GYPSUM SPELEOTHEMS OF FREEZING ORIGIN

Seasonal freezing affects the development of gypsum speleothems in caves of the Pinega area of the Russian European North including two types of deposits not previously described. One type, called gyp-sum yozh (hedgehog), grows in dense clay sediment within a high supersaturation environment. Originally growing in a direction away from the freezing front, they later enlarge almost symmetrically. Their shapes and characteristics are dependent on various factors and provide interesting comparisons with gypsum roses from arid regions. A second, very rare, type of gypsum speleothem appears to be pro-duced from concretions of gypsum powder accumulated in cavities within an underground ice body. Recrystallization of the gypsum is controlled by fluctuating local temperature and seasonal freezing in an environment of low supersaturation. The Pinega Karst is a north-trending region of sulfate and carbonate karstified rocks 600 km long and 100-200 km wide in the Arkhangel’sk Region of the Russian European North. The most interesting and best-studied caves are located on the territory of the Pinega State Nature Reservation and adjacent protected territories at the southeast border of the Belomor