Identifying relict periglacial features in watershed landscape and deposits of Borisoglebsk Upland, Central European Russia

Abstract

Watershed landscapes of the Central Russian Plain, which were subjected to the Late Pleistocene permafrost, bear witness to widespread cryogenic structuring. It is reflected both in semi-regular spots, blocks and polygons in soil and vegetation cover on arable fields and as vertically oriented wedge casts in surficial deposits. This study aimed to identify relict periglacial features in both the landscape and sedimentary sequence of the Borisoglebsk Upland to determine if there is a correspondence of these cast networks to the distribution of landforms and regular patterns of soil and vegetation cover. Combined interpretation of aerial and satellite multi-temporal imagery and detailed investigation of vertical cross-sections in gradually expanding geotechnical trenches including apparent magnetic susceptibility measurements allowed us to reveal and spatially correlate three generations of wedge casts, each buried by well-pronounced sedimentary units, and a specific bulbous type of cast. The type of cryogenesis, erosion and slope mass-movements changed from the Late Pleniglacial to Late Glacial, representing a good proxy in the watershed sedimentary cover for palaeoenvironmental reconstructions. However, regular polygonal patterns caused by these casts are almost erased in the modern topography whereas shallow dry gullies mostly inherit pre-Holocene wider linear depressions with no clear relationship to the buried cryogenic polygons.