Ancient Platforms Research Articles

Late Quaternary sediments on the carbonate platform off western India: Analogues of ancient platform carbonates

The Late Quaternary carbonate sediments and sedimentary rocks from the platform off western India were reviewed for their genesis and relationship with their ancient counter parts. Sub-marine cemented and vadose diagenetic limestones were recovered at different locations on the platform and, neomorphic limestones and caliche pisolites were recovered on the continental shelf south of the platform. Dolomites on the platform were primary and formed by microbial processes under hypersaline, sulphate-reducing conditions during the lowered sea levels. Aragonite ooids were formed from the mineralization of microbial filaments that enveloped their cortex portions. Phosphorites were found in organic-rich, aragonite muds on the continental slope adjacent to the platform and formed from the microbial mineralization of organic matter and replacement of carbonate by apatite during early diagenesis. Microbial processes thus played an important role in the formation of dolomites, ooids and phosphorites reported here and those in ancient deposits. Halimeda bioherms on the platform were grown luxuriantly from the nutrients brought by upwelling currents during the Late Pleistocene–Early Holocene sea level transgression and are similar to the Holocene–Recent deposits in the Indo-Pacific region. Lime muds were bio-detrital and formed primarily from the disintegration of Halimeda bioherms and carbonate skeletal on the platform and then exported to the slope. They resemble fine-grained limestones abundantly reported in ancient platforms. Thus, the different carbonate components on the platform are genetically related to their ancient ones and serve as Late Quaternary analogues for the ancient platform carbonates.

Влияние траппового магматизма на нефтегазоносные горизонты (юг Сибирской платформы)

The lack of determination of the hydrocarbon distribution regularities in the areas with widely developed basalt complexes significantly complicates the estimation of the prospects for the oil and gas potential of the ancient platforms. This is a challenge for the researchers of the Siberian Platform, which has recently become a new Russian oil and gas extraction base. For a long time, preceding the mass introduction of trap magma, the platform was subjected to intense deflection compensated by sedimentation with the formation of a large number of hydrocarbon deposits in the lower horizons of the sedimentary cover. The influence degree of widely manifested within the Siberian platform trap magmatism on the ontogenesis of oil and gas deposits has become the goal of the studies, which involve identification of the dependence between the thickness of the Osa production horizon and reservoir intrusions of dolerites, dependence of the phase state of deposits and the temperature gradient in individual fields in the south of the Siberian platform. The study uses the correlation methods for the lithologic and stratigraphic sections of the largest hydrocarbon deposits: Verkhnechonsky, Yaraktinsky, Kovykta, Srednebotuobinsky and others. The information is represented graphically in the diagrams. Having analyzed the data obtained according to the results of deep drilling in the known fields in the south of the Siberian platform, the authors have built linear graphs of the relationship between the thicknesses of the Osa productive horizon, salt-bearing fluid seal of Usolskaya suite and reservoir intrusions of Usolsky sill dolerites. Also the graphs of deposit phase state dependence on the temperature of fluid generation are constructed on the basis of the calculation of the possible formation depth of the field. There is a direct relationship between the thicknesses of fluid seal and reservoir intrusions of dolerites. It means that the horizon is preserved in the case when the fluid seal thickness increases as dolerite reservoir thickness increases. Gas condensate deposits are formed at higher temperatures.

A Model of Keyboard-Like Nonuniform Exhumation as a Possible Cause Zoning of Metallogenic Belts in Folded Areas (Eastern Transbaikalia and Southern Primorye)

Abstract —Zoning of metallogenic belts is observed in folded areas of all metallogenic epochs from Precambrian to Cenozoic. The changes observed across the strike of folded areas on geological mapping are usually treated as geodynamic, petrometallogenic, or temporal specialization of corresponding belts (terranes) and zones. However, there are serious petrological reasons to expect a significant downward change in the basicity of magmatites and the composition of related mineralization in folded areas. The change may be caused both by relationships between the densities of magmas and country rocks and by relationships between the solidus temperatures of different magmas and the thermal gradient pattern on the magma ascent path. More basic magmatites and related mineralization should be detained at the deeper levels of the lithosphere because of the higher density and higher solidus temperature of magmas. During orogeny, the vertical differential movements of several adjacent terranes located between deep-seated faults can create keyboard-like structures composed of parallel belts variously uplifted and subsided, similarly to white and black keys of a piano. In belts and blocks of such structures more uplifted and then more subjected to denudation, the ore-magmatic complexes earlier located at deeper levels can expose at the surface. As a result, zoning of metallogenic belts can form, which is totally or only partly related to the metallogenic specialization of structure-facies zones and terranes. The possibility of this origin of zoning of metallogenic belts is shown with the use of geophysical data for two important ore-producing regions of Russia — eastern Transbaikalia and southeastern Primorye. The above model is proposed as one of the possible ways of metallogenic-belt formation in some other folded areas. The author hopes that this work will stimulate a more profound analysis of the nature of metallogenic-belt zoning in the considered and other world regions with the use of modern geophysical methods. The use of the described regularities of the storied arrangement of magmatites of different basicity and oxidation states and genetically related hydrothermal ores may facilitate prospecting for ores of different metals and their 3D forecasting in keyboard-like structures of Phanerozoic orogens and ancient platforms.

Albite thermal barrier and alkaline granite-syenitenepheline-syenite rock association (series, formation, assemblage)

The object of research.The main goal of the work was to resolve the problem of the existence of rock associations: alkaline granites–syenites–nepheline syenites, which is found on all continents among ancient platforms and stabilized folded regions of different ages. Beginning with 70-th. of the past century, the absolute majority of the world's petrologists do not allow the possibility of a comagmatic formation of such a rock association due to the presence of a thermal albite “barrier” between phonolitic and rhyolitic melts.Materials and methods. Numerous data were used on the Ilimaussak alkaline massif from southern Greenland as the most thoroughly studied and widely known to petrologists around the world. The main methods of research were the development of physicochemical models of phase transitions and the construction of state diagrams.Results.Earlier, thanks to the author's work in the field of constructing state diagrams, the possibility of “destruction of thermal barriers” was demonstrated at the appearance of alumosilicate melts of biotite, amphibole, analcime and other minerals on the liquidus. The developed physicochemical models of phase transitions for specific rock associations of the Ilimaussak massif allowed us to prove the possibility of a comagmatic transition from nepheline-modal syenites to quartz-modal alkaline granites.Conclusions.The validity (correctness) of the theoretical constructs is proved by an almost perfect coincidence of the model and natural trends of the rock associations. This requires a certain composition of the initial melt and the optimal fluid pressure.

REGULARITIES OF THE DISTRIBUTION OF QUATERNARY SANDS OF DIFFERENT GENESIS ON THE TERRITORY OF RUSSIA

Sands are widespread in the upper part of the geological section and are an important study subject in engineering geology. They lie at the base of surface facility, serve as a reservoir of underground objects and actively used as a building material. One of the important scientific and practical tasks facing geological engineers is the study of the regularities of sands distribution by area and geological section. It is especially relevant for the vast territory of our country, but there is currently no generalizing regional engineering-geological summary on sandy soils of all Russia. The article presents a schematic map of the distribution of sands of the Quaternary of various genesis, which fully covers the territory of the country and is compiled taking into account the latest results of geological plotting and mapping. The regularities of the distribution of sandy soils on the territory of Russia as a whole and within separate regions are described: young and ancient platforms of the European part (Timan-Pechora, Scythian and East-European); the ancient Siberian platform; young West-Siberian, Yano-Kolyma and Zeya-Bureya plates; orogenes of the European part, Siberia and the Far East; Baikal rift zone, as well as on the shelves of numerous seas washing the shores of Russia. The distribution of sands on the area and the section is discussed, their association with different genetic complexes of Quaternary deposits and certain elements of the relief. The Quaternary age sands that are developed within the engineering-geological zone of joint distribution of permafrost and thawed rocks and zone of practically continuous distribution of permafrost are described in the cryolithozone, which covers more than half of the country’s territory.

Isopycnicity of cratonic mantle restricted to kimberlite provinces

The isopycnicity hypothesis states that the lithospheric mantle of ancient platforms has a unique composition such that high density due to low lithosphere temperature is nearly compensated by low-density composition of old cratonic mantle. This hypothesis is supported by petrological studies of mantle xenoliths hosted in kimberlite magmas. However, the representativeness of the kimberlite sampling may be questioned, given that any type of magmatism is atypical for stable regions. We use EGM2008 gravity data to examine the density structure of the Siberian lithospheric mantle, which we compare with independent constraints based on free-board analysis. We find that in the Siberian craton, geochemically studied kimberlite-hosted xenoliths sample exclusively those parts of the mantle where the isopycnic condition is satisfied, while the pristine lithospheric mantle, which has not been affected by magmatism, has a significantly lower density than required by isopycnicity. This discovery allows us to conclude that our knowledge on the composition of cratonic mantle is incomplete and that it is biased by kimberlite sampling which provides a deceptive basis for the isopycnicity hypothesis.

Results of the tectonic stress study of the Northern Eurasia regions

The article presents the results obtained by field tectonophysical methods applied to study tectonic stresses of the Northern Eurasia regions, including young and ancient platforms (West European, Timan–Pechora, Turan, West Siberian, East European, and East Siberian) and orogenic frame structures (Caucasus, Northern Tien Shan, Mongolia-Okhotsk system of mesozoids, and Sakhalin Island). Tectonic stress reconstructions provided the basis for analysing the influence of spreading in the North Atlantics and the Arctic on the stress state of the platforms in Northern Europe. A spatial boundary of the influence goes approximately along the margins of the Fennoscandian shield and the Russian plate in the north. Further southwards, the boundary is submeridional and extends from the western wing of the Byelorussian anteclise almost to the Eastern Carpathians. The stress reconstructions for this boundary show the WNW and W-E-trending axes of compression. The boundary line does not coincide with the Teisser-Tornquist line that represents the boundary between the platforms with heterochronous basements. However, it correlates well with heat flow anomalies. The boundary area is confined to the Baltic coast [Sim, 2000. Along the boundary area, near the Baltic Sea, there is an area wherein faulting is mainly caused by extension [Sim, 2000. In this setting, helium permeability is the highest, as shown by the crust map of the European part of the USSR [Eremeev,1983. Extension in this area is probably related to formation of young grabens in the Baltic shield. Changes in the compression axis orientation may be due to the alternating activations of the grabens in the submeridionalBotnicGulf and the latitudinalGulf of Finland. Reconstructions for individual faults show contradictions in the directions of shear displacements: both right- and left-lateral displacements are possible on the same fault segments, and the axes of compression can have either latitudinal or meridional orientations. The focal mechanisms of the Osmussaar andKaliningrad earthquakes (meridional and latitudinal axes of compression, respectively) give evidence of specific current neotectonic stresses in this area. Another zone is distinguished at 52°N from the above-described area. It is mainly sublatitudinal and detected along the southern flank of the Byelorussian anteclise. Further to the east, its orientation changes to SSW, and it roughly follows the SW boundary of theVoronezh anteclise. Reconstructions for the Ukrainian Shield, located south of this zone, show mainly the unstable orientations of the axes of compression. For the platforms inNorthern Eurasia, the tectonophysical methods reconstructed neotectonic stresses in the structures formed under the influence of intraplatform tectonic stresses. These are the residual gravitational horizontal compression stresses released by long-term denudation and uplifting of the structures, including the Khibiny massif of the Baltic Shield, theOlenek and Munsky massifs of the East Siberian platform. These structures are composed of the ancient Archaean-Proterozoic rock complexes, which have been subjected to predominantly vertical displacements for a long time, from the Paleozoic to the modern stage. Special attention should be given to the tectonic stresses ofSakhalin located at the boundary between the Eurasian and North American lithospheric plates. At the edges of these two largest plates, there are the Amur and Okhotsk microplates separated by theCentral Sakhalin fault, as described in some publications. Neotectonic stress reconstructions forSakhalinIsland show sublatitudinal compression and submeridional extension in the common stress field of shearing. The tectonophysical studies show that the neotectonic stresses differ in large structures: horizontal compression and shearing are typical of the uplifts (Kola Peninsula, Tien Shan, Sakhalin), while horizontal extension and extension with shearing are characteristic of depressions (Kandalaksha graben, depressions of theTatarGulf and theSea ofOkhotsk). Our studies provide the data on spacious ‘white spots’ in the modern stress maps ofNorthern Eurasia. The stress reconstructions for practically all the studied structures show that shearing is the dominant geodynamic regime in the study region.

The limited link between accommodation space, sediment thickness, and inner platform facies distribution (Holocene–Pleistocene, Bahamas)

AbstractCyclic facies variations in shallow‐water carbonate platforms often show repetitive facies patterns that are frequently interpreted to reflect the sedimentary response to variations in sea‐level related to changes in climate linked to orbital variations, the Milankovitch frequencies. Whether these shallow‐marine carbonates represent a complete infill of accommodation space, or are subtidal cycles, has been discussed in numerous papers. The extent to which the thickness of a single depositional cycle is a direct measure of the amplitude of relative sea‐level change is not fully understood. New shallow seismic data from Great Bahama Bank reveal that accommodation space created during the Holocene sea‐level rise is not filled in a predictable way. Three seismic horizons were identified: the seabed, the Pleistocene top, and a horizon within the Pleistocene. Depth surface and thickness maps of the Holocene and Pleistocene layers were combined with 326 in situ water‐depth measurements to assess the upper limit of the present accommodation space. The analysis showed that accommodation space and Holocene sediment thickness, and water depth are not correlated. In addition, the actual water depth and inner platform facies distribution showed no straightforward link. The energy distribution across the shallow‐water platform appears to control the facies type rather than water depth. Mud‐dominated sediments prevail in shallow low‐energy areas protected by a topographic barrier, whereas mud‐free coarse‐grained sediments mainly occur in deeper areas with hydrodynamic energy induced by strong tidal currents, ocean water influx, and winds. Hence, the uneven energy distribution not only results in unpredictable differences in the carbonate‐cycle thickness on the platform but also to a water depth independent facies distribution pattern within the inner platform. Therefore, care should be taken when deducing sea‐level signals from inner platform facies distribution and sediment thickness patterns on ancient platforms.

Underground hydrosphere and geofluids of the Earth’s crust and upper mantle

The physicochemical state of the water at various temperature and pressure conditions of the Earth’s interior has been characterized. Two groups of geofluidic systems for water have been established: subcritical ( T 374 ¸ 450 °C), which together with the hydrogeological system of structured waters constitute hydrophysical, hydro- and fluid-geological lithosphere zonation. Based on the systematization of data on the decrepitating of gas-liquid inclusions in minerals of rocks of various facies of metamorphism, as well as fluid manifestations in zones of global rifting, a high content of mineral substances in the composition of dense supercritical fluids and a high electrical conductivity of such fluids is established. Recognition of high “salt content” and high electrical conductivity of supercritical fluids opens new possibilities in interpreting local high-speed anomalies and anomalies of electrical conductivity in the Earth’s crust, revealed from deep seismic and magnetotelluric sounding data. It is shown that with the water condensate — a kind of liquid-phase “restite” from the sphere of supercritical fluids separation — the genesis of highly mineralized waters and brines is connected in the crystalline basement of ancient platforms. On the example of the lithosphere of Belarus, for the first time, deep boundaries of localization of both structured water and supercritical geofluids have been determined. The hydro- and fluid-geological zonation of the lithosphere and upper mantle has been established as a basis for solving the scientific and practical problems of tectonophysics, mineralogy, hydrogeology, genesis and distribution of different type’s minerals, including hydrogenogenic minerals. A thermophysical method for determining the depth and thickness of a zone of underground structured waters is proposed. The method is based on comparison of seismic and thermal characteristics of rocks with sub- and supercritical temperatures for water.

The proto-terrestrial mechanism of the appearance of water and early genesis of the global ocean

We consider chemical reactions for the appearance of water during the formation of the planet from cosmic gas and dust material to explain the early geological existence of the Earth’s hydrosphere. This process is fully supported by the resources of the initial substances and thermal energy. Thus, the concept of V.I. Vernadsly about the geological eternity of the World Ocean and ancient age of the oceanic lithosphere is supported. The identical high location of the ancient and modern continental platforms under the conditions of continual isostatical equilibrium in the asthenosphere–lithosphere–hydrosphere gives grounds to conclude that the ocean water depth is stable. Taking this into account, we can consider that the geological evolution of the Earth began in the conditions of the existence of the World Ocean when the mass of the hydrosphere only slightly exceeded the modern one.

Нефтегазоматеринские формации древних платформ России и нефтегазоносность

Нефтегазоматеринские формации древних платформ России и нефтегазоносность

Литолого-петрографические особенности низкопроницаемых карбонатных толщ древних платформ в связи с их нефтегазоносностью

Литолого-петрографические особенности низкопроницаемых карбонатных толщ древних платформ в связи с их нефтегазоносностью

Specific features of the distribution of trace and rare earth elements in recent bottom sediments in the lower course of the Severnaya Dvina River and White Sea

The paper discusses results of the lithogeochemical examination of recent bottom sediments in the lower course of the Severnaya Dvina River and White Sea. It has been established that the average con� centration of several trace elements (Hf, Sc, Co, Y, Ni, V, Cr, Zr, Ba, and others) therein correlates with the content of the silt-pelite fraction. Maximal concentrations of the majority of above elements are confined to the silty-clayey sediments at the Basin/Dvina Bay boundary. They localized near the coastal zone only for some clastophile (Zr, Cr, and others). Typical values of the hydrolyzate module, chemical index of alteration, and Al2O3/SiO2 ratio in the aleuropelitic and pelitic sediments of the Severnaya Dvina River delta, Dvina Bay, and the Dvina Bay Basin boundary suggest that these sediments are confined to sufficiently cold climate set� tings. Data points of sediment composition in discriminant paleotectonic diagrams are scattered over a large field probably due to high contents of the weakly weathered plagioclases, micas, and amphiboles, as well as the hydrogenic process promoting the accumulation of Fe and Mn. The PAASnormalized spectra of rare earth elements (REE) in bottom sediments of the Pinega and Severnaya Dvina rivers, marginal filter of the latter river, Dvina Bay, and the Dvina Bay Basin boundary are similar to the REE distribution in clayey rocks of the ancient platform cover (except for a slight positive Eu anomaly). The REE systematics and distribution pattern of compositional data points of recent bottom sediments in the GdN/YbN-Eu/Eu* and Eu/Eu*- Cr/Th diagrams and values of several indicator ratios of trace elements suggest that the studied rocks were formed by the mixing of clastic materials from geochemically contrast provenances: northwestern provenance (Kola-Karelia geoblock), which is mostly composed of the Archean and Early Proterozoic crystalline com� plexes, and the southeastern provenance (northwestern periphery of the Mezen syncline), which is almost totally composed of Phanerozoic sedimentary rocks. The latter provenance likely played a crucial role in the geochemical signature of recent bottom sediments over a significant area of the White Sea.

The evolution of the Siberian craton, petrogenesis and diamond potential of the mantle magmatic systems

The article reviews the history, main scientific fields and major results of the studies performed by the Laboratory of Petrology, Geochemistry and Ore Genesis and the Laboratory of Geology and Magmatism of Ancient Platforms.

Eurasia as the scene of the Late Cenozoic tectogenesis

This paper attempts to review the descriptions on the genetic series of neotectonic forms in Eurasia. Morphotectonically, the Eurasian continental block exhibits a radial-concentric pattern consisting of four kinds of tectonic units: platforms, rejuvenated and youthful mobile belts, and the continent-ocean transition zones. Vast areas of young and ancient platforms, such as Siberia, have experienced slow-rate Late-Cenozoic uplift and little interior deformation. The youthful orogenic belts are clustered into the giant Alpine-Himalayan megabelt. The rejuvenated mountain belts are characterized by a variety of structural-morphological types of orogens, such as domelike uplifts, block uplifts and intermountain basins. The continent-ocean transition zones in Eastern Asia, including marginal rifts and extensional basins, are resulted from interaction between the continental block and Pacific Ocean and Philippine Sea since the Late Cenozoic. One of the conspicuous features of Eurasia is that most areas lie in the largest geoid depression of the Earth, and the NS trending Uralian-Oman lineament expresses a break on the geoid slope, implying a relationship to deep structure, including density inhomogeneities, downward to the core-mantle interface. Besides, the Eurasian continent fully demonstrates morphotectonic and recent geodynamic features of the Northern Hemisphere of the Earth, just in contrast to that of the Southern Hemisphere. It is best to view the surface morphotectonics and deep structure of the Earth as a geodynamic ensemble which has spawned the large-scale geomorphic features on the surface.

Global factors in dynamics of petrophysical processes

In classical description of structural-tectonic fragments of earth crust vast territories of ancient platforms are represented as geodynamically passive elements of lithosphere. That is why nature of various phenomena occurring on platform (landslides and karst-suffosion processes, rock bursts and gas explosions in mines, pipeline breaks, etc.) is usually associated solely with processes of exogenous changes in geological environment, formed by rocks of sedimentary cover [Natural Hazards in Russia, 2002]. However, results of many years investigations of geodeformation regimes of geodynamically (seismically) active and platform regions allowed experimentally establish [Rudakov, 2009] that in preparation of catastrophic geodynamic phenomena (earthquakes and volcanic eruptions) prominent role played by processes of global change of stress-strain state of lithosphere due to processes of self-organization under influence of Earth velocity rotation variations. In particular, it was shown that these processes are reflected in changes of fluid dynamic regimes of fault structures of East European Platform (EEP), influencing processes of exogenous geological environment transformation, and, appearing in rocks of sedimentary cover by local geodynamic processes and phenomena. For example, it was found that dynamics of accidents on routes of gas pipeline networks of EEP is connected with wave motion of platform, as well as with processes of cyclic fluid transmission in fault transcontinental and regional tectonic formations that form dynamics of karst-suffosion processes in territories of Moscow depression [Rudakov, 2008]. Continuing to investigate links in chain of cause-effect dependence of local geodynamic phenomena and processes from processes of global change in stress-strain state of earth's crust, we made spectral and correlation analysis of a half century (49 years) time series of mean annual cases of karst gap formation in Dzerzhinsk, Nizhny Novgorod region in comparison with variations of water level in Oka River, which flows in area, variations in Earth's rotation and change in solar activity. It allowed to trace development of karst-suffosion processes influenced by changes in fluid dynamic regimes in region controlled by variations in stress-strain state of earth's crust in region associated with variations in Earth's rotation and changes in solar activity, controlling climate changes on Earth as a whole, and in each particular region of planet. Note that problem of assessing influence of solar-terrestrial relationships in processes of terrestrial atmosphere, hydrosphere, and even biosphere, after A.L. Chizhevsky concerned by many researchers [Rivin, 1989] but geological and geophysical aspects of this problem are practically not affected. Especially not enough investigated processes that control in platform conditions development of exogenous processes, such as karst-suffosion. And in this respect opportunity to examine longterm observations, of the Dzerzhinsk karst observatory” of Nizhny Novgorod region allowed, as it seems to us, to take another step toward assessing extent of planetary processes influence on dynamics of geodynamic processes of local scale. Fig. 1 shows original time series of mean annual variations of Earth's rotation velocity (relative value), solar activity (Wolf numbers), cases of karst gaps in Dzerzhinsk and water level in Oka river, which were analyzed on basis of calculation spectral-temporal and correlation characteristics of these time series and their components identified by energy filtering. Fig. 2 shows calculated values of cross-correlation function (CCF) between analyzed time series.

Mikhail M. Odintsov’s contribution to development of the mineral and raw materials complex of the Eastern Siberia

The publication is devoted to the role of Mikhail M. Odintsov, Corresponding Member of the USSR Academy of Sciences, and his scientific school in solution of fundamental problems related to regularities of occurrence of endogenic mineral resources at ancient platforms. Based on mineragenic zonation data on the southeastern segment of the Siberian platform, Mikhail M. Odintsov determined the location of the AngaroViluisky ore belt that controls deposits and ore occurrences of magnetite, sulfates of copper and nickel, gold, base metals, barite, сelestine, and diamonds. Fundamental concepts proposed and developed by Mikhail M. Odintsov contributed significantly to studies of structures and evolution of ancient platforms and facilitated development of modern forecasting concepts concerning exploration of primary and alluvial deposits of diamonds in the southern part of the Siberian craton.

Review on the monograph Historical Minerageny volumes 1–3, 2005–2008 by N. N. Zinchuk, A. D. Savko, and L. T. Shevyrev; Voronezh State University

A major review of the deposits of mineral resources of all ages and all types on the Earth’s surface has recently been published. Data on the main types of metallic and nonmetallic deposits of the world from the Archean to the Cenozoic are systematized. The huge body of data is of considerable importance both for the comprehensive analysis of mineragenic pro� cesses and for revealing geodynamic trends in the crust and mantle, as well. The material is presented in three volumes. Volume 1 is concerned with a global review of the data on the spatiotemporal distribution of mineral resources; Vol� ume 2 is devoted to the mineral resources of ancient platforms; and Volume 3 comprises a description of deposits in mobile belts (fold regions). The descrip� tions of objects (deposits and their groups) are system� atic, complex, and comprehensive. A convenient hier� archic system is elaborated for easy orientation among the multitude of different objects. The succession of “mineragenic process” (forma� tion of metallic and nonmetallic mineral resources) is considered in two dimensions. The first coordinate— type of geodynamic settings—is expressed in the data arrangement by volumes: the first volume is devoted to global trends in the distribution of deposits; the second volume deals with deposits on platforms; and the third volume concerns deposits in orogenic belts. The sec� ond coordinate is distribution in time according to the basic orogenic epochs: Early Precambrian, Riphean (Late Precambrian), Caledonian (Early Paleozoic), Early Hercynian (Middle Devonian–Early Carbonifer� ous), Late Hercynian (Middle Carboniferous–Middle Triassic), Kimmerian (Late Triassic–Jurassic), Early Alpine (Cretaceous), and Late Alpine (Cenozoic). Voluminous factual material is generalized in the

Ancient continental margins and comparative analysis of their oil-and-gas bearing

Analysis of peculiarities in the distribution of hydrocarbon accumulations within the basins of Phanerozoic continental margins, which had completed their evolution, and complicated peripheral regions of ancient Laurasian and Gondwanian platforms nowadays, has enabled us to reveal certain regularities related to two stages in the evolution of sedimentary basins. The first stage of evolution of sedimentary basins (period of existence of the continental margin proper) is related to large accumulations of fluid and gaseous hydrocarbons in the margins of continents belonging to the Laurasian megablock; for the margins of continents belonging to Gondwana, this period was reflected in the formation of large gas accumulation only (in the Permian). At the second stage of sedimentary basin evolution, large oil and gas accumulations were formed in areas associated with fore deeps, which were laid in the boundary of the Gondwanian platforms and fold belts. In comparison, in fore deeps that emerged in the marginal parts of Laurasian platforms, less significant accumulations of fluid and gaseous hydrocarbons were found (Table 1). The results of comparative analysis in oil-and-gas bearing basins located in the margins of the Laurasian and Gondwanian megablocks would help in purposeful exploratory works for oil and gas.

Methodology of assessing endogenous component deep groundwater

This paper discusses the problems of separating the endogenous components of deep groundwater. We suggest utilizing the boron/bromine ratio for determining the endogenous components in groundwater from the lower levels of the sedimentary cover. This paper suggests methods for calculating the boron/bromine and boron/chlorine ratios for brines in ancient platforms, and thermal water in tectonically active regions and in regions of present active volcanism.