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

Journal of the Geological Society. 2022. Vol. 179. No. 5. Article jgs2021-135.

Ekaterina V. Garankina, Lobkov V., Shorkunov I., Belyaev V.

Watershed landscapes of the Central Russian Plain being subject of 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-orientated wedge casts in surficial deposits. The research aimed at identifying relict periglacial features both in landscape and sedimentary sequence of the Borisoglebsk Upland to determine if there is a correspondence of those 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 to reveal and spatially correlate three generations of wedge casts, each buried by well-pronounced sedimentary units, and a specific bulbous kind of casts. Type of cryogenesis, erosion, and slope mass-movements shifted 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 those casts are almost erased in the modern topography while shallow dry gullies mostly inherit pre-Holocene wider linear depressions with no clear respect to the buried cryogenic polygons.

Keywords: East European Plain, mantle loams, past permafrost, thermal-contraction cracking, ice wedges, pseudomorphs, cryoturbations, cover beds