Genesis of the ridge-hollow relief of the West Siberian plain

To determine the genesis of the ridge-hollow complex, a study was made of the texture of the bedding and structure of sediments, the granulometric and mineralogical composition of five technogenic sections and one natural geological outcrop. The following types of texture of layering were distinguished: textures of convergent layering and stratigraphic disagreements; regressive-rhythmic texture of layering in the zone of articulation of the hollow lakes with the slopes of the ridges; a tight-fitting type of texture with elements of selfcompaction layering in the initial stage of epigenesis. In the sediments of ridges, the silt-pelite fraction is 80-85 %, and the mineralogical composition is characterized by an extremely low content of fractions of heavy minerals: single grains of siderite, tourmaline, amphibole, pyrite; very rarely ilmenite, almandine, pyroxene. Well rounded quartz grains, fragments of carbonates, and pyritized fragments of foraminifera predominate. Nevertheless, an increase in heavy fractions (pyrite, magnetite, ilmenite, almandine, zircon, etc.) was noted in the sediments of the ridges at the borders of their junction with lake terraces. Apparently, this is due to an increase in the concentration of heavy minerals due to abrasion modeling 56 А.В. Поздняков, Ю.С. Пупышев, А.В. Пучкин, Т.Ш. Фузелла of ridges during the period of lake transgressions, accompanied by the removal of pelitic-silty-sand fractions. In the texture of the stratification of coastal lake sediments, bottom ripples and xenolith-like inclusions are established, which indicate that lake transgression was carried out in the period after the formation of the ridge-valley relief. According to the textural, structural and geomorphological features of the ridges, the strict consistency of their orientation and the regular increase in the height of the watershed surface of the ridges in the northeast (60-65 °) direction to their end; coordinated parallelism and length from 5 to 100 km, the ridges are classified as linear sand dunes, similar to the safe dunes of Central Asia and the Sahara. The main relief-forming force was free turbulent jet flows, which formed blowing troughs and wind gradients directed to the slopes of the trenches that bound them. At the edges of the hollows, where, according to the laws of dynamics of self-limitation of free jets, the wind speed decreased and sand accumulated, giving rise to the formation of ridges. The formation of a ridge-hollow complex is presented as a self-organizing self-similar process of isomorphic development of paragenetically related aeolian-accumulative ridges and deflation-denudation hollows. The idea posed by M.G. Grosvald and his like-minded people about the grand catastrophic floods resulting from the breakthrough of glacial dams within the northern part of the West Siberian Plain is unfounded. The formation of the ridge-hollow complex apparently occurred at the borders of the Pleistocene and Holocene and was predetermined by a sharp change in the ecological situation (and climate), which caused the total destruction of the vegetation cover (and wildlife) and the exposure of sea and lake sand and pelitic strata, which became the arena for the development of aeolian processes.

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