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Stratigraphy and Geological Correlation
Journal Prestige (SJR): 0.581  Citation Impact (citeScore): 1 Number of Followers: 2  Subscription journalISSN (Print) 0869-5938 - ISSN (Online) 1555-6263 Published by Springer-Verlag  [2468 journals]
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- Regional Stratigraphic Schemes of Bathonian–Upper Jurassic and Lower
Cretaceous Continental Deposits of the Lena River Basin, Eastern Siberia-
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Abstract: Abstract The refined regional stratigraphic schemes of Bathonian–Upper Jurassic and Lower Cretaceous continental deposits of the Lena River Basin are presented. The schemes present structural-facies zones, horizons, and flora-bearing layers with updated lists of characteristic plant assemblages.
PubDate: 2025-02-20
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- Magnetostratigraphy of the Danian Stage of the Volga Right Bank Region
near Saratov: Article 1. Klyuchevskaya Member–the Lower Syzran
Subformation-
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Abstract: Abstract Magnetostratigraphic data on the Klyuchevskaya Member and the lowermost of the Lower Syzran Subformation, which composed the lowermost of the Paleocene (Danian Stage) in the north of the Volga Right Bank Region near Saratov, are determined for the first time. A stratotypical section of the Klyuchevskaya Member near the settlement of Klyuchi and the section near the settlement of Tyoplovka are characterized by magnetozones of different polarities: the analogs of chrons C29n, C28r, and C28n, on the basis of which the Klyuchevskaya Member is compared with the NP2–NP3 zones by calcareous nannoplankton. The sedimentation rates and the period of the formation of the deposits are estimated. The presence of differentiated tectonic movements at the beginning of the Paleocene is substantiated by results of detailed magnetostratigraphic correlation of sections, as well as geochemical data, and gentle inclination of the bottom of the early Danian basin to the southwest is suggested from anisotropy of magnetic susceptibility.
PubDate: 2025-02-20
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- Occurrence of a Spectacular Glossopteris Flora from the Late Permian Beds
of Madhupur Village, Talcher Basin, India and Their Connotations on
Palaeoclimate and Biostratigraphy-
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Abstract: Abstract An affluent and well-preserved collection of plant megafossils is recovered from the Lower Kamthi sediments of Madhupur Village, Talcher Basin, Odisha, India. It comprises Sphenophyllales (Trizygia speciosa), Filicales (Neomariopteris hughesii), Equisetales (Schizoneura gondwanensis, equisetaceous stems), Ginkgoales (Rhipidopsis gondwanensis) and Glossopteridales (Glossopteris with 45 species, Palaeovittaria kurzii and stem casts). The palaeovegetation of the studied area has also been portrayed. The lithology of the studied section and the record of a good number of middle and broad mesh forming petiolate Glossopteris leaves, presence of Sphenophyllales and Filicales and the absence of a typical Triassic element (Dicroidium) in these beds suggest their affiliation with the Lower Kamthi Formation of Late Permian/Lopingian epoch (Wuchiapingian–Changhsingian age). The study of the macrofloral assemblage demonstrates warm, humid and temperate climatic conditions during the deposition of sediments in the Early Kamthi, unlike the arid conditions during the deposition of sediments in the Late Kamthi (Induan to Olenekian). The occurrence of a large number of petiolate leaves is indicative of the prevalence of high velocity winds at that time. The recovery of a good number of plant megafossils and the absence of coal reveal that the sediments were deposited in a quiet and still water environment. There might be fairly high relief in this area, and a quick burial of the sediments and plant material might have happened in a fluvio-lacustrine settings. Lithology of the beds shows that despite a fair humidity, the Lower Kamthi sediments did not attain maximum maturity.
PubDate: 2025-02-20
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- Rb–Sr Systematics and U–Pb Age of Carbonate Rocks of the Staraya
Rechka Formation, the Vendian of the Anabar Uplift, Northern Siberia-
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Abstract: Abstract— The results of Sr-chemostratigraphic study of carbonates of the Staraya Rechka and Nemakit-Daldyn formations which make up the upper part of the Precambrian cover of the Anabar Uplift in Northern Siberia are presented. A Pb–Pb age of the Staraya Rechka Formation dolostone has been obtained (549 ± 25 Ma, MSWD = 1.4) for the first time. An improved stepwise dissolution procedure was used to determine the 87Sr/86Sr, 206Pb/204Pb and 207Pb/204Pb isotopic ratios in carbonates rocks. The methodology for studying the Rb–Sr systematics included the chemical removal of about a third of the crushed sample [fraction L(Rb–Sr)1] by preliminary acid leaching in 0.2N CH3COOH and subsequent partial dissolution [fraction L(Rb–Sr)2] of the remaining part of the sample in CH3COOH of the same concentration. The Pb–Pb isotopic systematics of dolostones was studied by six to nine-step dissolution in 0.5N HBr. Chemical procedures resulted in the removal of secondary epigenetic carbonate material, which improved the quality of Sr-chemostratigraphic and U–Pb geochronological information. The initial 87Sr/86Sr ratios in the least altered carbonate material [fraction L(Rb–Sr)2] of the Staraya Rechka Formation dolostone are 0.70822‒0.70836, and in the Nemakit-Daldyn Formation limestone, 0.70854–0.70856. The Pb–Pb age of early diagenesis of dolostones of the Staraya Rechka Formation (549 ± 25 Ma) was calculated from fractions [L(U–Pb)2–L(U–Pb)n], where n for different samples varied in the range from 6 to 9. Epigenetic carbonate fractions L(U–Pb)1 are characterized by a Pb–Pb age of 360 ± 190 Ma (MSWD = 0.8). The obtained results prove that the Staraya Rechka Formation of the Anabar Uplift belong to the Late Vendian (Late Ediacaran), allowing them to be confidently correlated with the carbonate rocks of the upper part of the Yudoma Group of the Uchur-Maya region and to include the named strata into a single Yudoma Complex of Siberia.
PubDate: 2025-02-20
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- The Locality of Fossil Plants Juldybaevo (Kungurian Stage, Lower Permian,
Republic of Bashkortostan, Russia) and Its Position in the System of
Kungurian Phytoorictocoenoses of the Eastern European Platform-
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Abstract: Abstract The article is devoted to the characteristics of the Juldybaevo floristic assemblage of the Republic of Bashkortostan, Russian Federation. This assemblage has an Early Permian (Kungurian) age and includes a number of representatives of Permian spore and gymnosperm plants, which are characteristic of the Early Permian stage of the florogenesis of the Western Angaraland. The information about the regional geology and stratigraphy of the Cis-Uralian Foredeep is given. A detailed description of the Juldybaevo floristic assemblage is given. This assemblage includes representatives of the equisetophytes, pteridosperms (lyginopteridophytes), ginkgophytes, vojnovskyopsids, and conifers. The main trends in the evolution of the Early Permian floras of the Western Angaraland are analyzed. The authors’ ideas about the paleogeographic and paleoclimatic conditions of the Juldybaevo flora are presented.
PubDate: 2025-02-20
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- New Ostracod Genera Bathoniella (Bathonian and Lower Callovian of the East
European Platform and Northern Germany) and Parabathoniella (Lower and
Middle Bathonian of Scotland). Part 2: Evolution and Biostratigraphy-
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Abstract: Abstract— The results of comparative morphological and ontogenetic analyses of the ostracods Bathoniella Tesakova (East European Platform (EEP) and Northern Germany, Bathonian–lower Callovian) and Parabathoniella Tesakova (Scotland, lower–middle Bathonian) suggested their origin from representatives of the genus Glyptocythere Brand et Malz with reticulate ornamentation (Europe, Bajocian–Bathonian). The West European Parabathoniella evolved from G. comes Br. et Malz, while East European Bathoniella evolved from G. tuberosa (Khabarova). Both ancestral taxa evolved from the West European G. concentrica Br. et Malz, which migrated to the EEP with formation of the allopatric G. tuberosa in the late Bajocian. A replacement name G. pseudotuberosa Tesakova, nom. nov. is proposed for G. tuberosa Br. et Malz, 1962 from the lower Bathonian of Germany, a junior homonym. The development of ornamentation and linear dimensions in the lineage of reticulate Glyptocythere demonstrates a complete cycle of morphogenesis with paedomorphosis and magnification in Bajocian species and subsequent gerontomorphosis and minification in Bathonian representatives and their descendants Bathoniella in the Bathonian and early Callovian. The stratigraphic continuity of successive species made it possible to recognize new lineage zones in the EEP: G. tuberosa in the terminal upper Bajocian–lower Bathonian (Michalskii–Besnosovi zones), B. prima in the terminal lower Bathonian–upper Bathonian (Ishmae Zone–lower part of the Calyx/Infimum Zone), B. milanovskyi in the upper Bathonian (presumably the upper part of the Calyx/Infimum Zone)–lower Callovian (Elatmae Zone), B. paenultima in the lower Callovian (Subpatruus Zone, C. surensis, C. subpatruus, C. uzhovkensis biohorizons) and B. ultima in the lower Callovian (Subpatruus Zone, Ch. saratovensis Biohorizon–Calloviense Zone). Additionally, the B. milanovskyi Zone is recognized in Northern Germany. The species Parabathoniella elongata (Wakefield) from the lower and middle Bathonian of Scotland appears to have been the only member of the West European genus. Its homologous acquisition of bathoniellid sexual dimorphism at the same time as B. prima Tesakova allows a pan-European correlative level based on the first appearance of these species in the geological record to be drawn.
PubDate: 2025-02-20
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- Trilobites and Biostratigraphy of the Cambrian Section of the
Khantaysk-Sukhotungusskaya-1 Well, Northwest of the Siberian Platform-
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Abstract: Abstract Almost the complete Cambrian sequence was uncovered in the Khantaysk-Sukhotungusskaya-1 well. Five formations have been established in the well: Chopkо, Ust-Brus, Shumnaya, Krasnoporozhskaya, and Sukharikhа. Their deposits belong to the lower Tukalandian, Mokuteian, and Omnian Region Stages of the Upper Cambrian (corresponding to the lower part of the Aksaian Stage and the Saksian Stage) and to the Glyptagnostus stolidotus Zone, Layers with Tomagnostella sulcifera, Layers with Lejopyge, Layers with Anomocarioides, and Layers with Linguagnostus of the Middle Cambrian, as well as Layers with Pagetiellus porrectus of the Lower Cambrian. The G. stolidotus Zone established in the well is a paleontological subdivision directly underlying the stratotype of the Omnian Region Stage, which is located in the natural section of the Chopko River. Five new Middle Cambrian trilobite species have been described: Ammagnostus minutus sp. nov., Parasolenopleura siberica sp. nov., Onchonotellus arealis sp. nov., Pseudanomocarina falcata sp. nov., and Toxotiformis tchopkiensis sp. nov.
PubDate: 2025-02-20
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- Bivalve-Based Stratigraphy of the Toarcian of Eastern Siberia and
Northeastern Russia (Family Oxytomidae Ichikawa, 1958). Part 2. Ontogeny.
Classification and Taxonomic Assessment of Characters. Phylogeny. System
of the Family Oxytomidae. Taxonomic Descriptions-
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Abstract: Abstract The system of the family Oxytomidae (subfamily Oxytominae) was revised based on Mesozoic material from different stratigraphic levels, using our own and museum collections. Variability of the hinge plate and byssal block of shells in the ontogeny of these mollusks was assessed using the age periodization method. Taxa were classified using a posteriori character weighting. Relationships between taxa were established by the constant presence of a character or assembly of characters in morphologically similar taxa. To establish the relationship, the similarity of homologous characters was used—the shape of the ligament pit at the postlarval stage, the type of the ligament pit at the juvenile stage, the subtype of the ligament pit and the subtype of the lower margin of the ligament pit at the subadult stage, the type of the byssal furrow, the type of the byssal notch, the presence of a protuberance, the presence of an inclination of the ligament area relative to the shell axis. The phenoclines of these characters were identified and the directions of morphological evolution within the subfamily Oxytominae were reconstructed based on the study of ontogenetic and evolutionary variability in the shape of the ligament pit, byssal ear, and the anterior and posterior wing of the left valve. The chronoclines were reconstructed based on the chronological succession of taxa with unidirectional changes in characteristics. When the phenocline and chronocline coincided, probable phylogenetic relationships between the taxa were suggested. The transformation of the ligament pit of the Jurassic-Cretaceous Meleagrinella and Arctotis is accepted as the main cluster of the phylogeny of the family Oxytomidae in the Jurassic. Based on the phylogenetic reconstruction, the composition of the subfamily Oxytominae was emended. It contains three genera—Oxytoma, Meleagrinella, and Arctotis. Using the method of morphometric assessment of morphological characteristics, the index species of the Pliensbachian-Aalenian oxyto-zones and of the Beds with oxytomids were systematically described and compared with other species in the taxonomic clade.
PubDate: 2024-11-20
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- Bivalve-Based Stratigraphy of the Toarcian of Eastern Siberia and
Northeastern Russia (Family Oxytomidae Ichikawa, 1958). Part 3.
Toarcian–Lower Aalenian Zonal Scale Based on Oxytomids. Bivalve-Based
Stratigraphy and Correlation-
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Abstract: Abstract As a methodological basis for spatio-temporal modeling of the studied sedimentary series, the relational-genetic space-time concept of Steno–Vernadsky and V.I. Vernadsky’s paradigm of biological time. The biochronological approach to the development of a zonal scale as an independent methodological direction is defined. Based on a revision of the phylogenetic system of the family Oxytomidae, a spatiotemporal framework of the zonal scale was constructed. The direction of the time scale is determined by the sequence of index species interconnected by a single chronocline of changes in the states of the characters of the ligament block. The direction of evolution in the phylogenetic lineage Meleagrinella–Arctotis, combined with periods of stable state of some characters, has its own (relational) time, therefore the scale is considered as biochronological and is a tool for dating sediments. According to paleontological and stratigraphic criteria, the elementary divisions of the scale—Oxyto-zones are phylozones, deposits containing the species representing segments of the phylogenetic lineage of the genera Meleagrinella and Arctotis. The updated Toarcian and Lower Aalenian zonal scales consist of six oxyto-zones. In the boundary deposits of the Upper Pliensbachian, Beds with Meleagrinella deleta are recognized. In the Upper Aalenian–Lower Bajocian boundary deposits, Beds with Arctotis sublaevis are recognized. In the Upper Toarcian–Lower Aalenian, an auxiliary biostraton is recognized—parallel Beds with Oxytoma jacksoni. The correlation potential of the scale was assessed based on tracing oxyto-zones in sections of Eastern Siberia, Northeast Russia, Germany, France, Western and Arctic Canada. In the terminal part of the Pliensbachian, the Beds with Meleagrinella deleta are recognized in the Siberian, Far Eastern and Western European paleobiogeographic provinces within the Arctic and Boreal-Atlantic regions. In the Lower Toarcian, the Meleagrinella golberti and Meleagrinella substriata oxyto-zones of were identified in the Arctic, Boreal-Atlantic and Boreal-Pacific paleobiogeographic regions. In the upper part of the Toarcian and in the Aalenian–Lower Bajocian, the Meleagrinella prima, Arctotis marchaensis, Arctotis similis oxyto-zones and Beds with Arctotis sublaevis were recognized in the Siberian and Far Eastern provinces within the Arctic paleobiogeographic region, parallel Beds with Oxytoma jacksoni were traced in the Arctic and Boreal-Pacific paleobiogeographic areas. Tracing oxyto-zones and Beds with oxytomids allows the intra- and interregional correlation at the zonal and substage levels.
PubDate: 2024-11-20
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- Bivalve-Based Stratigraphy of the Toarcian Deposits of Eastern Siberia and
Northeastern Russia (Family Oxytomidae Ichikawa, 1958). Part 1. A Brief
Outline of the Development of Views on the Toarcian Zonal Stratigraphy in
Northeast Asia. History of the Study of Oxytomids. Materials and Methods
of Fossil Study-
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Abstract: Abstract Interpretations of the stratigraphic range of the Toarcian Stage in Northeast Asia are analyzed using the concept of historical dynamics of science. Although Lower-Middle Jurassic deposits have been studied for more than a hundred years, and the biostratigraphic framework has been developed, some problems of the Lower and Middle Jurassic stratigraphy of Eastern Siberia and Northeastern Russia remain unresolved. These include substantiation of the lower and upper boundaries of the Toarcian and analysis of the completeness of the Toarcian Stage represented in sections. It is shown that current bivalve zonal scales for Eastern Siberia and Northeastern Russia are based on different principles, constructed to successions of taxa belonging to different families, and are used independently in the two regions. By identifying the structural and logical components of the research process, three stages are recognized in the history of the study of the family Oxytomidae Ichikawa, 1958. The relevance of the study of the bivalve family Oxytomidae is substantiated. New methods are developed for studying bivalves with a pterineoid hinge: growth stages, typification of the hinge apparatus, zoning and morphometry. The method of growth periodization of mollusk shells makes it possible to identify oxytomid growth stages in shells of different sizes. Use of a shell zoning method allows the relative boundaries of shell parts to be determined, and development of a unified terminology for morphological traits used in describing taxa. The method of hinge typification facilitates the study of ontogenetic changes in bivalves with a pterineoid hinge and helps clarify the phylogeny of the group. The morphometric method allows for a quantitative assessment of the characters used in the description of taxa and statistical testing of hypotheses about evolutionary transformations.
PubDate: 2024-11-20
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- Developments in the Cretaceous Stratigraphy of Crimea. Part 2. Upper
Cretaceous and Conclusions-
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Abstract: Abstract This is the second part of the paper on the Cretaceous of the Mountainous Crimea. A lot of new data has been received during last ten years. This paper summarizes the state of knowledge of the Upper Cretaceous stratigraphy, selected biostratigraphic groups (ammonites, belemnites, ostracods, foraminifers, gilianelles, nannoplankton) and magnetostratigraphy. Ammonite and belemnite biostratigraphic subdivisions are proposed for the first time for the Crimean Upper Cretaceous. Foraminifera-based biostratigraphy is updated, and new biostratigraphic units are proposed and correlated with the European scale. Stratigraphic hiatuses are recognised in the succession of southwestern Crimea: the base and the top of lower Cenomanian, upper Coniacian–lower Santonian, Campanian/Maastrichtian and Cretaceous/Paleogene boundary intervals.
PubDate: 2024-11-14
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- Upper Jurassic Volgian Stage and Lower Cretaceous Ryazanian Stage of the
Panboreal Biogeographic Superrealm-
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Abstract: Abstract The history of study of the Upper Jurassic Volgian Stage and Lower Cretaceous Ryazanian Stage, their geographic occurrence, and use in world practice, subdivision, and correlation are considered. The data on the occurrence of various groups of macro- and microfossils (ammonites, bivalves, radiolarians, dinocysts, and marine vertebrates) in the Volgian and Ryazanian are reviewed. In spite of significantly different lifestyle of all these groups, the Volgian and Ryazanian assemblages are highly similar in the entire Panboreal Superrealm, on one hand, and significantly different from coeval Tethyan fauna, on the other hand. The biostratigraphic scales of these stages based on successions of ammonites, bivalves, radiolarians, and dinocysts are analyzed. It is shown that the substage boundaries of the Volgian are reliably traced along the entire Panboreal Superrealm. None of the boundaries, except for the base of the Volgian, corresponds even to a zonal boundary of the Tethys–Pantalassa Superrealm. A similar situation is also observed in the Ryazanian: its lower boundary, as well as the Lower–Upper Ryazanian boundary, does not coincide with any well-traced boundary in the Tethys–Pantalassa Superrealm. The necessity of using the Volgian and Ryazanian in geological studies is substantiated for all Russian regions with abundant Boreal deposits, as well as inclusion of these stages to the General Stratigraphic Scale in parallel with the Tithonian and Berriasian. We suggest the cancellation of the Decree of the Interdepartmental Stratigraphic Committee of Russia about the transition of the Volgian into regional stratigraphic subdivisions, as well as the reconsideration of the correlation scheme of the Volgian and Ryazanian accepted in the same decree.
PubDate: 2024-11-14
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- Middle Ordovician of the Gorny Altai: Litho-Biostratigraphy and
Justification of Boundaries of Regional Units-
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Abstract: Abstract New paleontological and biostratigraphic data were obtained for a series of Middle Ordovician sections in the Charysh-Inya and Uimen’-Lebed’ structural-facial zones (SFZ) of the Gorny Altai. Regional stratigraphic stages, namely, the Kuibyshevo and Kostinsky horizons, are discussed in detail. By graptolites, the complete stratigraphic volume of the Kuibyshevo regional unit is defined as following zonal succession: (1) sinodentatus/Cardiograptus/Oncograptus, sinodentatus, (2) austrodentatus, (3) dentatus; and the Kostinsky regional unit within the lentus/balhaschensis/kirgisicus Zone. Beds with conodonts Eoplacognathus pseudoplanus were distinguished in the Batun Section of the Kostinsky Horizon; the same-age beds with conodonts Semiacontiodus asymmetricus–Parapanderodus striatus were distinguished in the Baraniy-1 Section. For the first time in the Voskresenka Formation, in the stratotype of the Kuibyshevo Horizon (Maralikha Section), a brachiopod assemblage was found and identified.
PubDate: 2024-11-14
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- On the Genesis of Quaternary Deposits in the Yaloman-Katun Zone of the
Altai Mountains and the Practicability of Introducing the Catafluvial
Genetic Type-
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Abstract: Abstract The paper discusses the research and methodological aspects of introducing the new term “catafluvial deposits” into genetic classification of Quaternary deposits. For this purpose, fieldwork was carried out aimed at studying terrace complexes within the Yaloman-Katun zone of Gorny Altai, which has recently become a unique natural laboratory for investigating hypothetical glacial superfloods. Based on original materials and data from other areas with similar geological and physico-geographical conditions, it is concluded that the introduction of a separate genetic type “catafluvial” is currently premature.
PubDate: 2024-11-14
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- Taxonomic Composition of the Hauterivian Bryozoan Assemblage in the
Environs of Gunib Village (Dagestan)-
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Abstract: Abstract The Lower Cretaceous bryozoan assemblage in the environs of Gunib village in Dagestan is described for the first time. The studied section is located in the zone of development of the Gapshima Formation (Hauterivian) deposits. The bryozoan assemblage is characterized by high taxonomic diversity and includes 32 taxa from four suborders of order Cyclostomata: Tubuliporina (24 taxa), Cancellata (1 taxon), Articulina (1 taxon), and Cerioporina (6 taxa). Because of the poor preservation of the colonies, most taxa are defined in open nomenclature. Therefore, the true diversity of cyclostomes in the study area is not fully recognized. The assemblage includes the taxa which are similar to bryozoans previously described from different levels from Valanginian to Barremian of Switzerland and France and, partly, from the lower Hauterivian of Germany (Mecynoecia icaunensis (d’Orbigny), Mesenteripora marginata (d’Orbigny), M. reticulata (d’Orbigny), Poriceata ardescensis Walter, Apsendesia neocomiensis d’Orbigny, Diplocava biformis (Roemer), “Heteropora” arborea Koch et Dunker, and Elea periallos Taylor). The main difference of the Gunib assemblage from the Valanginian–Hauterivian assemblage of Switzerland and France and the lower Hauterivian assemblage of Germany is the presence of bryozoans from the family Eleidae, but it differs from the Barremian assemblage of France in the absence of Cheilostomata representatives. Among the studied cyclostomes, bryozoans with vertically growing colonies predominate. Some of these bryozoans are bilateral leaf-shaped, while others had thin cylindrical branches. Reticulate and massive colonies are rare, while encrusting bryozoans, which grow over erect colonies, are quite numerous.
PubDate: 2024-11-14
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- Geology and Paleontology of the Unique Mansurovo Locality of Early
Triassic Tetrapods and Ichnofossils (Orenburg Region, Russia)-
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Abstract: Abstract— This paper discusses the geology of the unique Mansurovo tetrapod and trace fossil locality in the Orenburg Region of Russia (Gostevskaya Formation, Lower Olenekian Substage, Ustmylian Horizon). Sections of 16 trenches are described bed-by-bed and correlated throughout. Based on fossils (Wetlugasaurus malachovi grouping of the Wetlugasaurus Fauna) and lithology, the Mansurovo section correlates with the middle part of the stratotype section of the Gostevskaya Formation (Buzuluk Depression of the East European Platform). The site geology suggests that the four recognized geological members of the section were formed in a varying channel-floodplain environment during alternating depositional cycles. The depositional settings were reconstructed based on rock structure and texture and microlithological examination of thin sections. The tetrapod faunal assemblages, macrofloral remains and unique trace fossil assemblages are also studied. Based on the lithology and facies analysis, the depositional environment is reconstructed for the locality, showing the irregular riverine depositional pattern due to the wandering of river channels and their periodic drying out in a hot and semi-arid climate during the Early Olenekian. Taphonomy of fossil occurrences suggests that the burial took place in a riverine depositional environment affected by strong currents, and that the Temnospondyli probably died in subaquatic conditions.
PubDate: 2024-09-20
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- Stratigraphic Chronology and Mechanisms of Formation of Bottom Sediments
at the Mouth of the Grøndalen River (Grøn-Fjord, West Spitsbergen)
during the Period of Climatic Changes-
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Abstract: Abstract The results of the study of bottom sediments and water of the estuary of the Grøndalen River (Grøn-Fjord, West Spitsbergen) are presented. The stratigraphic features of the sedimentary strata are determined. The chronology of changes in geoecological environmental conditions has been established using radioisotope dating methods. The main factors influencing sedimentation in the study area are air temperature and precipitation during the period of predominance of low temperatures. It is shown that climate fluctuations determine the chronological sequence of the sedimentation rate and the change of the lithotype of the bottom sediment toward fine fractions.
PubDate: 2024-09-20
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- The Upper Ordovician Katian Stage Bryozoans from the Dzheromo Formation of
the Moyerokan River Section (Northern Siberian Platform) and Their
Paleogeographical Significance-
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Abstract: Abstract In the upper part of the Dzheromo Formation (Dolborian Regional Stage, Katian Stage, Upper Ordovician) along the Moyerokan River (Northern Siberian Platform), seventeen bryozoan species were revealed, seven from which, owing to the poor preservation of the colonies, were identified in an open nomenclature. The bryozoans belong to ten genera from four orders: Cystoporata (Constellaria vesiculosa (Modzalevskaya in Modzalevskaya et Nekhoroshev), Lunaferamita' sp.), Trepostomata (Calloporella sp. 1, Calloporella sp. 2, Stigmatella sp., S. convestens Astrova in Ivanova et al., Batostoma varians (James), Orbignyella moyerokanensis sp. nov., Leptotrypa sp.), Fenestrata (Parachasmatopora sp.), and Cryptostomata (Phaenopora plebeia Nekhoroshev in Modzalevskaya et Nekhoroshev, P. pennata Nekhoroshev, P. erecta Nekhoroshev in Modzalevskaya et Nekhoroshev, P. carinata Nekhoroshev, P. viluensis Nekhoroshev in Modzalevskaya et Nekhoroshev, Phaenoporella sp., and Ph. multipora Nekhoroshev). The genera Lunaferamita, Orbignyella, and Parachasmatopora were first found in the Ordovician of the Siberian Platform, and the genus Calloporella was found in the Dolborian Regional Stage. The species O. moyerokanensis sp. nov. is endemic to Northern Siberia, while the majority of the species have a wide geographic distribution. The studied bryozoan complex demonstrates some connection with bryozoan assemblages from the Taimyr Peninsula, Kotelny Island, the Sette-Daban Ridge, and Mongolia at the species level. At the generic level, it is close to the bryozoan assemblages from Laurentia, Baltica, the Argentine Precordillera, and China.
PubDate: 2024-09-20
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- Age and Sources of Rocks of the Kodar Group of the Udokan Complex (Aldan
Shield): Results of Geochemical, U–Th–Pb (LA-ICP-MS) Geochronological
and Nd–Hf Isotopic Studies-
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Abstract: Abstract The results of geochemical and Nd isotopic studies of rocks and U–Th–Pb (LA-ICP-MS) geochronological and Hf isotopic studies of detrital zircon from metaterrigenous rocks of the Kodar Group of the Udokan Complex (Aldan Shield) are presented. It is established that the age of rocks of the Kodar Group is 1.99–1.91 Ga, whereas the age of rocks of the Chinei and Kemen groups of the Udokan Complex is 1.90–1.87 Ga (Kovach et al., 2018, 2023a). This allows us to raise the issue of recognition of the Kodar Group as an independent stratigraphic subdivision. The terrigenous rocks of the group were sourced from the Archean igneous and metamorphic rock of the Chara–Olekma Geoblock and probably the Kalar and Kurulta blocks of the Stanovoi suture zone, as well as the Paleoproterozoic (2.04–1.99, 2.08, 2.20, and 2.30 Ga) complexes of active continental margins or ensialic island arcs in the western–northwestern and southern (in the present-day coordinates) frame of the Chara–Olekma Geoblock, which are unidentified in the region at the current erosion level. Erosion of rocks of magmatic arcs and the continental slope led to the deposition of rocks of the Kodar Group in a retroarc foreland basin, whereas further collapse of the orogen and the formation of an intracontinental extension basin were responsible for the deposition of terrigenous rocks of the Chinei and Kemen groups. The obtained data indicate widespread previously unidentified Paleoproterozoic continental crust formation at about 2.04–1.97 Ga in the western part of the Aldan Shield.
PubDate: 2024-09-20
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- Developments in the Cretaceous Stratigraphy of Crimea. Part 1.
Introduction and the Lower Cretaceous-
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Abstract: Abstract This paper summarizes the state of knowledge of the Cretaceous stratigraphy of the Mountainous Crimea and selected biostratigraphic groups and magnetostratigraphy. The first part of the paper discusses the Early Cretaceous, its stratigraphy, selected fossil groups and magnetostratigraphy of the Mountainous Crimea. The data on the figured reference sections were updated in terms of biostratigraphic zonation. Selected fossil groups represented in the paper include ammonites, organic-walled dinoflagellate cysts, ostracods, calpionellids and nannoplankton. The description of each group contains an information on the main publications, types of biostratigraphic units and their distribution, fossil assemplages, images of the most important fossils, and brief discussion on the correlation. Some of the ammonite index fossils are figured for the first time. The magnetostratigraphy summarizes latest data published mostly in Russian for the whole Early Cretaceous succession of the Mountainous Crimea.
PubDate: 2024-09-20
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