This investigation was funded by a CNRS-UAS exchange program. This is LDEO-7203 contribution.

1 - Introduction

1The Kyiv region of eolian deposition is located at the northern boundary of the Ukrainian loess domain (fig.1). Because of its geographical position, the Kyiv loess region links both the glaciated northern and unglaciated southern stratigraphies. Furthermore, located in the central part of the Eurasian loess belt, the region is also important for correlation with Western and Eastern European loess stratigraphies (Rousseau et al., 2001). The Upper Pleistocene sequence in Kyiv loess series is well exposed, thick (up to 22 m) and yields a detailed stratigraphy.

2According to the Ukrainian Pleistocene stratigraphy (Veklitch, 1993), eight units are determined between the Dnieper unit and the Holocene (tab. 1). The till of Dnieper glaciation spreads all over this territory and yields then a reliable stratigraphical marker. The Dnieper glaciation has been correlated with the Saalian glaciation (Gozhik, 1995; Veklitch, 1968).

3The Upper Pleistocene of the Kyiv loess region is clearly divided into two major sequences (fig. 2 & 3). The lower sequence consists of fully developed soils of a temperate climate intercalated with thin loesses if any (the Kaydaky-Pryluky units). The upper sequence consists of the Uday - Prychenomorsky loess units with weakly developed embedded Vytachiv and Dofinivka soils. The boundary between these two sequences is distinct and often sharp. Pollen data from the forest soils of the Kaydaky unit represent the typical succession of the vegetation of the Mikulino (Eemian) interglacial (Gerasimenko, 1988a, 2006). Recent aminostratigraphic studies of the Dnieper loams overlying the till showed that they have been deposited during marine isotopic stage (MIS) 6 (Oches et al., 2000). The PrylukyKaydaky pedocomplex overlying the till has been dated from 150,000 to 100,000 years BP, and the TL age of the Uday loess has been estimated at about 70-58 Kyr (Shelkoplyas et al., 1986). Pedological succession of the Pryluky-Kaydaky pedocomplex is similar to that of PKIII and PKII in Central Europe. Based on these evidences, the Pryluky-Kaydaky pedocomplex, with thin loess intercalated between individual soils, is believed to correspond to MIS 5, whereas the Uday loess to MIS 4 (Rousseau et al., 2001). Thus, the upper five units of the Ukrainian stratigraphical framework (tab. 1) represent the last Pleniglacial.

4In another correlation of Ukrainian and Central Europe stratigraphies, the Pryluky unit is compared with MIS 5, but the overlying part of the sequence also corresponds to the Pleniglacal (Lindner et al., 2002). The latter is supported with TL dates younger than 28 Kyr for the Bug loess unit, and 44-35 Kyr for the Vytachiv soil unit (Shelkoplyas et al., 1986).

5The Pleistocene of the Kyiv loess region has been extensively studied (Veklitch, 1968; Veklitch et al., 1984; Sirenko & Turlo, 1986; Gerasimenko, 1988a,b; 2001, 2006). However, data presented in this paper enable us to propose a more detailed stratigraphy and to present a higher resolution dynamics of paleoenvironments for the last Pleniglacial of the studied region.

2 - Materials and methods

6Paleopedological, palynological and malacological investigations have been performed in order to reconstruct paleoenvironments of the last Pleniglacial in the Kyiv loess plain. Twenty-three loess-soil sequences have been described and correlated based on lithology and pedology (fig. 1 & 4). A particular attention was devoted to particles <0.001 mm as in paleopedology, they are most important because they participate in translocation processes in soils and indicate forest pedogenesis.

7Paleopedological investigation was performed according to Veklitch et al., (1979). A soil complex comprises soils of the initial, optimal and final phases of pedogenesis. These soils are marked from the bottom up by indices “a”, “b” and “c”. Soils of the soil forming maximum (“b”) are usually strongly expressed. They are interpreted as corresponding to the relative climatic optimum. Soils of initial and final phases (“a” and “c”) indicate a cooler climate, at the transition to a cold unit. Reconstruction of soil types is based on soil morphological study and on applied analytical methods (grainsize and bulk chemical analyses, humus and carbonate content). Content of clay fraction, content of iron and aluminum sesquioxides (R₂O₃) and SiO₂:R₂O₃ molecular ratios are interpreted as indices of soil weathering intensity. Factors of fossilization are examined (e.g. gleyification, carbonate impregnation) to reveal a primary genetic type of a paleosol. The loess units are also subjected to physical-chemical study to recognize their paleoenvironmental characteristics.

8The pollen samples processing involve treatment with HCl, Na₄P₂0₇, HF, KOH and separation in heavy liquid (KdI₂ +KI) with specific gravity 2.2. In the pollen diagram of the Stari Bezradychy section, a number of pollen grains counted per sample is between 100 and 400. Some non-arboreal taxa are combined into groups: xerophytes (Artemisia, Ephedra, and Chenopodiaceae), hydrophytes (water plants: Typhaceae, Sparganiaceae, Alismataceae, Potamogetonaceae) and Herbetum mixtum (all herbs, with exception of xerophytes). Thus Herbetum mixtum includes mainly mesophytic herbs. The transfer functions of vegetation and pollen spectra based on surface samples (Arap, 1976; Dinesman, 1977; Grichuk & Zaklinskaya, 1948) are used in the interpretation of pollen diagrams.

9The combination of palynological and paleopedological approaches allows to consider the relationship between pollen spectra formation and pedogenesis, and between sedimentation and pedogenesis. Together with mollusk data, it strongly improves reliability of paleoenvironmental reconstructions.

10Sediment was sampled for mollusk analysis. 5 kgs of sediment were taken and washed on a 0.5 mm mesh sieve. The shells (entire or broken) were picked up and identified, if possible, at the species level, then counted. For broken shells, the number of fragments was captured as entire individuals by following Puisségur’s (1976) or Lozek’s (1964) rules. The identification of the shells at the species level allows then to use their present ecological characteristics in order to better characterize past environments from sediments where they quite often correspond to the main paleoindicator (Rousseau, 1989; Rousseau et al., 1990; Moine, 2008).

3 - Results

3.1 - The Uday (ud) loess unit

11The Uday (ud) loess unit lies at the base of the interval studied. It is represented by rather thin loess - 0.2-0.7 m, up to 1.1-2.5 m in depressions (fig. 3b, c, e). The characteristic feature of the Uday loess is a higher content of clay fractions <0.001 mm and especially <0.01 mm (39.8-49.9%) than in the other loess units (18.8-36.2%). Fine silt is about 11.9-26.5% (2.4-11.8% in the other loess), whereas silt (0.01-0.05 mm) is about 40.9-42.4%. In connection with a high clay content, SiO₂:R₂O₃ ratio is narrow - 9.92-11.16 (commonly in loesses - 13.50 -17.12). The content of CaCO₃ is very high (up to 23%), whereas of humus very low (less than 0.5%).

12Pollen from the Uday loess has been studied in two sections of the Kyiv loess plain: Stayky (Veklitch et al., 1984) and St. Bezradychy (Gerasimenko, 2001) (fig.7). The first one represents the deposits of an old plateau, whereas the second one – the deposits of a paleodepression. All pollen spectra are dominated by non-arboreal pollen (NAP). Chenopodiaceae, Artemisia and Poaceae prevail on plateau, whereas in depressions, pollen of more mesophytic Herbetum mixtum dominates. Though, due to the presence of Herbetum mixtum, even in a plateau locality, the NAP content of the Uday loess is more diverse than in the other loess units. Pinus, Betula and few Alnus represented arboreal pollen (AP). Pollen of arctic-boreal plants Betula sect. Nanae and Fruticosae appear in deposits of the paleodepression.

13Several generations of crack structures and astructural cryoturbations are connected with the Uday unit and deform the underlying Pryluky soils. The primary ground veins filled with humic material are up to 1.5 m long, and disturb the lower boundary of the Pryluky chernozems. The thin separate fissures filled with loess material dissect the upper boundary of the chernozems. Some of them are also 1.5 m in length. An intricate network of thin fissures is observed, if excavations expose the soil surface. Some of crack structures are twofold (filled both with humic and loess material), which is usually regarded as an expression of frost action. In depressions, in a subsoil of the chernozems, thin horizontal humic streaks are observed. It is presently believed that humus acids penetrated through cracks and formed streaks in the overmoistured layer above frozen substrata. On paleoslopes, the ground veins are bended, obviously due to the later solifluction processes. No mollusk shells have been identified in our samples.

3.2 - The Vytachiv (vt) soil unit

14The Vytachiv (vt) soil unit is mainly represented by a polygenetic soil (0.5-0.7m thick), described as a brownlike one (Veklitch et al., 1984; Sirenko & Turlo, 1986). Nevertheless, in sections of paleodepressions, the pedocomplexes of Vytachiv unit are observed (fig. 2e,m, 3ab, d-e, 4a-c). The complete Vytachiv pedocomplex includes three paleosols “vt_1b1”, “vt_1b2”, “vt_3b”, separated by thin loess layers, and a weakly developed soil “vt_3c”. The Vytachiv soils are not characterized by thick and well-developed profiles typical for interglacial soils of the temperate climatic belt. The lower “vt_1b1” and “vt_1b2” soils are similar, brown-colored, with prismatic structure, the “vt_1b1” soil with strong signs of gleying and sometimes pseudogleying. Both are rich in clay (28-34%) and R₂0₃ (13-15%), leached of carbonates, which form expressive whitish C_Ca horizons in subsoils (fig. 5b & 6a). The “vt_1b1” soil is characterized by some biogenic accumulation of CaO and humus (0.6%). The great abundance of small iron-manganese concretions caused by gley processes is very typical. The “vt_b2” soils are less humic and more decalcified, signs of eluvial-illuvial processes (initial downward clay translocation) can be observed. All above allows suggesting that the lower Vytachiv soils are a kind of brown forest soils (Cambisols) developed in a boreal climate on carbonate rich substrata.

15Both “vt_1b1” and “vt_1b2” soils are characterized by the highest content of AP for the Pleniglacial deposits (fig.7). AP is sharply dominated by Pinus, especially in “vt_1b1” soil. Only few pollen grains of Picea, Betula and broad-leaved taxa were found at this interval. In the “vt_1b2” soil, broad-leaved taxa are more abundant, though their amount is still less than in the interglacial forest soils of the Pryluky and Kaydaky units, and less than in the Holocene forest soils of the region (Gerasimenko, 1988a, b). Soils of depressions contain more pollen of broad-leaved trees than those on the plateau (Veklitch et al., 1984). NAP is dominated by Herbetum mixtum, and spores are prominent in the “vt_1b2” soil.

16The “vt_3b” soils have a darker grayish color and a higher humus content (0.7-1.1%) than the lower Vytachiv soils (fig. 5b & 6a, b). The soils are rich both in CaO and R₂O₃, as well as in clay particles. Carbonates are not leached from soil profiles, though in depressions, leached soil varieties are also observed (fig. 5b & 3b) as well as the soils with signs of initial illuvial processes (fig. 5b & 6a). Multiple krotovinas indicate a considerable biologic activity, typical for soils of open landscapes. The “vt_3b” soils evidently belong to a loessic rendzina soil type (Mollic Cambisol). Present rendzinas are formed on carbonate substrata under relatively continental climatic conditions. With an increase of moisture, they would evolve into brown forest soils (Duchaufour, 1970).

17Pollen content of the “vt_3b” soil is dominated by NAP, and mainly by Herbetum mixtum (fig. 7). The broadleaved taxa are very rare and presented only by Tilia.

18The final stage of soil formation “vt_3c” is represented by a thin (0.2-0.3 m) incipient soil of light-brown color (fig. 2e, 3a & 4a, c). The soil profile is not differentiated into horizons, only whitish C_Ca horizon is observed in subsoil. The contents of humus, clay and R₂0₃ are lowermost in the Vytachiv pedocomplex (fig. 6b). Pollen spectra of the “vt_3c” soil are similar to those of the “vt_b3” soil and dominated by NAP, with a high share of Herbetum mixtum, especially Asteraceae (fig. 7). Pinus prevails in AP, very few pollen grains of broad-leaved taxa still occur, though pollen of cold-resistant Betula sect. Nanae and Fruticosae appear.

19The loess layers between “vt_1b1”, “vt_1b2” and “vt_3b” soils (fig. 2m, 3b, 4a, b, 5b & 6a) are characterized by a low humus content and high carbonate content (about 13%). They are as rich in clay and R₂0₃, as the Vytachiv soils, and less rich in silt content than typical loess. It is obviously controlled by a partial reworking of thin loess layers with the following pedogenic processes. Pollen contents of intra-Vytachiv loess differ from those of the soils (fig. 7). NAP dominated, and Poaceae are more abundant than Herbetum mixtum, especially in the “vt₂” loess. AP is represented only by boreal taxa: Pinus and Betula. Arctic-boreal species of Betula sect. Nanae et Fruticosae occur in the “vt₂” loess, whereas few Picea in the “vt_1b1-2” loess. The thin separate ground veins dissect the boundaries of the “vt_1b2” soil.

3.3 - The Bug (bg) unit

20The Bug (bg) unit is the most thick loess bed in the Pleistocene series of the Kyiv region, continuously distributed throughout this area. The mean thickness of the Bug loess is about 5m, in places up to 18 m. In the Quaternary sequence of the region, the Bug loess is characterized by the highest silt content, especially in the upper loess beds. The lower sub-unit of loess “bg₁” is a bit darker than the upper one, somewhat richer in humus, clay and R₂0₃ (up to 12.42%). SiO₂:R₂0₃ ratios are 13.44-15.33, whereas in the upper Bug sub-unit “bg₂” they are 17.2-17.5 (fig. 5a, b & 6a, b). Presence of 1-6 incipient soils within the “bg₁” sub-unit is the other characteristic feature (fig. 2d, k, l, 3f & 4a-c). Soils are thin (0.1-0.3 m), somewhat darker and more brownish than loess, with C_Ca horizons in subsoil and signs of slight gleying above their upper limits. They have lower content of carbonates than loess and somewhat higher contents of humus and clay, but not of R₂O₃ (fig. 5b & 6b).

21Pollen contents of the “bg₁” and “bg₂” sub-units are different, as well as of the “bg₁” loess and embedded embryonic soils (fig. 7). In the “bg₁” loess, Poaceae dominates NAP, whereas Herbetum mixtum is second in abundance. Cyperaceae is noticeable in the lower part of the sub-unit. In the sections of plateau (Veklitch et al., 1984), counts of Chenopodiaceae and Artemisia are higher. Pinus prevails in AP, though Betula, Alnus and Salix are also frequent. Pollen of arctic-boreal plants Alnaster and Betula are more abundant than pollen of arboreal forms of Alnus and Betula. A proportion of arctic-boreal plants increase to the upper part of the “bg₁” sub-unit, whereas a share of mesophytic Herbetum mixtum decrease, and Cyperaceae disappear. Pollen spectra of embryonic soils are richer in Herbetum mixtum than in Poaceae. The AP content is higher than in loess, pollen of arboreal forms of Betula dominated over pollen of its shrub forms. The incipient soil bg_1e4 (fig. 7) has the highest AP and Herbetum mixtum contents, few Picea appear and ferns are abundant. In the “bg₂” sub-unit, pollen of Poaceae decreases, while Artemisia, Chenopodiaceae and Asteraceae increase in number. Betula sect. Nanae et Fruticosae become more abundant, whereas Alnus, Salix and Picea disappear.

22Cryodeformations, connected with the Bug unit, are observed along the limits of the upper Vytachiv soil. They are ground cracks (‘pots‘) with almost the same width as length, and form polygonal structures. The separate thin ground fissures are also abundant.

23Mollusk data from the “bg₁” loess sub-unit are very few and correspond to the classical poor terrestrial assemblage of steppe fauna composed of Pupilla species (muscorum, alpicola, loessica and sterri) associated with Vallonia tenuilabris and Succinea oblonga. The mollusk species of the incipient soils have been identified in Grebeni site and also indicate a very spare environment with very few species. The species diversity is similar to that observed in “bg₁” loess sub-unit. Nevertheless, the assemblage is strongly dominated by Succinea oblonga and Vallonia tenuilabris, which characterized moister environments than in “bg₁” loess.

24The mollusk assemblage in the “bg₂” sub-unit is also similar to “bg₁”. The assemblage observed in Grebeni locality, indicates colder conditions of a tundra-like environment, with the typical Columella columella community including C. columella, Vallonia tenuilabris, Pupilla muscorum, P. loessica, P. alpicola, and Trichia hispida.

3.4 - The Dofinivka (df) soil unit

25The Dofinivka (df) soil unit is not of frequent occurrence in the Kyiv loess region. It can be mainly observed in the sections of young slopes and is represented by weakly developed soils of small thickness (0.4-0.8 m). In depressions, they have brown-colored soil profiles, not differentiated into genetic horizons, with the exception of C_Ca in subsoil (fig. 2k & 3d-i). The soils are leached, slightly enriched in clay and R₂0₃ as compared to their loess substrata, have low humus content and some biogenic accumulation of CaO in the upper part of profiles (Gerasimenko, 1988c). The soils of depressions are similar to a brown rendzina type. Upwards the slope, they are replaced by thin chernozem-like soils (fig. 3jm). These soils are grey-colored but much less developed than typical chernozems, poor in humus (less than 0.6%) and rich in CaCO₃ (up to 9%), with high position of carbonate horizon in the soil profile. Accumulation of clay and R₂0₃ is not characteristic (fig. 5a).

26Pollen contents of the brown rendzinas and chernozem-like soils are different. In the latter, AP, Pinus, Poaceae and spores counts are lowermost in the Quaternary pollen record of the region (fig. 7), whereas Artemisia count is the highest one, and Chenopodiaceae pollen becomes also prominent. NAP content of brown rendzinas is dominated by Herbetum mixtum, though Artemisia pollen percentages are also higher than in the other Upper Pleistocene units (Gerasimenko, 1988b). A characteristic feature of both Dofinivka soil types is the prevalence of Betula in AP. Arboreal Betula sect. Costatae dominates, but some pollen of Betula sect. Nanae and Fruticosae also occur, and in brown rendzina soils, few Salix, Alnus and Corylus are present.

3.5- The Prychernomorsky loess unit (pc)

27The Prychernomorsky loess unit (pc) is often not separated from the Bug loess unit, as the Dofinivka soil occur rarely. Otherwise, Prychernomorsky unit appears below the Holocene soil as a thin loess layer - 0.2-1.0 m, up to 1.5 m (fig. 2k & 3d-m), rather similar by its physicalchemical characteristics to the Bug loess (fig. 5a). The Prychernomorsky loess often includes more sand fraction (up to sandy loams) than the Bug loess. In pollen content of the loess, AP count is very low, only 4% in places (Gerasimenko, 1988a, b). Pollen of Betula sect. Nanae and Fruticosae are an important component of AP (fig. 7). NAP is strongly dominated by Artemisia, though second place in abundance belongs to Herbetum mixtum: Rosaceae (mainly Potentilla type), Asteraceae, Caryophyllaceae. Pollen percentages of Poaceae, Cyperaceae and spores contents are very low. At the present, pollen spectra dominated by Asteraceae (especially Artemisia) and Caryophyllaceae, with arboreal pollen (<25%) presented by shrub Betula, Alnaster and Salix, are typical for the cold steppes of the Central Yakutia (Tomskaya, 1979).

28No mollusk species has been identified from the Prychernomorsky unit.

4 - Paleoenvironmental interpretation

29During the Uday interval of loess deposition, a cold and continental climate existed, recorded by cryoturbations and appearance of arctic-boreal plants. The area of Kyiv plain has been covered by sparse steppe vegetation. Few trees, represented only by boreal taxa (pine, birch and alder) could survive on southern slopes, whereas dwarf birch grew in wet depressions, together with rather abundant Herbetum mixtum. The steppes on plateau were dominated by xerophytic, nevertheless, the proportion of mesophytic herbs was still noticeable. Obviously the climate of the Uday stage was less arid than during the other intervals of loess deposition. It also fits well with lithological characteristics of the Uday unit. The grain-size content and mean thickness of the Uday loess show that the conditions for silt transportation and accumulation were not as favorable, as during the other loess units. Some enrichment of Uday deposits in clay and R₂0₃ may also indicate a wetter climate. During the Uday stage, typical development of astructural cryoturbations could occur only under significant ground moisture supply. At the same time, thin fissures, observed in the second generation of Uday cryoturbations, are presently described in arid regions, with small amount of snow in winter. This allows suggesting that the cold and wet climate at the beginning of the Uday unit was later changed into cold and arid.

30The Vytachiv soil unit shows evidences of contrast environmental changes during its formation. By the pedological and pollen characteristics, the soils of the Vytachiv complex were formed in a cooler climate than the modern one of the region and represent interstadial conditions. The lower soils of the complex (“vt_1b1” and “vt_1b2”) are similar to boreal brown forest ones (Cambisols). The “vt_1b1” soils were formed under periodical income of excessive moisture, which alternated by rather arid conditions. They are frequently gley and pseudogley varieties. The “vt_1b2” soils were formed under permanent sufficient but not excessive precipitation. The vegetation on both soils was dominated by light pine forest (or forest-steppe) with rare spruce, birch and alder, and with rich mesophytic herb cover. Few broadleaved taxa (Quercus, Ulmus, Tilia and Carpinus) grew in refugia provided by gullies and valleys of the dissected loess plain. Judging from the proportion of broad-leaved taxa, the “vt_1b2” soil represents the warmest interval of the Vytachiv unit. During the formation of the “vt_3b” soil, humus and carbonate accumulation, as well as intensive pedofaunal activity, indicate a decrease in precipitation, as compared to the earlier phases of Vytachiv complex formation. Carbonate leaching and clay translocation occurred only in the soils of depressions. An increase in climatic continentality is confirmed by pollen data: mesophytic meadow steppes covered the studied area, the woods grew only in gullies, and broad-leaved species (with exception of Tilia) disappeared. Presently Tilia cordata L. goes farther to the east, into more continental climatic regions, than the other broad-leaved taxa.

31The climate of the final stage of Vytachiv soil formation “vt_3c” was not drier than that of the “vt_3b” phase (Herbetum mixtum peaks in “vt_3c”). Nevertheless, the appearance of dwarf birches shows that it possibly was colder. During the “vt_c” stage, either the conditions for soil formation were unfavorable or the duration was very short. The intra-Vytachiv loess deposition occurred in open landscapes. Steppe coenoses were less mesophytic than during the phases of Vytachiv soil formation and even drier than during the Uday stage. This feature, as well as the disappearance of broad-leaved species, indicates continental and cold climate, particularly for the sub-unit “vt₂”. Dwarf birch grew then, and frost desiccation of underlying soils took place. The size and positioning of the ground fissures point to a small amount of snow in winter.

32Thus, the Vytachiv time interval consists of three interstadials alternated with two stadials. The climate was cool and wet at the first interstadial “vt_1b1”, warmer at the second interstadial “vt_1b2”, and more arid at the last one, getting rather cold at its end. The “vt_3c” sub-unit represents an interstadial-stadial transition. The climate of the intra-Vytachiv stadials was cool and dry for the first one (“vt_1b1-2”) and colder and more continental for the second one (“vt₂”).

33The Bug loess unit corresponds to the stage of the most intense silt accumulation in the Kyiv loess region. Loess was deposited under periglacial steppe environment, with spread of arctic-boreal plants and development of cryoturbations. The cryoturbations typical for the Bug unit are regarded as a result of deep ground freezing under a cold continental climate (Velichko ed., 1973). At the beginning of the early Bug sub-unit “bg₁”, steppes, indicated also by the terrestrial mollusks of the Pupilla fauna, were dominated by mesophytic herbs including Ranunculaceae and Cyperaceae. The Poaceae coenoses prevailed during the rest of the sub-unit, and finally, at the “bg₂” sub-unit, Artemisia-Poaceae steppes spread. This succession shows a progressive increase in climatic continentality, a conclusion supported also by lithological data. Xerophytization of the vegetation cover to the end of the Upper Pleistocene stage of the strongest loess accumulation in the Upper Pleistocene has been also shown for the Russian plain (Bolikhovskaya, 1995; Grichuk, 1972). The arboreal vegetation of the “bg₂” sub-unit was less diverse than at the “bg₁” sub-unit, and arctic-boreal shrub birches were more frequent. The climate became not only drier but also colder to the end of the Bug unit, as it is also characterized by the occurrence of the Columella mollusk fauna.

34Short climatic fluctuations are recorded in the Bug incipient soils. They show an initial development of pedogenic processes, which started with the weakening of silt accretion. The leaching of carbonates points to a wetter climate than for the loess deposition. It is confirmed by predominance of mesophytic herbs in steppe coenoses during incipient soils formation and by some spread of arboreal vegetation, including moisturedemanding spruce. The incipient soil bg_1e4 was the wettest interval of the Bug unit, with meadow associations, rich in ferns. A strong reduction in arctic-boreal elements of vegetation in the incipient soils as compared to the loesses indicates a warmer climate during the soil formation. The incipient soil bg_1e2 was formed in boreal forest-steppe (even with few Corylus). This soil is richer in clay and R₂0₃ and more decalcified than the other Bug sub-units and represents the warmest interval of the Bug stage. The gleying, developed above the upper soil limits, indicates periodical excessive ground moisture, also evidenced by the terrestrial mollusk fauna dominated by the moisture-loving Succinea oblonga. It is possibly connected with re-establishment of a water-impenetrable frost layer at the end of a phase of incipient soil formation.

35By the pedological and pollen data, the climate of Dofinivka soil unit was extra-continental and rather cold. The Dofinivka humic soils were regarded as analogues of the most continental facies of chernozems, which presently occur in the East Siberian steppes (Veklitch et al., 1984; Sirenko & Turlo, 1986). In the Dofinivka soils, the humus content is lower and carbonate content is higher than in the Siberian chernozems. It allows the suggestion that they were formed under more continental climatic conditions. The Dofinivka brown rendzinas are similar to the present soils described in the Trans-Baikal region, under birch forest-steppe, with shrub birch and willow in the second layer of sparse woods and with mesophytic herb layer (Nogina, 1964). In the Dofinivka unit, such vegetation could exist only in the wetter depressions, whereas the plateaus were covered by dry Artemisia steppe. It was the most xeric vegetation pattern for the Pleniglacial in the Kyiv loess plain.

36During the Prychernomorsky loess deposition, the studied area was covered by treeless steppes with predominance of Artemisia. Herbs from Asteraceae, Caryophyllaceae and especially Rosaceae families were frequent, as they presently are in the Central Yakutian steppes, keeping together the unstable substrata (Tomskaya, 1979). The significant amount of sand particles in grain-size content of the Prychernomorsky loess also indicates to intensive erosion processes. Judging from Artemisia and Betula sect. Nanae and Fruticosae pollen percentages, the climate of Prychernomorsky stage was colder than during the Dofinivka stage, but probably less arid. The suggested environmental dynamics in the Kyiv loess plain during the Pleniglacial is shown in fig.8.

5 - Discussion

37The Pleniglacial in the Kyiv loess plain consists of three main loess units (the Uday, Bug and Prychenomorsky) separated by two soil units (the Vytachiv and Dofinivka). The Uday, Bug and Vytachiv are permanent components of the regional loess cover, whereas the Dofinivka and Prychernomorsky units can be mainly observed in the sections of depressions. Chronostratigraphy and correlations for the Pleniglacial units are based on their TL-ages (Shelkoplyas et al., 1986) and paleoenvironmental characteristics. The dates around 70 - 58 kyr B.P., yielded by the Uday loess, as well as its basal position in the Upper Pleistocene loess sequence, both permit to attribute the Uday unit to the Lower Pleniglacial (MIS 4). The Vytachiv pedocomplex have been TL-dated between 44 yr and 35 kyr B.P., and includes three interstadial soils. During the Pleniglacial, the weathering and pedogenic processes were the strongest just at the times of these soils development. It is proposed to attribute the Vytachiv unit to the Middle Pleniglacial (MIS 3). The TL-ages of the thickest Bug loess unit are younger than 28 kyr B.P, which allow its correlation with the Upper Pleniglacial (MIS 2), the major stage of loess deposition in Europe. Such a correlation of the Ukrainian units have been already suggested (Gerasimenko, 1999; Gozhik et al., 2001; Rousseau et al., 2001). The ¹⁴C ages of the Prychernomorsky loess 15 kyr, 17 kyr B.P., (Veklitch, 1993) show that this unit corresponds to the uppermost part of the Pleniglacial.

38The chronostratigraphical setting of the Dofinivka soil is not finally solved. In the Kyiv Dnieper region, the unit is underlying the Upper Paleolithic, ¹⁴C dated to 17 - 14 kyr B.P. In the stratotype area of Dofinivka unit near the Black Sea, its ¹⁴C ages are 17 - 15 kyr B.P. (Gozhik et al., 2001). In the Pleistocene Stratigraphical Framework of Ukraine (Veklitch, 1993), the Dofinivka unit is attributed to the Middle Pleniglacial, whereas the Vytachiv unit is regarded as the last interstadial of the Early Glacial, and the Bug unit as the Early Pleniglacial. It was based on the TL-dates around 60,000 yr for the Vytachiv unit, and around 70 - 50 kyr B.P. for the Bug unit. Nevertheless, ¹⁴C-ages for the Bug loess in the same Stratigraphical framework (Veklitch, 1993) are given as 14.4 - 10 kyr B.P. The recent dating of the Vytachiv unit showed 35.1 - 31.55 kyr B.P. by ¹⁴C, 44 - 29 kyr B.P. by ESR LU, and 48.3 - 32.1 kyr - by U/Th method (Gerasimenko, 1999; Chabai, 2005). Evidently the Vytachiv unit is a terrestrial equivalent of MIS 3, and the Dofinivka unit corresponds to warm climatic oscillations after the Last Glacial Maximum. This is also supported by the harsh environments of Dofinivka unit (fig. 8), more appropriate in the studied area for a climatic impulse of the Upper Pleniglacial than for Middle Pleniglacial interstadials.

39Comparison with western Upper Pleistocene sequences shows common features both in loess stratigraphies and environmental evolution in Ukraine and Western Europe. One of the most complete record of the Pleniglacial is presented in the Nussloch sequence, Upper Rhine area (Antoine et al., 2001, 2002; Hatté et al., 1998, 2001; Rousseau et al., 2002, 2007) which we use as a key section for the correlation. The boundary between the Early Glacial and Pleniglacial in both regions corresponds to disappearance of the humic soils and start of massive loess deposition – the Pryluky-Uday units boundary in Ukraine and the boundary between basal soil complex (Sequence I) and loess and eolian sands (Sequence II) in Nussloch. The sequence II, as well as the Uday loess, has been deposited in open environment of cold continental climate, with development of cryoturbations (including solifluctions). The data both from Ukraine and Rhine valley indicate relatively humid conditions, as compared to the other loess units. The increase of aridity to the end of the Lower Pleniglacial is suggested for both regions. The Nussloch sequence have been formed in a particular geomorphologic context, favoring eolian deposition, and so provides a higher resolution record of environmental dynamics than the sequences of the Kyiv loess plain, sheltered by the Dnieper Uplands. For instance, in the sections of the Dnieper valley, a weak incipient soil is found within the Uday unit, which probably might be correlated to the arctic brown soil of Sequence I (Lower Pleniglacial). Located in a broad wind-opened valley, the Nussloch section is marked by the significant sand contents in the Lower Pleniglacial deposits. Nevertheless, clay contents in the loess of this unit, as well as iron content, are still higher than in the Upper Pleniglacial ones (Sequence IV). It is also a particular characteristic of the Uday loess unit in the Kyiv plain. In western and eastern Europe the Lower Pleniglacial environments were not most favorable for coarse silt accumulation and for deposition of thick typical loess.

40In Ukraine, two loesses, separating the three Vytachiv soils, represent the Middle Pleniglacial, whereas in Rhine area, it is recorded in the Sequence III, consisting of two soils with organic deposits and loess in between. The Middle Pleniglacial cambisols of the Rhine valley, as well as rendzinas and boreal brown soils, described in the Kyiv loess plain, both indicate that the bioenergetic recourses of pedogenic processes did not favor the development of thick mature soils. Pollen contents both of the Vytachiv soils and the organic deposits in the Rhine area also show that the climate was cooler than temperate one, and interstadial conditions existed. The soils of Kyiv plain and the Rhine area are marked by the highest contents of clay, iron and C_org in the Pleniglacial sequence of the regions. Nevertheless Vytachiv soils are much richer in these components than cambisols at Nussloch, which can be related to much higher sedimentation rates in the wind-open Rhine valley. The permanent accretion of new sediment, including sand particles, hampered soil weathering, which, on the contrary, could develop in a low-dynamic depositional environment of the Kyiv loess plain.

41More accurate correlation of the Middle Pleniglacial subunits may be based on comparison of the Nussloch records with the recently dated Vytachiv sequence at the Kabazi II site, Crimea (Gerasimenko, 1999; Chabai, 2005). At Nussloch, the ¹⁴C ages of the Upper Cambisol and its subsoil are 34 - 31.1 kyr B.P., whereas for the subsoil of the upper Vytachiv soil “vt₃”, they are 35.1 - 31.55 kyr B.P. At Nussloch, an average age of the organic deposits, overlying the Lower Cambisol, is 32.23 kyr B.P., and for the layers, overlying the second Vytachiv soil “vt_1b2”, it is 32,800 yr B.P. Both these contemporaneous sub-units are very rich in Pinus pollen: 70% in the organic deposits of Nussloch and 76-89% in the Ukrainian section. The top layers of the Lower Cambisol have been dated to 42,100 yr B.P., whereas the second Vytachiv soil yielded 44 - 39 kyr BP. It is believed that the

42Lower Cambisol corresponds to Moershoofd and Hengelo, though does not record the cold Hasselo stage between them (Antoine et al., 2001). In Ukrainian sequences, the correlation of the middle soil “vt_1b2” with Hengelo and the lower soil “vt_1b1” with Moershoofd have been proposed (Gerasimenko, 1999, 2001), also based on TL-dates in 48 - 44 kyr B.P. for the Vytachiv unit (Shelkoplyas et al., 1986). The upper Middle Pleniglacial soil in both records is attributed to Denekamp.

43The western and eastern sequences reflect rather similar environments of the Middle Pleniglacial subunits. The Lower Cambisol and the lower Vytachiv soils (“vt₁”) indicate the increase of edaphic humidity. In particular, the redistribution of iron and manganese as concretions is very characteristic for both of them. Pollen in the Ukrainian sequences and snails in the Rhine valley point to forest-steppe environments. Both the Upper Cambisol and the upper Vytachiv soil (“vt₃”) are richer in organic matter and indicate more intensive biological activity than in the lower soils. Environments of the loess sub-units, preceding the upper soil units, were cold in both regions, but drier in the Kyiv loess plain.

44The Upper Pleniglacial in both regions is a major stage of loess deposition, and is marked by frequent short climatic fluctuations recorded in tundra-gleys in the Rhine Valley and in incipient soils in the Kyiv plain. The difference in the initial soils varieties shows a wetter climate, prevailing in the western regions. Nevertheless, the similar pedogenic processes are reflected in both types of soils. They are redistribution of carbonates to the base of the profile, reduction of iron, a slight enrichment in organic matter and increase of biological activity (even mole galeries are related to the lowermost incipient soil in the Kyiv loess plain). These latter soils are marked by enrichment in iron and clay in both depositional records. Terrestrial snails and pollen show predominance of open landscapes during the formation of incipient soils, but an abundance of snails associated to an increase in AP indicate some climatic improvement as compared to loess environments, at least in the Kyiv plain. In this region, the incipient soils in Kyiv loess plain are not cryoturbated that possibly shows less wet and cold climate than in the Rhine valley.

45The initial soils are related to the middle sub-unit of the Upper Pleniglacial in the Rhine area and to the lower and middle part of the Upper Pleniglacial in Ukraine. The upper part of the Pleniglacial in both regions reflects an arid climate of homogenous loess deposition. The second pulse of loess accumulation, limiting the wetter phase with tundra-gleys in Nussloch sequence, is dated 22 - 19 kyr B.P. No dates are available for the incipient soils in the Kyiv loess plain. Nevertheless, in the other areas of Middle Dnieper region, a weak soil ¹⁴C aged of about 21 kyr B.P. followed by homogenous loess deposition has been observed (Veklitch, 1993). Considering it is an equivalent of the upper incipient soil in Kyiv loess plain, the beginning of the arid Upper Bug sub-unit would be in correspondence with the Nussloch records.

46The equivalent of the Dofinivka soil is possibly the gelic gleysol overlying the loess with the Eltvilleer tuff dated 19.5 - 19 kyr BP. In the sections of the Dofinivka stratotype area (near the Black Sea), its age is ¹⁴C estimated between 19 and 15 kyr BP (Gozhik et al., 2001). The climate of the Kyiv plain was then considerably drier than in the Rhine area during the corresponding time span. According to the dates obtained, the Prychernomorsky loess in Kyiv loess plain corresponds to the last pulse of loess sedimentation recorded in the Nussloch section. Both units are not thick, are lithologically similar to the loess of the preceding loess deposition phase and directly underlie the Holocene soils.

6 - Conclusions

47The loess-paleosol sequences in the Kyiv loess plain, Ukraine, document a rather complex record of environmental changes during the Pleniglacial. The paleoenvironmental information derived from lithological, pedological, palynological and malacological studies is in general well correlated. The start of Pleniglacial in Ukraine corresponds to the boundary between the chernozem soils of the Early Glacial (the Pryluky unit) and the first thick loess deposition (the Uday unit). The Pleniglacial includes three main loess units separated by two soil units. The middle loess unit (Bug unit) corresponds to the most intensive loess deposition, and the lower soil unit (Vytachiv unit) shows the strongest development of pedogenic processes during the Pleniglacial. The loesses were formed in open environments dominated by steppe. Rather mesophytic steppe vegetation of the start of Pleniglacial (Uday unit) were changed to more xeric ones, dominated by Poaceae (Bug unit), and then to the most xeric associations, dominated by Artemisia (Prychernomorsky unit, the uppermost loess bed of the Pleniglacial). The significance of arcticboreal elements of vegetation also increased from the Uday to Prychernomorsky unit. The climate becomes more continental and harsh since the beginning up to the end of the Pleniglacial.

48The environments of paleosol formation were rather diverse and changed from forest-steppe, with small admixture of broad-leaved trees in the forests (“vt_1b1” and “vt_1b2” soils) to continental boreal forest-steppe (the lower Bug soils), and from mesophytic steppe (“vt_3b” and “vt_3c” soils) to xeric cold steppe (the Dofinivka soil). The paleosols in succession from the beginning to the end of Pleniglacial also show trend to increase of climatic continentality from the beginning to the end of the Pleniglacial.

49The chronological setting of the loess-soil units in Ukraine allows correlating the Uday loess with Early Pleniglacial, the Vytachiv soil unit with the Middle Pleniglacial, and the Bug - Prychenomorsky units with the Upper Pleniglacial. The sedimentary and environmental sequences in Kyiv loess plain provide similarities with western European loess-soil records, and particularly with the Nussloch high-resolution records. The correlation of the Nussloch Sequence II with the Uday loess, and Sequence IV with the Bug - Prychernomorsk units is proposed. The Dofinivka unit may be an equivalent of the gelic gleysol above the Eltviller tuff. The Vytachiv pedocomplex of three interstadial soils with intercalated loesses is well correlated with the Nussloch Sequence III, also including three interstadials. Three Vytachiv soils are subsequently related to Moershoofd, Hengelo and Denekamp interstadials of Western Europe.

50The Kyiv and Nussloch sedimentary sequences show the similar pattern in alternation of wet and dry phases during the Pleniglacial, including the development of incipient soils in the Upper Pleniglacial. Nevertheless, the sections of Kyiv loess plain generally reflect a drier climate than in the Rhine area. It is in agreement with more continental position of the Ukrainian loess domain. The Kyiv loess-paleosol sequences also indicate lower sedimentation rates than in the Rhine valley, especially for the Early and Middle Pleniglacial. The lower wind velocities, as well as abundant gullies, typical landforms of a loess plain and possible vegetation refugia, might provide a favorable background for preservation of some elements of broad-leaved flora in the Kyiv loess plain during the Middle Pleniglacial interstadials. The stronger development of pedogenic processes in the Vytachiv unit and in the Bug embryonic soils, as compared to their Nussloch equivalents, also might be related to the calmer depositional environment in the Kyiv Plain. A lower wind activity yields both a stabilization of surfaces and a milder climate, and both factors favorable for soil development. Parallel changes in the Pleniglacial environmental dynamics detected in western and eastern sedimentary sequences show that the recorded environmental events were related to a global climatic control.