The article reviews the degree of the main taxonomic features expression in the shell of fossil bivalves for various forms of preservation. It is shown that a combination of such forms of preservation as an internal mold and an imprint can often be more preferable than the shell form of preservation for a more complete taxon characterization. For the first time, an image of a bivalve shell with a preserved color pattern is given for the Permian deposits in Northeast Russia.

The Late Permian pectinid species Aviculopecten volucer Lutkevich et Lobanova (Late Wuchiapingian-Early Changhsingian), previously considered to be a junior synonym of the Middle Permian Vnigripecten phosphaticus (Girty), is reinstated to a valid species. Unusual shell morphology and ornamentation of Aviculopecten volucer make it possible to assign it to a new genus Voluceropecten gen. nov. and a new monospecific family Voluceropectinidae fam. nov. An emended diagnosis of the genus Vnigripecten Muromzeva is presented.

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.

A new genus of Permian pectinoid bivalves of the family Heteropectinidae, Kolymopecten gen. nov. with the type species K. kolymaensis (Maslennikow) is described from the Lower–Middle Permian deposits of the Boreal Superrealm (Northeast Russia). The genus also includes K. mutabilis (Licharew) and K. praekolymaensis sp. nov. All members of the new genus have quite simple morphology: their weakly convex right valve is ornamented with simple radial bifurcating ribs of two orders, while the left valve is much more convex and ornamented with intercalating ribs of up to five orders. The geological history of Kolymopecten is briefly reviewed. Kolymopecten is one of the few “ancient” genera of Permian bivalves that survived the Late Kungurian regional extinction, which affected all major benthic groups. Representatives of the genus are among the most widespread pectinoid bivalves in the Northeast of Russia, often forming mass accumulations, especially in the Artinskian-Kungurian beds.

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.

The Sr chemostratigraphic characteristics of marine sediments of the Lower Permian in the Omolon massif of Northeast Asia have been obtained for the first time based on a study of well-preserved brachiopod shells. The 87Sr/86Sr ratio in brachiopods from the Lower Permian regional horizons (regional stages) is within the following ranges: 0.70786–0.70794, Orochian; 0.70744–0.70786, Ogonerian; 0.70745–0.70748, Koargychanian; and 0.70742–0.70735, Khalalian. The obtained Sr-isotope data demonstrate good agreement with the standard variation curve of the 87Sr/86Sr ratio in the Permian Ocean. New Sr-isotope data can be used to correlate the units of the Regional Stratigraphic Scale of Northeast Russia directly with the stages of the International Permian Stratigraphic Scale. Based on recent data, the Asselian age of the Orochian regional stage of the lower part of the Permian section in the Omolon massif has been proved, and the regional correlation of the Upper Sakmarian interval established previously from biostratigraphic data has been refined.

The earliest known representative of the genus Pinna, P. pacata sp. nov., is described from the Lower Permian deposits of the Shakhtau Reef (South Urals, Russia). Until now, the earliest representatives of Pinna were known from the Lower Triassic. The new species adds to the list of species ancestral to Mesozoic forms, which allows the Ural Strait to be considered as one of the centers of Late Paleozoic mollusk diversification.

A new and most ancient species of the genus Pinna, P. pacata sp. nov., has been described from the Lower Permian deposits of the Shakhtau reef (southern Urals, Russia). Until now, the most ancient finds of representatives of this genus were known from the Lower Triassic. The new species adds to the list of species ancestral to Mesozoic forms, which makes it possible to consider the Ural Strait as one of the centers of Late Paleozoic mollusk diversification.

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.

This article presents the results of major, trace, and rare-earth element study of the Permian terrigenous rocks of the southern part of the Omolon Massif. The lithochemical studies showed that sediments were accumulated in a warm climate with episodes of some cooling. The Omolon Basin had a normal salinity, with alternating oxic–anoxic environments. The interpretation of the obtained data indicates that the deposits accumulated in the basin are associated with the marginal continental island arc (Okhotsk–Taigonos volcanic arc). Probable sources were basic and intermediate arc volcanics, as well as acid igneous rocks (volcanics of the Kedon Group) and metamorphic complexes of the basement of the Omolon Massif.

A detailed record of the δ13Сorg value has been obtained for the first time in Permian mudstones of the Taskan Basin (Omulevka Block, Northeast Asia) covering the interval from the Upper Kungurian, Roadian, Wordian, Capitanian, and Lower Wuchiapingian stages. The value of δ13Сorg varies from –23.81‰ (mid-Kungurian) to –26.97‰ (lower Wuchiapingian). Three δ13Сorg negative excursions were clearly distinguished in the section including the upper part of the Kungurian Stage of the Lower Permian, the lower part of the Capitanian, and the boundary between the Capitanian and Wuchiapingian stages. These excursions are in good agreement with the episodes of mass extinction that we established earlier [12], and they are most likely associated with periods of activity of island-arc magmatism in the region during the Permian.

The problems of taxonomy of Permian pectinoid bivalves are briefly considered in the context of the study of the well-known Upper Paleozoic genus Streblopteria M’Coy and its evolution in Northeast Russia. Two new stratigraphically important species are described from the Lower and Middle Permian deposits of the Omolon Massif: S. parenensis sp. nov. and S. gracilicosta sp. nov.

The earliest oyster-like bivalves of the genus Prospondylus Zimmermann are discovered in the Lower Permian (Upper Asselian–Sakmarian) of the South Cis-Urals. Previous confirmed findings were only known from the Lower-Middle Permian deposits of North America (Kungurian–Wordian) and the Upper Permian of Germany (Wuchiapingian). A new species Prospondylus shakhtauensis Biakov, sp. nov. is described.

Paleontological evidence of the presence of Wordian bivalves in the Middle Permian deposits of the Omolon massif, which were originally described by N. Newell from the Word Formation of the Glass Mountains (West Texas), is presented for the first time. The Kolymia multiformis bivalve zone of the Bocharian regional horizon is found to contain pectinids of the genus Heteropecten, H. gyrtyi (Newell) and H. gryphus (Newell), which make it possible to correlate this zone confidently with the Wordian Stage of the Permian of the International Chronostratigraphic Chart and indicate the relationship between the Kolyma–Omolon basins and the North American basins.

The article discusses the results of studying the material composition of Permian terrigenous deposits in the Dzhigdali, Gizhiga, and Khivach formations in the southeastern part of the Omolon massif. The obtained data interpretation is based on the petrographic research and widely used petrochemical and discriminant paleogeodynamic diagrams. The lithochemical study showed that the deposits had accumulated under conditions of a moderately warm climate with some cooling episodes in the active continental margin settings. Clastic material entered the sedimentary basin from several provenance areas: the Permian Okhotsk-Taigonos volcanic arc, the Precambrian basement of the Omolon massif, and volcanic rock fields of the Kedon series.

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.

Кратко рассмотрено историческое развитие биполярного рода Myonia в перми Северо-Востока России, представители которого нередко являются доминантами пермских сообществ. Описаны два новых вида: M. kutygini sp. nov. и M. komiensiformis sp. nov.

The paper briefly considers the historical development of the bipolar genus Myonia in the Permian of Northeast Russia. Representatives are commonly dominant in Permian communities. Two new species are described, namely, M. kutygini sp. nov., and M. komiensiformis sp. nov.