Hilltops Transformation at Marginal Zone of Middle Pleistocene Glaciation, Borisoglebsk Upland, Central Part of Russian Plainтезисы доклада Тезисы

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[1] Hilltops transformation at marginal zone of middle pleistocene glaciation, borisoglebsk upland, central part of russian plain / Е. В. Гаранкина, П. В. Андреев, В. Р. Беляев et al. // Abstracts of the 6th International Conference on “Palaeo-Arctic Spatial and Temporal (PAST) Gateways, 16-20 April 2018. — Durham, 2018. — P. 74–75. The Upper Volga region is one of the stratigraphic references for reconstructing geomorphic evolution of northern part of the Russian Plain since termination of the last Middle Pleistocene glaciation (Moscow – Saalian, MIS6) thanks to a large number (>20) of reference sections described in details. At the same time, interpretations and correlations remains controversial for two main reasons: i) different backgrounds and basic concepts adopted by different research groups studying the same set of sections; ii) lack of absolute dating. Since the degradation of Moscow ice cover, prominent geomorphological events at its marginal zone concentrated largely within the fluvial network. Hence, most of the landscape development reconstructions have been strongly biased towards understanding the fluvial landforms, sediment sequences and corresponding incision-widening-infill cycles. However, thorough understanding of clearly notable fluvial activity cycles creating the existing complex hydrographic network does not shed sufficient light on much slower and lower-amplitude evolution of interfluves characterized by a variety of genetic and morphological types (i.e. typical moraine ridges or hills, dead-ice moraine knob-and-kettle topography, glacial melt-water channels and outwash plains, glaciolacustrine depressions, etc.). The case study area of Borisoglebsk Upland adjoins long-existing tectonic depression with inherited subsidence trend since Pre-Quaternary. Its central part is occupied by Nero Lake providing continuous and prolonged sedimentary record for the basin. The existing palaeolandscape reconstructions for the surroundings are based entirely on integration of the lake sedimentary sequence, valley infills and correlated geoarcheological sites, reflecting local confined conditions. However, deciphering another part of the local environmental change history carved into the interfluve morphology and surface sediments has a great potential to support reliable extrapolation to regional-scale generalizations. Moreover, in most of the studies interfluve surfaces are considered as relatively simply arranged geomorphic, lithogenic and pedogenic background. Origin of texturally differentiated sod-podzolic soils of the region is also a matter of ongoing debate. Contribution and relative importance of surface gleyization, lessivage and podzolization, on one hand, and sedimentation features, on the other, into their formation and evolution has not yet been determined. Nevertheless relic components such as remnants of periglacial microtopgraphic features are observed almost everywhere in the landscape and soil cover structure, testifying dominance of fundamentally different environmental conditions during their formation. In order to decipher this natural archive, almost devoid of traditional palaeoenvironmental proxies, interdisciplinary research of interfluve surfaces and slopes geomorphic structure, lithology, textures and pedogenic properties of sediments has been carried out. It involved combination of several independent approaches including detailed geomorphic descriptions, DGPS profiling, topographic maps and remote sensing data analysis (open source satellite imagery, global satellite DEMs, aerial photography using UAV), thorough description and sampling of one new hilltop geological section (4 m deep) and 20 cores up to 9 m deep along the selected transect. Integrating the available results, we propose a detailed scenario of the interfluve landscape evolution over the last ca. 150 ka at the Moscow glaciation marginal zone. It includes stages of ice cover degradation and successive glaciofluvial-glaciolacustrine transformation during the end of the Middle Pleistocene when supraglacial and moraine-dammed proglacial lakes strongly controlled rates and distribution of erosion and sedimentation. At the hilltops, they were followed by relatively slow morpholithogenic evolution with continuous polygenic soil formation and superimposed cryogenic periods. Simultaneously, upper parts of glacial depressions (meltwater channels and dead-ice moraine kettles) have been gently infilling and flattening by lacustrine, alluvial and colluvial deposits with at least one distinctive period of fluvial incision during the Late Pleistocene. The present-day fluvial network often inherits ancient meltwater channels, however, does not penetrate as far into the most elevated parts of interfluves.

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