KALENICH A.P., IVANOV G.I., MOROZOV A.F.

Northern State Scientific-Production Company of Marine Geological Prospecting ("SEVMORGEO"), Russia,

The Federal Subsoil Resources Management Agency, Russia

Since 1995 “Sevmorgeo” State Company in conjunction with other Russian partners has been providing multidisciplinary geophysical survey in the Barents and Kara Seas.

Integrated geophysical operations including deep seismic reflection and refraction shooting, gravity and magnetic survey, continuous seismic profiling and deep seismic sounding have been carried out in accordance to All-Russian program focused on creating grid of reference seismic lines and deep wells. The reference network consists nowadays of: line 1-АР, line 2-АР, line 3-АР, line 4-АР.

Simultaneously with reference network Sevmorgeo carried out gravity and magnetic fields survey covering almost all the Barents and Kara region.
Deep geological model of the Barents and Kara shelf was created on the base of comprehensive studies. It was possible to study contacting zones of the shelf with neighboring tectonic blocks of the continent and determine particularities of tectonics and geological history of the Crust and upper mantle structures located in this continent-to-ocean transition zone.

Modern tectonic pattern of pre-Cambrian crystalline basement of the Barents and Kara area is determined by interplay of big blocks: Svalbard (Barents) shelf plate, Timan-Pechora area and Kara shelf plate. In the south of the Kara paleobasin Paleozoic sedimentary cover is underlain by basic layer which is interpreted as a relic of an ancient oceanic basin.

Gravity and magnetic zoning as well as data obtained from the reference lines make it possible to identify general structure of the basement and interface of its blocks.

Boundaries of the basement blocks, their structure and composition can be also identified from geological data. Tectonic age of the basement units can be determined based upon direct geological investigations, isotope and paleontology dating of the base of Riphean-Paleozoic sedimentary cover.
Novaya Zemlya stay apart from the other islands of the Barents-Kara region, for their folded structures were formed within the shelf, whereas the Svalbard, Franz Joseph Land and Severnaya Zemlya were located along the outer margin of the shelf. Novaya Zemlya divide the Barents-Kara shelf into western and eastern zones. These islands are thought to be key members for development reconstruction of the region.

Analysis of pre-Cambrian history of the Novaya Zemlya basement, study of evolution and geology of different structural Proterozoic and Phanerozoic units make it possible to reconstruct geodynamics of blocks from the present time back to the earliest stages of the basement formation.
Typical feature of the Novaya Zemlya is that this ridge is not expressed in geophysical (gravity and magnetic) fields. Direct geological investigations show that pre-Cambrian basement of the Novaya Zemlya consists of three different tectonic blocks – Northern, Central and Southern. Each of the blocks is characterized by different “maturity” of the Crust, its own history of development in the Cambrian and different age of joining. That is accordingly reflected in composition and evolution of sedimentary and endogenic Paleozoic sequences.

Basement of the Svalbard (Barents) plate is mainly represented by pre-Baikalian units. These units outcrop within the central block of the Novaya Zemlya. It was determined from these outcrops that granitization and metamorphization of pre-Baikalian schists and marbles took place during Grenville (maybe Gothian) dislocations coinciding with consolidation of protocontinental crust.

The basement of the northern block of the Novaya Zemlya orogene makes part of the Kara plate. Within this block on the Severnaya Zemlya and northern Taimyr the sedimentary section can be clearly correlated as an undisturbed stratigraphic sequence from the Mid Riphean to Permian. Crystalline basement here is of pre-Riphean age, i.e. at least Late Karelian.

According to existing geological and geophysical data the Timan-Pechora basement with southern block of the Novaya Zemlya and Vaigach Island on its north-eastern margin was consolidated in the Late Proterozoic – Cambrian, i.e. is of Baikalian age.

Evolution study of magmatic sequences of different age in the tectonic blocks of the Novaya Zemlya shows steady succession in magmatic processes. It is evidently that development of magmatic series in every tectonic block of the Novaya Zemlya is determined by consolidation age of crystalline basement and depends directly on to what extent the basement was reprocessed at the earliest stage of its transformation, i.e. on “maturity” of crystalline basement.

Paleofacial and structural-tectonic studies of Phanerozoic sediments show that there are several types of sedimentary sections characterizing different sedimentation environments within the Novaya Zemlya orogene. The sections of the Central block with its basement consolidated in the Grenville are mostly correlated with those within paleobasin of the Svalbard plate. Riphean-Phanerozoic sediments of the Northern block consolidated in the Karelian time can be correlated reliably with the northern Taimyr and Severnaya Zemlya sections of the same age, and may be thought to be formed within the isolated Kara paleobasin. Ordovician-Permian sedimentary units developed in the southern Novaya Zemlya and Vaigach were evidently deposited in transition zone – in the north-eastern periphery of newly-formed part of the East-European craton and South-Kara depression.
Conclusions:

- Novaya Zemlya divide the Barents-Kara shelf into western and eastern zones. These islands are thought to be key members for development reconstruction of the region

- Mosaic-block structure of the pre-Cambrian basement made of crystalline blocks of different age, including blocks with relic oceanic crust is characteristic of the Barents-Kara region.

- Blocks of pre-Cambrian basement were at time parts of big Archean-Proterozoic cratons. The Kara shelf plate made a part of the Siberian craton, Svalbard (Barents) shelf plate – of the North American (Laurentia), Timan-Pechora area – of the Baltic craton.

- These areas of crust destruction determined future evolution of big troughs (including rifts) where Late Paleozoic-Mesozoic oil and gas source rocks, collectors and traps of different types were deposited.

OIL AND GAS OF ARCTIC SHELF 2008