HISTORY OF FORMATION OF THE RIVERS OF SOUTH PRILIMENIUM IN HOLOTSEN

Abstract

The riverbed in the course of its evolution is subject to deformations, manifested in the form of erosion of the channel and floodplain, sediment transport and accumulation. Knowledge of the history of the development of river channels in the conditions characteristic of a given territory allows us to assess their future evolution. The aim of the study was to identify the features of the formation and evolution of the hydrographic network of Southern Priilmenye in the Holocene. These features are mainly associated with the last Valdai glaciation. Firstly, rivers arose only after the retreat of the glacier and are about 11 to 14 thousand years old. Secondly, their development was controlled by a changing erosion basis, depending on the level of the subglacial lake, which formed on the southern periphery of the glacier during its retreat. Thirdly, the evolution of watercourses occurred in conditions of compensatory deformational elevation of the territory. As a result, rivers formed on the territory of Southern Priilmen'e, in the initial stage of their development, meandering freely along a wide and almost flat plain composed of fluvioglacial deposits. Then, as the erosion basis decreased, the channels incised into the water-resistant glacial deposits of the Valdai horizon. In the last millennium, vertical erosion sharply increased, which is associated with overcoming difficult to wash out fluvioglacial Quaternary loamy rocks and the direct impact of the flow on the underlying Devonian sediments, and at present, according to our estimates, it reaches 1-3 cm per year. As the riverbeds cut in, the planned deformations slowed significantly. The channels develop, although not to the full extent, by the type of forced meandering.