Выполнено комплексное биостратиграфическое, литологическое и геохимическое изучение пород керна скважин, пробуренных в бассейне реки Кюленке. Исследование найденных ископаемых остатков, состава пород, анализ распределения трилобитов и изменения литолого-геохимических характеристик отложений позволили выявить особенности строения маркирующих горизонтов, провести корреляцию разрезов скважин и обнажений, сопоставить отдельные интервалы кембрийских отложений с региональными зонами Юдомо-Оленекского фациального региона Сибирской платформы. Установлено, что породы куонамской свиты обогащены ураном (U), наблюдается прямая связь между содержанием U и органическим углеродом (С орг) пород, характерная для черносланцевых отложений нижнего и среднего кембрия из обнажений востока Сибирской платформы. Впервые выявлена связь радиоактивности пород по гамма-каротажу с содержанием U и С орг в породах кембрия. We have studied biostratigraphy, lithology and geochemistry of drill cores from the Kyulenke River basin. The study of fossil remains and rock compositions, the analysis of trilobite distributions and changes in the lithological and geochemical characteristics of the sediments made it possible to identify structural features of the marker horizons, to correlate borehole sections and outcrops, to compare individual Cambrian intervals and the regional zones of the Yudoma-Olenek facies region of the Siberian Platform. The study has shown rocks of the Kuonamka Fomation to be enriched in uranium (U) and revealed a direct relationship between the contents of U and organic carbon (C org) in the analyzed rocks, typical for the lower and middle Cambrian black shale deposits sampled from the outcrops in the eastern parts of the Siberian Platform. For the first time, a relationship of rock radioactivity by gamma-ray logging with the contents of U and C org in Cambrian rocks was established.

Trilobites of the genus Calodiscus Howell, 1935 from the Lower Cambrian of the Siberian Platform are revised. It is shown that two of the four species described from the Lower Botomian (Lower Cambrian) of the General Stratigraphic Scale of Russia, C. helena (Walcott, 1889) and C. granulosus Jegorova et Shabanov, 1972, differ significantly from typical representatives of the genus. The assignment of these species to a new genus, Paracalodiscus, in the family Weymouthiidae Kobayashi, 1943, is substantiated. The other two species (Calodiscus resimus Repina, 1972, and C. schucherti (Matthew, 1896)), although they also show some differences from the type species, are retained in Calodiscus Howell, 1935.

The Verkhnyaya Lena Group (Є2–3vl) has been studied in a section on the right bank of the Malaya Chuya River. Concentrations of main oxides and some trace elements (Cr, V, Ni, Cu, Zn, Rb, Sr, Zr, Ba, U, Th, Y, Nb, and Cl) have been determined in samples using an X-ray spectral fluorescence (XRF) analysis. The normative mineral composition has been determined based on the results of the XRF analysis using the MINLITH software. Based on geochemical data, intervals of change in the weathering features (physical/chemical and arid/humid weathering) are clearly differentiated in the denudation area, which are fixed by variations in the values of the Al2O3/K2O and Ln(Al2O3/Na2O) ratios and concentrations of V, Cu, Zn, Rb, and Ni, as well as the normative mineral composition. Apparently, Cr was transported to the basin exclusively by the aeolian process in this case and marks periods of increased wind transport intensity. Under conditions of tectonic activation and progressive isolation of the Upper Lena paleobasin, the described lithological and geochemical features provide some information about the climate changes that accompanied these events.

Two new trilobite species of the genus Oryctocephalus Walcott, 1886, Oryctocephalus doliiformis sp. nov. and Oryctocephalus molodoensis sp. nov., are described from the Amginian Stage of the Middle Cambrian of the Siberian Platform. They were found in the middle part of the Kuonamka Formation in sections on the Molodo and Muna rivers.

New assemblages of skeletal fossils chemically extracted from carbonates of the Cambrian Stage 2-Drumian Stage are reported from the lower reaches of the Lena River as well as from the Khorbusuonka, Malaya Kuonamka, and Bol'shaya Kuonamka rivers in northern part of the Siberian Platform. The fauna studied with scanning electron microscopy includes brachiopods, molluscs, hyoliths, halkieriids, chancelloriids, tommotiids, lobopodians, palaeoscolecidans, bradoriids, echinoderms, anabaritids, hyolithelminths, and sponges showing similarity to previously described fossil assemblages from Siberia, Laurentia, and Gondwana. The material includes emended descriptions of Halkieria proboscidea, Hadimopanella knappologica, Archaeopetasus typicus, and first descriptions of Hadimopanella foveata Kouchinsky sp. nov. and Archaeopetasus pachybasalis Kouchinsky sp. nov. Affinity of Archaeopetasus to chancelloriids is suggested. Finding of an in-place operculum in a planispiral shell of Michniakia minuta enables reinterpretation of this form as a hyolith, not a mollusc. The cambroclavids Cambroclavus sp. and Zhijinites clavus and the earliest echinoderms belonging to the Rhombifera and Ctenocystoidea are reported respectively from the lower Botoman stage and Botoman-Toyonian transitional beds, correlated with Cambrian Stage 4. Carbon isotopes are analysed from sections of the Chuskuna (upper Kessyusa Group), Erkeket, Kuonamka, Olenyok, Yunkyulyabit-Yuryakh, Tyuser and Sekten formations. A major part of the delta C-13 record is obtained from the Cambrian Stage 4-Drumian Stage strata which remain incompletely characterised by chemostratigraphy. The Lower Anomocarioides limbataeformis Carbon isotope Excursion (LACE) from the Drumian Stage of the Khorbusuonka River is introduced herein. New chemostratigraphic data are used for regional and global correlation and facilitate study of the evolutionary development of animals and faunas through the "Cambrian explosion".

––In this paper we present a stratigraphic scheme for the subdivision and correlation of the Cambrian deposits in the south of the cis-Yenisei area of West Siberia, which was adopted as a current scheme by the decision of the Interdepartmental Stratigraphic Committee in 2018. This scheme is based on the data from stratigraphic test wells (Lemok-1, Averinskaya-150, Tyiskaya-1, Vostok-1, Vostok-3, Vostok-4, etс.). In the study area, two structure-facies zones were identified: Kas (Lemok-1, Averinskaya-150, Tyiskaya-1, Vostok-4, and Eloguiskaya-1 wells), where sedimentary complexes accumulated in a salt subbasin, and Ket’ (Vostok-1 and Vostok-3 wells) with the deposition in an open sea basin. The boundary between these structure-facies zones is drawn along the inferred N–S-trending barrier reef zone. The rubrication in this paper is compiled in accordance with the requirements of the Stratigraphic Code of Russia for explanatory notes for regional stratigraphic schemes. Local stratigraphic subdivisions (formations, strata) are described and compared with the adjacent Turukhansk–Irkutsk–Olekma facies region of the Siberian Platform.

—We studied the middle Cambrian unit of the Kuonamka Formation section on the Kyulenke River (Siberian Platform) and performed its biostratigraphic subdivision based on trilobites. The middle Cambrian section has intervals corresponding to the regional zones of the Amginian Stage. Six levels with mass accumulation of fauna remains have been identified: Two levels are located within the Ovatoryctocara Zone; the third level is at the boundary between the Ovatoryctocara and Kounamkites zones; the fourth layer is confined to the roof of the Triplagnostus gibbus Zone; and the fifth and sixth levels are located within the Tomagnostus fissus–Paradoxides sacheri Zone. The composition of rocks and bitumens of their organic matter (OM) has been studied, including the geochemical specifics of the mineral components of rocks (iron, sulfur, and CO2) and of saturated hydrocarbons of bitumens as well as noncarbonate carbon isotopes in the OM. It has been established that the OM sedimentation took place under normal aeration of the sea basin waters, without hydrogen sulfide contamination of the bottom waters. The intensity of chemical and biochemical transformations of mineral and organic components during diagenesis was controlled by the contents of organic carbon and sulfate ion, the activity of the anaerobic prokaryote community, and the rate of sediment mineralization. We have also established relationships between the content of organic carbon in potentially oil source rocks and the contents of iron oxide, total sulfur, and sulfide and sulfate sulfur as well as the ratios of saturated hydrocarbons. The alternation of highly carbonaceous black shales and carbonaceous rocks is apparently due to a change in the composition of biologic communities of microorganisms (sources of hydrocarbon biomarkers) and in the intensity of OM transformation during diagenesis. We assume that the OM transformation included sulfate reduction and dealkylation of high-molecular steroids in the unconsolidated OM-enriched marine sediments with the participation of bacteria. The intensity of these processes depended on the mass of the primary OM, the amount of sulfate ion, and, hence, the pH and Eh of the medium.

—We present a model of the stratigraphic and lateral distribution of Cambrian deposits in the Vilyui hemisyneclise, based on an analysis of drilling data and interpretation of seismic data. The study shows a series of formations and sequences penetrated by wells (Syugdzher saddle, Khorgochum monocline, Ygyatta depression, Tyukyan–Chybyda monocline, Arbai–Sinyaya megaswell, etc.). In the areas where the Cambrian was not penetrated by wells, the distribution of Cambrian deposit was inferred based on the available seismic data. The distribution of the Kuonamka Horizon formed by Cambrian organic-rich rocks is characterized in detail. These are the Kumakh and Sinyaya–Kutorgina sequences and the Inikan and Kuonamka formations. It has been found that the Kuonamka Horizon was deposited during two stages, Botomian and Toyonian–early Mayan. The horizon is overlain by younger deposits of the Mayan Stage, with characteristic cross-bedding structures. Schemes of facies zoning of the Cambrian for Botomian, Toyonian–early Mayan, and middle Mayan times were constructed based on the most recent geological and geophysical understanding of the Vilyui hemisyneclise.

Строение кембрийских отложений вилюйской гемисинеклизы по результатам комплексного анализа данных бурения и сейсморазведкиГубин И. А., Конторович А

—Based on the materials collected by L.N. Repina in the southern Hövsgöl area (Mongolia) in 1986–1988, we describe three sections and identify lower Cambrian trilobites. The sections of Mt. Hurtel Harna and along the Ujigin Gol River were studied earlier. We consider trilobites that have been found in these sections for the first time: Redlihia zharkovi, Lermontoviella shanganica, Erbia granulosa, Kootenia siberica, and Parapoulsenia lata. The section along the ravine of the Zuun-Shuvuutyn-Sair Brook and the findings of trilobites in it are described for the first time. The found new trilobites make it possible to correlate the coeval lower Cambrian strata in the southern Hövsgöl area, Altai–Sayan folded area, and western Siberian Platform and refine the age of the certain parts of the Egyin Gol, Ukhaa Tolgoi, and Ujigin Gol formations.

Tommotiida finds from the Lower Cambrian of the Khairkhan Section located within the Central Tuva trough were characterized for the first time. The assemblages of small shelly fossils are represented by species of the genera typical for the Upper Atdabanian age, such as Tannuolina, Kelanella, Lugoviella, and Microdictyon. Sclerites of four different morphotypes were identified for the Lugoviella ojmuranica species.

This paper describes for the first time the entire Cambrian skeletal problematics from the parametric well Vostok-1 (Tomsk oblast, eastern part of the West Siberian Plate) found in the Lower Cambrian Churbiga Formation, Middle Cambrian Pudzhelga Formation, and Upper Cambrian Kondes and Shedelga formations. The investigation has made it possible to detail the biostratigraphic division of the Lower Cambrian in the studied well using the small shelly fossils and to reveal confinement of the main findings of problematic skeletal remains to the shallow carbonate shelf settings.

We present new magnetostratigraphic results obtained for the Drumian stage (504.5–500.5 Ma; Epoch 3/Middle Cambrian) from the Khorbusuonka sedimentary section in northeastern Siberia. They complement previous data that did not allow the determination of a reliable estimate of the geomagnetic reversal frequency during this time. Magnetization of the samples is carried by a mixture of magnetite and hematite in various proportions. Thermal demagnetization makes it possible to distinguish two magnetization components. The low unblocking temperature (<350°C) component has a steep inclination and likely originates from remagnetization in a recent field. At higher temperatures, the magnetization isolated possesses the two polarities. Its direction is usually well determined; however, for a noticeable set of samples, a strong overlap between the demagnetization spectra of the two components prevents the determination of reliable directions, although their polarities are well established. The directions from 437 samples define a sequence of 78 magnetic polarity intervals, 22 of which are observed in a single sample. Biostratigraphic data available from the Khorbusuonka section indicate that the duration of the studied section is ∼3 Myr. A geomagnetic reversal frequency of 26 reversals per Myr is therefore estimated for the Drumian, reduced to 15 reversals per Myr if only the polarity intervals defined by at least two consecutive samples are retained. This is an extreme reversal rate, similar to that reported for the Late Ediacaran (late Precambrian), ∼50 Myr earlier, and proposed to be potentially linked to a late nucleation of the inner core. The reversal frequency appears to have drastically dropped for ∼3–4 Myr from a value probably >20 reversals per Myr during the Drumian to ∼1.5 reversals per Myr during the Furongian/Upper Cambrian. Such a sharp decrease is consistent with a transition at a ∼1-Myr timescale, probably caused by threshold effects in core processes, between two geodynamo modes, one characterized by reversals occurring at frequencies ranging from 1 to 5 reversals per Myr, and the other marked by hyperactivity of the reversing process, with reversal rates >15 reversals per Myr.

The Vendian–Cambrian transitional strata of the Igarka Uplift (northwestern Siberian Platform), originally erected as the Sukharikha Formation, are one of the key objects revealing evolution of marine ecosystems in the late Vendian. Herein we describe dwelling burrows Skolithos and Arenicolites from dolostones in the middle Sukharikha Formation (Nemakit-Daldynian Regional Stage). High density and local distribution of these burrows in the Sukharikha Formation demonstrate that the terminal Vendian shallow-marine sediments became occupied by vertical-burrowing benthic organisms, mirrored in the geological record as an archetypical Phanerozoic ichnoassemblage ( Skolithos ichnofacies).