THE INFLUENCE OF GEOLOGIC-GEOMORPHOLOGIC CONDITIONS ON THE FORMATION AND SPATIAL DISTRIBUTION OF BEDLOAD SEDIMENTS OF THE EASTERN-EUROPE'S RIVERS

Abstract

The map of channel-forming bedload sediments of the Eastern Europe rivers compiled by the author shows the two main patterns. Firstly, difference in the bedload grain size is associated with the different geomorphic and orographic provinces drained be the rivers. Secondly, on the lowland rivers there is a prominent negative trend of bedload grain size from the north to the south. First tendency emphasizes strong control which geological and geomorphic structure, mainly bedrock lithology and surface gradient, have over bedload grain size. The second trend can be explained by the distribution of Pleistocene glacial and fluvio-glacial deposits over the East European Plain. Rivers with gravel or sand-gravel channels are widespread in its western and northern parts where valleys are cut into the Middle and Late Pleistocene glacial deposits rich in coarse particles up to boulders. Widespread occurrence of silty and sandy-silty bedload in the rivers of the southern regions is associated with fluvial reworking of loessy loams accumulated under periglacial conditions and clayey marine deposits left by transgressions of the Black and Caspian seas. The rivers of central and eastern parts of the East-European plain commonly have sandy bed-load sediment. Fluvio-glacial deposits of the outwash plains are the main source of sandy particles as well as older alluvial sands left from the ancient rivers of the East-European plain.