represented in the map showing geophysical types of the Earth's crust. The Smolevichy-Drogichin suture zone correspond to a contact of the Vilnius and Minsk blocks that differ essentially in the deep crust structure. The Mazury-Mogilev zone of tectomagmatic activation in the east part of Belarus is clearly delineated by a boundary between the Vitebsk and Bobruysk blocks and corresponds to a deep mantle fault. Its central and western parts are not distinguished by the crust types, but are traced in potential fields as crustal faults. The Polotsk-Kurzem zones is clearly shown in changing submeridional and northeastern strikes of crustal blocks in central Belarus with sublatitudinal orientation of the Central Lithuanian, Braslav and Nevel blocks. As the studied zones are considered to be promising for ores, an attention should be paid to the other deep mantle faults distinguished in the map showing geophysical types of the Earth's crust. Summing up we can say that deep mantle faults are linearly stretching geological bodies that separate crustal blocks with various geophysical types of the deep crustal structure, penetrate to subcrustal layers of the upper mantle and are described by the following properties: their extent is several times more that the crustal thickness, width is compared with a half crustal thickness; high disjunctive dislocation, i.e. dislocation by faults initiated at different depths; material weathering relative to separated blocks; lateral material inhomogeneity in strike in the upper and middle crust; often present-day activation of deep tectonic and physical processes shown in high seismicity and variation of the gravity and magnetic fields in time; faults operate as canals along which deep fluid and magma material is delivered from the bottom crustal zone (lower "basaltic" layer and "mantle-crust mix" layer) or, possibly, directly from the astenosphere to the upper crustal layers.
A.V. Gavrilov
Problems of physical and geological modelling as applied to searching for clastic pipes in Belarus. pp. 115--121
Abstract: Search for kimberlites using geophysical methods in the Belarussian region is persued under difficult geological conditions. The diatrem effect in the observed geophysical field is essentially weaken by heterogenities of adjacent and overlying rocks. Some questions of improvement of physical and geological modelling techniques according to the Belarussian region conditions are considered in this paper. The physical and geological modelling analysis allows a rational distribution of boreholes. The physical and geological modelling method and direction of search are illustrated by a specific example of the Cuper anomaly. Original conditions and works carried out works are described below by stages. The most important moment of physical and geological modelling is the determination of the average magnetisation of an object. There are three ways for this value determination: the first one is the use of the well-known formula J=Y• 0.5• T0, the second way consist in the magnetisation determination from a value of a sharp change of the vertical component of magnetic field DZ at the transition from nonmagnetic rock to magnetic body of a pipe J=-DZ/4p; the third way is to estimate the magnetisation in the central part of an anomaly from the value of the vertical component of magnetic field in selecting magnetic masses corresponding to the observed anomalous magnetic field. Some problems of gravitational modelling based on the rock density estimation and recognition of zones inside pipes are discussed in details. The advanced stage-by-stage methods physical and geological modelling with respect to the available geological and geophysical information (e.g., data of drilling) provide a sufficient flexibility of the techniques suggested.
V.G. Nikulin
Estimation of the accuracy of location of calibration explosions in the Baltic region using some seismological systems of observation. pp. 121--127
Abstract: Foreign seismological bulletins provide information of local seismic events in the Baltic region. It is important to clear up the nature of seismic events, as a lot of explosions are made in the region. However, there are evidences of historic and recent earthquakes. The estimation of the accuracy of location will promote this problem resolution. A difference between the true and observation epicenters of calibration explosions in Lithuania was correlated with parameters cited in seismological bulletins of North Europe, GBF NORSAR and REB PIDC. Equations obtained will estimate an error in locating epicenters of seismic events in the Baltic region. An example of identification of seismic events in northeastern Latvia is discussed.
Abstract: Geomorphological, geological and facies evidences suggest that neotectonic motions influenced the development of the Sozh river floodplain and its sediments during the Holocene. An evidence of this influence is the damping character of the river sedimentogenesis. The sedimentation conditions are reflected in the distributions of macro- and microelements, as well as of natural and technogenic radioisotopes. Geochemical indices of paleoclimatic and neotectonic depositional environments in some periods of the Holocene, hypergene processes of ferruginization, sorption, as well as those processing at geochemical barriers, buried ones included, have been distinguished. The floodplain section near the village of Odnopolie was recognised as a marker, and a section of the Sozh river valley - as a standard one for stratigraphic subdivisions and paleogeographical reconstructions of alluvial lithogenesis in the Holocene.
V.A. Kuznetsov, V.A. Generalova
Sorption-desorption of technogenic radioisotopes by the Sozh river floodplain formations. pp. 137--141
Abstract: The sorption and desorption properties of river silt, floodplain turf, humus horizon of the Sozh river floodplain have been studied experimentally. Solutions of ammonium and iron chlorides, peat humic acids, as well as infusions of meadow grasses and cattle-breeding farm effluents have been used as leaching reagents. The absorbing capacity of river silt for Sr-90 and Cs-137 comprised 75 and 45%, of floodplain turf - 95 and 82% of the total isotope inventories. Desorption properties were respectively (%): 13.10 and 28.25; 8.65 and 13.40 in muriate solutions, 12.80 and 21.35; 9.05 and 14.25 in infusions of grasses, 15.85 and 29.45; 9.25 and 17.63 in cattle-breading effluents. When Cs-137 or Sr-90 are abundant these are bound in forms capable of making ion-exchange desorption and may be leached in amounts as much as 30% of their total content. When radioisotopes are held in alluvial silt and floodplain turf containing the organic matter and mineral dispersion particles, Sr-90 is attracted to the organic component and Cs-137 -- to the mineral one.
V.M. Shimanovich, S.A. Akudovich
Methods of calculation of the trace elements averages for samples restricted by the lower detection limit. pp. 144--147
REVIEWS. pp. 148--149
CHRONICLE. pp. 150--158
COMMEMORATIVE DATES. pp. 159--160
BEREAVEMENTS. pp. 161--162
 Academy |