Stratigraphic subdivision of the Quaternary deposits was accomplished on the basis of the results from lithological, biostratigraphical and radiometric examination of borehole core. Marine and glacial deposits were identified by lithogenetic criteria. The latter are mainly represented by moraines. Marine beds contain Tiltim, Ob and Kazantsevo foraminiferal assemblages previously described by V.I.Gudina (1976). Tiltim association by its zoogeographic nature is arctic assemblage with predominance of arctic and boreal-arctic species. The Ob association is chiefly represented by warm-water forms, which form about 65% of the total association as to the number of species (28 out of 45). These are in the main boreal and arctic-boreal species. The cold-water group is less numerous in species number and forms about 27%. Typical are Miliolinella pyriformis (index-species for biostratigraphic zone), Miliolinella grandis grandis, M. grandis pumilionis, Retroelphidium subclavatum and R.obesum. The assemblage as a whole is arctic-boreal. Kazantsevo foraminiferal association is most rich and representative numbering up to 25 species and subspecies. A warm-water group is represented by boreal and arctic-boreal species, which form about 64%. They dominate in association by number of species (16 out of 25) as well as by number of specimens. The association as a whole is arctic-boreal, closer to boreal (one Luzitanian species Sigmomorphina undulosa). Retroelphidium, R.boreale, Haynesina magna, Quinqueloculina deplanata make their first appearance in the Upper Pleistocene deposits and Quinqueloculina deplanata, Haynesina magna occur only in Kazantsevo deposits. The age of the Ob beds is defined by TL method between 246 ± 23 and 370 ± 31 th.y. and the age of the Kazantsevo beds within 153 ± 15 th.y. and ESR method dates at 121.9-134.8 th.y. In general stratigraphic succession marine horizons alternate with glacial deposits of Zyryanka (Weichselian, Wurm), Bakhta (Riss) and Shaitan (Mindel) glaciations. Geological structure of the Quaternary series is characterized by numerous entrenchments and breaks. Glacial strata infill the hollows of glacial ploughing overdeepened to 190-240 m below sea level. Marine beds compose the depressions but locally they may be found on the projections of buried paleorelief.
