Fluvial chronology in the East European Plain over the last 20 ka and its palaeohydrological implications

Abstract

A database containing 983 absolute ages of fluvial deposits was interpreted in palaeohydrological terms and 646 dates were found associated with 754 local palaeofluvial events – geomorphic or sedimentological traces of changing fluvial activity. Combined probability density functions of high- and low-activity dates were used to detect time intervals of different palaeohydrological status. After low fluvial activity during LGM, two palaeohydrological epochs were designated: extremely high activity in the end of MIS 2 (ca. 18–11.7ka before CE 2000–b2k), and much lower activity in the Holocene. Within the Holocene, two hierarchical levels of hydroclimatic variability were designated according to their duration and magnitude – regional palaeohydrological phases (centuries to few millennia) and regional palaeofluvial episodes (decades to few centuries). Tendency is rather clear of activity lowering in the first half and rise in the second half of the Holocene. Extremes within the palaeohydrological phases were designated as 19 palaeofluvial episodes: 7 high activity HA-episodes, 8 low activity (stability) LA-episodes and 4 contrast, or complex, CA-episodes. In most cases changes of fluvial activity were most likely induced by changing amounts of spring snowmelt runoff. Most distinct correlation of temperature and hydrological regimes was found in the Late Holocene: high fluvial activity corresponded to cold climatic phases (Little Ice Age), low activity, to warm phases (Medieval Climatic Optimum, current climate warming). The suggested fluvial chronology was compared with independent hydroclimatic archives such as palaeosoils and lake levels. Correlation with soil formation/alluviation epochs was found very close, with some exceptions in the Early Holocene. Correspondence of fluvial activity to the Caspian Sea level changes is rather high in the second part of the Holocene and is poor before 4–5ka b2k, which can be explained by insufficient data behind both types of reconstructions. Correlation of changes in fluvial activity within a west–east transect over Europe revealed relatively poor correlation in the Early and Mid Holocene and much higher synchronism since 3.0ka b2k, which may indicate increasing role of westerlies in controlling European climates in the Late Holocene. Throughout the whole Holocene, changes of fluvial activity over EEP were governed by natural climate forcing until the last few centuries when land use changes induced accelerated hillslope and gully erosion.