General Stratigraphy Of Postglacial Sedimentary Cover Of Vladimir Opolie

Ch. 8. P. 109–110.

Ekaterina Garankina, Shorkunov I., Lobkov V.

Editor of translation: Ekaterina Garankina

At the southernmost range of mantle loams distribution, so-called loess islands (Makeev, 2012) show some resemblance to the profound loess-paleosol sequences of the extra-glacial areas (Velichko, 1990). They commonly occupy relative topographic highs that inherit pre-Quaternary erosional uplands capped with thin glacial tills (Fig. G). In contrast, surrounding lower-lying outwash plains are majorly devoid of the loamy cover representing the easternmost branch of the European eolian sand belt (Zeeberg, 1998). Considered one of the largest loess islands on the Russian Plain, a plateau referred to as the Vladimir Opolie rises to 232 m a.s.l. (Fig. E). Its flat and gently sloping watersheds are composed of MIS6 glacial till hooded by a thick loess-like loamy cover (State geological map of Quaternary deposits, O-37-XXXV, 1968). A number of archeological sites reflect the prolonged human occupation history of the area since the Early Paleolithic (Sukachev et al., 1966; Kuzmin et al., 2014) corroborated by the high degree of anthropogenic deforestation and large plowing coverage since the Early Mediaeval time (Makarov et al., 2017, 2020; Dobrovolskaya et al., 2020). And as the former has triggered a thorough examination of postglacial sedimentary exposures in the region (Tseytlin, 1965; Sukachev et al., 1966; Moskvitin, 1967; Velichko et al., 1996a,b; Alifanov et al., 2006, etc.) the latter has presented an opportunity of investigating the spatial landscape heterogeneity of extensively cultivated fields (Velichko et al., 1996a,b; Alifanov, 1995; Zhurbin & Fedorina, 2017; Ovchinnikov et al., 2020, etc.). Thereof intrinsic heterogeneity of loess-like mantle and soil cover was argued concerning the postglacial landscape dynamics (Makeev & Dubrovina, 1990; Gugalinskaya, 1997; Kleber & Gusev, 1998; Gugalinskaya & Alifanov, 2005; Makeev, 2009, 2012; Makeev et al., 2015). Late Pleistocene periglacial phenomena were considered to have played an important part in differentiating deposition and pedogenesis and creating fine geological and landscape patterns (Berdnikov, 1976; Velichko et al., 1996a,b; Alifanov, 1995; French, 2007; Kabała et al., 2022; Woronko et al., 2022, etc.). A.A. Velichko distinguished three paleocryogenic horizons in the loess-like mantle. The oldest Smolensk horizon indicated mostly by solifluction features was referenced to the Early Glacial. The overlying Vladimir horizon is considered to be of the late Middle Valdai (28–23 ka) (Velichko et al., 1996a,b) or the early Late Valdai (Velichko et al., 2006, 2011) age includes both solifluction and cryoturbation footprints and wedge-shaped deformations in the southern regions. Pronounced thermal contraction cracking of the latest Yaroslavl horizon manifests in two separate phases reflecting the Late Pleniglacial (LGM) and Late Glacial (Younger Dryas) coolings respectively (Velichko et al., 1996a,b, 2006). However, Sycheva et al. (2020, 2021) argued for the LGM timing of the Vladimir horizon with both stages of the Yaroslavl horizon bound to short Late Glacial cooling. A series of buried paleosols intercept the sedimentary sequence of cold epochs with remnants of the Mikulino (MIS5e) interglacial, Krutitsy (MIS5d), and Bryansk (MIS3) interstadial pedogenesis (Velichko, 1958; Velichko et al., 1996a,b). Velichko et al. (2011) consider two MIS5 paleosols of the Mezin soil complex to be disturbed by the Smolensk cryogenic deformations. Bryansk paleosol with low organic content, thereby, reflects the late MIS3 relative warming accompanied by Vladimir cryogenic deformations. Overlying thick MIS2 deposit hosts 2 phases of Yaroslavl wedge casts maintaining both dark relict humus horizon (RHH) and actual soil cover. Although the origin of RHH is still controversial passing either as Late Glacial (Gugalinskaya & Alifanov, 1995; Gugalinskaya et al., 2001; Makeev, 2009; Makeev et al., 2015) or Holocene (Alexandrovskiy, 1996) in age, its contemporaneous spatial differentiation is distinctly bound to the polygonal net of Yaroslavl wedge casts. Soils with RHH qualified as Mollic and Gleyic Luvisols are associated with polygonal troughs while polygon interiors are occupied by Calcic Luvisols without RHH (Makeev, 2012; Makeev et al., 2015). The former have higher organic matter content and are almost devoid of carbonates compared to the latter where both the matrix is calcic and carbonate nodules occur. Nodes of polygonal wedge troughs are often occupied by rounded depressions 30–50 cm deep and 10–20 m wide (Makeev et al., 2015). On slopes, the polygonal pattern usually transforms into soil stripes or dells (Antonov et al., 1992; Czudek, 1993; Eremenko et al., 2010; Sycheva et al., 2020; Khudyakov et al., 2020) that are thought to inherit the wedge troughs running downhill and occasionally utilized by linear erosion. However, majorly smoothed in the modern topography of gently sloping arable fields, those polygonal and linear patterns are still emphasized exclusively by soil and vegetation cover variations (Velichko et al., 1996a,b). Reflected in spectral characteristics of satellite and aerial images, such landscape patterns are addressed as cropmarks (Andrieux et al., 2016a,b; Ewertowski et al., 2017) and used as indicators of the past periglacial condition.

Integration of thorough morphological investigation supported by analysis of spatial and depth distribution of textural, magnetic susceptibility, organic and carbonate matter properties at the key sites at the Borisoglebsk Upland and Vladimir Opolie allowed us to reveal the high heterogeneity of sedimentary and soil cover conditioned by relict periglacial features yet demonstrating sufficient reproducibility across the entire marginal zone of the MIS6 (Moscow) glaciation. – Postglacial thickness show contrasting stratigraphic sequence reflecting stable sedimentary environments at each stage of landscape development. The predominant colluvial trend of re-deposition shifts upwards to local shallow lacustrine sedimentation with increasing eolian input. During the Late Pleniglacial, the eolian agent prevails as both sediment source and deposition mechanism. Since the Oldest Dryas, the colluvial re-deposition once again takes the leading part in the Late Glacial landscape transformation and Holocene soil cover evolution. The main patterns of spatial heterogeneity were enabled at stages of surface stabilization due to negligible sediment transfer when cryogenic and pedogenic processes repeatedly transformed the postglacial stratum. – At the key site, the first in situ soil body is a buried paleocryosol correlated with the regional MIS3 pedogenesis (Bryansk or Sungir paleosol). The overlying pronounced loess unit reflects a contrastingly dry cold sedimentation environment strongly affected by another interstadial pedogenesis in a rather warmer climate presumably at the time of the Main Deglaciation (end of the Late Pleniglacial, Trubchevsk paleosol). – Three wedge-cast horizons each separated by pronounced loess or colluvial deposition represent distinct changes in the periglacial environment from the formation of wider composite wedges in host sediments with higher water capacity to severely dryer settings enabling the development of more narrow composite wedges and initial earth wedges. The cryogenic sequence culminated with the occurrence of smaller but organic-rich soil wedges reflecting the last cold episode of the Late Glacial (the late phase of Yaroslavl cryogenic horizon, Younger Dryas). Therefore, two older wedge-cast horizons at the base and on top of the thick loess stratum are correlated with two separate cold stages – the onset of LGM (Vladimir cryogenic horizon) and the Oldest Dryas (early (main) phase of Yaroslavl cryogenic horizon). That points to a period of warm Luvisol-like pedogenesis in-between suggesting distinct climate warming during the Trubchevsk Late Pleniglacial interstadial. – Late Glacial elevation amplitudes of the polygonal wedge cast networks are almost completely leveled due to the prolonged erosion trend at the key site. Despite that, the differentiation of the actual soil cover inherits that polygonal pattern. Polygon interiors, adjacent rims, and dells occupying the polygonal troughs running downhill display the high contrast of soil microcombinations. However, the transverse troughs where wedge casts are exposed and significantly truncated show no distinction in soil distribution from polygon interiors. Thus, the actual soil cover is not sensitive to the cryogenic pattern per se but reflects the surficial deposit re-distribution with respect to buried cryogenically constrained erosional landforms. – Postglacial thickness of the Vladimir Opolie replicates the same stratigraphic sequence of sedimentation, pedo-, and cryogenesis typical of loess-paleosol series of extraglacial southern regions. Simultaneously its type of environmental record with the welded architecture of Late Pleistocene and Holocene soil bodies and intervening erosion episodes is more comparable with the palimpsest record of mantle loams at the neighboring glacial uplands. Interfluvial soils of the region can be regarded as Late Pleistocene – Holocene pedocomplexes.

Keywords: late Pleistocene, mantle loams, cover beds, glacial till, bipartite sediments, stratigraphy

In book

Valdai Periglacial Field Symposium Guidebook, 27–30 August 2023 [Electronic edition]

Гаранкина Е. В., Константинов Е. А., Лобков В. А., Макеев А. О., Панин А. В., Шоркунов И. Г., Бричева С. С., Захаров А. Л., Карпухина Н. В., Куст П. Г., Лазукова Л. И., Лебедева М. П., Посаженникова В. С., Рудинская А. И., Русаков А. В., Самусь А. В., Сычев Н. В., Украинцев В. Ю., Шеремецкая Е. Д. M.: -, 2023.