SHIPILOV E.V., SHKARUBO S.I. , KARIAKIN J.V.
ММBI Kola SC RAS, Russia, MAGE, Russia, GIN RAS, Russia

The Jurassic--Cretaceous stage in geological evolution of the Barents Sea region was characterized by sudden changes in tectonogeodynamic and sedimentation settings that resulted in substantial transformations of the Earth's crust and accumulation of variable (in thickness and lithology) sediments.

Based on marine geological--geophysical data, this paper analyzes geological events and tectonogeodynamic processes in the Barents Sea versus Amerasian regions during the Jurassic--Cretaceous.

The geodynamic evolution of the Arctic basin remains debatable, although most researchers consider it a Late Mesozoic structure related to the initial destructive (riftogenic) activation that produced the first generation of young oceans (Canada and Amerasian Basins). This is evident from different materials indicating that, at least in the Jurassic (when the northern part of the Central Atlantic already existed), all transgressions toward the present-day North Sea and West Arctic margin advanced from the north, where a vast deep ocean-type basin was probably located.

The existence of such an oceanic basin during the Mesozoic (since the Triassic) is also evidenced by a specific (highly diverse) marine biota.
Available paleotectonic reconstructions show the longitudinal position of the spreading axis in the Amerasinan Basin. The extinct spreading axis was reconstructed based on the anomalous magnetic field in the Canada Basin.

Several models have been proposed to explaining the formation of the region. The rotation mechanism of the Amerasian Basin formation is the most substantiated model confirmed by geological--geophysical data and paleogeodynamic reconstructions. According to this model, the Amerasian Basin developed in two phases.

The first phase of tectonic activation corresponds to an "unsuccessful" (or incomplete) riftogenic event during the Aalenian--Bathonian-Tithonian time that resulted in the formation of wide semigrabens along the Arctic margin of Alaska. This inference is supported by the stratigraphic and structural analysis of sediments and drilling data on the continental margin of Alaska and neighboring areas.
In the Barents Sea region, this phase commenced with subsidence of the area and transgression of a northern sea basin that reached the Pechora Plain in the terminal Bathonian.

Lacustrine-alluvial sedimentation gave way to coastal--marine and marine ones. Consequently, typical Early and Middle Jurassic sandy sequences were replaced by sandy-clayey sediments since the Callovian and mainly clayey sediments in the Late Jurassic.

In the South Barents Basin, which was not as yet separated by the Luddlov Ridge, the studied period was marked by more drastic changes. In the Middle Jurassic, the basin acquired a new structural appearance as a result of the formation of rises and tectonic scarps mainly in peripheral zones. This is evident from the presence of gritstone and conglomerate units in borehole section located along the periphery of the basin. Judging from the occurrence of these rocks in the interval from the uppermost Lower Jurassic to the uppermost Middle Jurassic, differentiation and formation of provenance was a prolonged process. The transportation paths of detrital material changed as well. Therefore, the Middle Jurassic is locally separated from the Upper Jurassic by an unconformity (presumably angular) related to change in the inclination of some paleofloor areas. It should be noted that no such features are observed in the depocenter section: sandstones in the Upper Jurassic sequence are replaced by clayey sediments in Borehole Arkticheskaya.

According to our observations (summer of 2002), gritstones of the Kanin Peninsula are presumably Middle Jurassic rocks. Abundant ammonites, belemnites, and bivalves are most likely pre-Late and Late Jurassic forms similar to those from boreholes drilled at the offshore continuation of the Pechora Plate.