From micromorphology to palaeoenvironment: The MIS 10 to MIS 5 record in Paudorf (Lower Austria)

Catena 117 (2014) 60–72

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From micromorphology to palaeoenvironment: The MIS 10 to MIS 5 record in Paudorf (Lower Austria) Tobias Sprafke a,⁎, Christine Thiel b,c, Birgit Terhorst a a b c

Institute of Geography and Geology, University of Würzburg, Am Hubland, 97074 Würzburg, Germany Nordic Laboratory for Luminescence Dating, Department of Geoscience, Aarhus University, DTU Risø Campus, Frederiksborgvej 399, 4000 Roskilde, Denmark Centre for Nuclear Technologies, Technical University of Denmark, Risø Campus, Frederiksborgvej 399, 4000 Roskilde, Denmark

a r t i c l e Keywords: Middle Pleistocene Loess Polygenetic soils Micromorphology Post-IR IRSL Lower Austria

i n f o

a b s t r a c t The loess–palaeosol sequence (LPS) in Paudorf, Lower Austria is characterised by varying dust sedimentation rates, re-deposition with admixture of local rock fragments, erosion and pedogenic overprinting. Detailed semi-quantitative micromorphological analyses reveal the complex genesis of the palaeosols/pedocomplexes and the palaeoenvironmental conditions present during their formation. Our genetic model of landscape formation is underpinned with luminescence (post-IR IRSL) ages; the resulting chronological framework indicates that the basal loess sediment was deposited during marine isotope stage (MIS) 10. The overlying lower pedocomplex experienced a complex genesis in a forest-steppe environment during MIS 9. In the sand– loess sediment of MIS 8 a (forest-)steppe palaeosol (MIS 7) developed. The overlying MIS 6 loess sediment shows several intercalated Cryosols. The upper pedocomplex is a Chernozem (MIS 5c[–a?]) developed in a mixture of re-deposited Cambisol (attributed to MIS 5e), dust and local material. This study shows that the palaeoclimatic conditions in the study region were comparable to those of Central Europe during the last two glacial periods, whereas the conditions were more comparable to the Pannonian Basin climate during the last three interglacials. © 2013 Elsevier B.V. All rights reserved.

1. Introduction Loess–palaeosol sequences (LPS) are complex palaeoenvironmental records located in the planet's temperate belt. These climate archives present in these sequences are important to the better understanding of landscape responses to major climatic fluctuations during the Quaternary. Pedogenesis (occurring during stable periods) or dust sedimentation (occurring during periods of activity) depends on temperature, humidity and vegetation cover; these control the formation of these terrestrial sequences (Catt, 1991; Kemp, 1999). The (quasi-) continuous LPS in the loess plateaus of China, Central Asia, and Southeastern Europe have been used as references for Eurasian loess research (cf. Bronger, 2003; Marković et al., 2011), but additional geographic locations need to be investigated to allow the reconstruction of the regional characteristics of the palaeoenviroment. Lower Austria is of particular interest in this respect because of its key location between oceanic and continental climates. Fink (1956) designated an area at the eastern margin of the Bohemian Massif as ‘transition area’ between the ‘humid-’ and the ‘dry loess landscape’. In the area around the city of Krems, the large ‘loess river’ Danube (cf. Smalley et al., 2009) leaves the narrow Wachau Valley (Bohemian

⁎ Corresponding author. Tel.: +49 931 31 86168. E-mail address: [email protected] (T. Sprafke). 0341-8162/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.catena.2013.06.024

Massif) and enters the Eastern Alpine forelands; the LPS around Krems are the thickest in Austria. However, these sequences are polygenetic and because of their topographic position (on slopes) they contain discontinuities; this complexity results from unsteady dust sedimentation, re-deposition, admixture of local material, pedogenic overprinting, and erosion. This has recently been shown for Paudorf by Sprafke et al. (2013) using detailed field analyses, granulometry and high-resolution carbonate and colour measurements. At the beginning of the 1970s (Fink, 1969, 1976), it was realised that the complexity of the sequences and the lack of reliable dating techniques prevented straightforward interpretations and correlations. Because of this the former type localities in Lower Austria (i.e., Krems, Göttweig and Paudorf; Brandtner, 1954, 1956; Fink, 1954, 1956, 1961; Götzinger, 1935) lost their importance. The first attempt to establish a reliable chronological framework for Lower Austrian key sites made use of both thermoluminescence (TL) dating and amino acid racemisation (Zöller et al., 1994). In more recent studies, Thiel et al. (2011a,b,c) presented post-IR infra-red stimulated luminescence (post-IR IRSL) ages for several Lower Austrian sites, including the upper part of the classic LPS Paudorf (Thiel et al., 2011b). It appears that this technique is not prone to significant overor underestimations in the applicable time range (Buylaert et al., 2012) and so unambiguous correlations with the marine isotope record and other LPS now seem possible. Even if supported by a reliable chronology, the extraction of palaeoenvironmental information from polygenetic sequences is

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challenging. Climate proxies derived, for example, from magnetic parameters, granulometry or (bio-)geochemistry (e.g., Antoine et al., 2009; Bokhorst et al., 2009; Buggle et al., 2011; Maher et al., 2003; Zech et al., 2009) are influenced by different sediment sources, re-deposition and pedogenic overprinting. In contrast, the microscopic study of soils and sediments provides a useful approach to unravelling the development of (palaeo-)environments. The role of micromorphology in studies of loess–palaeopedology (particularly for the study of the balance between sedimentary and pedogenic processes and for the reconstruction of development stages) has been recognised and such studies have been undertaken by many authors (cf. Kemp, 1999 and references therein). The components may be investigated in an at least semiquantitative way, but also in the form of a qualitative ‘functional investigation’ (Stoops, 2003). The fundamental soil equation introduced by Dokuchaev (1883) suggests that, in similar parent material and relief position, the degree of soil development during periods of morphologic stability under closed vegetation cover is primarily a function of climate and time. The macroscopic and microscopic identification and description of pedogenetic phases (cf. Fedoroff et al., 2010; Kühn et al., 2006) is a robust approach to obtaining qualitative to semi-quantitative palaeoenvironmental information. This study uses a detailed micromorphological investigation together with post-IR IRSL dating to obtain a solid chronology for the LPS Paudorf. Basic descriptions and analyses of parts of the classic LPS Paudorf (Fink, 1954, 1976) and selective studies on chronology (Fink, 1976; Noll et al., 1994; Thiel et al., 2011b; Zöller et al., 1994), malacology (Fink, 1976) and micromorphology (Kovanda et al., 1995) have already been published and these are also used here to strengthen the palaeoenviromental reconstruction dataset. Our study focuses on the two pedocomplexes and the other palaeosols recorded in the LPS Paudorf. The resulting data provide the foundation for a genetic model which includes the major stages of landscape formation. The results are discussed with respect to other loess records from Austria and the Pannonian Basin. 2. The Paudorf study site Paudorf locus typicus is a 70 m long and 12 m thick outcrop in an abandoned brickyard in the northwest of the village Paudorf (Fig. 1). It is located at 265 m above present day sea-level (a.s.l.), on the lower slope of the Waxenberg (500 m a.s.l.; Figs. 1 and 2-A). The surrounding mountains consist predominately of granulite, composed of quartz,

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orthoclase, oligoclase, garnet, and biotite (Matura, 1989). The polygenetic downslope LPS is subdivided into eight major units, each consisting of several subunits/horizons (Fig. 2-B; for a detailed description see Sprafke et al., 2013). The most prominent units are two pedocomplexes: the upper (P2) is ~1 m thick and classically referred to as ‘Paudorfer Bodenbildung’ (e.g., Fink, 1976). It has a brownish colour with characteristic reddish speckles (P2c). The lower pedocomplex (P7) is more than 2 m thick. In the lower part a blackish-brown A horizon (P7g) and a light brownish B horizon (P7h–i) are visible below a colluvial layer (P7f). The middle part of the pedocomplex is made up of reddish-brown B horizons (P7c–e). This is covered by a brown A(B) horizon (P7b), with a colluvial layer in the uppermost part (P7a; Fig. 2-A and B). Throughout the sequence silt and fine sand of aeolian origin dominate the substrate. Coarser detritic components have a clear granulitic composition, which can be related to the upper slope area. The units P1, P3 to P6 and P8 consist mainly of a yellowish-grey substrate that forms subpolyhedral to blocky aggregates. The aggregation of the substrate is probably caused by ‘loessification’ (cf. Smalley et al., 2011; Svirčev et al., 2013). The units P1, P3 to P5 and P8 are, in general, dominated by silt (51–63%) and have carbonate contents varying between 10% and 25%; unit P6 has exceptional high sand contents (32–43%) and lower carbonate contents (b 10%; Fig. 2-B, cf. Sprafke et al., 2013). The upper part of this unit is intercalated by a brownish horizon (P6b). Unit P5 is characterised by three bleached horizons (P5a,c,e) interpreted as Cryosols. Unit P4 is made up of heterogeneous loess sediment with weak bleached areas. Unit P3 is most comparable to typical loess as it has the highest silt content and few coarser components (Pye, 1995). The upper pedocomplex (P2) has been assigned to MIS 5 (Thiel et al., 2011b; Zöller et al., 1994). The sequence below unit P2, which includes several palaeosols and the more than 2 m thick lower pedocomplex (P7), formed during the Middle Pleistocene (Thiel et al., 2011b). The Eemian (MIS 5e) palaeosol, which is included in unit P2, has not reached the pedogenetic development of a Luvisol, which is typical for Central Europe (e.g., Frechen et al., 1999; Jary and Ciszek, 2013; Semmel, 1968; Terhorst et al., 2002). In contrast, the lower pedocomplex is in its middle part characterised by enhanced weathering and the occurrence of clay coatings; the relatively strongly weathered middle part is bracketed by horizons attributed to a more continental climate. The question of whether the more intensive pedogenesis is a function of time or of climate remains open (Sprafke et al., 2013).

Fig. 1. Location of the studied loess–palaeosol sequence (LPS) Paudorf. Indicated are also the locations of the LPS Göttweig-Furth (GF) and Göttweig-Aigen (GA).

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Fig. 2. Overview of the outcrop in Paudorf. (A): Outcrop and sampling positions outside the Paudorf II sequence. (B): Composite sequence showing sampling depths and grain size distributions (modified after Sprafke et al., 2013). (C): Luminescence sampling positions from P8. Correlation to the standard sequence is made (brown lines) according to stratigraphic observations.

3. Methods 3.1. Micromorphology A total of 18 undisturbed samples were collected from the main palaeosol/pedocomplex horizons and labelled according to the subunits (Fig. 2-A and B). Blocks were air-dried, impregnated with hardening resin, cut in slices, mounted on a glass slide and polished to a thickness of 25–30 μm (cf. Beckmann, 1997). Detailed semi-quantitative analyses were made under a Leica DMRB polarising microscope in plane polarised and crossed polarised light (PPL, XPL) following the guidelines of Stoops (2003).

3.2. Luminescence dating Samples for luminescence dating were taken by hammering metal tubes into the cleaned loess wall; the positions are indicated in Fig. 2. The tubes were opened under red light, and the outer material (1–1.5 cm) was discarded. The samples were treated with 10% HCl and 10% H2O2 in order to remove carbonates and organics, respectively. The polymineral fine grain fraction (4–11 μm) was obtained by repeated settling and washing.

The polymineral fine grains were mounted on aluminium discs from an acetone suspension. Six aliquots per sample were measured on an automated Risø TL/OSL reader (DA-20; Thomsen et al., 2006) equipped with a calibrated 90Sr/90Y beta source. For all samples, the post-IR IRSL protocol (single aliquot regenerative procedure) described in Thiel et al. (2011a) was employed: After a preheat of 320 °C (60 s) the aliquots were held at 50 °C and stimulated with IR diodes (emission at 870 nm) for 200 s; this stimulation was followed by a second IR stimulation at 290 °C (200 s; referred to as pIRIR290). The response to a test dose of ~160 Gy was measured in the same manner prior to a hightemperature IR illumination (325 °C for 100 s). The luminescence was detected through a Schott G39/Corning 7-59 filter combination in the blue-violet region. The initial 2 s of the decay curve were integrated minus a background from the last 60 s. Samples for dose rate determination were taken from immediately around the tube samples. The material was dried, ashed (450 °C, 24 h) and ground (and thus homogenised) prior to casting in wax. The casts were stored at least 3 weeks prior to gamma counting to ensure equilibrium between radon and its daughter nuclides. Cosmic dose rate calculation is based on the data presented in Prescott and Hutton (1994). For all samples, a water content of 15 ± 5% and an a-value of 0.08 ± 0.02 (Thiel et al., 2011b) were used for calculation of the total dose rate to the samples.

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Table 1 Results of semi-quantitative micromorphological analyses. The classification corresponds to the recommendation of Stoops (2003) and is as follows: – = none, * = very few, ** = common, *** = frequent, **** = dominant, ***** = very dominant. Feature relations as illustrated in Figs. 3, 4 and 5 are discussed in Section 5. The palaeosols are highlighted in grey. aQuantified relatively to their overall abundance (voids — overall porosity) bQuantified relatively to their overall abundance (clay minerals — abundance). Porostriated and granostriated b-fabrics are subdivisions of striated b-fabrics (Stoops, 2003), but are treated separately in this table.

4. Results 4.1. Micromorphology The results of the semi-quantitative analyses of microscopic components are summarised in Table 1 and described in the following sub-sections. The relations of the micromorphological features and their qualitative information about sequential processes are discussed in Section 5.

4.1.1. Coarse mineral fraction Almost all grains are subangular to angular. The admixture of hydrothermally altered/pre-weathered local substrate and synto postpedogenic admixture of unweathered allochtonous components due to pedoturbation did not allow for an unambiguous estimation of the degree of in situ weathering during pedogenesis. Fig. 3-A exemplifies a granulite fragment with garnet crystals, partly altered to clay hydrothermally or by intensive ancient weathering.

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In each sample except P2b and P5e (sub-)angular granulite fragments of N2 mm can be detected. Granulite or its mineral components dominate the sand fractions. In general, rock fragments dominate the coarse sand fraction, whereas the finer fractions contain single minerals like quartz, orthoclase, plagioclase, and garnet. The latter is most frequently found in the sand rich unit P6c. Biotite is mostly of fine sand size, especially in the P5 and P6b sections. Overall, the mineralogical spectrum in the fine sand is more diverse than in the coarser fractions. The silt fraction contains mostly quartz and feldspars, with a broad spectrum of silicate minerals, especially in the samples taken from units P5 and P6c. Primary carbonates are present to varying degrees, although most parts of the lower pedocomplex (unit P7) are free of primary carbonates. It has to be noted that fine silt minerals could not be identified unambiguously under the optical microscope; they are often incorporated in the micromass. 4.1.2. Secondary carbonates and clay Secondary carbonates are present in various forms throughout the sequence (Table 1). Micrite appears in the form of impregnations (Fig. 5-A) and hypocoatings in the upper pedocomlex (P2), next to infillings of needle-fibre calcite (lublinite; cf. Durand et al., 2010). In the thin sections from P5 and P6 as well as in the upper and lowermost parts of the lower pedocomplex (P7) micritic hypocoatings and impregnations are also common. In the central parts of unit P7, infrequent micrite infillings are the only type of secondary carbonates; they appear concentrated in larger pores. Unit P8 is most rich in micrite, which is partly present in the form of lublinite. In unit P2, dense sparitic infillings in the form of calcified root cells (CRC) are the prevailing type of secondary carbonates. Loose infillings or crystals dispersed in the groundmass are commonly disturbed CRC (Fig. 5-B). Calcified earthworm casts are a common form of calcite nodules in unit P2. In both samples from unit P5 dense sparitic infillings are present, differing in their morphology from CRC (Fig. 4-A). Overall, these samples as well as those from the lowest units of the sequence show a large amount of sparite. In the upper parts of unit P7, only little sparite is present; further down the sequence it is missing. The upper pedocomplex shows a high content of clay minerals (Fig. 5-C and D), whereas in the samples from unit P5 (Fig. 4-A) and unit P8 they are more or less absent. The lower pedocomplex (unit P7) is most rich in clay minerals in the groundmass, especially in the central parts (P7c–e; Fig. 3-C and D). Above and below, the clay content is lower (Fig. 3-B). The majority of the clay is randomly oriented (speckled b-fabric). In P7c–e (Fig. 3-C), to some extent in P2 (Fig. 2-D), and in P6b, more oriented clay is common; in the latter sample, clay often surrounds coarse grains. Clay coatings can only be observed in the lower pedocomplex (P7; Fig. 3-D, E and F). In the lower part of P7b, only traces of very thin clay coatings can be found. Down to P7e–f the quantity of this pedofeature increases continuously. Only few examples of potentially undisturbed illuvial clay appear in the middle part of unit P7. In P7f few thicker clay coatings are visible; these appear occasionally as semi-continuous (Fig. 3-E) and mostly as fragments (Fig. 3-F). Single fragments of redeposited clay coatings can be observed in P5a (Fig. 4-A) and P6b. 4.1.3. Further features and overall structure In P7d, above the units that are significantly enriched in illuvial clay, iron nodules are a common redoximorphic feature. In the upper parts of both pedocomplexes there is enrichment of typic/ nucleic manganese nodules. Dendritic manganese nodules show no clear trend in their distribution. A striking feature is the presence of charcoal fragments in almost every sample, with the highest concentration in P2b. In contrast to the lower pedocomplex (unit P7), which is more or less free of carbonates, the upper pedocomplex (unit P2) contains mollusc fragments. In general, the samples from the upper pedocomplex exhibit the highest porosity of all samples. Channels are common and compound packing voids are frequent due to the mostly granular and partly

subangular blocky structure of the substrate (Fig. 5-A and D). The microstructures of the samples from units P5 and P6 as well as from the lowermost parts of the sequence are mostly apedal with a low porosity. An exception is P6b which shows a well-developed granular structure (Fig. 4-B). It should be noted that the Cryosol samples from P5 do not show lenticular structures but only few domains with oriented elongated minerals (Fig. 4-A). The lower pedocomplex (unit P7) contains areas of granular and subangular blocky microstructure (Fig. 3-F). Compound packing voids in this more compact unit (compared to P2) are reduced at the expense of vughs. The clay rich central parts of unit P7 contain planar voids. 4.2. Luminescence measurement performance and age estimates The measurement protocol passed all standard quality tests (Wintle and Murray, 2006). In a previous study on the same section, Thiel et al. (2011b) have conducted a dose recovery test (their sample 1404) using the same measurement settings as in our study. Without subtraction of a residual dose, which was on average ~13 Gy, the measured to given ratio was 1.04 ± 0.02, and with subtraction of the residual dose it was 0.99 ± 0.02. These values are clearly in the acceptable range of ±10% around unity, independent of the residual subtraction. In several studies on pIRIR290, the size of any residual has been a matter of debate (e.g., Stevens et al., 2011) and it is not clear how much of the residual signal originates from thermal transfer and how much is a truly unbleachable component (Buylaert et al., 2011, 2012). In the case of old samples, a residual signal of ~13 Gy (equivalent to ~4.5 ka) is small compared to the measured equivalent dose; because of this we did not correct our measured equivalent doses for any residual. Further, we did not correct for any signal loess due to anomalous fading. Fading measurements for the Paudorf section have been presented in Thiel et al. (2011b); the data imply negligible signal loss. In addition, Buylaert et al. (2012) have clearly shown that the pIRIR290 signal is stable over the time of interest and thus no fading correction is needed. A summary of dose rates, equivalent doses and ages is given in Table 2. The dose rates are all around 3 Gy/ka; these are typical of dose rates found in Lower Austrian loess (e.g., Thiel et al., 2011a,b,c; Zöller et al., 1994). The average equivalent doses range from 386 ± 8 Gy (sample 123043) to ~ 900 Gy (for the three lowermost samples). It is interesting to note that the measurements even in the high dose region are very reproducible, as indicated by the small error (given as standard error). The ages for this section (below the Paudorf soil) range from 123 ± 10 ka to N300 ka (Table 2 and Fig. 6). 5. Phases of development and palaeoenvironmental reconstruction On the base of sedimentological and pedological analyses, Sprafke et al. (2013) argued for the overall polygenetic character of the LPS. In the following section, the genesis of the LPS Paudorf is reconstructed using both published data and the relations of micromorphological features. With the exception of the upper pedocomplex, different phases are described first based purely on observations; then the findings are discussed with respect to the pIRIR290 dating results. 5.1. The basal loess (unit P8) and the lower pedocomplex (unit P7) 5.1.1. Parent material, pedocomplex formation and burial The genesis of the basal sandy loess (unit P8) can be attributed to aeolian sedimentation and loessification. In temperate latitudes, conditions favourable for these processes were present during glacial phases; therefore periglacial conditions most probably existed during the development of the loess-like sediment. The genesis of the lower pedocomplex (unit P7) can be subdivided into four main phases (cf. Fig. 7). Phase 1: The lowermost palaeosol (P7g–P7i) appears as a slightly truncated degraded Chernozem (Phaeozem), with a dark-brown A horizon

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Fig. 3. Photomicrographs of the lower pedocomplex (unit P7). Feature relations are discussed in Section 5.1. (A): Pre-weathered granulite fragment. Note the network of clay neoformations (birefringent) along cracks of the big garnet crystals (isotropic). (B): Speckled to striated b-fabric, few sand-grains with granostriated b-fabric. (C): Clay (partly oriented) in the groundmass. The area is free of clay coatings, except for the rounded aggregate of clay coatings in the left side of the micrograph. (D): Fragments of clay coatings scattered in the groundmass. (E): Relatively thick clay coatings, partly disturbed. (F): Fragment of thick clay coating and partly granular microstructure.

and few crotovina typical for forest-steppe ecosystems (cf. Bronger, 1976). The buried mollic horizon has only a weakly developed granular structure, which can be explained by fossilisation. The lack of primary carbonate and the presence of clay in the A horizon (P7g) as well as the secondary carbonates in the B horizon (P7h–i) and especially in the Ck horizon (P8) support the classification. The few areas of higher concentrations of clay in P7g can be explained by an admixture from above due to bioturbation.

Phase 2: Colluvial processes, macromorphologically evidenced by rock fragments oriented parallel to the slope in unit P7f, occurred after the formation of the Phaeozem. In general, the sand contents in P7f and the overlying horizons are significantly increased compared to the lower units. This reflects a reduced dust component and more input of local sediment caused by slope processes. The partly well-developed clay coatings and their fragments in P7f (Fig. 3-E and F) can be explained by illuviation from above and bioturbation processes.

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Fig. 4. Photomicrographs from units P5 and P6. (A): Groundmass dominated by silt (including primary carbonate) and micrite (secondary carbonate). Elongated minerals (mica) display some orientation. Fragment of clay coating in the middle of the right side, below dense sparitic infilling, different from calcified root cells (CRC). (B): Well-developed granular structure.

Phase 3: The units P7c–e are completely decalcified. It is the most intensely weathered part of the Paudorf LPS, as evidenced by the large amount of clay. Unit 7d contains more gravel, coarse sand and charcoal; it is interpreted as a colluvial layer. The only carbonates are micrite infillings, mostly present in larger voids, occasionally next to manganese hypocoatings. Dendritic manganese nodules are present throughout the LPS and are not diagnostic for pedogenesis. Thus, micrite in this part of unit P7 postdates pedogenesis.

The micromorphology shows an irregular pattern of pedality and pedofeatures. Areas with granular microstructure and apedal domains with channels and vughs can be explained by bioturbation, whereas planar voids are a result of clay shrinking. It has been suggested that granular microstructure can also be related to cryogenic processes (Van Vliet-Lanoë, 2010); however, this is not the case for the lower pedocomplex because a more evenly distributed granular structure would be expected related to cryogenic processes. The granules

Fig. 5. Photomicrographs of the upper pedocomplex (unit P2). Feature relations are discussed in Section 5.3. (A): Micrite impregnation on granular aggregates in channel free of micrite hypocoatings. (B): Dense sparitic infilling and sparite crystals in pores and in the groundmass. (C): Decalcified clay rich soil fragment with sharp boundaries and silty to fine sandy area, including carbonate. (D): Decalcified clay rich domain in groundmass (grano- and porostriated b-fabric) and in granular aggregates.

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have a composition and birefringence comparable to the groundmass (Fig. 3-F), indicating chemical weathering prior to a phase dominated by bioturbation. There are no clay coatings on the numerous channel walls but they are unevenly distributed around smaller aggregates (Fig. 3-E), or are present as fragments (Fig. 3-D and F) and less frequently as larger rounded aggregates (Fig. 3-C) incorporated into the groundmass. It is not clear whether the fragments and aggregates are signs of a re-deposition phase during two phases of clay illuviation or if they are a result of very intense pedoturbation (cf. Kühn et al., 2010). Phase 4: The degree of weathering decreases from the lower to the upper part of P7b. Primary carbonates, numerous channels and dark pigmentation give evidence of humification/bioturbation processes, reduced weathering intensity and increased dust input in a steppe environment. Charcoal pieces and high sand contents most likely originate from re-deposition, which also explains the admixture of primary carbonate and the lack of a well-developed granular structure.

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material. A temporary colluvial phase during MIS 9c and a subsequent onset of a further phase of clay redistribution is likely, given the global trend of temperature decline (cf. Fig. 6) and the various forms of disturbed clay coatings. After MIS 9c, the climate was more continental, as indicated by a humic steppe soil with primary carbonates in the upper parts of the pedocomplex. The mature development of P7c–e can be explained in two ways: the maturity can be regarded as function of time (ongoing weathering in forest-steppe ecosystem) or as function of parent material (carbonate free, pre-weathered parent material). Bronger et al. (1998) explained the enhanced weathering of the MIS13 to MIS 15 palaeosol (their F6) with a prolonged time for pedogenesis. Frechen et al. (2007) interpreted a Bt horizon recorded in a LPS in SW-Germany and dated to MIS 3 (middle last glacial) as having developed in sediment derived from an eroded soil; these authors also concluded that the maturity of their soil was driven by parent material and not climatic causes or time. 5.2. Sequence between the lower and the upper pedocomplex (units P6 to P3)

Burial: Increasing dust accumulation, re-deposition of sand (derived from disintegrated granulite and granulite fragments of local origin) characterise the degradation of the environment and the end of significant pedogenesis. 5.1.2. Reconstruction of the palaeoenvironments (MIS 10 to MIS 9) The pIRIR290 ages from above and below unit P7 (270 ± 24 ka and 316 ± 27 ka) suggest the formation of the pedocomplex during MIS 9 (Table 2, Fig. 6). It should be noted that these ages are close to (or beyond) the expected dating limit for feldspar, based on the shape of the dose–response curve, and so we cannot exclude the possibility that the material is older than suggested here. Nevertheless, we assume in the argument below that the ages do not suffer from gross systematic error; the following palaeoenvironmental reconstruction is suggested for the basal loess (P8) and the lower pedocomplex (P7; Fig. 7) based on the development stages discussed above. During MIS 10, periglacial conditions resulted in dust movement, i.e., loess deposition. In MIS 9e, a Phaeozem developed in the loess during a forest-steppe environment. In MIS 9d, degradation took place under cooler climate conditions, which caused re-deposition and partially truncation of the Phaeozem. However, there is insufficient evidence for periglacial conditions in this period. Global records show that MIS 9c was cooler than MIS 9e (cf. Fig. 6 and references therein). The relatively strong weathering of P7c–e is remarkable in this context. Clay illuviation might be explained by significantly moister conditions, resulting in a forest ecosystem with Luvisol development. However, it is more likely that P7c–e developed in a substrate which was already free of carbonates and partly weathered. MIS 9d was probably too mild and moist for significant aeolian dust movement, which might have resulted in an input of fresh primary carbonate to the mixture of soil sediment and local (silicate) Table 2 Summary of dose rates, equivalent doses, and ages. Dose rates were calculated using a mean a-value of 0.08 ± 0.02 and a water content of 15 ± 5%. s.e. = standard error, n = number of aliquots. For details see text. Horizon

Lab code

Dose rate (Gy/ka) ± 1 s.e.

n

Equivalent dose (Gy) ± 1 s.e.

Age (ka) ± 1 s.e.

Pau I-x Pau I-y P3c P4a P4c P4e P6a P6c1 P7f P8-1 P8-2

123040 123041 123042 123043 123044 123045 123046 123047 123048 123049 123050

3.03 3.00 3.04 3.15 3.25 3.05 3.25 2.71 3.10 2.83 3.09

6 6 6 6 6 6 6 6 6 6 6

424 458 418 386 438 537 614 731 905 895 933

140 153 138 123 135 176 189 270 292 316 302

± ± ± ± ± ± ± ± ± ± ±

0.25 0.24 0.25 0.25 0.27 0.26 0.26 0.22 0.20 0.23 0.25

± ± ± ± ± ± ± ± ± ± ±

13 8 10 8 12 24 18 29 20 14 54

± ± ± ± ± ± ± ± ± ± ±

12 13 12 10 12 17 16 24 20 27 31

5.2.1. Phases of development in the interplay of local and climatic influences This part of the LPS is composed of loess sediments, one brownish and several bleached horizons (cf. Fig. 2-B). As in typical loess (cf. Pye, 1995), quartz and feldspar dominate the silt fraction. These minerals are also very abundant in the coarse grain fraction; this reflects local geology (Matura, 1989). A clear local signal can be deduced from the presence of sand to gravel sized granulite fragments and garnet. Broader varieties of silicates and carbonates represent the dust component in the less weathered and less sandy units. For this part of the LPS three main phases can be distinguished. Phase 1: In unit P6, the substrate has less silt and primary carbonates than in the units above and appears to be dominated by a re-deposited local substrate. The significant silt component probably reflects an aeolian origin. Blocky to subpolyhedral aggregates, typical of loess, suggest a cold steppe (tundra) environment resulting in the process of loessification (cf. Pécsi, 1990; Smalley et al., 2011; Svirčev et al., 2013). Phase 2: On macroscopic scale P6b is a light-brownish horizon with inhomogeneous and disturbed appearance; it can be interpreted as soil sediment. A crotovina-like pattern and higher carbonate contents in the upper part of P6c are evidence for in situ alteration. On a microscopic scale the horizon has a well-developed granular microstructure. It contains primary carbonates and is characterised by a partly granostriated micromass. These, at first glance contrary characteristics, can be explained by polygenesis: a Chernozem (granular structure, primary carbonates) developed in pre-weathered substrate which was mixed with fresh (aeolian) sediment by colluvial processes. It has to be assumed that prior to re-deposition a soil existed which reached at least the weathering degree of a Phaeozem (granostriated clay, Ck horizon). Phase 3: P6b is strongly truncated. The overlying units P5 to P3 are significantly enriched in silt and carbonates, suggesting increased dust accumulation under cold and dry climate conditions. The strong truncation of P6b also reflects the degrading environment. Several Cryosols of varying intensities are present, which reflect moister periods with reduced sedimentation rates (cf. Antoine et al., 2009; Bibus, 1974). It is interesting to note that – for as yet unknown reasons – the Cryosols P5a and P5e lack a lenticular structure, which in general develops by frost change processes when water is present (Van VlietLanoë, 2010). 5.2.2. Reconstruction the palaeoenvironments (MIS 8 to MIS 6) The two pIRIR290 ages from below and above P6b resulted in 270 ± 40 and 189 ± 16 ka, respectively. The (potentially) polygenetic brownish (forest-)steppe palaeosol P6b developed most likely during MIS 7 and

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Fig. 6. Composite profile correlated with the marine isotope record (Cohen and Gibbard, 2011; Lisiecki and Raymo, 2005). The correlation is based on pIRIR290 ages. For details see Section 5.

Fig. 7. Simplified genetic model for the lower pedocomplex (P7) during MIS 9. Main processes and average environments are indicated for each phase. A forest-steppe environment is assumed, degrading to a steppe ecosystem in the final phase. The formation of the Luvisol is caused by ongoing weathering of decalcified and pre-weathered substrate.

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was strongly truncated, probably at the onset of MIS 6. Considering the pIRIR290 ages and potential palaeoenvironments, the entire silt and carbonate enriched sequence (units P5 to P3) intercalated by Cryosols, developed during MIS 6 under periglacial conditions. The decrease in Cryosol intensity from P5 to P3 can be correlated with the decrease in global temperatures during MIS 6 (cf. Fig. 6 and references therein). Unit P3 and the upper parts of unit P4 represent the phase of highest dust sedimentation rates; all ages group in the range between 150 and 130 ka. In these sediments the upper pedocomplex developed when dust sedimentation ceased to be significant. If erosional phases are excluded, the average sedimentation rate was at least ~150– 200 mm/ka. It should be noted that the age of sample Pau I-y (right hand side of the outcrop) differs from the age of sample P4a, which was taken from the same depth relative to the upper pedocomplex (unit P2). Horizons apparently differ in thickness along the outcrop, which hampers an unambiguous correlation of the loess sediments below the upper pedocomplex of the Paudorf I section and the Paudorf II section, and furthermore highlights the complexity of the sequence. 5.3. Upper pedocomplex (unit P2) and youngest loess (unit P1) The upper pedocomplex (unit P2) shows a combination of features which record its complex genesis. The reddish-brown pigmentation and the abundance of clay in the groundmass (Fig. 5-D) appear to be inconsistent with the high carbonate content. This apparent contradiction is based on the suggestion that iron oxidation and clay neoformation, which lead to the development of a Bw horizon, mostly take place after the carbonate buffer has been leached (Scheffer, 1966; Blume et al., 2010). Secondary carbonates could have precipitated in a drier climate after the formation of the Bw horizon. However, Bronger (1976) has detected primary carbonates in the groundmass of the upper pedocomplex (cf. Table 1, Fig. 5). Therefore, he concluded that the upper pedocomplex is a typical Chernozem. It needs to be mentioned that Bronger (1976) reinterprets the general conclusion of Scheffer (1966) and assumes the possibility of synchronous iron oxidation, clay neoformation and carbonate leaching in Cambisols of the Carpathian (Pannonian) Basin. The luminescence ages presented for the loess above and below the pedocomplex (Thiel et al., 2011b; Zöller et al., 1994) clearly point to a genesis during MIS 5. Sprafke et al. (2013) suggested that the upper pedocomplex might be a Chernozem developed in a re-deposited Eemian Cambisol. Our micromorphological data support this interpretation. A genetic model for the pedocomplex is illustrated in Fig. 8 and the formation stages are described below. As the pedogenetic phases in the polygenetic MIS 5 palaeosol cannot be dated separately, we suggest a chronological framework based on a comparison with wellresolved MIS 5 palaeosol stacks such as Stillfried A (Fink, 1954; Zöller et al., 1994) or PKII/PKIII in Dolní Věstonice (Antoine et al., 2013). 5.3.1. Parent material formation The genesis of the parent loess sediment, based on dust sedimentation, local material admixture and loessification, is attributed to periglacial conditions during MIS 6 as described in Section 5.2.2. Phase 1: In a temperate (sub-)humid climate with moderate seasonality of MIS 5e, a reddish-brown Cambisol with enhanced clay content developed in a forest ecosystem by relatively shallow decalcification, oxidation and slight chemical weathering. Clay coatings or at least fragments of clay coatings are not present in the thin section; therefore the final developmental stage of the Eemian (MIS 5e) soil is not a Luvisol but a Cambisol. Phase 2: Clay is unevenly distributed in the groundmass. Granules caused by bioturbation are often enriched in clay (Fig. 5-D). In some cases, decalcified clay-enriched aggregates with sharp boundaries are located directly next to silty to fine sandy domains with carbonates

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(Fig. 5-C). These feature relations suggest a disturbance during the formation of the Eemian palaeosol due to re-deposition (fragments of Bw-material) and bioturbation (uneven distribution, clay rich granules). The macroscopic frost structures visible at the lower boundary of P2d and the slope-parallel oriented rock fragments indicate that the Eemian Cambisol was truncated and re-deposited under periglacial conditions, i.e., MIS 5d. During this phase aeolian input caused the admixture of primary carbonate grains. Phase 3: Bioturbation and humification without significant decalcification led to the formation of a typical Chernozem during improved climatic conditions (MIS 5c). The parent material is a mixture of re-deposited Eemian Cambisol, local silicate material and fresh dust with carbonate. Sparite and micrite formed syngenetically with the Chernozem; this is deduced from carbonates affected by bioturbation, such as calcified root cells (cf. Barta, 2011) that are partly incorporated into the groundmass (Fig. 5-B) and micrite impregnated granules in channels without micritic coatings or hypocoatings (Fig. 5-A). A piece of charcoal was found in P2b that is impregnated by micrite and is therefore predating the impregnation. The admixture of charcoal to the groundmass can be attributed to phase 2. The Chernozem developed under a steppe environment; synpedogenic carbonate in the steppe soil formed due to fresh dust input in MIS 5d and the close Ck horizon of the Eemian Cambisol (P3a). This is in contrast to the lower pedocomplex (unit P7), which developed in a comparable time range under only slightly moister climatic conditions. Without fresh dust input during MIS 9d and the long vertical distance to unit P8, a carbonate buffer was lacking and chemical weathering continued over a longer period. Burial: The upper pedocomplex was successively buried by increasing dust input under periglacial conditions. The pIRIR290 age of 106 ± 12 ka in the transition of units P2 and P1 (Thiel et al., 2011b) indicates that pedogenesis during MIS 5a is not recorded at Paudorf. This is in contrast to the TL age of 54 ± 6 ka from loess sediment above the upper pedocomplex by Zöller et al. (1994); more dating is needed to resolve this discrepancy. The last glacial loess sediment could not be differentiated further. 6. Regional correlations 6.1. MIS 10 to MIS 9 The lower pedocomplex of Paudorf has previously been correlated with the ‘Göttweiger Verlehmungszone’ (‘Göttweig soil’; Götzinger, 1935; Fink, 1976), which has recently been dated to N350 ka (Thiel et al., 2011b). From the set of the dating results presented here, it can be stated that there is no temporal overlap between unit P7 in Paudorf and the ‘Göttweiger Verlehmungszone’ even though some uncertainties arise due to the upper dating limit of pIRIR290. The lower pedocomplex (unit P7) in the LPS Paudorf can be correlated with MIS 9 and represents on average a forest-steppe environment, interrupted by at least one major period of erosion/colluviation. The presence of a clay illuvial horizon is a function of time/parent material. Compared to Upper Austria, where MIS 9 is represented by Bt horizons attributed to forest-ecosystems (Terhorst, 2007, 2013; Terhorst et al., 2012), the MIS 9 complex in the Paudorf LPS represents more continental conditions. It has to be noted that for this time span no numerical ages exist for Upper Austrian sites; Preusser and Fiebig (2009) obtained ages pointing to MIS 7 for the soil correlated with MIS 9 by other authors (cf. Terhorst et al., 2012 and references therein). Phaeozems are common MIS 9 palaeosols in the Pannonian Basin, for example the V-S3 in Stari Slankamen, Serbia (Bronger, 1976, 2003; Marković et al., 2011). In Batajnica the V-S3 soil is identified as polygenetic, with a lower AB and an upper A horizon; two pedogenetic phases are deduced from two peaks in the magnetic susceptibility (MS) record (Marković

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Fig. 8. Simplified genetic model of the genesis for the upper pedocomplex (P2) during MIS 5. Main processes and average environments are indicated for each phase.

et al., 2009). In Paks, Hungary, the development of the Basaharc Lower (BA) pedocomplex is slightly more advanced, in the direction of a Phaeozem-Cambisol (Bronger, 1976). This palaeosol is correlated to MIS 9 and exhibits a double MS peak as well (Marković et al., 2011; Sartori et al., 1999), although this rather likely correlation could not be confirmed by numerical ages due the dating limit of luminescence (pIRIR290) (Thiel et al., in press).

6.2. MIS 8 to MIS 6 For the Krems region our study is the first presenting dating results falling into MIS 8 and MIS 7; no palaeoenvironmental reconstructions from other sites in the region are available (cf. Terhorst et al., 2011). In Göttweig-Furth, Göttweig-Aigen (Fig. 1) and Joching, loess packages dated to the penultimate glacial are exposed (Terhorst et al., 2011; Thiel et al., 2011b; Zöller et al., 1994), but neither detailed investigations nor proxy analyses are available. Although it may be partly eroded, it is evident that loess attributed to MIS 8 in Upper Austria is scarcely present; this can be compared with the reduced amount of dust accumulation during this period at Paudorf. However, this contrasts with the thick MIS 8 loess at Paks (e.g., Thiel et al., in press). In Upper Austria, Bt-horizons of truncated Luvisols which developed in a forest ecosystem have been correlated with MIS 7 (Terhorst, 2007, 2013; Terhorst et al., 2012). P6b, very likely the remnant of a MIS 7 pedocomplex at Paudorf, appears as a relatively thin and weakly developed palaeosol compared to the two welldeveloped Phaeozems BD1 and BD2 at Paks, each with a distinct MS peak, or the thick V-S2 pedocomplex at Batajnica (Bronger, 1976, 2003; Marković et al., 2009, 2011; Sartori et al., 1999). Because of this, we must assume a polygenetic development of P6b with later truncation at the onset of MIS 6. Loess–Cryosol sequences that formed during glacial stages under slightly varying climatic conditions are frequently observed in Central and Western European last glacial loess (Antoine et al., 2001, 2009; Semmel, 1968) and penultimate glacial loess (Bibus, 1974, 2002), but have not been reported in the Pannonian Basin (Fitzsimmons et al., 2012; Marković et al., 2008). The LPS Süttő (Hungary, NW of Transdanubian Hills) seems to be close to the southeastern limit of the formation of last glacial Cryosols; in this sequence these palaeosols are not reported from MIS 6 (Novothny et al., 2011). Cryosols in last and penultimate glacial sequences in Lower Austria (Haesaerts et al., 1996; Thiel et al., 2011a,c) indicate that environmental conditions during the last two glacials were, in contrast to conditions during interglacial palaeoenvironments, comparable to those in Central Europe.

6.3. MIS 5 In the east of Lower Austria at Stillfried (locus typicus) a stack of an Eemian Cambisol with three superimposed early last glacial Chernozems (Bronger, 1976; Fink, 1954) depicts comparable palaeoclimatic conditions in better resolution. This is mainly interesting for the perspective of the last interglacial palaeoclimate. The Eemian palaeosols in the loess region to the north (Moravia) and to the west of the Bohemian Massif are Bt horizons of truncated Luvisols attributed to forest ecosystems (Antoine et al., 2013; Bronger, 1976, 2003; Fink, 1956; Frechen et al., 1999; Terhorst et al., 2002). In the Pannonian Basin, MIS 5 is often represented by buried Chernozems or Phaeozems attributed to (forest-)steppe ecosystems (Bronger, 1976, 2003; Marković et al., 2009, 2011). This supports the assumption that Lower Austria is situated in a transition position between oceanic and continental (palaeo-) climate (cf. Fink, 1956). 7. Conclusions We have presented a detailed semi-quantitative analysis of micromorphological features in combination with a qualitative study of the relationships between features to reconstruct the formation phases of the polygenetic Paudorf LPS. The admixture of sand-/gravel-sized sediments from local silicate rock to aeolian dust (relatively rich in carbonates) is a crucial element in the understanding of the sedimentary and the pedogenic dynamics. We also discussed the genesis of the LPS with respect to a chronological framework provided by pIRIR290 ages. The lowermost part of the sequence consists of loess deposited under periglacial conditions during MIS 10. During MIS 9 a pedocomplex formed in a forest-steppe environment. The formation of a Phaeozem in MIS 9e was interrupted by a degradation of the climate resulting in reduced vegetation cover and active geomorphodynamics (MIS 9d). The maximum degree of weathering occurred during MIS 9c; climatic conditions do not need to have been significantly different from MIS 9e. Subsequently degradation to a steppe environment then occurred and local material mixed with carbonate-rich dust accumulated during MIS 8. In MIS 7 a (forest-)steppe palaeosol developed that was truncated at the onset of MIS 6. The penultimate glacial is represented by dust accumulation, loessification and re-deposition, interrupted by phases of pedogenesis (Cryosols) during moister periods. The uppermost pedocomplex (‘Paudorfer Bodenbildung’) is a Chernozem (MIS 5c[–a?]) that developed in a re-deposited (MIS 5d) Eemian Cambisol. Only for the upper pedocomplex (MIS 5) can correlations with LPS from the region be established. The environmental conditions during the two previous glacial–interglacial-cycles can at present only be reconstructed in the Paudorf LPS, which makes it an important

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regional palaeoenvironmental archive. Compared to Upper Austria, where the last interglacials resulted in the formation of Luvisols under forest ecosystems, our study shows that the climate in the Krems area was more continental during the interglacials of the last 350 ka. The soils formed mostly under forest-steppe ecosystems, more comparable to the conditions in the Pannonian Basin. The presence of Cryosols in sequences of the last and the penultimate glacial in Lower Austria indicate that conditions during glacial phases were, however, more comparable to Central Europe. Acknowledgements The authors would like to thank Ximena Suarez Villagran, Michael Zech, Roland Zech and most of all Sergey Sedov for valuable scientific support and discussion. Alicia Medialdea and Joy Mailand-Hansen (Nordic Laboratory for Luminescence Dating) are thanked for technical assistance. Furthermore, we are grateful for the financial support of the Universitätsbund Würzburg e.V. 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