Frasnian Stage Research Articles

The Frasnian stage of the Upper Devonian in Nakhichevan Autonomous Republic (Southern Transcaucasia)

Marine carbonate-terrigenous deposits of the Lower (partially), Middle, and Upper Devonian, rich in coral-brachiopod and other fauna, are widespread across the territory of the Nakhichevan Autonomous Republic. Various ore and non-metallic minerals are associated with these deposits: the Gyumushlug and Yaydzhinsky polymetallic deposits, etc. Further ex-pansion of the mineral resources of the study area, as well as the challenges associated with the establishment of large-scale geological mapping in this region, make the development of a detailed stratigraphic scheme crucial. An indispensable condition for the creation of such a scheme is the study of the most characteristic groups of ancient organisms, among which brachiopods play a dominant role in the organic world. Devonian deposits in the Southern Transcaucasus are distributed over a limited area – in the western part of the Na- khchivan Autonomous Republic – but they are widespread here and are represented by all three well-characterized faunal divisions. For the first time, a diagram has been compiled, reflecting the sequence of appearance and distribution over time of Devonian brachiopods. On this basis, a scheme for the zonal division of the Devonian deposits in the region has been developed, identifying 20 biostratigraphic zones and 16 stratigraphic units (formations). This study summarizes the scattered information contained in various sources on the paleontology and stratigraphy of the Devonian period in the region. The identified brachiopod zones are linked to standard conodont zones. The great importance of brachiopods is determined by the fact that they are one of the most effective groups of fauna not only for dating sediments in natural outcrops, but they also provide good results for broad interregional correlations. Based on the macrofaunal complex, the Frasnian age of the sediments within the formation in question is firmly established. A detailed biostratigraphic scheme with zonal division of the Devonian deposits of Transcaucasia was developed, based on the most important stages in the development of the brachiopod fauna. Biostratigraphic zones, formations, and subformations identified in the Devonian deposits of the Nakhchivan Autonomous Republic and adjacent areas, based on the study of the entire complex of organic remains, mainly brachiopods and cono- donts, can be compared with corresponding deposits of typical sections of Western Europe (Ardennes and Eifel Mountains) and many regions of Eurasia. The obtained data are of practical importance for theoretical geologists, prospectors and developers.

Литологическая характеристика колганской свиты юго-западной части Восточно-Оренбургского сводового поднятия

Based on the study of core material, the lithological features of the deposits of the Kolgan formation of the Frasnian stage in the southwestern part of the East Orenburg arch uplift are considered. This formation is an important oil and gas play. Since picking, almost nonintermittent prospecting and exploration works have been carried out. A large bulk of heterogeneous material is received and processed, which complement and expand the knowledge of the geological structure and genesis of sediments. The research was carried out by petrographic and lithological methods. As a result, 5 lithotypes were identified according to the ratio of carbonate and terrigenous components and structural and textural features. It was found that the carbonate component prevailed in all the selected lithotypes, which distinguished this formation from other similar sections, where terrigenous rocks predominated. The presence of bioturbation of varying degrees of intensity and the presence of tempestites is characteristic.

Icriodus multidentatus sp. nov. and I. quartadecimensis sp. nov.—New Conodont Species from the Frasnian Stage of the Southern Timan

Icriodus multidentatus sp. nov. and I. quartadecimensis sp. nov.—New Conodont Species from the Frasnian Stage of the Southern Timan

Palynological Data on the Givetian and Frasnian Stage Boundary within the East European Platform

Palynological Data on the Givetian and Frasnian Stage Boundary within the East European Platform

Reference Sections, Fossil Ichthyofauna and Sr Isotope Signature of the Lower Frasnian Sediments of the Latvian Saddle and Orsha Depression, Belarus

The article provides a lithological description of the sections of the Lower Frasnian Stage of the Upper Devonian: the Zhelon Regional Stage and the Saria Beds of the Sargaevo Regional Stage, exposing in the basin of the Saryanka river, the Latvian Saddle. The complete lithological description of the Sargaevo and Semiluki sediments of the Frasnian Stage in the Gralevo quarry of the Vitebsk region, Orsha Depression has been presented. Macro- and micro-dimensional remains of heterostracans, placoderms, acanthodians, sarcopterygians, actinopterygians, as well as scolecodonts and conodonts have been found in the Lower Frasnian sediments; their photographic images are presented. For the first time, the Sr isotope composition was measured in the remains of ichthyofauna from the Zhelon and Sargaevo sediments of Belarus. On the basis of palaeoichthyological and taphonomic data, lithology and Sr isotope composition of ichthyofauna fragments, depositional environments in the Zhelon and Saria times were clarified, and the distant sections were correlated. The 87Sr/86Sr values in ichthyofauna samples from the Saria Beds in sections of the Latvian Saddle (sections of Kalyuty 5a and 6, Virenka 1) and the Orsha Depression (Gralevo quarry) lie within similar ranges: 0.70825–0.70842 and 0.70837–0.70856, respectively. The 87Sr/86Sr values in the ichthyofauna from the Zhelon sediments in the Kalyuty 2 and Obukhovo 1 sections (Latvian Saddle) vary within 0.70898–0.70932 and 0.71065–0.71102, respectively. High 87Sr/86Sr values in the fossil ichthyofauna of both regional stages suggest that the Early Frasnian palaeobassin was significantly desalinated, and the salinity in the Saria palaeobassin was comparable to the salinity of the modern Baltic Sea.

Ostracod zonation of the Givetian-Frasnian boundary interval in the Timan-North Urals Region

Research subject.Ostracods and Givetian-Frasnian boundary deposits of the Timan-North Urals Region.Materials and methods.The work was based on the results of studying ostracods from the stratotype sections of the Southern Timan, which are considered referential for regional and global correlations. The analysis of the distribution intervals of the most significant taxa was based on the results of previous studies, both published and archival materials on the Timan-Urals Region. Ostracods were considered in association with conodonts, which is an important criterion for applying a reasonable biostratigraphic subdivision. The use of different-scale regional cyclicity of sedimentation and individual “marking” levels of manifestation of global events were shown.Results.The ostracod distribution in the Givetian-Frasnian boundary interval of the Timan-Northern Urals region was analyzed. The following most significant taxa were identified: Cavellina devoniana, Cavellina uchtensis, Cavellina batalinae, Cavellina chvorostanensis, Nodella faceta, Nodella ex gr. hamata. The correlation of established assemblages with ostracods from the Franco-Belgian basin was shown. The difference consists in the absence of a polyzygid assemblage with Polyzygia beckmanni beckmanni, which was established at the base of the Nismes Formation of Belgium near the historical boundary between the Givetian and Frasnian stages. The determined relationship of biostratigraphic data in combination with the transgressive-regressive sequence of sedimentation shows a more reasonable solution to the problem of the position of the lower boundary of the Frasnian stage of the Upper Devonian in the Timan-Northern Urals Region.Conclusions.An updated version of the scheme of zonal subdivision of the Givetian-Franian boundary interval in the Timan- Northern Urals region has been developed, taking into account the ostracod distribution of the Cavellinidae and Nodellidae families, as well as the discrepancies in the levels of the first appearance of index species and the boundaries of zones in the regional stratigraphic scheme. The correlation of ostracod zones relative to the conodont scale is shown.

Kedzydshor Formation and conodonts of the Lower Frasnian on the Izyayu River (South of the Tchernyshev Uplift)

Research subject. Conodonts of the Lower Frasnian Kedzydshor Formation of the southern part of the Tchernyshev Uplift. Materials and methods. Materials obtained during a study of the section of the Kedzydshor Formation located on the Izyayu River were used. The biostratigraphic subdivision of the section was based on taxonomic definitions of conodonts and correlations with the Standard and Frasnian conodont zones. Results. In comparison with the stratotype of the Kedzydshor Formation, carbonate-argillaceous deposits cropping out on the Izyayu River are represented by fragments of the middle and upper parts of the Kedzydshor Formation in the stratigraphic range of the Lower falsiovalis Zone of the standard conodont zonation of the Lower Frasnian. The predominantly carbonate interval of the section is conventionally correlated with the FZ1 conodont zone, while the overlying terrigenous interval – with FZ2. The polygnatid and polygnatid-ancyrodellid conodont biofacies dominate in the section under study. Conclusions. New data on the distribution of cono donts across the Kedzydshor Formation in the Izyayu River section were obtained. The obtained data were compared with the local stratigraphic units of the Timan-North Urals Region. The Kedzydshor Formation is one of the most complete sequences of the Middle-Upper Devonian transition, thus representing the basis for searching and substantiating the position of the debatable lower boundary of the Frasnian Stage of the Upper Devonian.

О проблеме границы среднего и верхнего девона на Восточно-Европейской платформе

A brief overview of the history of the identification of the Frasnian Stage (Upper Devonian) and the determination of its lower boundary in the stratotype region is presented. The characteristics of the Givetian-Frasnian boundary deposits in the East European platform and the stratigraphic significance of the regional event levels are considered. Debatable issues on the age definition of the boundary deposits are discussed; tasks for the further investigations are set.

Geological prerequisites for the search for rocks with increased reservoir properties in domanic type sediments on the territory of the Republic of Tatarstan

Domanic type deposits generally is abundant in Tatarstan Republic and other territories. They are feature with oil-source rocks (black shales), which partly generated hydrocarbons. However, due to their high hydrocarbon contain, domanic type deposits construing as unconventional reservoir rocks, that may be commercial significant. Based on Russian and foreign experience in the development of such deposits, the prospects for their exploitation are associated with the searching for formations with increased reservoir properties and light oil. In this work we are analyzed the stratigraphic distribution of domanic type deposits in the Kama-Kinel system of depressions and beyond them. It is shown that such deposits in the Kama-Kinel system of depressions have a thickness about 300 m and cover the stratigraphic range from semiluk horizon of the Frasnian stage to Tournaisian stage. But out of depressions these rocks occurred only in semiluk horizon. The reason of it is high dissection of the bottom of the Domanic sedimentation basin in the Late Frasnian-Tournaisian ages due to the evolution of the Kama-Kinel system of depressions in the east of the Russian Plate. The results of our own research show that carbonate and carbonate-siliceous rocks enriched in organic matter are the most common lithotypes in the Domanic type deposits. Also, we constantly found carbonate breccias and less secondary dolomites in the studied geological columns. In the last two types of rocks, we found higher values of porosity, openness, and a lighter composition of hydrocarbons. Based on the results of the author’s research and the literature observation, it follows that the development of carbonate breccias and secondary dolomites will be in the sides of the Kama-Kinel system of depressions. We consider that they are as the most promising objects for the search for industrial profit in the Domanic type deposits.

On the possible role of magmatism in the atasu type strathiform mineralization (Central Kazakhstan)

Purpose. Studying the geological features of large industrial Atasu type ore objects. Methodology. Critical analysis of literature and stock materials, comparative analysis of geological factors characteristic of stratiform ores, stages and peculiarities of formation depending on the processes of volcanism, analysis of the results of isotope dating of rocks. Findings. Participation of volcanism (magmatism) processes in forming deposits of ferromanganese and barite-polymetallic ores of the Atasu type was minimal. It was expressed only in the development of a dissected pre-Famennian paleorelief favorable for the accumulation of metal-bearing silts and in the development of local hydraulic seals, which made it possible for the metal-bearing waters to circulate. Magmatic formations are protrusions of more ancient pre-Famennian Givetian-Franian volcanic structures. Originality. The pre-ore age of subvolcanic intrusions partially confirmed by the results of determining the absolute age, from the samples taken in the quarry of the Ushkatyn deposit that amounted to 373 4 million years, which corresponds to the middle of the Frasnian stage. The presence of three Atasu type ferromanganese deposits in the amagmatogenic Aidagarly graben-syncline also confirms this hypothesis. The genesis of deposits of the Atasu type is considered as sedimentary-hydrothermal one, associated with the processes of diagenesis and catagenesis. Practical value. Predicting the possibility of finding deposits of the Atasu type in graben-synclines throughout the entire area of the Devonian volcano-plutonic belt.

Devonian succession in the East-Zilair zone: conodont-based subdivision and paleontological verification

Research subject. Conodont-based biostratigraphic subdivision of the monotonous siliceous-terrigenous sequence stratigraphically underlying the Famennian Zilair Formation.Materials and methods. Conodont imprints on the bedding planes from our own collections along with the data from other researchers were used for dating and subdivision of siliceous formations.Results. Our study of conodonts from the deposits underlying the Zilair Formation at a number of intersections on the eastern side of the Zilair synclinorium showed that the stratigraphic scale of the straton, previously recognised as the “Betrinskaya Formation”, should be revised. Numerous collections from well-known and many new localities have proved that the terrigenous-siliceous deposits occurring stratigraphically below the graywackes of the Zilair Formation, in fact constitute the sequence of the entire Devonian section and include characterised by conodonts intervals of the upper Pragian and Emsian stages of the Lower Devonian, the Eifelian and Givetian stages of the Middle Devonian, and the Frasnian stage of the Upper Devonian. These deposits compose a lithologically homogeneous straton – the Novousmanovo succession with siliceous rocks prevailing in its section. The isolation of indicative siliceous members, in particular the Ibragimov horizon, is inexpedient due to the lithological uniformity of the succession as a whole, and its facies variability along the lateral. The limestone members included in it are dated by conodonts. They belong to different stratigraphic intervals and occur in situ in the section.Conclusions. The sediments stratigraphically underlying the Zilair Formation and fully comparable with the identified Novousmanovo succession are developed in the Kuragan-Sakmara zone (Akchura (D1), the remote facies of the Utyagulovo (D2 ef) and Sarbai (D2-D3f) Formations). In the West Magnitogorsk zone in the Voznesenka-Sakmara subzone below the Zilair Formation in a similar siliceous succession, a sequence in conodont zones of stratigraphic intervals of the Eifelian and Givetian stages (D2) and Frasnian stage (D3) united into the Aktau Formation are revealed.

Diagenetic stages of oil-saturated sandstones of the pashyisky horizon at the Romashkinskoye oil field

It was identified three stages of reservoir rock formation of the Pashyisky horizon of the Frasnian stage of the Upper Devonian at the Romashkinskoye field, based on optical microscopic studies. The first stage, associated with clastic deposits sedimentation and marked by clastic grains dense structural packing formation, close to cubic. The second diagenetic stage of quartz sandstones is associated with the subsidence stage of sediments into the burial zone. During this period were actively proceeding the processes of grains mechanical deformation, blastesis of quartz clasts, the formation of siderite fragments, and fibrous chalcedony, partially metasomatic replacing clay layers in sandstones. The third diagenetic stage in quartz sandstones is associated with the migration of underground gas-water solutions. Analysis of the transformation degree of the Pashyisky horizon quartz sandstones at different areas of the Romashkinskoye field revealed the relationship between the intensity of secondary diagenetic processes and the degree of rocks oil saturation. Keywords: pashyisky horizon; oil; sandstone; reservoir; diagenesis.

Upper Paleozoic reef systems of the Rubezhinsky Trough (southern part of the Buzuluk Depression)

Background. The Rubezhinsky Trough has been remained one of the most poorly studied petroleum areas of the Orenburg region to date. At present, Gazprom Neft conducts systematic exploration work within the trough at five license areas of the South Orenburg Cluster. Aim. The purpose of this article is representation of preliminary new dates on a geological structure of paleozoic reef systems within the Rubezhinsky Trough. Materials and methods. The main original materials for the work are the results of the interpretation of the 3D seismic carried out at four license areas. In addition, results drilling and regional sedimentation models were involved for analysis. Results. Regional models of Upper Paleozoic reef systems of the Rubezhinsky Trough have been extensively detailed as a result of the interpretation of 3-D seismic data within the South Orenburg cluster. It was first established that isolated reefs were formed in the interval of the Ardatovian and Mullinian regional stages (Givetian Stage of Middle Devonian) of the research area. Ardatovian-mullinian isolated reefs are covered with clay deposits and represent potential lithological traps for petroleum deposits. Isolated reefs, isolated carbonate platforms and the southern margin of the vast South-Buzuluk carbonate platform with barrier reef systems have been identified for the Frasnian Stage. Isolated frasnian reefs are potential hydrocarbon traps. Barrier frasnian reefs together with increasing them early famennian ones form a series of structural hydrocarbon traps in the overlapping complexes. The significant progradation of the margin of the famennian carbonate platform towards the Pre-Caspian paleobasin is established. Famennian progradation complexes form several large clinoforms which are potentially forward looking for the search for structural-lithological petroleum traps. The barrier reef system has been confirmed for the evaporite-carbonate complex of the Okskian regional stage. Okskian reefs border the late visean epicratonic carbonate platform. Relatively large reefs of the carbonate platform barrier system were identified in the interval from Podolskian regional stage (Carboniferous) to Asselian Stage (Permian). This barrier system has progradational architectures towards the Pre-Caspian paleobasin that was formed from the end of the Middle Carboniferous to the end of the Artinskian Age of the Early Permian. Podolskian-asselian barrier buildings predefine the development of structural hydrocarbon traps of various sizes in overlapping Lower Permian deposits. Conclusions. A preliminary analysis of 3-D seismic data indicates the significant role of the paleozoic reef systems in the formation of the sedimentary complex of the Rubezhinsky trough.

Comparison of source rocks from the Lower Silurian Longmaxi Formation in the Yangzi Platform and the Upper Devonian Semiluksk Formation in East European Platform

Due to the depletion of conventional hydrocarbon resources, both China and Russia are giving more attention to the exploration and production of unconventional oil and gas resources, especially those generated and accumulated within source rocks. In an attempt to further understand the mechanisms of these resources, detailed mineralogical, lithological, and geochemical studies were performed to compare source rock samples from i) the Longmaxi Formation of the Lower Silurian in the Sichuan Basin (China), and ii) the Semiluksk Formation of the Frasnian Stage of the Upper Devonian in the Volga-Ural region of the East European Platform (Russia). The results showed that the main mineral of the source rocks of both formations is chalcedony that formed during an outpouring of deep fluids onto the sea bed. Simultaneous thermal analyses of this mineral indicated similar thermophysical properties to those of the hydrothermal-sedimentary chalcedony from jasper. Moreover, a direct relationship between the chalcedony content and the total organic matter content in the samples from the two formations was established. The presence of biophilic chemical elements in the siliceous component of the source rock samples indicate that high total organic content values were likely due to the presence of biophilic chemical elements in deep fluids, which led to the large-scale development of biota and subsequent accumulation of organic matter during sedimentation. The findings also revealed that the organic matter in the source rocks of the two regions was at different stages of maturity. The organic matter in samples from the Volga-Ural region was less mature and only at the early stage of oil generation, whereas the organic matter in samples from the Sichuan Basin reached both oil and gas generation stages. The Longmaxi Formation is already in the shale gas exploration and development stage, and the Semiluksk Formation could also be regarded as an exploration target for shale oil reservoirs.

Shell Microstructure in Representatives of the Genus Lingulipora Girty from the Frasnian (Upper Devonian) Deposits of Southern Timan

The microstructure of the shell material in the protegulum brephic shells, and adult shells of Lingulipora gradata Batrukova, 1955 from the Upper Devonian deposits (Frasnian Stage) of South Timan is described. The structure of the interior part of the ventral valve was studied. The character of porosity was different in two species of the genus Lingulipora.

ВЫЯВЛЕНИЕ НЕОДНОРОДНЫХ СЛОЕВ И ЛИНЗ КОЛЛЕКТОРОВ В ТЕРРИГЕННЫХ ОТЛОЖЕНИЯХ

The possibilities of localizing residual oil reserves in depleted deposits of Tatarstan oilfield analyze in the article. The object of the study is the Pashian deposits of the Frasnian stage, Upper Devonian of the Almetyevskaya area, Romashkino oilfield. Possibilities of bypassed oil searching are considered. Sedimentation and heterogeneity of strata in the terrigenous Devonian sediments within the study area are analyzed in the paper. The analysis was carried out on the basis of well logging data. A detailed correlation of strata has been carried out, and members have been identified according to the rhythm of the layers’ occurrence in the Pashian horizon. The distribution of reservoirs and seals was studied based on the results of the detailed correlation. The analysis is based on a systematic analysis of the research object, which made it possible to consider the problem from different sides. The analysis of structural surfaces, maps of total and oil-saturated thicknesses, porosity, oil saturation, net-to-gross content and dissection along the upper and lower Pashian deposits was carried out. The influence of the structural factor on the reservoir properties of the formations is analyzed. The analysis made it possible to assess the heterogeneity of reservoirs in area and section and to predict the bypassed oil reserves localization.

Features of sedimentation and volcanism of the Tastauskaya rift structure in Central Kazakhstan

Research subject. A meridional Tastau rift structure located in the Famenian sub-latitude rift system of Central Kazakhstan was investigated, including the specific features of its constituent sediments and volcanism, as well as the stages of its development.Materials and methods. The study was based on data collected during a long period of fieldwork, including a detailed study of the sequence of sedimentation processes, large-scale geocarting, sampling for various types of precision analyses.Results. The typomorphic features of the main rock types were determined. It was shown that basaltoid rocks occurred in the form of pillow structures with a hyaloclastite matrix between the pillows. Siliceous shales are saturated with thin ash silicic acid material. A geological scheme of the Tastau structure and its specific features was presented in a series of cross-sections. The developmental stages of this structure were established. The structure was referred to the rift type.Conclusion. The material and structural features of the investigated Tastau section are shown to be typical of the entire rift system of Central Kazakhstan. The pre-rift (Frasnian) stage is characterized by continental volcanism in the form of highpotassium and ultra-potassium rhyolite ignimbrites composing an encialic island-arc structure. These volcanites belong to the shoshonite and high-potassium lime-alkaline petrochemical series. The rift stage itself began in the Early Famenian age with the formation of a system of narrow deep troughs, into which the sea from the neighbouring Zhongaro-Balkhash sea region started to ingress. The conglomerates are characterized by thin flattened isometric pebbles, whose well-polished surface is similar to that of pebbles in modern sea beaches. The sandstones exhibit a high level of lamination and are characterized by poorly pelletized clastic material. The clastic material is represented by the underlying Frasnian rhyolitic ignimbrites carried in from the sides of the trough. The mature rift stage is characterized by the accumulation (under marine conditions) of pillow basalts and hyaloclastites and thin-layered silicite-clay-carbonate shales with abundant ash. The postrift stage is responsible for the formation of layered limestones of the Lower Tournaisian, developed also widely beyond the specified rift trough.

Верхнедевонские отложения (франский ярус) северо-запада Русской платформы: палеомагнитные данные

Paleomagnetic determinations for the Devonian strata of the Main Devonian Field, available in the international paleomagnetic data base, do not make it possible to construct both detailed magnetostratigraphic scales and reliable trajectories of the apparent polar wander path of the paleomagnetic pole. This is primarily due to the insufficient amount of data that determine modern reliability criteria. Obtaining more complete series of reliable paleomagnetic determinations is one of the important tasks of paleomagnetic studies. The paper presents new paleomagnetic determinations from a collection of rocks of the Frasnian stage of the Upper Devonian (Ilmen and Bureg Beds of the Semiluky Formation), sampled on the southern shore of Lake Ilmen, east of the village. Korostyn in 2009. Magnetomineralogical studies were carried out to determine the magnetic minerals of carriers of natural remanent magnetization. Three characteristic components of natural remanent magnetization have been identified. Two components correspond to the Late Paleozoic magnetization reversal (in the Carboniferous and Permian times). The third, bipolar component of the Frasnian age passes the reverse polarity test of the geomagnetic field.. The obtained position of the paleomagnetic pole by the bipolar component of the natural remanent magnetization is consistent with the available data on the section of the Late Upper Devonian of the Main Devonian Field.

Local Sealing Technique to Improve Production String Integrity Reliability

The paper discusses the problem related to production casing leak repairs in the wells at the sites of PJSC Tatneft. The investigation showed that the most common and frequent problems occurring in the drilling facilities of the company are associated with the Serpukhov-Oka, Famennian and Frasnian stages. It has been found that high fluid loss, or absorption, is the major cause leading to well production string leak. The method of installing a profile liner in the borehole areas with high or complete loss of returns was proposed to prevent production casing string leaks and to improve the string integrity. The new technique involving a profile liner installation contributes considerably to string protection and integrity due to its metal wall thickness and squeeze cementing job quality in the string interval.

Definition of Foraminiferal Zones in the Famennian Stage (upper Devonian) of Tajikistan

AbstractSeven foraminiferal zones [Parathurammina dagmarae–Saltovskajina scitula–Neoarchaesphaera, Septaglomospiranella primaeva, Quasiendothyra (Eoquasiendothyra) bella, Q. (Eoendothyra) communis, Q. (E.) regularis, Q. (Q.) kobeitusana–Endoglomospiranella imminuta, and Q. (Q.) konensis–End. Nigra] have been identified from Famennian Stage carbonate sections in Tajikistan and compared to foraminiferal sequences from the Franco-Belgian Basin, the Russian part of the Eastern European Platform, the Ural Mountains (Russia), and Kyrgyzstan. The lower Famennian boundary is marked by the rapid extinction of all Frasnian Stage multicameral forms, which are replaced by a complex of single-chambered foraminifers of the P. dagmarae–S. scitula–Neoarchaesphaera Zone. This boundary practically coincides with the base of the middle Palmatolepis triangularis conodont zone. The upper Famennian boundary is recognized by the sharp change from endothyroid foraminifers of the Quasiendothyra konensis–Endoglomospiranella nigra Zone to a complex of simple mono- and bilocular forms of the Carboniferous Bisphaera malevkensis–Earlandia minima Zone. This boundary in the most intensely studied section at Shishkat is located 16 cm below the boundary of the Siphonodella praesulcata and S. sulcata conodont zones.