Data from West Siberia (Gorny Altai and West Siberian Plain) show that stone blocks and erratic boulders transported from remote areas not necessarily record past glacial events, even in the presence of hilly landforms. Stacks of boulders may result from erosion of glacial tills (moraines) and megaf lood deposits, rockfall events or ice rafting in ice-dammed lakes. Only basal tills can be indicators of paleoglaciers, while ablation tills form by solif luction in interglacial conditions. The Saldzhar Fm. in Gorny Altai produced by megaf loods about 90 ka BP correlates with terrace IV (Biya terrace) of the Ob in the West Siberian Plain. The formation of first ice sheet in the Upper Pleistocene Gorny Altai area was coeval with the Late Pleistocene glacial maximum in northern West Siberia about 90 ka ago. Older megaf lood deposits (Middle Quaternary Inya Fm. in Gorny Altai) can be provisionally correlated with the Bakhtin glacial event of the paleoglacial zone of the northern West Siberia, which comprises the Samarovo (marine isotope stage (MIS) 8) and Taz (MIS 6) tills. Megaf lood deposits are reliable geological markers that can make reference for intraregional correlations of sediments in West Siberia.
