This article is published in - Institut für Geographie

This article is published in - Institut für Geographie

This article is published in:
Zeitschrift für Geomorphologie , Suppl. 1 (2014)
Volume 58, 27-50
doi:10.1127/0372-8854/2013/S-00163
Landscape aridification in Central Germany during the late Weichselian Pleniglacial –
results from the Zauschwitz loess site in western Saxony
Tobias Lauer#1,2, Hans von Suchodoletz#1, Heiko Vollmann1, 4, Sascha Meszner3, Manfred
Frechen2, Christian Tinapp1, Lisa Goldmann1, Susann Müller5 and Christoph Zielhofer1
#
These authors contributed equally to this study.
1
Leipzig University, Chair of Physical Geography, Johannsiallee 19 a, 04103 Leipzig, Germany
Leibniz Institute for Applied Geophysics, Stilleweg 2, 30655 Hannover, Germany
3
University of Technology Dresden, Institute of Geography, Helmholtzstrasse 10, 01069 Dresden,
Germany
4
Deutsches GeoForschungsZentrum GFZ, Hydrology section, Telegrafenberg, 14473 Potsdam,
Germany
5
Johann Wolfgang Goethe University, Institut of Physical Geography, Altenhöferallee 1, 60438
Frankfurt am Main, Germany
2
Abstract. In Zauschwitz (Western Saxonian loess area, Central Germany), a ca. 7 m thick loesspalaeosol sequence underlain by fluvial gravels and sands was investigated in order to study regional
palaeoenvironmental changes during the late Weichselian Pleniglacial. The lithostratigraphic
classification of the loess-palaeosol sequence was combined with polymineral fine grain luminescence
dating using the pIRIR290 approach, and correlated with similar loess-palaeosol-sequences from
Central Saxony. Doing so, we obtained information about a climatic shift from more humid to more
arid conditions during the late Pleniglacial, due to changes in the landscape dynamics of the study
area: At ca. 30 ka, braided river floodplain accumulation of the nearby Weisse Elster river was
followed by a phase of decreased fluvial activity, allowing initial loess deposition on top of the fluvial
sands and gravels. This period was characterized by cold but still quite humid conditions, as indicated
by reworked loess and the occurrence of several tundra gley soils. Subsequently, a cold and more arid
period of dust accumulation followed after ca. 22 ka. Intensive anthropogenic activity almost totally
redeposited the Holocene black soil, demonstrating the attractiveness of the fertile loess area for early
human settlement.
1. Introduction
The buildup of loess deposits and the formation of intercalated palaeosols react very
sensitively to climatic changes, i.e. to changes of temperature and humidity. Hence, loesspalaeosol sequences are very valuable terrestrial archives for palaeoenvironmental conditions
on a regional scale (e.g. Semmel 1978, An et al. 1991, Rousseau et al. 1998, Muhs & ArthurBettis III 2003, Bibus et al. 2007, Buggle et al. 2009, Antoine et al. 2013). Loess
accumulation mostly correlates to periods of cold and arid climate (full glacial conditions),
whereas reworked and layered loess gives evidence for periods of slightly more humidity.
Intercalated soils correlate to interstadial and interglacial periods with stable morphodynamics
due to a denser vegetation cover (e.g. Meszner et al. 2011).
The aim of this study, investigating a loess-palaeosol-sequence of about 7 m thickness
underlain by fluvial sands and gravels in Zauschwitz (Saxony), is to contribute to the loessbased palaeoenvironmental research in the Western Saxonian loess area south of Leipzig
(Figs. 1, 2). Loess deposits of this area were already studied by Lieberoth (1963), Göbler
(1966) or Ruske & Wünsche (1968) during the last decades. However, in contrast to the
Central Saxonian loess area (Lommatzscher Pflege, Fig. 2) where detailed research was
recently carried out (e.g. Meszner et al. 2011, Meszner et al. 2013), apart from singular
studies (e.g. in Zeuchfeld by Kreutzer et al., this volume, see Fig. 2) there is still poor
knowledge about the loess chronostratigraphy of Western Saxony and southern SaxonyAnhalt. This holds especially true for the northernmost border of the loess belt
(“Lössrandstufe”, Fig. 2). By correlating our results with the composite profile provided for
the Central Saxonian loess area by Meszner et al. (2013), we were able to establish the first
detailed loess chronostratigraphy for Western Saxony and to obtain information about late
Weichselian Pleniglacial environmental changes in this area.
2. Study area
Geological and geomorphological setting
The Zauschwitz loess exposure (51°10′ 51″N, 12°15′38″E; 130 m a.s.l.) is located about 20
km southwest of Leipzig, Saxony. This area is part of the Leipzig Basin (Leipziger
Tieflandsbucht, Fig. 1), forming the southernmost part of the Northern German Lowlands.
Below unconsolidated Quaternary and Tertiary sediments, folded and non-folded rocks (e.g.
granites) of the Variscian Orogenesis can be found (Eissmann 2008). In the course of the
Tertiary Alpine Orogenesis, uplift of the adjacent southern mountain ranges (Thuringian
Forest, Ore Mountains) and isochronic subsidence of the Leipzig Basin took place (Fig. 1). In
the following, the Leipzig Basin was filled with marine and terrestrial unconsolidated Tertiary
sediments (Eissmann 1997a). The Eocene North Sea transgression and the accompanying rise
of the groundwater level resulted in the formation of widespread peat layers (Wagenbreth &
Steiner 1990). A subsequent coverage of the peat/swamp areas by sediments from the
southern foreland finally resulted in the formation of the Central German lignite beds
(Eissmann 1997b).
During the Quaternary, the Leipzig Basin was covered several times by Scandinavian glaciers
(Eissmann 2002) (Fig. 1). Today, the Leipzig Basin is part of the Central German type area
for the Saalian and Elsterian glacial cycles. Here, in the transitional zone between ice-covered
glacial and ice-free periglacial areas all glacial sedimentological units of the Elsterian and
Saalian periods are preserved, documenting advance and retreat of the Scandinavian glaciers
(e.g. Eissmann & Litt 1994, Junge 1998, Eissmann 2008). The different glacial phases are
represented by specific sedimentological units distinguished by textural, structural and
geomorphological characteristics (e.g. grain-size, ice wedge casts), their mineralogical
composition (e.g. carbonate content, heavy metals, heavy minerals) as well as by
palaeontological and palynological markers (Müller et al. 1988, Eissmann 2002, Hoffmann &
Eissmann 2004).
During the Weichselian glaciation, the region was permanently ice-free (periglacial area),
resulting in the deposition of aeolian sediments: Loess, sand-loess and drift sand were blown
out from the nearby floodplains, thereby forming the Saxonian loess area. This loess belt is
located at the transitional zone between the Northern German Lowlands and the Uplands of
the Ore Mountains (Erzgebirge) adjacent to the south (Figs. 1, 2). In the Central Saxonian
loess area Weichselian loess deposits with thicknesses up to 20 m can be found (Meszner et
al. 2011). Older loess deposits originating from the Saalian or Elsterian glacial cycle were
mostly eroded by subsequent advances of Scandinavian glaciers or by periglacial or fluvial
erosional processes, respectively, and are thus only rarely found in the region (e.g. Fuhrmann
et al. 1977).
The Zauschwitz exposure is located in the Western Saxonian loess area, where up to 10 m
thick Weichselian loess deposits can be found. In contrast, north of Zauschwitz only
fragments of a thin sand-loess cover (< 1 m) and cryoturbated loess are preserved today
(Haase et al. 1970) so that the exposure is located just south of the so-called “Lössrandstufe”
(Fig. 2).
Location of the Zauschwitz exposure in relation to the valley of the Weisse Elster river
The Zauschwitz exposure is found at the western slope above the valley of the Weisse Elster
river (Fig. 3). The present orientation of this valley developed after melting of the last
Elsterian glaciers. The river created a five kilometer wide valley between the cities of Zeitz
and Leipzig that was filled with gravels and sand during the early Saalian period (Saale-
Hauptterrasse; fQSf in Fig. 3). Subsequently, these fluvial sediments were covered by glacial
till during the older Saalian glaciation (Drenthe-stage), the last appearance of glaciers in this
region at all (Fig. 1). During the following latest part of the Saalian glacial and during the
Eemian interglacial, the Weisse Elster river only used the eastern part of the valley where it
has cut into older sediments (Eissmann 1997b). Therefore, remaining early Saalian gravels
build a terrace-body only on the western side of the recent valley today, partly covered by a
thin layer of glacial till. During the Weichselian period, the valley was filled with gravels and
sands again (fQW in Fig. 3). Up to now, the transitional zone between these younger
Weichselian gravels and the older Saalian terrace is assumed to be located at the western edge
of the Holocene valley, despite the fact that glacial till is missing on the Saalian gravels there.
However, since both terraces contain the same material they could not be distinguished
lithologically yet.
During former investigations of Holocene valley sediments in the former Zwenkau lignite
mine ca. 5 km to the north of Zauschwitz, Weichselian gravels below Holocene floodloam
deposits and assumed early Saalian gravels (located further to the west) were exposed on a
distance of three Kilometers (Tinapp 2002). However, a boundary between Saalian and
Weichselian gravels could not be identified. Accordingly, a radiocarbon date of small wood
pieces taken from a sandy layer in the assumed Saalian gravels was dated to 37.3 ± 0.8 cal. ka
BP (LZ-1490: 32.8 ± 0.49 BP, calibrated with Calpal-online), falling into the Weichselian
Pleniglacial. Thus, there is strong evidence for the existence of Weichselian gravels extending
much further to the west of the Weisse Elster valley than formerly assumed (cf. Eissmann
1997b; fQW? in Fig. 3).
3. Methods
The Zauschwitz loess exposure is outcropped along the walls of a former brick yard. The
exposure was first described by Göbler (1966) who distinguished 13 different layers
(including the Holocene soil material on the top). We reinvestigated the Zauschwitz exposure
during several field campaigns in 2011 and 2012. The different units of the loess-paleosol
sequence were described, and samples for laboratory analyses were taken every 5 cm.
Luminescence dating
A chronological framework for the investigated sediments is a prerequisite to link periods of
loess deposition, soil development and phases of reworking with palaeoenvironmental
changes. The dating method of choice was luminescence dating, determining the time elapsed
since last sunlight exposure of sediment grains which correlates with the time of deposition
and following burial.
All steps of sample preparation and age determination (equivalent dose measurements and
gamma ray spectrometry) were conducted at the luminescence laboratory of the Leibniz
Institute for Applied Geophysics (LIAG) in Hanover.
Five luminescence samples for polymineral fine grain (4 –11 µm) dating were taken from the
Zauschwitz exposure using light-tight steel tubes. After destroying carbonate and organic
matter with HCl and H2O2, respectively, the polymineral grain size 4 –11 µm was isolated by
several cycles of washing and settling in Atterberg cylinders (Frechen et al. 1996). The
obtained polymineral fine grain fraction was finally mounted on aluminium discs from a
suspension in acetone.
Equivalent dose (De)-measurements:
All luminescence measurements were conducted on a Risö TL/OSL reader equipped with a
90
Sr/90Y source (dose rate ca. 5.65 Gy/min) for irradiation, and LEDs transmitting at 870 nm
for stimulating the feldspar signal of polymineral fine grain samples. The luminescence signal
was recorded in the blue-violet wavelength region by using a filter combination of Schott BG39 and Corning 7-59.
For De-measurements, a pIRIR290 (post-IR-IR measurement at 290°C) approach similar to
Thiel et al. (2011a) was chosen, and the measurement steps are outlined in Table 1. In this
approach, the feldspar signal is stimulated at elevated temperatures after depleting the IRSL
signal at 50°C, since the latter is generally affected by anomalous fading (Wintle 1973,
Huntley & Lian 2006). Anomalous fading is a signal instability causing age underestimation
if not corrected properly, and laboratory fading corrections show high uncertainties for
samples showing nonlinear dose-response curves (Huntley & Lamothe 2001, Kars et al.
2008). The pIRIR290 signal was found to be very stable so that fading corrections are regarded
as not necessary (Thiel et al. 2011b).
Before starting De-measurements, the applicability of the chosen pIRIR290 protocol was tested
by applying a dose recovery test on samples Zausch-Lum 5 (oldest sample) and Zausch-Lum
1 (youngest sample). Six aliquots from each of these samples were bleached under a solar
simulator for 4 h. Afterwards, an artificial dose close to the expected natural dose was applied
to respectively 3 aliquots, and it was tested how precisely this dose could be recovered by the
pIRIR290 dating protocol. The other respectively 3 aliquots were used to measure the
remaining dose residuals after solar lamp bleaching. To do so, the dating protocol as outlined
in Table 1 was applied directly after light exposure.
Further tests on the bleaching behavior of the pIRIR290 signal were conducted by exposing
aliquots of samples Zausch-Lum 5 and Zausch-Lum 1 to daylight. Respectively 3 aliquots
from each sample were bleached for 4 h and 10 h. These tests were executed in June 2013.
After daylight exposure, dose residuals were measured by using the pIRIR290 protocol (Table
1).
Dose rate / gamma-ray spectrometry
Material for dose rate estimation was taken at the same positions as the samples for
luminescence dating.
50 g of each sample were stored for 4 weeks in a sealed baker to avoid any radon-related
radioactive disequilibrium. Afterwards, the concentration of potassium, thorium and uranium
was measured on a HPGe (High-Purity Germanium) N-type coaxial detector.
An a-value of 0.09 ± 0.02 (describing the sensitivity of the sample-material to α- in
comparison with β–radiation) was taken from the literature (Rees-Jones 1995), and dose rate
conversion factors following Guerin et al. (2011) were used. For calculating the cosmic dose
rate the procedure after Prescott & Hutton (1994) was used, considering sediment thickness,
geographical position and altitude. Due to opening of the loam-pit some decades ago and thus
drying of the exposure for a rather long time, the in-situ water content was not measured.
Instead, the water content was estimated to be at 15 ± 10 % for samples Zausch-Lum 4 –
Zausch-Lum 1 (Frechen et al. 1997). Only for the lowermost sample (Zausch-Lum 5) a water
content of 25 ± 10 % was assumed, since the recent ground water table is just below the
lowermost part of the Zauschwitz exposure. The wide error (10 %) for the estimated water
contents was taken with respect to the uncertainties of these assumptions.
Total dose rates of the 5 samples varied between 4.3 Gy/ka and 4.6 Gy/ka and are listed in
Table 2.
Carbonate content
A classification of the carbonate content is necessary to identify zones of pedogenesis
indicated by decalcification, as well as units of secondary carbonate enrichment. Furthermore,
variations in carbonate content might indicate changes within the source area of the loess.
Hence, carbonate content is an important marker for lithostratigraphic classification.
Carbonate content was obtained following the Scheibler procedure. 1–10 g of material were
filled into an Eijkelkamp Calcimeter apparatus. Subsequently, 4N HCl was added
continuously until the reaction ceased. The measured volume of CO2 produced during the
reaction was finally used to calculate the carbonate content.
Magnetic susceptibility
Magnetic susceptibility χ depends on concentration and grain size of magnetic particles in
soils and sediments, and due to their strong magnetizability ferrimagnetic minerals (e.g.
magnetite, maghemite) mostly dominate the magnetic signal (Walden et al. 1999). Increases
of χ can be caused by different factors as e.g. a change of the source of magnetic minerals,
strong heating, an enrichment of charcoal (Dearing 1999, Goudie 1998, Ibouhouten et al.
2010, Zielhofer et al. 2010, 2012) and/or pedogenetic processes with the neoformation of
ferromagnetic particles (e.g. Evans & Heller 1994, Sun & Liu 2000, Blake et al. 2006).
Frequency dependent magnetic susceptibility χfd is only grain-size dependent, indicating the
presence of minerals at the single domain/superparamagnetic border (< 30 nm). The latter
minerals are known to be mostly formed by pedogenesis (e.g. Torrent et al. 2007). Thus,
increases of χfd generally indicate the existence of pedogenetic processes that had overprinted
a sedimentary body.
Magnetic susceptibility and frequency dependent magnetic susceptibility were measured
using a Bartington MS3 magnetic susceptibility meter, equipped with an MS2 B dual
frequency sensor. Before measurement, the material was softly ground, densely packed into
plastic boxes, and subsequently volume magnetic susceptibility κ was measured with low
(0.465 kHz) and high (4.65 kHz) frequency. By normalizing the low-frequency measurement
(κLF) with the mass of a sample, we obtained mass-specific magnetic susceptibility χlf,
subsequently called χ. Frequency dependent magnetic susceptibility χfd (in %) was calculated
with the formula:
χfd = (χ(LF) – χ (HF))/χ (LF) * 100
Grain size
A characterization of the granulometric composition of different sedimentary units can be
used to obtain i) information on former sedimentary processes (e.g. aeolian vs. fluvial, or
palaeowind speed) or ii) to indicate zones of pedogenesis with the neoformation or
translocation of clay.
Grain size analyses were conducted on every 2nd sample (10 cm intervals) using Laser
Diffractometry (Beckman-Coulter LS 13320 PIDS laser diffraction particle size analyzer).
Before measurement, samples were treated for at least 12 hours with ammonium hydroxide (1
% NH4OH) in overhead tube rotators for dispersion. No further chemical treatment was
applied. Afterwards, test measurements were conducted on 20 different samples to achieve
the optimal sample dispersion. Every sample was measured 5 times, and depending on
reproducibility the average of 5 to 3 measurements was taken. In order to obtain the
characteristics of a large spectrum of the grain size distributions, we used a U-ratio similar to
that of Vandenberghe et al. (1985) based on the formula 63.4 –15.6 µm/5.61–15.6 µm, and the
fine sand content 63 – 200 µm.
Micromorphology
An oriented undisturbed soil sample was taken from the transitional zone between the recent
black soil material and the uppermost loess layer L1 (Fig. 4). The sample was air-dried and
impregnated with Oldopal P 80-21. Subsequently, the hardened block was cut and sliced into
70 × 50 mm thin sections which were described at 50 – 400 magnification under a polarizing
microscope mainly using the terminology of Bullock et al. (1985) and Stoops (2003).
4. Results and interpretation
Lithological subdivision of Zauschwitz loess exposure
The bottom of the loess sequence is formed by fluvial sands and gravels of the Lower Terrace
of the Weisse Elster river (Figs. 3, 4). Although those sands and gravels were not exposed
during our field-campaigns in 2011 and 2012, they could be reached by drilling in a depth of
80 cm below the bottom of the outcropped profile.
The lower part of the exposure (705 – 537 cm) is built by units N5 and N4 (Fig. 4). Both
show strong hydromorphic features (oxide rings, iron and manganese concretions), and are
separated from each other by a layer of sandy material. Both contain redeposited carbonate
concretions.
Above N4, a complex of two gley soils (N3 b and N3 a) was found between 537– 400 cm, N3
b with a thickness of 72 cm and N3 a with a thickness of 65 cm. These tundra gley soils are
characterized by numerous iron and manganese concretions and an intensive cryogenic
overprinting as evidenced by sand or clay dominated lenses mixed into the substrate. The N3
b tundra gley soil is distinguishable from the overlying N3 a tundra gley soil by a more
intense yellowish coloring. The basal parts of both N3 b and N3 a are marked by horizontally
orientated carbonate concretions.
The overlying Ll3 loess layer (400 – 295 cm) is characterized by cryogenic features such as
small frost cracks and ice wedges in its lowermost part. Ll3 hosts small carbonate nodules,
iron and manganese stains and shows a general hydromorphic marbling. The whole loess
layer is laminated (“gestreifter Löss” or “Schwemmlöss”), and shows sub-layers with
thicknesses of some millimeters up to a few centimeters.
Above 295 cm, the N2 tundra gley soil is developed. N2 is about 50 cm thick, cryogenically
deformed and hosts horizontally orientated carbonate nodules that most likely point to a
redeposition process. N2 marks a clear stratigraphical zone of transition between the reworked
and cryoturbated sediment units in the lower and middle part of the Zauschwitz exposure and
the overlying homogeneous loess.
The upper part of the Zauschwitz exposure contains two loess-layers (L2: 245 –155 cm and
L1: 135 – 90 cm) that show no signs of reworking or cryogenic overprinting. Both layers
show only weak hydromorphic overprinting as indicated by slight marbling (partly
iron/manganese staining), and in L1 crotovinas containing material from the overlying
Holocene black soil can be found. In a depth of about 1 m carbonate nodules (Lösskindl)
belonging to the Holocene soil appear. L1 and L2 are separated by a weakly developed tundra
gley soil (N1) between 155 and 135 cm.
Between 90 and 65 cm below the recent surface, the ‘pure’ loess grades into the overlying
Holocene black soil material, that is partly mixed with yellowish loess. Since this material
shows additional features of reworking as e.g. findings of charcoal and broken prehistoric
ceramics, it was classified as an M-horizon and not as an in-situ soil. Due to a moist chroma
of the mollic horizon clearly > 2, the soil material was classified as originating from a
phaeozem (FAO 2006).
The micromorphological sample taken at the transitional zone (“Verzahnungsbereich”)
between the Holocene black soil material and the L1 loess layer (Fig. 4) should give detailed
information about Holocene pedogenesis, and answer the question whether parts of the in situ
soil are preserved in Zauschwitz or not. Here, the micromass is brown and darkly dotted due
to finely distributed organic matter. The material shows a channel (Fig. 5a) and partly spongy
(Fig. 5b) microstructure as a result of intensive bioturbation. Voids are dominated by channels
and chambers. Furthermore, numerous excrements of earthworms and enchytraeidae worms
indicate bioturbation as the dominant soil forming process (Fig. 5c). Some of these
excrements are formed of calcareous material from the underlying loess (L1), and can be
identified in the thin section by their lighter colour and calcitic crystallitic b-fabric especially
under crossed polarizers (Fig. 5d). The admixture of loess plays an important role in
maintaining a high content of calcium carbonate as a prerequisite for the stabilization of the
characteristics of a mollic horizon.
Luminescence chronology
Dose recovery tests conducted on samples Zausch-Lum 5 (lowermost sample) and ZauschLum1 (uppermost sample) could successfully recover the given dose of ca. 130 Gy (ZauschLum 5) and ca. 75 Gy (Zausch-Lum 1). The measured/given dose ratio for Zausch-Lum 5 was
1.07 ± 0.01 and 1.09 ± 0.02 for Zausch-Lum 1 (without subtracting De residuals). Hence, in
both cases the De determined by the pIRIR290 measurement slightly overestimated the given
dose, but in each case the result was within a deviation of < 10 %.
Measured mean De-residuals determined on 3 aliquots after bleaching for 4 h under solar
simulator were 14.9 ± 1.4 Gy for sample Zausch-Lum 5 and 18.4 ± 1.4 Gy for sample ZauschLum 1. If these residuals are subtracted from the De’s obtained by the dose recovery tests, the
measured/given doses are at 0.95 ± 0.01 (Zausch-Lum 5) and 0.85 ± 0.04 (Zausch-Lum 1).
Hence, the dose recovery for sample Zausch-Lum 5 is slightly optimized by subtracting
residuals whereas for Zausch-Lum 1 the result turns out to be less satisfying.
The dose residuals measured after daylight-bleaching for 4 h were at 11.4 ± 1.3 Gy for sample
Zausch-Lum 5, and at 12.3 ± 0.1 Gy for sample Zausch-Lum 1. After bleaching for 10 h, the
residuals could further be reduced to 10.0 ± 1.1 Gy (Zausch-Lum 5) and 10.5 ± 0.6 Gy
(Zausch-Lum 1), respectively. The results show that daylight bleaching was more effective
than bleaching under the solar lamp, and that dose residuals can be decreased by increasing
the bleaching time.
It is known that the pIRIR290 signal is much harder to bleach than the IR50 signal (see Fig. 6),
and the question whether and how residual doses should be subtracted from measured De’s for
age calculation is still under debate. Whereas e.g. Lowick et al. (2012) subtracted residual
doses determined by measuring aliquots after bleaching for 24 h under a UV lamp, Thiel et al.
(2012) showed that the pIRIR290 signal can be reduced to a very low level under natural
conditions. They obtained a pIRIR290 age of 1.3 ± 0.6 ka for a modern analogue sample from
Tunisia. Using samples from different regions, Buylaert et al. (2012) showed that the amount
of the residual dose increases with the De value (increasing residuals with increasing burial
period) and the fitted line of their samples had an intercept of 4 ± 2 Gy. Since this intercept
was similar to the residual dose obtained from their modern analogue samples, they concluded
that a contribution of the residual dose to their De-values was about 5 Gy. A new approach for
residual correction was recently proposed by Li et al. (2013), who suggested an intensity
subtraction method to account for the residual dose.
It is important to note that the residual dose at time of deposition (after a natural transport
cycle) might be lower than the residual dose measured after a burial period of several ka and
the following exposure of the material to a solar lamp. Nevertheless, not correcting for
residual doses would most likely produce maximum ages. Thus, when thinking about the
amount of the residual dose one must consider the way of sediment transport prior to burial:
One can assume that the loess of the Zauschwitz exposure was first transported in a fluvial
(braided river) system where it was temporarily deposited, before it was finally deflated and
transported by wind. Furthermore, after its deposition at the Zauschwitz exposure the material
was most likely not buried directly. Hence, although there was probably only a relatively
short aeolian transport of about 20 km between the valley of the Saale river as the main dust
source (indicated by elevated carbonate contents of the loess, see below) and Zauschwitz, the
natural bleaching time might have been for several hours or even days. Based on this
assumption an estimated value of 10 Gy was subtracted from all measured De-values for age
calculation, according to the residuals measured after 10 h of sunlight exposure (rounded
mean value).
Measured De-values and calculated luminescence ages are shown in Table 2. All samples
yield similar luminescence ages, ranging from 22.2 ± 1.4 ka (Zausch-Lum 5) to 18.1 ± 1.2 ka
(Zausch-Lum 1).
Although there are no age inversions inside error bars and thus the chronostratigraphy seems
to be reliable, stratigraphic correlations show that the luminescence ages of the lower part of
the loess sequence (below N2, Fig. 4) seem to be be significantly underestimated (see
discussion below). However, the chronostratigraphy generally shows that the loess-sequence
in Zauschwitz was obviously accumulated within a relatively short period during the late
Weichselian Pleniglacial, i.e. mostly during the Last Glacial Maximum (LGM) ranging from
26.5 to 19/20 ka following Clark et al. (2009).
It also has to be considered that no fading corrections were conducted for the pIRIR-ages
from Zauschwitz. Thiel et al. (2011b) showed that no fading corrections were mandatory for
their samples when using the pIRIR290 signal, and also Buylaert et al. (2012) show that it is
unlikely that the pIRIR290 signal was affected by significant fading. Hence, a significant age
underestimation for the Zauschwitz samples due to fading is not assumed. Nevertheless,
Lowick et al. (2012) mentioned that remaining dose residuals might mask the fading effect,
and generally a separation of both effects (fading and residuals) is difficult. Thus, the obtained
ages have to be taken as rough age estimations.
Carbonate content
Apart from the mostly decalcified Holocene soil-material, the whole loess sequence contains
carbonate in different percentages (Fig. 4). In the lower part (N5 and N4), carbonate content
drops to values mostly < 5 %, whereas carbonate contents vary between 16 % and 9 % in the
upper part of the profile (L2, N1, L1). Generally, the content of CaCO3 decreases with
increasing depth, except for some peaks in zones with secondary carbonate enrichment, the
most prominent peak being at the base of N3 a were also carbonate concretions can be found.
Following Haase et al. (1970) the average carbonate content of Eastern/Central German loess
is 8 –12 %, but can reach maximum values of up to > 20 % close to areas with the large
occurrence of limestones as for example in parts of Thuringia. Accordingly, the carbonate
content of Weichselian loess in the region west of the Weisse Elster river is relatively high,
due to Muschelkalk limestone that is widespread in the catchment of the Saale river (Fig. 1).
The Saale river bed is regarded as the major source for aeolian dust in the Zauschwitz region
during the Weichselian Pleniglacial (Neumeister 1971).
Magnetic susceptibility
In Zauschwitz, lowest χ-values (around 0.1 * 10-6 m3/kg) are found in units N5 and N4 at the
bottom of the exposure (Fig. 4), probably due to a destruction of the magnetic signal by strong
hydromorphic processes that were observed in these layers (Hanesch & Scholger 2005).
Upwards, χ-values are only very slightly changing up to layer N2: Here, in a depth of about
280 cm close to the lower limit of that layer χ-values are at about 0.15 – 0.13 * 10-6 m3/kg,
and above they slightly jump to values of about 0.2 * 10-6 m3/kg in the overlying loess.
Interestingly, a similar trend was also described for loess sequences from Central Saxony at a
similar stratigraphic position, ascribed to a change of sedimentation conditions (Baumgart et
al. 2013, Fig. 9). Therefore, similar to the situation in Central Saxony one can obviously use
magnetic susceptibility as an indicator to distinguish between laminated and homogeneous
Upper Weichselian Pleniglacial loess.
The most significant increase in χ-values is seen at the transition from the mostly unweathered
loess L1 to the overlying black soil material, where χ-values up to 0.9 * 10-6 m3/kg are found
(Fig. 4). Similar values were reported by Hanesch & Scholger (2005) for black soils in
Austria, and by Jordanova & Jordanova (1999) for a chernozem in Bulgaria. Similarly, low
values of χfd (mostly < 2 %) in the Late Pleniglacial loess sequence are strongly increasing in
the overlying Holocene black soil material as well, reaching values of almost 10 % here. Such
high values of χfd indicate high biological activity producing a large amount of ultra-fine
superparamagnetic particles, so that the magnetic enhancement was obviously caused by
Holocene pedogenesis. Although the seesaw-pattern of χfd in the Pleniglacial part of the
sequence was caused by measurement errors due to low absolute values of χ, one peak with
values up to 4 % in unit N3 a between 408 and 472 cm seems to be recognizable. This could
indicate a somewhat more intensive pedogenesis in this layer, compared with the other
Pleniglacial soils of the profile.
Granulometry
The grain size data show relatively strong variations in the lowermost part of the Zauschwitz
exposure, with a coarsening-up tendency starting in N5 until a fine sand content of about 15
% is reached in the sand layer separating N5 and N4. Above, a fining-up sequence (N4) is
found and sand decreases to 0 % in the upper part of N4 (Fig. 4). Additionally to its
geomorphological position quite close above fluvial gravels and sands, this interplay between
coarsening- and fining up patterns supports the idea of partly fluvial deposition of the
sediments in the lowermost part of the outcropped Zauschwitz exposure.
From the upper part of N4 up to the lower boundary of N2 grain sizes generally increase.
This is reflected by fine sand as well as by the U-ratio, with one interruption by lower values
in unit N3 a. Scattering grain sizes in the layered loess-unit Ll3 reflect different grain size
patterns in the singular layers of the laminations. In the upper mostly undisturbed part of the
sequence starting with N2, grain sizes become generally finer again (Fig. 4). A similar trend
of increasing grain sizes in layered late Pleistocene loess and smaller grain sizes in overlying
undisturbed loess was observed by Antoine et al. (2013) for the Dolní Vĕstonice loesspalaeosol sequence in southern Bohemia.
Generally, the tundra gley soils within the Zauschwitz exposure (N1, N2, N3a, N4, N5,
although not N3b) are characterized by finer grain sizes when compared with the intercalated
loess-layers Ll3, L2 and L1. This is seen in low values of both fine sand and the U-ratio
(black arrows in Fig. 4).
5. Discussion: Evidences for palaeoenvironmental changes during the Late Pleniglacial
Basal part (Fluvial sands and units N5/N4)
For the fluvial sands and gravels below the Zauschwitz exposure no chronological data are
available yet. According to Fuhrmann (1976) they should originate from the late Saalian
period. However, a Weichselian age of the gravels below the Zauschwitz loess exposure is
much more likely: i) Luminescence dating results obtained from the lowermost part of the
exposed sediments in Zauschwitz (although probably somewhat underestimated) are not older
than the late Weichselian Pleniglacial. Additionally, in case of an early Saalian age of the
gravels as formerly assumed, late Saalian, Eemian and Early- to Mid-Weichselian sediments
would be missing here. ii) Furthermore more recent stratigraphic investigations close to
Zauschwitz gave evidence of only one homogenous terrace body of the Weisse Elster river
there, and a 14C-age of 37.3 cal.ka BP obtained from that terrace suggests that Weichselian
gravels most likely extend much further to the west of the recent valley than previously
assumed. Consequently, a Weichselian age of the fluvial gravels and sands should be assumed
(fQW? in Fig. 3).
The overlying silt-dominated sediments forming N5 and N4 could be interpreted as aeolian
sediments. Göbler (1966) described the sandy layer between N5 and N4 at 630 cm as
evidence for an erosional period during the early Weichselian. However, our luminescence
dating yielded Weichselian Late Pleniglacial ages for these sediments. Furthermore,
significant shifts in grain sizes (including the sandy layer) demonstrate that this basal part
must be interpreted as the transitional zone between the Weichselian Weisse Elster floodplain
and the proximal areas of dust accumulation.
The hydromorphological features of N5 and N4 were already mentioned by Fuhrmann (1976)
who consequently termed the material “Sumpflöss” (swampy loess). According to that author,
the manifold mollusk fauna indicates a wet/swampy environment.
The residual-corrected (although probably somewhat underestimated, see below)
luminescence age of 22.2 ± 1.4 ka (Fig. 4) shows that the initial loess deposition at
Zauschwitz did not start before ca. 30 ka. Thus, unit IV and the lower parts of Unit III of the
Central Saxonian composite profile (Meszner et al. 2013) are not preserved in Zauschwitz
(Fig. 8).The rather late start of loess deposition in Zauschwitz was obviously due to enhanced
activity of the nearby Weisse Elster river prior to the onset of loess deposition until ca. 30 ka:
Accordingly, Mol (1995) reports a strong decrease of discharge of the Weisse Elster river due
to aridity during the late phase of the Weichselian Pleniglacial. Furthermore, from the Central
Saxonian loess area Meszner et al. (2013) report at least slightly more humid conditions for
their sedimentary unit III, following with more arid conditions starting somewhat after 30 ka.
Middle part (N3 b/a and Ll3)
The occurrence of two mighty tundra gley soils (N3a, N3b) as well as the laminated loess
indicate active reworking of the aeolian material in the middle part of the sequence (N3b to
Ll3).This points to still quite wet conditions during that period.
Following Meszner et al. (2013), Pleniglacial tundra gley soils indicate reduced dust
accumulation rates in which the surface was repeatedly activated by thawing during summer.
The authors postulate permanent water saturation for the active layer during the thawing
season due to lowered evaporation. This corresponds with the observed bleaching of our
tundra gley soils at Zauschwitz. Smaller grain sizes found in Zauschwitz tundra gley soils
(arrows in Fig. 4) agree with reduced dust accumulation rates, since they indicate lower wind
speed and/or more stabilized land surfaces (reducing dust mobilization) during those periods.
Accordingly, Antoine et al. (2013) observed smaller grain sizes in late Pleistocene tundra gley
soils in the Dolní Vĕstonice loess-palaeosol sequence in southern Bohemia as well. The
laminations in loess layer Ll3 might indicate the alternation of snow coverage with melting
and reworking of the loess during summer, a process that finally leads to thin layering.
Based on the lithostratigraphy and the low values of mass specific magnetic susceptibility the
middle part of the Zauschwitz exposure can most likely be correlated with unit IIb of the
composite profile from Central Saxony (Figs. 8 and 9). Furthermore, the small peak of χfd in
N3a (Fig. 4) indicates more intensive pedogenesis in this layer, confirming its correlation with
the quite intensive fBvc’s of unit IIb in Central Saxony (Fig. 8).
However, quartz (4 –11 µm) OSL-age estimates for that unit presented by Meszner et al.
(2013) range from 25.1 ± 3.4 ka to 28.0 ± 3.8 ka (Ostrau site), and from 26.7 ± 3.3 ka to 31.1
± 4.1 ka at Seilitz. Hence, those ages are significantly older than our age estimates obtained
by pIRIR290-luminescence, ranging between 21.3 ± 1.8 and 22 ± 1.4 ka. Since our
lithostratigraphic and magnetic correlation is interpreted to be quite robust, our pIRIR290 ages
seem to be underestimated by some ka. Causes for this underestimation could be some
anomalous fading of the luminescence signal (e.g. Lowick et al. 2012), or strong bleaching of
the residual dose in natural conditions – caused by long exposure of the material in this part of
the profile to sunlight due to repeated reworking – as described by Thiel et al. (2012).
Nevertheless, the latter cause might have contributed to an age underestimation of maximum
about 2 ka if taking into account the dose rates and the estimated residuals of 10 Gy.
Upper part (N2, L2+L1 and Holocene soil)
The upper part of the Zauschwitz exposure starts with tundra gley soil N2, separating the
layered and reworked loess below from the mostly undisturbed loess above. The N2 tundra
gley soil is known from the Central Saxonian loess area as well, and is situated at the bottom
of unit IIa (Meszner et al. 2013). Thus, N2, L2, N1 and L1 can most likely be correlated with
unit IIa from the Saxonian composite profile (Fig. 8). Inside error bars, our pIRIR290 age
estimates (20.9 ± 1.4 and 18.1 ± 1.2 ka) fit quite well to the quartz (4 –11 µm) luminescence
ages from Central Saxony for unit IIa (between 21.7 ± 2.8 ka and 15.1 ± 2.8 ka, Meszner et al.
2013). However, this is at odds with the underlying unit IIb where our pIRIR290 ages from
Zauschwitz significantly underestimate those from Central Saxony. Apart from a stronger
bleaching of the residual signal in the lower parts of the profile due to intensive reworking
(see above), a change of sedimentation conditions as indicated by the jump of mass-specific
magnetic susceptibility at the base of N2 (Fig. 9) could have been linked with a change of the
sediment source so that the feldspars could show different fading-characteristics. However,
these assumptions are rather speculative yet and have to be investigated in detail by further
studies.
A similar lithostratigraphic shift from laminated to homogeneous loess during the late
Weichselian Pleniglacial was observed in several other loess areas in Europe as well: Antoine
et al. (2013) showed such a transition for the Dolní Vĕstonice loess-palaeosol sequence in
southern Bohemia. Likewise, for the Lower-Rhine-Maas area Schirmer (2000) describes
laminated loess (“Hesbaye-Löss”), subdivided by wet soils (“Erbenheimer Nassböden”) that
is overlain by yellowish and almost undisturbed loess from the last glacial maximum
(“Brabant-Löss”), subdivided by dry and wet soils. In the Dutch-Belgian loess regions,
Vandenberghe et al. (1998) labeled the laminated loess as “Middle Silt Loam” (MSL),
separated by a strong tundra gley soil (“Nagelbeek-horizon”) from the undisturbed loess
called “Upper Silt Loam” (USL). From Zeuchfeld (Saxony-Anhalt, Fig. 2), Kreutzer et al.
(this volume) report a similar transition from underlying laminated to hardly disturbed loess
occurring between 30.7 and 22.6 ka.
The relatively homogenous loess of layers L1 and L2 represents a Pleniglacial period when
less humidity was available compared with the environmental conditions before. Hence,
similar to other studies from Central Europe (e.g. Antoine et al. 2013, Meszner et al. 2013)
our data indicate a cold and dry climate in Central Western Saxony during the latest
Weichselian Pleniglacial.
The black soil material at the top of the profile shows intensive Holocene soil formation and
subsequent reworking, and thus reflects the mild climatic conditions of the present interglacial
as well as intensive human activity. The latter is not surprising, since the area was one of the
most densely populated regions of Central Germany during prehistoric times (Tinapp 2002,
2008, Bergemann 2012). The settlement history dates back to the early Neolithic so-called
“Linienbandkeramik” period, and the diversity of artifact findings even in some dm depth
ranging from the Neolithic to the Slavic period demonstrates the attractiveness of the area for
human settlement due to the high fertility of the loess soils. Due to erosion and reworking, the
present Holocene soil cannot be seen as an insitu phaeozem. Nevertheless, in the transitional
zone between the colluvial deposits and the uppermost loess layer (L1), in situ black soil
material is most likely preserved as evidenced by results of the micromorphological analysis:
Features indicating a dislocation or colluviation of material like charcoal fragments, artifacts
or dislocated aggregates of older soil material could not be observed here. Instead, the
material of the transitional zone is characterized by intensive bioturbation and fine organic
material being homogenously distributed and closely associated with mineral components, a
typical attribute of mollic horizons. Black soils as that developed in Zauschwitz are
widespread in Central Germany, where due to its position in the lee of the Harz-mountains
(Fig. 1) a relatively dry subcontinental climate is found (cf. Eckmeier et al. 2007).
6. Summary and conclusions
The Zauschwitz loess sequence provides a terrestrial sediment archive hosting information on
the Western Saxonian palaeoenvironmental history during the late Weichselian Pleniglacial.
Due to stronger fluvial activity of the Weisse Elster river prior to ca. 30 ka, Early-/Middle
Weichselian loess or the Eemian interglacial soil are not found here. Instead, fluvial sediments
were deposited. The onset of loess sedimentation at Zauschwitz was only facilitated by
decreased fluvial activity of the Weisse Elster river, allowing a sedimentation of aeolian
sediments on top of the fluvial gravels and sands of the Weisse Elster river after ca. 30 ka.
Strong reworking features, tundra gley soils and laminated/cryoturbated loess of the lower and
middle part of the Zauschwitz loess exposure demonstrate cold but still quite humid regional
conditions during the first part of the Last Glacial Maximum until ca. 22 ka. This period was
followed by mostly undisturbed loess sedimentation (represented by units L2 and L1),
indicating an arid and cold palaeoenvironment during the later part of the Last Glacial
Maximum, i.e. the latest Weichselian Pleniglacial. Smaller grain sizes of the tundra gley soils
found in the loess sequence indicate less dust transport during these periods, caused by lower
wind speed and/or more stable landscape conditions.
Thus, the sequence of basal fluvial and overlying loess sediments in the Zauschwitz loam pit
indicates a progressive landscape aridification of the region during the late Weichselian
Pleniglacial after ca. 30 ka.
Acknowledgements
We are grateful to Dr. Birgit Schneider and Katja P lmann from Chair of Physical
Geography (Leipzig University) for supervising student lab works in the context of this study.
We are grateful to Sonja Riemenschneider from the Leibniz Institute for Applied Geophysics
(LIAG) in Hanover (Germany) for preparation of luminescence samples and for grain size
measurements. Furthermore, we want to thank Dr. Sumiko Tsukamoto and Sabine Mogwitz
from LIAG for gamma ray spectrometry measurements. We are grateful to Sumiko
Tsukamoto for scientific support.
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Tables
Table 1
Measurement sequence of luminescence dating, applying the pIRIR290 approach similar to
Thiel et al. (2011a, b). In contrary to those authors, the IR50 bleach was conducted for only
100 s instead of 200 s (see e.g. Fu et al. 2012). At the end of each measurement cycle a
hotbleach was conducted (step 9) to clean out residuals. IR measurements were started after
holding the aliquots at measurement temperature for 5 s, in order to account for isothermal TL
signal contribution (cf. Fu et a. 2012).
Table 2
Luminescence data and results of gamma-ray spectrometry: De-values were estimated using
the pIRIR290 approach. De1 shows the mean De-values without subtracting residuals, whereas
for age calculation 10 Gy were subtracted from all De-values to account for residuals (De2).
Mean De-values are quoted with their standard errors. A recycling ratio > 10 % was used as a
rejection criteria for measured De-values. Recycling ratios are quoted with their standard
errors.
Figures
Figure 1
Overview of the study area with ice marginal positions of Elsterian and Saalian stages in
Central/Eastern Germany (modified after Eissmann 2002, 2008). During the Weichselian
Glacial, the study site (star symbol) was under periglacial conditions so that several meters of
loess could be accumulated. The occurrence of triassic Muschelkalk-limestone in the Saalecatchment is indicated with hatching (www.umweltbundesamt.de), and the area of Fig. 2 is
indicated with a dashed frame.
Figure 2
Distribution of loess deposits in Central Germany after Haase et al. (1970). The Zauschwitz
loess profile (big star symbol) is located at the northernmost border of continuous loess
distribution in Saxony (Lössrandstufe). The loess sites of Zeuchfeld in Saxony-Anhalt
(Kreutzer et al., this volume) and Seilitz/Ostrau in the Central Saxonian loess area (Meszner
et al. 2013) are marked with small star symbols.
Figure 3
Geological cross-section through the valley of the Weiße Elster river close to Zauschwitz. The
cross-section was generated based on the modified Lithofacies-map (LQZ1 : 50000) of
Leipzig. The location of the profile is indicated with a black rectangle.
Figure 4
Zauschwitz profile with lithostratigraphical subdivision, pIRIR290 luminescence-ages, results
of magnetic susceptibility, carbonate and grain size measurements.
Figure 5
Photographs from the micromorphological thin section taken in the transitional zone between
the uppermost loess L1 and the overlying black soil material on the top of the profile (Fig. 2).
a) bioturbate channel microstructure, b) bioturbate spongy microstructure, c) lumbricidae
excrements d) the same as c, but with crossed polarizer. The lighter colour of the infilling due
to the admixture with loess from underlying loess L1 is clearly recognizable.
Figure 6
Decay curves of the IR50 and pIRIR290 signal from sample Zausch-Lum 3. The pIRIR290 signal
is measured after depleting the IR50 signal for which higher fading rates are expected. In
difference, the elevated temperature pIRIR290 signal is characterized by high stability (Thiel et
al. 2011b). However, the pIRIR290 signal is harder to bleach than the IR50 signal.
Figure 7
Dose response curve from sample Zausch-Lum 3 using the pIRIR290 signal. After measuring
the natural luminescence signal, the zero regenerative dose signal (R1; Di = 0 Gy) was
detected. Subsequent, four (artificial) regenerative doses (R2 –R5) were applied to build up
the growth curve and afterwards the R2-measurement cycle was repeated (R6) to determine
the recycling ratio (R6 / R2). The sensitivity corrected natural signal (Lx/Tx) was then
interpolated into the curve to obtain the equivalent dose (De).
Figure 8
Correlation of the Zauschwitz loess profile with the composite profile of the Saxonian Loess
area (Meszner et al. 2013). Quoted luminescences ages of the composite profile (right side)
are fine grain quartz ages (4 –11 µm) and show the age ranges (minimum/maximum) obtained
for the profiles Seilitz and Ostrau.
Figure 9
Correlation between the trends of magnetic susceptibility in Zauschwitz with those from
Seilitz and Ostrau in Central Saxony.