A detailed study of cross-sections of the earliest (Late Permian) representatives of Otoceras Griesbach (O. concavum Tozer) from the base of the Nekuchan Formation in the upper reaches of the Vostochnaya Khandyga River in Southern Verkhoyanie allowed features of ontogenetic shape changes to be clarified. Trends in changes in the main parameters of the shell during its growth have been determined, the cyclical nature of the narrowing and expansion of the shell has been identified, and the sequence of changes in the shape of the whorl cross-section has been established. The formation of carinae and the development of the tricarinate shape of the venter were recognized. Identification of shell shape transformations in the ontogeny of O. concavum contributes to the diagnosis of small-sized Otoceras and can serve as the basis for subsequent reconstruction of the evolution of morphogenesis in Otoceratidae. The pentacarinate form of the external part of the whorl observed at the middle stage of ontogeny may be a character inherited from the ancestral genus Avushoceras Ruzhencev.

A vertical sequence of brachiopods has been established in the section of the Tit-Ary in the northern part of the Tuora-Sis uplift of the lower reaches of the Lena River. In the Tit-Ary section, Upper Cambrian are overlain by Upper Carboniferous (Gzhelian) and Early Permian (Asselian) deposits, which are characterized by the Jakutoproductus protoverkhoyanicus and Jakutoproductus verkhoyanicus zones. The Tit-Ary section is the first of those established in the lower reaches of the Lena River, with exposed boundary Carboniferous-Permian beds.In the Tit-Ary section, the possibility of paleontological and chemostratigraphic substantiation of the Carboniferous-Permian boundary in Eastern Siberia has appeared.

Changes in the values of δ13Соrg in the lower part of the Permian deposits, obtained in the Kuba-lakh Section of the lower reaches of the Lena River and integrated with biostratigraphic data are detected in northeastern Russia for the first time. A comparison with isotope-carbon trends identified in the Asselian and Sakmarian stages of the Southern Urals is proposed. Based on the established sequence of negative shifts of the carbon isotope composition of organic matter, a conclusion is made that the Carboniferous–Permian boundary in the Kubalakh Section is located at the 80 m thick gap in section. The first data independent of the biostratigraphic and paleontological records are obtained on the Late Asselian age of the Tuora-Sis Formation beds containing the Bulunites ammonoid association, the stage assignment of which has been debated for many decades. The chronostratigraphic indefinite interval between the Asselian and Samarian stages is significantly reduced to the upper parts of the Jakutoproductus lenensis Beds. The data obtained indicate that the continuation of the work on the chemostratigraphy of stable carbon isotopes has good prospects for substantiating the division into stages and the interregional correlation of the Lower Permian deposits in Verkhoyanie.

Kungurian ammonoids had high taxonomic diversity, but were distinguished by an extremely high level of endemism and sharp geographic differentiation. Therefore, outside the regions containing the most important conodont taxa, the Artinskian-Kungurian boundary based on ammonoids must be established through indirect evidence due to the lack of common species with potential global stratotypes of the lower boundary of the Kungurian. A long-term study of the reference sections of the Echian and Tumarian regional stages and their ammonoids made it possible to change the understanding of the bio- and lithostratigraphy of the Artinskian-Kungurian boundary deposits of the Kuranakh structural-facies zone of Western Verkhoyanie. Clarification of the upper boundary of the Khabakh Formation in the stratotype section led to the fact that the ammonoids previously belonging to this formation began to be considered in the lower part of the Orol formation. They characterize the Paratumaroceras? sp. nov. biostratigraphic beds of the lower part of the Tumarian Regional Stage. At the current level of knowledge, the ammonoid substantiation of the Artinskian–Kungurian boundary in Verkhoyanie is difficult due to the existing hiatus corresponding to the Khabakh formation and its age analogues. However, the appearance at the base of the Tumarian Regional Stage of the first paragastrioceratids with a ventral sinus in transverse sculpture (Paratumaroceras? sp. nov.) suggests that the boundary in question is located near the base of the indicated regional stage or even combined with it. For further clearer identification of the Kungurian lower boundary in Verkhoyanie, new studies of the Echian–Tumarian boundary deposits in typical sections, independent of paleontology, are necessary. Such research should primarily include isotope-stratigraphic subdivision and high-precision U-Pb dating.

The Kuznetsk Basin (Kuzbass) is one of the largest coal basins in Siberia and a reference area for the ancient Angaraland continent. The proximity of the Kuzbass and Siberian Platform caused their biotic similarities in the Late Palaeozoic. However, due to biota endemism, the Kuzbass Upper Palaeozoic does not correlate directly with the International Chronostratigraphic Chart (ICC). This paper discusses radioisotopic (CA-ID-TIMS) dating of zircons from a volcanic tuff located in the Starokuznetsk Formation (Fm). This level matches the interval of the Balakhonka/Kolchugino (B/K) floral change in Kuzbass, i.e., the gradual replacement of cordaitoid-dominated wet forests (Balakhonka flora) with more arid fern–pteridosperm–cordaitoid assemblages (Kolchugino flora). New age (276.9 ± 0.4 Ma) directly correlates the Starokuznetsk Fm with the Upper Kungurian of the ICC. We compared the Kuzbass data with data of the Western Verkhoyanie, where Middle Permian ammonoids (Sverdrupites assemblage) occur in strata recording the B/K floral change. The available (ICC) and new datings indicate the lag between the B/K floral change in low (Kuzbass) and high (Verkhoyanie) latitudes of Angaraland. The B/K floral change in the Kuzbass began in the early Late Kungurian and was completed by the end of this age. In contrast, the B/K floral change in Verkhoyanie began at the end of the Late Kungurian and was completed in the Late Wordian. The delay in the floral changes at different latitudes of Angaraland suggests that existing interregional correlations need further improvement.

For the first time, shell cross-sections were made for the most ancient (Late Permian) representatives of the genus Otoceras. From these cross-sections, ontogenetic changes in the shell shape of O. concavum Tozer were reconstructed at size stages ranging from tiny to very large. A moderately wide shell with a moderately narrow umbilicus narrows intensely to its tiny size, becoming a narrow shell. At the stage of very small size, the shell expands, again becoming moderately wide, and the umbilicus narrows slightly, remaining moderately narrow. However, at small sizes, the change in these characteristics occurs in the same direction, but with increased intensity. Moreover, important changes are observed at the medium-sized stage, when the expansion of the shell stops and the umbilicus becomes narrow. At the end of the studied ontogenesis, the morphological development of the mollusk was aimed at the formation of a moderately narrow shape with a very narrow umbilicus. Of the variety of shell shapes previously established among ammonoids, numbering 35 types, representatives of the species O. concavum throughout the studied ontogenesis had only three: subdiscocone, tumaricone, and pachycone. Finally, the constructed ontogenetic model clearly demonstrated the features of the development of the cross-sectional shape of O. concavum shells during their growth, emphasizing ontogenetic trends in changes in the most important parameters of the shell. We conclude that the identified transformations of the shell shape contribute to the diagnosis of small-sized Otoceras, and can serve as the basis for the subsequent reconstruction of the morphogenetic development of the family Otoceratidae.

Brachiopods from the upper Khalpirkian Regional Stage of the Tiryakh-Kobyume section of the Kobyume structural-facies zone of Southern Verkhoyan were studied. The collection is dominated by Strophalosia? vollossovitschi (Fredericks) and Cancrinella? sp. Single spiriferids are assigned to Crassispirifer monumentalis Abramov et Grigorjeva and Cr. aff. monumentalis Abramov et Grigorjeva, which indicate that the host deposits belong to the Crassispirifer monumentalis beds. These beds were previously established by us only in the lower part of the Khalpirkian Regional Stage. A review of reliable finds of brachiopods of the terminal assemblage, confined to the Khalpirkian regional stage of the Upper Permian, is given. The assemblage is dominated by strophalosiids represented by Wyndhamia gijigensis (Zavodowsky), Marginalosia? magna Abramov et Grigorjeva, Subtaeniothaerus lungersgauzeni Solomina, and Strophalosia? aff. vollossovitschi (Fredericks). «Magadania» sp. and Cancrinella? sp. identified from linoproductids. An important element of the terminal assemblage are the spiriferids Crassispirifer monumentalis. Athyridids of the Khalpirkian Regional Stage, known only in its lower part, are represented by Cleiothyridina nikolaevi Grunt, Cleiothyridina sp., and Bajtugania sp. In the studied regional stage are also finds of terebratulids attributed to Marinurnula? aff. mantuanensis (Campbell) and M.? aff. chivatschense (Zavodowsky). No brachiopods are known at the top of the Khalpirkian Regional Stage, while the rhynchonellids Piarorhynchia sp. appear at the base of the Regional Stage. At the beginning of the Khalpirkian time, the brachiopod community had an extended area in the shelf zone of the Verkhoyan Sea along the coastline of Angaraland. Subsequently, this area was reduced, initially dividing into two independent subareas confined to the East Kharaulakh and South Verkhoyan sectors. In the late Khalpirkian time, the brachiopod community concentrated only in the Kobyume zone, where it ended its existence during the end-Permian mass extinction. Some taxa of the identified brachiopod assemblage have been traced in the Okhotsk region, the Ayan-Yuryakh anticlinorium, and the Omolon massif.

As a result of the monographic study of the Early Permian brachiopods from the Kubalakh and Chekurovka sections, a zonal correlation of the Asselian–Sakmarian deposits, respectively, of the Ust-Lena and Bulkur structural facies zones (SFZ) was performed. The Jakutoproductus verkhoyanicus (including layers with Jakutoproductus lenensis in the upper part of zone), Jakutoproductus insignis, Jakutoproductus terechovi, and Jakutoproductus rugosus zones are established in both SFZ (up-section). In the Kubalakh section, the Jakutoproductus verkhoyanicus Zone is present in full and conformably superposes the Upper Carboniferous Jakutoproductus protoverkhoyanicus Zone, while in the Chekurovka section, the lower part of the J. verkhoyanicus Zone unconformable overlies Upper Cambrian formations, and the lower part of this zone is probably absent in the section. In the direction from the Kubalakh section to the Chekurovka one, a significant reduction in the thickness of all established biostratigraphic units is observed, and their total thickness decreases by more than two times.

A biostratigraphic division of the Lower Permian into brachiopod zones of Jakutoproductus verkhoyanicus , Jakutoproductus insignis , Jakutoproductus terechovi , and Jakutoproductus rugosus is observed within the Northern and Western Verkhoyanie. According to the literature, only the complex of the lower biostratigraphic unit ( Verkhoyanicus Zone) was previously confidently established in the Southern Verkhoyanie. Meanwhile, representatives of the two middle zones were not observed, and the presence of the index species of the Rugosus zone was only indicated in the southern part of the region (Yudoma River Basin). A monographic study of the brachiopod collection from the Upper Olchan Subformation of the stratotype of the Olchan Formation (Khospohchon section) allowed us to rethink the biostratigraphic division of the Asselian-Sakmarian deposits in the Southern Verkhoyanie. The brachiopods of the Upper Olchan Subformation of the Khospohchon Creek (Menkule River Basin) belong to three successive biostratigraphic zones: Verkhoyanicus , Insignis , and Terechovi . Information on the presence of representatives of the species Jakutoproductus rugosus Ganelin in the Southern Verkhoyanie leads to the assumption that all four biostratigraphic zones of the Asselian-Sakmarian deposits of Verkhoyanie are present in this region. Three upper zones ( Insignis , Terechovi , and Rugosus ) demonstrated a direct correlation with the Ogonerian Regional Stage of the Omolon massif by their common zonal species. The new results indicate the need for a comprehensive study of the key sections of the Olchan Formation to substantiate the Carboniferous-Permian and Asselian-Sakmarian boundaries in Verkhoyanie using both biostratigraphic and chemostratigraphic methods.

The base-Artinskian Stage GSSP is defined at 0.6 m above the base of bed 4b at the Dal'ny Tulkas section in the southern Urals of Russia (53.88847N and 056.51615E). This point corresponds to the First Appearance Datum of the conodont Sweetognathus asymmetricus, which is part of a well-defined and widely distributed lineage. Additional markers for correlation include a radioisotopic age interpolated between 290.1 and 290.5 Ma, a strontium isotopic ratio of.70767, and many additional fossils groups, particularly ammonoids and fusulines, but also including small foraminiferans, radiolarians, and palynomorphs. Finally, the boundary occurs within a transgressive succession, near, or at a maximum flooding surface in many sections, thereby forming a distinctive sequence stratigraphic signature in the field. The Artinskian Stage is the third stage of the Lower Permian or Cisuralian Series.

A vertical sequence of brachiopods was revealed at the base of the Verkhoyanian terrigenous complex of the Tit-Ary section in the northern part of the Tuorasis uplift of the lower reaches of the Lena River. As a result of the study of these brachiopods, it was established that in the indicated section, the Upper Cambrian dolomites are overlain by Gzhelian and Asselian deposits, characterized by brachiopods of the Jakutoproductus protoverkhoyanicus and Jakutoproductus verkhoyanicus biostratigraphic zones. This is the first proven fact of the presence of Upper Carboniferous deposits in the area. It is concluded that within the Tuorasis uplift from south to north, the upper age limit of the unconformity between the Cambrian and the Upper Paleozoic is growing older, while the base of the Verkhoyanian terrigenous complex is built up by the Permian basal beds and the Gzhelian deposits of the Upper Pennsylvanian. The Tit-Ary section is the first of those established in the lower reaches of the Lena River, with exposed boundary Carboniferous-Permian beds.

Ammonoids Paramexicoceras aldanense Popow were found at the base of the Nekuchan Formation (upper part of the Changhsingian) in the Dyby River basin, Verkhoyan region. The first discovery of goniatites of the Upper Permian in northeastern Asia made it possible to clarify the biostratigraphic subdivision of the Permian–Triassic boundary deposits. The Otoceras concavum zone was reduced in its lower part due to identification of the Paramexicoceras aldanense beds at the base of the Nekuchanian Regional Stage. The data obtained were indicative of the fact that the genus Paramexicoceras previously considered as long-lived belonged to the youngest and short-lived taxa of Cyclolobidae representing the terminal goniatite phase. This record made it possible to compare the Nekuchanian base in the Southern Verkhoyan region with the upper part of the Foldvik Creek Group in East Greenland.

Reconstructions of the cross sections of two specimens of the type species of Neouddenites , N. andrianovi Ruzhencev from the Kungurian of Western Verkhoyanie, revealed patterns in its ontogenetic transformation. The species is characterized by slow expansions of the medial spiral, which only stops at the last whorl. The shell shape continuously changes from very wide in the first whorl to very narrow in the last whorl. The umbilicus expands slightly at the beginning of ontogeny, making the shell evolute. The umbilicus then strongly narrows, and at the last whorl the shell becomes completely involute. Significant changes in the shape of the whorl cross-section are observed throughout ontogeny allowing recognition of four successive stages, designated here as “ Eocanites ”, “ Pronorites ”, “ Prouddenites ”, and “ Neouddenites ”. Neouddenites andrianovi was found to lack lateral grooves and ventrolateral ridges, previously considered to be diagnostic characters of the genus Neouddenites .

An extensive collection of fossil brachiopods, all assigned to the Wuchiapingian Stage, was recovered from the lower part of the Imtachan Formation along the Ustupnyi Creek (right tributary of the Setorym River) in the Southern Verkhoyanie. It comprises strophalosiids (Strophalosia? aff. vollossovitschi (Fredericks), Strophalosia? sp., Subtaeniothaerus lungersgauzeni Solomina, Marginalosia? magna Abramov et Grigorjeva), spiriferids (Crassispirifer monumentalis Abramov et Grigorjeva, Crassispirifer cf. monumentalis Abramov et Grigorjeva, Crassispirifer sp.), athyridids (Cleiothyridina nikolaevi Grunt, Cleiothyridina sp. 1, Bajtugania sp.), and terebratulids (Marinurnula? aff. mantuanensis (Campbell), Marinurnula? sp.). The identified assemblage is associated with brachiopods from the lower part of the Khalpirki Formation of the Western Verkhoyanie, the appearance of which marks the boundary between the Dulgalakhian and Khalpirkian Regional Stages and also substantiates the lower boundary of the Crassispirifer monumentalis Zone. Single finds of Crassispirifer cf. monumentalis in the lower part of the Middle Imtachan Subformation indicate that the entire lower subformation and the lower part of the middle subformation belong to the C. monumentalis Zone. There are no reliable finds of brachiopods at higher levels of the Imtachan Formation.

This article summarizes the results of our study of the Early Permian brachiopods collected 5.9-6.3km northwest of the village of Chekurovka that were used to develop the first biostratigraphic zonation of the Asselian-Sakmarian deposits on the left bank of the lower reaches of the Lena River.At the base of the Permian section, the Jakutoproductus lenensis Beds were identified.They are overlain by the Jakutoproductus insignis Zone with numerous shells of the index species.The Jakutoproductus terechovi and Jakutoproductus rugosus Zones, which are characterized by index species, occur even higher in the section.The boundary between the Khorokytian and Echian Regional Stages is defined by the first occurrence of J. insignis at the base of the Insignis Zone.The identified zonal sequence is identical to the previously studied Kubalakh section on the right bank of the lower reaches of the Lena River.However, the thickness of the biostratigraphic zones on the left bank is reduced by half, and a significant lower part of the Khorokytian Regional Stage (below the Lenensis Beds) is missing because it falls on the stratigraphic break between the Cambrian and Permian deposits.The zonation performed shows that there is a direct correlation between the Chekurovka section and the Asselian-Sakmarian deposits of Western Verkhoyanie and the Omolon Massif due to common index species of the biostratigraphic units.

Стратиграфическое положение аммоноидей рода Paramexicoceras Popow в пермско-триасовых отложениях Южного Верхоянья

This article discusses the history of the study of the Late Carboniferous-Early Permian genus Somoholites, and changes in views on its taxonomy, species composition and diagnostic characters. Most species of this genus come from Russia. Several species are known from the USA, Canada, Indonesia (Island of Timor), Japan, and probably China. Based on the study of materials from Bashkortostan (Shakhtau quarry), Verkhoyansk Region and the Polar Urals, and published data, the diagnostic characters of the genus are re-evaluated, and its diagnosis and species composition are emended. It is concluded that the South Ural Somoholites described as S. beluensis does not differ significantly from another species from this region S. shikhanensis and should be considered under this name.

A. sobopolensis sp. nov., a new species of Inoceramus-like bivalves of the bipolar genus Aphanaia from the Lower Permian deposits of the Southern Orulgan Ridge (northern Verkhoyansk Region, Northeast Russia) is described.

The Kygyltasian Regional Stage is widespread throughout the Verkhoyansk Region, where it reflects a large transgressive-regressive cycle of the Verkhoyanian terrigenous sedimentation. Over the years, a huge amount of material has been accumulated on biostratigraphic division, facies features, and paleontological characteristics of this large stratigraphic unit, but its age is still debatable. The main fossils in the upper part of the Kygyltasian Regional Stage are higher plants, the remains of which were studied in the last century using outdated taxonomy. This study is devoted to revision of the collection of fossil plants from the type locality of the Kygyltasian Regional Stage (Western Verkhoyanie) in order to clarify the taxonomic composition and the age of the Upper Kygyltasian floristic association. The dominant cordaite leaves in the association were studied using the morphological and microstructural methods. This made it possible to clarify the previous paleontological definitions of the genus Noeggerathiopsis and bring them in line with modern taxonomy. The species Noeggerathiopsis heteroclitus Tolstych and N. khorokytica Tolstych were validated for type specimens. The following species were identified from the Upper Kygyltas Subformation of the Levyi Khorokyt section: Cordaites heteroclitus (Tolstych), C. cf. neuburgae Gluchova, C. cf. zalesskyi Durante, C. krychtofovichii (Radczenko), Cordaites? khorokytica (Tolstych), Cordaites sp. 1, Cordaites sp. 2, Cordaites sp. 3, Cordaites sp. 4, Rufloria (Praerufloria) ex gr. theodorii (Tschirkova et Zalessky) S. Meyen, Samaropsis skokii Neuburg, S. cf. pauxilla Zalessky, S. aff. pumila Suchov, S. aff. auriculata Neuburg, Cordaicarpus baranovii Suchov, Crassinervia sp., Astrogaussia sp., Sphenophyllum cf. thonii Mahr, Sphenophyllum? sp., Sphenopteris sp., Paracalamites sp. Based on the results of the study, the Upper Kygyltasian floristic association of the Western Verkhoyansk Region was compared with floristic associations of the Alykaeva Formation (Kuzbass) and the Upper Kata Subformation (Tunguska basin). From the above, the Late Carboniferous age of the upper part of the Kygyltasian Regional Stage follows. The results obtained are in good agreement with the correlation of the Verkhoyanian Carboniferous-Permian deposits for marine invertebrates.