Transformation of local kettle holes based on geological and geophysical evidence, Borisoglebsk Upland, Central European Russia

Abstract

Late Pleistocene evolution of Central European glacial landscapes is often narrowed down to the impact of postglacial linear erosion. Yet extensive watersheds in the marginal zone of MIS6 glaciation were protractedly affected by the postglacial flattening in periglacial and interglacial conditions. Local sediment sinks such as kettle holes and dry valleys infilled throughout the postglacial stage can serve not only as records of paleoenvironmental changes but also for assessing the scales of watershed denudation and landscape transformation since the last glacial cover degradation. We attempted to use electrical resistivity tomography for paleogeomorphological survey of a local flat-bottomed depression previously studied by conventional lithological and stratigraphic approaches. The obtained geophysical profile showed a contrasting picture of the relatively higher-resistive glacial base embedded with low-resistive lenses 3-25 m thick a top. The latter were correlated with the postglacial loamy deposits of colluvial and lacustrine origin that infilled the lows of initial glacial topography. It was revealed that the depression has a particularly complex inner structure embodying at least two buried kettle holes divided by a large glacial ridge almost buried under the postglacial infill. They functioned as separate basins during much of the Late Pleistocene and have probably merged only at its final stages. The geophysical cross-section also showed a quite variable bottom relief of each kettle with significantly steeper slopes than the modern sides of the depression. Thus, electrical resistivity tomography prospecting proved to be useful for detecting the postglacial loamy infills of initial lows of the MIS6 glacial topography and can be further employed to better understand the actual scales of the postglacial redeposition and landscape modeling during the last 150–130 ka.