N. A. Malyshev

Tectonic history and petroleum geology of the Russian Arctic Shelves: an overview

Abstract The Eastern Barents, Kara, Laptev, East Siberian seas and the western Chukchi Sea occupy a large part of the Eurasian Arctic epicontinental shelf in the Russian Arctic. Recent studies have shown that this huge region consists of over 40 sedimentary basins of variable age and genesis which are thought to bear significant undiscovered hydrocarbon resources. Important tectonic events controlling the structure and petroleum geology of the basins are the Caledonian collision and orogeny followed by Late Devonian to Early Carboniferous rifting, Late Palaeozoic Baltica–Siberia collision and Uralian orogeny, Triassic and Early Jurassic rifting, Late Jurassic to Early Cretaceous Canada Basin opening accompanied by closure of the South Anyui Ocean, the Late Mesozoic Verkhoyansk–Brookian orogeny and Cenozoic opening of the Eurasia Oceanic Basin. The majority of the sedimentary basins were formed and developed in a rift and post-rift setting and later modified through a series of structural inversions. Using available regional seismic lines correlated with borehole data, onshore geology in areas with no exploration drilling, and recent Arctic-wide magnetic, bathymetry and gravity grids, we provide more confident characterization of the regional structural elements of the Russian Arctic shelf, and constrain the timing of basin formation, structural styles, lithostratigraphy and possible hydrocarbon systems and petroleum play elements in frontier areas.

Concerning the issue of paleotectonic reconstructions in the Arctic and of the tectonic unity of the New Siberian Islands Terrane: New paleomagnetic and paleontological data

The New Siberian Islands terrane, represented on the Arctic shelf by the archipelagos of the New Siberian Islands and De Long Islands, is one of the key structures of the Arctic. However many questions of its structure, borders and formation history are under intense discussion. During the international expedition in 2011 we solved many problems concerning structural geology, paleontology, petrology and geochronology. A particular attention was given to obtaining paleomagnetic data for the sedimentary and igneous rocks of the archipelago. The primary objects of paleomagnetic studies were the Early Paleozoic sedimentary rocks of the Kotelny (Anzhu) and Bennett (De Long) islands. In this paper we present new paleontological data, including the first one for conodonts of the New Siberian Islands, which help us to specify the age of the Early Paleozoic deposits of the studied sections. In these sections we took a series of paleomagnetic samples. The match of the paleomagnetic directions we determined for Bennett Isl. and Kotelny Isl. indicates the tectonic unity between the territories of the Anzhu and De Long archipelagos. These first paleomagnetic data allow us to affirm that at least from the Early Ordovician the rocks of the Anzhu and De Long archipelagos formed within the same New Siberian Islands terrane, that is to say, on the same basement.

A new model of the geological structure and evolution of the North Kara sedimentary Basin

Based on the new seismic data, the geological structure and evolution of the North Kara Basin are presented. The North Kara Basin formed as an Early Ordovician rift system. Approximately at the Devonian-Carboniferous boundary, the North Kara Basin suffered intraplate compressional deformations, which caused formation of inversion swells, and then it was covered by a thin Carboniferous-Permian or Permian cover. The Urvantsev Trough probably comprising Late Ordovician evaporites was distinguished in the north-eastern part of the basin. Paleozoic folded deformations took place within the limits of the Vize-Ushakov and Central Kara rises.

New data on Upper Carboniferous–Lower Permian deposits of Bol'shevik Island, Severnaya Zemlya Archipelago

We present here a detailed study of the Upper Carboniferous–Lower Permian stratigraphy of Bolshevik Island in the Severnaya Zemlya Archipelago, consisting of the analysis of sedimentary structures and lithostratigraphy, U/Pb detrital zircon dating and structural studies. The preserved sedimentary structures suggest that the studied strata were deposited in a relatively small meandering fluvial system. U/Pb dating of detrital zircons reveals that the Upper Carboniferous–Lower Permian sandstones contain a primary age population ranging from 450 to 570 millions of years, with a predominance of Early–Middle Ordovician zircons. This detrital zircon distribution indicates that the studied formations were derived locally from the erosion of Lower Ordovician deposits of Bolshevik Island or elsewhere in the archipelago. Our structural studies suggest that Upper Carboniferous–Lower Permian deposits are deformed into a series of west–north-west verging open asymmetric folds, suggesting a west–north-west direction of tectonic transport and that deformation across the island is post-Early Permian in age.

The Late Permian-Triassic system of rifts of the South Kara sedimentary basin

Based on the new geophysical survey data within the South Kara basin, a system of rift troughs was established. The time of formation of the rifts was the Late Permian-Early Triassic by analogy with that of the West Siberian basin. It is probable that inversion processes took place in the Middle Triassic in rifts, located close to Novaya Zemlya. Morphologically, the rifts are represented mainly by semi-grabens. In plan view, they form closed isometric basins, similar in shape to pull-apart basins, which formed as result of sinistral transtension. The Upper Triassic sediments are widespread throughout the basin, forming the lower part of the post-rift sedimentary cover.

The structure and seismostratigraphy of the sedimentary basins of the East Siberian Sea

The interpretation of the data of a seismic profile grid in the territory of the East Siberian Sea is performed. Four seismic complexes in the section of the sedimentary cover are distinguished: Aptian-Albian (synrift), Upper Cretaceous (synrift), Paleocene-Eocene (postrift) and Oligocene-Quaternary (postrift). In the East Siberian Sea two rift phases have been discovered: the Aptian-Albian main phase and the Late Cretaceous additional phase. The rifting conditions were later replaced by transpression that had preceded the formation of a regional unconformity horizon dated by the Cretaceous-Paleogene boundary. The clinoform complexes that formed of sediments that were transported from the east are recorded over the regional unconformity boundary in the complex of the Paleocene-Eocene postrift deposits.

Tectonic zoning of Wrangel Island, Arctic region

The Northern, Central, and Southern zones are distinguished by stratigraphic, lithologic, and structural features. The Northern Zone is characterized by Upper Silurian–Lower Devonian sedimentary rocks, which are not known in other zones. They have been deformed into near-meridional folds, which formed under settings of near-latitudinal shortening during the Ellesmere phase of deformation. In the Central Zone, mafic and felsic volcanic rocks that had been earlier referred to Carboniferous are actually Neoproterozoic and probably Early Cambrian in age. Together with folded Devonian–Lower Carboniferous rocks, they make up basement of the Central Zone, which is overlain with a angular unconformity by slightly deformed Lower (?) and Middle Carboniferous–Permian rocks. The Southern Zone comprises the Neoproterozoic metamorphic basement and the Devonian–Triassic sedimentary cover. North-vergent fold–thrust structures were formed at the end of the Early Cretaceous during the Chukchi (Late Kimmerian) deformation phase.

The Ordovician Urvantsev Evaporite basin in the Northern part of the Kara Sea

157 The presence of Ordovician evaporites in the North Kara sedimentary basin, like the Severnaya Zemplya archipelago and the Timan Pechora basin, was pre dicted [8]. In the northwest part of the North Kara basin, specialists of OAO Sevmorneftegeofizika and other organizations have distinguished the evaporite trough containing salt diapirs [2]. Based on the seismic profiling data, we also analyzed the evaporite part of the basin (the so called Urvantsev trough; see Fig. 1) [4]. In the present communication, we characterize this trough, substantiate the age of salts and give a con cept about the Early Paleozoic Paleogeography of the North Kara region. Distinguishing the evaporite basin. The boundaries of the trough (basin) are not precisely outlined yet. To the west, it is confined by the large Vize Ushakov rise; to the south, there are the Nalivkin megabar and sev eral rises of smaller size; northern boundary of the basin has not yet been strictly determined. Figure 2 shows the cross section of the Urvantsev trough, where one can see the boundaries in the form of relative rises. In the trough proper, diapir like structures are clearly identified and can be interpreted as salt structures of different morphological types. Figure 3 gives examples of salt structures. In the cross section of the Urvantsev trough, a regional angular uncomformity can be clearly distin guished. It likely divides the Ordovician–Devonian and Carboniferous–Cenozoic complexes [4]. In the Ordovician–Devonian complex, the synrift and pos trift deposits can be identified. It is seen in Fig. 2 that the evaporite deposits nearly coincide with the men tioned boundary between the two age complexes. A characteristic feature of the Urvantsev trough is salt diapir manifestation (Figs. 2, 3). Here we can identify salt diapirs and salt pillows. All evaporite bod ies are typically about five kilometers in width at their base, and this parameter remains nearly the same up through the section. In the rock stratum formed after evaporite accumulation, so called “growth layers” can be found: these are sedimentary sequences that formed synchronously to the growth of salt diapirs. These growth layers are found in different intervals of the section, from the supposed Silurian to the sup posed Devonian. It follows from this point that salt diapirs grew for a long time during the Silurian and Devonian. Since the upperlying deposits of the sup posed Carboniferous–Permian sharply cut the rocks deformed with salts, one of the important phases of salt body growth took place before the Paleozoic sedi mentary cover started to form. In some cases, bound aries of salt diapirs are represented by surfaces of gen tle fault or stripping types (rollover type structures) (Figs. 2, 3b, 3c). These surfaces form against the back ground of diapir growth. Above some diapirs, we can see the caldera like depressions suffered very young (obviously Quater nary) sinking (Figs. 3a, 3b). This indicates Quaternary age of their formation. In this period, the Kara Sea region was repeatedly covered with glaciers and suf fered isostatic sinking, while rising occurred in the interglacials. We can suppose that it is the ice cover and its melting that caused caldera like sinking of blocks above salt diapirs. Such sinking might be related to dis solution of salts or to fresh water effect. The salt diapirs intruded into the Silurian and Devonian deposits. The Silurian ones are, by analogy to the sections of Severnaya Zemlya, represented by shallow water carbonates. The Urvantsev trough is likely a rare case of salt diapirs rising into the thick car bonate strata during the formation of the latter. Determination of evaporite age. The age of evapor ites can be estimated based on correlation to the ana logs from Severnaya Zemlya and based on analysis of how sedimentary strata of different ages are distributed in seismic profiles. There are two main levels in which evaporites (gypsum and anhydrite) are manifested in The Ordovician Urvantsev Evaporite Basin in the Northern Part of the Kara Sea

Marginal continental and within-plate neoproterozoic granites and rhyolites of Wrangel Island, Arctic region

The paper presents new data on the U–Pb zircon age, as well as results of isotopic geochemical analysis, of granites and rhyolites from Wrangel Island. The U–Pb age estimates of granites and rhyolites are grouped into two clusters (~690–730 and 590–610 Ma), which imply that these rocks crystallized in the Late Neoproterozoic. Granitic rocks dated back to 690–730 Ma are characterized by negative εNd(t) values and Paleoproterozoic Sm–Nd model age. The older inherited zircons corroborate the ancient age of their crustal source. The granitic rocks pertain to involved peraluminous granites of type I, which form at a continental margin of the Andean type and can be compared with coeval granites and orthogneisses from the Seward Peninsula in Alaska. Rhyolites and granites ~590–610 Ma in age are distinguished by a moderately positive εNd(t) and Mesoproterozoic model age. It is suggested that they have a heterogeneous magma source comprising crustal and mantle components. The geochemical features of granites and rhyolites correspond to type A granites. Together with coeval OIB-type basalts, they make up a riftogenic bimodal association of igneous rocks, which are comparable with orthogneisses (565 Ma) and gabbroic rocks (540 Ma) of Seward Peninsula in Alaska.

Modeling of the Thermal Evolution of the Sedimentary Cover and the Maturity of Organic Matter in the Source-Rock Sequences of Sedimentary Basins of the East Siberian Sea

In this paper 2D and 3D modeling of thermal evolution of sedimentary cover and OM evolution of the source-rock sequences (SRSs) of the East Siberian Sea were conducted. The distribution of the temperature and reflection of vitrinite in sedimentary cover is presented along the composite seismic profile of the section. Maps of the distribution of the temperature of sedimentary sequences, reflection of vitrinite of the SRSs for various temporal boundaries, and the degree of OM transformation of the SRSs for the presentday stage of evolution were plotted. The evolution of OM maturity and possible processes of hydrocarbon generation of the SRSs were analyzed on the basis of modeling results.