РАЗНОВОЗРАСТНЫЕ ДРЕВНИЕ АЛАСЫ НА СЕВЕРО-ВОСТОКЕ РОССИИ

Thermokarst lakes and alases are widespread in the North-East of Russia. These structures are part of Quaternary deposit of the region and mostly of Holocene age. The alas complex of the older age is less common. Here we present the study of alas complex sections as old as Lower – Upper Neopleistocene from the Laptev Sea coast (Oyagoss yar, Shirokostan peninsula). The principal composition of these structures of different ages is quite similar. Their formation is correlated with warm intervals when the moisture content increased. Melting of the ice-rich sediment took place locally. Accumulation of the melted water increased the melting and lead to formation of separated thermokarst depressions where succession of the lake-bog-soil sediments with ice-wedge casts (pseudomorphosis) began to accumulate. Current research expands the knowledge about distribution of the alas complex in the north-eastern Russia, allows to recognize its features (the presence of tabers, lacustrine sediments with a complex of pseudomorphs along the ice wedge, the increase in grain size of lacustrine sediments from the center to the periphery of the basins, a large number of values of allochthonous peat in the middle and autochthonous in the top of alas strata), and suggests how to extract paleogeographic information from this type of deposit.