The thermal evolution of the permafrost in the sedimentary section of the Tyumen superdeep SG-6 well has been numerically reconstructed using the ICE2020 software package, which is part of the GALO flat basin modeling system. The thermal evolution of the sedimentary strata in the last 3.5 My is considered as the final stage of the basin modeling, whose formation began with continental rifting in the Late Permian. Abrupt climate changes in the late Pliocene–Holocene led to a decrease in the rock temperature by 15–20°C in the upper 1–1.5 km of the SG-6 sedimentary section. The maximum thickness of the permafrost in the study area was about 711 m, reached 2.6 Mya. The maximum thickness of the permafrost for the last ice age (23–18 thous and years ago) was 412 m, reached about 14.5 thousand years ago. According to our modeling, the modern base of the permafrost is at the depth of 311 m and is degrading with the rate about 13 m/1000 y. The results of our calculations with a database of climatic data limited to the last 50 and 100 thousand years differ markedly from the modeling results with the complete database for the last 3.5 My.

The paleoclimate evolution curve of the South Kara Sea basin over the past 250 Myr, which is necessary for numerical reconstruction of its thermal history, was plotted using data from a large number of works devoted to studying of the paleoclimate of the Arctic sector of the West Siberian Basin. For the period from 260 to 65 Mya, the construction of the paleoclimate curve was based on a series of paleotectonic reconstructions of the studied area. The reconstruction of the climatic history of the Cenozoic was based on a detailed study of climate variations in Eurasia over the past 65 Myr. The history of sharp climate fluctuations in the last 3.5 Myr was based on information from a large number of works devoted to studying of the regional paleoclimate in the Pliocene-Quaternary. Studies published in the literature speak in favor of the limited size of the glacial covers formed within the South Kara basin. This makes it possible to neglect the effect of the porosity of sedimentary rocks from the glacial cover load in comparison with the similar effect of the load of sediments removed by erosion in the Miocene. Any correction to the paleoclimatic data due to the thermal influence of the ice sheet with its limited thickness should not exceed the error in determining the data themselves. Peculiarities in the change in temperature and the salinity of pore waters with depth determine the existence of various forms of permafrost in the shelf areas of the Arctic seas.

A scheme of formation of the sedimentary blanket of the South Kara basin is considered, which can further be used for numerical reconstruction of its thermal history. The scheme is based on our analysis of the literature information on the structure and geological history of the Barents-Kara region. This information included an interpreted seismic profile crossing the studied area, drilling data from four wells located along the profile (the University, Rusanov, Leningrad and Kharasavey ones), measurements of the heat flow and deep temperatures in the basin. The proposed scheme considers the formation of the basin as a series of sedimentation stages with various combinations of clay shales, siltstones and sandstones and sedimentation in the Cretaceous and Paleogene with their subsequent erosion in the Miocene. The erosion amplitude is estimated by the observed change in the porosity of sedimentary rocks with depth. The initial heat flow in such a model should correspond to the flow of modern axial zones of continental rifting or be lower for the areas remote from the corresponding segments of the Late Permian-Early Triassic continental rifting system.