Проведенные исследования и анализ опубликованных данных нацелены на совершенствование высокоразрешающего биостратиграфического расчленения верхней юры и нижнего мела эталонного разреза на п-ове Нордвик, Анабарский залив, море Лаптевых. Это позволило установить в разрезе последовательности из 13 биостратонов по фораминиферам, 9 биостратонов по диноцистам и 8 с палинофлорой в ранге зон и слоев. Полученные новые данные дали возможность обосновать стратиграфическую непрерывность этого разреза в интервале нижнего и средневолжского подъярусов, где ранее предполагался крупный стратиграфический перерыв. Установленные зональные подразделения имеют разный корреляционный потенциал. Рассмотрены разные версии расчленения разреза по аммонитам и обоснована используемая шкала. По кальцисферам/известковым диноцистам выявлен реперный уровень, позволяющий осуществлять глобальные корреляции и увязывать приграничные толщи юры и мела Тетиса и арктических регионов. Обсуждено магнитостратиграфическое расчленение изученного разреза и его сопоставление с тетическими регионами. Показано, что кривая вариаций δ13Cорг в верхней юре и нижней части валанжина отражает фациальные изменения и с учетом биостратиграфических данных может служить инструментом для корреляций в разных регионах Северного полушария. Для верхневолжского подъяруса и бореального берриаса установлена цикличность изменений изотопного состава углерода. В исследованном разрезе определено распределение значений геохимических параметров (Сорг, δ13Cорг и водородного индекса), показана геохимическая стратификация разреза и вариации породообразующих оксидов. В основании паксинской свиты (верхневолжский подъярус) установлена резкая смена значений геохимических параметров. Определен интервал распространения «подповерхностного максимума хлорофилла». Проведенные исследования показывают, что высокие значения Сорг с легким изотопным составом первого диастеренового геохимического подгоризонта формировались за счет высокой биопродуктивности фитопланктона и накопления органического вещества в благоприятных для его сохранности восстановительных условиях. Анализ содержания основных породообразующих оксидов в изученных породах позволил выявить определенные вариации химического состава изученных отложений, отражающие изменения минералого-петрографических характеристик. The goal of this study was to improve the high-resolution biostratigraphy of the Upper Jurassic and Lower Cretaceous in the type section on the Nordvik Peninsula, Anabar Bay, Laptev Sea. The results were used to identify a succession of 13 foraminiferal biostratigraphic units, 9 dinocyst units, and 8 palynofloral biostratigraphic units in the rank of zones and local zones. Based on new data, the stratigraphic continuity of this section is proved for the Lower and Middle Volgian, where a major stratigraphic hiatus was previously assumed. The established zones have variable correlation potential. Different versions of the subdivision of the section based on ammonites are discussed and the proposed scale is justified. A reference level based on calcispheres/calcareous dinocysts is defined providing global correlations and calibration of beds near Jurassic-Cretaceous boundary in the Tethyan and Arctic regions. The magnetostratigraphic subdivision of the studied section and its comparison with the Tethyan regions are discussed. Together with biostratigraphic data, the proposed δ13Corg curve in the Upper Jurassic and lower part of the Valanginian can be a tool for detailed correlations in different regions of the Northern Hemisphere. The cyclicity of carbon isotope composition in the Upper Volgian and Boreal Berriasian and isotope events in the Volgian and Lower Valanginian are determined within the Arctic region. The distribution of geochemical parameters (Corg, δ13Corg and hydrogen index) is determined in studied section, geochemical stratification of the section and variations in major oxide compositions are demonstrated. A sharp change in geochemical parameters is identified at the base of the Paksa Formation (Upper Volgian). The distribution interval of the “subsurface chlorophyll maximum” is determined. The study shows that high concentrations of isotopically light organic carbon in the first diasterene geochemical subhorizon were caused by high phytoplankton productivity and were deposited under reducing conditions favorable for preservation of organic matter. The analysis of major oxide compositions of the studied rocks revealed that variations in the chemical composition of the studied rocks reflect changes in their mineralogy and petrography.

goal of this study was to improve the high-resolution biostratigraphy of the Upper Jurassic and Lower Cretaceous in the type section on the Nordvik Peninsula, Anabar Bay, Laptev Sea. The results were used to identify a succession of 13 foraminiferal biostratigraphic units, 9 dinocyst units, and 8 palynofloral biostratigraphic units in the rank of zones and local zones. Based on new data, the stratigraphic continuity of this section is proved for the Lower and Middle Volgian, where a major stratigraphic hiatus was previously assumed. The established zones have variable correlation potential. Different versions of the subdivision of the section based on ammonites are discussed and the proposed scale is justified. A reference level based on calcispheres/calcareous dinocysts is defined providing global correlations and calibration of beds near Jurassic-Cretaceous boundary in the Tethyan and Arctic regions. The magnetostratigraphic subdivision of the studied section and its comparison with the Tethyan regions are discussed. Together with biostratigraphic data, the proposed delta 13Corg curve in the Upper Jurassic and lower part of the Valanginian can be a tool for detailed correlations in different regions of the Northern Hemisphere. The cyclicity of carbon isotope composition in the Upper Volgian and Boreal Berriasian and isotope events in the Volgian and Lower Valanginian are determined within the Arctic region. The distribution of geochemical parameters (Corg, delta 13Corg and hydrogen index) is determined in studied section, geochemical stratification of the section and variations in major oxide compositions are demonstrated. A sharp change in geochemical parameters is identified at the base of the Paksa Formation (Upper Volgian). The distribution interval of the "subsurface chlorophyll maximum" is determined. The study shows that high concentrations of isotopically light organic carbon in the first diasterene geochemical subhorizon were caused by high phytoplankton productivity and were deposited under reducing conditions favorable for preservation of organic matter. The analysis of major oxide compositions of the studied rocks revealed that variations in the chemical composition of the studied rocks reflect changes in their mineralogy and petrography.

—Concepts of the stratigraphy of the coastal and shallow-sea sections of the uppermost Middle Jurassic and Lower Cretaceous, exposed on the right bank of the Anabar River, have radically changed many times. The performed study and analysis of the published data are aimed at refining the bio- and lithostratigraphic subdivision of the section, substantiating its stratigraphic completeness, and describing the identified stratigraphic units in detail. Comprehensive biostratigraphic studies of the uppermost Bathonian — the lowermost Boreal Berriasian reveal a sequence of nine biostratigraphic units with dinocysts and palynoflora in the ranks of zones and local zones. Some of the palynological biostratigraphic units have been identified for the first time. Foraminiferal assemblages of the boreal standard zones are recorded in the sections under study. The obtained biostratigraphic data and analysis of all known ammonite occurrences make it possible to demonstrate the stratigraphic continuity of the section in the Anabar River region, despite the reduced thickness of the stratigraphic units. The stratigraphic position of the boundary between the Sodiemykha and Buolkalakh formations is accurately defined. According to the interpretation proposed, the basal horizon of the Buolkalakh Formation is associated with a beginning of a new major sedimentation stage in the late Oxfordian–early Kimmeridgian, identified as the lower boundary of lithostratigraphic units of different ranks throughout the entire Arctic Region and partially in the Boreal Region. The lithogeochemical parameters of the studied formations are obtained for the first time. The content of Corg in the studied samples does not exceed its Clarke values, and the pyrolytic parameter Tmax indicates that the organic matter is immature and the petroleum potential is low. The considered organic matter of the rocks is characterized by a heavy isotope composition of carbon, suggesting its mostly terrigenous genesis.

Представления о стратиграфии прибрежнои мелководно-морских разрезов верхов средней юры и низов мела, вскрытых на правобережье р. Анабар неоднократно кардинально изменялись. Проведенные исследования и анализ опубликованных данных нацелены на уточнение биои литостратиграфического расчленения разреза, обоснование его стратиграфической полноты, детальное и комплексное описание выделенных стратонов. Комплексные биостратиграфические исследования разреза верхов бата – низов бореального берриаса позволили выявить последовательности из девяти биостратонов в ранге зон и слоев с диноцистами и с палинофлорой. Часть палинологических биостратонов установлена впервые. В исследованных разрезах прослежены фораминиферовые комплексы зон бореального стандарта. Полученные новые биостратиграфические данные и анализ всех известных находок аммонитов позволили обосновать стратиграфическую непрерывность Анабарского разреза, несмотря на сокращенную мощность стратиграфических подразделений. Уточнено стратиграфическое положение границы между содиемыхаинской и буолкалахской свитами. В предлагаемой интерпретации базальный горизонт буолкалахской свиты фиксирует новый крупный этап осадконакопления в конце оксфорда – начале кимериджа, прослеживаемый как нижняя граница разноранговых литостратонов по всему Арктическому и частично Бореальному регионам. Впервые толща охарактризована литогеохимическими параметрами. Содержание Сорг в исследованных образцах свит не превышает его кларковых значений, а пиролитический показатель Tmax свидетельствует о низкой зрелости органического вещества и невысоком нефтегазогенерационном потенциале. Исследованное органическое вещество пород характеризуется тяжелым изотопным составом углерода, что позволяет предполагать его преимущественно террагенный генотип.

The Volgian-Valanginian succession of shallow-water deposits from the Olenek section(Anabar-Lena region,Arctic Siberia)has been studied by sedimentological and palaeontological methods.High-resolution biostratigraphy of studied interval is based on the ammonites,foraminifers,marine and terrestrial palynomorphs.Foraminiferal and palynological zones have important regional implications providing well-constrained bios-tratigraphy of the Anabar-Lena region.Sedimentological studies together with ecological analysis of the associations of microbenthos,microphytoplankton and terrestrial palynomorphs allow the palaeoenvironmental reconstructions for the marginal area of the Anabar-Lena palaeosea and coastal land areas.

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

The Volgian-Valanginian shallow-water deposits from the Olenek key section (Anabar-Lena region, Arctic Siberia) were studied by sedimentological, palaeontological and geochemical methods. High-resolution biostratigraphy of the studied interval is based on ammonites, foraminifera, and marine and terrestrial palynomorphs. An almost complete succession of ammonite zones provides biostratigraphic control for the upper part of the Buolkalakh Formation and the boundary between the Volgian and Boreal Berriasian stages. Foraminiferal and palynological zones have important regional implications providing well-constrained biostratigraphy of the Anabar-Lena region. Several levels important for interregional correlations are defined in the Volgian and Berriasian on the basis of taxonomic changes in microfossil assemblages as well as lowest and highest occurrences of indicative taxa. Combined sedimentological, geochemical studies and ecological analysis of microfossil associations (foraminifera, marine and terrestrial palynomoprhs) allowed the palaeoenvironmental reconstructions for the marginal area of the Anabar-Lena palaeosea and coastal land areas.

Investigation of the Upper Callovian to Lower Kimmeridgian microfossils from the Makar'yev reference section (Unzha River, East European Platform) has been carried out. The section is characterized by ammonite debris and abundant associations of benthic and planktic foraminifers. It is a perfect object for stratigraphic and paleoecological researches. The biostratigraphic distribution of foraminifers from the Makar'yev section allows one to identify standard foraminifera zones of the East European Platform, as well as to upgrade some of them. The analysis of vertical and lateral ammonites and foraminiferal distribution, completed with lithostratigraphy, has precised the stratigraphic volume and position of boundaries of several Ethological units.An improved stratigraphic scheme for the Kostroma area of the Moscow Depression is proposed. Analysis of the composition, structure, and dynamic changes of the foraminiferal assemblages has been performed. The morphofunctional analysis of foraminiferal genera has for the first time identified how foraminiferal morphogroups differing in their life style and feeding strategy varied with short-term paleoenvironmental changes. These morphogroup changes allow establishing four ecostratigraphic levels. These paleoecological data have been calibrated along with geochemical factors. They have shown a crisis of foraminiferal association during the Late Oxfordian and Early Kimmeridgian. A similar crisis has also been discovered in the north of Siberia, which may be an argument for its global distribution. The analysis of the taxonomic composition and the density of foraminiferal associations, in parallel with the structure of the association, has revealed a succession of transgressive and regressive events during the Late Callovian-Early Kimmeridgian. It allows the typification of each assemblage in relation with each event and underlines the occurrence of second-order sea-level fluctuations (middle part of the Middle Oxfordian and the earliest Kimmeridgian). (C) 2016, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.

Three new species of Saracenaria from the Lower Cretaceous of the Ust’-Yenisei District are described. S. gerkei sp. nov. is recorded in the Valanginella tatarica, Recurvoides obskiensis Foraminiferal Zone (KF2, upper boreal Berriasian–Valanginian). S. vologochanensis sp. nov. and S. pjasinensis sp. nov. are characteristic of assemblages of the beds with Cribrostomoides infracretaceous, Cribrostomoides sinuosus (KF4, terminal Lower Valanginian–basal Hauterivian). Detailed comparisons of new species with other most closely similar morphotypes are provided.

Micropaleontologic analysis of Early Cretaceous deposits of South-east part of Ust’-Yenisei region results in the revision of foraminifer taxonomical composition. Microbenthos communities of the Upper Berriasian, Valanginian and Lower Hauterivian are reconstructed, and the succession bionomical zones are revealed.

This paper is concerned with study and comparison of Berriasian, Valanginian, and lower Hauterivian foraminifer associations in northeastern West Siberia. Micropaleontological analysis of the Lower Cretaceous deposits of the Ust'-Yenisei region has given an insight into the taxonomic composition of microfossils in the studied sections. Analysis of the stratigraphic occurrence of foraminifers has revealed four successive biostratons in zones and beds. Communities of Berriasian, Valanginian, and earliest Hauterivian microbenthos are reconstructed, the regularities of their evolution are established, and the succession of bionomic zones is determined.

The micropaleontologicalanalysis of Upper Bathonian Valanginiandeposits of the Ust-Yeniseiand Yamal regions of West Siberia allowed a detailed biostratigraphic subdivision and correlation of the studied sections, a revision of specific zone assemblages.

Recent integrated studies of Mesozoic reference sections of the Anabar area (northern Middle Siberia, Laptev Sea coast) and the reinterpretation of all the previous data on a modern stratigraphic basis permit considerable improvement of the bio- and lithostratigraphic division and facies zoning of Jurassic and Cretaceous sediments in the region. Analysis of abundant paleontological data allows the development or considerable improvement of zonal scales for ammonites, belemnites, bivalves, foraminifers, ostracods, dinocysts, and terrestrial palynomorphs from several Jurassic and Cretaceous intervals. All the zonal scales have been calibrated against one another and against regional ammonite scale. Reference levels of different scales useful for interregional correlation have been defined and substantiated based on the analysis of lateral distribution of fossils in different regions of the Northern Hemisphere. It provides the possibilities to propose and consider parallel zonal scales within the Boreal zonal standard for the Jurassic and Cretaceous periods. A combination of these scales forms an integrated biostratigraphic basis for a detailed division of Boreal-type sediments regardless of the place of their formation and for the comparison with the international stratigraphic standard as far as a possible use of a set of reference levels for correlation.