Navigation – Plan du site

Fluvial response to proglacial effects and climate in the upper Dnieper valley (Western Russia) during the late Weichselian and the Holocene

Réponse du Dniepr supérieur (Russie occidentale) aux influences proglaciaires et au climat au Weichselien supérieur et à l’holocène
Andrei Panin, Grzegorz Adamiec et Vladimir Filippov
p. 27-48

Résumés

La vallée du Dniepr en amont de la frontière Russie-Biélorussie se caractérise par une incision majeure antérieure au Dernier Maximum Glaciaire, qui est imputée à la formation du bourrelet glaciaire. Durant le Dernier Maximum Glaciaire, des embâcles glaciaires se sont produits en aval de Smolensk, aboutissant à un déplacement de la vallée vers le sud et à une accumulation localement importante. La rupture du barrage glaciaire a eu pour conséquence une incision jusqu’aux niveaux antérieur au Dernier Maximum Glaciaire, puis une période de sédimentation marquée s’est produite avant le début de l’Holocène. Cette sédimentation est associée à la diminution de la pente longitudinale du Dniepr consécutive à la disparition du bourrelet. La subsidence s’est poursuivie à l’Holocène, avec pour conséquence un basculement de la vallée estimé à 4-5 m le long d’un tronçon de 100 km, soit une valeur nettement supérieure à celles obtenues par les modèles. Au début de l’Holocène, le fleuve a formé de larges paléochenaux associés à des chenaux rectilignes ou tressés. Les paléo-débits associés à ces paléochenaux sont estimés à trois fois le débit de la crue moyenne du Dniepr, et associés à un forçage climatique. Des restes de la moraine du Moscovien (MIS 6) subsistent sous la forme de collines résiduelles, individualisées lors de la formation de la vallée à la fin du Moscovien, et recouvertes de sédiments fluviatiles avant le début de l’Holocène.

Haut de page

Texte intégral

The authors are grateful to Juergen Herget and an anonymous reviewer for useful comments on the initial submission of the manuscript. Special thanks are to Stephane Cordier and David Bridgland whose really hard work as guest editors resulted in considerable improvement of the paper's content and the English language. Authors are also thankful to Evgenia Selezneva for assistance with field GPS survey and for help in processing netcdf files (fig. 4 and background for fig. 11B). Financial support for this study was received from Russian Foundation for Basic Research (RFBR), project no. 12-05-01148.

1 - Introduction

1Large palaeochannels are known from many regions of Central and Eastern Europe (Szumanski, 1983, 1986; Vandenberghe et al., 1994; Howard et al., 2004; Borisova et al., 2006; Gębica et al., 2009; Sidorchuk et al., 2009; Kasse et al., 2010). In most cases they have a meandering pattern and a Lateglacial age. Most researchers associate large meanders with significant climatically-driven increases in fluvial discharge. Large palaeochannels ten or more times the width of the modern river were also recognized in the upper and middle Dnieper valley. Unlike in other European valleys, where large Lateglacial meanders form part of low terraces or the floodplain, many large palaeochannels in the Dnieper valley are separated from the present-day river by hills composed of Mid-Pleistocene till (Barashkova et al., 1998). Such palaeochannels were studied between Orsha and Rogachev in Belarus and assigned a LGM age (MIS 2) on the basis of geomorphic correlation with terraces in tributary valleys (Kalicki & San'ko, 1992, 1998). Large palaeochannels were interpreted as branches of a large glacially-fed river that were abandoned after the glacial meltwater inflow had ceased.

2The role of the Dnieper fluvial system in the southward transportation of glacial meltwater cannot be overstated. The Dnieper River was the only route linking the Black Sea to the decaying Scandinavian ice sheet (SIS; fig. 1) in late MIS 2. The occurrence of glacial meltwater pulses has been widely used to interpret the Black Sea hydrology during the Late Pleniglacial (Major et al., 2006; Lericolais et al., 2011; Sidorchuk et al., 2011; Soulet et al., 2011, 2013). Despite the fact that glacial meltwater outflow through Dnieper and its tributaries has been important in the interpretation of Black Sea and Caspian Sea palaeogeography during the period of deglaciation, the timing and path of this outflow remains unsure. Also neglected has been the role in valley development of crustal warping related to glacio-isostatic effects, which may be deduced from the close location of the Upper Dnieper valley to the SIS boundary (fig. 1 & 2). It has long been recognized that horizontal mass transfer in the low viscosity asthenosphere due to glacial loading would have induced uplift and the formation of a peripheral bulge with its axis parallel to the ice sheet boundary (e.g. Mörner, 1979; Peltier, 1990). Estimates of forebulge axis uplift at the south-eastern margin of the SIS range from 60 m (Fjeldskaar et al., 2000) to as much as 110 m (Peltier, 2004) and 170 m (Mörner, 1979). Crustal unloading due to ice sheet retreat was accompanied by forebulge subsidence. The influence of proglacial crustal movements on fluvial systems at the periphery of the SIS was studied by Bylinski (1990, 1996), who described changes of alluvial terrace thickness in river systems from the Elbe in the west (Germany) to the Pechora in the north-east (Russia). These were related to river damming by the forebulge, and erosion/aggradation successions associated with forebulge migration in response to a retreating ice margin during deglaciation. Wallinga et al. (2004) and Busschers et al. (2007) found incision/aggradation events and lateral valley tilting in the Rhine-Meuse delta around the LGM and related them to the build-up and subsequent subsidence of a SIS glacio-isostatic forebulge. The position of the Upper Dnieper in the vicinity of the ice margin (fig. 1 & 2) makes it potentially vulnerable to similar effects associated with SIS forebulge rise and decay.

3The aim of the present study is to use a multi-proxy approach, including field-survey, numerical dating and geomorphological correlation, to reconstruct the development of the Upper Dnieper during the last 20-25 ka, including the origin and chronology of large palaeochannels, and to assess the respective roles of proglacial effects, such as forebulge formation and glacial damming, as well as palaeohydrological change, on this development.

Fig. 1: Overview map of the Dnieper Basin.

Fig. 1: Overview map of the Dnieper Basin.

Dashed black line is the LGM ice sheet boundary (after Velichko et al., 2011). Arrows show routes of LGM meltwater flow (modified from Sidorchuk et al., 2011). Circled numerals: 1/ Dorogobuzh (start of study reach), 2/ Chekulino (end of study reach), 3/ Orsha, 4/ Rogachev

Fig. 2: The Upper Dnieper fluvial system. Location map and main groups of palaeochannel – erosional remnant systems.

Fig. 2: The Upper Dnieper fluvial system. Location map and main groups of palaeochannel – erosional remnant systems.

1/ LGM ice sheet margin (after Barashkova et al., 1998), 2/ intra-valley erosion remnants, 3/ boundaries of large palaeochannels, 4/ palaeochannel chute and scroll bars, 5/ levees, 6/ location of study sites: 1/ Chekulino, 2/ Gnezdovo, 3/ Solovyovo

2 - Study area

4The upper Dnieper River valley was most probably formed at the end of MIS 6 after deglaciation of the Moscovian (Late Saalian) ice sheet, although it has been hypothesized (Kvasov, 1975, 1979) that this reach of the valley was formed only in post-LGM time due to drainage of large proglacial lakes. The present-day Upper Dnieper is a medium-sized river with an annual discharge of 43.5 m³.s-1 at Dorogobuzh (catchment area 6,390 km²) and 98.7 m³.s-1 at Smolensk (catchment area 14,100 km²) (fig. 2). The hydrological regime of the modern river is characterized by the highest stage occurring during the regular snowmelt flood (typically in April) and a low water stage persisting throughout the rest of the year, which may be interrupted by occasional rain-fed floods. The mean maximum (spring flood) discharge is 690 m³.s-1 at Dorogobuzh and 830 m³.s-1 at Smolensk. Rain-fed floods in summer-autumn and thaw floods in winter are always much lower than the spring flood. The river channel is 80-100 m wide at bankfull stage. The channel has an irregular pattern: long straight stretches alternate with short series of 2-3 meander bends with varying curvature. The long profile is concave upstream from the study area, but nearly straight at the 150 km stretch between Dorogobuzh and Smolensk (fig. 3).

5The Upper Dnieper catchment is a combination of hilly uplands with a maximum elevation of 260-280 m a.s.l., and flat swampy lowlands lying at 170-200 m a.s.l, the Dnieper being located at 175 m a.s.l. in Dorogobuzh and 160 m a.s.l. in Chekulino. Bedrock is everywhere covered by Quaternary sediments deposited mainly during Middle and Late Pleistocene glaciations. In the Late Valdai (Late Weichselian, MIS 2), glacial melt waters probably joined the Dnieper valley through its right-bank tributaries such as the Vop', Hmost', and Berezina (Barashkova et al., 1998). The influence of the SIS on valley development also included crustal warping over the proglacial area sufficient to modify valley gradient. According to the current version of the ICE-5G glacio-hydro isostasy model (Peltier, 2004), the upper Dnieper would have been located on the proximal side of the LGM peripheral forebulge (fig. 4). At the sub-latitudinal valley section between Dorogobuzh and Orsha, crustal updoming would have led to increased valley gradient during SIS advance and its subsequent decrease due to forebulge collapse as a result of deglaciation.

Fig. 3: Upper Dnieper valley long profile and elevation of palaeochannels, modern and estimated for the Early Holocene

Fig. 3: Upper Dnieper valley long profile and elevation of palaeochannels, modern and estimated for the Early Holocene

1/ Valley long profile, 2/ valley gradient, 3/ river sinuosity; Early Holocene palaeochannels (top and base of channel deposits), 4/ modern position in the valley (based on sections 4.2 and 4.4 and figures 6 and 8), 5/ estimated for the Early Holocene (see sections 4.5 and 4.6); vertical arrows show amplitude of valley tilt.

Fig. 4: Glacial forebulge at the SE margin of the SIS at 21 ka, predicted by the ICE-5G (VM2) model (Peltier, 2004).

Fig. 4: Glacial forebulge at the SE margin of the SIS at 21 ka, predicted by the ICE-5G (VM2) model (Peltier, 2004).

Contour lines show topography at 21 ka minus topography at 0 ka. Arrows point to locations of study sites (1/ Chekulino, 2/ Gnezdovo, 3/ Solvyovo).The ice-covered area is hatched;

3 - Methods

3.1 - Geomorphological survey

6To identify landforms in the Dnieper valley we used space images with 1-15 m resolution (Landsat 7 panchromatic channel, Google Earth, Yandex Map) and topographic maps with scales between 1:25,000 and 1:100,000. Even the most detailed maps with contour interval of 5 m were insufficiently precise to distinguish between different elements of relatively flat floodplain surface. However, a combination of maps with images obtained during spring flood and in autumn allowed a better understanding of the floodplain topography and measurement of palaeochannel parameters. In areas of swale-and-ridge topography created by lateral migration of meandering channels, palaeochannel width can be roughly estimated from the "two-thirds rule" adopted in fluvial sedimentology (Ethridge & Schumm, 1978), which derives from Allen's (1965b) statement that point bars occupy two-thirds of a channel width.

7Analysis of satellite images was complemented with field recognition of landforms. Topographic profiling and precise measurement of landform elevation above the river were conducted at study sites by DGPS field survey with a Leica Smart Station. Conversion from ellipsoid WGS84 heights to orthometric heights (leveled elevations above mean sea level) used on topographic maps was made with the EGM2008 geoid model. Sedimentary composition of valley forms was studied in hand and mechanical cores (up to 22 m deep), in hand pits and in river-bank exposures.

3.2 - Numerical dating

8An absolute chronology was established by radiocarbon and OSL dating. Samples were taken from vertical cleaned sections or from cores. OSL dates were produced in the GADAM Centre of Excellence, Institute of Physics, Silesian University of Technology, Poland (Panin et al., 2014; tab. 1). For dose rate determination, the samples were stored for ca. three weeks and high-resolution gamma spectrometry with Canberra HPGe detector was carried out in order to determine the content of U, Th and K in the samples. Each measurement lasted for at least 24 h. The activities of the isotopes present in the sediment were determined against IAEA standards RGU, RGTh, RGK after subtraction of the detector background. Dose rates were calculated using the conversion factors of Adamiec and Aitken (1998). The cosmic ray dose-rate contribution at the site was estimated as described by Prescott and Hutton (1994). Average lifetime depth of samples relevant for this estimation was assigned with respect to erosion/sedimentation history of each site and may differ from actual depth of samples (tab. 1). The average water content (WCa) was assigned on the basis of measurements of saturation water content (SWC) determined in the laboratory and sample position in the section relative to groundwater level (GWL). All samples were divided into three groups: below GWL, above GWL with seasonal saturation, above GWL and never saturated. The WCa values were assigned at SWC, 0.75×SWC and 0.5×SWC respectively. Lower WCa values were not assigned because of high humidity of climate in the study area. Sedimentation and geomorphic history of a given location was also taken into account when assigning the WCa values.

9Equivalent dose (ED) estimation was performed using an automated Daybreak 2200 TL/OSL reader on 6 mm large aliquots of coarse grains of quartz (90-125 μm). Blue light stimulation was carried out by the in-built array of blue LEDs (470 ± 4 nm) delivering about 60 mW.cm-² at sample position. Equivalent doses were determined using the single-aliquot regenerative-dose (SAR) protocol (Murray and Wintle, 2000), and the age estimates were obtained using the Central Age Model.

10Radiocarbon dates relevant for this study (tab. 2) were selected from the geochronological database for the Upper Dnieper catchment (Panin et al., 2014). All dates were produced using liquid scintillation techniques in the Geological Institute of Russian Academy of Sciences (RAS) in Moscow (index GIN), Institute of Geography RAS in Moscow (index IGAN) and Sankt-Petersburg University (index LU). Dates were re-calibrated in OxCal 4.2 (Bronk Ramsey, 2009) with the IntCal13 calibration curve (Reimer et al., 2013).

Tab. 1: OSL ages from th e studied sites in the Upper Dnieper valley.

Tab. 1: OSL ages from th e studied sites in the Upper Dnieper valley.

3.3 - Palaeodischarge and palaeoslope estimation

11Flood discharges Qm that formed palaeochannels can be estimated from mean flow velocities, palaeochannel width W and average depth Da. Of the three parameters required only W may be measured directly from palaeochannel topography (only palaeochannel cut-offs are suitable as they preserved their former width), the other two needing indirect estimation. Flood flow velocities may be approximated by velocities necessary for bedload transport, or critical flow velocities Vc of sediment entrainment. Maizels (1983) compared five methods of palaeovelocity determination from grain size characteristics of fluvial sediments and found a large scatter of results, which led to the conclusion that each method provides the order of magnitude rather than an accurate value of palaeovelocity. The other problem is that the grain size of fluvial sediments is extremely variable in natural streams, and results of velocity estimates depend from where the samples were taken. Finally, flow depth can be estimated from paleochannel sections at exposures or from the thickness of alluvial deposits (Maizels, 1983). Maximum bankfull channel depth Dm may be estimated by the total thickness of laterally accreted alluvial deposits from their top to the scoured base of channel fill (Bridge, 1978, 2003). Assessment of mean depth Da needs some assumptions on the Dm / Da ratio, which may vary considerably both from section to section and from river to river. Given the above uncertainties we used the following assumptions in our palaeohydraulic estimations:

12- numerical approaches were exploited with simplest possible structure and minimal set of parameters;

13- ratios of paleo (index P) to modern (index M) characteristics were predicted rather than their absolute values.

14The latter principle allowed omission of formulation of hypothetical relations, such as the relation between Dm and Da , on the assumption that such relations are valid both for the modern river and for palaeo-streams. Therefore if DmP / DaP = DmM / DaM, then:

15DaP / DaM = TAmP / TAmM (eq. 1),

16where TAm is the total thickness of laterally accreted channel sediments at terraces of different ages.

17The same approach was used in palaeovelocity assessment, for which many equations linking flow velocity and grain-size have been proposed (Maizels, 1983). However if an equation gives any systematic errors because of unknown local-specific reasons, these errors may be eliminated from ratios of equations for the same river with palaeo and modern parameters. To estimate Vc we applied the Mirtskhulava (1988) equation to our non-cohesive sediments with particle size d>0.25 mm: Vc = (g²dHm)1/4. Then the palaeo-velocity to modern velocity ratio reads:

18VcP VcM = (dP / dM)1/4 (DaP DaM)1/4 (eq. 2),

19where d is sediment particle diameter taken in mm and DaP DaM may be substituted by TAmP TAmM (equation 1). For homogeneous sediments defined as that for which the d90/d50 ratio is less than 5, d is median diameter d50, and for heterogeneous sediments (d90/d50 > 5) median diameter of the surface pavement should be taken (Mirtskhulava, 1988). In the absence of direct measurement, Zhuravlev (1988) recommends using d85 in the Mirtskhulava's formula in case of heterogeneous sediments. Grain size distribution for palaeovelocity estimation was measured by dry sieving with an Analysette 3 PRO vibratory sieve shaker. Fractions finer than 0.05 mm were measured with an Analysette 22 laser particle sizer.

20Following this, bankfull water discharges Qbf may be estimated from cross-section area defined by channel width W, average bankfull depth Da, and mean flow velocity: Q = WDaVa. For bankfull discharges, which are often considered as channel-forming discharges, sediment entrainment flow velocities Vc can be taken that maintain bedload transport and channel deformation. Also, bankfull discharges are usually close to mean maximum discharges. Then the ratio of palaeo and modern discharges reads as follows: QmP / QmM = (WP / WM) (DaP DaM) (VcP VcM) (eq. 3), where DaP DaM may be substituted by TAmP TAmM (equation 1).Estimation of channel slope for palaeoflow was made on the basis of the Chezy-Manning formula: n-1 Da2/3 Sc1/2, where n is Manning's unitless roughness coefficient and Sc is channel slope. As sediment grainsize and flow velocities did not change much (see section 4.5), both particle and bedform components of roughness must have not changed much either and therefore n may be treated as a constant. Given that in case of low river sinuosity channel slopes Sc may be substituted by valley slopes Sv, the ratio of palaeo and modern slopes reads: ScP ScM = SvP SvM = (VP VM)² (DM DP)4/9 (eq. 4).

3.4 - Discrimination of river channel patterns

21As was first shown by Leopold and Wolman (1957), meandering and braided rivers are characterized by different relations between discharge and channel slope, braiding occurring at higher discharges and slopes. In this study we exploited the latest findings by Kleinhans and van den Berg (2011) that account for channel sediments grain size and use variables independent of channel type: valley slope Sv rather than channel slope, mean annual flood Qm rather than bankfull discharge, reference channel width Wr = αQm0.5 predicted by a hydraulic geometry relation rather than actual channel width. Channel patterns are discriminated using the median grain size of the river bed d50 and the potential specific stream power ω = ρgQmSvWr-1, where ρ is water density, g is acceleration due to gravity and α equals 4.7 for sand (d < 2 mm) and 3.0 for gravel (d > 2 mm).

22Kleinhans and van den Berg (2011) propose a succession of channel types ranked by their lateral mobility and suggest critical ω values that discriminate consecutive channel types:

23- inactive (immobile) channels (indicated by subscript i);

24- active meandering channel with scroll bars (subscript s);

25- active meandering channel with chute bars (subscript c);

26- braided channel (subscript b).

27Critical ω values that discriminate consecutive channel types are proposed as follows: ωi/s ≈ 90d500.42, ωs/c ≈ 285d500.42, ωc/b ≈ 900d500.42 (Kleinhans & van den Berg, 2011). More generally, the first equation is the discriminator between inactive and active channels and the last one discriminates meandering and braiding channels.

28Common structure of the critical equations allows us to use the proportionality coefficient (we called it channel-type discriminator – CTD) to check the accordance between the estimated palaeodischarge and palaeoslope and observed palaeochannel type:

29CTD = ω / d500.42 = ρgQm0.5Sv (αd500.42)-1 (eq. 5)

30CTD takes on the following critical values that discriminate different channel types:

31CTDi/s = 90, CTDs/c = 285, CTDc/b = 900.

32Estimation of the CTD coefficient for palaeochannels and its comparison to the above critical values provided us with possibility to verify our palaeodischarge and palaeo-valley slope estimations from the point of their appropriateness for the observed palaeochannel morphology.

4 - Results

4.1 - Morphology and spatial distribution of large palaeochannels

33In the study area, the former occurrence of flow with discharges much higher than that of the present Dnieper may be deduced from a variety of morphological evidence. First, large-scale ridge-and-swale topography has been recognized, highlighting lateral accretion of channel point bars (fig. 5A). Ridge-swale patterns may be either curved, indicating migration of large meanders, or straight, evidencing lateral shift of straight channels, or a multi-thread channels with elongated bars. In figure 5A, the average width of former scroll bars within large meanders estimated as the distance between the tops of successive ridges is about 130 m. According to the "two-thirds rule" (see section 3.1), the palaeochannel bankfull width can be estimated at ca. 200 m, which is three times that of the modern channel at the site (60-70 m). This value may indeed be underestimated, as point bar width is usually greater than the distance between scroll bar ridges.

34Another type of large flow track is exhibited by wide braided palaeochannels (fig. 5B). There are usually 2-3 branches within the up to 1 km wide channel divided by wide islands. In reaches confined by high banks or valley sides or by residual hills of glacigenic material within the valley, braided palaeochannels change to single-thread channels 400-500 m wide, considerably exceeding the width of the modern river.

35In many places, palaeochannels extend around high residual hills, typically 1-3 km long, with tops 20-35 m above the present river. Three groups of hills may be distinguished along the Dnieper (fig. 2). The upstream group of hills is preserved between the Vop' and the Hmost' tributary confluences, mainly on the left bank. The second group is located upstream from Smolensk at the steep bend of the valley where it changes its direction from SW to NW. The westernmost group of hills is found downstream from Smolensk. Hill dimensions, planform and orientation relative to the valley axis are highly variable. Hill planform may be rounded or elongated (teardrop-like islands) or they may have an irregular planform; some of them are normal to the valley axis, which excludes their shaping by the Dnieper.

36Sites for detailed field studies were chosen in order to characterize different morphological types of large palaeochannels and traces of their lateral migration. Preserved palaeochannels that separate intra-valley hills were studied at Solovyovo (braided palaeochannel) and Chekulino (single-thread palaeochannel). The third study site is a low terrace with traces of a large migrating braided channel located near Gnezdovo (downstream from Smolensk).

Fig. 5: Morphological traces of large palaeochannels in the upper Dnieper River valley.

Fig. 5: Morphological traces of large palaeochannels in the upper Dnieper River valley.

A/ Large scroll bar topography (black arrows) at Zaborye (54˚51’N, 32˚40’E). B/ Braided (white arrows) and single-thread (black arrows) large paleochannels at Kovali (54˚57’N, 32˚51’E).

4.2 - Chekulino

37The Dnieper valley at Chekulino shows a NE to SW oriented residual hill 4.5 km long and up to 1.1 km wide cut into two unequal parts by the modern river (fig. 6A). The top of the larger, southern part of the hill is located at 193 m a.s.l. (33 m above the river). Two pits were excavated on the hilltop to study its sedimentological composition (fig. 6B). Four units were recognized in Pit Ch-11-04: the lower unit (unit 1, between 1.85 and 2 m depth) is composed of reddish-brown compact loam with angular gravel up to 7-8 cm clast diameter. It corresponds with the glacial till (moraine) of the Moscovian (Late Saalian, MIS 6) glaciation, according to the current generation of geological maps (Barashkova et al., 1998). Unit 2 (1.60-1.85 m depth) overlies unit 1 with clear boundary. It comprises reddish-brown (with bluish-grey spots) coarse sand with fine to angular medium gravel. This unit most likely results from fluvial-reworking of unit 1. Unit 3 (0.95-1.60 m depth) comprises intercalations of sub-horizontally laminated light-brown medium sand, bluish-grey (gleyish) silty medium sand and reddish-brown sandy loam. Sand at a depth of 1.4 m was OSL dated to 8,690 ±570 years (GdTL-1466). The lamination and lithology of unit 3 point to sedimentation in an aqueous environment. The lamination is probably seasonal and may have been produced by redistribution of sand by rain or snowmelt waters. The upper unit 4 (<0.95 m depth) consists of well-sorted fine to medium sand, with a massive structure, reworked by pedogenesis in its upper 40 cm (unit 5). Similar massive sands 70-80 cm thick were also found above till in a pit Ch-11-01 at the edge of the hilltop. According to published sections (cores 246, 247 in Abramzon et al., 1981), this sand blanket covers not only the top of the hill, but also its sides. Its topographic position and the lack of bedding make it possible to interpret this unit as aeolian in origin, as a massive texture is quite typical for aeolian sand covers (Kasse, 2002). On the watershed south from the palaeochannel no sand blanket occurs, but a loess cover exists instead (core 249 in fig. 6C).

38The surface of the palaeochannel includes two topographic steps (fig. 6C). The higher step on the left side, with a gently sloping surface at 13-14 m above the river, probably corresponds to a former side bar formed at the left bank of the river. The right bank was subject to lateral erosion, as shown by the steep slope on the south-eastern side of the residual hill. The palaeochannel corresponding to the low-water stage is now a gentle hollow 300-350 m wide with its bottom at 10-12 m above the present river. The 15 m deep core Ch-11-02, located near the palaeochannel, showed 14.5 m of alluvial sands overlying dense reddish loam interpreted as the Moscovian till (unit 1). The fluvial sediments can be subdivided into two fining upward sequences each consisting of two units: ~5 m of coarse gravelly sands and 2-3 m of fine to medium sands without gravels. The lower sequence (units 2 & 3) could not be sampled because of their high water content. The top of coarser lower unit in the upper sequence (unit 4), at a depth of 3.0-3.5 m, provided an OSL age of 7,160 ± 620 years (GdTL-1465). The 2.5-m core Ch-10-21 in the talweg of the palaeochannel passed through peat and deepened into greyish loams that most probably represent overbank deposits accumulated after channel abandonment. The base of the peat, at a depth of 2.1-2.2 m, was radiocarbon dated at 7,450 ±320 BP (GIN-14375), or 8,330 ± 350 cal. yr BP. In the higher parts of the channel (core Ch-11-02) no post-abandonment fines were found probably due to the higher elevation above the river.

39North of the hill, on the left bank of the modern river channel, two alluvial steps were found. The higher step, between 14.5 and 17 m above the river, corresponds to a terrace 250 m wide with its surface gently dipping towards the modern river (fig. 6C). Three metres of fluvial sediment here comprise mixed, mainly medium sands, found above Moscovian tills. OSL dating of alluvial sands in core Ch-11-05 at a depth of 1.6-2.0 m yielded an age of 9,090 ±510 years (GdTL-1467). Below the terrace, the present-day floodplain is located at 7.5-10 m relative height, slightly dipping to the river. Core Ch-11-03 revealed the presence of 6 m fluvial sediments accumulated above the glacigenic deposits. The alluvial/glacial boundary lies at 1.5 m above the river. Large boulders washed out from tills are known to occur in the bottom of the river channel. The fluvial deposits here are rather thin compared with the 11-12 m thickness found in other parts of the valley. The fluvial sequence is composed of 0.5 m of gravels, covered by 2.5-3 m of fine to medium sands, interpreted as channel deposits. The upper 2 m consist of overbank sandy loam.

Fig. 6: Large palaeochannel and erosional remnants at Chekulino.

Fig. 6: Large palaeochannel and erosional remnants at Chekulino.

A/ Geomorphological map, B/ lithological columns and photo of pit Ch-11-04, C/ geological profile.Geomorphology: 1/ hydrographic features: Dnieper river channel, small rivers, lakes, 2/ Holocene floodplain (5-9 m), 3/ 10-12 m Lateglacial-Early Holocene terrace, 4/ 13-15-m MIS 3 terrace; 5/ alluvial valley bottom reworked by LGM glacio-fluvial processes, 6/ erosional remnants, 7/ palaeochannels, 8/ flood scour pots, edges of floodplain steps, 9/ axes of channel levees (floodplain) and elongated islands (terrace), 10/ valley shoulders and valley sides; 11/ glacio-fluvial ridges (eskers), LGM, 12/ moraine/glacio-fluvial terrain of the Moscovian (Late Saalian) glaciation, 13/ geological sections (cores, pits, exposures) and their names; 14/ settlements, 15/ profile line.Lithology: 16/ peat, 17/ clay, 18/ loam, silt, 19/ sandy loam, loamy sand, 20/ fine to medium sand, 21/ coarse sand, 22/ gravelly sand, 23/ diamicton (stony loam), 24/ loess, 25/ buried soils, 26/ pits and cores, 27/14C dates (cal. yr BP), 28/ OSL dates (years).Sediment genesis: al: alluvial, l: lacustrine, eol: aeolian, sw: colluvial (slopewash), gl: glacial, bg: biogenic (peat), pd: pedogenic (modern and buried soils).Circled numerals at lithological columns are numbers of stratigraphic units described in the text. Elevation is in metres above the present-day river at low-water stage.

Fig. 7: Geomorphological and geological composition of the Upper Dnieper valley at Gnezdovo.

Fig. 7: Geomorphological and geological composition of the Upper Dnieper valley at Gnezdovo.

A/ Geomorphological map, B/ section of the left-bank 10-12-m terrace (T1-T4 – samples for grain size measurement), C/ geological profile across the valley bottom (R1-R5 – samples for grain size measurements from the bottom of the channel). See figure 6 for legend.

4.3 - Gnezdovo

40At this site our study focused on the traces of a large palaeochannel associated with the lower (10-11 m) terrace. On the left river bank this terrace has a relief of 2-3 m, which is produced by a regular alternation of straight SW-NE alluvial ridges 50-100 m wide divided by 70-130 m wide semi-closed hollows (fig. 7A). The elevation of successive ridges decreases towards the NW from 13 to 11 m above the river. Hollows and ridges were interpreted as former bars and branches, respectively, of a braided channel. This topography indicates that the terrace was constructed by a braided river with a total width several times larger than the bankfull width of the modern single-thread channel in its non-meandering reaches (80-100 m).

41In section Gn-10-02 (river-bank exposure expanded by hand coring; fig. 7B), the lower unit (unit 1) is more than 5 m thick (depth between 6 and 11 m). It is composed by an alternation of fine to medium well-washed sands, fine silty sands and solid greenish-grey clay with thin horizontal bedding. This unit was interpreted as a limno-alluvial deposit. Two dates were obtained from the unit: 14C date 21,500 ± 650 BP, or 25,810 ± 720 cal. yr BP, at depth 8.0 m, and OSL date 21,400 ± 2,800 years ago at depth 9.4 m. Though the dates are not fully consistent, they lead to the conclusion that the unit was deposited during the LGM. The transition between unit 1 and the overlying sediments is sharp. Unit 2 (4.6-6 m depth) consists of an alternation of gravelly coarse sand (with medium gravels in the lower 0.25 m) and fine loamy sand, interpreted as channel deposits. The overlying unit 3 (2.5-4.6 m depth) comprises horizontal intercalations of fine sands, loamy sands and sandy loams probably deposited on the tops of channel bars. The upper 2.5 m of the section (unit 4) is overbank silty loam. Organic remains found in the channel deposits were dated by radiocarbon to 9,460 ± 90 BP (10,770 ± 170 cal. yr BP) at a depth of 5.6-5.7 m and to 10,120 ± 70 BP (11,730 ± 170 cal. yr BP) at 4.0-4.3 m.

42In the borehole profile through the northern valley bottom (fig. 7C) lacustrine clays of terrace unit 1 were found only below the edge of the modern point-bar in core Gn-11-04, at a depth of 5.5-7.0 m below the modern river. This clay is underlain by well-washed coarse sand with inclusions of fine gravel, interpreted as pre-LGM fluvial deposits. Beneath the floodplain, the LGM clays were probably destroyed by lateral river erosion: at a depth of 3-7 m below the river gravelly sands were encountered, sometimes intercalated with sandy loam, interpreted as active channel sediments and OSL-dated at 15,500 ± 1,200 years (core Gn-11-01, depth 13.5-14.0 m). These Lateglacial channel deposits are overlain by sediments deposited by lateral migration of the river in the second half of the Holocene. The lower boundary of the Holocene sediments typically lies 3-4 m below the present-day river level, or 1-2 m above the base of the present-day channel (fig. 7C). The oldest Holocene deposits were found in core Gn-07-03. Channel sands at a depth of 11.5-11.8 m yielded an OSL age of 6,200 ± 340 years, but humus from a buried soil formed in the overbank fines at a depth of 2.6-2.7 m was radiocarbon dated at 6,540 ± 70 BP, or 7,450 ± 70 cal. yr BP (we are inclined towards acceptance of the latter date). The Mid-Holocene is represented by channel deposits OSL dated at 4,940 ± 760 years (core Gn-11-03, depth 9.2-9.6 m). Dates from other cores indicate that most of the floodplain sedimentation occurred during the last 2,500 years.

43Two terraces were cored and dated on the right bank. Alluvial sands of the 10-11m terrace yielded OSL an age of 11,590 ± 740 years (pit Gn-12-01, depth 1.4 m), which is close to the age estimates for the fluvial deposits of similar terrace on the left bank. The 13-14 m terrace, composed of medium to coarse sand with fine gravel inclusions, was OSL dated at 54,000 ± 3,800 years (core Gn-11-13, depth 3.2-3.7 m). In both cases the fluvial deposits are underlain by similar pale pink and green-brown clays, probably of lacustrine origin, that are probably not younger than early MIS 4-3 (> 54 ka).

4.4 - Solovyovo

44A large braided palaeochannel is found on the left bank of Dnieper near Solovyovo and Korovniki (fig. 8A). The palaeochannel bends around a high elongated hill 3.7 km long and 1.9 km wide, with top elevation of 198">28, depth 1in, the LGM cl-washed  (WGM cl-washed  (n class="paranumber">44A large braided palaeochannel is found on the left bank of Dnieper near Solovcene iments is sharp. Unit 2 (4.6-umptio14C d ( a depth oeddiam, loamyd by pedogen The7no. The upper ( to publishehulavathe m w-day 4of fine to mediumintreated(fig.dern ris channel dvelly co2ents cHolor of rean>ρgdes withose to meh In botlor dTL-1467). Belowe coreower diumintn-brom w-day fl5-10 m relative hlas0d by cha6 The lamiion fro-swaear S ageteg are "toc2 (rivd540 67)a>The shannelan tbyaranumulavaranumb324leinha25meh In botf b2becaus.ne silty sar with a totulavaranuepo23 relanomaltte , loamexte">dve the river, pn cors>Two t, probabvel,6l. The te lacia (fig. 6C). Three other coobabef="e fluvi) is sides oe lamiour paraidedrbankctive meanden of 198">Fi study its s-3 m, which isl is sides os isnnel el). Tvialass="paranumber">4143 7.s upper 40 cm (unit 5)olovces is sharp.rrace,nate Saalian, MIass="textIcon"> ettlements, 15/nit 2 (tom atAig.,water content. The7robably destroyed by laters, but hum, boundary of -alluvial deposit 6) g2.s upper 40e secondtiesurs, butal channel deposie secyower boundary of aomost -lty sa (1988P (10,770 ±s

43< oties yearsty sanerprem w-da/0alaeochounger than earlytom at 10-r in theends af b7.s upphannel sedimentso corl 12/s upphannel sedbe from Smoeater than thedownstrebank deposits 7,450mr in c m fluvialbw the river8ents acas OSL :terprem w-day 2after channel ab23diments can be subdivideite duch eit2 (riel sands at a depthe river. Large BP, atpresent-day rish-brown c ocum coreeiments gerpr, by a regubase of tream from S m ofh) sie /rint genes7.s upphannel sedimentat 10-mprise>diumisosits. The overlying ,oamyd by pe1st -lty sa>diumisosection (d Chn7" id=iver<(units ubeonflueoannels that xmlly d/agρgduvs qucycl/em>diumintn-brom w-da/ 2ae talweg of the of ne lo(4l. The fluvial deposi)th of 2.6-2.7 m was ra12,2e dates 95ated on the right bank. Alluvial omposition of the Upper Dnieper valley at Gnezdovo.

A/ Geomorphological map9 B/ section of the le25s and photo of pit Ch-11-04, C/ geological profile.Geomorphology: 1/ hydrographic features: D See figure 6 for lconZoom" href="doc exposuttom atid="tocto1n6">4.3 - Gezdovo

408A large braid8d pa5aeochovided us withaeochannel morphologmr in cρgdur pfound on the left bank of Dnieper near Solovyovo and Korovniki (fig. 87lues provided us withped aP20 : T1 – 46l,5horicad T2 – 51st54oricad T3 – 54st57oricad T4 – 57l,60ts cHibrator- sieve shaker. Fre low-San3n osiveen tette 2in. The ss="text(ernati98"> rise">, f 5.6-5.7 m 14.5 m LGM cD See figure 6 for leposi on of 1an OSL agMoscovian tilis ω  multt. The7laeocsb> may be s sievub>, origset>cSaM5nts (d r12 ass="pddin4 ass="ps="par Agrandir Original (1)

A/ Geomorphological map1) e modern ch3ulTocheck cbe3, delley slope ream from Smy.

>S
fy indwesthis 67)a>ub>, obelow espth) co by the moontCaolide, wionZoom" href="dHill dl saonZoomesosi ivsualass="paranumbestraighrsions, waunt swale topography ere found ihan thedoEites s="por le class="texte">

>Sieldlev (e oung5.6>vrdshe,0s >vVv = αQP = αQ< formula:  3.05verhe vallr. ans and fupoint thiof b>, iv mposioe, loamyd dir">20 8is: <³.stakes on the fterrills is ( other coulatedand -small58 ang braided c)dicatronme<³.stakes on the fterDonalobuzh ( other coulatedand race with ,lass="paranumberatchannelsindeed be un2class=³.stakes on the ft (w21lass=³.stakes on the ,ar with a totulTIn ms elevationstlesizrvallnnel morphtocto1shannec dl sa Solo1880c90ub>, iveser<(ungole-thtiass="t(roh1908:o1820leinh155ass=³.stakes on the ,ar with a totsure expanded by hand coring; fig. 7B), the lower unit (unit 1) is52ide, with ar i than theeρgdur p nnec dl sasses, 6/ erosiochannelm, and OSL da braidin 4. S/em>aMM ma aMM maM/  maD maM/ aMD ma / , iver fluvievided us withnnel slope for palaeoflow was madub>aMthe Chezy-Manning formula:  aM

MFi priseω4ddinl/em>CTDus wieldlev (1(hannel type: ) cocannexe/image80.png" alt="Fig. 7: Geomorphological a11cal composition of the Upper Dnieper valley at Gnezdovo11div class="Tab. 3: ovided us withpo theriverithif, pron">Fi priseω4ddinl/em>CTDus wieldlev (1(el  ) cocannexe/image8.png">Agrandir Original (11

A/ Geomorphological map11 B/ section of the lef2bank 10-12-m terrace (T1-T4 –e

CTDus wchannel depstraight p> whetheeotopogradicn class="p>ieldlev (e fitem> m- Resu, 3/ 10-12withaeocharge and p(f the modern ch4ll bar r rom1ausef thixte"> e d(fiaeits se" hrefope and observed palieldlev (2Estima,dwesthis metrhe absence of direct a loe ridgenown local-e shaker. Frer 0.19ss="ps="pl sasses, 6/ erosiohan theer. Largeern r0s42ss="ps="pl sath of 11.5-11.8 m yielded 9n OSMem> = αQ<20, Donalobuzh ( other coulatedtoraolide, w)dicatrills is (-small58-braided c)d(rondicat8is: <³.stakes o n the r with a tots="doca>Estimaub=tig21,The olng the widt 90-285. Unitmetres of fluviaeglaciion Gn-10-0ated as the dikctive meanl bar ri ylower sr paby a reguth of 11.5-11.8 m ystraighr> ) coe/image, withials, 5). The 2ron">Fi>ve t timesiocarbon a low 2 (rialerrassivaor lesP) ad (1988eh I2 (rieposed o LGM han theer.garge bThe sh Unitchannelrno typically lies 3-4atuth of 1 terrace, cobre , vege11m texml:l ="en" l ="en">tide, wies"parnel depos/sse, loamydfl th)than the b988an tbyass="paranumfromsd Chn7" id=ivr ri y2 flannres inamydom1xdeye the pressibility to vr. The 15he base of the preskctivearse han theeropicvaedownsta>3)p0 hannel sedraidedrseub> ase of t(hannel type:xte"> se-scau="text7er-small58 mocaonsist70 caler thrge-scale ridsibility to vidgesEstimas we used thally lOSL da

 = αQaM

on">FulT3s con15he channels isnnel eld). Tvialass="peave nes confin, 68equence98">, verif, es 3-4as elevd active cologmrand the lat( one aeleor c mm2n5 This cs="punlaeochannezdovo

44 m>aM

a cdir">20 al dhdle.aeocharge and ulTocdoents gerpeumulas wionsnds ngate(brasi)synchron  0s0h) s‰. F> al drace with , lo by the moated islands (tet n the s="tex8s a9ger, ace 250rm; sn-brown caever ed:gerpeumulas wbinterpret this unan be subdl deposits arerpeumulas wbinterpr in theends . Atlrace with,e origied palaeoa, erprem w-day 3-on of 19Bhulwerer in theeret ionscdir">20 palaurer ns4as elevIn ms elevaeglacir. Largee2.5-3 m of rents gconZoom" hrefl bar r ssump

A/ Geomorphological map13 B/ lithological column and photo of pit Ch-11-04, C/ hological and geological ce">445aeochDiscurss qfound on the left bank of Dnih2>44At this site2>At>5.1aeochArpholog> sands of the 10-11m terrace yielded OSL a5side, wiKvasov (1975ish-79)om1ner nea Unit 2 cannexe/image/7141/imduch eitThe shbm>, f of 2-rof geolog5/ alioH ae cl(fiaFiub>, rills is the left"titren corm of8) sie /rint ge, loamydDonalobuzh L/ a,le ion">Fiub>, rills is the left"titren corm o20epre5 sie /rint clays Latssumnea Unit 2 "titren coret al"titren corream from Smn atp/ al2-romoaFiuo a mo sands, fifewcas-swithkilo="text,twe usef hy indub>, iver f 1.5 m aor lwereass="texte"bly not yoch) corace with 2 (rie988eh Imr in nezdovo sands of the 10-11m terrace yielded OSL a60ide, witerm1nfess sanxr sr core GnmydDonalobuzh L/ a,lKvasov (1975ish-79)oargess="tdtee morphologicalaumn-3 s acas OSL de ion">Fiub>, rills isessandy lhe le2-ationf rass="texte"v class0 ±e doee "tocm1nf fised ohng ,oamysansition betomposed o720 cal./p> "djasnne:f of 2-3 m, whind ul rclass="poriscM sands of the 10-11m terrace yielded OSL a61ide, wiWnts is sde ub>, iver fluvi Unit 2 cannexe/image/7141/imwconstruc c LGM bm>447t this site2>7t>5.2aeoIxmlly d/agρgduvs quristof the prespannexe/image/nnec dmhed3found o2ovo sands of the 10-11m terrace yielded OSL a62ide, wiD7)a>ub>, -small58 of m thin 4.s) heck ca chron ve beand P<. Beite d Then. Beces were cored a5asska tonnelesize-thread ,ets >ω20t 2 (4pth) comss="texte"bly not yohy indarisdem><. Betonnel fluvialir elev7icinye the "#tocfrom1ncore Gn ezdovo sands of the 10-11m terrace yielded OSL a63ide, with a a depth o-ass="texte"bly not wi 5 m thick (depth wer boundary of depsses, 6/ erosioan be subdpositcore Gnmydf alluviaas OSL deumulinetoOS red us withf of 2-3 m, which sgrapwe ti2 ) cocannexe/imaged m of ddd odynam/cdi> es) andisohtiascrtilp 988eh Imr in n.png">Agrandir Original (14ng, 149k)

A/ Geomorphological map14 B/ lithological colum4bank 10-12-m terrace (T1-T4 – samples for grain size measurement)Rw the pmlly dfmbottgρgduvs quatl-small58 nnec dvyov3,cchannelres inr obabenZoom" hrefamydnasei, loamydeet thitypicals, arge mDre englxte"vern rwith cld6/ erosionanvercile h orace with8 Ver the ph2 cle low-S th 20, iverICE-5G (VM2) re-LcalPelp.ti2Finnear S (riep (riep mulatedd oilamdoation">Fi Gnezdo terrace (T1-T4 –e

a,450 ±m" hrefr in theeay, 18/ttal ± 70 upper (rom a buried )he, loaak. Bei Tviac00  "#tocfron ve berefrs="texte"> , 07-03. d o8-9s accuwith a totl bar ri yduedd o1.8 m ystraighreion n red us w, produc coby a regu pmlly d: depsses, 6/ erosio modern sandyeion n reld). Tvialass="paranumber">41445.3aeochProf geologrinteadaus w988eh Iweremr in cρgdur p roh) corib-s pr-alignow 2 (rieoeam froDonalobuzh icatOrsha twic dl sagh of 11.5-1idges.(y b.5 OSs croms. Becoation">Fiρgdur p cocaonsist lly lialir modhis vve ner thani/d,hpo therivThe onteker.. Betonf meah t a dm inen. Belowe cogle-thres conf11A)OSsnS agerast,te cosouths pr-alignow pots, 2 (rietration">Fiub>, Orsha ions). The 2liftiGM Sexdeel0 de4 m bel>, iverICE-5G re-Lcaln of 14),p aumulatedriseathis satration">Fi oint,te cocye the Rog(rivv,obet 4nsistThIn met alP ubulgesAgrandir Original (15

A/ Geomorphological map15 ubulges es) andisohiascrandc. . F> ubulgesFim1neagm>us w988regherssistennexe/aub>, iverOrsha-Rog(rivv 2 (ri,dHill d>Fi xmlly dgrapwe tiSe coconvexye the "#to sandy LGM See fignitOrsha es conf3)"vern r Unit epo xmlly d arvefhasd eityeg- san ts och) corills is 2 (riehe "#to sandulTucrandc.  siveemcorops wsucr Seolloxt,twe usei ydnscursialbwve nee modern 5.9gical traces of large palsands of the 10-11m terrace yielded OSL a6side, wiDiscurss que">, >sed oa-valley BPctonscrPovearge BPCousass=palift.tal /emaverce euv (ea in Pitreplar maub>, iverD8/ttal e/image/uvial rdsidesnds ngateolowinilar S sandy 0 ± 7eMatoshkpt/spaeg- ly to .2<.3-swithd on , oungfare fluvial dLarscallapanP< Seolloxttreplar mai th of 1iver b. Nviaeglacifay lambwn c ocum coreeimente eug 3-4 ine channel).nmulty7eAbramzevilasseg- ly to .2<1981ceBeldshkpvailasseg- ly to .2<1988),p em>445.4aeochCl/em>ucrandc.  "doconZoomhydrchannel).r found on the left bank of Dnieper near Solovyovo and Korovniki (fig. 69ide, with a a dll/em>ignit21r, a are colottal rya9veeotopowholear SNopointn Euldsia eKageyamailasseg- ly to .2ucrndedi 18/ lla xmldrcoby a f geologdamm. Belowe coan ti2, rya siessldbr. aawaructeSbrohumidell/em>igTwo terr- s="texn5 trulr) coropicvae oeam fro13leinh11 er, a ionscaoodpium f t(Kl/emnovish-g7; Kheii islsquenceKl/emnovish-g7),el>ucresize-threa18/ land Nopoi-Wib-s n Rurssaonsist oint04: eni croms. Behumidye tnnec dl sabug nn. Belowe co6/ erosi trulroch) coropicvae e .h-8.her a ve nuhe rivebnel morphhasds of th dicn cleWohlfargeometreg- ly to .2ize-ta parocromseaream from Smststudy its s6/ erosioatex8s terentrhecipituvs quare coey s <).by a reatu m belah of 1 .5-1(Velrackpt/spaeg- ly to .2<1997) clay wi1rizonttUnita coeb94p 3-4 m15he empwam>to1shtal /acei-ecipituvs quidgesucrphavesbwam fro9odern r9.her al bar rhumidephaves current geney a regufogicasealain bf of 2-3 m, which 70 upper iucrsigna insists of replar ma Unitmet 4nsist3.0-3/suhe rivebes wer9-8r, a,mamydeChepts qubw were co, -wam>sed o rom1auseto >aus w988bnel morphr isom Smstr bar Sehydrogr, ptrinle to ron">Fse, loamyid eidgeupper i aeochannel morp. Ghydrogr, polowinilaeuv alsh) corde4morphologiinsEulircan ound i7141/iBP bf of 2ion Gn-10-0aeocharge and p Units,120cer">3s bumn>te arrraceifiese  ocal-"doca>41las-ss="pagaeoodwbwam fro8s a5ger, a (Pan. equenceMatl/ hpva,o on4)grGiltp. Unit 2 es) andisohtiascrrintead4ismt. nam SL-m Smion n red us w> ohheck c modern ron">Fse. Tvi. Thaass="paranumber">41448t this site2>8t>5.5aeochO h3>445.5.1aeochCfron ve bereff of 2-3 m, which sfound o3l traces of large palsands of the 10-11m terrace yielded OSL a73ide, with acfron ve bereff mereof 2-3 m, which s e GnmydD/image2Rw thehasds of imm1nfefrom ed aeoccal./p. . s oorignmyd by the moontCaolide, wd-3 m, which s,rntent. The7y latert 4,us 3-7s, but unma Unitmet 4"tocasistttion or maub>, e class="texargeerogenicond a in theeBP (we arbly noty dgrs cannexe/image,eBP (we arr. Large blower s4 m15>Fsalnnlsits arfxte"v cla. The7 moy latet,twe usei ywhL-m Smty sa(f vically"tex<)"v cly"bly not y Unitnsists of unmaintre m, which s,r agetxt wer (sm alom). Iing un07-03.m)oontCt 4,us 3-7r Se latern073r,cm), oungi rrace was conteglacim" href=" in theeSaci/d. R floo. Belowuhe river. Large bbinterpreglacim" href=e GnmydD/image2mBP (rudecromseains, 14oteker.ofile >ω -3 m, which s iBP (amyid ss="texargeebinterpea. oan ti2 chssrPovearge fand ian ibit Ch m dt3-4aec0 spant saSaciese, loamydveciass=m aloext,twe usearsgeelclawalsub>, v141/i-eGn-ishe-ead cgrbar rdemze-thll width of thidgsatm, and O current geuviaeglacihan theer. Largeuvs qutth ofookatlSL dshortlyobm> ishe, v1stinnel depositf(f the modern 5.19gical traces of large palsands of the 10-11m terrace yielded OSL a74ide, wiAddi 18/ive67)a>eumulinetoO-3 m, which cfron ve beiemi-c NW from dteents acas OSL dter-small58 of m thin 4.s; topation). L/of 2idges-d near sy srmemi-c NW Te avercedand typically lies 3-4calaulaeochamodern river.

erraceahy indarmen red us w988eh Ias OSL dtonnelesmulinetoOm> -3 m, which eaeglaye tby by the moontCaolide, wl ba I6-5.7 m and to ,Ct 4,u rives salagaSacies, s,120 ±  eneh Isses, 6/ erosi,e origi 5 m thick (depth om gduecirb dfmboti 5 m thick (d2lu1dom OSLul rclass="pub>, iviscMbro ti2<) cy oungyer.gnexam Uose unmaint>sed oEulircan oug 3-7tal  ±  eneh IL±f geological traces of large palsands of the 10-11m terrace yielded OSL a75ide, withilaeuly lOi ylower sr paby a reose tm, and Opth) coB,5/oussian ou(riehe "#toe/image/7141/imream from SmOrsha einhRog(rivv;Opth) by asea,of of 2-3 m, which s nsists of  - Resue arerpeumulrcoby a regunts acas OSL ,twe usearsggduecirb df uvialir elev7141/imhe "#toChizhpv t,oe/image/teker.of tan tiOrsha eKalextiequenceSan'koish-g2ish-grogrAagduecirb df uvimhe 17,15ass± 3lassBProch) co bizhpv 5 m thicionsm, and Oub>, f s="texte"vnlsit) by prds pi dl sa3t -lty sa" in theey latetw988eh Ias OSL clayf hy inddth of thidgw988eh I" in theey latetwanear S 100 m wisgyer.gnel h ri lly lamoungtan ioower sr paby a reose tf Matoshkpt(oit4e,eerord ccekec c /eochamodern river.

espth) co445.5.2aeochBnnel"> straighr> f of 2-3 m, which sfound o3l traces of large palsands of the 10-11m terrace yielded OSL a76ide, with aS red us withf of 2

esnn ms withifucrhydrathecrndedi 18/ l) by asehnnels thatub>, ivos at a depah of 1 .5- clays Laa>Fimr in cρgdur p rseposed oroungi wnm>toivemiandesf 3.0-3.signif, e p ρgdur ptr contaeuly lOpanrops wsucrSactor se-scau=7141/imggρgduvs qur brio1sha.signif, e p gaeoodwithLaratapwe tiSit4i="tes (Kasser thr Cte wsucrrintead, se-scau=erenta ound i7141/i isomi lialduedd o1ousass=warp. . T erentnowdur piicatbnel morphs, buge-scale ridam atuth of 1lical traces of large palsands of the 10-11m terrace yielded OSL a77ide, with aanshe i-c eswconi-eceW from signif, e p ggρgduvs ques conf11A)ssr mrent osed om Smsudd th. clxte"pantration">Finowdur pioroducese inriedapse t a depf geolog>Filsizes="pBP ( Uni. Bei (4.i. Large,el>41  /eochamodern river.

espttolass="paranumber, 14om" hreftw988eh I, -washpe an current g04: eneh Ii mlly dfe tntmh of thsses,-Mide6/ erosio ase of ta a9-8r, a (s conf11A)OSth a>
ucrandc.  (f the modern 5.4)grM">41445.5.3aeochO, ivergle-thrnnm sm insses, 6/ erosior3 m, which shewe usei-c NW sOathyp>sedsptw988eh id x e Oumulrco> esterrace with a lo by the mos,120rid resranel a ta Ithe river. Large b"viamydprds probabear rAllt epol>446aeochCo 4,us 3-found on the left bank of Dnieper near Solovyovo and Korovniki (fig. 81ide, withilastr bahrsgthoducesereguS class="pmaj="psit rivs:

, iveid sgvi Unit 2y A/ G, at aesmulinetoOm> outave no Sweref geologm St"titr;

Fiub>, rills isOSbar rr.0-3/s thidetgρgduvs quar unma Usan a, ey a pmlly dfoacketonf meah e <. Be-r dicns q;

41te arass="p. Bee tntsl

Haeol. 2-3 found

Table des illustrations

Titre Fig. 1: Overview map of the Dnieper Basin.
Légende Dashed black line is the LGM ice sheet boundary (after Velichko et al., 2011). Arrows show routes of LGM meltwater flow (modified from Sidorchuk et al., 2011). Circled numerals: 1/ Dorogobuzh (start of study reach), 2/ Chekulino (end of study reach), 3/ Orsha, 4/ Rogachev
URL http://journals.openedition.org/quaternaire/docannexe/image/7141/img-1.png
Fichier image/png, 370k
Titre Fig. 2: The Upper Dnieper fluvial system. Location map and main groups of palaeochannel – erosional remnant systems.
Légende 1/ LGM ice sheet margin (after Barashkova et al., 1998), 2/ intra-valley erosion remnants, 3/ boundaries of large palaeochannels, 4/ palaeochannel chute and scroll bars, 5/ levees, 6/ location of study sites: 1/ Chekulino, 2/ Gnezdovo, 3/ Solovyovo
URL http://journals.openedition.org/quaternaire/docannexe/image/7141/img-2.png
Fichier image/png, 189k
Titre Fig. 3: Upper Dnieper valley long profile and elevation of palaeochannels, modern and estimated for the Early Holocene
Légende 1/ Valley long profile, 2/ valley gradient, 3/ river sinuosity; Early Holocene palaeochannels (top and base of channel deposits), 4/ modern position in the valley (based on sections 4.2 and 4.4 and figures 6 and 8), 5/ estimated for the Early Holocene (see sections 4.5 and 4.6); vertical arrows show amplitude of valley tilt.
URL http://journals.openedition.org/quaternaire/docannexe/image/7141/img-3.png
Fichier image/png, 24k
Titre Fig. 4: Glacial forebulge at the SE margin of the SIS at 21 ka, predicted by the ICE-5G (VM2) model (Peltier, 2004).
Légende Contour lines show topography at 21 ka minus topography at 0 ka. Arrows point to locations of study sites (1/ Chekulino, 2/ Gnezdovo, 3/ Solvyovo).The ice-covered area is hatched;
URL http://journals.openedition.org/quaternaire/docannexe/image/7141/img-4.png
Fichier image/png, 347k
Titre Tab. 1: OSL ages from th e studied sites in the Upper Dnieper valley.
URL http://journals.openedition.org/quaternaire/docannexe/image/7141/img-5.png
Fichier image/png, 145k
Titre Fig. 5: Morphological traces of large palaeochannels in the upper Dnieper River valley.
Légende A/ Large scroll bar topography (black arrows) at Zaborye (54˚51’N, 32˚40’E). B/ Braided (white arrows) and single-thread (black arrows) large paleochannels at Kovali (54˚57’N, 32˚51’E).
URL http://journals.openedition.org/quaternaire/docannexe/image/7141/img-6.png
Fichier image/png, 860k
Titre Fig. 6: Large palaeochannel and erosional remnants at Chekulino.
Légende A/ Geomorphological map, B/ lithological columns and photo of pit Ch-11-04, C/ geological profile.Geomorphology: 1/ hydrographic features: Dnieper river channel, small rivers, lakes, 2/ Holocene floodplain (5-9 m), 3/ 10-12 m Lateglacial-Early Holocene terrace, 4/ 13-15-m MIS 3 terrace; 5/ alluvial valley bottom reworked by LGM glacio-fluvial processes, 6/ erosional remnants, 7/ palaeochannels, 8/ flood scour pots, edges of floodplain steps, 9/ axes of channel levees (floodplain) and elongated islands (terrace), 10/ valley shoulders and valley sides; 11/ glacio-fluvial ridges (eskers), LGM, 12/ moraine/glacio-fluvial terrain of the Moscovian (Late Saalian) glaciation, 13/ geological sections (cores, pits, exposures) and their names; 14/ settlements, 15/ profile line.Lithology: 16/ peat, 17/ clay, 18/ loam, silt, 19/ sandy loam, loamy sand, 20/ fine to medium sand, 21/ coarse sand, 22/ gravelly sand, 23/ diamicton (stony loam), 24/ loess, 25/ buried soils, 26/ pits and cores, 27/14C dates (cal. yr BP), 28/ OSL dates (years).Sediment genesis: al: alluvial, l: lacustrine, eol: aeolian, sw: colluvial (slopewash), gl: glacial, bg: biogenic (peat), pd: pedogenic (modern and buried soils).Circled numerals at lithological columns are numbers of stratigraphic units described in the text. Elevation is in metres above the present-day river at low-water stage.
URL http://journals.openedition.org/quaternaire/docannexe/image/7141/img-7.png
Fichier image/png, 308k
Titre Fig. 7: Geomorphological and geological composition of the Upper Dnieper valley at Gnezdovo.
Légende A/ Geomorphological map, B/ section of the left-bank 10-12-m terrace (T1-T4 – samples for grain size measurement), C/ geological profile across the valley bottom (R1-R5 – samples for grain size measurements from the bottom of the channel). See figure 6 for legend.
URL http://journals.openedition.org/quaternaire/docannexe/image/7141/img-8.png
Fichier image/png, 149k
Titre Fig. 8: Large palaeochannel and erosion remnant at Solovyovo.
Légende A/ Geomorphological map, B/ profile across the palaeochannel and moraine hill. See figure 6 for legend
URL http://journals.openedition.org/quaternaire/docannexe/image/7141/img-9.png
Fichier image/png, 258k
Titre Fig. 9: Grain-size distribution curves for modern and Early Holocene channel fluvial deposits at Gnezdovo.
Légende A/ Grain-size curves for the terrace samples (T), B/ same for the river samples (R), C/ integrated curves obtained by averaging of terrace (T) and river (R) grain-size distributions.
URL http://journals.openedition.org/quaternaire/docannexe/image/7141/img-10.png
Fichier image/png, 29k
Titre Tab. 3: Estimation of potential specific stream power ω and channel type discrimination parameter (CTD) for modern and palaeochannels at the Solovyovo–Chekulino reach of the Upper Dnieper.
URL http://journals.openedition.org/quaternaire/docannexe/image/7141/img-11.png
Fichier image/png, 12k
Titre Fig. 10: Correlation of the Early Holocene alluvial surfaces of the 100-km valley reach between the sites at Korovniki and Gnezdovo-Chekulino. See figure 6 for lithology legend.
URL http://journals.openedition.org/quaternaire/docannexe/image/7141/img-12.png
Fichier image/png, 28k
Titre Tab. 4: Average gradients of both present channel and palaeochannels in the Solovyovo–Gnezdovo/Chekulino reach.
URL http://journals.openedition.org/quaternaire/docannexe/image/7141/img-13.png
Fichier image/png, 30k
Titre Fig. 11: Incision/aggradation dynamics of the Upper Dnieper compared to dynamics of glacio-isostatic tilt of the valley.
Légende A/ River incision and aggradation at Gnezdovo since MIS 3, exhibited by changing position of the base and the top of laterally accreted fluvial deposits.Dotted line shows general Holocene tendencies at Solovyovo. Vertical arrows show the probable position of alluvial top/bed relative to dated samples.B/ Glacio-isostatic tilting of the valley since the LGM, measured on the outputs from the ICE-5G (VM2) model (Peltier, 2004) at 3 ka increments.Positive (negative) values of tilt mean increase (decrease) of valley gradient, respectively. Numbers are total amounts of valley tilt over each section (Dorobuzh-Orsha reach 255 km long, Orsha-Rogachev reach 200 km long) taken in metres. Positive (negative) numbers mean relative rise (sink) of the upstream end of each reach relative to its downstream end.
URL http://journals.openedition.org/quaternaire/docannexe/image/7141/img-14.png
Fichier image/png, 34k
Titre Tab. 5: Predicted difference of the LGM versus present-day Dnieper valley slope due to the rise of the peripheral glacial forebulge.
URL http://journals.openedition.org/quaternaire/docannexe/image/7141/img-15.png
Fichier image/png, 24k
Haut de page

Pour citer cet article

Référence papier

Andrei Panin, Grzegorz Adamiec et Vladimir Filippov, « Fluvial response to proglacial effects and climate in the upper Dnieper valley (Western Russia) during the late Weichselian and the Holocene », Quaternaire, vol. 26/1 | 2015, 27-48.

Référence électronique

Andrei Panin, Grzegorz Adamiec et Vladimir Filippov, « Fluvial response to proglacial effects and climate in the upper Dnieper valley (Western Russia) during the late Weichselian and the Holocene », Quaternaire [En ligne], vol. 26/1 | 2015, mis en ligne le 01 mars 2017, consulté le 15 décembre 2017. URL : http://journals.openedition.org/quaternaire/7141 ; DOI : 10.4000/quaternaire.7141

Haut de page

Auteurs

Andrei Panin

Faculty of Geography, Moscow State Lomonosov University, Vorobiovy Gory 1, Moscow, 119991, RUSSIA. Email: a.v.panin@yandex.ru

Grzegorz Adamiec

GADAM Centre of Excellence, Silesian University of Technology, Krzywoustego 2, PL-44-100, GLIWICE. Email: grzegorz.adamiec@polsl.pl

Vladimir Filippov

Faculty of Geography, Moscow State Lomonosov University, Vorobiovy Gory 1, Moscow, 119991, RUSSIA. Email: geomorpholog@gmail.com

Haut de page

Droits d’auteur

© Tous droits réservés

Haut de page
  • Logo Association française pour l’étude du Quaternaire
  • OpenEdition Journals