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Representatives of the bivalve genus Unionites Wissmann are found in the Upper Permian deposits of Northeast Russia, together with the typical high-Boreal Inoceramus-like bivalves Intomodesma sp. Previously, Unionites had been considered exclusively Triassic–Early Jurassic and were only recently found in the Upper Permian of Italy. The finding of representatives of the genus Unionites in the Boreal Upper Permian indicate increased connections of high-Boreal basins and Tethys Superrealm towards the end of the Permian, which began as early as the Middle and Late Wuchiapingian. A new species U. kobyumensis Biakov is described.

Permian marine bivalves of the Pronchishchev Ridge (North Siberia) were systematically studied for the first time.. The presence of the Middle and Upper Permian with five biostratigraphic levels was established based on fossil findings. In the Middle Permian, these are the bivalve Kolymia inoceramiformis–K. plicata (undivided) and Kolymia multiformis zones, and in the Upper Permian—the Maitaia bella Zone (Beds with Phestia ex gr. ovata), Maitaia belliformis Zone, and Intomodesma costatum Zone. The bivalve assemblages from the Middle and the lower Upper Permian (up to the Intomodesma costatum Zone) are similar in their taxonomic composition to those from the Western and Northern Verkhoyansk regions. The uppermost Permian fossil assemblages (Intomodesma costatum Zone) are different. They are represented almost exclusively by monotaxonic aggregations of the large pectinoid Streblopteria rotunda (Lutkevich et Lobanova) and rather rare representatives of the genus Intomodesma. The marine basin of the present-day Pronchishchev Ridge had stable links with the Verkhoyansk basin throughout almost the entire Permian. This basin was very shallow and may have experienced episodes of desalination. In the end of the Permian, the paleogeographic situation changed, and the connection between the Pronchishchev Ridge and the East Taimyr basins became more pronounced. Most characteristic bivalve species are illustrated, and a new species Kolymia rutskovi Biakov, sp. nov. is described.

The U–Pb dating of zircons from two samples taken in the stratotype sections of the Middle Permian Gizhiga Formation in the Omolon Massif has been carried out for the first time. Weighted average ages of 266 ± 2 and 265 ± 3 Ma taking the error into account are consistent with the Capitanian age calculated previously by paleontological determination. The observed detrital zircon population has made it possible to identify a few source areas in the Omolon Basin. Pre-Permian zircons are related to erosion of basement deposits of the Omolon Massif and the Middle Paleozoic volcanic rocks of the Kedon Group, while the Permian zircon population is due to the tuff supply from the Okhotsk-Taigonos volcanic arc.

Inoceramus-like bivalves of the bipolar species Atomodesma variabile Wanner were first found and precisely associated with the Upper Permian (Wuchiapingian) section in the Southern Verkhoyansk Region. The appearance of this exotic taxon in Boreal basins is associated with the short-term invasion of several Tethyan taxa into high-Boreal basins due to transgression. It is concluded that the similarity of the Permian marine biota from the Boreal and Notal (Gondwanan) paleobiogeographic superrealms is largely due to periodic invasions of notal elements into Boreal basins. The species A. variabile is described and illustrated.

The first study results on foraminifera from the Permian–Triassic boundary deposits in the southern Verkhoyansk region (the lower part of the Nekuchan Formation, Suol section located in the basin of Setorym River, a tributary of the East Khandyga River) are presented. The studied foraminifera constitute a novel group for this section and have not been used in paleontological-stratigraphic studies. The foraminiferal assemblage is represented exclusively by ammodiscids (Ammodiscus, Glomospira, and Glomospirella genera), among which Ammodiscus septentrionalis Gerke dominates. The distribution of foraminifera in the Suol section is compared to the previously constructed carbon isotope curve, which reflects global environmental changes. Three intervals are identified in the stratigraphic distribution of foraminifera. In the lower interval, foraminifera are relatively numerous and diverse. In the middle interval, foraminifera are not detected; the maximum negative values of δ13Corg isotope is also recorded here. This interval obviously corresponds to the main extinction episode in the Tethyan basins. In the upper interval, a gradual restoration of the abundance and structure of the foraminiferal complex occurs. A comparative analysis of the distribution and dynamics of taxonomic reorganization of the foraminiferal assemblages from the Permian–Triassic deposits within the Suol section and the assemblages from the Tethyan and Boreal sections has been carried out; as a result of this analysis, the common features and regularities are established. Brief descriptions of four foraminiferal species and a plate with their images are given.

A diverse marine invertebrate fauna was found in the Echij Formation (Sakmarian–Artinskian) at the Arkachan, Chelge, and Nizhnyaya Dielendzha sections, all Western Verkhoyansk Region, North-East of Russia. The biostratigraphic sequence of ammonoid, brachiopod, bivalve, and foraminiferal assemblages in the Echij Formation of the Western Verkhoyansk Region is studied. Five ammonoids units are identified in the Echian Regional Stage (“Horizon”): Uraloceras subsimense, Uraloceras omolonense, Neoshumardites triceps hyperboreus, Eotumaroceras endybalense, and Eotumaroceras subyakutorum beds. The first two divisions contain ammonoids of the Arkachanian association, and the last three contain the Endybalian association. The boundary between the Sakmarian and Artinskian stages is established at the base of Neoshumardites triceps hyperboreus beds. In the Sakmarian interval of the Echij Regional Stage of the Verkhoyansk Region, a brachiopod biostratigraphic sequence similar to that of the Kolyma–Omolon Region is observed: Jakutoproductus insignis, Jakutoproductus terechovi, and Jakutoproductus rugosus zones. In the lower part of the Artinskian stage, Uraloproductus stuckenbergianus beds are identified, which are characterized by a rich brachiopod assemblage ( Peregoedov et al., 2009 ), not typical for Verkhoyansk Region. The bivalves, identified in the Lower Echij Subformation, presumably belong to the Merismopteria permiana, Cypricardinia eopermica, and Cypricardinia borealica zones of the Ogonerian Horizon of the Kolyma–Omolon Region. Bivalves of the Middle and Upper subformations are characteristic of the Edmondia gigantea and Aphanaia lima zones of the Koargychanian Regional Stage (“Horizon”). The foraminifera complex identified in the Echij Formation is compared with the complex of the lower part of the Sandy Foraminifera horizon of the northeast of the Siberian platform, to which the Tustakh Formation belongs. The beginning of the wide distribution of the Early Permian foraminifera in the Western Verkhoyansk Region was recorded at the base of the Artinskian. The Sakmarian–Artinskian boundary interval in the Verkhoyansk Region is characterized by three significant biotic events: the replacement of the brachiopod Jakutoproductus by Inoceramus-like bivalves, the first appearance of the Endybalian ammonoid association, and biotic invasions from the Uralian and North American regions. An important factor of the Late Sakmarian–Early Artinskian events was a large sea level rise (the Echian transgression), which significantly changed the environmental conditions for East Siberian marine invertebrates, and contributed to the spread of new faunas.

For the first time very low values (up to 0,706707) of the ratio 87Sr/86Sr were recorded in the biogenic carbonates of the Omolon massif (Northeast Asia) of the Capitanian age. These results are in good agreement with previously obtained data on limestones in Japan (Kani et al., 2013; 2018). In general, the strontium ratio curve constructed by us repeats the well-known world trend, differing by its somewhat underestimated (by an average of 0,000-0,0008) its values. The Capitanian strontium minimum can be associated with the entry into the ocean of significant amounts of lightweight femic strontium due to a sharp increase in paleospreading. The maximum values of the strontium ratio, obtained from the middle part of the Intomodesma evenicum bivalve Subzone are 0,706986, which corresponds to the upper part of the Wuchiapingian stage.

For the first time very low values (up to 0.706707) of the ratio 87Sr/86Sr were recorded in the biogenic carbonates of the Omolon massif (Northeast Asia) of the Capitanian age. These results are in good agreement with previously obtained data on limestones in Japan (Kani et al., 2013; 2018). In general, the strontium ratio curve constructed by us repeats the well-known world trend, differing by its somewhat underestimated (by an average of 0.0005–0.0008) values. The Capitanian strontium minimum can be associated with the entry into the ocean of significant amounts of lightweight femic strontium due to a sharp increase in paleospreading. The maximum values of the strontium ratio, obtained from the middle part of the Intomodesma evenicum bivalve Subzone are 0.706986, which corresponds to the lower part of the Changhsingian stage.

A late Ladinian to early Carnian radiolarian assemblage was found for the first time in the Pravyi Vodopadnyi Creek Section, Omolon Massif, Northeastern Russia. The assemblage consists of early Carnian radiolarian species that were previously described from sections of Kotelnyi Island (New Siberian Islands) (Glomeropyle aculeatum, G. cuneum, and Pseudoeucyrtis annosus) and species known from the late Ladinian of the Dzugadzak Section (Omolon Massif) (Glomeropyle algidum and Pseudostylosphaera omolonica). The taxonomic composition (dominance of genus Glomeropyle) indicates the high-latitude (boreal) nature of the assemblage. The taxonomic affinity of coeval radiolarian assemblages of the late Ladinian and early Carnian of the Omolon Massif and New Siberian Islands provides the basis for estimation of radiolarian correlation of the boreal Triassic.

The change in marine bivalve communities at the Carboniferous–Permian transition of Northeast Asia has been analyzed for the first time. A significant increase in the taxonomic diversity of the group occurs near the Carboniferous–Permian boundary, most likely, due to the invasion of a number of thermophilic elements from the more southerly basins into the Omolon Basin, associated with a short-term global warming episode. The position of the Carboniferous–Permian boundary in Northeast Asia is considered. A conclusion is made that this boundary in the Kolyma–Omolon–Chukchi region is most likely located within the Verchojania mirandus–Prothyris elongatus complex Zone.

It is proposed that unstable temperature conditions in the Late Wuchiapingian and Early Changhsingian (Late Permian) changed in the Boreal Superrealm to less contrasting climatic conditions in the Late Changhsingian and Early Induan (the formation time of trap formation of the Siberian Platform), with a stable trend of increasing temperature in the Early Triassic. The problem of the absence of signs of mass extinction of marine organisms at the Permian–Triassic boundary in the Boreal Superrealm is discussed.

We propose an updated ammonoid zonation for the Permian–Triassic boundary succession (the lower Nekuchan Formation) in the Verkhoyansk region of Siberia: (1) Otoceras concavum zone (uppermost Changhsingian); (2) Otoceras boreale zone (lowermost Induan); (3) Tompophiceras morpheous zone (lower Induan); and (4) Wordieoceras decipiens zone (lower Induan). The Tompophiceras pascoei zone, previously defined between the Otoceras boreale and Tompophiceras morpheous zones, is removed in our scheme. Instead of this the Tompophiceras pascoei epibole zone is proposed for the lower part of the Tompophiceras morpheous zone. New and previously published nitrogen isotope records are interpreted as responses to climatic fluctuations in the middle to higher palaeolatitudes of Northeastern Asia and these suggest a relatively cool climatic regime for the Boreal Superrealm; however the trend towards warming across the Permian–Triassic boundary transition is also seen. The evolutionary development and geographical differentiation of otoceratid ammonoids and associated groups are considered. It is likely that the Boreal Superrealm was their main refugium, where otocerid, dzhulfitid and some other ammonoids survived the major biotic crisis at the end of the Permian. The similarity of ontogenetic development of suture lines of Otoceras woodwardi Griesbach and O. boreale Spath gives some grounds for suggesting a monophyletic origin of the genus Otoceras, having bipolar distribution.

Based on new extensive collections and revision of the previously known bivalve Inoceramus-like mollusks, the faunal characteristics of the Delendzhian–Dulgalakhian (Wordian–Capitanian) boundary beds of the Middle Permian of lower reaches of the Lena River (northern Verkhoyansk Region, northern Siberia) are amended. The upper part of the Delendzhian beds is characterized by abundant and diverse representatives of Inoceramus-like bivalves of the genera Kolymia, Evenia, and Okhotodesma. All of them became extinct at the Delendzhian–Dulgalakhian boundary. In the lower part of the Dulgalakhian Horizon, individual Maitaia bella Biakov occur; somewhat upward in the section, there is Atomodesma sp. From the upper part of the Delendzhian Horizon, a new species, Kolymia peregoedovi sp. nov., is described. Permian kolymiids are figured.

Taxonomic data on Permian bivalve mollusks and the structure of the middle part of essentially volcanogenic section on the Nyavlenga River in the northeastern Okhotsk Region, Armano-Viliga Folded Zone are reported for the first time. Fossil fauna is composed exclusively of Inoceramus-like bivalves of the genera Kolymia, Cigarella, Okhotodesma, and Maitaia, which frequently form shell rocks and date the Bocharian Horizon (upper part of the Wordian Stage) as the Middle Permian. Lithologic and paleontological characteristics of the beds are considered; it is shown that volcanites are widespread; turbidites and diamictites similar to those previously investigated in the Okhotsk and Ayan-Yuryakh basins are recorded. Permian kolymiids are figured.

Middle Permian Inoceramus-like bivalves of the genera Kolymia Licharew and Cyrtokolymia Astafieva endemic to the East Boreal Biogeographic Realm are considered. Cyrtokolymia, previously regarded by the author as endemics of the Verkhoyansk–Okhotsk Province and including only the type species, are also recorded in the Kolyma–Omolon Province, where they are represented by the endemic species C. bobini sp. nov. An emended diagnosis of the genus Cyrtokolymia is provided. The genus Kolymia comprises about 30 species. The greatest diversity of Kolymia (24 species, 13 of which are endemic) is known from the Verkhoyansk–Okhotsk Province, which is the center of diversification of this genus. The Kolyma–Omolon Province is characterized by 12 species, only three of which are endemic. In other provinces of the East Boreal Realm, only individual members of Kolymia are known. From the Middle Permian of the Omolon Massif, northern Verkhoyansk Region, and Penzhinsky Ridge, the following new species are described: Kolymia posneri Muromzeva, Kusnezov et Biakov, sp. nov., K. pontoneica Biakov, sp. nov., K. simkiniformis Biakov, sp. nov., and Cyrtokolymia bobini Biakov, sp. nov.

Four high-precision U-Pb CA-IDTIMS dates for the Roadian (lower Guadalupian) of 274.0 ± 0.12 and 273.1 ± 0.1 Ma and for the Wuchiapingian (lower Lopingian) of 260.16 ± 0.39 and 258.14 ± 0.20 Ma were obtained from Permian tuff beds in the periphery of the Okhotsk Massif, N-E Russia. The beds are well constrained within the local lithostratigraphic and regional biostratigraphic framework. Besides regional bivalves and brachiopod faunas, the ammonoid Sverdrupites harkeri occurs close to the recovered Roadian tuffs. This ammonoid provides direct correlation of the tuffs with the Kazanian Stage on the Russian Platform and the Roadian Stage in the Canadian Arctic, where the conodont index species of the Roadian Stage Jinogondolella nankingensis gracilis and Sverdrupites harkeri and other Roadian ammonoids are documented from the Assistant Formation. Our review of the Kungurian-Roadian-Wordian successions in the main well-studied regions suggests that the base of the Roadian Stage should be extended down to approximately 277 Ma and the Roadian-Wordian boundary should be placed at approximately 271 Ma. The new calibration of the Roadian Stage reduces the duration of the enormously long Kungurian Stage from about 10 Myr approximately to 6.0–6.5 Myr. If the proposed calibration is correct, the duration of Guadalupian Series would be almost twice as great as in the previous estimates. Our results also suggest a possible correlation of the P3 alpine glacial event in the Eastern Australia with the Wordian and possible uppermost Roadian Stages. This P3 event corresponds with the disappearance of ammonoids and conodonts in the upper Roadian and Wordian in high-latitudes regions, i.e. N-E Russia, Russian and Canadian Arctic and Australia, perhaps due to extreme cooling of these areas. The new radioisotopic ages in the Okhotsk Massif and surrounding regions improve the numerical calibration of the palynological zonation in the Eastern Australia and provide a direct correlation of the regional biostratigraphic brachiopod and bivalve zonation of N-E Russia with the International Geologic Time Scale. This zonation becomes a solid and reliable regional correlation tool within the vast territory from Taymyr and East Siberia to entire N-E Russia and Transbaikalia.

The first results are presented for U-Pb SHRIMP-II dating of zircons from the upper part of the Khivachian regional horizon (stage) of the Regional Stratigraphic Scale (RSS) of the Permian in northeastern Russia. The obtained isotope age of 255 ± 2 Ma is close to that of the present boundary between the Wuchiapingian and Changhsingian stages of the Permian system in the International Stratigraphic Scale (254.1 Ma). Based on the distribution of bivalves—Intomodesma spp. and Claraioides aff. primitivus (Yin)—in the sections considered, their relations to the stratigraphic positions of the samples considered and dated formerly, and in view of the interregional correlation of recent δ13Сorg data for clayey rocks, one may assume with certainty that most of the regional zone of Intomodesma costatum corresponds to the upper part of the Wuchiapingian stage. Here, the Changhsingian stage in northeastern Asia complies only with the uppermost part of this zone within the I. postevenicum subzone and, partially, of Otoceras layers within the Otoceras concavum zone.

We have obtained the first detailed δ13Сorg record in Permian-Triassic boundary sediments in deepwater facies in Northeast Asia (Kolyma–Omolon region, Balygychan Basin). Our data show good convergence both with the Setorym River section (South Verkoyansk region), where the Permian-Triassic boundary has been determined approximately, and with a number of other sections of Permian-Triassic boundary sediments in the Boreal and Tethyan Superrealms, in particular, in the Buchanan Lake section in Arctic Canada, the Festningen section on Spitsbergen, the Wadi Shahha section on the Arabian Peninsula, and published sections in the Dolomites.

The Regional Stratigraphic Scale (RSS) of the Permian deposits in northeastern Russia represents the only complete stratigraphic succession of Permian marine deposits distinguished in Russia, which serves as a standard at the correlation of Permian deposits of all regions of the eastern part of the Boreal Biogeographic Superrealm. However, a high level of faunistic endemism makes it extremely difficult to correlate directly stratons of the RSS with stages of the International Stratigraphic Scale (ISS) of the Permian deposits. The first U–Pb SIMS age datings of zircons from felsic tuffs of the Omchak Formation of the Ayan-Yuryakh Anticlinorium (the lower part of the Permian Khivachian Horizon of the RSS of northeastern Russia) allowed us to obtain the important reference level for the Upper Permian subdivision of the Permian RSS. The zircon age of 257.1 ± 3.0 Ma is in good agreement with the stratigraphic position of the studied sample, which makes it possible to correlate the surrounding deposits with the Wuchiapingian Stage of the Permian deposits in the International Stratigraphic Scale.

Geographical and stratigraphical ranges of the bipolar nuculanid bivalves of the genus Glyptoleda is considered. In the Boreal Biogeographical Superrealm, Glyptoleda is only known in the eastern (high boreal) part: in the Novaya Zemlya and Verkhoyansk–Okhotsk provinces. Glyptoleda is recorded for the first time in the Kolyma–Omolon Province. Possibly, the appearance of glyptoleds in the northern Eurasian basins was associated with cooling episodes. A new species, Glyptoleda parenica sp. nov., is described from the Kungurian–Roadian beds of the southeastern framing of the Omolon Massif.

The Atkan Formation in the Ayan-Yuryakh anticlinorium, Magadan province, northeastern Russia, is of great interest because of the occurrence of deposits of apparent “dropstones” and “ice rafted debris” that have been previously interpreted as glacial. Two high-precision U–Pb zircon ages, one for an intercalated volcanic tuff (262.5 ± 0.2 Ma) and the other for a boulder clast (269.8 ± 0.1 Ma) within a diamictite of the Atkan Formation, constrain the age of the Atkan Formation as Guadalupian (middle Permian). Sedimentologic study of the Atkan Formation casts doubt on the glacial nature of the diamictites. Deposition of rocks of the Atkan Formation temporally correlates with the Capitanian interglacial event in the southern hemisphere that recently was calibrated with high precision CA-TIMS. The previously proposed climate proxy record based upon warm-water foraminifera, which corresponds closely to global climate fluctuations, is compared with the glacial record of eastern Australia and indicates that the Capitanian was a time of globally warm climate. The sedimentology of Atkan Formation, the record of diversification of both fusulinids and rugosa corals, global sea-water temperature, and sea-level fluctuations agree well with high latitude paleoclimate records in northeastern Russia and eastern Australia. Major components of the Atkan Formation, the volcanic rocks, are syngenetic with the sedimentation process. The volcanic activity in the nearby regions during middle–late Permian was quite extensive.

A new species, Eoshumardites popowi Kutygin sp. nov., is described from the Upper Carboniferous of the upper reaches of the Paren’ River in the Gizhiga Province of the Kolyma–Omolon Region. The ontogeny of the sutural and shell morphology of the new species is described. In the level of sutural organization, E. popowi occupies an intermediate position between E. lenensis (Popow) and E. sublenensis Klets. It has been suggested that Eoshumardites evolved from the genus Syngastrioceras rather than Aktubites and, on this basis, a new monotypic endemic family, Eoshumarditidae, has been proposed. This family existed in the Kasimovian synchronously with members of the family Parashumarditidae.

Despite a lack of detailed sedimentologic analyses, diamictites in the Middle Permian Atkan Formation were previously interpreted as glaciomarine and glacially-influenced marine deposits. This interpretation allowed this unit to play a prominent role in paleoclimatic and biogeographical reconstructions associated with presumed bipolar glaciation during the late Paleozoic ice age (LPIA). In this sense, the LPIA is considered to be a close analog to bipolar glaciation and climate change during the Cenozoic. Here, results are presented that challenge the glacigenic interpretation for these strata and negate interpretations of the bipolar nature of the LPIA. The 400 to 1500-m-thick Atkan Formation was deposited in back-arc basins associated with activity of the Okhotsk–Taigonos volcanic arc along the leading edge of Pangea as it drifted across the North Polar Circle. The occurrence of tuffs, volcanic clasts, and glass shards indicate derivation from a nearby arc. Cooling and solidification of some clasts during sedimentation is suggested by the occurrence of clasts with embayments and protrusions that extend into the surrounding matrix, clasts with columnar-like jointing, and alteration of the matrix surrounding some clasts. CA-TIMS dating of tuff zircons indicate a late Capitanian age, which is consistent with fossils within the strata. Bedded diamictites deposited as debrites dominate. These diamictites, which occur as tens of m thick downlapping packages that thicken then thin upward, were deposited as prograding and abandoning sediment gravity-flow fans. Chaotic and folded strata formed as slumps. Graded sandstones and conglomerates were deposited as turbidites, and mudstones were deposited as mudflows, low-density turbidites, and hemipelagic deposits. Striated clasts and outsized clasts piercing bedding were not observed in the study area. Strata above and below the Atkan Formation contain abundant graded beds and deep-water trace fossils indicating deposition as turbidites. The combination of debrites, turbidites, slumps, volcanic grains (clasts, glass, and tuffs), and an absence of glacigenic indicators suggest that Atkan strata were deposited in deep-water basins associated with the development of the volcanic arc rather than due to glacial activity. These findings are significant as they require reconsideration of current views of LPIA glaciation and suggest that ice sheets were limited to Gondwana.

We present new data on the structure and age of the upper Permian strata in the basin of the Setorym River (tributary of the Vostochnaya Khandyga River) in the South Verkhoyansk region, represented by the Imtachan Formation and the lower part of the Nekuchan Formation. Based on the new findings of bivalve fossils from the Intomodesma costatum Zone, as well as on the study of carbon isotopes in the shells and carbon isotopes of the organic matter of the host mudstones, we have for the first time proved the completeness of the Permian section. The detailed description of the contact between the Imtachan and Nekuchan Formations bears evidence for a certain continuity of the lithologic characteristics of the sandstones. The sharp lithologic contact between the formations reflects not a regional sedimentation hiatus but a shift of depositional settings from the upper parts of a delta to the deep shelf, caused by forced marine transgression. It is concluded that there was no long-term hiatus between the accumulation of the Imtachan and Nekuchan Formations. Images of the most characteristic species of bivalves and crinoids from the Imtachan Formation are presented.

Beds with ammonoids are recognized as a result of the study of goniatitids and prolecanitids from the Nyut, Khuren, and Ayan-Yuryakh in the Okhotsk Region. Beds with Neopronorites tenkensis, assigned to the Upper Artinskian Substage, correspond to the upper part of the Echian Horizon of the Verkhoyansk Region. Beds with Paragastrioceras–Baraioceras characterize the middle part of the Kungurian Stage and correlate with the upper sunhorizon of the Tumarian Horizon of the Verkhoyansk Region. Beds with Sverdrupites harkeri correspond to a biostratigraphic subdivision with the same name widely distributed in the Vekhoyansk-Kolyma Region and assigned to the Roadian Stage. The new species Neopronorites tenkensis is described.

The characteristics of the main biotic groups of the Permian marine basins of northeastern Asia are provided. They include nine animal phyla: sarcodines, sponges, cnidarians, arthropods, bryozoans, brachiopods, mollusks, echinoderms, and conodonts. The distribution of the fauna was nonuniform and controlled primarily by the depth of their habitats. Dominating groups were foraminifers, brachiopods, bivalves, and gastropods. The most diverse fauna inhabited the Omolon Basin, where almost all the above groups have been recorded. A distinctive feature of the Permian biota of northeastern Asia is wide distribution of bipolar taxa in all faunal groups.

Core hole no. AKh-1 has been drilled within the Anabar-Khatanga oil and gas fields, on the left bank of Khatanga Bay. To date only data on the upper 972.5 meters of the core have been examined in detail and processed by the authors; however, we obtained unique materials displaying lithoand biostratigraphic features of the section of Permian deposits. In the explored part of Permian deposits we can very clearly distinguish the top of the Tustakh Formation and the Lower and Upper Kozhevnikova formations. The assemblages of flora, foraminifers, brachiopods, marine and nonmarine bivalves are characterized and results of palynological analysis are presented.

The conodont genera Hindeodus and Streptognathodus are reported for the first time within the Carboniferous–Permian transition in the northern high latitudes of the Paren' River, Omolon Massif, NE Russia. Several fossil groups, including brachiopods, bivalves, scaphopods and microgastropods were found to be prolific in the invertebrate-dominated bioherms. These bioherms occur within predominantly siliciclastic sequences with extremely poor fauna, whereas in the studied bioherms the diversity of the bivalves and brachiopods exceeded observed diversity elsewhere in coeval facies in NE Russia. The bioherms are biostratigraphically constrained as uppermost Pennsylvanian to lowermost Cisuralian based on ammonoids. The very unusual peak of bivalve and brachiopod diversity and the occurrence of conodonts that require minimum sea water temperatures of at least 10–12 °C indicate a short lived, but significant warming event at that time, at least of provincial significance. This event most likely corresponds with a short-lived warming event recently discovered in the east of the southern hemisphere, in Timor and Australia. Thus, the event is possibly of global significance.

The most ancient representative of Permian Inoceramus-like bivalves, Aphanaia kletzi sp. nov., from the Upper Sakmarian of the Western Verkhoyansk Region (northeastern Asia) is described. It is established for the first time that the first kolymiids appeared in the northeastern Asian basins in the latter half of the Sakmarian rather than at the end of the Artinskian. The age of the record is reliably dated by the ammonoid genera Uraloceras and Neoshumardites.

A late Changhsingian bivalve complex including species from the genera Palaeonucula, Dacryomya, Malletia ?, Sarepta ?, Myalina, Pteria, Maitaia, and Unionites is discovered in northeastern Asia for the first time. The transition from the Permian to the Triassic in high-boreal basins has been shown to include two extinction episodes similar to those observed in the low-boreal basins and apparently evoked by trap volcanism activation in Siberia. Changes in benthic foraminifera diversity and vertical distribution of ammonoidea of the genus Otoceras in transitional Permian-Triassic deposits also are considered. Images of bivalves from the most typical taxa are presented.

Historical development of Permian Inoceramus-like bivalves of the genus Praekolymia Biakov endemic to the Verkhoyansk-Okhotsk and Kolyma-Omolon provinces is briefly considered. Two new earliest representatives of the genus (Praekolymia kaschirtzevi sp. nov. and P. barajensis sp. nov.) from the Lower Permian of the western Verkhoyansk are described.

This paper is dedicated to the global correlation of the marine Permian-Triassic boundary layers based on some published and original data on the δ 13 Corg and δ 13 Ccarb values obtained for the section along the Suol Creek (Setorym River, southern Verkhoyansk region). The section includes six carbonisotope inter� vals readily distinguished in the corresponding curves obtained for several Permian and Triassic reference sec� tions in Eurasia and North America including palleontologically well substantiated sections of central Iran, Kashmir, and South China. This provides grounds for assuming the Permian-Triassic boundary's position in the Suol Creek section as being close to the carbonisoto pe minimum of Interval IV. In the light of new data, the upper part of the Upper Permian Changhsingian Stage in Siberia is proposed to correspond in range to the Otoceras concavum range zone, and the lower substage of the Lower Triassic Induan Stage, to the Tom� pophiceras pascoei and Wordieoceras decipiens zones. The Otoceras concavum Zone of the Verkhoyansk region in its new understanding is likely correlative with the upper Changhsingian Hypophiceras triviale Zone of Greenland. Carbonisotope intervals II, III, IV, and V defined in the Permian-Triassic boundary layers of the Verkhoyansk region, which are traceable in several reference sections of Eurasia and North America, evi� dently coincide with the period of some intensification of the volcanic activity in the initial late Changhsin� gian and with the first phases of extensive eruption of Siberian trappes in the terminal Changhsingian and ini� tial Induan ages. New data imply the probable survival of some ammonoid species from the superfamily Oto� ceratoidea after the mass extinction of organisms in the terminal Permian Epoch.

Historical development of Permian Inoceramus-like bivalves of the bipolar genus Maitaia Marwick in northeastern Asia is briefly considered. Five new species (Maitaia vedernikovi sp. nov., M. kusnezovi sp. nov., M. orulganica sp. nov., M. regularicostatum sp. nov., and M. tobonnoensis sp. nov.) from the Middle and Upper Permian of the Omolon Massif, northern, western, and southern Verkhoyansk Region are described.

The problems of the intra- and regional correlation of Permian sections of Northeastern Asia are considered based on a new zonal biostratigraphic bivalve scale. The interregional correlation was performed for the Permian deposits in the eastern part of the Boreal Superrealm and some adjacent regions. The possibilities and problems of bivalve-based correlation of Permian sediments in extraboreal regions are discussed.

Historical development of Middle Permian Inoceramus-like bivalves of the genus Kolymia Licharew, which are endemic to the East Boreal Biogeographic Realm, is briefly discussed. Five new species, Kolymia gydanensis sp. nov., K. taskanica sp. nov., K. milievskyi sp. nov., K. churavtsovi sp. nov., and K. astafievae sp. nov., from the Middle Permian of the Omolon Massif, northeastern frame of the Okhotsk Massif, northern Verkhoyansk Region, Balygychan and Omulevka Blocks are described.

Extensive new data obtained during the recent decade on several Permian reference sections in the northern, western, and southern Verkhoyansk region; the Balygychan block; the Omolon massif; and some adjacent regions provided grounds for substantial refining of the Permian bivalve zonal scale of northeastern Asia. The modified version of this scale includes 24 biostratigraphic units ranked as zones, subzones, and faunal beds. Zonal assemblages of bivalve mollusks were refined and supplemented, and the age of the zones was specified and substantiated. The stratigraphic distribution of the defined bivalve taxa is illustrated by a special detailed table.

An analysis of the dynamics of diversity of bivalve species in Northeast Asia in the Permian period allowed us to reveal a number of events when it significantly increased or decreased. Four major mass extinction events were established for bivalves: at the end of the Early Permian, in the Early Capitanian age, at the the Capitanian-Wuchiapingian boundary and at the end of the Late Permian. Along with extinction events, five events of taxonomic radiation/innovation were distinguished: Early Asselian, Middle Kungurian, Early Roadian, Late Wordian, and Early Changhsingian. Revealing of these biotic events has been confirmed by the dynamics of biodiversity in other major groups of Permian fauna (foraminifers, brachiopods, ammonoids). Moreover, they are evidenced in different basins by changes in the character of sedimentation, isotope parameters, eustatic variations and other environmental factors. Most of the events can be traced far beyond Northeast Asia. Their manifestation is associated with general reasons (variations in endogenous regime of the Earth and associated stress effects on the biota). According to this, results of studying these events can be used for global correlations.

In the development of Permian bivalves of northeastern Asia, the following five large stages have been recognized: Asselian-Middle Artinskian, Late Artinskian-Kungurian, Roadian-Wordian, Capitanian-Early Wuchiapingian, and Late Wuchiapingian-Changhsingian. The boundaries between stages correspond to great biotic events and frequently display a sharp change in species diversity of bivalves. During the Permian, brachiopods were gradually replaced by bivalves; this was promoted by repeated sharp changes in the environment.

Historical development of Permian Inoceramus-like bivalves of the genus Aphanaia Koninck in northeastern Asia is briefly considered. Five new species from the Lower Permian of the western Verkhoyansk Region and Omolon Massif are described: Aphanaia waterhousei sp. nov., A. budnikovi sp. nov., A. kutygini sp. nov., A. dulgalakhensis sp. nov., and A. korkodonica sp. nov.

The paper considers the biogeography and palaeogeographic implications of the Permian marine bivalve faunas of Northeast Asia, with a focus on the dynamic relationships between biotic similarities and palaeogeographic distance through an interval of ca. 50 million years. A stage-by-stage time series analysis of the biotic similarities between two previously recognized biochores in Northeast Asia, the Kolyma–Omolon and Verkhoyan–Okhotsk provinces, has been carried out using both the Jaccard and Dice similarity indices based on the spatio-temporal distributions of 355 Permian marine bivalve species in Northeast Asia. The outcome of this analysis, combined with other empirical data and previously published tectonic, sedimentological and palaeontological information, suggests that (1) the bivalve faunas from these two provinces were distinctive from one another as two separate biochores throughout all but the earliest (Asselian) Permian stages and (2) the biotic similarities between the Verkhoyan–Okhotsk and Kolyma–Omolon provinces remained consistently low since Sakmarian, all falling well below the minimum threshold of the Jaccard index of 0.42 required for distinguishing marine biotic provinces. We interpret these below-threshold Jaccard biotic similarities as an indication of significant palaeogeographic separation between the Verkhoyan-Okhotsk and Kolyma–Omolon provinces, which is in turn considered to indicate rifting and sea-floor spreading of the Omolon microcontinent and associated terranes and island arcs away from the North Asian craton, at least from the Sakmarian to the beginning of the Late Permian. Palaeo-distance separation appears to be the primary and most significant biogeographic determinant in accounting for the differences in the spatial distribution of most Permian bivalve species in Northeast Asia. Several other variables also appear to have played a significant role, including regional climate conditions, ocean currents and merged island chains as geographic barriers. In particular, the relatively high biotic similarity between the Verkhoyan–Okhotsk and Kolyma–Omolon provinces during the Late Wuchiapingian and Changhsingian may have been related to the shallowing of the deep-water basins (Oimyakon, Ayan-Yuryakh, Balygychan and Sugoi basins) that had previously separated the two provinces and the flooding (submergence) of the Okhotsk–Taigonos volcanic arc system, thus allowing the invasion of lower latitude warm-water Palaeotethyan and even Gondwanan species into Northeast Asia.

Palaeozoological, palaeobotanical and geochemical analyses of Lower Permian to the lowermost Cretaceous sediments exposed in the southern Russian Far East (Bureya–Jiamusi–Khanka superterrane and the Sergeevka terrane), and higher latitude areas (northern Russian Far East and Spitsbergen) suggest a direct relationship with global climatic events defined by the data from oxygen-isotopic palaeotemperatures. Several positive carbon-isotopic anomalies discovered within the uppermost Cisuralian, Guadalupian, early Lopingian and Aalenian–Bajocian intervals are possibly connected to strong hydrological intermixing of oceanic waters under the influence of considerable thermal gradients.

New concepts of systematics and phylogeny of the Permian Inoceramus-like bivalve mollusks of the eastern part of the Boreal zone are discussed based on analysis of the group’s historical development. All taxa studied are referred to the family Kolymiidae Kusnezov, which is divided into two subfamilies, Kolymiinae and Atomodesmatinae. In the subfamily Kolymiinae, two new genera are described: Praekolymia with the type species P. archboldi sp. nov. and P. urbajtisae sp. nov., and Taimyrokolymia with the type species T. ustritskyi sp. nov. In the subfamily Atomodesmatinae, two new genera, Costatoaphanaia and Okhotodesma, are described. The development of the group is shown to be generally autochthonous with some invasions (genus Atomodesma and, probably, Trabeculatia) from extraboreal regions.

Fossil biota and detailed biostratigraphy of the Permian northeastern Okhotsk and Ayan-Yuryakh sedimentary basins located in the northern Okhotsk region are characterized. The biota core is represented by bivalves associated with gastropods, brachiopods, and other faunal groups. It is shown that a new regional stratigraphic scale of northeastern Russia based on brachiopods and bivalves may be used for subdivision of Permian sections in these basins. Fossil assemblages have many features in common with their counterparts from the Verkhoyansk region; at the same time, there are endemic species and the big group of species characteristic of the Omolon basin. The upper part of the Khivach regional horizon is subdivided into subzones based on the evolutionary lineages of the Maitaia and Intomodesma genera. Changes in the taxonomic composition of coeval communities in different basins are shown to be largely controlled by the basin depths and facies environments. Impoverished fauna of the Ayan-Yuryakh basin was less diverse in taxonomic aspect, represented almost entirely by bivalves (mostly Inoceramus-like) accompanied by rare gastropods. The discovered taxa are figured in majority, and table of their stratigraphic distribution is presented.

The main features of the tectonics, Permian paleogeography, biota, structural-facies zonation of the Kolyma–Omolon region are analysed. The characteristics of the Permian regional stratigraphic scale of the Kolyma–Omolon region are described. The Permian deposits of the Kolyma– Omolon region are divided into four regional stratigraphic subdivisions, ranked as superhorizons, which in turn are subdivided into nine horizons. These horizons are further subdivided into 18 provincial zones (‘lones’ in accordance with Russian stratigraphical nomenclature). Most of the lones distinguished have dual index species, representing the dominant brachiopod and bivalve species. The chosen nominal species of these lones are, as a rule, related to each other phylogenetically, and as such they represent key stages in the evolution of their respective taxonomic groups through the Permian. The resultant biostratigraphic scale is adopted as a regional one for the Kolyma–Omolon, Chukotka, and southeastern part of the Verkhoyan–Okhotsk regions. Almost all the lones distinguished can also be recognized in the Verkhoyansk region, and many of the lones are also traceable outside Northeast Asia. q 2006 Elsevier Ltd. All rights reserved.

This report summarizes data on the Permian deposits of the Verkhoyansk–Okhotsk region (tectonics, paleogeography, fauna, flora and stratigraphy). The Verkhoyansk–Okhotsk region covers the area of the Verkhoyansk fold-and-thrust belt. The Permian deposits of this region were formed on the passive continental margin of the Angarida Continent, the ancient Siberian Continent, situated within the Siberian Platform. This continental margin developed as the result of continental break-up in the Late Precambrian. Late Precambrian to Jurassic (including Permian) sediments were deposited on a passive margin with a continental shelf extending out into an ocean towards the northeast. During the Permian, exclusively terrigenous sediments were deposited over a vast territory in the Verkhoyansk paleobasin forming part of this continental margin. The Permian deposits are divided into six regional stratigraphic units ranked as horizons (=regional stages), which in turn are subdivided into faunal zones and beds serving as the basis for intra-regional correlation. In the Late Jurassic–Cretaceous the continental margin sediments were converted into a foreland fold-and-thrust belt due to the collision of the Siberian Platform with the Kolyma–Omolon and Okhotsk continental blocks.

Distribution of members of the thermophilic genus Pteronites in the Upper Paleozoic beds of northeastern Asia is briefly considered. A new species, Pteronites magnus sp. nov., from the Lower Permian of the Omolon Massif is described.

It is well known that the Permian‐Triassic transition was marked by significant changes in the biota and sedimentation settings. Evidence for the development of anoxic environments in various world areas during events at the Permian‐Triassic transition in both shallow- and deep-water settings are reported in [1‐8 and others]. Such data have been unavailable thus far for the Russian territory. The study of Permian‐Triassic boundary deepwater sediments in Northeast Asia provided the first evidence for H 2 S contamination of bottom waters in this region. Both shallow- and deep-sea basins existed in Northeast Asia during the Permian Period [9]: Ayan-Yuryakh, Balygychan, Sugoi, and Gizhiga. They were characterized by avalanche sedimentation, which was responsible for accumulation of thick (up to 7 km) sandy‐clayey and volcanogenic (frequently, turbidite) sediments with impoverished fossil assemblages. The fossils are represented by Inoceramus-like bivalves and subordinate ctenodont bivalves and gastropods ( Straparolus ). In the terminal Permian, the system of sea basins in Northeast Asia experienced some shoaling. In deep marginal sea basins, bathyal settings recorded by the accumulation of turbidite sequences gave way to shallower conditions comparable with deep shelf settings, which differed, however, from typical shelf environments. They reflected substantial shoaling of marginal basins in response to the global regression in the terminal Permian [10]. The rocks are characterized by abundant structural distortions and traces of intense bioturbation (distinctly or vaguely patchy structures). Benthic fossils are more common as compared with the underlying strata. The sea basins became deeper during the Permian‐ Triassic transition. This is evident from the change in the sedimentation pattern in the section: the complete disappearance of distorted bedding, spotty structures, and any other signs of vital activity of benthic organisms, as well as their remains. Instead, thin horizontal and, less commonly, oblique lamination appears. The rocks become fine-grained. All these features imply intense activity of contour currents and lack of benthic life. Such a lithological change in deep-water settings is characteristic of spacious areas of Northeast Asia extending from the Verkhoyansk region to the Taigonos Peninsula. Lower Triassic sediments (up to the Tompophiceras pascoei Zone) lack benthic fossils and bioturbation. The Orotukan segment of the Balygychan basin is one of the most promising areas for the study of the Permian‐Triassic boundary sediments (Fig. 1). The upper part of the Permian section (200 m) is represented here by foliated silty argillites of the Pautovaya Formation, while the lower part of the Triassic sequence is composed of silty argillites with thin siltstone laminae of the Gerba Formation [10]. The Late Permian (late Changhsingian) age of the upper Pautovaya Formation is substantiated by a finding of an impression of the bivalve Claraioides aff. primitivus (Yin) [11]. The Early Triassic age of the Gerba Formation is confirmed by ammonoid Tompophiceras pascoei (Spath) remains found several kilometers northwest of the study section 70‐80 m above the Permian‐Triassic boundary. The rocks are characterized by an elevated C org content (0.91‐0.95% on average, up to 4.92% in some samples), which makes them similar to carbonaceous black shales [12]. Organic matter is finely dispersed. Its origination is most likely related to zoo- and phytoplankton [13]. The above-mentioned lithological features of rocks and lack of benthic fossils indicate that the sediments accumulated in anoxic settings. Kholodov and Nedumov, who studied Quaternary and Tertiary sediments of the Black Sea region [14] and Cretaceous organic-rich clayey rocks of the Atlantic [15], suggested using the Mo/Mn ratio as an indicator of anoxic environments. They established that Mo/Mn values ranging from 0.0 n to 0. n correspond to H 2 S-contaminated environments in