PROBLEMS OF DIFFERENTIATION AND CORRELATION OF ALLUVIAL DEPOSITS OF THE NEO-PLEISTOCENE IN THE LOWER OB REGION

Abstract

The Upper Neo-Pleistocene alluvial deposits lie in a close hypsometric position in outcrops of the Lower Ob Region right bank. Their top usually does not rise above the level of 5 m above the tow-path edge. At the same level, glacial erratic masses of the Middle Pleistocene alluvium were recorded in a number of areas. The height of the 1st and 2nd sites of terraces (on average from 5 to 10–15 m) depends on the thickness of subaerial deposits overlapping the alluvium. The 3rd terrace above flood-plain of the Bolshaya (Big) Ob has no geomorphological expression, since the alluvium of the first Late Neo-Pleistocene interglacial period without ablation is drape overlain by parallely bedded precipitates of the glacier-ice-blocked lake of the first Late Neo-Pleistocene glaciation. Thus, the height of sites of terraced surfaces does not directly correlate with the age of their alluvial basement. Therefore, the geomorphological method for differentiation of river sediments is not effective for this region. In addition, the problems of differentiation and correlation of alluvial deposits of the Lower Ob Region right bank are complicated by the presence of fluvioglacial incisions of deglaciation stages of the Middle Neo-Pleistocene and Upper Neo-Pleistocene glaciations.