МОРФОДИНАМИКА РЕЧНЫХ ДОЛИН ЛЕВОБЕРЕЖЬЯ АНГАРЫ

Abstract

The article presents the results of the first stage of a comprehensive (hydrological, paleogeographic, and landscape-geomorphological) study of the development of river valleys on the left bank of the Angara. An analysis of fluctuations in the maximum runoff performed with the use of difference integral runoff curves, identified six periods of change in water content of the rivers under study according to the maximum annual discharges for the period from the beginning of observations to 2019. Basing on the analysis of the structure and composition of the floodplain alluvium in the foothill and plain areas, the features of the Holocene sedimentation in the valley of the Belaya River were revealed. The existing ideas about the chronology of the formation of the floodplain massifs are presented in detail. Differences in the facies structure of the floodplain deposits in the piedmont and plain parts of the basin reflect the morphodynamics of the floodplain-channel complexes. For the sections of the foothill part of the basin, there is noted a lack of facies of the near-channel shoal. At the same time, the age of the sands of the floodplain facies here is much younger (800–900 years) than in the lower part of the basin (2.5–3.4 thousand years), which indicates the dynamics of the channels in the foothill part. A number of pronounced changes in sedimentation within the studied floodplains (8.8 thousand cal. BP, 3.4 thousand cal. BP) chronologically correlate with regional climatic changes, which may indicate a significant role that climate andclimate-driven changes in fluvial activity played in the formation of floodplains in the study area. The use of evolutionary series of plant communities in floodplain complexes is possible when typing the morphological elements of the valley during the transition from channel to floodplain states. In the future, this approach could serve as a criterion for the identification of overgrowing invariants when comparing valleys of different basins, but under similar morphodynamic conditions.