Quaternary International 152–153 (2006) 14–30 Loess/paleosol/cryogenic formation and structure near the northern limit of loess deposition, East European Plain, Russia A.A. Velichko a, , T.D. Morozova a , V.P. Nechaev a , N.W. Rutter b , K.G. Dlusskii b , E.C. Little c , N.R. Catto d , V.V. Semenov a , M.E. Evans e a Institute of Geography, Russian Academy of Sciences, Staromonetny, 29, Moscow 109027, Russia b Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E3 c Canada–Nunavut Geoscience Office, P.O. Box 2319, Iqaluit, Nunavut, Canada X0A 0H0 d Department of Geography, Memorial University of Newfoundland, St. John’s NL, Canada A1B 3X9 e Institute for Geophysical Research, University of Alberta, Edmonton, Alberta, Canada T6G 2E3 Available online 13 March 2006 Abstract Quaternary loess/paleosol series and cryogenic phenomena within the East European Plain, Russia, are less studied near their northern limit than at their southern extents. The multi-disciplinary study of two loess/paleosol/cryogenic sections were carried out in the Moscow and Vladimir regions of Central European Russia, not far from the glacial limits of the Middle and Late Pleistocene. Generally, loess deposition within these regions has undergone syn- to post- deposition processes as evident from the laminated character, as well as post depositional soil moisture and temperature conditions that have commonly given rise to gleyzation and cryogenic deformations. The Middle Pleistocene Dnieper loess is calcareous here, but the Upper Pleistocene loess has been leached of carbonates. Both Upper and Middle Pleistocene paleosols have strong pedogenic features allowing their genesis to be determined whereas cryogenic deformations and other post-depositional features allow for the more detailed interpretation of cold epoch processes. Given these loess characteristics, the Moscow and Vladimir loess region may be considered as a specific facies of the East European loess area. The proposed Moscow–Vladimir loess region exhibits the complete sequence of stratigraphic units that are correlative with well known sequences along the southern part of the East European Plain. In the Moscow–Vladimir region, however, several horizons exhibit well developed cryogenic phenomena that indicate permafrost conditions and sufficient moistening during most of the cold epochs. Cryomorphic and hydromorphic processes have a strong influence on the composition and structure of loess formation. The Salyn paleosol of the Mikulino (Eemian) Interglacial time demonstrates strong clay illuviation as well as Kamenka and Inzhavino paleosols of the Middle Pleistocene age, both of which developed under boreal to sub-boreal climatic conditions. In contrast, the Bryansk and Romny interstadial paleosols have gleyic properties that suggest formation during incipient (discontinuous) permafrost conditions. r 2006 Elsevier Ltd and INQUA. All rights reserved. 1. Introduction The East European Plain comprises the most extensive area of the Quaternary loess/paleosol sequences in Europe (Fig. 1), extending from the Black and Azov Seas to the Smolensk-Moscow Upland (Velichko, 1990). Sections studied in that region provide detailed information on the Pleistocene climatic macrocycles and stratigraphic se- quences of the region. The most comprehensive studies of loess, paleosols and Quaternary cryogenic phenomena have been performed in the southern portions of the East European Plain (Veklich, 1979; Morozova, 1981; Mat- viishina, 1982; Velichko et al., 1964, 1984, 1998). Prior to 1990, only a few key sections provided stratigraphic and paleoenvironmental information about the loess/paleosol/ cryogenic series of the central portion of this plain (Bolikhovskaya et al., 1976; Udartsev, 1980, 1982; Velich- ko et al., 1984; Velichko, 1990). During the last decade several additional key sites were studied along the Oka, Volga and Kama river basins (Fig. 1)(Dlusskii, 1997; Dlusskii et al., 1997; Glushankova, 1998; Makeev and Velichko, 2000; Dlusskii, 2001; Little, 2002; Little et al. 2002; Dodonov and Velichko, 2003). These three river ARTICLE IN PRESS 1040-6182/$ - see front matter r 2006 Elsevier Ltd and INQUA. All rights reserved. doi:10.1016/j.quaint.2005.12.003 Corresponding author. E-mail address: [email protected] (A.A. Velichko).
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ARTICLE IN PRESS
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Quaternary International 152–153 (2006) 14–30
Loess/paleosol/cryogenic formation and structure near the northernlimit of loess deposition, East European Plain, Russia
aInstitute of Geography, Russian Academy of Sciences, Staromonetny, 29, Moscow 109027, RussiabDepartment of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E3
cCanada–Nunavut Geoscience Office, P.O. Box 2319, Iqaluit, Nunavut, Canada X0A 0H0dDepartment of Geography, Memorial University of Newfoundland, St. John’s NL, Canada A1B 3X9
eInstitute for Geophysical Research, University of Alberta, Edmonton, Alberta, Canada T6G 2E3
Available online 13 March 2006
Abstract
Quaternary loess/paleosol series and cryogenic phenomena within the East European Plain, Russia, are less studied near their northern
limit than at their southern extents. The multi-disciplinary study of two loess/paleosol/cryogenic sections were carried out in the Moscow
and Vladimir regions of Central European Russia, not far from the glacial limits of the Middle and Late Pleistocene. Generally, loess
deposition within these regions has undergone syn- to post- deposition processes as evident from the laminated character, as well as post
depositional soil moisture and temperature conditions that have commonly given rise to gleyzation and cryogenic deformations. The
Middle Pleistocene Dnieper loess is calcareous here, but the Upper Pleistocene loess has been leached of carbonates. Both Upper and
Middle Pleistocene paleosols have strong pedogenic features allowing their genesis to be determined whereas cryogenic deformations and
other post-depositional features allow for the more detailed interpretation of cold epoch processes. Given these loess characteristics, the
Moscow and Vladimir loess region may be considered as a specific facies of the East European loess area.
The proposed Moscow–Vladimir loess region exhibits the complete sequence of stratigraphic units that are correlative with well known
sequences along the southern part of the East European Plain. In the Moscow–Vladimir region, however, several horizons exhibit well
developed cryogenic phenomena that indicate permafrost conditions and sufficient moistening during most of the cold epochs.
Cryomorphic and hydromorphic processes have a strong influence on the composition and structure of loess formation. The Salyn
paleosol of the Mikulino (Eemian) Interglacial time demonstrates strong clay illuviation as well as Kamenka and Inzhavino paleosols of
the Middle Pleistocene age, both of which developed under boreal to sub-boreal climatic conditions. In contrast, the Bryansk and Romny
interstadial paleosols have gleyic properties that suggest formation during incipient (discontinuous) permafrost conditions.
r 2006 Elsevier Ltd and INQUA. All rights reserved.
1. Introduction
The East European Plain comprises the most extensivearea of the Quaternary loess/paleosol sequences in Europe(Fig. 1), extending from the Black and Azov Seas to theSmolensk-Moscow Upland (Velichko, 1990). Sectionsstudied in that region provide detailed information on thePleistocene climatic macrocycles and stratigraphic se-quences of the region. The most comprehensive studies ofloess, paleosols and Quaternary cryogenic phenomena have
e front matter r 2006 Elsevier Ltd and INQUA. All rights re
been performed in the southern portions of the EastEuropean Plain (Veklich, 1979; Morozova, 1981; Mat-viishina, 1982; Velichko et al., 1964, 1984, 1998). Prior to1990, only a few key sections provided stratigraphic andpaleoenvironmental information about the loess/paleosol/cryogenic series of the central portion of this plain(Bolikhovskaya et al., 1976; Udartsev, 1980, 1982; Velich-ko et al., 1984; Velichko, 1990). During the last decadeseveral additional key sites were studied along the Oka,Volga and Kama river basins (Fig. 1) (Dlusskii, 1997;Dlusskii et al., 1997; Glushankova, 1998; Makeev andVelichko, 2000; Dlusskii, 2001; Little, 2002; Little et al.2002; Dodonov and Velichko, 2003). These three river
A.A. Velichko et al. / Quaternary International 152–153 (2006) 14–30 15
basins are situated along the northern limit of loessdeposition and very close to Middle-Upper Pleistoceneglacial limit on the East European Plain. Correlative UpperPleistocene loess units are described as much thinner andgleyed on the central East European Plain (Velichko, 1990,1999). Middle Pleistocene paleosols and loesses werestudied at several localities and correlated with those ofUpper Don River basin (Glushankova, 1994, 1998;Dlusskii, 2000, 2003; Little et al., 2002; Dlusskii andMorozova, 2003). Within this region there is abundantevidence of cryogenic deformations of the Upper andMiddle Pleistocene age loess–paleosol series (Udartsev,1982; Velichko et al., 1996a, b; Morozova and Nechaev,1997; Velichko, 1999; Dodonov and Velichko, 2003).
2. Geographic position
The northern margin of the region under considerationlies within the albeluvisols subzone (southern taiga). Themajor part of the region belongs to modern zone of greyforest soils (greyic luvisols) and luvic chernozems. Thesections B and G are located on slightly elevated flatinterfluves known under a local name ‘‘opolye’’. The Bsection is located at the southern portion of Vladimir
Opolye and the G section at the southern part of Podolsk-Kolomna Opolye.Its climate is of temperate continental type, with
annual precipitation about 450–550mm, T1 ¼ �10 1C,TVII ¼+18 1C (Dobrovolsky and Urusevskaya, 1984).The research presented herein examines questions con-
cerning features of loess–paleosol–cryogenic (LPC) forma-tion north of the traditional region of loess study. Thispaper discusses materials on the two key sites featuringnumerous paleosols and cryogenic phenomena. TheGololobovo (the G section) and the Bogolyubovo (the Bsection) sections were selected across the Oka River basinof the central East European Plain. A multi-disciplinaryapproach with emphasis on the pedogenic and cryogenicproperties was applied to estimate loess and paleosolpeculiarities at these northernmost localities (Fig. 1).Detailed studies within this region may give insight intorelationships between glacial and periglacial regions duringdifferent cold epochs of the Pleistocene.The B section is situated at the right bank of the Nerl’
River valley near the town of Vladimir (N5611003300,E4012604500). The interfluve, which is the site of a claybrick pit, is about 150m asl; it has been considered to be akey locality since ca. 1981 for understanding LatePleistocene paleosols and cryogenic phenomena (Morozo-va, 1981; Udartsev, 1982; Velichko et al., 1996a, b). All ofthe principal chronostratigraphic units of the Late Pleisto-cene and a till of the Middle Pleistocene age are pre-sented there. The G (Gololobovo) section (N5510203600,E3813304000) lies 170 km southwest of Bogolyubovo inthe Moscow Region. The clay pit is excavated within theinterfluve of Kolomenka River adjacent to a large ravineentering the river valley near Zarechny village. The present-day surface is about 176masl near the clay pit. The UpperPleistocene loess/paleosol sequence at the G site has beenstudied since 1974 (Dobrodeev, 1974; Sycheva, 1978;Udartsev, 1980, 1982; Little et al., 2002). However theMiddle and Lower Pleistocene loess/paleosol/glacial se-quence was first described in 1998 (Velichko 1999; Velichkoet al., 2000a). This section possibly exhibits the bestpreserved Middle and Upper Pleistocene loess/paleosolsequences of the Moscow region.
3. Methods and materials
3.1. Field methods
Both the B and the G sections are artificial exposures ofinterfluve plateaux on the upper part of gentle slopes andlocated at brickyard’s clay pits. The trench Bogolyubovo-1-88 (i.e. B1) was sampled for geochemical and mineralogicalanalyses as well as for the micromorphological studies in1988. However, some other trenches (B2 to B5) wereadditionally studied for paleocryogenic purposes. The pit’swall cuts through a peripheral part of a cryogenicpolygonal block attributed to the Yaroslavl cryogenichorizon (CH) at the B1 trench (Table 1). Four consecutive
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Table 1
Late and Middle Pleistocene chronostratigraphic subdivisions in glacial and loess-periglacial regions on the East European Plain
West. Europe, gl acial regions
East. Europe, glacial regions Periglacial regions Cryogenic horizons
Holocene Altynovo loess Yaroslavl Trubchevsk soil Late Weichselian Late Valdai glaciation Desna loess Vladimir
Stage II Stage Borisoglebsk loess Stupino phase “b”
Interstadial Interstadial Late Inzhavino interstadial soil
Fuhne Glaciation
Stage I
Glaciation (Pechora?)
Stage Loess
Loess
Stupinophase “a”
Holstein interglacial Likhvin interglacial Inzh
avin
o so
il
com
plex
Early Inzhavino interglacial soil
Elster II stage Korostelevo loess Oka Interstadial Vorona
interstadial soil
Elster Glaciation
Elster I stage
Oka Glaciation
Loess Interglacial IV Voigstedt
Muchkap Interglacial
Vor
ona
soil
co
mpl
ex
Early Vorona interglacial soil
Stage C Don glaciation Don loess Don Interglacial III Okatovo
interglacial Rzhaksa soil
Stage B Setun glaciation Bobrov loess
BR
UN
HE
S C
HR
ON
Interglacial II Interglacial(Krasikovo?)
Stage A Glaciation (Pokrovka)
?
Cro
mer
com
plex
Interglacial I Akulovo interglacial B
alas
hov
soil
com
plex
Balashov interglacial soil
Dorst Stage
Ten
tati
ve s
ubdi
visi
on
Likovo glaciation
MA
TU
YA
MA
CH
.
Kostroma Interstadial
?
A.A. Velichko et al. / Quaternary International 152–153 (2006) 14–3016
ARTICLE IN PRESSA.A. Velichko et al. / Quaternary International 152–153 (2006) 14–30 17
trenches were sampled at the G section in 1996. They areGololobovo-1-96, Gololobovo-2-96, Gololobovo-3-96 andGololobovo-4-96 (G1, G2, G3 and G4, respectively); theseare described in Little (2002). In summary, the G1 and G2trenches show the Upper Pleistocene loess/paleosol/cryo-genic sequence and the top of the Middle Pleistocenesediment (Dnieper loess, Table 1) whereas the G3 and G4trenches demonstrate the Middle-Lower Pleistocene loess/paleosol/cryogenic sequence. Several additional trenchesfrom which the data is presented for the first time herein,were described in 1997 at the 100-m long pit wall(Gololobovo-1-97 to Gololobovo-7-97). These new datafrom Gololobovo provide some extra information for theMiddle Pleistocene cryogenic phenomena and soil defor-mations.
Detailed descriptions and drawings were made aftercleaning each of the trenches. Two series of samples werecollected from each stratigraphic unit and soil horizon: (1)bulk samples for geochemical and grain size analyses and(2) undisturbed samples for micromorphological study.Selected Upper Pleistocene stratigraphic units weresampled for additional mineralogical and bulk densityanalyses. The bulk density sampling was performed forselected samples both at the internal part of cryogenicpolygons and at the axial part of wedge-like cryogenicstructure at the B section. At the laboratory this analysiswas performed by the standard core technique (Klute,1986).
Cryogenic phenomena were investigated using both thetraditional technique of Quaternary pedogenesis andsedimentology study and the special procedure of paleo-cryogenesis investigations. The latter consists of theidentification of diagnostic indices of fossil cryogenicfeatures, meso- and microtexture analysis, and the estima-tion of the impact of past cryogenesis on the structure ofthawed deposits (Morozova and Nechaev, 1997). Bulkmagnetic susceptibility (w) was continuously measured atthe G section directly in the field using a KT-5 device with apickup diameter equal to 7 cm. Six large oriented sampleswere taken at the lower portion of the G4 trench formagnetization and magnetic mineralogy study.
3.2. Laboratory methods
Several geochemical and physical techniques were usedfor all 93 samples obtained from the B and G sections.Percent of organic carbon was determined by K2Cr2O7oxidation and recalculated to the soil humus content with a1.72 ratio (Zyrin and Orlov, 1980). Carbonate content wasdetermined by the volumometric method and recalculatedto CO2 equivalent (Arinushkina, 1970). Grain size analysiswas performed by pipette technique for all samples(Kachinskii, 1966). No HCl treatment was performed and250 mm wet sieving was used for sand separation withpipette analysis. Total iron, aluminium and silica wereobtained by ignition from selected samples at the G sectionand recalculated to sesquioxides ratios (SiO2/Al2O3 and
SiO2/Fe2O3) to estimate the components translocation byweathering processes (Arinushkina, 1970).Magnetic susceptibility was rechecked in the laboratory
by KLY 2 device for the selected samples. The measure-ments were performed along three axes in order to assessthe anisotropy of w for the rocks. Magnetic polarity andmagnetic mineralogy were studied using the standardtechnique (Khramov, 1982; Evans and Heller, 2003). Thenatural remnant magnetization of rocks (Jn) was measuredby the JR-4 instrument after holding the samples in thescreen for 1.5 months.In order to determine the characteristic (primary)
magnetization (J0n), a series of heatings to 400 1C at a step
of 50 1C were performed. Control determinations of theprimary remnant magnetization of rocks were accom-plished in an alternating magnetic field (stage-by-stage) to150mT. The analyses were carried out on the SQUIDmeter in the Paleomagnetic Laboratory, Institute ofGeophysics, Polish Academy of Sciences. A componentanalysis of data on the demagnetization (Jn) of rocks wasperformed. It has been established from the Zijdervelddiagrams obtained as a result of demagnetization ofsamples by temperature and alternating magnetic field thattwo or three components of Jn can be distinguished in therocks. The first component, measured at 100 1C, has arandom direction and represents the residue of laboratoryviscous magnetization. The second component that ismeasured in the temperature interval 200–250 1C is of aviscous nature due to J0
n the influence of the present-daymagnetic field. The separation of the characteristic direc-tion is observed after heating samples up to 250 1C (seldomup to 310 1C). From the Jn(t) curves, magnetite is the maincarrier of magnetization of the rocks. Hematite is onlypresent in negligible amounts.Micromorphological description and microphotography
were conducted on thin sections of loess, paleosols andmodern soils to refine interpretation of geochemicalanalyses and to reconstruct the soil’s genesis. Thin sections(about 0.03mm thick) were prepared using the techniquesuggested by Mochalova (1956) with some modifications.Terminology used to describe microfabric and otherfeatures was that of Bullock et al. (1985) and Gerasimovaet al. (1996).Silt fraction mineralogy was described by mineral grain
counting using a petrographic microscope by TA Khalche-va, Laboratory of Evolutionary Geography, Institute ofGeography, Russian Academy of Science, Moscow,Russia. The ratio of the stable minerals (zircon+tourma-line) to the unstable (amphiboles+pyroxenes) was calcu-lated for the Upper Pleistocene deposits at both sections.This ratio was previously named as the K1 weatheringcoefficient by TA Khalcheva (Velichko et al., 1984). Itdemonstrates the degree of Quaternary sediments weath-ering and can be used as an indicator of the degree ofpedogenic transformations.The soil classification and the atlas of the World
Reference Base for Soil Resources (WRB) (1998), as well
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as Classification of Soils of Russia (1997) were applied toreferences of the present-day soil cover and diagnosedpaleosols. Texture classes used in this article are based onthe Canadian System of Soil Classification (1998).
4. Geological framework and chronostratigraphy of
Quaternary deposits
Pre-Quaternary geologic strata within the eastern marginof the Moscow Syncline are of Mesozoic age. Theyprimarily consist of Upper Jurassic black shale and poorlyconsolidated sandstone with minor Lower Cretaceousglauconitic sandstone. Locally, Carboniferous limestoneis exposed at the surface.
Quaternary deposits in this region overlie the erodedCarboniferous and Jurassic bedrock surface. The Quatern-ary surface occurs at 130–150masl within the limits ofinterfluves and descends to 80–100masl along river valleys.Since the region was repeatedly invaded by ice sheetsduring the Pleistocene (see Fig. 2 in Little et al., 2002;Velichko and Shik, 2001), the present day topography alsoexhibits some inherited features related to buried glaciallandforms.
Chronostratigraphic units identified in the studiedsections. There are several horizons recognized in theLPC series, which not always provide materials for reliabledating. The regional chronostratigraphy is based onrelationship between the LPC sequence and Quaternarytill horizons, on a few 14C dates, on morphotypicalproperties of the paleosols, as well as on correlation withkey sections which formed the basis of the generalstratigraphic scheme of the East European loess region(Velichko, 1990).
At the B section, both Don and Oka ice sheets overranthe area during the Early Pleistocene, whereas the Dnieperice sheet modified the landscape during the MiddlePleistocene (Table 1 and Fig. 1). In contrast, the G sectionis situated about 20 km south of the Dnieper ice sheet limit,and therefore was covered only by Early Pleistocene icesheets. The Lower Pleistocene sediments exposed in thissection comprise till presumably of Oka glaciation and asandy silt of the final stage of the same glaciation. Near theB section the Pre-Dnieper glaciolacustrine and glaciofluvialsands and clays are confined to depressions of pre-glacialtopography; most of the Pre-Dnieper sediments wereremoved from interfluvial elevations by the Dnieper icesheet. Deposits of Dnieper age are tills and glaciofluvialsands in the Vladimir region (B section), whereas loessesand glaciolacustrine sediments dominate the vicinities of Gsection. The Post-Dnieper deposits form two complexes:alluvium comprising three river terraces and loess-likedeposits of interfluve plateaux. The term ‘‘loess-likedeposits’’ is usually applied to deposits of loessial group,which differ from classical loess in some lithological andgeochemical characteristics (such as higher proportion ofsand and clay fractions).
Some OSL dates have been obtained for sedimentsexposed in the Likhvin section, also located in the Okadrainage basin (see Fig. 1). There, at 1m below the Dniepertill base, a sample of loess-like loam was OSL-dated at4201714 kaBP. In the Gololobovo section, loess-likedeposits overlying the Dnieper till and attributed to theMoscow stage were dated at 4122715 kaBP. There is aLPC series exposed both in Bogolyubovo and Gololobovosections, as well as the Likhvin section, and having manystructural features in common. The loess-like deposits ofMoscow age form parent rock for the polygenetic Mezinsoil complex; the latter comprises an earlier forest paleosolof interglacial type and another one of interstadial type.Morphotypical characteristics of the paleosols (Morozova,1981) as well as correlation with lacustrine-boggy depositscontaining Mikulino flora (Velichko et al., 1984), theearlier phase of the Mezin complex—Salyn paleosol—corresponds to the Mikulino Interglacial. The interstadialKrutitsa paleosol developed on the Sevsk loess belongs tothe second phase. The Mezin complex is overlain by theKhotylevo loess (dated to the first half of the Valdai coldepoch) that forms parent rock for the Bryansk paleosol inall the three sections. It has been confidently defined asinterstadial soil on the base of its morphotypical char-acteristics (the latter will be considered below in moredetails). Besides the genetic profiles, the 14C dates(32–24 kaBP) are in good agreement with those obtainedfor a section near the Bogolyubovo—25,5007200 yearsBP (Velichko et al., 1996a). The Khotylevo loess hasbeen OSL-dated at 347kaBP in the Gololobovo sectionand at 47077 kaBP in the Likhvin section (Little et al.,2002).The Middle Pleistocene LPC series are quite distinguish-
able in the Gololobovo section. Their age is mostlyestimated on the ground of the paleosols morphotypicalcharacteristics, and corroborated by the age of underlyingtill attributable to the Oka (Elsterian) glaciation (Velichkoand Shik, 2001). The Late Pleistocene Mezin soil complexis developed there on thinly laminated loess-like depositsattributed to the Dnieper ice age; the deposits are heavilygleyed (possibly, during the Romny Interstadial—see Table1) (Velichko et al., 2005).Below this horizon, there is the Kamenka soil complex
developed on a thin loess-like loam (the Orchik loesshorizon). It includes a paleosol belonging to an earlierforest phase of the interglacial characteristics (the earlyKamenka paleosol) and a paleosol of the later phase, thatis interstadial—late Kamenka—phaeozem. Below, there isanother—Inzhavino—soil complex. In common with theupper one, it consists of the main interglacial paleosol(early Inzhavino) and of interstadial—late Inzhavino—one. The Inzhavino soil complex developed not only onloess (Borisoglebsky horizon), but on glacial till as well.The uppermost portion of the till is occasionally replacedby lacustrine-boggy shallow-water deposits. The above-mentioned glacial and glaciofluvial and glaciolacustrinesediments are considered to be of Oka (Elsterian) age,
ARTICLE IN PRESSA.A. Velichko et al. / Quaternary International 152–153 (2006) 14–30 19
while the overlying Inzhavino soil complex is attributed tothe Likhvin (Holsteinian) Interglacial.
A number of CHs have been identified in the sequence.The lowermost one occurs in the horizon A1 of theInzhavino soil complex as deformations of phase ‘‘a’’ of theStupino CH. Sediments correlatable with the Borisoglebskloess contain ice-wedge pseudomorphs, (the ice wedges inquestion are attributed to phase ‘‘b’’ of the Stupino CH).
An early Dnieper CH at the base of the Dnieper depositsdisturbs the Romny paleosol profile. Two more CHs arefound within the Dnieper and Moscow loess horizons. Inthe glaciated region the Dnieper CH occurs under the baseof the till of this glaciation, while the Moscow CH cuts thetop of this till epigenetically.
Cryodeformations of phase ‘‘a’’ of the Smolensk CHdistort A2 and Bt horizons of the Mezin soil complex,while later deformations attributed to phase ‘‘b’’ of thesame CH are seen in its A1 horizon. Deformations of theVladimir CH distorted the Bryansk paleosol. Yaroslavlcryogenic deformations (both ‘‘a’’ and ‘‘b’’ phases) are seen
Fig. 2. Stratigraphy of the Bogolubovo section (after Velichko et al.,1996a). Ex
loess; 5—Ah horizon of Bryansk paleosol; Mezin soil complex: 6—Redeposit
horizon of Salyn paleosol; 8—iron nodules and bands; 9—gleyic features.
at the top of the post-Bryansk loess, below the base of theHolocene soil.
5. Results of multidisciplinary studies
5.1. Bogolyubovo (‘‘B’’) section
5.1.1. Lithology and geochemistry
The lithic characteristics of the sediments at the B section(i.e., textural analyses) warrants the subdivision of thesection into three main units. The loamy skeletal till isexposed at the base of this section (Fig. 2). No clastscoarser than 1mm occur above the C horizon of the Mezinpedocomplex. The pedocomplex was formed in the MiddlePleistocene silty loam with 22–40% of sand (450 mm)fraction and 30–40% of coarse silt (10–50 mm) fraction(Fig. 3). The Khotylevo loess of the same compositionburied the Krutitsa paleosol of the Mezin pedocomplex(Figs. 2 and 3). At the middle part of the Bryanskpaleosol solum a change of grain size was observed. The
ed material of Krutitsa paleosol Ah horizon; 7—fragments of Ae and Bt
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Fig. 3. Lithology and properties of sediments at the B1 section (modified from: Velichko et al., 2000b).
A.A. Velichko et al. / Quaternary International 152–153 (2006) 14–3020
overlapping loess-like sediment contains 40–50% coarsesilt and less than 5% sand (Fig. 3). It is silty clay at the topof Bryansk paleosol and silty clayey loam at the modernsoil solum. Therefore, the coarse silt loessial fractiondominates the Upper Pleistocene loess/paleosol series.However, different sources of the sediments are evidentfor Late Valdai loesses versus all of the older sediments.The clay-free grain size distribution confirms the morpho-logical data regarding Mezin pedocomplex disturbance andstratification of its Krutitsa phase Bt horizon. A compar-ison of bulk and clay-free grain size distribution showspedogenic clay accumulation at Bt horizons of both theHolocene and Salyn soils and presumably at the Bghorizon of the Bryansk paleosol (Fig. 3).
Bulk density studies of undisturbed central part of thecryogenic polygons revealed density increasing at all the solaand decreasing at relatively unaltered loess horizons (Figs. 2and 3). Extremely high bulk density (up to 1.93 g/cm3) hasbeen recorded in the upper part of the Mezin pedocomplexat a depth of about 5m. In tracing the same horizonlaterally, significant changes in the bulk density were alsofound. Thus, at the margin of a depression 8–10m wide(presumably resulted from ice wedge melting) all thehorizons to a depth of 3–4m show an increase in the bulkdensity in comparison with the central part of the cryogenic
polygon. The increase amounts to 6% in the Bt horizon ofthe Holocene soil, to 15% in the Late Valdai loesses, and to13% in the Bryansk paleosol. Such a considerable growth inthe bulk density values within the buried depression isundoubtedly due to higher moisture content of the soil in thenegative landform and possibly to finer texture.Of special interest are the results of bulk density
measurements along axis of a large wedge-like structureas compared with those measured in the enclosing depositsof thermokarst depression. The base of the Holocene soil—Bt—horizon is much lower in the axial part of thestructure. The visual observations agree with data on bulkdensity. At the axis the values are about 1.8 g/cm3 at thedepth of 2m from the day surface. The same tendencytowards somewhat higher bulk density in comparison withnear-contact zone is still distinct downward (Fig. 3).Taking into account the fact that the wedge-like structureis filled with coarser deposits than the enclosing ones, onemay safely suppose active filtration of water taking placethrough the axial part of the structure.
5.1.2. Paleopedological studies
The Bryansk interstadial soils developed in subpolarenvironments. The soils are diagnosed as cryosols (tundra-gley). Strong gleyzation (Ag–Bg–Cg) and ooidal cryogenic
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microstructure are their most typical features. The B-fabricof groundmass is circular striated (Fig. 4a). Iron hydroxidenodules are found through the whole solum and formconcentrations in the underlying gleyed silty loam.Numerous crotovinas found in the paleosol containremains of various small mammals—dwellers of openlandscapes of periglacial forest-steppe (Lagurus luteus, L.
sibiricus) (Baryshnikov and Markova, 2002). Similar fossilremains are also found in cryopedoliths in NortheastEurasia (Gubin et al., 2003). Pollen assemblages containBetula nana and Alnaster fruticosa (Gurtovaya, 1981).Humus material from Bryansk paleosol was dated at the Bsection using the standard technique at 25,5007200 yearsBP (Fig. 2) (Velichko et al., 1996a).
The Krutitsa 14C interstadial soil of the Mezin complex isheavily disturbed by solifluction and forms a number ofsub-horizontal humus-rich interlayers. Though essentiallytransformed by cryopedological post-burial processes, thesoil matrix still maintains evidence of dominant humusaccumulation processes (Fig. 4b).
Fig. 4. Micromorphological features of loess/paleosol formation of the
Bogolyubovo section. (a) Aggregates in the Bryansk paleosol. PPL. (b)
Humus horizon of the Krutitsa paleosols. PPL. (c) Bt horizon of the Salyn
paleosols. Coatings. PPL.
Table 2
Humus group composition in the humic horizons of interstadial soils in the O
Sections Soil units Organic
carbon, %
Bogolyubovo (Velichko et al.,
1996a, b)
Bryansk 0.30
Krutitsa 0.66
Berkeevo (Dlusskii et al., 1997) Romny 0.18
Late Kamenka phase 0.47
Late Inzhavino phase 0.13
Troitsa (Dlusskii et al., 1997) Romny 0.32
Kamenka 0.43
The Salyn paleosol of the same soil complex correspondsto the Mikulino interglacial and is very rich in claycoatings. They strongly suggest clay illuviation during theinterglacial (Fig. 4c).Acidity (pH) measurements indicate neutral to slightly
acidic present-day conditions for the entire B1 section. Nocarbonates were found in the matrix (though rare concre-tions of the doll type do occur). The organic carboncontent is relatively low in paleosols and loess of thissection, but significant elevated carbon contents areobserved in the Ah horizons of the Bryansk and theKrutitsa interstadial paleosols (Fig. 3). Humus composi-tion appeared to be predominantly of the fulvate type in allthe soils (Table 2). Humin (i.e. unextractable residue)proportion in all the fossil soils increases with the age of thesoil. As for optical density of humic acids, maximum valuestypical of humus accumulation horizons are established inthe soils dated to the Krutitsa interstadial time. A lowoptical density indicative of immature humus characterizesthe Bryansk soil (Table 2).The mineralogical composition of Upper Pleistocene
loess/paleosol horizons in the B section features polymicticassociation of more than 30 minerals. Minerals of lightfraction are dominant in this association. Primarily, theyare quartz, feldspars (plagioclases and potassium-sodiumfeldspars) and muscovite. In the heavy fraction, proportionof opaque minerals is rather high. The weatheringcoefficient K1 keeps stable values (about 3.0) along loesshorizons but increasing in each soil solum. It is 4.8 at thetop of the Bryansk paleosol but reach the highest value(5.4) at the top of Krutitsa paleosol solum (Fig. 3)(Velichko et al., 2000b, 2004).
5.1.3. Paleocryogenic studies
The deposits on Figs. 2 and 3 were disrupted by large-scale cryogenic deformations of the Yaroslavl CH. Thesedeformations, being a geological base of the polygonal-blocky microrelief, represent the cryogenic structures ofphase ‘‘a’’ of this CH. At that time, cryogenic processesdeveloped in conditions of the most severe continentalclimate that ever occurred in the Pleistocene. They formedthe cryogenic polygonal relief, whose transformation after
ka River basin (HA—humic acids, FA—fulvic acids)
Humus, % CHA/CFA Humin, % of
organic carbon
Optical density
of HA, E465
0.52 0.47 53.7 0.18
0.14 0.79 61.4 0.23
0.31 0.33 77.8 0.09
0.81 2.17 59.6 0.23
0.22 0.43 76.9 0.13
0.55 0.14 75.0 0.13
0.74 0.80 79.1 0.21
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degradation of the permafrost lead to relict cryogenicmorphosculpture formation (Velichko, 1965). Four ancientpolygon systems were described in the Bogolyubovo claypit. Each of them contains a major wedge-shaped structure.The inter-block zones lie 12–20m apart, placing this reliefas a small and medium polygonal type (Velichko et al.,1996b).
The studied cryogenic structures of this horizon aredifferentiated into two parts: the wider upper one to adepth of 2.6–2.7m and relatively narrow wedge-likelower part with apophysis penetrating to a depth of 4.0m(Fig. 3). They form a system of wedge-like structuresidentified as ice-wedge pseudomorphs over ice wedges,according to their morphological features and stratigraphicposition in the B section.
The structures underlie the modern soil and are distinctfrom about 1.5m due to cauldron-like deformation filledwith reddish-brown loam; the lower contact of the loam isfringed with numerous subvertical veinlets of ferrigination.The middle and lower parts of the structures are filled withmottled reddish-yellow loam with abundant dendritic dark-rusty veinlets; the latter penetrating into enclosing deposits(Fig. 2). The upper parts of the structures are emplacedinto loam where the structure’s boundary is indistinct.Over the depth interval of 1.8–2.3m, the loam acquiresbluish-grey hue due to gley process, which are typical of theburied active layer and is rarely observed at the site. Thematerial of this gleyed horizon partly penetrates into thestructure (trench B5). It is usually distinguished by adifference between enclosing and infilling matter, andlocally by the presence of microfaults. The main bodiesof the structures are better seen against the background ofthe Bryansk fossil soil.
Cryogenesis of the Bryansk soil (Vladimir CH) studied inthis section is through plastic deformation of the primarysediments (Fig. 2). They are represented by oblique curvedlaminae and ‘‘tresses’’ at the upper and lower boundaries ofthe layer. Deformations of this kind suggest dynamicprocesses resulting from seasonal thawing and freezing inthe active layer. Traces of very dynamic translocation ofthe sediments, and the location of section B5 (on interfluveslope) suggest that slumping processes may have alsoaccompanied and intensified the dynamic seasonal cryo-genic processes.
The strong seasonal frost characteristics of this horizonsuggest a prominent cold interval following Bryansk soilformation. Further, as these structures, and the Bryanskpaleosol are buried by loess, the cold interval appears tohave triggered an increase in loess deposition. Given thestratigraphic position of this loess relative to the datedBryansk Paleosol, we associate this interval of loessdeposition with the Vladimir cryogenic stage; a coldinterval less severe than the LGM. Characteristic cryo-morphic evidence, such as frost cracking and spot-medallion formation proceeded along with widely spreadsolifluction and cryoturbations support this association.The upper part of the Mezin pedocomplex (the Krutitsa
soil, Fig. 2) also bears evidence of active cryogenicdeformations of phase ‘‘b’’ of the Smolensk CH. The soilmaterial is preserved as redeposited humus-reach inter-layers, strongly distorted by solifluction and cryoturbation.That cryogenic epoch of the early Valdai featured smallthermal gradients and predominantly non-structural de-formations.The Late Pleistocene relict cryogenic complex within the
B key site is well described and confidentially interpreted.The region under consideration shows evidences ofcryogenic processes related to three cryogenic stages ofthe Late Pleistocene.
5.2. Gololobovo (G) section
5.2.1. Lithology and geochemistry
The lithology of Middle-Upper Pleistocene loess/paleo-sol series was described by Velichko et al. (2000a) andsummarized by Little et al. (2002). The sediments exposedat the G section consist primarily of silty clay to silty clayloam and demonstrate several lithological units along thesection (Fig. 5). The complicated sedimentation history ofQuaternary loess/paleosol sequence in this section isdescribed on the base of the extended set of analyses.The loamy till was described at the base of the
Gololobovo clay pit. This till underlies the Inzhavinopaleosol with no evidence of strong fluvial erosion on thecontact but with some strong cryogenic deformations in thetop. At the G4 trench a silty loam, with sporadic 3–4mmsize rounded feldspar and quartz grains was observedbelow the Inzhavino paleosol solum. This gleyed unit hasmore than 12% fine sand, but coarse silt dominates(53–69%, Fig. 6). Obviously this silty loam is originallyloess derived from an adjacent glacial source. A well-sortedfine sand layer of 2-m thick lies below the till. Both thesand and the till are also exposed in scarps along theKolomenka River, northwest of the brickyard. The till maybe attributed either to the Oka or Don glaciations of theLower Pleistocene, until additional thermoluminescenceand palynological data are obtained.No particles coarser than 1mm occur upward of the
Inzhavino paleosol solum (Fig. 5). This solum was formedin non-laminated silty loam with coarse silt fractiondominating (53–61%). Presumably it is loess stronglyaltered by soil formation. The lower part of Inzhavino soilsolum has 11% of fine sand fraction (Fig. 6) and eventuallyseparated from the upper part of this solum by both sandand clay content. The lower portion of the Kamenkapaleosol solum has some evidences of stratification but theupper portion of this solum consists of non-laminated siltyclay. A comparison of bulk and clay-free grain sizedistributions suggests a pedogenic origin of the clayaccumulation (Fig. 6). The ‘‘loessial’’ fraction (10–50 mm)still dominates (30–46%), but its content decreases upwardalong the juvenile gley soil solum of probably Romny age.The bluish grey silty clay (unit 2 at G4 and unit 6 at G3)
buried the Middle Pleistocene series of clustering paleosols
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Fig. 6. Lithology and properties of sediments at the Gololobovo section.
Fig. 5. Gololobovo section. Lithology and pedogenic features.
A.A. Velichko et al. / Quaternary International 152–153 (2006) 14–30 23
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(Fig. 5). This stratified silty clay unit is 1.0–1.4-m thick atthe studied trenches and has strong gley properties andabundant large iron neoformations. The unit was inter-preted as a loess material redeposited by water, likely in alacustrine or glacio-lacustrine setting due to the absence ofobvious stratification. Coarse silt content increases up-wards and gley features are less pronounced but stratifica-tion is still observed (Figs. 5 and 6). The yellowish brownsilty loam unit is 2.5–3.0m thick. It was dated as4122 kaBP at the upper portion and is probably ofDnieper age (samples GCSL3 and GCSL4, Fig. 5) (Little etal., 2002). This secondary loess unit is subdivided into astratified lower part (units 4 and 5 at G3) and weaklystratified but strongly carboniferous upper portion (unit 3at G3). Carbonate content as well as stratificationpronunciation decreases downwards gradually along theDnieper loess. The Mezin soil complex of Late Pleistoceneage was described at the top of G2 and at the bottom of G1trench (Fig. 5). Its profile is free of carbonates to 1.5mbelow the presumable paleosurface and has some pedo-genic clay accumulation at the upper part of Bt horizon ofSalyn paleosol. Probably it is a separate sediment unit,because of the higher sand content in comparison withDnieper loess (5–6% vs. 0.1–3.5%). Therefore the sharpboundary by carbonate content between Salyn soil solumand Dnieper loess could be either lithological or pedogenicby origin. Bryansk paleosol and Mezin pedocomplex arepartly superposed at this section.
The coarse silt fraction eventually dominates (43–54%)along Upper Pleistocene sediments at the G1 section (Fig.6). However, differentiation by fine sand content indicatesa weak stratification of all these sediments. This stratifica-tion is weakly pronounced morphologically only at themiddle part of Late Valdai loess (units 6 at G1). All of theUpper Pleistocene sediments are carbonate-free and havemore or less pronounced gley mottling and Fe–Mnsegregations. Both Altynovo and Desna loesses haverelatively high content (6–11%) of fine sand fraction incomparison with Holocene soil (o1%) Bryansk paleosol(Khotylevo loess) and even with Mezin pedocomplex(1–3%), suggesting stronger winds or a more proximalsource of these loess units.
5.2.2. Paleopedological studies
The present-day greyic luvisol at the top of G1 sectionhas well-pronounced humus maximum and evidences ofpedogenic clay translocation (Fig. 5). In comparison withthe B section, this surface soil has less pronounced featuresof the Middle Holocene soil formation. It does not have aburied Ah horizon, and relict polygonal relief is notpronounced near the section. However the presence ofweak Ah horizon development from 0.6 to 1.1m (evidentfrom fine granular structure,) suggests that the initialstages of the present-day soil development may have beencumulic (regosolic), forming in tandem with aeoliandeposition. This Holocene soil altered only the upperportion of the Altynovo loess. Gley mottling and lack
of carbonates are the only pedogenic influence on theAltynovo loess (Fig. 5).The weakly stratified silty clay loam in the middle part of
the Late Valdai loess has gley mottling and abundant roottraces along channel pores. This unit has sand (9–11%),but coarse silt dominates (Fig. 6). Thus this loess materialwas redeposited and marks an paleosurface. Probably thislevel corresponds to the gleyed regosolic Trubchevsk soil
formation.The interstadial Bryansk paleosol is more gleyed but
weakly deformed by solifluction here in comparison with Bsection. It has no krotovinas. Two Ahg sub-horizons areseparated by mottling and gley process degree at its solum.However, the K1 weathering coefficient is twice as high inthe Bryansk paleosol as in the Desna loess above (Velichkoet al., 2000a). The Bryansk soil has a weak pronouncedhumus maximum at the lower portion of solum (Cg2horizon, unit 10 at G1 section, Figs. 5 and 6). Granularmicrostructure was observed in thin sections but nostructure was observed in the field. The biogenic micro-structure, in addition to increases in humus content,suggests this paleosol had a weak Ah horizon. The gradualupper transition to the Desna loess indicates that soil is acumulic regosol.The Mezin pedocomplex has high humus content (0.67%)
and granular structure in the Ah horizon. The Krutitsa andthe Salyn paleosols are not subdivided at this section bypedogenic features but two phases of the Smolensk CH arestill observed. In contrast to the B section, the upper partof the Mezin soil complex has no evidence of erosion.However, both strong solifluction and small-polygonfissures disturbed this profile in the G section. The fissuresare filled with humus material and penetrate to the Bthorizon (Fig. 5). The solum is differentiated equally by ironand aluminum, and pedogenic clay accumulation isrevealing in Bt horizon by comparison of clay-free grainsize distribution and bulk grain size distribution (Fig. 6).Micromorphological data confirm clay illuviation andhumus accumulation at the Mezin pedocomplex profile.The bleached Ae horizon with platy structure is presentedbelow the Ah horizon (Fig. 5). Also, some krotovinas up to4 cm in diameter are presented at the Bt horizon. Thereforethe Salyn paleosol of the Mezin pedocomplex can beinterpreted as a luvisol and lessivage was probably thedominant process of this soil formation (Fig. 7a). Onlyhumus accumulation can be suggested for the Krutitsapaleosol. Thus, this soil can be presumably classified as ahumic regosol (Little, 2002) or as a cold steppe phaeozem(Velichko et al., 2004).Pedogenically unaltered Dnieper silt of Middle Pleisto-
cene age is exposed below the Mezin pedocomplex at theG3 section (Fig. 5). The upper portion of the Dnieper siltyloam is porous and retains some microfeatures of typicalloess, but the lower part is marked by bluish grey silty clay(unit 6 at G3). Micromorphologically, this lower unit ispoorly aggregated (with rare ooidal aggregates). There areconcentric iron neoformations to 15 cm in diameter with
ARTICLE IN PRESS
Fig. 7. Micromorphological features of loess/paleosol formation of the Gololobovo section. (a) Arrows indicate illuviated clay infillings of Bt horizon in
the Salyn phase of Mezin soil complex. PPL. (b) Granular structure of Ah Bt horizon in the late phase of Kamenka soil complex. PPL. (c) Granular
structure of Ah Bt horizon in the late phase of Inzhavino soil complex. PPL. (d) Humus-clay coatings and ferrugination of voids in Bt horizon of early
phase of Inzhavino soil complex. PPL. (e) Clay coatings in Bt horizon of early phase of Inzhavino soil complex. PPL.
A.A. Velichko et al. / Quaternary International 152–153 (2006) 14–30 25
dense rust-coloured nuclei. The structure of these concre-tions shows that they were formed slowly in a water-saturated ground mass.
Following the stratigraphic scheme, this level is theinterstadial Romny paleosol, a gleyed regosol (Table 1).Micromorphological analysis shows numerous poorly andmoderately developed isometric aggregates with ooidalmicrostructure of B-fabric clay plasma. There are abun-dant inclusions of a humus-rich material with fragments ofclay-humus coatings in channel-shaped voids (Fig. 7e),suggesting that the parent material of this soil includesaggregates derived from the Kamenka complex.
The Kamenka paleosol complex features AhBt–Bt1–Bt2profile in the G4 trench (Fig. 5). There are two paleosolsidentified in the complex, which belong to different stagesof soil formation. The earlier paleosol—Early Kamenka—is a forest soil with an (A)–Bt1–Bt2 profile. The paleosol oflater stage—the Late Kamenka interstadial—seems to berepresented by a humus horizon (AhBt) lying directly onthe Early Kamenka paleosol.
The late Kamenka horizon features strong secondaryferrugination in its upper part but still has strong fine
granular structure (Fig. 7b). This AhBt horizon is brownand has clay coatings. Other features are abundant SiO2
powder on its aggregates and depletion microzones. Thereare a few krotovinas up to 10 cm in diameter, twice as bigas those in the overlying Krutitsa interstadial paleosol ofthe Mezin paleosol complex. This suggests more grasslanddominant over forest environment for the late Kamenka.The solum is poorly differentiated by aluminum but hasevident differentiation of iron. Argillic features are alsodiagnosed by comparison of clay-free and bulk grain sizedistribution (Fig. 6). Probably, both lessivage and surfacegley processes took part in its formation. The lateKamenka soil was interpreted as a phaeozem with luvisolproperties.There is evidence of an earlier stage of soil formation in
the Kamenka paleosol complex at the G4 trench. Thepaleosol of this stage—Early Kamenka soil—consists ofBt1 and Bt2 horizons. Micromorphologically, the ground-mass of the Bt horizons has strong blocky structure andmany thick compound-layered coatings of humus-clay andiron-clay composition. Locally coatings fill inter-aggregatepores completely. Two generations of the coatings were
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observed: (1) thick and older compound layered humus-clayey coatings and (2) younger ones, also humus-clayey incomposition, but less thick and not laminated, presumablyformed after coatings of the first generation had beendestroyed. Hypothetically, the older generation of coatingscorresponds to the same earliest stage of the Kamenkapaleosol complex. Previously this soil was attached to theInzhavino paleosol as a final stage of polygenetic soilformation (Velichko et al., 2000a). However in light ofadditional data, it is more likely the earliest stage of theKamenka paleosol complex (Little, 2002). This point ofview is in agreement with paleopedological data from themost representative Likhvin section (Dlusskii, 2001, 2003).
As noted above, the Kamenka paleosol was eventuallyeroded during or just after its burial. At the G4 trench theeroded humus-reach material is preserved only in the deepdepressions penetrated from the Romny paleosol to the Bthorizons of the Kamenka paleosol. The humus content is0.55% in some interlayers. Aggregates in some of inter-layers are powdered with SiO2. Probably this material waseroded from the former Kamenka paleosol Ah and Aehorizons. The genesis of these depressions is not clear. Asseen in section G4, they form pits 1.5-m wide and 2-m deep.The peripheral upper parts of these ‘‘pits’’ can be traced as4-m wide. Micromorphological investigation providessome evidence of their history. Thin sections of samplestaken from the material filling the ‘‘pits’’ show macro andmeso-aggregates, with channel voids and fragments ofthick humus- and iron-enriched clay coatings. Thegroundmass is rich with amorphous organic fine material.Coal-like particles (presumably plant residues) are com-mon, very small, fissured and with completely destroyedcell structure.
The oldest Middle Pleistocene unit at the G section is theInzhavino paleosol complex (Fig. 5). It features anAh–Ae–Bt–Btg solum, which is strongly differentiated byiron. However, the aluminum content is practically stablealong the profile (Fig. 6). Grain size distribution showssharp increases of the percentage of sand and coarse siltfractions in the subsurface horizons as compared with theAh horizon. Micromorphological observations confirmexistence of this lithological differentiation within theInzhavino paleosol parent material. The humus contentpeak in the Ah horizon is weak but distinct (0.29%).Micromorphologically, the humus horizon has moderate tostrong granular structure (Fig. 7c) overprinted by twogenerations of humus clay coatings. There are some SiO2
powdered aggregates and zones depleted of plasma. The Aehorizon is platy olive yellow silt and has the lowest contentsof clay, organic matter and iron (Fig. 6). This horizon isstrongly disturbed and forms fissures penetrating into theBt horizon with strong blocky structure. Both Ae and Bthorizons contain abundant Fe–Mn nucleic and digitatenodules up to 3–6 cm in diameter. Two types of claycoatings are described in the Bt horizon. They were foundin pores of different types and have different structure andcomposition. Coatings marked by higher humus content
are restricted to channel-like voids (Fig. 7d). Coatings ininter-aggregate pores are mostly thicker and of ferrugi-nous-clayey composition (Fig. 7e).The Ah horizon thickness (0.4m) in combination with
the presence of Ae horizon below suggest polygeneticcharacter of the Inzhavino paleosols complex. Thelithological differentiation of Ah horizon and the rest ofthe solum below supports this conclusion. The only humusaccumulation features the final stage of the paleosol andprobably corresponds to the Late Inzhavino interstadialpaleosol. There is a paleosol profile below identified as theinterglacial Early Inzhavino (Likhvin, Holstein) paleosol.On the base of argillic features and differentiation by
iron this paleosol could be diagnosed as eluvial surface gleysoils or stagnic podzol–luvisol. The specific gley-eluviationprocess was described for similar modern soils by severalauthors (Kovda and Rozanov, 1988; Gerasimova et al.,1996).
5.2.3. Paleocryogenic studies
Long-term studies performed by the team of theLaboratory of Evolutionary Geography (Institute ofGeography, Russian Academy of Science) permitteddistinguishing at least 7 horizons marked by cryogenicactivities (paleocryogenic horizons) in the G section. Hencethis section plays a key role in studies of Quaternarypermafrost dynamics in central Russia.Three Late Pleistocene CHs, well pronounced in the G
section, have been studied in detail as a component of theLate Pleistocene loess/paleosol/cryogenic formation of theEast European Plain (Table 1). The strongest permafrostdeformations of the Late Pleistocene are related to theYaroslavl CH. The described loess/paleosol units areoverprinted by large deformational structures, which canbe considered as pseudomorphs over ice wedges, accordingto their morphological features and stratigraphic position.They form a system of wedge-like structures which occursdirectly under the base of the Holocene soil solum andreaches 2.0–2.5m into underlying loess. The wedges are0.5–0.7m wide (in the upper part) and the polygonsize is about 20–25m (Udartsev, 1980, 1982; Morozovaand Nechaev, 1997).The middle of the Late Pleistocene CHs (Vladimir CH)
produced a noticeable effect on the Bryansk fossil soil. Itssolum was strongly disturbed by structures of tundramedallion type and solifluction processes. The oldest CH ofLate Pleistocene age is the Smolensk horizon disturbing theMezin soil complex. In the section under consideration it isseen as earth fissures related to small cryogenic polygons(phase ‘‘a’’) and solifluction processes (phase ‘‘b’’). Thesmall polygon fissures that are 0.2-m wide at the Ae/Bthorizon penetrate to the bottom of the Mezin soil complexand indicate significant seasonal gradients of temperatureand humidity at the end of Salyn soil formation.The youngest Middle Pleistocene CH occurs within the
Dnieper deposits at the contact of bluish grey silty clay andyellowish brown silty loam. The contact is broken by a
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system of wedge-like structural deformations identified asice-wedge pseudomorphs of Dnieper CH (Udartsev, 1980).The wedge structures are 12–15m apart and reach into thebluish clay and older deposits to a depth of 3m.
An older paleocryogenic horizon is recorded near the topof Romny paleosol. In exposures where the Romny soilwas heavily disturbed or eroded, the horizon is recogniz-able at the contact between the humus horizon of theKamenka soil and overlying gleyed silty clayey. The trenchGololobovo-1-97 situated 250m north of the G4 one showsdistinctly festoon-like contact between the bluish clays andthe Kamenka soil top. The clay lenses penetrate the Ahhorizon of the soil to a depth of 0.5m at regular intervals,forming wavy outlines of the contact. Near trench G3,annular deformations consisting of bluish clays alternatingwith dark humus-reach material penetrate some 1.5m intoBt horizon of the Kamenka soil (units 5 and 6 at the G3trench). The Ah horizon of this soil is completely erodedthere. Annular structures (seen in vertical wall) of similarmorphology have been observed by Nechaev in thepresent-day active layer in the west of the Yamal Peninsulaabout 701N (Velichko et al., 2000a). Still more complicateddeformations of the horizon were described in the north-western part of the brickyard clay pit. Bluish-grey gleyedand dark-grey humus-rich layers form variously distortedtongues and pockets that intrude into underlying depositsby 1.5–2.0m and more. They are usually fringed with adistinct rusty-brown band of ferrugination 5–10 cm wide.In this case the deformations may be either cryogenic orconvective in origin.
The pit-like depressions described above are obviouslyrelated to this CH. They have no evidence of linear watererosion but the Kamenka paleosol and probably Romnypaleosol material was involved into these deformationslocally. Zelikson (Laboratory of Evolutionary Geography,Institute of Geography, Russian Academy of Science,Moscow, Russia) studied pollen and spores in the samplescollected from one of the structures at the Gololobovo-5-97trench situated 140m north of the G4 section (Velichko etal., 2000a). It appeared that only samples taken from lowerpart of the pit contained pollen. As no indicative taxa weredetermined, it appeared impossible to date the deposits.The environments, however, could be diagnosed withconfidence. Characteristics of the flora are boreal taxa,widely distributed. Taking into consideration the totalcomposition of the flora, the presence of Ephedra andAlnaster suggests the spectra being formed within a glacialepoch, probably at the very beginning of an interstadial.The latter suggestion is substantiated by the fact that theuppermost sample in the sequence features greater amountof arboreal taxa (including Abies) than the lower samplesattributable to earlier phases. Therefore, it is not incon-ceivable that the small pit-like landforms were formedduring the Romny soil formation epoch.
Generally it is likely that after the Kamenka andpresumably Romny paleosols had been fully developed,the deformations of this horizon were filled with material
derived from these soils. It was probably followed bycryoturbation of water-saturated groundmass. This CHcould be correlated to the beginning of Dnieper glacialepoch based on its stratigraphic position.The oldest of the Middle Pleistocene CHs is related to
the top of the Inzhavino paleosol, recently named theStupino CH (Velichko, 1999). Similar to the Smolensk CH,two phases of deformations are separated at this level. Theyounger (phase ‘‘a’’) deformations cracked Ae and Bthorizons of the Inzhavino paleosol. As seen in the trenchGololobovo-7-97 that situated 50m north of the G4 one,there is a band of rusty-brown ferrugination 1–2 cm thickin the Ae horizon. Below this band, there are numerousearth veins. They are sub-vertically oriented and filledmostly with material derived from Ae horizon. Thesefissures are 0.5–1.0m apart, 5–10 cm wide at the top, and0.7–1.4m deep. Probably the Ah horizon was very thin andweak that time, because no humus-rich material fills in thefissures. This generation of small fissures indicate severecontinental climate with strong seasonal gradients oftemperature and ground moisture. Above the ferruginatedband, the Ae and Ah horizons of the Inzhavino soil areinvolved into complicated involutions of solifluction origin.They are deformations of the phase ‘‘b’’ of the Stupino CH.These deformations indicate permafrost conditions andseasonal thawed layer at the paleosurface of Ah horizon.Therefore paleocryogenic data supports a polygeneticorigin of the Inzhavino paleosol.The CH of Early Pleistocene age was described at the top
of loamy skeletal till exposed at bottom of the Gololobovoclay pit. This till could be either Oka or Don on the basis ofits stratigraphic position. Both large plastic deformationsand pseudomorphs over ice wedges are preserved at thislevel, indicating that permafrost conditions were developedon this territory even in the Lower Pleistocene.
5.2.4. Paleomagnetic studies
Magnetic susceptibility was studied over the whole LatePleistocene sequence (Fig. 5). The characteristics weremeasured directly in the field using a KT-5 device andpartly also in laboratory by a KLY device, and the resultsthus obtained appear to be in reasonable agreement.Magnetic susceptibility measured in G-1-96 (Gololobovo
section) ranges from 202� 106 to 629� 106 SI-units (Fig. 7a).The Mezin soil complex exposed at the base of the section isdistinct for its higher magnetic susceptibility values—up to629� 106 SI-units.The Dnieper horizon exposed in G-3-96 is loess-like
loam (sandy loam) in the upper part and more gleyed loam(clay) in the lower part. The magnetic susceptibility variesaccordingly. In the upper part of the horizon (to a depth of1.6m) the susceptibility ranges from 271 to 369� 106 SI-units, while in the lower gleyed part it amounts to152–240� 106 SI-units (Fig. 7b).The magnetic susceptibility of the lower part of the
Dnieper loams (clays) and pre-Dnieper paleosols wasmeasured in G-4-96 section. The upper part of the exposed
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sequence features rather low susceptibility values—115–201� 106 SI-units. At a level of A2Bt horizon of theUpper Kamenka soil the magnetic susceptibility steeplyrises and reaches 643� 106 SI-units in the upper part of Bthorizon; from that level downward it decreases graduallyto 380� 106 SI-units. Still lower, at the base of the UpperKamenka soil, there is a second peak of magneticsusceptibility—up to 732� 106 SI-units. Downwards thesusceptibility decreases gradually through A1 horizon ofthe Lower Kamenka soil, reaches its minimum (189� 106
SI-units) in the sandy loam of the A2 horizon, and rises to350� 106 SI-units in the upper part of Bt horizon at thebase of the exposure.
Six oriented samples were collected from the exposure in1996: base of A2Bt horizon (1 micro-level) and Bt horizon(4 micro-levels) of the Upper Kamenka soil, and A1horizon of the Lower Kamenka soil (1 micro-level). A totalof 18 cube-shaped samples (with 20mm edge) have beenstudied. Demagnetization at temperatures 150–400 1C (by50 1C steps) produced slight changes (not more than 5–71)in the orientation of magnetization, suggesting directmagnetization of the interval. No noticeable deviationfrom the recent magnetic field orientation was recorded.The samples show considerable viscous magnetization(60–81% of In). To determine the minerals responsiblefor natural remanent magnetization, saturation curveswere taken in the magnetic field up to 10 kOe. The mineralprimarily responsible for magnetic characteristics of thedeposits is fine-grained magnetite. Fine-grained magnetiteis present in much smaller quantities.
6. Discussion
A comparison of recent multi-approach data withprevious stratigraphic, paleopedological and paleocryo-genic data for the East European Plain southward of theOka River Basin under consideration has produced somenew results.
Thick loesses cover interfluve plateaus and river terracesalong the Don and Dnieper river basins south of the regionunder study. Upper-Middle Pleistocene loesses and paleo-sols are common on interfluves south of the study regionand could be correlated along the central part of the EastEuropean Plain. The Upper Pleistocene as well asMiddle and Lower Pleistocene sediments attributed withseveral horizons of cryogenic phenomena there. Howeverthese CHs leave sola recognizable, and evidence of soilerosion is relatively rare on interfluve plateaus (Velichko,1999). Unlike the southern areas, loess has intermittentdistribution near its northern limits, as was shown for theOka River Basin. The Upper Pleistocene loesses andpaleosols are common along opolye areas but the MiddlePleistocene loess/paleosol series occurs in the Oka RiverValley (Velichko et al., 1996b; Dlusskii, 1997). Incomparison with southern sections, all loesses are morealtered by soil formation because of lesser thicknesses. Insome cases their structure, colour and even texture were
eventually changed during past warm epochs. However,even in these cases the loess sediments retain relatively highcontents of coarse silt (10–50 mm) and have almost nocoarse sand. They still cover interfluves as a mantle buthave abundant evidence of translocation and erosion. Itsstratification as well as gleyic properties are arguments torecognize them as secondary loesses in some cases. Anotherunique feature of the northern loesses, with the exceptionof Late Dnieper loess, is a lack of carbonates. Pedogenicleaching during warm epochs alternating with sufficienthumidity during cold epochs could be assumed as a causeof this effect.Strong eluvial differentiation of interglacial paleosol sola
provides a basis for reconstruction of individual stages ofinterfluve soil formation. The most mature humus proper-ties are typical of paleosols attributed to the Krutitsa, lateKamenka and late Inzhavino. Interstadial Bryansk andRomny paleosols feature immature humus properties, withprevalence of fulvoacids. Similar features of humuscomposition in the Late and Middle Pleistocene soils werenoted in other sections on the East European Plain(Bolikhovskaya et al., 1976; Morozova, 1981; Glushanko-va, 1994, 1998; Dlusskii et al., 1997). All interglacial soilsnear the northern limits of loess area have texturedifferentiation and lessivage evidence. Some of them havealbic horizons and feature strong eluviation. The albichorizon is not pronounced morphologically in the inter-glacial Early Kamenka paleosol or modern soil (greyicluvisol). These soils feature mostly lessivage properties andare attributed to the transitional soil zone from the luvisolto the chernozem area.Up to nine horizons of paleocryogenic phenomena and
some cryogenic features of interstadial paleosols provideinformation for cold stage environment reconstructionalong the periglacial region. Features vary from seasonalsmall-polygon cracking to huge ice wedges and displayingvariable water and moisture gradients. The permafrostconditions in the region were as severe as on the present-day Arctic Ocean coast at least three times during Late andMiddle Pleistocene. Low-temperature continuous perma-frost conditions were reconstructed for these intervals.Some of the CHs are evidence of sufficient or even excessmoisture during cold intervals on this territory. Theysupplement data obtained by features of loess horizon andindicate the peculiarity of this region versus the typicalloess area southward.Although excess moisture conditions during several
intervals interglacial paleosols and present-day soils havehigher MS in comparison with most of the loesses, themaxima of MS are attributed to Bt horizons of the soils,which is probably linked to iron components illuviation. Inthe southern part of the East European Plain the highestvalues are attached to humus-rich surface horizons ofpaleosols (Tsatskin et al., 1998). Interglacial paleosolsgenerally have as low MS as loesses, as both are gleyed.Therefore, near the northern limits of the loess area somedifferences occur in comparison with both Chinese and
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Alaskan (and Siberian) types of MS trends (Evans andHeller, 2003).
Cumulatively, all of these features make a strongargument to consider the Oka River basin and probablythe whole northernmost part of the continuous loess areaas a peculiar region. During all of the warm epochs as wellas cold intervals, moisture conditions of a more or lesscontinental climate affected the loess/paleosol formation.Even the present-day climate is moderately continentalhere. Quaternary cryomorphic processes made strongchanges in original features of loesses and paleosols. Thusnot only loess and paleosol but loess/paleosol/cryogenicformation was developed near the northern limits ofEuropean loess area.
7. Conclusions
The studies performed on the Bogolyubovo and Golo-lobovo sections permit the following conclusions aboutspecific features of the loess/paleosol/cryogenic series at thenorthern limits of its occurrence:
1.
Although common, loess deposits are found in theregion as an intermittent system. Unlike their southernanalogues, the loess horizons feature distinct layering,reduced content of carbonates and lesser porosity. Atthe same time, their occurrence as a mantle and arelatively high content of the typical ‘‘loessial’’ fraction(10–50 mm) as well as the presence of fossil soils andpaleocryogenic horizons in the sequence suggest a singleloess formation.
2.
Morphological and geochemical characteristics of theinterglacial fossil soils indicate argillic properties be-longing to the subboreal soil-climatic belt up to theboreal belt boundary. Interstadial fossil soils areregosols in this area and usually feature cumulic andgleyic properties.
3.
Most of the paleocryogenic deformations show distinctevidence of low-temperature continuous permafrost.
4.
The paleomagnetic studies performed on the loess/paleosol series near the northern limit of its occurrencerevealed high values of MS in Bt horizons of interglacialpaleosols and much lower values both in loess horizonsand in gleyed interstadial paleosols.
5.
There are strong arguments to consider the northernpart of the East European loess area as a specific loessregion distinguished by strong influence of cryomorphicand hydromorphic processes on the composition andstructure of loess formation.
Acknowledgements
We thank our colleagues from the Institute of Geogra-phy (Russian Academy of Sciences, Moscow, Russia) forcontribution with palynological (Dr. EM Zelikson),mineralogical (Dr. TA Khalcheva) and organic matter
(Dr. OA Chichagova) analyses and also S. Balzer (Uni-versity of Alberta) for assistance with the manuscriptpreparation and helpful comments. This study was partlyfunded by the Natural Sciences and Engineering ResearchCouncil of Canada (Grant to NW Rutter) and the RussianFoundation for Basic Researches (Grants # 01-05-64566,01-04-49303, 04-05-64599 and 01-05-64568) and NSH-1851.2003.5.
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