Quaternary glaciation in North-Western Siberia - New evidence and interpretation

The Pleistocene history of North-Western Siberia is hotly discussed by researchers, as the extension and impact of ancient glaciers are subjected to major revision. The representative object for this study is the Siberian Uval (an upland at the right-hand bank of the Ob' River). The Uval contains some stony debris, and for a long time researchers considered it as a moraine of an ice sheet. However, the Siberian Uval represents a predominantly sandy 30-40-m river terrace. Its origin is associated with development of the river network, ice-floe drift, tectonics, and marine ingressions. Well-developed paleosols in the terrace body add to the picture of the development. The first paleosol was encountered at a depth of a few meters, and two 14C dates, 25693-27748 cal BP (SOAN-7550) and 34740-35440 cal BP (Beta 410187), confirm the soil formation as Karga (MIS3). The second paleosol is in the center of undisturbed section of 30-40-m terrace, and its 14C dates (>45 ka BP, SOAN 7551, SOAN 7552; >43.5 ka BP, Beta 410188). The warmer paleobotanical spectra obtained from it, may suggest that the paleosol formed in the beginning of MIS5. The stony debris either underlies or overlies the first paleosol and represents rare boulders and pebbles embedded in the top sandy part of the terrace. The debris is a result of ice-floe drift. Ancient glaciers developed only in the mountains surrounding northwestern Siberia only, and then the stony moraine material could be spread by river ice-floe drift during the river floods and sea-water ingressions. Extrapolations relying on the data obtained by study of modern glaciers in the mountains surrounding northwestern Siberia, as well of relics remained by ancient glaciers, confirm this conclusion.