Aeolian dynamics at the Orlovat loess–paleosol sequence, northern Serbia, based on detailed textural and geochemical evidence

Aeolian Research 18 (2015) 69–81

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Aeolian dynamics at the Orlovat loess–paleosol sequence, northern Serbia, based on detailed textural and geochemical evidence Igor Obreht a,⇑, Christian Zeeden a, Philipp Schulte a, Ulrich Hambach b, Eileen Eckmeier a, Alida Timar-Gabor c,d, Frank Lehmkuhl a a

Department of Geography, RWTH Aachen University, Templergraben 55, D-52056 Aachen, Germany Chair of Geomorphology, Laboratory for Palaeo- and Enviro-Magnetism, University of Bayreuth, D-94450 Bayreuth, Germany Faculty of Environmental Science, Babesß-Bolyai University, Fântânele 30, 400294 Cluj-Napoca, Romania d Interdisciplinary Research Institute on Bio-Nano-Science of Babesß-Bolyai University, Treboniu Laurean 42, 400271 Cluj-Napoca, Romania b c

a r t i c l e

i n f o

Article history: Received 31 October 2014 Revised 17 June 2015 Accepted 17 June 2015 Available online 3 July 2015 Keywords: Loess Serbia Grain-size X-ray fluorescence (XRF) Paleowind Košava

a b s t r a c t Previous investigations showed that the Orlovat loess–paleosol section, northern Serbia, is characterized by irregularities in sedimentological properties, magnetic susceptibility and color of the sediment. Here, we applied granulometric analysis and X-ray fluorescence (XRF) analyses to study how the sedimentation at the Orlovat site was conditioned by specific geomorphological or climatic conditions. Grain-size analysis is an established method and one of the most frequently used paleoenvironmental proxies of loess deposits, and is complemented here with high resolution XRF analysis on sand-free samples to obtain a more detailed insight into paleoenvironmental conditions and weathering during the past 160 ka. The geomorphological conditions of the surrounding area and variations in wind speed over time are of great importance for a better understanding of loess–paleosol deposits. The Orlovat section was exposed to special depositional conditions, which differ from other sections studied in the Carpathian Basin. Sand was delivered during interglacials, most probably from the Deliblato Sands by the southeast Košava wind. This study highlights the importance of an integrated sedimentological approach for reliable paleoenvironmental reconstruction. Ó 2015 Elsevier B.V. All rights reserved.

1. Introduction Loess–paleosol sequences (LPS) have been recognized as sensitive records of past climatic and environmental change (e.g. Derbyshire et al., 1997; Kukla, 1977; Smalley et al., 2011; Stevens et al., 2008). Distribution and origin of loess can give important information about the paleowind direction (e.g. Muhs and Benedict, 2006; Pye, 1995), and also paleowind strength can be reconstructed by grain-size distributions (e.g. Vandenberghe and Pissart, 1993; Vandenberghe et al., 1998; Xiao et al., 1995; Yang and Ding, 2014). LPS are commonly observed in the vicinity of the Danube River and present one of the most valuable terrestrial archives in Southeastern Europe (e.g. Buggle et al., 2009). Smalley and Leach (1978) reviewed the origin and distribution of Danubian loess and suggested that loess in the Middle and Lower Danube region originates predominantly from alluvial deposits of lowland rivers, specifically the Danube itself and its tributaries.

⇑ Corresponding author. Tel.: +49 (0) 241 80 96460. E-mail address: [email protected] (I. Obreht). http://dx.doi.org/10.1016/j.aeolia.2015.06.004 1875-9637/Ó 2015 Elsevier B.V. All rights reserved.

Recently, the geochemical investigations of Buggle et al. (2008), Újvári et al. (2008) came to the same conclusion. LPS in the Vojvodina, northern Serbia, have come into focus of European Pleistocene paleoclimate and loess research during the last years. Previous studies in Serbia used stratigraphy (Basarin et al., 2014; Markovic´ et al., 2008, 2012), magnetic properties (e.g. Basarin et al., 2011, 2014; Buggle et al., 2009; Liu et al., 2013; Markovic´ et al., 2009), grain-size variations (Antoine et al., 2009; Bokhorst et al., 2009, 2011; Markovic´ et al., 2006, 2007; Vandenberghe et al., 2014; Zech et al., 2013), iron mineralogical (Buggle et al., 2014) and malacological proxies (Markovic´ et al., 2004, 2014a) as well as AAR (Amino acid racemization) relative (Markovic´ et al., 2005, 2011) and absolute luminescence geochronology (Fuchs et al., 2008; Schmidt et al., 2010; Stevens et al., 2011; Timar-Gabor et al., 2015) to investigate paleoenvironments. All mentioned studies focused on the central, northern and western part of the Vojvodina in Serbia. The eastern part of the Vojvodina, known as the (Serbian) Banat region, has been hardly investigated for paleoclimatic and paleoenvironmental changes. However, some archeological findings in the Serbian and Romanian part of the Banat region (e.g. Ba˘ltean, 2011; Hahn,

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1977; Kels et al., 2014; Sitlivy et al., 2012) indicate the presence of modern humans (Homo sapiens sapiens) during the Upper Paleolithic, imbedded in terrestrial sediment. For this reason, special attention is paid to the Orlovat section, the only investigated section in the Serbian part of the Banat region (Lukic´ et al., 2014; Markovic et al., 2014b). The Orlovat section is situated on the edge of the Tamiš loess plateau (Fig. 1). Popov et al. (2008, 2012) proposed that the Tamiš plateau is a remnant of a once much larger plateau. Besides its paleoclimatic value, the Orlovat section is also interesting from a sedimentological point of view due to its situation at the slope of the plateau. In previous studies based on rock magnetic (Markovic et al., 2014b) and color (Lukic´ et al., 2014) analysis, it was observed that this section has a unique sedimentology differing from all other investigated sections in Serbia. However, these studies could not answer whether these differences are due to different geomorphological conditions, slope sedimentation processes (e.g. redeposition of older reworked soil material) or systematic differences in climate evolution between the Banat region and the central, western and northern Vojvodina. The aim of this study is to investigate if sedimentation and weathering processes at the Orlovat section were determined by specific geomorphological, environmental or/and climatic conditions. Special attention is attributed to the surrounding geology and geomorphology. Grain-size analysis and X-ray fluorescence (XRF) analysis are applied in this study, aiming at a better understanding of sedimentological processes. Textural analysis is a well-established method and one of the most frequently used paleoenvironmental proxies of loess deposits (Ding et al., 2002; Prins et al., 2007; Vandenberghe et al., 1997; Yang and Ding, 2014). In contrast, geochemical analyses constitute a relatively novel approach in the Vojvodina region (Bokhorst et al., 2009; Buggle et al., 2008, 2011, 2013; Zech et al., 2013) and previous studies applied only a low resolution of geochemical proxy values. Since this study generates high resolution geochemical element data for the first time in the region, one of its aims is to give better insight into the mutual dependence of elements within this section. Elemental data is also used to obtain a more detailed understanding of weathering during the past 160 ka, and to evaluate the reliability of weathering indices.

2. The Orlovat site in northeastern Serbia 2.1. Study site and geomorphological setting The investigated LPS is exposed at a brickyard in the village of Orlovat (45°150 N, 20°350 E, 88 m a.s.l.), 25 km southeast of the city Zrenjanin in the Vojvodina region, northern Serbia. The mean annual air temperature and annual precipitation recorded at the nearby climate station of Zrenjanin is about 11.2 °C and 622 mm (with high interannual variability and a dry period during the summer months) (Hrnjak et al., 2014; Tošic´ et al., 2014). The studied section is situated at the edge of the smallest loess plateau in the Vojvodina, the Tamiš loess plateau. This slightly elevated geomorphological unit is located between the floodplain of the Tamiš River (on the northeast, east and southeast) and the paleochannels Petra and Šozov on the west and northeast (Popov et al., 2012; Fig. 1). The Orlovat section is located at the southeast edge of this plateau and the profile was probably influenced by slope processes during its formation. The published luminescence chronology and absence of L1SS1 (units nomenclature according to pan-European loess stratigraphic model proposed by Markovic´ et al., 2015) pedocomplex indicates a hiatus in sedimentation between around 40 and 13 ka (Markovic´ et al., 2014b).

2.2. Sampling strategy During April and May 2012, the Orlovat profile was carefully cleaned and sampled for sedimentological analyses, including rock magnetic properties (Markovic´ et al., 2014b), sediment color (Lukic et al., 2014), granulometry and geochemistry. Samples for rock magnetic properties, color of the sediment and grain-size analysis were taken in 5 cm resolution, while the geochemistry samples were taken in 10 cm resolution with 5–10 cm gaps around transition zones. Eight samples were collected for luminescence dating using metal tubes. Samples from the modern soil were taken only from the lowermost ca. 20 cm, because the uppermost ca. 40 cm of the soil have been influenced by human activities. This study reports results from grain-size, multi-elemental (XRF) and CaCO3 content analyses. 3. Materials and methods 3.1. Grain-size and geochemical analysis All samples were air-dried, homogenized and sieved (<2 mm). Subsamples of 0.1–0.3 g fine-earth (<2 mm) were pre-treated with 0.70 ml of 20% hydrogen peroxide (H2O2) at 70 °C for 12 h. This process is repeated until a bleaching of the sediment occurs (Allen and Thornley, 2004), but not longer than three days. To keep particles dispersed, the samples were treated with 1.25 ml, 0.1 M sodiumpyrophosphate (Na4P2O710H2O) for 12 h (Pye and Blott, 2004). The particle size was measured by a LS 13320 Laser Diffraction Particle Size Analyser (Beckman Coulter), which divides the samples in 116 grain-size classes with a range of 0.04–2000 lm with an error of 2% (1r). Each sample was measured four times in two different concentrations to increase the accuracy. Afterwards, all measurements with reliable obscuration were averaged. To calculate the grain-size distribution the Mie theory was used (Fluid RI: 1.33; Sample RI: 1.55; Imaginary RI: 0.1) (Özer et al., 2010; ISO 13320-1, 1999). The particle size fractions were defined by employing the ISO standard 14688 (2002), where clay is represented with particles smaller than 2 lm, fine silt from 2 to 6.3 lm, medium silt from 6.3 to 20 lm and coarse silt from 20 to 63 lm (Blott and Pye, 2012). In past studies of Serbian LPS that compared grain-size data using the sieve and pipette method with laser measurements (Antoine et al., 2003, 2009; Konert and Vandenberghe, 1997), the clay fractions were proposed to be the fractions <4.8 lm (Antoine et al., 2009), <5 lm (Obreht et al., 2014) or <5.5 lm (Bokhorst et al., 2009) for laser grain-size measurements. Based on the results of the Orlovat loess sequence and the different characteristics of the measurement instruments, the clay fraction is defined to be <2 lm. However, also the particles <5 lm are reported for a better comparability with already published data. For the present study, the element concentrations of 10 major elements and 14 trace elements were determined. The bulk sediment samples were sieved down to 63 lm and dried at 105 °C for 12 h. An 8 g-quantity of the sieved material was mixed with 2 g Fluxana Cereox wax, homogenized and pressed to a pellet with a pressure of 19.2 MPa for 120 s. The measurements were conducted by means of a pre-calibrated method. Loess and paleosol samples were analyzed in duplicate for major and trace element abundances with polarization energy dispersive X-ray fluorescence (EDPXRF) using a SpectroXepos. The CaCO3 – content was determined gas-volumetrically using a Scheibler apparatus after dissolution of carbonates with HCl (10%) (Schaller, 2000; ISO 10693, 1995). 3.1.1. Ratios and chemical weathering indices Chemical weathering indices are based on the concept on mineral alteration, where the selective removal of soluble and mobile

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Fig. 1. The study area. (A) Map of the Vojvodina region with the geographical positions of the main loess sections (Markovic´ et al., 2014b, modified). (B) A geomorphological map of the Tamiš loess plateau surrounded by the Tamiš and Begej river valleys (Popov et al., 2012, modified).

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elements from a profile section is compared to a relative enrichment of immobile and non-soluble elements (e.g. Fedo et al., 1995; Harnois, 1988; Kronberg and Nesbitt, 1981; Yang et al., 2004). Ratios of bulk elements and weathering indices have been successfully used for the reconstruction of paleoenvironmental conditions of LPS (e.g. Jeong et al., 2008; Kels et al., 2014; Muhs et al., 2008; Varga et al., 2011; Yang et al., 2006). The chemical weathering indices used in this study are the Chemical Index of Alteration (CIA = ((Al2O3/(Al2O3 + Na2O + CaO⁄+K2O)) ⁄ 100) (Nesbitt and Young, 1982), the Chemical Proxy of Alteration (CPA) = (Al2O3/(Al2O3 + Na2O)) ⁄ 100 (Buggle et al., ´ (Cullers, 2000)) and (CaO + Na2O + 2011) (also known as CIW MgO)/TiO2 ratio (Yang et al., 2006). The A–CN–K diagram (Al2O3–(Na2O + CaO⁄)–K2O diagram) (Nesbitt and Young, 1984) informs about weathering and sorting effects of aluminosilicates, as well as the initial composition of the unweathered material (e.g. Nesbitt and Young, 1989; Nesbitt et al., 1996). 4. Results and discussions 4.1. Grain-size distributions and their change with stratigraphy The grain-size density distribution curves from the individual stratigraphic units of the Orlovat section are presented in Fig. 2, and the high resolution profile records of the individual

Fig. 2. Density distribution curve for the main stratigraphic units of the Orlovat section.

grain-size fractions, GSI (Antoine et al., 2009) and U-ratio (Vandenberghe and Pissart, 1993; Vandenberghe et al., 1998) are given in the Fig. 3. The grain-size <2 and <5 lm fractions have very similar distributions (see Fig. 3) and are therefore described together. From the bottom of the profile at 10 m to 9.4 m, the relative contribution of clay fractions increases from ca. 12.3% to ca. 20.6% and the fine (<5 lm) fraction increases from 20.3% to 30.3%. Until 5.4 m the contribution of this fine fraction decreases almost linearly to 8.8% for clay and 14% for <5 lm fractions, and then increases almost to its maximum values at ca. 4.2 m (19.5% for clay and 28.6% for fine particles). From 4.2 to ca. 2.5 m a general decreasing trend can be observed. From here until the top of the section the data have no trend, with maximum values for this part of the section around 1.3 m (17.5% for clay fractions). Also the fractions 2–22 and 5–22 lm have similar distributions and thereby only 2–22 lm will be described. From the bottom of the profile at 10 m to ca. 8.1 m the amount of the medium silt fractions decreases from ca. 39% to 27%. From 8.2 to 5.4 m data are similar with low fluctuations around 29%. From 5.4 to 5 m the medium silt fractions increase from 27% to 34.5%. Up to 4 m values are similar in the range between 33% and 35%. From 4 to 1.8 m the distribution of the medium silt fractions increases to 42.7%. Above 1.8 m the medium silt particles have large fluctuations in their abundance to the top of the profile with the highest amount of 48.7% at 0.5 m depth. The coarser silt particles (22–63 lm) generally have low fluctuations within the Orlovat section ranging from 29% to 37.5%. From the base of the profile to 9.4 m, the contribution of the coarse silt decreases from 36.2% to 30.7%. From there to 7.4 m values are stable in the range of 30–32%. An increase of coarse silt from 7.4 to 5.5 m was interrupted by a decrease between 6.6 and 6.4 m. From 5.5 to 4 m coarse silt decreases from 37.7% to 28.9% and then increases until 2.2 m to the maximum contribution of 37%. From 2.2 to 0.5 m the contribution shows a decreasing trend with large fluctuations. The sand fractions range from 8% to 30%. From the bottom of the profile to 8 m, the sand fractions increase from 10% to 27.8%. From 8 to 5.4 m the sand fractions reach highest amount of 29.9% with no obvious trend. From 5.4 to 1.8 m, the sand fraction decreases.

Fig. 3. The grain-size proxies, U-ratio, GSI and CaCO3 content related to the pedostratigraphy. Ages shown in ka next to the sequence represent the results of luminescence dating (Markovic´ et al., 2014b).

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Fig. 4. Direct comparison between >44 lm fractions obtained from the Orlovat, Titel (Markovic´ et al., 2008) and Surduk (Antoine et al., 2009). The profiles are plotted on their depth scales.

Above 1.8 m, the sand fractions slightly increase with large fluctuations and no trend can be observed. Granulometry of the Orlovat section is depicted in Fig. 4, where fractions >44 lm of the Orlovat section are compared to the same fraction distribution of the Surduk section (Antoine et al., 2009) at the Srem loess plateau (south of the Fruška Gora Mountains, see Fig. 1) and the Titel section (northwest of the confluence of the Danube and Tisa, Markovic´ et al., 2008) at the Titel loess plateau. The Orlovat section contains higher concentrations of coarser fractions (>44 lm) in the paleosol S1 than the Surduk and Titel sections. Contrarily, the Surduk and Titel sections contain coarser fractions within the loess. Furthermore, the paleosol S1 at the Orlovat section is much ticker than at the other sections, while the thickness of the Last Glacial loess unit L1 is considerably lower at Orlovat. The figure in Appendix A presents the normalized grain-size distribution of particles <63 lm. It can be observed that the clay fractions have a similar pattern as the bulk sediment grain-size distribution. The highest changes can be observed for the coarse silt fractions which are relatively stable in the bulk sediment distribution. 4.2. Geochemical analyses 4.2.1. Calcium carbonate The amount of CaCO3 in bulk samples of the Orlovat section is presented in Figs. 3 and 5–7. The CaCO3 content is high and varies from 9.2% to 31.8% (average 19.3%). From the bottom of the profile to 9.5 m the CaCO3 content increases to 31.8%. In the paleosol S1 unit, the CaCO3 content gradually decreases from 9.5 to 6.5 m, with lowest values of 10.3%, while it increases again between 6.5 and 5.5 m. The increase in CaCO3 content continues until 5 m (highest values are 22.5%). Above 5 m the CaCO3 content rapidly decreases and has stable values around 15% until 2.8 m. Between 2.8 and 2.2 m the CaCO3 content shows an abrupt increase up to 26.5%. Constantly high values occur between 2.2 and 0.5 m, while the modern soil is highly depleted in CaCO3 (9.2%).

4.2.2. Major and trace elements The concentration of major elements is presented in Fig. 5 and Appendix B. All the major element values are normalized and presented as percentage values. Despite the methodological approach using the sand-free samples, SiO2 is still dominant in all samples. The SiO2 values vary between 51.5% and 63.1% (average 56.1%). Al2O3 reaches values between 12.8% and 15.42% (average 14.3%). CaO is also a major contributor to the sediments at Orlovat, and ranges from 7.8% to 20.4%, with an average of 14.4%. The FeO content varies from 5.1% to 6.1% (average 5.7%). The MgO contribution varies from 7.8% to 3.7% (average 4.6%) and its distribution does not show any correlation with other minerals. Other elements are present in much smaller concentrations. K2O contributes with 2.00–2.73% (average 2.3%), Na2O with 0.99–1.49% (average 1.2%) and TiO2 is in the range of 0.90–1.09% (average 1%). MnO contributes with 0.10– 0.14% (average 0.11%) to the sediment. All major elements (except P2O5) show a clear shift of values between 2.8 and 2.2 m. Trace element (Rb, Sr, Ba, Pb, Th, Zr, Nb, Y, V, Cr, Ni, Cu and Zn) contents are displayed in Fig. 6 and Appendix B. The distinct shift between 2.8 and 2.2 m of all elements can also be observed in the trace element concentrations. All trace and major elements except MgO, P2O5 and Sr have a similar pattern of distribution (except that CaO has the opposite trend). In general, the decreasing trend of values from the bottom of the profile to 9.5 m is followed by an increasing trend of values until 6.5 m. Between 6.5 and 3.2 m a general decrease of values is observed, whereas between 3.2 and 2.6 m values show an increasing trend. An abrupt decrease in values between 2.6 and 2.2 m is observed, continued with a gradual decrease to the top of the section. MgO is characterized by an increase in values from the bottom to 9.8 m, an abrupt decrease can be observed until 9.4 m (from 8% to 4%). Above that up to 6.3 m values are stable around 4%. From 6.3 to 3.8 m values are increasing with highest peaks at 6.1, 5.4 and 4 m. Above this level, values decrease until 2.8 m, followed by an increase until 2.2 m. From 2.2 m to the top of the profile values gradually decrease. Sr mirror the MgO with the opposite trend.

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Fig. 5. The rock magnetic proxies (Markovic´ et al., 2014b), major elements (normalized and presented in percentages values) and CaCO3 content related to the pedostratigraphy.

Fig. 6. The rock magnetic proxies (Markovic´ et al., 2014b), trace elements (presented in ppm values) and CaCO3 content related to the pedostratigraphy.

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Fig. 7. The rock magnetic proxies (Markovic´ et al., 2014b) simple ratios, weathering indices and related CaCO3 content related to the pedostratigraphy. Ages shown in ka next to the sequence represent the results of luminescence dating (Markovic´ et al., 2014b).

The P2O5 content shows almost constant values in a narrow range from 1.19% to 0.27%, except for the uppermost 1 m where the values rapidly increase to 0.75% (average 0.3%).

4.2.3. Elemental ratios and weathering indices Elemental ratios are presented in Fig. 7. The Th/Ni ratio does not show any particular trend. The values are scattering, but an abrupt shift in values can be observed from 4.3 to 4 m. The Zr/Ni and Zr/Si ratios show no trend below 4.2 m. From 4.2 to 4 m, a rapid increase is observed for these ratios. Until 2.5 m both ratios show a decreasing trend. From 2.5 m to the top of the profile, the Zr/Ni ratio shows an increasing trend while the Zr/Si ratio has relatively stable values in a narrow range. The Al2O3/K2O ratio has a quite narrow range of values from the bottom of the profile to 5 m. From there to 2.8 m the values decrease. From 2.8 m to the top of the profile values are in a narrow range, and show a small increase from 1.5 to 0.6 m. Thereafter, values decrease in the modern soil. From the bottom of the profile to 2.5 m, the SiO2/Al2O3 ratio shows values in a relatively narrow range with slightly little higher values from 7.5 to 5.5 m and 4.5–2.5 m. From 2.5 to 2.1 m, values rapidly decrease. From 2.1 m to the top of the profile a gradual decreasing trend can be observed. The Ba/Sr and Rb/Sr ratios are similar and are therefore described together. Both ratios show a decrease in values from the bottom of the section to 9.5 m. From there to 8.5 m values increase. From 8.5 to 6.3 m depth, values are fluctuating without a trend. From 6.3 to 5.2 m values decrease again. Between 5.2 and 2.3 no trend can be observed. From 2.3 to 2.1 m values rapidly decrease, and from 2.1 to 1.6 m values are relatively stable. Above 1.6 m, values gradually increase until the top of the modern soil. Weathering indices are presented in Fig. 7. The values of CIA and CPA are scattering and do not show any systematic enrichment in any particular lithostratigraphic unit. A gradual decreasing trend characterized by a large fluctuation of values can be observed in the S1 paleosol pedocomplex. The strong enrichment of values can be observed from 5.4 to 3.8 m, with an abrupt decrease of values at 4 m. Above, values decrease until 3.5 m. From there to 2.7 m no trend is observed and values are characterized by large fluctuations. From 2.7 m to the top of the profile values have an increasing trend with great fluctuations and an abrupt decrease at 1.4 m. The (CaO + Na2O + MgO)/TiO2 ratio increases from the bottom of the section until 9.5 m and then decreases up to 8.6 m. A weaker decreasing trend continues up to 6.2 m. From 6.2 to 2.3 m values

do not show a clear trend, have small fluctuations and vary between 25 and 35. From 2.3 to 0.6 m values are generally high. In the uppermost 0.6 m values rapidly decrease to the minimum values at the top of the profile. All ‘‘Na-type’’ weathering indices (CIA, Index B, CIW, PIA, and the CPA) show a very similar trend, therefore here only the CIA and the CPA are presented (Fig. 7). As the analyses were not done on CaCO3 free samples, the (CaO + Na2O + MgO)/TiO2 ratio is influenced by the CaCO3 content. Therefore is not reliable for weathering and will not be discussed here.

4.3. Stratigraphy and chronology A detailed description of the Orlovat section and stratigraphic interpretation was presented by Markovic´ et al. (2014b). A stratigraphic labeling scheme for the Vojvodina was established by Markovic´ et al. (2015), where the loess and paleosol stratigraphic units were designated with letters L (loess) and S (soil), and are numbered with increasing age. It should be noted that the usual stratigraphic unit for MIS 3, a weak interstadial pedocomplex (L1SS1) in the Vojvodina region, is missing. The stratigraphic units are defined by Markovic´ et al. (2014b) as follows, starting at the bottom of the profile: (I) L2 represents loess accumulated during MIS 6. (II) S1 is characterized by the interglacial paleosol corresponding to MIS 5. This interglacial soil complex is divided into three different paleosol formations. (III) L1 represents a loess unit mainly corresponding to the Last Glacial (mostly represented by loess matching roughly the time of MIS 2 and MIS 4, but also the Holocene loess in uppermost part). Finally, (IV) S0 represents the modern soil (Fig. 5 and Table 1). According to this lithostratigraphy (Markovic´ et al., 2014b) and data obtained in this study, we revise the stratigraphy from Markovic´ et al. (2014b), and divide the profile into nine different stratigraphic units (Figs. 3 and 7; Table 1). The lowermost four units are divided according to the lithostratigraphy, where unit 1 is L2 loess, unit 2 is a strongly developed olive brown and blocky AB horizon (9.5–8.1 m depth), unit 3 represents a light olive brown paleosol (8.1–6.6 m depth) and unit 4 includes three granular paleosol horizons. Further division of the profile is based on different patterns in grain-size or element concentration observed in L1 loess, and presented as follow: Unit 5 is associated with an increase of clay particles after a transition from the paleosol to a pure loess unit at ca. 4 m depth.

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Table 1 Correlation of lithological units with Marine isotope stages (MIS) and depth. Stratigraphic units

MIS

Sedimentary units

Depth (m)

L2

6

Unit 1

10–9.5

S2

5

Unit 2 Unit 3 Unit 4

9.5–8.1 8.1–6.6 6.6–5.5

L1

4–2

Unit 5 Unit 6 Unit 7

5.5–4.0 4.0–2.8 2.8–2.2

L1

2–1

Unit 8

2.2–0.6

S0

1

Unit 9

0.6–0.0

The constant increase of clay is characterizing this whole unit until a weak interstadial paleosol. Above the weak interstadial paleosol, unit 6 extends up to a depth of 2.8 m. This unit is characterized by a decrease of the clay content. In this unit clay and sand do not seem to be complementary. Both clay and sand decrease in contribution while the silt fraction increases. Unit 7 extends 0.6 m from 2.8 to 2.2 m depth. In this unit the clay fractions are relatively stable. Although the grain-size does not show high fluctuations or a trend, an abrupt shift can be observed in the content of the most chemical elements. Unit 8 is presenting a loess layer with two weakly developed paleosols. A very slight increase of clay particles is observed in the weak paleosols when compared to the overlying loess layer, but generally this part of the profile has stable clay values. This unit shows a different grain-size pattern compared to all units below because the high complementary fluctuations have been observed in medium and coarse silt. Unit 9 corresponds to the modern soil. This unit is characterized by a relatively high input of sand and coarse silt. 5. Discussion 5.1. Granulometry as an indicator of wind dynamics Previous studies (Lukic´ et al., 2014; Markovic et al., 2014b) investigating the Orlovat section showed that this section was exposed to different sedimentological conditions during the past 160 ka. The granulometry for the Orlovat section confirmed a unique sedimentology for the Carpathian Basin, due to a higher sand content in the soil and elevated clay content in the loess (Fig. 3). The grain-size distribution curves of all stratigraphic units (Fig. 2) from the Orlovat section indicate aeolian sedimentation throughout. It can be concluded that redeposition did not play a major role in the sedimentation process, though a minor contribution of slope processes cannot be excluded. It is particularly interesting to investigate the input of the coarse fractions in the soil and the highest contribution of clay content in the loess. To explain the cause(s) of a higher content of coarser fractions in the soils, two factors appear most likely here: (1) stronger wind activities and/or (2) a different/closer source of the sediment material during soil formation. According to the lithostratigraphy and the datings, the S1 soil corresponds to MIS 5. No strong wind activities and high dust fluxes have been inferred from any other LPS in the Carpathian Basin for this time period. High sedimentation rates of loess are only characteristic for the glacial period (Bokhorst et al., 2011; Buggle et al., 2009; Fitzsimmons et al., 2012; Újvári et al., 2010, 2014b). However, during recent conditions, the southern Banat is under the influence of a strong southeast wind called Košava (Barbu et al., 2009; Unkaševic et al., 2007). It is possible

that the Košava wind prevailed in the southern part of the Banat also during previous interglacials, and that it may have been strong enough to influence a large region. An additional argument for the Košava wind as a dominant wind during the paleosol formation at the Orlovat section is the presence of the Deliblatska pešcˇara (Deliblato Sands) as a potential source area. The Deliblato Sands, a sand field situated southeast from the Orlovat section (Fig. 1), could have acted as a source of sand which has contributed to the modern soil and the S1 paleosol at Orlovat. It was proposed that alluvial fans and overbank deposits of big lowland rivers are the main source of loess material in Carpathian Basin (e.g. Smalley and Leach, 1978; Smalley et al., 2009). However, also local rocks exposed in the surrounding mountains of specific loess sites may contribute to the aeolian dust input (e.g. Újvári et al., 2012). In case of the Orlovat section, the Deliblato Sands southeast of the section exposed to the strong southeast Košava wind could strongly contribute to the grain-size content. Therefore, we propose the Deliblato Sands to be an important source area of aeolian sediments during the MIS 5 interglacial in addition to the river systems. This hypothesis can be seen as an indicator of a dominant southeast wind during MIS 5 in the South Banat region as a whole. Furthermore, this southeastern wind may have an influence on a larger region, because the higher contribution of coarser fractions in the S1 paleosol is also observed at the Titel section (Markovic´ et al., 2008), relative to the Surduk section (Fig. 4). The suggestion that the Košava could have influenced the sedimentation on the Titel loess plateau is in agreement with findings by Zeeden et al. (2007), who observed that the depressions on the Titel loess plateau have a preferential northwest–southeast orientation, probably influenced by aeolian deflation. Those morphological patterns indicate that the Košava wind may have (had) a stronger influence on the Carpathian Basin than previously known, because the direction of landforms are aligned in the direction of the Košava, and beyond these geomorphological properties high contents of coarse material is present in a large area. Markovic´ et al. (2008) pointed out that during the Last Glacial cycle, a higher deposition of coarser material occurred during the Early Pleniglacial in the south Carpathian Basin. Contrarily to that, the Orlovat section contains a relatively small contribution of coarser particles during the Early Pleniglacial compared to the other sections in the Carpathian Basin (Fig. 4). Bokhorst et al. (2011) proposed that beside reduced wind speed, a shift in the source area caused by a change in the wind direction may have influenced accumulation rates and contributions of coarser material. Generally it is proposed that the Carpathian Basin was under the influence of north and/or northwest winds during the Last Glacial (Bokhorst et al., 2011; Markovic´ et al., 2008; Sebe et al., 2011). Therefore it is more likely that a higher contribution of finer and medium fractions at the Orlovat section witness the change of wind directions, and thus provenance, rather than wind speed. A shift from southeastern winds during MIS 5 to north/northwest winds during MIS 4 would imply a change in the source area. There are no source areas rich in coarse particles north of the Orlovat section, and therefore north/northwest winds would not be suitable for the accumulation of coarse material. Concluding, the most likely scenario would be that during MIS 5 strong southeast winds were dominant over the south Banat region, possibly having an influence on the wider region, while during MIS 4 north/northwest winds prevailed. During this period, the investigated section was most probably continuously exposed to far distance transport of particles. Sedimentation rates during MIS 3 and MIS 2 were low or/and sediment formed within this period was eroded (see Section 5.4) and Orlovat may not present a continuous record. Therefore it is not possible to reconstruct aeolian detailed dynamics for this

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period from Orlovat. According to the luminescence ages (Timar-Gabor et al., 2015), the uppermost 2 m (units 8 and 9) mostly present Holocene sediment. It may be expected that during the Holocene a higher sand abundance would be recorded at the Orlovat section as the southeast winds should characterize interglacials. Although there are some excursions of the higher sand content, they are well below the high values observed during the formation of the S1 paleocomplex. However, comparing the Orlovat section to the other sections in the Carpathian Basin, the Holocene part is characterized by very high accumulation rates (in particular unit 8). Since no high accumulation was observed elsewhere, southeastern winds could explain these unusually high accumulation rates at Orlovat. A lower sand contribution in comparison to the S1 paleosol may be explained by the additional new and closer source area which was not present during S1 paleosol formation (see Section 5.4.). This new source area could dilute the contribution of sand originating from the Deliblato Sands with finer particles. Also, high accumulation rates induced by the strong wind activities could explain the delay in onset of the Holocene soil formation. Hence, it can be concluded that southeast winds prevailed during the Holocene. It can be reliably asserted that southeastern winds prevailed during MIS 5 and the Holocene, but we are more careful with the statement that the termination of these wind occurred during MIS 4. It is known that during the Holocene until the 18th century (before it was anthropogenically forested) the Deliblato Sands represented an active dune field area (Bukurov, 1982). It might be assumed that during MIS 5 this was also the case. However, it may be possible that during the Last Glacial, the Deliblato Sand was consolidated under a stable vegetation cover, and therefore, could not be the source area for the coarser particles. Even a higher precipitation during the interglacial may not have been a strong controlling factor of the plant cover in sandy areas, as it percolates fast. A higher evapotranspiration during interglacials is not favorable for a regular vegetation growth as well. A dune field with no vegetation cover would have been more active and would have possibly been located closer to the Tamiš loess plateau than today (see Fig. 1). During the Last Glacial, although the precipitation was lower, the lower evapotranspiration could provide higher soil moisture favoring a vegetation cover on the dune field. Some studies have even proposed a pattern of ‘‘warm and dry interglacials’’ and ‘‘cold and humid glacials’’ as a potential regional phenomenon (Obreht et al., 2014; Zech et al., 2009; Zech et al., 2013). Therefore, the vegetation cover of the dune field during the glacial could have prevented further deflation of sand and its accumulation in the loess layers. In addition, very high sedimentation rates observed at the Titel loess plateau during glacial conditions (Fig. 4) could be better explained with southeast winds, since the Danube and Tisa rivers as the main source area are located south and east from the plateau. Similar conclusions can be applied to the eastern part of the Srem loess plateau, where the Danube as the main source area is located east of the plateau. Observed high sedimentation rates could be hardly explained by the north/northwest winds proposed by Sebe et al. (2011). It is possible that contrary to the north Carpathian Basin, where the north/northwest winds prevailed (Sebe et al., 2011), the south Carpathian Basin was permanently under the influence of southeastern winds. Besides, it can be confidently claimed that southeastern winds were prevailing at the south Banat region during the Last Interglacial, we here cannot prove or rule out their existence during glacials. 5.2. A grain-size perspective for the reconstruction of paleoenvironmental conditions As already shown in study of Obreht et al. (2014), clay fractions do not necessarily represent a sensitive paleoclimate proxy. It was

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noted earlier that the usual grain-size patterns, in particular in the clay content, do not necessarily document enhanced rates of pedogenesis during the Holocene and MIS 5 (Stevens et al., 2011), as higher sediment accumulation rates during glacial periods may mask evidence of pedogenesis such as clay mineral formation. The higher clay content in loess units can be a product of continuous weathering during low accumulation rates. The abundance of sand particles in clay-poor layers and vice versa speaks in favor of this hypothesis. In the Carpathian Basin, the magnetic susceptibility is generally enriched in paleosols due to a higher amount of ferrimagnetic minerals formed during pedogenesis and clearly reflects changes in pedo- and lithostratigraphy (e.g. Buggle et al., 2009, 2014; Liu et al., 2013; Markovic´ et al., 2009). However, Markovic´ et al. (2014b) observed irregularities in the magnetic susceptibility at the Orlovat section associated with a gradual transition between the bottom of the S1 and the L1. This transition of magnetic susceptibility is comparable to the contribution of clay and sand fractions in the S1 paleosol, and can be explained by the grain-size distribution in the S1 paleosol. Sand fractions usually have a lower magnetic susceptibility than other grain-size fractions due to the diamagnetic properties of quartz. The correlation between an increase of sand and a decrease of magnetic susceptibility can indicate that the sediment was influenced by an input of sandy material during the soil formation. Higher values in magnetic susceptibility should be expected if the sand was present before the soil formation started (e.g. Jary and Ciszek, 2013). It is very likely that units 3 and 4 represent a syngenetic soil that formed while coarser material accumulated and did not overprint the already formed paleosol. The high sedimentation rates characterized by coarser fractions could partly mask pedogenetic features, such as the clay translocation and the magnetic susceptibility, but they may not completely mask the formation of soil. We can conclude that at the Orlovat section the granulometry is not only dependent on paleoenvironmental and paleoclimatic conditions, but also on the textural distribution of the accumulating material, which might have different source areas. The unusually high sedimentation rates during the humid periods have also been observed in the Chinese Loess Plateau (e.g. Stevens et al., 2008; Stevens and Lu, 2009). At the Orlovat section, the high sedimentation rates of coarser particles did not completely mask the formation of soil(s). Also, low accumulation rates observed in the upper part of unit 5 and unit 6 (characterized by a higher clay contribution) did not enable soil formation. This might indicate that soil formation during warm and humid periods (interglacials) cannot easily be masked by high sedimentation rates. Furthermore, low sedimentation rates cannot (always) enable soil formation during cold and dry period such as glacials since precipitation is an important factor. According to d13C values from the Carpathian Basin (Hatté et al., 2013; Obreht et al., 2014; Schatz et al., 2011; Zech et al., 2013), Mediterranean-like climate with precipitation in spring and autumn was dominant during the last interglacial, as the precipitation during the warmest period will increase the abundance of C4 vegetation (Yang and Ding, 2006). Although summer precipitation was low, the high productivity of biomass was enabled over the year (Obreht et al., 2014). Lukic´ et al. (2014) presented that the Melanization Index (the color measurement proxy indicating an accumulation of humus and humic substances in the soil) shows much higher values in the S1 paleosol than in loess units with rich clay fractions. We propose the annual duration of vegetation cover and biomass productivity during the year (probably related to the length of the growth period) as an important factor for the formation of humus. This also shows that soil formation during periods with high biomass production such as MIS 5 could not be easily masked by increased accumulation rates. During glacial conditions, the annual

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production of biomass was probably much lower due to a shorter growth period. 5.3. Geochemical characteristics (simple ratios and weathering indices) From major elements, Al2O3 and CaO are highly influenced by the CaCO3 content throughout the whole section. A similar pattern can be observed for Na2O and K2O. MgO does not show any correlation to grain-size and CaCO3 content. However, just the simple comparison of element contents can be biased due to a systematic enrichment or dilution of carbonate and quartz minerals. On the other hand, element ratios are usually a reliable proxy for the geochemical characterization of the sediment. The simple ratios Ba/Sr and Rb/Sr are assumed to indicate weathering and have been widely used in the studies of the Carpathian Basin (Bokhorst et al., 2009; Buggle et al., 2011; Újvári et al., 2008, 2014a; Varga et al., 2011) (Fig. 7). Buggle et al. (2011) suggested that these ratios are influenced by the CaCO3 content. Schatz et al. (2014) indicated that such a correlation has not been observed at the Tokaj sequence (Hungary). At the Orlovat section, Ba/Sr and Rb/Sr ratios are not strongly influenced by the CaCO3 content. A reason for this may be that Sr is highly correlated to MgO at the Orlovat section. This should not be considered as a general rule, as in other studies from the Carpathian Basin (e.g. Bokhorst et al., 2009; Buggle et al., 2008; Varga et al., 2011) it seems that the Sr content is controlled by the distribution of both, MaO and CaCO3. Although weathering indices highly fluctuate, the general trends clearly show similarities to grain-size data. Decrease in finer fractions indicates a decrease of Al2O3, while increase in coarser particles indicates an increase of Na2O and vice versa. The weak paleosol at the top of unit 5 is characterized by low values of CIA and CPA, probably due to a high input of relatively coarse particles. One should be careful with interpretations of weathering indices in loess–paleosol units, as these can be highly influenced by grain-size changes. Unit 7 shows unsystematic and large fluctuations in the weathering indices, though grain-size distributions are relatively stable. Considering the luminescence ages, this may confirm that this layer contains erosional surfaces and relocated sediment. In contrast to the units below, units 8 and 9 provide CPA and CIA values that are characteristic for the Carpathian Basin region, having lower values in loess than in the modern soil. Some similarities can be observed between weathering indices and grain-size distributions, but they do not strongly correlate in these units. Therefore, the interpretation of weathering based on elemental ratios and weathering indices may be biased at the Orlovat section, as the ratio values are highly influenced by the grain-size distribution, especially in units 1–6.

enriched in coarser fractions, whereas Ni is generally preserving a signature of the provenance (Újvári et al., 2014a). Also the Zr/Si ratio may reflect changes in the parent material. Th/Ni is a good indicator of igneous chemical differentiation processes since Th is incompatible, whereas Ni is a compatible element within the igneous systems (McLennan et al., 1993). The SiO2/Al2O3 ratio can represent a change in parent material, but also a change in variations of sedimentary sorting linked to the distance of transportation (Hao et al., 2010). The Al2O3/K2O ratio is influenced by weathering, but changes in the ratio can show a dominance of K-feldspar contribution, as can be achieved by the A–CN–K diagram. All studies performed in the Carpathian Basin (Schatz et al., 2014; Újvári et al., 2008) and the Lower Danube Basin (Buggle et al., 2008, 2011) have shown a common pattern of weathering presented within the A–CN–K diagram (Fig. 8). All samples from these studies plot on a line parallel to the A–CN join. This pattern presents a distribution of material with different extents of chemical weathering, resulting in a predominant removal of silicatic Ca and Na due to the greater destruction of plagioclase and a relatively slow removal rate of K from K-feldspar. At the Orlovat section samples are also plotted on the line parallel to the A–CN join. However, samples are not plotted within one line, as it was observed in studies before, but have three different patterns of distribution. Samples of units 1–5 vary on the line that has a similar distribution as in the previous studies. The distribution line of samples of unit 6 are slightly dislocated toward the K apex, and the distribution line of samples from units 7 to 9 are even more dislocated toward the K apex (Fig. 8). Although there are three different patterns, the distribution of values within each pattern varies exclusively on the line parallel to the A–CN join. Hence, these patterns are not influenced by differences in K-feldspar weathering, as the weathering line shows a clear destruction predominantly of plagioclase, but rather a change in parent material K-feldspar content. The samples of units 1–5 are similar to results from previous studies and contain less K-feldspar than the other units at this section. Unit 6 presents a transition zone from an old to a new provenance of material enriched in K-feldspar, whereas units 7–8 are completely exposed to a new source. This can be also observed using the Al2O3/K2O ratio (Fig. 7). Since units 1–5 have similar weathering pattern as other sections in the Carpathian Basin, it may be assumed that the

5.4. Potential changes in source material The provenance of coarser material and sand in the S1 paleosol unit was discussed in Section 5.1. The Deliblato Sands are probably the source of coarser and sand fractions, whereas transport mechanism is most probably the Košava wind. However, provenance of fine and medium fractions cannot be concluded based on the dominant wind directions. Although the elemental ratios and weathering indices do not reliably represent the weathering processes at the Orlovat section, some ratios, which are not influenced by weathering and pedogenesis, may be used to investigate the provenance of the sediment. The elements Th and Zr are enriched in felsic rather than in mafic rocks, because they are highly incompatible during most igneous melting and fractionation processes (Taylor and McLennan, 1985). For example, Zr/Ni ratios are useful in some cases, as Zr is

Fig. 8. A–CN–K diagram.

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provenance for these units can be found in the Danube and/or Tisa River sediments. Buggle et al. (2008), Újvári et al. (2008) concluded that the geochemical results cannot prove an accurate provenance, but rather can rule out some areas as source area. Accordingly, neither the Danube nor Tisa could be more precisely favored or ruled out as a source area here. However, it can be claimed that sediments from one or both of these rivers were the main sediment source area. Even a contribution of particles from the Deliblato Sands should not have a very different signal, as these particles primary originate from Danube sediment. Differences are expected to be limited to grain size and sorting during aeolian transport. A gradual change in source of material within unit 6 can be best explained by a gradual approach of new source material. Only rivers could be a source area that can approach to the Orlovat section gradually. Since the geochemical imprint of the new source differs from the Danube and Tisa River signals, the only possible source could be the relatively small Tamiš and Begej Rivers. However, the catchment areas of these rivers are geochemically unexplored and therefore this hypothesis cannot be confirmed or ruled out. Nevertheless, relatively low and stable (do not exceed 50 ppm; Fig. 6) Ni contents exclude all areas with mafic and ultramafic rocks as source area. Therefore, the Tamiš and/or Begej Rivers as a new source area and the southwest Carpathian Mountains as a provenance area seem to explain observed changes well. The enhanced fluvial dynamics of a paleo-Tamiš river could explain the hiatus observed at the Orlovat section. Fluvial activities probably eroded sediment accumulated after 40 ka. Studies from the south Carpathian Basin showed a relatively strong developed interstadial paleosol (L1SS1) at 40 ka (Fuchs et al., 2008; Schmidt et al., 2010; Stevens et al., 2011). Since a paleosol did not develop/preserve, erosion before 40 ka seems a plausible explanation. According to the luminescence ages, units 7–9 mostly correspond to the Holocene. These units are characterized by K-feldspar rich material, probably originating from the Carpathian Mountains. However, not only the K-mineral abundance suggests a change of source material, but the SiO2/Al2O3 ratio (Fig. 7) gives evidence of a new pattern in sorting of grain-size, which is linked to different transport distances. A higher SiO2/Al2O3 ratio in the units 8 and 9 confirms a change in the distance of the source area. Additionally, small rivers establish a new grain-size pattern in units 8 and 9 where complementary fluctuations can be observed in medium and coarse silt, whereas the fluctuations of medium silt are mostly influenced by sand in the units below. Therefore, it can be assumed that sedimentation during late MIS 2 and the Holocene was mainly conditioned by smaller rivers as the source area (according to the current situation influenced by the Tamiš River). Contrary, during MIS 4 the sedimentation was mainly connected to long-distance transport.

6. Conclusions Our study confirmed that the Orlovat section was exposed to different sedimentological conditions as compared to other sections studied in the Carpathian Basin. The grain-size and geochemical data enabled us to provide a better insight into sedimentological conditions. Despite the slope position, it seems that slope-related processes did not play a major role. The sedimentological conditions are probably related to different geomorphological features in the vicinity of the section. Differences in the dominance of wind direction played a major role for the sediment accumulation. We assume that the high sand input of the S1 paleosol and also elevated impute into the modern soil is strongly influenced by the Deliblato Sands as source area. The Košava wind with a southeast–northwest wind direction is proposed as a

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transport mechanism and the most dominant wind for the South Banat region. The source material for the accumulation of loess has changed a few times during the last 160 ka at the Orlovat section, and it is assumed that the source and its distance from the Orlovat section triggered different paleosignals and influenced the sediment accumulation rates. Therefore, we would like to highlight the importance of understanding changes of source area and material, as well as factors controlling loess accumulation, such as wind directions and sediment supply. Acknowledgments The investigations were carried out in the frame of the CRC 806 ‘‘Our way to Europe’’, subproject B1 The Eastern Trajectory: ‘‘Last Glacial Paleogeography and Archeology of the Eastern Mediterranean and of the Balkan Peninsula’’, supported by the DFG (Deutsche Forschungsgemeinschaft). We are grateful to Nemanja Tomic´, Dragan Popov and Rastko Markovic´ for the help in the field. We thank Marianne Dohms for her help with laboratory analysis and Janina Bösken for commenting on the manuscript.

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