ИСТИНА

Massive ice beds at the artic coastal lowlands of Western Siberia are mostly relics of Pleistocene epoch. The mechanisms and conditions of the formation of massive ice beds are debatable. To create or prove regional paleogeographic models, detailed comprehensive studies of ice and enclosing deposits with the reconstruction of the history of sedimentation and freezing are necessary. In August 2022, during the Earth's Cryosphere Institute expedition, massive ice and enclosing sediments in the area of the Marre-Sale weather station, previously studied in detail by many researchers, were described and sampled. In the coastal cliff of the Kara Sea, 25 m high, a section of Quaternary deposits with wedge ice and massive ice beds (the "upper" massive ice beds of the Marre-Sale key site) was studied. The upper part of the section is represented by continental sandy deposits, including syngenetic wedge ice up to 12 m in height. Massive ice occurs at a depth of 11–12 m from and is presented by two adjoined lenses 0.4 and 0.75 cm thick. The top and bottom of the ice lenses are inclined, and the contact with the host sands is unconformable – the ice lenses cut the layering of the host sandy stratum. At a depth of 12 m, the massive ice is dissected by the tail of wedge ice. Massive ice beds contain almost no sediment inclusions, and the crystals of ice are big (individual crystals have a size of more than 10 cm), which indicates relatively slow freezing. Such a structure shows that this massive ice was formed earlier than the Late Pleistocene wedge ice during intrasedimental freezing of a water-saturated sandy stratum. The study was supported by the Russian Science Foundation project No. 23-27-00218.