No 6 (2019)

Sedimentary basins of the East Siberian sea and the Chukchi sea region and the adjacent area of Amerasia basin: seismic stratigraphy and stages of geological history
Nikishin A.M., Startseva K.F., Verzhbitsky V.E., Cloetingh S., Malyshev N.A., Petrov E.I., Posamentier H., Freiman S.I., Lineva M.D., Zhukov N.N.

The seismic stratigraphy scheme for the shelf basins of the East Siberian Sea and the Chukchi Sea region and the adjacent deep-water part of the Amerasia basin has been developed, and mega-sequences (or tectonostratigraphic units) with proposed age of 125–100, 100–80, 80–66, 66–56, 46–45, 45–34, 20–0 Ma are distinguished. Zhokhov foredeep basin of the Late Jurassic‒Neocomian age is distinguished between the New Siberia and De Long islands. Three main phases of rifting are identified on the shelves in the region with ages of 125–100, 66–56 and 45–37 Ma. The main phase of continental rifting occurred in the Podvodnikov and Toll basins 125–100 Ma. The typical clinoform accumulation of sediments occurred at the edge of the shelf 66–20 Ma. We identified three syntectonic epochs of the formation of clinoform complexes with ages of 66–45, 45–34 and 34–20 Ma. The phase of uplifting and compression in the region of Wrangel Island happened ≈66 Ma. The relatively monotonous tectonic setting with approximately the same thickness of the sedimentary cover began from 20 Ma.

Геотектоника. 2019;(6):3-26
Influence of the upper-mantle convective cell and related Pacific plate subduction on Arctic tectonics in the late Cretaceous–Cenozoic
Kononov M.V., Lobkovsky L.I.

The paper considers the history of the spreading of the Eurasian basin. The sharp deceleration of the spreading rate in the Eocene about 46 million years ago, which is fixed by the distribution of linear magnetic anomalies, is noted. That jump in velocity is clarified from the perspective of the geodynamic model but shouldn’t be explained by the northern motion of Greenland. The geodynamic processes of the Pacific subduction zone generate an upper mantle convective cell with return flow dragging the Arctic continental lithosphere in the direction of the Pacific subduction zone. The geodynamic mechanism is confirmed by seismic tomographic mantle sections of the northeastern margin of Asia and the numerical model of the upper mantle convection of the active continental margin. It is the activity of the upper mantle convective return cell, which is determined by the runoff volume and, ultimately, the speed and direction of the Kula plate and Pacific plate subduction vectors in the subduction zone, affects tectonics and kinematics of the plates of the Eurasian basin. In the Middle Cretaceous–Middle Eocene and for about 73 Ma the return cell has been active, since the Kula and Pacific plates move north and submerged orthogonally beneath the Central Arctic. After the Middle Eocene geodynamic reorganization about 47.5 million years ago, oceanic plates in the Pacific Ocean begin to move to the northwest. As a result, the transport of the oceanic Pacific Ocean lithospheric substance to the arctic convective return cell has practically ceased. After the restructuring, the spreading of the Eurasian basin slowed down about 46 million years ago to an ultra-slow regime. The main tectonic and geodynamic consequences of applying the proposed geodynamic model for the Arctic in the Late Cretaceous–Cenozoic are considered.

Геотектоника. 2019;(6):27-45
Fold-thrust deformations of the isl. New Siberia (Novosibirsky islands, Russia): age, morphology and genesis of structures
Golionko B.G., Basilyan A.E., Nikolsky P.A., Kostyleva V.V., Malyshev N.A., Verzhbitsky V.E., Obmetko V.V., Borodoulin A.A.

Detailed lithologic, stratigraphic and structural studies of fold-thrust structures were conducted on the island New Siberia. We have established, the jointly deformed complexes of the Upper Cretaceous–Middle Neopleistocene are overlapped by undeformed sediments of the Upper Neopleistocene. This fact confirms the completion of the deformation process at the end of the Middle Neopleistocene. An additional argument excluding the ancient age of dislocations is the result of the fission track dating for apatites. The resulting track ages of apatites significantly exceeded the age of deformed rocks, which was reliably established by the other methods. In deformed complexes, unlithified permafrost rocks predominate. Folded structures are characterized by joint deformation of sedimentary rocks, formation ice and ice-ground, inconsistency of fold orientation and different direction of structural evolution in the northern and southern parts of the island New Siberia. Considering the correspondence of the established age of dislocations to the age of the largest Pleistocene glaciation, all these facts allow us to state that the fold-thrust deformations of the island New Siberia are glaciodislocations.

Геотектоника. 2019;(6):46-64
Tectonic setting of the middle-late cambrian deposits of isl. Bolshevik and isl. Troynoy (Russian Arctic): a case of clastic rocks from metaterrigeneous complexes
Fokin P.A., Yapaskurt V.O., Nikishin A.M.

The new data on the tectonic settings and sedimentational circumstances of the Middle-Late Cambrian deposits of the southern part of the North Kara terrane, presented in our research, the data induced from the studies of clastic rocks in the basement metaterrigeneous complexes of Troynoy island (archipelago Izvestia CEC) and the northern part of Bolshevik island (archipelago Severnaya Zemlya). The sandstones of both regions are similar in the lithic wacke composition and contain the same groups of rocks fragments. Clastic zircons and Cr-spinels from sandstones of both regions have the same Zr/Hf and TiO2/Al2O3 ratios, respectively.

The similarity of even-aged sediments from both regions can be explained by their accumulation due to the demolition of detrital material from a single source eroded area, which is a segment of the accretionary uplift of the Timan‒Severnaya Zemlya orogenic belt, with the newly formed continental Neoproterozoic-Cambrian crust. The low – and medium-grade metamorphosed terrigeneous complexes dominated in the structure of the source area. Presence of volcanic and intrusive complexes in the source area is marked by clastic Cr-spinels with geochemical signatures of volcanic arc and suprasubductional ophiolites origin. By the beginning of the Ordovician, the Middle Late Cambrian sediments were also crushed, metamorphosed, and included in the structure of the Timan‒ Severnaya Zemlya orogenic belt.

Peculiarities of petrographic and grain-size composition and sorting of the sandstones from the north of Bolshevik island are more typical for the sediments of gravity turbidite flows, in deep or relatively deep water conditions. The deposits of Troynoy island could be formed at shallow and coastal-marine environments.

Геотектоника. 2019;(6):65-77
Suprasubduction volcanism of Chukotka terrane in the late jurassic– early cretaceous (Arctic region, Russia)
Vatrushkina E.V., Tuchkova M.I., Sokolov S.D.

The age and geodynamic position of the volcanic source of the Upper Jurassic–Lower Cretaceous deposits of Western Chukotka were determined. Products of synchronous volcanism were revealed by detailed lithological studies. Following sedimentological analysis results we established an admixture of pyroclastic material in the Oxford-Kimmeridgian deposits of the Chukotka microcontinent, indicating the effect of synchronous volcanism on sedimentation. It was shown that the source of pyroclastic material was the intraoceanic Kulpolney island arc, which existed in the northern part of the Proto-Arctic Ocean.The accumulation of the Tithonian‒– Valanginian deposits occurred in the back-arc basin at the edge of Chukotka microcontinent. Characteristics of the Tithonian‒– Berriasian sandstones are given, which contain significant proportion of ash material in the matrix, as well as lithoclasts and monomineral grains of volcanic origin, predominant in the clasts. With the use of geochemical analysis of volcanic pebbles, the presence of the differentiated series from basaltic andesites to rhyolites in the volcanic source is proved.

The suprasubduction origin of the volcanic source is established. The cessation of volcanic activity in Valangin era is confirmed by lack of presence of synchronous pyroclastic material and an insignificant amount of volcanic clasts in Valanginian sandstones. The obtained data of U–Pb isotope dating of zircons isolated from the Tithonian-Valanginian sandstones and andesite pebbles of the Tithonian conglomerates made it possible to determine the time for the existence of suprasubduction volcanism on the Chukotka margin in the period of 150–140 Ma.

Геотектоника. 2019;(6):78-91
Crustal structure, tectonic subsidence and lithospheric stretching of the princess Elizabeth trough basin, East Antarctica
Leitchenkov G.L., Galushkin Y.I., Guseva Y.B., Gandyukhin V.V., Dubinin E.P.

This paper considers crustal structure, seismic stratigraphy, thermal evolution and lithospheric stretching of the deep-water basin located on the East Antarctic passive margin in the Princess Elizabeth Trough. Seven of the Middle Jurassic to Quaternary seismic sequences was identified based on interpretation of multichannel seismic data. The information about seismic stratigraphy and crustal thickness (calculated from gravity data) along the section crossing the Princess Elizabeth Trough was used for numerical modeling of the thermal regime of the lithosphere, tectonic subsidence of the crystalline basement and lithospheric stretching. Modeling shows that calculated tectonic subsidence is possible only under the assumption of crustal extension before the deposition (during the crustal doming at the early rift phase). Maximum stretching factor in the basin ranges from 1.1 to 2.0 for the period which preceded the deposition and 2.8 for the period of the rift-related deposition.

Геотектоника. 2019;(6):92-104

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