Bipartite Sediments within the Moscow (Saalian) Glacial Limits of the Russian Plain: Mineralogy, Micromorphology and Soil Formation Framework

Kust, P.; Makeev, A.; Lesovaia, S.

Авторы: Kust Pavel, Alexander Makeev, Sofia Lesovaia
Сборник: Field Symposium of the INQUA PeriBaltic Working Group "From Weichselian Ice-Sheet Dynamics to Holocene Land Use Development in Western Pomerania and Mecklenburg". Abstract Volume
Тезисы
Год издания: 2019
Место издания: German Research Centre for Geosciences GFZ Potsdam
Первая страница: 53
Последняя страница: 55
DOI: 10.2312/gfz.b103-19012
Аннотация: http:/doi.org/10.2312/GFZ.b103-19012 Macro- and micromorphological characteristics, as well as textural and mineralogical properties of soils on a reddish brown Saalian basal tills of Moscow (Late Saalian / Warthe / MIS 6) deposits, covered only with a thin veneer of sands, sandy and silty loams - the cover layer, are discussed. Basal till and the cover layer forms bipartite sediments - an important component of landscapes in northern Europe, including the centre of the Russian Plain. Our numerous laboratory studies allow to confirm that the formation of the cover layer took place close in time to the deposition of the basal till, and the cover layer resulted from rewashing of the till surface by temporary streams with local aeolian input. This was established by spatial field studies - similar lithological features of the cover layer and the basal till; laboratory analyses - similar coarse fragments, uniform distribution of geochemical indexes may – all these indicate such type of deposition of the cover layer (Makeev et al. 2019). Numerous OSL datings of the cover layer which vary from late Moscow (Saalian) to Early Valday (Weiselian) time also support, that such bipartite sediments are among the oldest soil parent materials subjected to pedogenesis starting from the time of their deposition (MIS 6) till now. Transformation degree of basal till and cover layer under the influence of pedogenesis have been studied in four key sites of following regions of the Russian Plain: Moscow, Yaroslav, Tver and Archangelsk. It was estimated using a set of morphological methods: X-ray high-resolution microtomography on Skyscan 1172 (Bruker) for visualization and morphometric analysis of the internal microstructure in non-disturbed natural samples of peds; micromorphology on the polarizing microscope BX51 (Olympus) and photo scanner 9000 MarkII (Canon); submicromorphology on SEM GSM 6060a (Jeol) and set of analytical methods including clay mineralogy. Many lithological features show high stability under the pedogenetic impact. Such features look similar for the lower soil horizons (BC and C) formed in the basal till at a depth of approx. 2m and for horizons subjected to intensive pedogenesis (Bt1 and Bt2 horizons at a depth of approx. 60 cm). These morphological key features include: high weathering through the whole strata; bright reddish-brown color (up to 5YR 6/6 by Munsell soil color chart) inherited from sediments mobilized by the glacier; overconsolidated matrix-supported fabric with low porosity as a result of big pressure under the glacier; till architecture including sand lenses, shearing features, folding, thrusting and rotational structures, tension fractures and other evidences of emplacement of matrix within the mobile sediment. Clay mineralogy in the bulk samples also shows several key features: a) uniform composition of the basal tills part in the all studied key sites; b) difference between cover layer and basal till part; c) uniform changes in the clay mineral composition with increasing depth (from 2Bt1 horizon to 2BC) and its correlation with geographical position of the key site; d) local and profile differences between clay mineral composition of the cover layer. Figure 1. Stability of lithological features. a: lithological discontinuity, a clear border between the cover layer and basal till part; b: 3D structure of E horizon (cover layer) with fragments of the 2Bt horizon (basal till part); c, d: shearing zone on the top of basal till part. I – cover layer fragments, II – basal till fragment (NII – left, NX – right) Studying these soils as pedosedimentary sequences allowed to identify the following set of features: pre-depositional, syndepositional, pedogenic (of different developmental stages). The abundance of relic pedogenic features allows regarding such sequences as surface paleosols. The research was supported by the Russian Foundation for Basic Research (project №17-04-01221) and the Russian Science Foundation (project №16-17-10280).
Добавил в систему: Куст Павел Германович

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Bipartite Sediments within the Moscow (Saalian) Glacial Limits of the Russian Plain: Mineralogy, Micromorphology and Soil Formation Frameworkтезисы доклада Тезисы

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