ИСТИНА

The north of Western Siberia is the main area of massive ice bed distribution in the Russian Arctic. Their origin is most often associated with permafrost aggradation in the Pleistocene. This aggradation could be either a result of the ice sheets recession or a result of the freezing of sediments that have risen above the sea level as a result of its relative fall. Despite numerous and effective geochemical methods for studying massive ice, the reconstruction of freezing conditions and ice formation mechanisms requires, first of all, a detailed description of both the macrostructure of ice bodies and ice cryofacies. Here we present typical cryofacies of massive ice beds, studied in thin sections of ice monoliths in the cold laboratory of the Faculty of Geography, MSU. Massive ice monoliths were collected during expeditions of the Earth's Cryosphere Institute and Faculty of Geography, MSU, in 2019-2022. The “upper” massive ice from the Marre-Sale area, western Yamal, has cryofacies similar to those in massive ice in lake sediments on the right bank of the Norilskaya River. Large ice crystals (up to 10 cm) and a few suspensions of fine debris (but with large blocks of clay at Norilskaya River) can indicate ice formation during the slow freezing of the enclosing deposits under stable freezing conditions. Layered massive ice near Amderma, Yugorsky Peninsula (>4.5 m thick, overlayed by marine clays), and massive ice near the Vaskiny Dachi research station in Central Yamal (>3 m thick, overlayed by continental sediments) are characterized by a large variety of cryofacies. Crystal size depends on the content of mineral inclusions. A variety of cryofacies indicates the formation of these massive ice beds in changing freezing conditions. The study was supported by the Russian Science Foundation project No. 23-27-00218.