The basin consists of three baths, which are separated by horstlike
uplifts. The gravimetrically estimated thickness of basin sediments
ranges from 300 to 500 m (Zorin et al., 1989). The sediments
have been drilled at several localities; two boreholes 210 and 114m
deep (sites 20 and 21 in Fig. 2) were described by Ufland et al.
(1971). The borehole data show that the central part of the basin
consists of lacustrine and fluvial silt and sand. The lacustrine facies
are dominant in the upper 130 m of the sedimentary sequence. At
the periphery these fine-grained sediments interleave with pebbles
and boulders. On the surface, the relief of the initially flat lacustrine
plain has been strongly re-worked by rivers, permafrost and thermokarst,
and there are abundant alluvial/proluvial fans and
moraines at its periphery (Fig. 3A).