Some taxa of belemnites, bivalves, gastropods, and brachiopods, previously unknown in the Russian Far East (except for Eastern Siberia and Northeast Russia), of both Tethyan and Boreal Arctic origin, have been recorded in the Middle Jurassic of the Soloni River (Bureya River basin). In particular, bivalve assemblages were found to increase in abundance throughout most of the Bajocian section at the Soloni River, similar to what is observed in Siberian sections. However, the first appearance of some species of the genus Grammatodon and trigoniids was recorded in this area much earlier than in Siberia. This, combined with a revision of the taxonomic composition of previously recorded fossils, has made it possible to refine the biostratigraphic subdivisions of not only the studied section, but also the uppermost Lower–Middle Jurassic marine deposits of the Bureya Trough as a whole. The age ranges of the local lithostratigraphic units have been refined to a greater degree. It has been established that the Sinkal’tu Formation corresponds to the Upper Toarcian–lowermost Lower Bajocian, the Epikan Formation to the uppermost Lower Bajocian, the El’ga Formation to the Upper Bajocian, and the Chagany Formation to the Bathonian–Callovian. Data on the palynological assemblages identified in these formations are provided. The recent studies of cephalopods and bivalves from Siberia, the Russian Far East, and southern Alaska have led to the development of a refined interregional correlation scheme for Bajocian deposits in these regions.

Some taxa of belemnites, bivalves, gastropods and brachiopods, previously unknown in the Russian Far East (excluding eastern Siberia and North-East Russia), of both Tethyan and Boreal Arctic origin, were recorded in the Middle Jurassic of the Soloni River (Bureya River basin). In particular, it was revealed that bivalve assemblages increase in number up-section throughout most of the Bajocian at the Soloni River, much as they do in Siberian sections, but the first appearance of some species of the genus Grammatodon and trigoniids was recorded here much earlier than in Siberia. All this, combined with the revision of the taxonomic composition of fossils recorded earlier, made it possible to refine the biostratigraphic subdivision of not only the studied section, but also of the uppermost Lower to Middle Jurassic marine deposits of the Bureya Trough as a whole. Age ranges of the local lithostratigraphic units have been brought to a higher degree of refinement. It was established that the Sinkal’tu Formation corresponds to the Upper Toarcian–lowermost Lower Bajocian, the Epikan Formation to the uppermost Lower Bajocian, the El’ga Formation to the Upper Bajocian, and the Chagany Formation to the Bathonian–Callovian. The data on the spore-pollen complexes identified in these formations is provided. The most recent findings of the studies on cephalopods and bivalves from Siberia, the Russian Far East, and southern Alaska are summarized to refine the interregional correlation scheme of Bajocian deposits of these regions.

The first records of dinocysts and foraminifers in the Middle Jurassic deposits of the Russian Far East and their taxonomic affiliation are reported. The use of foraminiferal and ostracod assemblages as a tool for biostratigraphic subdivision and correlation of the Middle Jurassic sections of this region is very difficult due to the poor preservation and limited occurrence of these microfossils. Findings of the dinocysts Endoscrinium galeritum,Tubotuberella cf. apatela,Wanaea fimbriata, and Meiourogonyaulax cf. caytonensis raise the question of correcting the stratigraphic range of the lithological formations recognized in the Middle Jurassic.

The study of Triassic paleontology and stratigraphy of various regions of northeastern Russia and adjacent Arctic shelf is essential not only for improving and refining zonal biostratigraphic schemes, interregional and global correlation of Triassic deposits, and resolving problems of stratigraphic boundaries but also for developing and substantiating a new generation of Triassic stratigraphic schemes, which could serve as the stratigraphic basis for different regional and detailed geological investigations of the Arctic. The results of the study were used to improve existing zonal scales based on various groups of fauna and palynomorphs, develop a more detailed biostratigraphic subdivision of the Triassic, and characterize individual horizons using both terrestrial and marine palynomorphs. The zonal scales are calibrated to each other and to the regional zonal scale of the Triassic of Siberia and northeastern Russia, which provides the subsequent correlation with the International Chronostratigraphic Chart of the Triassic System. The set of coeval zonal scales for the Triassic of Kotelny Island sections based on ammonoids, nautiloids, coleoids, bivalves, brachiopods, and foraminifers and the analysis of microphytoplankton and terrestrial palynomorph assemblages are a useful tool for detailed subdivision and correlation of the eastern part of the Laptev Sea shelf and adjacent regions of northeastern Russia.

The geological study of the Mesozoic sections of the New Siberian Islands archipelago and Asian coastal sections of the Arctic Ocean plays a key role in tying the results of comprehensive studies with seismic data on the Laptev Sea shelf and the western part of the East Siberian Sea. Therefore, it is extremely important to improve the subdivision of the Triassic system of the New Siberian archipelago and to define the position of the system in the structure of the Laptev Sea shelf sedimentary basin. The results of our study were used to improve and refine the lithostratigraphic subdivision of the Triassic in the study area and to recognize a distinct interregional stratigraphic marker, i.e., the Czekanowski Formation (lower Olenekian). In terms of genetic, structural, and sedimentological features, the Triassic strata were grouped into two Groups: the Reshetnikov Group (Induan-upper Ladinian) and the Svetlaya Group (Ladinian-Rhaetian), reflecting major stages of sedimentation. For the Triassic of the eastern Laptev Sea shelf and adjacent onshore areas, the facies zonation scheme has been developed and refined on a unified basis. Based on their structure, the Phanerozoic sections of the study area can be considered as a part of the intermediate structural stage of the Laptev Sea plate at the margins of the Siberian craton.

The article presents the results of palynological studies of the Middle Jurassic deposits, exposed by natural outcrop 7B on the river. Kelimyar and represented by the Kelimyar suite. The studied outcrop is located on the territory of the Yana-Anabar facies area of marine sedimentogenesis. The Aalenian palynozone was established in the section, and rare taxa of dinocysts were identified, which do not allow one to divide the section into this group of unicellular algae.

Successions of Jurassic strata located in the Arctic region normally yield rich assemblages of terrestriallyderived and marine palynomorphs, reflecting relatively warm air and sea-surface temperatures. The land plant floras were prone to the development of local communities and regional provincialism, whereas the marine biotas thrived across extensive open marine areas with high productivity, resulting in the rapid evolution of dinoflagellate cysts (dinocysts) following their earliest fossil record in the Triassic. Dinocysts exhibit low taxonomic richness and provide low biostratigraphic resolution throughout the Lower Jurassic sections. By contrast, they are diverse in Middle and Upper Jurassic strata where they provide excellent biostratigraphic markers for correlating and dating both surface and subsurface sections. Over twenty formal and informal biozonations based on the firstand last occurrences of dinocysts have been erected in Alaska, Arctic Canada, the Barents Sea region, Greenland and northern Russia, many of which are correlated with macrofossils, including ammonites, that occur in the same sections. This paper presents a compilation of 214 Jurassic palynostratigraphic events (118 first occurrences and 96 last occurrences) that have regional chronostratigraphic value in the Circum-Arctic, based on their published records. Each event is correlated with the base of a chronostratigraphical unit (including formal stages and sub-Boreal ammonite zones), or as an estimated percentage above the base of the chronostratigraphical unit relative to the entire unit. The relationships of each event to stages and key fossil zonal schemes is shown on chronostratigraphic plots using the 2020 version of TimeScale Creator®.

Palynomorphs from the Toarcian and Aalenian Djigiat Formation of Karachay-Cherkessia in the Kuban River Basin (North Caucasus, southwest Russian Federation) are reported for the first time. Five samples carefully selected for their biostratigraphical content were studied to document the palynological assemblages. Four samples (1, 2, 3, 4) were collected from pieces of rock with key index ammonite specimens, and sample 5 comprises fragments of ammonite shells from a sideritic concretion. Three of these samples (4, 2 and 1) yielded relatively abundant and diverse aquatic microplankton (acritarchs, dinoflagellate cysts, prasinophytes and zygnematalean algae) and terrestrial palynomorphs (pollen and spores); the remaining two samples (3 and 5) were less productive and contained fewer than 50 palynomorph specimens. The study of the dinoflagellate assemblages provided characteristic and key information. These are the uppermost Toarcian Nannoceratopsis Assemblage and the uppermost Toarcian to lowermost Aalenian Parvocysta Suite Assemblage. The former is overwhelmingly dominated by Nannoceratopsis with sparse numbers of the Parvocysta suite, and the latter yielded more diverse and common specimens of Parvocysta and its relatives. This is consistent with the hypothesis that the Parvocysta suite migrated from the Boreal Realm further south into Laurasia during the Toarcian. Certain dinoflagellate cysts such as Mancodinium semitabulatum and Scriniocassis spp., which are typical of Europe and much of Greater Laurasia are absent. Composition of the pollen and spores proved relatively out to be monotonous, and cannot be subdivided. However, in general, the composition of the assemblages of spores and pollen is consistent with the Toarcian–Aalenian transition.

The article presents preliminary results of palynological studies of the Lower-Middle Jurassic deposits, uncovered by the natural exposure of 7A on the Kelimyar river and represented by the Kelimyar Formation. The Toarian biostraton with Valvaeodinium aquilonium is identified in the section. As a result of studies in the Lower Aalenian samples, only rare dinocysts taxa were identified that did not allow to divide the upper part of the section on this group of unicellular algae.

The results of palynomorph biofacies analysis of the Lower and Middle Jurassic deposits of Western and Eastern Siberia are presented. A comprehensive study of different groups of palynomorphs (spores and pollens, dinoflagellate cysts, acritarchs, prasinophytes, Zygnematales algae, etc.) was carried out. Detailed analysis of the distribution of separate taxa and quantitative proportions of various groups of microphytofossils in sections of Western and Eastern Siberia allowed combinations of palynomorphs reflecting different facies types to be established. In total, nine ecological-facies associations were distinguished—from continental, coastal marine, and shallow-water to typical marine deep-water.

This paper presents the results of palynological study of the Lower–Middle Jurassic strata recovered from Tulai-Kiryaka 1 Borehole, Eastern Siberia. The Zimnyaya, Airkat, Kiterbyut, Korotkiy, Aprelevskiy and Arangastakh formations were studied. The borehole is situated on the territory of the Yana-Anabar facies area of marine sedimentogenesis. Five biostratons with spores/pollen and three biostratons with dinocysts were established for the Pliensbachian - Aalenian.

An analysis of the current state of research in the field of Boreal-Tethyan correlation of the Middle Jurassic marine sediments of Siberia is given. Further perspectives are closely related to the obtaining and mutual coordination of the results of bio- and chemostratigraphic, biofacial and biogeographical studies of the Middle Jurassic of Siberia and adjacent territories, and is thus expected to reveal a set of calibrated markers (traces of biotic and abiotic events) that will contribute for interregional and global correlations.

The Jurassic-Cretaceous terrigenous complex of the Laptev and East Siberian Seas is of considerable interest as a potential exploration target. However, the key Jurassic and Cretaceous sections of the New Siberian Islands have been poorly studied. The results of this study were used to provide a detailed micropaleontological description of these sections and substantiation of the previous lithostratigraphic subdivision. We first identified a series of Boreal standard zones in the Jurassic and Cretaceous sections, based on the foraminifers, ostracods, dinocysts, and terrestrial palynomorphs. Our results, along with the published data on ammonites, bivalves, and terrestrial palynomorphs and the results of radiometric dating, provide more precise constraints on the stratigraphic position of the identified lithostratigraphic units. The results of this study can be corroborated by seismic data to explore offshore areas of the Laptev and East Siberian Seas. We also present detailed data on the geochemistry of organic matter from the Pestsovaya Formation (Hettangian-lowermost Upper Pliensbachian). (c) 2018, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.

Information on Jurassic palynomorphs from the Greater Caucasus is potentially of great importance, but its availability to the international research community is severely limited. New palynological data for Toarcian deposits of the Western Caucasus are recorded in the present paper. Particularly, dinoflagellate cysts are described for the first time from the Bagovskaja Formation; palynomorphs are found in sandstone levels within this unit. The most representative assemblage includes pollen (with predominant bisaccate pollen), spores (Cyathidites being commonest), and dinoflagellate cysts amongst which the predominant taxon is Nannoceratopsis spiculata. The dinocyst assemblage implies a late Toarcian age for the upper part of the Bagovskaja Formation. On the basis of these new palynostratigraphical results, the range of the formation is extended; previously, only the lower part had been dated on ammonite evidence.

This paper presents the results of a palynological study of the natural outcrops of the Lower and Middle Jurassic on the Kelimyar River (Outcrops 5, 6, 7, 14, and 16) and two boreholes, Middle-Nakynskaya and Ygyata-Tyungskaya 1, in Eastern Siberia. The Ukugut, Tyung, Motorchuna, Suntar, Kyrin, and Kelimyar formations were studied. Six biostrata with dinocysts were established for the Upper Sinemurian–Toarcian. The analysis of the stratigraphic ranges of dinocysts in the sections allowed the identification of the stratigraphic ranges for important genera of dinocysts, which enabled the updating of the geochronology of some biostrata. Three main stages of the evolution of dinocysts in the Early Jurassic in the Siberian Paleobasin were characterized by the appearance, diversification, and disappearance of some orders of dinocysts at certain times. Seven biostrata (beds with characteristic palynoassemblages) were established for the upper Sinemurian–Toarcian on the basis of the study of the taxonomic composition of spores and pollen of land plants and successive changes in the composition of the palynospectra.

Mesozoic sections in the New Siberian Archipelago are important for understanding of the geology of underexplored shelf areas in the east of the Laptev Sea and in the west of the East Siberian Sea. They are reference sections for interpretation of seismic data in these regions. However, there are still many unresolved problems concerning the lithology, lateral extent, and age of Mesozoic deposits, as the sections have a complex structure and are heavily deformed. The performed research makes a basis for the first facies zoning of Jurassic and Cretaceous deposits in the New Siberian Islands and adjacent landmasses of continental Siberia at the junction of the Laptev and East Siberian Seas. The lithostratigraphic division of the Jurassic and Cretaceous is refined, being proposed for the first time for some stratigraphic intervals, and allows updating their lithostratigraphic division (or undertaking it for the first time for some stratigraphic intervals). Facies features of Jurassic and Cretaceous deposits allow the definition of three depositional series.

Palaeontological data on the Caucasus are highly important for large-scale stratigraphical and palaeobiogeographical assessment of the northern Tethyan margin, but this information is often scarce and not available in English. Field studies in the Northern Caucasus have now permitted to amass some new data. Two belemnite species are described from the stratotype section of the Kamennomostskaja Formation (Callovian, Middle Jurassic) near the town of Kamennomostskij in Adygeja (Northern Caucasus). These are Belemnopsis subhastata (von Zieten, 1831) and Rhopaloteuthis ominosa Gustomesov, 1968. The latter is a rare species, and the present find allows new insights into its taxonomy. A palyno-logical analysis of the belemnite-bearing sample was carried out, and a diverse assemblage of dinocysts, acritarchs and prasinophytes, plus pollen and spores recognised. The most abundant palynomorphs are Micrhystridium and Classopollis. Data on belemnites coupled with those on palynomorphs indicate the early Callovian age of the sample level. This interpretation differs slightly from previous conclusions based on ammonites and dinocysts. If this age is correct, the degree of condensation of Callovian deposits in the section studied was lesser than previously assumed.