Estimation of the permafrost thickness of the New Siberia Island based on geothermal data and numerical modeling

Abstract

The current ideas about the permafrost thickness on the New Siberia Island are very ambiguous both in terms of forming factors and in its magnitude (from 240 to 370 m), and in general are based on the assumption of the Pliocene beginning of rock freezing. In the last 20 years, new data have been obtained on the history of the region’s development in the Neopleistocene. They include the long existence of the New Siberia Island in marine conditions, which excluded the rocks freezing at that time, as well as the development of glaciation in the Middle Neopleistocene. These data indicate a significantly later onset of freezing of the island, which correlates with the nonstationarity of the temperature field of the frozen strata. The authenticity of the data is debated. The article is devoted to assessing the thickness of permafrost in accordance with three possible scenarios, allowing to take into account different points of view on the geological development of the region. The assessment is made using numerical modeling of the formation of frozen strata over the past 200 thousand years. One scenario includes the existence of glaciation during the Middle Neopleistocene, while in the other two it is absent. The last two scenarios differ in the stratigraphic schemes used. The reliability of the scenarios is assessed based on a comparison of the modeling results for each of them with geothermal data in a well on the island of New Siberia, obtained in the 1970s. The comparison results show that only the version with the existence of a glacier is consistent with the geothermal data. According to the data obtained, freezing of the island began under the glacier at the end of the Middle Neopleistocene, which existed in coastal-marine conditions. The most active increase in the frozen strata thickness dates back to the late Neopleistocene due to the drainage of the island. The obtained result is in agreement with new data on the age of the main geological bodies of the region, as well as with the idea of the glaciotectonic nature of dislocations in the Cretaceous — Middle Neopleistocene rocks.