Home – Home – Jornals – Russian Geology and Geophysics 2010 number 1

The overall jump in global demand for gas, and especially oil, gives rise to particular concern regarding mankind’s energy future. In the middle and late 21st century, the crucial role in securing oil and gas supply of mankind will be played by sedimentary basins in the Arctic Ocean deep-water area, including those of the continental shelf in Russia’s Arctic seas. There is a 0.90 probability that the initial in-place resources of hydrocarbons in the Arctic Ocean will be greater than 90 Btoe. The estimates predict the rise of oil and gas industries on the Arctic shelves in the near future.

Research on sedimentogenesis and geochemistry of the Arctic Ocean over the last 10–20 years has allowed direct (in situ) studies to be made for all types of sedimentary matter that mix together and form the bottom deposit. Contrary to common knowledge, river sediment turned out to be insignificant; instead, more important is the dispersed sedimentary matter (suspension) from the atmosphere, cryosphere (snow, ice), marine water, riverine water, biosphere (plankton and benthos), and anthroposphere (all types of pollutants), supplemented by the endogenic mater supplied from spreading zone of the Gakkel Ridge. The mixture is dominated by sedimentary material discharged from sea ice; hence, this type of sedimentogenesis is referred to as the ice-rafted marine sedimentogenesis.
Application of new methods and tools (including satellites, remote hydrooptical, hydrophysical, and hydroacoustic survey, etc.) and in situ analyses produced measurements of content, composition, and characteristics of all types of dispersed sedimentary matter, its fluxes (mg/m²/year), vectors of movement, and rates for different segments of the Arctic Ocean; observations were carried out continuously on different time scale, from hours–days to seasons and dozens of years. It is a new approach to the study of sedimentary matter that opens up a new possibility for a 4D quantitative sedimentology.

The large North Chukchi Basin in the northeastern Eurasian shelf is filled with up to 22 km of sediments, which is far thicker than filling a basin upon oceanic crust would require. The basin sedimentation began 380 Myr ago, and about 16 km of sediments have been deposited for the past 125 Myr, long after the oceanic crust would have completed its subsidence. This fact is in favor of the continental instead of oceanic crust origin. Rapid basin subsidence appears to be driven by a mechanism other than crustal stretching as the latter has no evidence over the greatest part of the basin area. The suggested basin formation model implies a transformation of gabbro into denser eclogite in the lower crust and related contraction of mafic rocks. To sustain consolidated crust beneath 22 km thick sediments, the layer of dense eclogites under the granitic layer must be at least ~25 km thick. The presence of basement flexures formed at several stages of the basin evolution indicates a considerable loss of lithospheric rigidity under the effect of fluid infiltration from small mantle plumes. The fluids catalyzed the eclogitization and thus increased the subsidence rate. Rapid subsidence apparently occurred in Barremian-Albian time, when the basin had accumulated up to 11.5 km of sediments. Besides the Early Cretaceous event, there were possibly several older events of rapid subsidence. This basin subsidence history, along with the evidence of steep lithospheric flexure, is a known feature of large petroleum basins. Therefore, the North Chukchi Basin may be expected to be an oil and gas producer.

The structure and geodynamic history of the northern Barents-Kara continental margin, which had formed mostly by the latest Paleozoic, have been investigated using offshore geological and geophysical data and geological evidence from adjacent landmasses. In the context of the suggested model, the Saint Anna trough is interpreted as a boundary tectonic element between the Svalbard and Kara plates. Thus, the study focuses on a complex tectonic node with its structure having implications for the trough origin, as well as for the history of geodynamic relations among Arctic cratons and microplates. Trough structures of different ages in the area, including the northeastern East Barents trough and the St. Anna trough, appear to be a zone of triple or T-shaped junction. The reported reconstruction of the trough system history since the Middle Paleozoic shows that the St. Anna trough joined the East-Barents system in the Late Permian-Triassic to become its new segment extending the system to the north.

In the northern and northeastern Siberian Platform, within the Anabar and Olenek zones, there are a number of hypergene bitumen accumulations (fields) and natural bitumen seeps, whose total resources are estimated at >5 bln tons. Bitumen fields are confined to a wide stratigraphic range from Precambrian to Mesozoic. A detailed geochemical study was performed for bitumens of the largest Olenek field, whose naphthides are localized mainly in Permian sandstones of deltaic and coast-marine genesis. Chromato-mass spectrometric analysis showed that normal alkanes are drastically reduced in the saturated fraction of the bitumens and most of terpanes are a homologous series of 25-norhopanes, which evidences the intense bacterial degradation of hydrocarbon pools.
Identification of bicyclic sesquiterpenes, tetracyclic onocerane, and other biomarkers testifies that the organic matter of source rocks was rich in higher-plants remains. The concentrations of steranes are low, whereas those of earlier unknown 8-14-secosteranes are rather high. The set of geochemical data on the Permian bitumens of the Olenek field, including the isotopic characteristics of carbon (δ¹³C of –25.8 to –31.3 ‰), suggests that the coeval oil source rocks of the passive continental margin (at the place of the present-day Verkhoyansk fold belt) were the main source of hydrocarbons for the field.
Assessment of oil and gas resources, including giant bitumen pools, and their exploration in the framework of “The fundamentals of Russian state policy in Arctic up to 2020” have become a top-priority problem. The refining products of petroleum might be an economically feasible raw material in the eastern Russian Arctic sector to be supplied via the Northern Sea Route.

Natural gas hydrate deposits have been estimated to store about 10% of gas in the hydrate form (even with regard to a higher concentration of gas in hydrates), proceeding from the known ratio of dissolved-to-deposited gas. This high percentage is largely due to the fact that the buffer factor in natural gas hydrate deposits is lower than that for free gas because of less diverse structural conditions for gas accumulation. Therefore, the available appraisal of world resources of hydrated gas needs a revision.
Hydrates in rocks are either syngenetic or epigenetic. Syngenetic hydrates originate from free or dissolved gas which was present in rocks in situ at the time when PT -conditions became favorable for gas hydrate formation. Epigenetic hydrates are derived from gas which came by migration into rocks with their PT -conditions corresponding to formation of gas hydrate.
In addition to the optimum PT -conditions and water salinity, economic gas hydrate accumulation requires sustained supply of natural gas into a specific zone of gas hydrate formation. This condition is feasible only in the case of vertical migration of natural gas along faults, fractured zones, and lithologic windows, or, less often, as a result of lateral migration.
Of practical importance are only the gas hydrate deposits produced by vertical or lateral gas migration.

Based on geomorphological, lithological, and facies characteristics of the East Arctic continental margin, we studied the main factors controlling the Late Cenozoic supply of organic matter (OM) to the bottom sediments of the rises of the central Arctic Ocean. Complex analysis of dispersed OM in the samples taken during the expeditions of the R/V Akademik Fedorov in 2000 and 2005 showed a significant difference between the sediments of the Lomonosov Ridge and Mendeleev Rise. The bottom sediments of the latter are strongly transformed and lack terrigenous components, as evidenced from the main geochemical characteristics (contents of C_org, C_carb, N_org, bitumens, and humic acids) and the composition and distribution of hydrocarbon molecular markers (alkanes, saturated and aromatic cyclanes). The obtained data evidence that ancient sedimentary rocks containing genetically uniform deeply transformed (up to mesocatagenesis) OM played a significant role in the formation of the Pleistocene-Holocene sediments of the axial part of the Mendeleev Rise.

The paper concerns issues of geology and metallogeny of the Russian Arctic, namely, limits of the Russian oceanic Arctic in the context of the continental origin of territories under jurisdictional dispute; geology and tectonic history of the region; distribution of mineral deposits; outlook for diamond, PGE, Ni, rare metals, gold, and bauxite resources development.
Advanced diamond exploration and development can be expected proceeding fr om geology of new potentially diamondiferous areas, the Phanerozoic history and composition of lithospheric mantle beneath the Siberian craton, which were controlled by the Siberian superplume at the Permian–Triassic boundary, and from new exploration approaches adapted to the prospecting conditions of Arctic Siberia.
According to the available knowledge of Ni and PGE mineralization in the Noril’sk region, it is reasonable to develop depleted ores and tailings (mining dumps at the Noril’sk and Talnakh deposits). However, the key solution consists in new large discoveries within the Dzheltula and Kharaelakh volcanic and plutonic complexes.
Gold production enhancement may be associated with black shale-hosted Au-As mineralization in the northeastern Russian Arctic, but the problem is in the lack of efficient and environmentally safe dressing technologies for these ores.
Most of rare metals in the area (Nb, Sc, Y, and other elements) are stored in the giant Tomtor field, which has a complex structure and history. A special technology designed for the Tomtor ores ensures more than 60% extraction of ore components.
Good prospects for the bauxite potential are expected from the Timan district, wh ere bauxite may occur in Vendian and Early Carboniferous formations.

The metallogeny of the Russian Arctic zone, with a high potential for U, platinum-group metals, Au, Sn, trace elements, etc., in its different sectors, has been controlled by the type of early continental structures and by the uniform Meso-Cenozoic evolution of the area. The suggested reasonable development strategy is to conserve and further develop the existing mining districts associated with known large fields and to discover new lode (U, Au, etc.) and placer deposits. It is important to provide scientific background and environmental monitoring in the area at the stages of mineral prediction, exploration, and development.

This paper reports new petrographic and mineralogical data on the Manchary kimberlite pipe, which was discovered south of Yakutsk (Central Yakutia) in 2007–2008, 100 km. The pipe breaks through the Upper Cambrian carbonate deposits and is overlain by Jurassic terrigenous rock masses about 100 m thick. It is composed of greenish-gray kimberlite breccia with a serpentine-micaceous cement of massive structure. The porphyry texture of kimberlite is due to the presence of olivine, phlogopite, and picroilmenite phenocrysts. The SiO₂ and Al₂O₃ contents of the groundmass are indicative of typical noncontaminated kimberlites. The groundmass has a significant content of ore minerals: Fe- and Cr-spinels, perovskite, magnetite, and, less commonly, magnesian Cr-magnetite. Pyropes occur in kimberlites as sharp-edged fragments and show uneven distribution. Chemically, they belong to lherzolite, wehrlite, or nondiamondiferous dunite–harzburgite parageneses. Garnets corresponding to lherzolites of anomalous composition make up 8%; this is close to the garnet content of Middle Paleozoic kimberlites from the Yakutian kimberlite province. The pyropes from the new pipe are compositionally similar to those from diamond-poor Middle Paleozoic kimberlites in the north of the Yakutian diamondiferous province. Chemically, pyropes from the Manchary pipe and those from the modern alluvium of the Kengkeme and Chakyya Rivers differ substantially. Consequently, the rocks of the pipe could not be a source of pyropes for this alluvium. They probably occurred from other sources. This fact, along with numerous “pipelike” geophysical anomalies, suggest the existence of a new kimberlite field in Central Yakutia.

Large diamond placers have been discovered in a Rhaetian basal horizon (Upper Triassic) in the north of the Sakha Republic (Yakutia) in the drainage areas of the Eekit, Nikabyt, Kelimyar, and Bur Rivers. The found diamonds and kimberlite indicator minerals are completely similar in typomorphic features to those from Carnian basal horizons but, in contrast to them, are well sorted, and pyropes show features of mechanical wear. Analysis of the geologic evolution of the study area, morphology of diamonds and indicator minerals, and composition of the latter showed that the Rhaetian sediments resulted from the erosion of Carnian placers.

Seismic surveys have been applied to investigate the structure of frozen ground, identify and contour natural and man-caused unfrozen layers in permafrost (taliks), constrain the position of the permafrost table in the Arctic inner shelf, and study the related coastal stability. They are the classic methods common in shallow seismic exploration and new techniques specially designed at the Institute of Earth’s Cryosphere (Tyumen’) for different wave components. The joint use of compressional and shear waves provides a higher-quality interpretation of seismic data in permafrost applications. In the case of a single wave component, shear waves are advantageous over P waves.

The paper concerns urgent problems of resources development in the Arctic shelf. A specially designed technology with the use of a coolant is suggested for winter mining at shelf deposits. The idea of the new technology stems from the concept of negative settling velocity of buoyant particles, which has been investigated in laboratory tests.