Visean Stage Research Articles

Formation Conditions and Hydrocarbons Generation Potential of Oil Source Rocks of South Tatar Arch and Surrounding Areas

The work studied the lithological and geochemical characteristics of oil and gas source rocks of the central part of the Volga-Ural oil and gas bearing province. The purpose of the work was to reconstruct their formation conditions, study the generation potential and maturity of organic matter, and examine prospects for industrial development. The rocks were studied macroscopically, as well as X-ray analysis, pyrolysis using the Rock-Eval method, SARA analysis, and gas chromatography-mass spectrometry. The formation of the Domanik deposits, Bobrikovsky and Pashiysky horizon mudstones, and Upper Kazan substage clays have all been proven to have occurred in a maritime environment. The content of organic matter in the rocks varies from 0.35 to 11.16%. Minute amounts of organic matter that are difficult to accurately in terms of their geochemical properties can be found in the clayey deposits of the Vereisky and Timan horizons. The Upper Kazan substage clays contain type II/ III kerogen. Mudstones of the Bobrikovsky and Pashiysky horizons, as well as Domanik deposits, contain organic matter represented by type II kerogen. The data obtained may indicate common mechanisms for the accumulation of sapropelic organic matter on the territory of the Volga-Ural basin from Pashian (Frasnian stage) to Bobrikovian (Visean stage) times. It was revealed that the studied deposits are at the stage of catagenesis (PC-MK1). At the same time, Domanik deposits have very good and excellent generation potential, which is characterized by the greatest maturity. Mudstones of the Bobrikovsky horizon have similar generation potential.

Evolution of the northeastern margin of the Kazakhstan paleocontinent: results of petro-geochemical study of sedimentary and volcanogenic-sedimentary rocks of the Zharma-Saur island arc zone

We carried out studies of petrography, petrochemistry, geochemistry and Nd-isotopy of sedimentary and volcanic rocks, as well as U‒Pb dating of detrital zircons from sandstones and tuff sandstones of four stratigraphic units of the Zharma-Saur island arc zone, located in the Middle-Late Paleozoic near the north eastern (in modern coordinates) edge of the Kazakhstan paleocontinent. The data obtained, geological structure and analysis of discriminant diagrams indicate that the formation of sandstones of the Givetian‒Frasnian sequence was the result of erosion and destruction of the Early Paleozoic igneous complexes of the Chingiz-Tarbagatai zone of the Kazakhstan paleocontinent. Tuff sandstones of the Koyanda formation of the Tournaisian stage and the Tersairyk formation of the Visean stage, distributed within the Vorontsov-Saur subzone, are mainly a product of rock destruction and volcanic activity of the Zharma-Saur volcanic arc. The feeding provinces for the sedimentary rocks of the Kokon formation of the Visean stage, which occupies most of the Zharma-Sarsazan subzone, were simultaneously the Caledonides of the Chingiz-Tarbagatai zone and the Early Carboniferous volcanogenic complexes of the Zharma-Saur volcanic arc. Our data show that the Zharma-Saur arc developed near the northeastern margin of the Kazakhstan paleocontinent at the end of the Late Devonian‒in the Early Carboniferous period.

Новые данные по изучению Серпуховских отложений разреза Белеуты

A working group of the International Subcommittee on Carboniferous Stratigraphy is working to determine the boundary of the Vise and Serpukhov stages. Comprehensive work was carried out with the aim of biostratigraphic substantiation of the most important boundaries of the Lower Carboniferous, including such priority boundaries as: Vise and Serpukhov, as well as studying the horizons of Vise and Serpukhov by conodonts, ammonoids and comparing them with foraminifera scales for international correlation of Kazakhstani divisions. The upper boundary of the Visean stage is adopted in the parastratotype in France. The border has not been studied enough. One of the best sections of the boundary deposits of the Vise and Serpukhov stages in Kazakhstan is the Beleuta section of the Zhezkazgan-Chu district. Geologists have been interested in Zhezkazgan-Chu district since the 18th century. One of the most studied sections is located on the Beleuty River near the confluence of the Sholaksai River in Zhezkazgan district in the Sholak mulda, it was described in the middle reaches of the Beleuta River on the right bank. The article presents the results of field paleontological and biostratigraphic work carried out in the Ulutau region (Central Kazakhstan). The purpose of these field works was to study the sections of the boundary sediments of the Vise and Serpukhov stages of the Lower carboniferous in order to clarify the correlation of regional stratigraphic units with units of the international stratigraphic scale, to substantiate the lower boundary of the Serpukhov carboniferous stage according to orthostratigraphic groups of fauna using modern methods. To achieve this goal, stratotypic sections were discovered and identified, their coordinates were established, boundary sediment layers were measured and described, lithological and paleontological work was carried out (including samples for fauna), spectrometric gamma-ray logging was carried out, organic remains, including foraminifera, were identified and described.

Oil deposits of the Visean stage of the northeastern part of the Tatarstan Republic

The sections of wells that have discovered oil-bearing deposits of the Bobrikian horizon, within the Aktanysh-Chishminsky trough in the northeast of the Tatarstan, are considered. In the terrigenous complex of the Bobrikian age, alternation of mudstones, siltstones, and sandstones is observed. According to the peculiarities of composition and porosity, mudstones and siltstones are classified as impermeable rocks, sandstone - as reservoir rocks. The study of sandy reservoirs showed that the rocks are characterized by a monomineral quartz composition, uniform oil saturation, fine-grained structure, massive texture. The porosity of sandstones is 15-20%. The pores are connected and form winding channels up to 0.1 mm in diameter. Sandstones form covers over the biogenic structures of the Tournaisian Stage, wedging out laterally and being replaced by dense siltstones. Good capacitive properties of the rock were acquired due to the leaching of calcite cement during the migration of water-oil fluids. Currently, sandstones contain oils with a predominance of light oil and medium paraffin fractions.

Well production after hydraulic fracturing in sandstone rocks in the north of the Perm region

Hydraulic fracturing is one of the most popular ways of increasing well production. The article investigates the results of hydraulic fracturing (HF) in sandstones of the northern Perm region territory (Tula–Bobrikovian oil reservoirs of the Visean stage). The oil of these sites has a high and medium gas content, and the rocks have a wide range of permeability values as well as natural cracking. Based on the value of the linear Spearman correlation coefficient, the most significant parameters affecting the efficiency of the HF are determined. A ranking of these parameters has been performed. The greatest influence on well productivity after HF is the bottomhole pressure and productivity indices before HF. The relationships between the geometrical dimensions of HF cracks and the volume of the injected proppant are shown. The dependencies of well parameters after HF on well parameters before HF are constructed. The permeability coefficients of the reservoir remote zone do not actually change much after HF and the permeability coefficients of the bottom-hole zone increase on average by 30%. The impact of the formation and bottomhole pre ssure values on productivity indices after HF has been noted. At the same time, the rate of oil production decrease after HF is also dependent on bottomhole pressures. Recommendations have been made on the selection of wells for HF at the site under study and similar production targets as well as their post-operation technology practices. Changes in well production after HF are forecasted depending on geological and technological parameters. The study was supported by the Russian Science Foundation, Project No. 19-79-10034.

ASSESSMENT OF OIL AND GAS POTENTIAL IN PRIMORSKAYA ZONE OF CARBONATE UPLIFT OF SOUTHERN PRECASPIAN SEDIMENTARY BASIN

The results of lithofacies studies and paleogeographic reconstructions of the Late DevonianEarly Visean stage and stratigraphic evolution of the Primorskaya zone of uplifts in the south of Precaspian Basin are presented. The complex geological structure of the region is mainly due to the influence of tectonic, volcanic and denudation processes on sedimentation. The spatial distribution of carbonate accumulations in the Primorskaya zone of the Precaspian Basin is determined by the different duration of sedimentation stages and the block structure of the basement. The results of the deep wells drilled in the recent years have made it possible to refine the internal geological structure, justification of new exploration objects in the Late Devonian strata and reevaluate the oil and gas potential and petroleum resources in the south of the Precaspian depression. After recent exploration works, the geological model for the onshore prospective structure traps has been improved, additionally prospective exploration objects have been predicted in the shelf of the Caspian Sea. The most of potential petroleum resources of the Primorskaya zone is the resources of the new offshore exploration objects in Caspian Sea. Non-structural traps can accumulate gigantic hydrocarbon volumes. This is a new highly prospective hydrocarbon exploration direction in the Precaspian Basin

SEDIMENTATION MODEL OF CARBONATE UPLIFTS OF THE COASTAL ZONE OF THE SOUTH OF THE CASPIAN SEDIMENTARY BASIN IN THE LATE DEVONIAN-EARLY VISEAN TIME

The results of lithological studies and paleogeographic reconstructions of the Late DevonianEarly Visean stage of development and features of the formation of the sedimentary complex of the Primorsky zone of uplifts in the south of the Caspian sedimentary basin are presented. The complex geological structure of the region is mainly due to the influence of tectonic, volcanic, and denudation processes on sedimentation. The results of drilling deep wells in recent years have made it possible to refine the internal structure, substantiate new objects in the Late Devonian complex, and reassess the prospects for oil and gas potential and predicted oil and gas resources in the south of the Caspian basin.

Assessment of the prospects for oil-bearing deposits of the Visean stage of the Western Zakamya region at the Tatarstan Republic

The structure of geological sections of the Visean stage of small oil fields in the Western Zakamya region of the Tatarstan Republic is considered. It has been established that potentially oil-bearing deposits are carbonate-terrigenous deposits of the Tulian-Bobrikian horizon and carbonate deposits of the Aleksininian horizon. In the Tulian-Bobrikian sediments, oil deposits are localized in fine-grained quartz sandstones, the cap rocks are dense claystones. Due to the small thickness of the layers of oil-saturated sandstones, their development is not very promising. In the deposits of the Aleksininian horizon, oil deposits are localized in cavernous limestones overlain by dense diagenetic dolomites. The thickness of the oil reservoirs is 2.0-2.5 m, which allows them to be considered as potential targets for development. The presence of sulfate mineralization in the pores of reservoir rocks suggests that the oil deposits of the Aleksininian horizon are at the initial stages of waterflooding..

Structural and mineralogical features of the Visean coal-bearing strata at the Kama coal basin

The sections of the coal-bearing strata of the Visean stage of the Kama coal basin in the territory of the Tatarstan republic are considered. It has been established that a coastal-marine terrigenous complex represents the coal-bearing strata. The complex is characterized by alternation of layers of coals, claystones, siltstones and sandstones. Coals lie at the base of the section, forming seams up to 10.0 m thick. Coals are allochthonous, formed due to the denudation erosion of peat deposits on land, the transfer of peat by water flows, and their sediment on the coastal part of the sea basin with normal salinity. The Visean caustobioliths can be classified as brown coals with a low degree of metamorphism. Their composition is dominated by the fusen component with scattered inclusions of liptinite and fusinite. In terms of material and petrographic composition, caustobioliths are classified as fusen varieties of gumite coals. In terms of the content of mineral impurities, the coals are low-medium ash, sulphurous.

SYSTEMATIC COMPOSITION, STRATIGRAPHIC DISTRIBUTION AND EVOLUTIONARY DEVELOPMENT OF GREEN ALGAE OF THE FAMILY PALAEOBERESELLACEAE MAMET ET ROUX IN VISEAN SEDIMENTS OF DONBAS

Brief information on the history of the study of green algae of the family Palaeoberesellaceae Mamet et Roux is given. Their systematic composition and stratigraphic distribution in the Visean deposits of the Donets Basin are analyzed. The results of the research permitted to distinguish three assemblages with paleoberezelides. It was found that the boundary of the lower assemblage takes place below the existed boundary between the Tournaisian and Visean stages, namely at the base of the Dokuchaevian Horizon. The upper Visean boundary cannot be traced by paleoberezelides. No algae were found in the siliciclastic deposits of the Stylian Horizon. The systematic and quantitative composition of algae of the family Palaeoberesellaceae Mamet et Roux became impoverished during the Visean. In Late Visean they played a subordinate role in relation to the other groups of algae. Nevertheless, they continued to evolve from quite primitive ones with a small set of morphological features, to more structured genera: appearance of pores, simple, dichotomously branched and with multiple branching. These features are generic of dasicladal algae, which were common in the Pensylvanian time (Berger S., Kaever M.J., 1992). The significant variability of this group and the complexity of their definition in thin sections is shown. In general, there are three paleoberezide assemblages in the Visean of Donbas: the assemblage characteristic of the Dokuchaevian and Glybokian horizons of the Upper Tournaisian−Lower Visean, the assemblage of the Sukhian Horizon of the Lower Visean and the assemblage of the Donetskian and Mezhevian horizons of the Upper Visean.

Taxonomy and Evolution of Visean–Roadian (Late Mississippian–Guadalupian) Lasiodiscidae

ABSTRACT The study of the test morphology of type specimens and newly collected foraminiferal material of the family Lasiodiscidae Reitlinger, 1956, from the Carboniferous (Visean Stage, Mississippian Subsystem) to Permian (Roadian Stage, Guadalupian Series) beds of Russia (East European Platform and Urals), Turkey, and Tajikistan (Darvaz) allowed a revision of the species composition of the genera Howchinia, Monotaxinoides, Eolasiodiscus, Turrispiroides, and Mesolasiodiscus. A new genus, Postmonotaxinoides, is described. The species Monotaxinoides transitorius, M. subplanus, M. gracilis, Eolasiodiscus donbassicus, E. galinae, Mesolasiodiscus tenuis, M. nigrans, Postmonotaxinoides horridus, P. costiferus, and P. grandis are redescribed based on new data of their test morphology. Their taxonomy is revised and new phylogenetic reconstructions for the species are proposed.

ON SYNONYMICS OF COAL SEAMS AND LIMESTONES OF THE CARBONIFEROUS SYSTEM OF THE LVIV-VOLYN BASIN

The results of regulation of synonymics of coal seams and limestones of the Carboniferous system of the Lviv-Volyn Basin taking into account ratified changes in its stratigraphic section are presented. It was noted that indices of coal seams appropriated by the previous investigators are out of accordance with the names of stages in the stratigraphic section of deposits of the Carboniferous system of the basin that were changed by the resolution of the Interdepartmental Stratigraphic Committee (ISC) of the USSR in 1974 and ISC of Ukraine in 2013.On the basis of detailed analysis and systematization of factual material and interpretation of logging data from prospecting holes of the coal fields of the basin the regulation of synonymics of coal seams and limestones was carried out in conformity with changes in the names of the stages in the stratigraphic section of the Carboniferous system or their age succession. The classification of the synonymics of Lviv-Volyn Basin is based on the notation corresponding to the names of the selected stages (their initial letters). In accordance with such a concept, the indexation of coal seams of the Visean stage begins with the lower layer of coal in the sediments of the Kulychkivska suite of the early Visean. The synonymics of coal seams and limestones of the Serpukhovian stage is replaced by the letters s and S, respectively. The synonymics of coal seams and limestones in the deposits of the Buzhanska suite, which refers to the Bashkirian stage of the Middle Carboniferous, is also replaced by the letters b and B. The system indexation we have conducted will allow us to develop a substantially updated indexing scheme for coal seams and limestones of Lviv-Volyn Basin coal deposits, which fully complies with the stratigraphic classification standards, has both scientific and applied value and is recommended for consideration and approval by ISC of Ukraine.

Feature space of the Atasu type deposits (Сentral Kazakhstan)

Purpose. Studying geological formations of the Atasu type deposits to identify prospecting criteria. Methodology. Analysis of literature and fund materials, comparative analysis of geological factors characteristic of stratiform ores, stage formation and metamorphism. Findings. The main features characteristic of the deposits of the Atasu type have been formed: their belonging to the lower strata of the Upper Famennian, Upper Devonian to the Visean stage of the Lower Carboniferous; complex composition of ferromanganese and polymetallic ores formed in three hydrothermal stages (sedimentary, metasomatic and vein ones), stratiform, lenticular, localized near volcanic edifices. Originality. The main geological criteria have been established that determine the belonging of the Uspensky ore belt in Central Kazakhstan deposits to the stratiform deposits of the Atasu type formed at different depths in continental rift valleys. The criteria include the age interval of the formation of ore deposits of the stratiform type, hydrothermal staging of mineralization (sedimentary, metamorphic, metamorphic (hydrothermal, dislocation multistage and dynamothermal)); localization of folded and post-folded subvolcanic intrusions near former volcanic edifices. Practical value. The main prospecting geological criteria (features) established for the Atasu type deposits can be used to form a feature space for predicting the areas of mineral deposits localization of the Uspensky ore belt of Central Kazakhstan formed in close time periods, in similar geological-geochemical, thermodynamic and geodynamic conditions.

The Basal Unit of the Verkhoyansk Sedimentary Complex, Northern Kharaulakh: Lithostratigraphy, Biostratigraphy, and Deposition Environments

Abstract —The origin and biostratigraphic constraints of the Krestyakh conglomerate remain among most controversial issues in the Late Paleozoic history of the Northern Kharaulakh basin. The Krestyakh conglomerate is a sequence of coarse sand to pebble-size sediments at the base of the Late Paleozoic Verkhoyansk clastic complex. According to geological, lithological, and sedimentation data, the Krestyakh conglomerate in the Atyrdakh Formation is composed of debrites i.e., deposits carried by debris flows that fill submarine canyons. The Verkhoyansk clastic deposition began at the middle Visean stage of the Early Carboniferous.

Petrophysical parameters of rocks of the Visean stage (Lokhvytsky zone of the Dnieper-Donets Depression)

The results of complex investigations of petrophysical properties of the Visean rocks from wells in Lokhvytsky zone of the DDD (sandstones and siltstones from depths 5060―5600 m and limestones from depths 5960―6200 m) are presented. The open porosity coefficient, specific and relative electrical resistivity, velocity of P-waves and S-waves, three-dimensional magnetic susceptibility of rocks are determined. The studies of electric and acoustic properties were carried out in atmospheric and simulated stratal conditions on dry and water saturated stratal model rocks. Relative decrease of the porosity coefficient with changing from atmospheric conditions to reservoir conditions is from 5,5 to 25 % (mean 11,5 %). The average value of specific electrical resistivity of sandstones is 1.2 times more than of siltstones, and 12 times more than of limestones. It has been found that due to the closure of micro-cracks and the deformation of the pore space, the electrical resistance of rocks tends to increase with pressure. There is no significant distinction in velocity parameters between dry sandstones and siltstones, however, limestones are characterized by higher velocity (approximately 30 %) of transversal waves. Saturated rocks have approximately the same average values of S -wave velocity. The average value of velocity of S -waves in sandstones is 17 % higher than in siltstones. It was established that three-dimensional magnetic susceptibility varies in wide limits. Sandstones are characterized by the highest value, this parameter for limestones is 58 times lower than for sandstones. By the mean values of the physical parameters of sandstones and siltstones, there is clearly a direct relationship between the magnetic susceptibility, density and electrical resistivity, and the reverse one with porosity. The results obtained can be used to determine the perspectivity of rocks of different composition, to modeling their properties for different depths and to quantify the structure of their pore spaces. Received dependencies between the various parameters permit to clarify the interpretation of wells geophysical researching data of the studied area.

Việt Nam Cát Bà Island Carboniferous Visean stage reef depositional facies analysis

Việt Nam Cát Bà Island Carboniferous Visean stage reef depositional facies analysis

The Carboniferous of the Moscow syneclise: Paleomagnetic data

New data for the Early and Late Carboniferous sections of the Russian platform (Moscow syneclise and Donbass) are presented. Magneto-mineralogical studies are carried out to identify the magnetic minerals—carriers of natural remanent magnetization. Extensive Late Paleozoic remagnetization of Carboniferous rocks is revealed. The obtained paleomagnetic data allowed us to determine the average paleomagnetic poles for the Gzhelian, Serpukhovian, and Visean stages of Carboniferous deposits of the Moscow syneclise.

A new Mississippian tetrapod from Fife, Scotland, and its environmental context

AbstractThe Visean stage of the Mississippian was a time of rapid tetrapod diversification which marks the earliest appearance of temnospondyls, microsaurs and the limbless aïstopods. Tetrapod finds from this stage are very rare and only a dozen sites are known worldwide. Here we announce the discovery of a new Visean site in Fife, Scotland, of Asbian age, and from it describe a new species of the baphetoid Spathicephalus. These specimens represent the oldest known baphetoid by three million years, yet belong to the most specialized members of the clade. Unlike typical baphetoids with large marginal teeth and palatal fangs characteristic of early tetrapods, spathicephalids had very broad flattened heads with a dentition consisting of a large number of small, uniform teeth. Spathicephalids were probably one of the earliest tetrapod groups to use suction feeding on small, aquatic prey. Palynological and sedimentological analysis indicates that the new fossil bed was deposited in a large, stratified, freshwater lake that became increasingly saline.

Paleomagnetism of carboniferous formations of the Russian platform: Reinvestigation of old collections

The collections of Carboniferous rocks from sections of the Russian Platform (Gzhelian, Moscovian, Bashkirian, and Visean stages) are studied. The new mean paleomagnetic poles are obtained from the Gzhelian, Moscovian, and Visean layers of the Carboniferous of the Russian Platform. In the redbed Gzhelian and Moscovian rocks, the natural remanent magnetization (NRM) components with the inclination shallowing are revealed, which is due to the presence of the large hematite particles or particle aggregates associated with the interaction between the magnetic and clay particles. Based on the obtained determinations and the results contained in the World paleomagnetic database, the trajectory of the apparent polar wander path (APWP) for the East European Platform is constructed in the interval from the Devonian to Early Permian. The Carboniferous kinematics of the East European Platform is estimated.

Использование вероятностно-статистических методов для деления пород на проницаемую и непроницаемую части (на примере терригенных отложений визейского яруса Софьинского месторождения)

Использование вероятностно-статистических методов для деления пород на проницаемую и непроницаемую части (на примере терригенных отложений визейского яруса Софьинского месторождения)