Mid-Holocene gullying indicating extreme hydroclimatic events in the centre of the Russian Plain

Abstract

At the Satino site in the center of the Russian Plain, major events of the Holocene erosion history are concentrated on sides of river valleys incised into smooth moraine landscape. Valley sides are dissected by Pleistocene gullies. Extraordinary for the Holocene was formation of four new permanent gullies. Three of them had appeared in the Late Atlantic – Early Subboreal time. One gully permitted direct dating of the fan base, which gave estimation of its appearance between 4.3-4.6 ka BP (cal). Two other gullies were constrained within the two intervals 5.2-5.5 and 5.9-6.2 ka BP (cal), based on assumed correlation with extreme runoff events dated over the area. After a long break of erosion, two of the gullies had exhibited the second phase of activity between 3.0-3.7 ka BP (cal). As in the Bronze Age no settlements are known in the study area and surroundings; human reinforcement of erosion was minor if any. The four intervals of extraordinary linear erosion on valley sides coincided with extremely high runoff events in streams of various sizes, which left prominent geomorphic and sedimentological features: meander arcs, coarse-grained alluvium, buried floodplain soils, etc. Altogether, this is considered to indicate a highly irregular climatic pattern in the area in the interval of 3.0-6.2 ka BP (cal) with several phases containing a series of extreme downpours, which had no analogs throughout the Holocene.