Kuonamka Formation Research Articles

Lithological and geochemical characteristics and sedimentary environments of the Cambrian high-carbon deposits in the east of the Siberian platform (Kyulenke river basin)

Relevance. The need to study high-carbon deposits as potential sources of hydrocarbons and ore minerals that can significantly increase the mineral resource of Russia. In addition, the analysis of lithological and geochemical features and the reconstruction of the sedimentation conditions of the Kuonamka Formation make it possible to more accurately judge the nature of the Lower and Middle Cambrian paleobasin in the east of the Siberian Platform. Aim. To identify lithological and geochemical features of the composition and determine the sedimentation environment of the Kuonamka Formation. Object. High-carbon deposits of the Kuonamka Formation uncovered by exploration wells on the eastern margin of the Mun arch of the Siberian platform in the Kulenke river basin. Methods. Lithological description of core material; mineralogical and petrographic analysis; X-ray diffraction, X-ray fluorescence and microelement analysis; determination of the content of sulfur and iron forms by wet chemistry; scanning electron microscopy using X-ray spectral microprobe; analysis of petrochemical modules. Results. It was established that the Kuonamka Formation in the studied sections has a consistent structure of four well-defined lithological-stratigraphic horizons. The composition of the deposits is predominantly mixed and is determined by variations in three main mineral groups: clay, carbonate and siliceous, in addition organic matter. The paper demonstrates different forms of organic matter confirming the mixed algal-bacterial genesis of the biocenosis of the Kuonamka basin. The revealed lithological features and lithochemical data indicate the accumulation of high-carbon deposits at a considerable distance from the drift sources in the depression zone of the open sea basin with weak circulation of bottom waters in anoxic conditions. The geochemical euxinic environment was dominant in carbonate-siliceous muds. Sedimentation occurred during one major transgressive-regressive sedimentation cycle being a typical sequence of filling a uncompensated deep depression.

Olenek–Anabar Composite Tectono-Sedimentary Element, northern East Siberia

Abstract The Olenek–Anabar Composite Tectono-Sedimentary Element (OLA CTSE) is located in the northern part of the Siberian Craton. Its structure and depositional history is controlled by two main tectonic events: (i) Mesoproterozoic rifting and (ii) Ediacaran–Cambrian (to Middle Devonian?) post-rift thermal subsidence. The sedimentary succession is mainly represented by Mesoproterozoic–Cambrian strata, including the black shales of the lower–middle Kuonamka Formation. The hydrocarbon potential of the OLA CTSE is defined by the presence of large superficial bitumen fields, anticlinal structures, large reefal build-ups and direct proximity to the potential source rock (Kuonamka Formation). A very scarce grid of seismic profiles and a lack of exploration wells limit the knowledge of the petroleum potential. The lack of seals and broad occurrences of faults, causing significant vertical permeability of sediment cover, and abundant occurrences of mafic and kimberlite magmatism are limiting factors with regard to the petroleum potential. Wells drilled during the Soviet era did not recover any commercial discoveries.

New Species of the Genus <i>Oryctocephalus</i> Walcott from the Middle Cambrian of the Siberian Platform

Two new species of trilobites of the Oryctocephalus Walcott, 1886 from the Amgan Stage of the Middle Cambrian of the Siberian Platform were described: Oryctocephalus doliformis sp. nov. and O. molodoensis sp. nov. wich were found in the middle part of the Kuonamka Formation in the Molodo and Muna Rivers sections.

Trilobites, Biostratigraphy, and Geochemistry of the Middle Cambrian Kuonamka Formation (Northeastern Siberian Platform, Kyulenke River)

Abstract —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.

THE STRUCTURE, COMPOSITION AND DEPOSITIONAL ENVIRONMENTS OF KUONAMKA FORMATION IN THE EAST OF ANABAR OIL-AND-GAS REGION

The structural features, lithological composition and sedimentation conditions of the Kuonamka Formation were identified in the analysis of core material uncovered by wells in the east of Anabar oil-and-gas region in the basin of the Kyulenke River. It was established that the studied highly carbonaceous rocks accumulated in deep-water conditions of the open sea in reducing, mainly euxinic environments.

STRUCTURAL CHARACTERISTICS OF VENDIAN-CAMBRIAN SEDIMENTS WITHIN THE NORTHTUNGUSKA OGR USING SEISMIC 2D DATA IN CONNECTION WITH PETROLEUM POTENTIAL

Complex interpretation of seismic and parametric drilling data is performed. The data for interpretation are obtained within the conjunction zone of the Kureyka syncline and the Anabar anteclise. As a result of complex interpretation the structural maps on the bottom of Vendian and the top of the Kuonamka formation are constructed. Map of the Vendian terrigenous complex was constructed. High prospects of oil and gas potential of the lower-middle Cambrian sediments are shown. Based on the analysis of logging data, core description and detailed correlation of time sections, the litho-acoustic models were compiled for two profiles crossing the barrier-reef system, and two-dimensional synthetic time sections were calculated. Obtained results confirm the correctness of the ideas about the internal structure of the Vendian-Cambrian complexes.

The Sukhana Sedimentary Basin, Siberian Platform: Source Rock Characterization and Direct Evidence of Oil and Gas Presence

Abstract —Despite the known large natural bitumen accumulations and oil seeps in several kimberlite pipes along the periphery of the Sukhana sedimentary basin, interpreted as direct evidence of petroleum potential, the basin still remains one of the least studied (by geological and geophysical methods) regions of the Siberian Platform. The platform cover of the basin is composed by Riphean, Vendian, and Cambrian clastic (terrigenous) and carbonate deposits reaching 5.5–6 km in thickness in the central part of the basin. The hydrogeological specifics of the basin is largely governed by its location within the northern geocryological zone (Olenek cryoartesian basin) and is expressed as a continuous distribution of permafrost aggraded into the permafrost zone of unique thickness. Direct indicators of ore and gas presence are the East Anabar, Central Olenek, and Siligir–Markha fields of natural bitumen and oil shows in kimberlite pipes of the Daldyn–Alakit region (Udachnaya pipe). The bituminous-carbonate sediments of the Khatyspyt Formation (Vendian, Ediacaran) and the highly carbonaceous carbonate–siliceous–shaly sediments of the Kuonamka Formation (lower–middle Cambrian) are the Sukhana source rock complexes. The geochemically substantiated genetic relationship between the natural bitumen deposits of the East Anabar field and the organic matter of the Vendian Khatyspyt Formation makes it possible to estimate the area of the spread of the latter far to the west, beyond the axial part of the basin. Gammacerane, inherited from the organic matter of the Khatyspyt Formation and ranking as well-preserved and most characteristic biomarker of these bitumens, provides a compelling evidence of their consanguinity. The bitumen and oil of kimberlite pipes in the south of the basin, in the area of reefs of the Siligir–Markha bar, are similar in all geochemical criteria to oils of the Nepa–Botuobiya anteclise. In particular, in primary geochemical characteristics (12- and 13-monomethylalkanes, unique secosteranes, identical carbon isotope composition, etc.) the oils of the Udachnaya pipe are identical to the Irelyakh oils (oil field in the Mirnyi arch). No accumulations of oil or natural bitumen genetically related to the highly carbonaceous Kuonamka Formation have been found within the basin. At the same time, “intraformational” shows of viscous oil, solid bitumen, and allochthonous bitumen (bitumen extracted with chloroform) were documented directly in the sections of the formation, which makes the sedimentary basin a very attractive target for “shale oil” exploration. As for the regional assessment of the petroleum potential of the entire basin, its axial part (Sukhana depression) complicated by local uplifts is of the greatest interest. Both the Khatyspyt and Kuonamka Formations are widespread there, with the thermal maturity of their organic matter corresponding to the oil window. In addition, the regional reservoirs at the Vendian–Cambrian boundary have good petrophysical properties on both the western and the eastern flanks of the basin.

Trilobites and biostratigraphy of the Kuonamka Formation, northern Siberian Platform (Olenek River)

A study of triobite distribution allowed a biostratigraphic subdivision of the Kuonamka Formation section exposed in the middle reaches of the Olenek River (18 km downstream of the village of Olenek). Through detailed description of the section, a biostratigraphic subdivision down to the level of biozones and faunal beds was performed. These are beds with Calodiscus–Triangulaspis annio, Delgadella ultima–Bergeroniellus expansus Zone, Lermontovia dzevanovskii–Neopagetina orbiculata Zone, Anabaraspis Zone, Cheiruroides arcticus– Pagetia horrida Zone, Kounamkites Zone, Triplagnostus gibbus Zone, and beds with Tomagnostus fissus–Paradoxides sacheri. These biostratigraphic subdivisions were correlated with regional zones of the Siberian Platform. The study also provides analysis of trilobite assemblages from the Lower/Middle Cambrian boundary interval, which was identified in the studied section and other previously described sections (Nekekit, Molodo, Boroulakh Rivers). In the studied section, the base of the Middle Cambrian is defined by the FAD of Cheiruroides arcticus, i.e., at the base of the Cheiruroides arcticus–Pagetia horrida Zone. This level correlates with a presumed lower boundary of Stage 5 of a new International Stratigraphic Chart for the Cambrian System.

Исследование состава газовой фазы, выделенной из горючих сланцев Куонамской формации различными способами

Исследование состава газовой фазы, выделенной из горючих сланцев Куонамской формации различными способами

Геохимия гетероатомных компонентов битумоидов куонамской свиты нижнего и среднего кембрия (северо-восток Сибирской платформы)

Геохимия гетероатомных компонентов битумоидов куонамской свиты нижнего и среднего кембрия (северо-восток Сибирской платформы)

New biostratigraphical constraints on the Lower and lower Middle Cambrian of the Kharaulakh Mountains (northeastern Siberian Platform, Chekurovka anticline)

The Cambrian section of the western limb of the Chekurovka anticline was studied, with layer-by-layer collection of animal fossils. This permitted us to refine the biostratigraphic division of this section. Four biostratigraphic units (beds) with small shelly fossils were identified: Lapworthella tortuosa, Lapworthella bella, Mobergella radiolata, and Rhombocorniculum cancellatum. They characterize most of the Tommotian and Atdabanian Stages of the Lower Cambrian. The Lower Tyuser Subformation and the Sekten Formation were constrained by small shelly fossils for the first time. Numerous trilobite finds helped to reveal intervals correlating with the Delgadella anabara–Nevadella and Judomia–Uktaspis (Prouktaspis) Regional Zones in the upper Atdabanian.The upper Sekten Formation (black shales) forms the Kuonamka Formation. Within this interval, the following trilobites were found: Triplagnostus gibbus, Tomagnostus sibiricus, Pseudanomocarina sp., Eodiscus oelandicus, Paradoxides sacheri, and Ptychagnostus aff. atavus. They are widespread in the vast territory of the eastern Siberian Platform, within the Kuonamka Formation.Also, Korobovia khorbosuonica, Charaulaspis postprimus, and Hebediscus convexus trilobites were observed, which had been found earlier in the Khorbosuonka River section (Olenek uplift). This permits a detailed correlation between these localities.Similarity was observed between Triangulaspis annio trilobites and young Charaulaspis. This casts doubt upon the fact that the first Triangulaspis annio finds in the northeastern Siberian Platform belonged to the upper Atdabanian.

A middle Cambrian fauna of skeletal fossils from the Kuonamka Formation, northern Siberia

An assemblage of mineralized skeletal fossils containing molluscs, hyoliths, chancelloriids, protoconodonts, lobopods, paleoscolecids, bradoriids, echinoderms and hexactinellid sponges is described from the middle Cambrian part of the Kuonamka Formation, exposed along the Malaya Kuonamka and Bol'shaya Kuonamka rivers, northern Siberian Platform. The sampled succession is attributed to the Kuonamkites and lower Tomagnostus fissus–Paradoxides sacheri biozones of the Amgan Stage of Siberia, correlated with Series 3, Stage 5—lower Drumian Stage of the IUGS chronostratigraphical scheme for the Cambrian. This work complements descriptions of molluscs from the same samples published by Gubanov et al. (2004) with additional material. It contains forms in common with coeval faunas from Australia, China, Western Gondwana, Avalonia, Laurentia and Baltica, increasing potential for global biostratigraphic correlation and understanding of palaeogeographic connections.

First record of dinocarida from Russia

A fragment of a relatively large (on the Cambrian scale) animal, apparently a dinocarid, was discovered in bituminous shale of the Middle Cambrian Kuonamka Formation of the Olenek River near the village Olenek in northeastern Siberia. The exact taxonomic position of the specimen cannot be determined because of to its incompleteness, but it does not seem to belong to any previously described dinocarid genus.

Kerogen from the Cambrian deposits of the Kuonamka Formation ( northeastern Siberian Platform)

Kerogens from the Lower and Middle Cambrian deposits of the Kuonamka Formation in the northeastern Siberian Platform have been analyzed by modern methods. We have determined the pyrolytic characteristics of insoluble organic matter and the contents of C, H, S, N, O, and the stable C isotope. The type and catagenesis of organic matter have been estimated, as well as the generating potential of oil source rocks. It has been found that the composition of kerogens taken from the Molodo River outcrops was affected by supergene processes and that the degree of their alteration is related to the organic content of rocks and their structure.

Lower-Middle Cambrian boundary in open shelf facies of the Siberian Platform

In the Early and Middle Cambrian (of traditional usage), three broad facies belts were developed over the Siberian Platform. The lithofacies belts comprise evaporitic-carbonate, reef-shoal, and open-marine environments. Trilobites assemblages are most diverse in the open-marine lithofacies (Judoma-Olenek facies), represented especially by the Kuonamka Formation, in the eastern part of the platform. Species, genera and families of trilobites gradually increased through the Middle-Cambrian boundary interval in the Kuonamka Formation. Protolenidae dominated in the time represented by the Lermontovia Zone. In strata assigned to the Anabaraspis Zone, the protolenids disappear, the paradoxidids appear, and the diversity of dorypygids increases. The number of trilobite families increases in the Oryctocara and Kounamkites zones. Well represented in the Kuonamka formation of the eastern Siberian Platform are three levels of trilobites that have potential for global correlation. They are the Oryctocephalus reticulatus (= O. indicus latus), Oryctocephalus indicus, and Ovatoryctocara granulatus levels. The Lower-Middle Cambrian boundary in the South China correlates to the lower part of the Kounamkites Zone of the Siberian Platform.

Middle Cambrian molluscs of ‘Australian’ aspect from northern Siberia

An assemblage of silicified helcionelloid molluscs is described from the Kuonamka Formation (Middle Cambrian Amgan Stage) of the Bol'shaya Kuonamka and Malaya Kuonamka rivers, northern Anabar Shield, northern Siberia. In addition to the new genera Kuonamkaella and Anabaroconus, the assemblage contains species of Yochelcionella, Eotebenna, Pseudomyona, and Protowenella. These latter genera were previously unknown from the Middle Cambrian of Siberia and indicate a strong affinity with coeval molluscan faunas from the Australian Middle Cambrian. The fauna provides evidence for close palaeogeographic links to East and West Gondwana, Baltica, and Laurentia during the Middle Cambrian, and facilitates biostratigraphic correlation between these crustal blocks.

The falling amplitude of carbon isotopic oscillations through the Lower to Middle Cambrian: northern Siberia data

Carbon and oxygen isotopes have been studied in Lower to Middle Cambrian fossiliferous carbonates from sections along the Malaya Kuonamka, Olenek, and Muna rivers of the Yudoma-Olenek facies belt, northern Siberian Platform. Marked temporal oscillations in delta 13C are recorded from shallow-water Nemakit-Daldynian to Atdabanian carbonates, as seen elsewhere on the platform. Rapid sea-level rise during the so-called "Sinsk event" led to starved-basin conditions from the middle Botomian (Bergeroniellus micmacciformis Zone) to late Amgan (Tomagnostus fissus Zone) and to deposition of organic-rich argillaceous carbonates of the Kuonamka Formation. Mayan carbonates were laid down during a phase of renewed and more rapid carbonate sedimentation, and relatively uniform delta 13C signatures fall from approx. +1.5omicron in the Anomocarioides limbataeformis Zone to near zero throughout the Lejopyge laevigata Zone. These results confirm that a long-term decline took place in maximal delta 13C values between the late Neoproterozoic and Middle Cambrian, accompanied by a dampening in the amplitude of shorter term oscillations. This was accompanied by a change from rift to drift patterns of crustal subsidence; from low to high sea levels; from an interior basin to outer platform locus for hydrocarbon source rocks; from rare to abundant metazoans in the biosphere; by the first major extinction in the Phanerozoic fossil record; and from "icehouse" to "greenhouse" conditions. We infer that factors leading to changes in the rate of carbon burial were amplified at times of low sea level, high climatic extremes, and a primitive biosphere (late Neoproterozoic), and dampened at times of high sea level, lower climatic variation, and a more advanced biosphere (Middle Cambrian).

'Orsten' type phosphatized soft-integument preservation and a new record from the Middle Cambrian Kuonamka Formation in Siberia

'Orsten' type phosphatized soft-integument preservation and a new record from the Middle Cambrian Kuonamka Formation in Siberia