Geological Quarterly, 2014, 58 (2): 235–250 DOI: http://dx.doi.org/10.7306/gq.1158 How to resolve Pleistocene stratigraphic problems by different methods? A case study from eastern Poland S³awomir TERPI£OWSKI1, *, Tomasz ZIELIÑSKI2, Jaros³aw KUSIAK1, Irena A. PIDEK1, Piotr CZUBLA3, Anna HRYNOWIECKA4, Anna GODLEWSKA1, Pawe³ ZIELIÑSKI1 and Marzena MA£EK5 1 Department of Geoecology and Palaeogeography, Maria Curie-Sk³odowska University, Kraœnicka 2c,d, 20-718 Lublin, Poland 2 Institute of Geology, Adam Mickiewicz University, Maków Polnych 16, 61-606 Poznañ, Poland 3 Laboratory of Geology, £ódŸ University, Narutowicza 88, 90-139 £ódŸ, Poland 4 Polish Geological Institute – National Research Institute, Marine Geology Branch, Koœcierska 5, 80-328 Gdañsk, Poland 5 Geological Enterprise POLGEOL S.A., Lublin Office, Budowlana 26, 20-469 Lublin, Poland Terpi³owski, S., Zieliñski, T., Kusiak, J., Pidek, I., A., Czubla, P., Hrynowiecka, A., Godlewska, A., Zieliñski, P., Ma³ek, M., 2014. How to resolve Pleistocene stratigraphic problems by different methods? A case study from eastern Poland. Geological Quarterly, 58 (2): 235–250, doi: 10.7306/gq.1158 Different methods have been used to determine the stratigraphic position of Pleistocene alluvial deposits, particularly fluvial interglacial deposits. Near-surface deposits of a meandering river, developed in point-bar and oxbow lake facies, in the Samica River valley (near £uków, eastern Poland) have been investigated. The fossil valley is incised into the till plain and the outwash. The fluvial succession is locally overlain by solifluction deposits. All the deposits underwent sedimentological analysis. The petrographic composition of basal till occurring in the vicinity of a fossil valley was determined with the method of indicator erratics. Fluvial deposits were examined by pollen analysis and plant macrofossil analysis of oxbow lake facies. Absolute dating methods were applied to the deposits (thermoluminescence methods: TL and additionally IRSL). Lithological differences between fluvial and the surrounding glaciofluvial deposits were identified and their lithostratigraphic position assigned. Petrographic analysis of till and palaeobotanical analyses of oxbow lake facies gave compatible results. Fluvial deposits were formed after the Sanian 2/Elsterian Glaciation, during the Mazovian/Holsteinian Interglacial. Luminescence dating of the fluvial deposits by the TLMAX method yielded the most relevant results (412–445 ka), which indicate that these deposits were formed during the end of the MIS 12 and beginning of the MIS 11 stage. Key words: chronostratigraphy, geochronology, interglacial meandering river, Pleistocene, Mazovian/Holsteinian, eastern Poland. INTRODUCTION Interglacial fluvial deposits are important for Pleistocene stratigraphy. In Central-Eastern Europe, a region glaciated several times, the pre-Holocene fluvial deposits have been investigated in borehole cores only. Their stratigraphic position was determined by palaeobotanical analyses of biogenic and clastic deposits, their superposition on till units, and their ages determined by thermoluminescence dating of clastic deposits (e.g., Lindner et al., 1982; Krzyszkowski, 1992; Marks and Pavlovskaya, 2003; Albrycht, 2004). We regard such interpretation of interglacial origin as incomplete if facies analysis is lacking. Unconsolidated deposits sampled from borehole cores cannot be studied sedimentologically. The aim of this paper is to describe fluvial deposits and to determine their stratigraphic position, focussing on a unique, near-surface deposit of a meandering river in the Samica valley near £uków in eastern Poland. This is the first report of these deposits. The following methods were used: (1) lithofacies analysis of the fluvial succession, (2) petrographic analysis of till from the till plain dissected by the palaeo-river, (3) palaeobotanical (pollen and plant macrofossil) analyses of biogenic oxbow lake deposits, and (4) luminescence dating of clastic channel deposits. The questions addressed in this paper are: (1) Which lithological features can be regarded as indicators of interglacial fluvial deposition? (2) Can the petrographic character of till be used to determine the stratigraphic position of fluvial deposits incised into the till plain? (3) Which palaeobotanical features of biogenic oxbow lake facies may be used to recognise its stratigraphic position? (4) Which thermoluminescence method is most useful for absolute dating of the fluvial deposits? SITE INVESTIGATED * Corresponding author: terpis@poczta.umcs.lublin.pl Received: June 10, 2013; accepted: December 23, 2013; first published online: March 25, 2014 The Pleistocene surface succession of the £uków region is traditionally classified as the youngest deposits of the Middle 236 S³awomir Terpi³owski et al. were measured to infer palaeochannel morphology and flow direction, while orientations of the longest gravel axes were used to interpret the till origin and direction of ice-sheet advance. Ductile and brittle deformation structures were noted and their dimensions and orientations measured. PETROGRAPHIC ANALYSIS Fig. 1. Correlation of glaciations and interglacials in Poland (Ber et al., 2007) with their equivalents in Western Europe (Cohen and Gibbard, 2010) Polish Complex: the Odranian Glaciation and Wartanian Stadial (cf. Terpi³owski, 2001; Ma³ek, 2004; Ma³ek and Buczek, 2009; Lindner and Marks, 2012), which are analogues of the Drenthe and Warthe units of the late Saalian of Western Europe (Fig. 1). The Wartanian Stadial ice-sheet limit is the boundary between two areas of distinctly different geomorphology (Fig. 2). The northern area is a morphologically and lithologically diverse marginal zone of the Wartanian Stadial ice sheet, formed by proximal outwash, eskers and kames. The southern area is a large outwash plain of the Wartanian Stadial ice sheet. It passes into the valley outwash trains of the upper reaches of the Krzna River and Bystrzyca Pó³nocna River with its main tributary – the Samica River. These outwash deposits fill the valleys, which cut into the flat till plain of the Odranian Glaciation. The fluvial deposits investigated (unit C) of the Samica River (Kolonia Domaszewska site) fill the fossil valley incised both into till (unit A) and outwash gravelly sands (unit B). Fluvial unit C is locally overlain by redeposited glacial deposits (unit D) (Figs. 2B and 3). The complete fluvial succession (unit C) is as follows: sands and gravels ® sands and silts (subunit C-1) ® organic and mineral deposits (subunit C-2; Fig. 3). Petrographic analysis was carried out only for the basal till (unit A) of the till plain (Figs. 2B, 3 and 4, log 1). This method is commonly used to analyse indicator erratics in Germany and Poland and to identify their source areas (e.g., Meyer, 1983; Vinx et al., 1997; Hoffmann and Meyer, 1999; Czubla, 2001, 2006; Lüttig, 2005; Górska, 2006; Górska-Zabielska, 2008; Czubla et al., 2010a, b). A sample containing approximately 1000 clasts of the coarse gravel fraction (>20 mm in diameter) was extracted from a till-bed exposed in the pit. Indicator rocks of precisely identified Fennoscandian provenance were separated and analysed using Lüttig’s method (1958), modified by Vinx et al. (1997) and Czubla (2001). Each indicator rock was assigned with geographical coordinates of the mid-point of its source area in Fennoscandia, and these (altitudes and longitudes separately) were added and averaged. The result was a geographical location of the mid-point of the source areas of indicator rocks in the till-bed studied – the Theoretical Boulder Centre (TBC; Lüttig, 1958), permitting individual samples extracted from glacial deposits to be compared. Based on crystalline (igneous and metamorphic) erratics only to avoid the effect of elimination of less resistant sedimentary rocks, the TBC was calculated and compared with the TBCs assigned for tills in the South Podlasie Lowland. The proportions of different rock groups were determined and, following the procedure deTable 1 Lithofacies code symbols used in this study Code T ST S SG G GS GSD D DS MATERIAL AND METHODS SEDIMENTOLOGICAL ANALYSIS Deposits of all Pleistocene units (A–D, Fig. 3) were investigated using sedimentological analysis. Units A, B, D and subunit C-1 were studied in the field. Subunit C-2 was studied from undeformed core obtained using an Eijkelkamp corer. The texture and structure of all units were analysed, together with the thickness, shape and extent of depositional bodies (lithofacies) and contacts between them. Lithofacies were labeled using Miall (1978) and Krüger and Kj³r (1999) codes with some modifications (Zieliñski and Pisarska-Jamro¿y, 2012; Table 1). The orientations (dips and dip directions) of beds and cross-laminae Description Texture C silts silty sands sands gravelly sands gravels sandy gravels diamictic sandy gravels diamicton (till) sandy diamicton organic or organic-clastic deposits (peats, gyttja) Structure m (m1) massive matrix-supported, gravels content <15% (for till only) h horizontal lamination/stratification r ripple cross-lamination f flaser lamination t trough cross-stratification l low-angle cross-stratification x cross lamination/stratification (in general) e erosional scour fill s stratified (for diamicton only) d deformed How to resolve Pleistocene stratigraphic problems by different methods? A case study from eastern Poland 237 Fig. 2. The £uków area A – location in the context of the ice-sheet maximum extent of the Wartanian/Warthe Stadial of the Odranian/Drenthe Glaciation (after Marks, 2004); B – geomorphological sketch (according to Terpi³owski, 2001; Ma³ek, 2004; Ma³ek and Buczek, 2009) scribed by Smed (1993), a map of the distribution of indicator erratics was drawn. PALAEOBOTANICAL ANALYSES Palaeobotanical analyses included pollen analysis and plant macrofossil analysis. They were based on the core (SO1) taken from a depth interval of 1.05–3.65 m using an Eijkelkamp corer (subunit C-2; Figs. 5 and 6). The core was sampled and analysed every 5–10 cm, depending on changes in pollen spectra. POLLEN ANALYSIS Material for pollen analysis was obtained using hydrofluoric acid method. Samples were treated with 10% HCl to remove carbonates, then boiled with 3.5% KOH. The mineral fraction was removed using 40% HF. The organic fraction was subjected to 238 S³awomir Terpi³owski et al. Fig. 3. Schematic cross-section through the Samica River valley in the Kolonia Domaszewska For location see Figure 2 Fig. 4. Sedimentary logs of units A and B in the Kolonia Domaszewska For their location see Figure 3; for lithofacies symbols see Table 1 How to resolve Pleistocene stratigraphic problems by different methods? A case study from eastern Poland A – d e p o s i t s o f t wo p a l a e o c h a n n e l s a n d l o c a t i o n o f s e d i m e n t a r y l o g s ; B – p l a n f o r m v i e w o f t h e p a l a e o c h a n n e l s 239 Fig. 5. Fluvial deposits of the fossil Samica River valley in the Kolonia Domaszew ska 240 S³awomir Terpi³owski et al. Fig. 6. Sedimentary logs of the fluvial units in the Kolonia Domaszewska For their location and explanations see Figures 4 and 5; for lithofacies symbols see Table 1 Erdtman’s acetolysis, the sporomorphs obtained were stained with acid fuchsine and washed with pure glycerine. Pollen spectra were counted on at least two slides. Usually 600–900 pollen grains of trees and shrubs (AP) were counted in samples with good frequency of sporomorphs. In samples with few sporomorphs – at least 300–400 grains of AP+NAP were counted. The results of pollen analysis of 33 samples are shown in a percentage diagram, prepared using POLPAL software (Nalepka and Walanus, 2003). The calculations of pollen and spore percentages were based on the sum of pollen grains of trees and shrubs (AP) and of terrestrial herbs and dwarf shrubs (NAP). The percentages of aquatic and lakeshore vegetation pollen of Pteridophyta and Bryophyta spores, algae, redeposited and non-determined taxa were calculated in relation to the sum AP+NAP+given taxon. The pollen succession is divided into local pollen assemblage zones (LPAZs) distinguished using criteria published by West (1970) and Janczyk-Kopikowa (1987). The names of the zones are derived from these taxa, which are predominant in or typical of a particular zone. PLANT MACROFOSSIL ANALYSIS Samples for analysis of plant macroremains (29 samples) were taken in correlation with ones used for pollen analysis. All samples were subjected to maceration using a 10% solution of KOH and detergents. 150 ml of sediment was soaked in water for ca. 24 hours and then boiled with KOH added. After the sediment was boiled to a pulp, the samples underwent wet sieve analysis using a 0.2 mm mesh sieve. The material remaining on the sieve was sorted under a magnifying glass. All plant remains qualifying for identification were isolated and placed in a mixture of glycerine, water and ethyl alcohol in ratio of 1:1:1, with thymol added. The material was stored in separate small “boxes”. The isolated plant remains were determined to species level, as far as was possible, considering the condition of the preserved material (cf. Hrynowiecka and Szymczyk, 2011; Stachowicz-Rybka, 2011). Samples from depths of 105, 120, 125 cm and 140–145 cm, were barren or contained only single unidentifiable fragments of plant tissues. The plant macroremains determined were included into local macrofossil assemblage zones (LMAZs) and correlated with LPAZs. LUMINESCENCE DATING The luminescence age of deposit is given by the ratio of the equivalent dose to the dose rate. The equivalent dose is defined as the irradiation dose absorbed by a sample in the laboratory, assuming that its luminescence intensity is the same as in natural conditions. The dose rate is defined as the energy of ionizing radiation absorbed by a sample in a unit of time (year, millennium). The age of six sandy-silty samples derived from point-bar facies (subunit C-1; for their location see Figs. 5 and 6) was estimated by thermoluminescence (TL). Although this method is not thought to provide good results for deposits older than 300–400 ka (Frechen et al., 1999; Bluszcz, 2000), we use it because some studies (Berger et al., 1992; £anczont et al., 2011; Kusiak et al., 2013) show that it is possible to accurately date deposits up to 500–800 ka. For control, two samples from log 1 were dated by infrared light stimulated luminescence (IRSL), which allows dating of deposits up to 300 ka (e.g., Yi et al., 2012). Material for analysis was prepared and measurements carried out in a room lit with Kaiser Spectral 590 lamps. In order to determine the equivalent dose (ED) the 45–56 mm polymineral fraction was separated by wet sieving, the mineral material being treated with 10% HCl and 30% H2O2. For TL dating the mineral grains were irradiated with a 60Co g source to 5000 Gy in the Institute of Nuclear Chemistry and Technology in Warsaw. After irradiation the samples were stored for three months. Before the TL measurements they were preheated at 160°C for 3 hours, the glow curves being recorded using a RA’94 thermoluminescence one-position reader (produced by Mikrolab Kraków, Poland) with an EMI 9789 QA photomultiplier. A BG-28 optical filter (380–500 nm) was used How to resolve Pleistocene stratigraphic problems by different methods? A case study from eastern Poland 241 Table 2 Description of the pIRIR290 and MET-pIRIR dating procedures of the IRSL method (Thiel et al., 2011; Li and Li, 2011) pIRIR290 Step 1 2 3 4 5 6 7 8 9 10 Treatment MET-pIRIR Observed Given dose, Di Preheat, 320°C for 60 s IRSL measurement, 200 s at 50°C IRSL measurement, 200 s at 290°C Give test dose, DT Preheat, 320°C for 60 s IRSL measurement, 200 s at 50°C IRSL measurement, 200 s at 290°C IRSL measurement, 100 s at 325°C Return to 1 Lx Lx Tx Tx Step 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 (Berger et al., 1992). The samples were heated up to 400°C at the rate of 10°C/sec in an argon atmosphere. To determine the equivalent dose the total-bleach technique was used. Luminescence intensity was determined in two different ways. Two regions under the glow curve were established at the light sum: (1) the 10°C wide region of the glow peak (TLMAX) (Kusiak, 2008; £anczont et al., 2011; Kusiak et al., 2013), (2) the 100°C wide region (270–370°C; TLINT) containing the glow peak (Frechen, 1992). The plateau test was carried out; for all samples the glow peak occurred within the plateau. IRSL measurements were made following the single aliquot regeneration (SAR) procedure (Murray and Wintle, 2000; Wallinga et al., 2000). The RisÝ TL-DA-20 automatic reader was used with the filter set (320–480 nm): Schott BG-39 and Corning 7-59. Table 2 describes the two dating procedures: pIRIR290 – luminescence reading at a temperature of 50°C and then at 290°C (Thiel et al., 2011) and MET-pIRIR – luminescence reading at a temperature of 50°C, and every 50°C up to 300°C (Li and Li, 2011). The dose rate was determined by means of gamma spectroscopy. Stationary spectrometers Mazar-01 and Mazar-95 with scintillation probes (produced by Polon-Izot Milanówek, Poland) and containers of Marinelli type with a volume of 470 cm3 were used. The measurement time for one sample was 80,000 s. Corrections were made for cosmic radiation (Prescott and Hutton, 1994) and for deposit moisture at the Treatment Observed Given dose, Di Preheat, 320°C for 60 s IRSL measurement, 100 s at 50°C IRSL measurement, 100 s at 100°C IRSL measurement, 100 s at 150°C IRSL measurement, 100 s at 200°C IRSL measurement, 100 s at 250°C IRSL measurement, 100 s at 300°C Give test dose, DT Preheat, 320°C for 60 s IRSL measurement, 100 s at 50°C IRSL measurement, 100 s at 100°C IRSL measurement, 100 s at 150°C IRSL measurement, 100 s at 200°C IRSL measurement, 100 s at 250°C IRSL measurement, 100 s at 300°C IRSL measurement, 100 s at 325°C Return to 1 Lx50 Lx100 Lx150 Lx200 Lx250 Lx300 Tx50 Tx100 Tx150 Tx200 Tx250 Tx300 18% level (Berger, 1988). The efficiency factor of alpha radiation in luminescence inducing was used (Benea et al., 2007). The concentrations of radioisotopes were converted into absorbed dose rates for a, b and g radiation, based on data published by Adamiec and Aitken (1998; Table 3). RESULTS SEDIMENTOLOGICAL ANALYSIS UNIT A Unit A is 3 m thick and built the eastern slope of the Samica River valley (Figs. 2B and 3). Massive diamicton – lithofacies Dm(m1) – contains a few elongated sandy clasts and rare gravels dispersed within the matrix (Fig. 4, log 1). Gravel fabric is very good (S1 = 0.7163). The directional distribution is symmetrical, with a distinct N–S mode (mean vector = 171°). The basal contact with sandy-gravelly glaciofluvial deposits is partly deformational. Some wedges filled with the diamicton are bordered by shear planes (normal faults and flexures). Their strike is W–E (mean vector = 85°), i.e. transverse to the orientation of elongated gravels within the diamicton. Diamicton of unit A displays features typical of basal till of lodgement type (Dreimanis, 1989). The massive structure, Table 3 Concentrations of radioisotopes (K, U, Th) and values of dose rate (Dr) Sample SPB-1 SPB-2 SPB-3 SPB-4 SPB-5 SPB-6 Depth [m] Sample No. Lub- K [Bq/kg] U [Bq/kg] Th [Bq/kg] Dose rate Dr [Gy/ka] 1.4 3.4 2.4 3.2 3.4 2.0 5181 5183 5186 5188 5189 5196 362 ± 16 351 ± 18 250 ± 13 387 ± 17 395 ± 21 116 ± 6 21.6 ± 1.9 31.9 ± 2.9 15.1 ± 1.4 28.1 ± 2.5 41.8 ± 3.1 10.8 ± 1.0 25.3 ± 1.3 26.5 ± 1.4 19.3 ± 1.1 30.9 ± 1.5 28.6 ± 1.4 6.7 ± 0.4 2.49 ± 0.12 2.78 ± 0.14 1.90 ± 0.15 2.90 ± 0.15 3.39 ± 0.16 1.02 ± 0.09 242 S³awomir Terpi³owski et al. deformational contact with underlying glaciofluvial deposits, and character of deformational structures derived from simultaneous lodgement and shearing along an ice-sheet sole (cf. Boulton and Hindmarsh, 1987; Hart and Boulton, 1991; Van der Meer et al., 2003). The well-developed gravel fabric together with transverse orientation of deformational structures support this genetic interpretation. These indicate ice-sheet advance from the North. UNIT B Deposits of unit B form a 600–800 m wide tract, oriented NNW-SSE (Figs. 2 and 3). It is the oldest terrace level in the present-day Samica River valley. Fine-grained sands with sandy-gravelly intrabeds prevail in unit B (Fig. 4, log 2). Trough cross-stratification (lithofacies St, SGt), mainly of large scale, is the most common depositional structure. The largest troughs (deeper than 1 m and longer than 10 m) usually contain the compound infill. In places the cosets of cross-laminae are divided by reactivation surfaces. In other cases, the structure changes within the sandy infill: low-angle cross-stratification (lithofacies Sl) is overlain by horizontal stratification (lithofacies Sh). The lower part of the trough is filled with sandy-clayey (diamictic) gravel with massive structure (lithofacies GSDm), whereas the upper part is made up of cross-stratified gravelly sand (lithofacies SGt). The beds of massive sand (lithofacies Sm) and gravel (lithofacies Gm), 40–50 cm thick, are a secondary lithofacies in unit B. In the upper part an ice-wedge cast 70 cm long was found. We interpret unit B as the sedimentary record of a valley sandur – elongated outwash confined by valley slopes. It derived from the retreat of the ice sheet which formed the surrounding till plain. Lateral shifting as well as extensive aggradation of braided channels were inhibited in this confined fluvial environment. Therefore the channel bed underwent frequent erosion and abundant troughs were formed. The trough cross-stratified beds St thinner than 0.5 m were linked with processes of local erosion and deposition in separation zones located distally to the three-dimensional dunes. The larger troughs are interpreted as the record of pools in the central areas of high-energy channels (Siegenthaler and Huggenberger, 1993; Marren et al., 2009). Their filling with sediment took place in a few phases, most probably during successive floods (see Olsen and Andreasen, 1995). Reactivation surfaces indicate frequent, short-term pulses of meltwater discharge. Vertical successions Sl ® Sh within large-scale troughs prove the deposition from transitional and supercritical currents which were generated by high flow velocity. Diamictic gravels at the base of some compound infills suggest that powerful ablation floods (with erosion of pools) were connected with flow-till surges which underwent initial fluvial redeposition (deposition of GSDm lithofacies; Pisarska-Jamro¿y and Zieliñski, 2014). This lithofacies is evidence for ice-sheet margin proximity (cf. Aitken, 1998). The beds of massive sand and gravel derived from abrupt aggradation are thought to represent the first phases of waning floods. Directional data of cross-beds show that proglacial meltwaters flowed towards the SSW (mean azimuth = 218°). Palaeocurrent distribution covers 180° with three main modes (towards the SSW, SSE and ESE) which reflect orientation of channels within a braided system. Lithofacies association St, Gt, Sh, generally similar to the studied unit B, has been found by Dobracki and Krzyszkowski (1997) in proximal Pleistocene outwash in NW Poland. UNIT C This is the main package of deposits investigated because it contains organic beds and an interglacial origin is inferred. It includes two fluvial subunits derived from: an active channel (subunit C-1) and an oxbow lake (subunit C-2; Figs. 3 and 5). Subunit C-1. This subunit is composed of sand, silty sand and silt (commonly occurring as rhythmites), with subordinate gravelly sand (Figs. 5 and 6). These deposits fill two stacked palaeochannels 50–70 m wide and up to 8 m deep. The upper palaeochannel is partly incised in the lower one. The packages of sand beds are characterized by low-angle (<15°) uniform dip (lithofacies Sl), transverse to the palaeochannel axes. Inclined parallel lamination predominates in the beds but there is also massive structure as well as planar cross-stratification where laminae dip opposite to the bed inclination. Therefore, these are packages of epsilon cross-stratification (ESC) type derived from point bars. Parallel, inclined lamination in sand is a record of deposition on the point-bar platform which gently sloped towards the thalweg. Sandy-silt beds within inclined beds (lithofacies STl) typically show parallel lamination, but flaser lamination has been also noted. The frequency of sandy-silt and silt components increases towards the tops of palaeochannel infills. Fining-up successions 30–70 cm thick are present within palaeochannel infills. They start from erosively-based coarse sand with granules (lithofacies SGl or SGp lithofacies) overlain by fine sand with parallel lamination (lithofacies Sl) and then by laminated sandy silt (lithofacies TSh or TSl). Channel deposits arranged in epsilon cross-stratification (ESC) indicate that palaeochannels were highly sinuous; this was a typical meandering river with bends of small radius (Miall, 1996). In terms of fluvial facies models, the deposits studied are regarded as the sedimentary record of a low-energy meandering river, as the channel facies studied comprises an association of fine-grained sand beds together with silty ones, i.e. epsilon cross-stratification (ESC) can be identified in this case with inclined heterolithic stratification (IHS) sensu Thomas et al. (1987). Similar fine-grained deposits of highly sinuous alluvial channels have been reported by Edwards et al. (1983), Gibling and Rust (1987), Smith (1987) and Wood (1989). Another typical meandering-river feature of the succession studied is the presence of a thick (1 m or more) silty package capping the palaeochannel sedimentary profile (cf. Blakey and Gubitosa, 1984). Directional data of bedding and stratification/lamination is also an important tool in environmental interpretation. Generally, the river flowed to the NNE (mean vector = 327°), i.e. opposing to the previous outwash system (unit B). Dip azimuths show a spread of 360° with polymodal distribution which is typical of highly sinuous (meandering) channels. The three main directions seen in the current rose diagram reflect primary channel directions: WWN and ESE represent point-bar lateral accretion, and N is connected with the main flow in the thalweg. All these features suggest a meandering river in a temperate climate. Subunit C-2. The oxbow of the younger palaeochannel is filled with about 2 m of organic and clastic deposits (Figs. 5 and 6). The sedimentary succession is as follows: massive silt (lithofacies Tm) ® massive organic deposits (lithofacies Cm) – gyttja with peat intercalations in the lower part, peat with gyttja intercalations in the upper part ® sandy stratified diamicton (lithofacies DSs) with massive gyttja intrabeds (lithofacies Cm) (Fig. 6). The lithologies and superposition of these members in subunit C-2 suggests deposition in an oligotrophic/mesotrophic lake which underwent progressive eutrophization and finally was filled with sediment of unit D. UNIT D In the transition zone between the palaeochannel and the till plain, the channel deposits are covered by a unit of sandy, stratified diamicton, which is up to 2 m thick in the axial part of the palaeochannel (Figs. 3 and 6). It consists of irregular, deformed beds of clayey sand and gravel with poor fabric (mean vector = How to resolve Pleistocene stratigraphic problems by different methods? A case study from eastern Poland Fig. 7. Source areas of indicator erratics recognized in the Kolonia Domaszewska till The circle’s area corresponds to the percentage of erratics in an analysed stone sample; graphic presentation method (circle map) after Smed (1993): 1 – ngermanland granite-gneiss; 2 – land and/or Nystad Pyterlite; 3 – land granite, Haga granite, land Rapakivi, land aplite granite, land granite porphyry; 4 – red Baltic quartz porphyry; 5 – Sala granite; 6 – Stockholm granite; 7 – Glöte porphyry; 8 – sen, Bredvad and K¯tilla porphyries, Garberg granite; 9 – Öje diabase and melaphyre, Dala sandstone, Digebergs sandstone and conglomerate;, 10 – Venjan porphyry; 11 – Siljan granite, Siljan Rapakivi, M¯nsta porphyry; 12 – red and brown Graversfors granites, Östgöta granites; 13 – red Sm¯land granites, Vislanda granite, Sm¯land porphyries; 14 – Kalmarsund and Tessini sandstones; 15 – Karlshamn and Spinkam¯la (Halen) granites; 16 – Kullaite, Scolithos and Hardeberga sandstones; 17 – Hammer and Vang granites, Bornholm gneisses; 18 – red Cambrian sandstones; 19 – red Ordovician limestones; 20 – Beyrichia limestone 243 S³awomir Terpi³owski et al. 94°). These alternate with discontinuous sand layers of crude stratification. Diamictic load casts (up to 1.5 m in amplitude), uniformly inclined folds and fractures with underlying fluvial sands are the most abundant deformation structures. Such features are typical of slope solifluction deposits (Steijn et al., 1995). The orientations of elongated gravels suggests that massflow redeposition took place from the till plain bordering the fossil valley to the east. PETROGRAPHIC ANALYSIS Fi g. 8 . P ol l e n di a gr a m fr om the K ol oni a D oma s z e w s k a (bor e hol e S O1 ) 244 Crystalline rocks (64.78%) are predominant in the group of Fennoscandian rocks of the basal till. Among these, indicator erratics are quite common – 15.66%. These are mostly rocks from land (43%), Sm¯land and Blekinge (26.9%) and Dalarna (12.9%; Fig. 7). The percentage of rocks from Uppland is very low (6.4%). This indicates that the ice sheet was supplied with rock material which originated mostly from south-western Fennoscandia. This conclusion is supported by the low percentage of carbonate rocks (15.51%) and the complete absence of dolomites in the Fennoscandian rock group. The high content of clastic rocks (as much as 18.97%) is an additional indicator of this “western” source area because most of the Lower Paleozoic sandstone outcrops occur in the western part of the Baltic Depression and in Sweden. The Theoretical Boulder Centre for the till in the site studied has the geographical coordinates 18.29°E and 59.13°N. It is similar to that calculated for the lower basal tills occurring in central-eastern Poland (Czubla et al., 2010a, b). This position of the TBC is characteristic for the till of the San 2/Elsterian Glaciation, i.e. Marine Isotope Stage MIS 12 (see Fig. 1). PALAEOBOTANICAL ANALYSIS The results of pollen and plant macrofossil analyses are shown together. Pollen spectra inform mostly about terrestrial vegetation at local and regional scales, while plant macrofossils serve as the basis for reconstructing lake vegetation, and indirectly also inform about the lake trophic levels. The pollen spectra belong to 5 local pollen assemblage zones (LPAZs; Fig. 8), and spectra of plant macrofossils to 5 local macrofossil assemblage zones (LMAZs; Fig. 9). LPAZs and LMAZs were designated with SO1 abbreviation and numbered from the base upwards. The lowermost samples of the succession investigated (from a depth of 310–365 cm) contained only sporadic sporomorphs so these were not shown in the pollen diagram. They contained macrofossils of dwarf birch (SO1-1 LMAZ – Betula nana, samples from 314–321 cm depth). The correlation of LPAZs and L MAZs is given in Table 4. SO1-1 Betula–Juniperus–Betula nana LPAZ (samples from 286–307 cm depth) is characterized by the predominance of Betula undiff. pollen (60–68%), gradually increasing pollen values of Pinus sylvestris t. (up to 15% in the upper sample of the zone), the occurrence of Picea, and sporadic pollen grains of Larix, Ulmus and Quercus. Among shrubs the pollen values of Juniperus are very high (up to 13.5%), while Salix pollen is frequent. The continuous percentage curve of Betula 245 Fi g. 9 . M a c r ofos s i l di a gr a m fr om the K ol oni a D oma s z e w s k a (bor e hol e S O1 ) How to resolve Pleistocene stratigraphic problems by different methods? A case study from eastern Poland 246 S³awomir Terpi³owski et al. Table 4 Correlation of pollen and macrofossil zones in the SO1 profile Local pollen assemblage zones Depth [cm] Local macrofossil assemblage zones SO1-5 Pinus LPAZ 105–128 SO1-4 Taxus–Quercus–Abies–/Carpinus/ LPAZ 128–158 SO1-5 LMAZ Salvinia natans–Azolla filiculoides LMAZ SO1-3 Picea–Alnus–Fraxinus–/Ulmus/ LPAZ 158–220 SO1-4 Carex rostrata–Urtica dioica–Ranunculus sceleratus–Nuphar LMAZ SO1-2 Pinus–Betula–Larix LPAZ 220–283 SO1-1 Betula–Juniperus–Betula nana LPAZ 286–307 SO1-3 Carex rostrata–Urtica dioica LMAZ SO1-2 Ranunculus sceleratus–Urtica dioica–Carex rostrata LMAZ nana t. (up to 7.5%) and high frequencies of Poaceae and Cyperaceae (up to 6.5%) attract attention. The zone reflects the development of boreal, open birch forests at the beginning of the interglacial and is correlated with the SO1-2 LMAZ (Ranunculus sceleratus–Urtica dioica–Carex rostrata; samples from 290–305 cm depth). Macrofossils of Betula nana and B. humilis (fruits) indicate a cool climate. At first the catchment was overgrown by vegetation to a small extent, which favoured solifluction processes (many Cenococcum geophillum sclerotia). Salix (represented by boxes) grew on the shores of the lake, as well as plants typical of eutrophic alder carr habitats, i.e. Urtica dioica, Ranunculus sceleratus, Potentilla repens and Stellaria nemorum. The rush belt was formed by Carex rostrata and Typha (tegmens). The presence of Potamogeton filiformis (endocarps) in phytocoenoses indicates that the lake water was cool and mesotrophic (Kolstrup, 1979; Matuszkiewicz, 2001; Vielichkevich and Zastawniak, 2006). It was also very transparent, and contained CaCO3 (Bennike et al., 1994), as also indicated by the occurrence of numerous statoblasts of Cristatella mucedo (kland and kland, 2000). SO1-2 Pinus–Betula–Larix LPAZ (samples from 225–278 cm depth), with similar values of Pinus sylvestris t. (up to 40%) and Betula undiff. (up to 41%) and a continuous percentage curve of Larix, represents the transformation of birch forests into pine-birch forests with larch. The vegetation of open areas was still widespread. This zone is correlated with the SO1-3 Carex rostrata–Urtica dioica (samples from 267.5–283 cm depth) and the older part of the SO1-4 Carex rostrata–Urtica dioica–Ranunculus sceleratus –Nuphar L MAZs (samples from 222.5–258.5 cm depth). Vegetation growing on the lake shore and forming the rush belt became impoverished due to a rise in water level, as indicated by the preserved remains (ephippia) of Daphnia sp. These indicate that the lake was deep, with quite cool water and a low trophic level (Szeroczyñska and Zawisza, 2011). SO1-3 Picea–Alnus–Fraxinus–/Ulmus/ LPAZ (samples from 160–215 cm depth). Upwards in the zone the pollen values of Pinus, Betula and Larix gradually decrease, those of Picea, Alnus, Fraxinus and Ulmus increase, and continuous percentage curves of Quercus, Taxus, Tilia and Corylus appear. The frequencies of Cyperaceae also increase considerably, and continuous curves of Artemisia and Humulus appear. Spores of Filicales monolete are frequent. This zone represents the beginning of the formation of wet communities of alder carr type with spruce, and ash-alder riverine forests, probably with oak (?Quercus robur). The latter species could have entered pine communities forming mixed pine-oak forests. The zone is correlated with the younger part of the SO1-4 LMAZ (samples from 172.5–212.5 cm depth). The remains of Urtica dioica and Stellaria nemorum indicate that these were abundant in the herb layer of the alder carr forests. Ranunculus sceleratus and Rumex maritimus grew on the exposed, muddy, periodically flooded shores. The remains of Carduus crispus (fruits) indicate that this probably grew in wet places. The sun-exposed slopes were the habitat for xerophytic Fragaria vesca (seeds), Dianthus arenarius (seeds) and Potentilla heptaphylla (seeds). The rush belt was again the habitat of many abundantly growing species. The predominant Carex rostrata formed high sedge rush. It was accompanied by Typha, Schoenoplectus lacustris, Sparganium emersum, S. microcarpum and Hippuris vulgaris. A considerable shallowing of the lake is indicated by the development of Nymphaeaceae, the main representative of which was Nuphar lutea (seeds). Potamogeton natans and P. dorofeevi (endocarps) as well as Ceratophyllum demersum (fruits) occured among submerged hydrophytes. The last of these occurs in eutrophic, stagnant or slowly flowing water, and is intolerant of considerable decreases in water level and of drying. However, the lake was meso/eutrophic as indicated by the occurrence of Najas flexilis with an ecological optimum in mesotrophic water. SO1-4 Taxus–Quercus–Abies–/Carpinus/ LPAZ (samples from 130–155 cm depth) is characterized by an increase in the pollen values of Picea up to 17%, Alnus up to 19%, Taxus up to 2% and Corylus up to 2.5%, decreasing frequencies of Betula undiff. to 2%, and values of Pinus sylvestris t. ranging from 31 to 50%. In the upper part of the zone the appearance of continuous pollen curves of Abies and Carpinus with maxima of 13 and 5%, respectively, and the occurrence of pollen of thermophilous plants (Pterocarya, Buxus, Hedera, Ilex, Ligustrum, Vitis, Viscum) is notable. Different taxa of the Ericaceae family are abundant among dwarf shrubs, and Salvina natans occurs among water plants. The zone represents forest communities of the beginning of the Mazovian (=Holsteinian) Interglacial optimum. These were wet forests of different types (riparian forests, spruce forests with alder, alder carr forests with yew), fir forests, and dry-soil forests with hornbeam, oak, maple and lime. Thermophilous shrubs and climbers occurred in these forests. The zone is correlated with the SO1-5 LMAZ Salvinia natans–Azolla filiculoides (samples from 132.5–162.5 cm depth). The occurrence of these two species of thermophilous water ferns, typical of shallow, warm lakes of the Middle Pleistocene, indicates a lowering of water level. The development of rush was hindered. Only reeds with Typha could have survived because dense mats of fern covered the surface of the oxbow lake. The development of macrophytes was hindered, among others of Nymphaeaceae, which completely disappeared. How to resolve Pleistocene stratigraphic problems by different methods? A case study from eastern Poland 247 Carpinus and Abies. This additionally supports the Mazovian age of the succession investigated. A distinct sign of its Middle Pleistocene age is also the occurrence of Pterocarya and Azolla, which did not occur in the Eemian and the Holocene. The pattern of vegetation development in the lake is also similar to that recorded in the plant macrofossils of lakes elsewhere in central-eastern Poland during the Mazovian Interglacial (cf., among others, Hrynowiecka and Szymczyk, 2011). SO1-5 Pinus LPAZ (samples from 105–125 cm depth) is characterized by a lower frequency of sporomorphs, which are mostly degraded, especially in the two top samples. Among AP Pinus sylvestris t. is predominant (54–66%), the values of Betula undiff. slightly increase (up to 10%). Abies (up to 3%), Picea (up to 7%), Alnus (up to 3%) and Carpinus (up to 1%) have continuous curves. Pollen of Ulmus, Fraxinus, Quercus and Taxus appear only sporadically. The values of Cyperaceae, Poaceae, Artemisia and Rumex acetosa are again slightly higher. The occurrence of Comarum palustre, Scheuchzeria palustris and Drosera rotundifolia, as well as the decreasing spore values of Filicales monolete suggests the development of a mire. Among plant macrofossils only tegmens of Typha sp. are found (sample from 112.5 cm depth). This zone reflects further domination by pine forests in the study area. The gradually increasing degree of destruction of sporomorphs and their decreasing frequency, as well as the change of the deposit into a mineral-organic one, indicate that a hiatus coincided with the younger part of the climate optimum. The succession described, i.e. boreal birch forests (SO1-1 LPAZ) and birch-pine forests with larch (SO1-2 LPAZ), which developed at the beginning of the interglacial, followed by alder-spruce communities with gradually appearing elements representing warmer climate (ash, elm, oak – SO1-3 LPAZ), and then with yew, fir, hornbeam, lime, maple and hazel (SO1-4 LPAZ), is typical of the older part of the Mazovian Interglacial. The latter zone contains several thermophilous plant elements indicating a warm and wet climate. These are, among others, climbers (Hedera, Humulus and Vitis), shrubs (Buxus, Ligustrum, Ilex and Viscum) and water ferns (Salvinia natans and Azolla filiculoides). Simultaneously occurring high values of fir and hornbeam, typical of the Mazovian optimum (Mamakowa, 2003), are not recorded in the pollen diagram. However, a very good correlation is found with the pollen diagram of the Mazovian succession from the nearby Domaszki site (cf. Pidek et al., 2011) reflecting the development of communities dominated by LUMINESCENCE DATING The equivalent dose and sample age values obtained using the TL method are shown in Table 5, and those obtained using the IRSL method are in Table 6. According to Li and Li (2011), in the MET-pIRIR procedure the deposit age should be determined using the average ED value (calculated ED values for 250°C and 300°C). The IRSLMET age shown in Table 4 was calculated in this way. The luminescence dates of the point bar deposits form two distinct groups. The younger dates of the point bar deposits were obtained by IRSL methods (MET-pIRIR: 303 ± 19 ka and 338 ± 21 ka, and pIRIR290: 352 ± 33ka and 364 ± 33 ka). These results are outside the range of applicability of these methods, which is determined at 300 ka because the higher values are underestimated in relation to the expected age (e.g., Yi et al., 2012). Therefore, the dating results obtained for the point bars using the IRSL methods are underestimated. The older dates of the point bar deposits were obtained using TL methods (TLMAX: 412–445 ka and TLINT: 408–631 ka). The age obtained by these methods may be overestimated due to short transport of the sediment before its deposition. Short sediment transport hinders total bleaching of the deposits (£anczont et al., 2013). Such a situation can be excluded in the case of point bars because channel deposits are formed in the middle and lower reaches of river valleys, i.e. a long distance Table 5 The equivalent doses and TL ages of the deposits determined by two means Sample SPB-1 SPB-2 SPB-3 SPB-4 SPB-5 SPB-6 Depth [m] Plateau test [°C] Max. TL curve [°C] Equivalent dose EDMAX [Gy] TLMAX age [ka] Equivalent dose EDINT [Gy] TLINT age [ka] 1.4 3.4 2.4 3.2 3.4 2.0 276–295 239–290 262–282 273–295 284–313 276–290 281 282 279 279 287 279 1106 ± 197 1198 ± 123 806 ± 121 1256 ± 177 1509 ± 226 422 ± 65 444 ± 80 431 ± 45 424 ± 64 433 ± 61 445 ± 67 412 ± 63 1283 ± 294 1134 ± 151 1190 ± 245 1183 ± 197 2138 ± 191 532 ± 90 515 ± 118 408 ± 57 626 ± 134 408 ± 69 631 ± 76 522 ± 99 Table 6 The equivalent dose and deposit age values determined using the pIRIR290 and MET-pIRIR procedures pIRIR290 Depth [m] Equivalent dose EDpIRIR290 [Gy] SPB-1 SPB-2 1.4 3.4 877 ± 70 1013 ± 76 SPB-1 SPB-2 1.4 3.4 1.00 ± 0.01 1.04 ± 0.01 Profile MET-pIRIR IRSLpIRIR290 age [ka] Equivalent dose EDMET-pIRIR250 [Gy] Equivalent dose EDMET-pIRIR300 [Gy] Equivalent dose EDMET-pIRIRmid [Gy] IRSLMET-pIRIRmid age [ka] 352 ± 33 364 ± 33 785 ± 53 914 ± 57 726 ± 55 968 ± 61 755 ± 30 941 ± 27 303 ± 19 338 ± 21 Recycling ratio 1.01 ± 0.01 1.01 ± 0.01 0.96 ± 0.01 0.99 ± 0.01 248 S³awomir Terpi³owski et al. from the source area. However, the wide time span of their deposition as indicated by the TLINT method is not plausible. This would include the period from MIS 13 to MIS 11, that is, two interglacial periods separated by a glacial (Fig. 1). In this case the meandering river pattern should have been transformed into a braided one during the glacial correlated with MIS 12; this is not recorded in the deposits investigated. Therefore, the most probable age of the point bar is given by the TLMAX method: 412–445 ka. This age corresponds to the final phase of the Sanian 2/Elsterian Glaciation and the beginning of the Mazovian (=Holsteinian) Interglacial (MIS 12-11; Fig. 1). The results of thermoluminescence dating indicate that the TLMAX method is the most reliable in the assessment of the section studied. Similar TL results (approx. 430 ka) have been obtained for silty sands underlying organic-clastic deposits of Mazovian/Holsteinian age in eastern Poland (Nitychoruk et al., 2005). These dates correspond to the end of the Sanian 2/Elsterian Glaciation (MIS 12; Fig. 1). SUMMARY OF RESULTS AND CONCLUSIONS Two waterlain Pleistocene successions of different origin have been identified by detailed sedimentological analysis of the present-day Samica valley infill: glaciofluvial unit B and fluvial unit C. These deposits are characterized by distinct textural and structural features. Glaciofluvial unit B, containing channelized facies, reflects a braided fluvial system typical of severe cold climate. By contrast, the younger unit C composed of point-bar (subunit C-1) and oxbow facies (subunit C-2) was deposited in a meandering river, a fluvial environment characteristic of a temperate climate. Moreover, these fluvial systems flowed in opposite directions: the glaciofluvial water flowed southwards, and the meandering river to the north. The stratigraphic position of fluvial unit C was determined by means of palaeobotanical analyses of oxbow lake deposits (subunit C-2) as well as indirectly by petrographic analysis of the till (unit A) in which the fluvial deposits are incised. Luminescence dating of point-bar deposits (subunit C-1) was carried out to estimate the age of fluvial unit C. Our findings lead to the following stratigraphic conclusions: 1. Petrographic analysis indicates that the basal till of the till plain contains indicator erratics typical of south-western Fennoscandia. The Theoretical Boulder Centre (TBC: 18.29°E and 59.13°N) is similar to that calculated for tills of the San 2/Elsterian Glaciation (MIS 12) in central-eastern Poland. Thus, the formation of the Samica River fossil valley started after this ice-sheet retreat. 2. Based on palaeobotanical analyses of the oxbow deposits, the succession was divided into five local pollen zones (LPAZs) and five local macrofossil zones (LMAZs). The first four L PAZs, correlated with the LMAZs, are typical of the older part of the Mazovian (=Holsteinian) Interglacial. They represent the following successive phases of vegetation development: – open birch forest at the beginning of the interglacial. A shallow lake with poor lakeshore vegetation, and cool and mesotrophic lake water; – birch-pine forest. A rise in water level in the lake and impoverishment of the lakeshore vegetation composition. The lake water was still cool and weakly mesotrophic. – Wet forest of alder carr type, and ash-alder riverine forest. The shallowing lake was surrounded by a wide belt of high sedge rush. The lake water was warm, meso/eutrophic; – thermophilous and hygrophilous forest communities around the lake, including a riverine forest with Pterocarya during the climatic optimum of the interglacial. The still shallowing lake was overgrown by water ferns – Salvinia natans and Azolla filiculoides. 3. The luminescence ages of the point bar deposits form two distinct groups: – younger ages were obtained by IRSL methods (MET-pIRIR: 303 ± 19 ka and 338 ± 21 ka, and pIRIR290: 352 ± 33ka and 364 ± 33 ka). The results are outside the range of applicability of these methods (300 ka), and so are underestimated; – older ages were obtained by TL methods (TLMAX: 412–445 ka and TLINT: 408–631 ka). As the deposition of the point bar deposits was continuous, we have to exclude the broad time span obtained by the TLINT method. The most probable age of these deposits is indicated by the results from the TLMAX method: 412–445 ka. These correspond to the end of the San 2/Elsterian Glaciation and the beginning of Mazovian/Holsteinian Interglacial (MIS 12-11). The results obtained using the three different methods are compatible, and indicate that the alluvial deposits under study were formed in a river channel and oxbow lake from the end of Elsterian to the optimum of the Mazovian (=Holsteinian) Interglacial. These are the first Holsteinian fluvial deposits to be studied sedimentologically in Poland and indeed in Central Europe. Other stratigraphical methods usefully complemented the palaeobotanical analyses. Lithofacies analysis enabled recognition of meandering river deposits typical of warm climatic conditions. Petrographic analysis of gravels larger than 20 mm, still rare as a technique, allowed assignation of till levels to particular glacial periods. The use of the TLMAX method in dating deposits older than 400 ka has been confirmed. Acknowledgements. This work has been financially supported by the Polish Ministry of Science and Higher Education project no. 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