Sedimentation rates on the floodplains of lowland rivers in the center of the European Part of Russia according to the study of soil-alluvial chronosequences

Abstract

The floodplain deposition rates for the Istra, Oka and Seim rivers valleys were estimated based on a combination of dating methods (radiocarbon, radiocesium and historical-archaeological) for various time windows of the Holocene. In addition, a new method to estimated sedimentation rate, based on the assessment of the degree of soil profile development of paleosols buried in alluvium was applied. Spatio-temporal differences in the rates of floodplain sedimentation have been established based on chronological and soil-geomorphological studies. It was found that sedimentation rates on the young floodplain of Seim and Istra rivers is 1.823 mm year1), 215 mm year1, respectively. While on the ancient floodplains of Oka and Seim rivers during different periods, the floodplain deposition rate varied within the range of 0.010.7 mm year1. The periods of increased sedimentation rates were short in time. Based on the study of a young, rapidly growing Istra River floodplain, the deposits of which are dated on the basis of historical and archaeological materials, new sedimentation rates that characterize the floodplains of the center part of the East European Plain were obtained: alluvium without signs of pedogenesis is formed at a sedimentation rate of more than 15 mm year1, with signs of pedogenesis at a rate of 215 mm year1, cumulative soils at a rate of 0.52 mm year1. Cyclic fluctuations in the sedimentation rate in the Holocene were established on the basis of14C and archaeological dates for to the Nikitino section located on the Oka River floodplain, where a large series of well-developed paleosols were distinguished. It was found that during periods with active accumulation of alluvium layers, sedimentation rate was about 2 mm year1, which is 20 times higher than in longer periods soil formation, when sedimentation rates were 0.070.14 mm yr1.