Loess–palaeosol sequences (LPSs) of the oceanic-influenced European loess belt underwent frequent post-depositional processes induced by surface runoff or periglacial processes. The interpretation of such atypical LPSs is not straightforward, and they cannot be easily used for regional to continental correlations. Within the last few years, however, such sequences gained increased attention, as they are valuable archives for regional landscape dynamics. In this study, the Siersdorf LPS was analysed using a multi-proxy approach using sedimentological, geochemical, and spectrophotometric methods combined with luminescence dating and tentative malacological tests to unravel Pleniglacial dynamics of the Lower Rhine Embayment. A marshy wetland environment for the late Middle Pleniglacial to the early Upper Pleniglacial was shown by colour reflectance and grain size distribution. Age inversions from luminescence dating paired with geochemical and sedimentological data reveal long-lasting erosional processes during the early Upper Pleniglacial, which were constrained to a relatively small catchment with short transport ranges. The upper sequence shows typical marker horizons for the study area and indicate harsh, cold-arid conditions for the late Upper Pleniglacial. In comparison with other terrestrial archives, the Siersdorf LPS shows that the Lower Rhine Embayment was more diverse than previously assumed, regarding not only its geomorphological settings and related processes but also its ecosystems and environments.
Die Lössprofile des ozeanisch beeinflussten europäischen Lössgürtels wurden häufig durch Oberflächenabfluss oder periglaziale Prozesse umgelagert. Die Interpretation solcher atypischen LPS ist nicht einfach und sie können nicht ohne weiteres für regionale bis kontinentale Korrelationen verwendet werden. In den letzten Jahren haben solche Sequenzen jedoch zunehmend an Bedeutung gewonnen, da sie wertvolle Archive für die regionale Landschaftsdynamik darstellen. In dieser Studie wurde das Lössprofil Siersdorf mit Hilfe eines Multi-Proxy-Ansatzes analysiert, der sedimentologische, geochemische und spektrophotometrische Methoden mit Lumineszenzdatierungen und versuchsweisen malakologischen Untersuchungen kombiniert, um die pleniglaziale Dynamik der Niederrheinischen Bucht zu entschlüsseln. Die Farbadaten und die Korngrößenverteilungen zeigen, dass das Profil vom späten Mittelpleniglazial bis zum frühen Oberpleniglazial in einem sumpfigen Feuchtgebiet lag. Altersinversionen aus Lumineszenzdatierungen gepaart mit geochemischen und sedimentologischen Daten lassen auf lang anhaltende Erosionsprozesse während des frühen Oberen Pleniglazials schließen, die auf ein relativ kleines Einzugsgebiet mit kurzen Transportstrecken beschränkt waren. Die obere Abfolge zeigt typische Markerhorizonte für das Untersuchungsgebiet und weist auf raue, kalt-trockene Bedingungen für das späte Obere Pleniglazial hin. Im Vergleich zu anderen terrestrischen Archiven zeigt das Siersdorfer LPS, dass die Niederrheinische Bucht vielfältiger war als bisher angenommen, nicht nur in Bezug auf ihre geomorphologischen Gegebenheiten und die damit verbundenen Prozesse, sondern auch in Bezug auf ihre Ökosysteme und Lebensräume.
Throughout the last few decades, loess–palaeosol sequences (LPSs) have been frequently analysed to reconstruct palaeoclimatic and palaeoenvironmental conditions of the terrestrial realms (Hatté et al., 2001, 2013; Marković et al., 2005; Kukla et al., 1988; Zech et al., 2013; Torre et al., 2020; Varga et al., 2011). Therefore, sequences are investigated, which are as complete and undisturbed as possible to allow interregional correlations (Marković et al., 2018; Lehmkuhl et al., 2016) or direct reconstructions of atmospheric conditions (Obreht et al., 2017; Rousseau and Hatté, 2021; Bokhorst et al., 2011). These aeolian LPSs were formed out of mineral dust, which was deposited on topographic barriers (Lehmkuhl et al., 2016; Antoine et al., 2016), biological crusts (Svirčev et al., 2013), or vegetation, typically grasses (Zech et al., 2013, 2011). The deposited dust undergoes quasi-pedogenic processes called loessification processes (Sprafke and Obreht, 2016), leading to its unique characteristics, such as its silty texture and porosity (Pécsi and Richter, 1996; Koch and Neumeister, 2005). Due to these properties, loess is prone to post-depositional reworking and erosion, especially by water (Meszner et al., 2013, p. 201), and in regions affected by permafrost, by periglacial activities and slope processes (Lehmkuhl et al., 2021, 2016). This proneness can lead to hiatuses in the stratigraphy (Obreht et al., 2015; Steup and Fuchs, 2017) or the reworking of sediments. Additionally, weathering and soil formation processes, such as decalcification, feldspar weathering, or lessivation of clay, can transform the pristine sediments on various scales and can give valuable hints on past environmental conditions (Fenn et al., 2020, 2021; Marković et al., 2018; Lehmkuhl et al., 2016).
The European loess belt (ELB; loess domain II sensu; Lehmkuhl et al., 2021), stretches from the shores of the English Channel (Antoine et al., 2003; Stevens et al., 2020) throughout Belgium (Haesaerts et al., 2016), Germany (Lehmkuhl et al., 2018), and Poland (Jary and Ciszek, 2013) towards Ukraine (Veres et al., 2018). Especially the western ELB (subdomain IIa sensu; Lehmkuhl et al., 2021), which is characterised by a humid, oceanic climate, was prone to erosional processes such as slope wash or solifluction (Lehmkuhl et al., 2016). These conditions led to frequent reorganisation processes of landscape systems due to widespread erosion throughout the ELB (Meszner et al., 2013), partially leading to relief reversals (Fischer et al., 2012; Kels, 2007; Lehmkuhl et al., 2015). The continental ice sheets to the north and the periglacially shaped central European uplands to the south dominated the Pleistocene palaeogeography of the ELB, acting as potential dust sources of Pleistocene loess deposits due to high production rates of detrital material (Baykal et al., 2021; Skurzyński et al., 2019, 2020; Vinnepand et al., 2022). Additionally, the climatic conditions and vicinity to continental and Alpine ice sheets induced periglacial conditions, especially during glacial and stadial phases (Jary, 2009; Lehmkuhl et al., 2021; Vandenberghe et al., 2014; Stadelmaier et al., 2021).
The results of these processes are, compared to other European loess regions like the Danube Basin (Marković et al., 2015), complex stratigraphic records with unconformities and polygenetic pedocomplexes in the western ELB. Therefore, complete Late Pleistocene LPSs, without any hiatuses or discordances, are scarce (Schirmer, 2002; Zens et al., 2018). Within the last few years, however, considerable attention was given to non-typical LPSs, which were either strongly reworked (Klinge et al., 2017; Steup and Fuchs, 2017; Meszner et al., 2014) or which were characterised by changing depositional milieus (Mayr et al., 2017; Sümegi et al., 2015; Hošek et al., 2017). These archives allow a detailed view of the interplay of climate, landscape development, and environment and are, therefore, a crucial addition to the vast set of Pleistocene sediment archives.
Here, we present geochronological and proxy data for a new LPS in the Lower Rhine Embayment (North Rhine-Westphalia, Germany). The Siersdorf (SID) LPS developed in a channel incised into an older Pleistocene terrace of the Meuse. It represents a high-resolution record of the transition from the late Middle (MPG) to the Upper Pleniglacial (UPG). Unlike typical LPSs from the area, the Middle Pleniglacial stadial conditions are not imprinted as a series of phases of differently intense soil formation processes but as a uniform unit of greyish-brownish silt, most likely linked to semi-terrestrial marshy conditions. In this study, we analyse the sedimentological, geochemical, and spectrophotometric data to unravel the genesis of this atypical sedimentary succession. The geomorphological and palaeoenvironmental ramifications are discussed in the framework of loess research in the Rhine catchment. The Siersdorf LPS is a crucial addition to the framework of Pleniglacial landscape reconstruction, as it is so far the first reported LPS from the Lower Rhine Embayment which records semi-terrestrial conditions during the late Middle Pleniglacial to Upper Pleniglacial. This reconstruction shows that the Pleniglacial Lower Rhine Embayment was more diverse than previously assumed, regarding not only its geomorphological settings and related processes but also its ecosystems and environments.
The Lower Rhine Embayment (LRE) is part of the European rift system and covers the southernmost part of the Lower Rhine catchment. It is situated on the transition of the central European uplands, namely the Rhenish Massif, and the northern German lowlands (Böse et al., 2022). As a loess region, the LRE is part of the western European maritime (Atlantic) loess subdomain of the ELB sensu (Lehmkuhl et al., 2021). This part of the ELB was dominated by North Atlantic climate conditions during the Late Pleistocene (Antoine et al., 2001, 2009; Fischer et al., 2021). Due to the oceanic climate and the accompanied high landscape dynamics (Fischer et al., 2017), the distribution and characteristics of loess deposits in the LRE are strongly site-specific, depending on geomorphological settings and related processes.
Four main geomorphological positions for LPSs can be summarised
(Lehmkuhl et al., 2016). LPSs in plateau
situations are often affected by erosion, both by surface runoff and by
deflation (Schirmer, 2016; Antoine et al., 2016).
Additionally, chemical processes such as (carbonate) solution and leaching
may affect these sequences. Slope positions in the LRE are especially prone
to erosional processes. Truncation, e.g. related to phases of widespread
erosion, may remove previously formed LPSs in their entirety
(Schirmer, 2016). Similar conditions have been reported from
adjacent regions of the ELB (Meszner et al.,
2013; Antoine et al., 2016). Besides fluvial relocation, processes such as
solifluction play a major role in slope positions (Lehmkuhl et al., 2016). Under periglacial conditions, a slope gradient of 2
The LRE builds the easternmost part of this maritime loess domain, which shows comparable stratigraphic records for the Late Pleistocene from northern France towards the study area (Haesaerts et al., 2011; Meijs, 2002; Schirmer, 2016; Antoine et al., 2014): the oldest sequence builds the last interglacial, i.e. Eemian, palaeosol, a truncated brown-leached soil complex. The Weichselian glacial succession starts with an early glacial (115–72 ka) complex, consisting of a grey forest soil and a steppe-like soil. The Lower Pleniglacial (LPG; 70–58 ka) is the phase with the first reported (and preserved) loess formation in central Europe (Frechen et al., 2003), accompanied by periglacial conditions. The Middle Pleniglacial (MPG; 58–32 ka) was characterised by reduced dust accumulation (Antoine et al., 2001), frequent relocation of older sediments and soils (Meszner et al., 2013), and phases of soil formation (Fischer et al., 2021; Schirmer et al., 2012). However, MPG sequences are often only preserved in geomorphologically favourable settings. The Upper Pleniglacial (UPG; 32–15 ka) was characterised by enhanced dust accretion and harsh, periglacial conditions (Lehmkuhl et al., 2021). Typical features for these periods are Gelic Gleysols (tundra gleys) and ice-wedge casts (Antoine et al., 2016). In the LRE, the UPG deposits show a typical succession encompassing inter alia the so-called Eben Zone (Schirmer, 2003).
Location of the Siersdorf LPS (black triangle)
The study site is located within the so-called Aldenhoven loess plateau as part of the Börde region of Jülich (Knaak et al., 2021). This plateau, situated between the Wurm, Inde, and Rur rivers in the foreland of the northern Eifel Mountains (Fig. 1), is slightly inclined towards the northeast (170–75 m a.s.l.). Vast loess blankets cover the palaeorelief, which is characterised by small dendritic river systems. These blankets mainly formed during the Late Pleistocene as dust was entrained from the Middle Pleistocene terraces of the Rhine, Meuse, and Rur rivers. Steps in the landscape, where loess thicknesses vary considerably within a few metres, are indicative of recent differential tectonic processes. Late Pleistocene to Holocene features approx. 1 km northwest of the studied sequence, such as solifluction layers or other stratigraphic markers, show tectonically induced offsets of approx. 1 m, indicating younger tectonic movements (Fig. S1 in the Supplement). Additionally, tectonics shaped the hydrological system, as river deflections are abundant in the study area.
The Siersdorf (SID) LPS was exposed during construction works of the Zeelink natural gas pipeline in the central part of the Aldenhoven loess plateau (Fig. 1). The investigated sequence is 6 m thick (Fig. 2) and developed within a channel of a presumably Middle Pleistocene terrace of the Meuse. The deposits of the Meuse covered large parts of the central LRE during the Pleistocene (Boenigk and Frechen, 2006). The incised channel acted as a sediment trap throughout the Late Pleistocene and Holocene. Based on field observations, the sequence can be subdivided into five main units: the base, unit I, is characterised by greyish-dark-brownish silts, which change colour during drying to grey. Nearby core drillings indicate strong hydromorphic overprinting of these layers (Fig. S2). The upper part of this layer shows a high abundance of mollusc shells and shell fragments. The overlying loess (unit II) is laminated and partially characterised by cryoturbation features. At the base of this relocated loess, a thin, blackish layer occurs. The laminated layer stretches from 4.8 to 3.5 m below surface. Small ice-wedge pseudomorphs frequently disturb the layering, which shows varying contents of silt and sand. On top of the layered loess adjoins an orange, wavy layer (unit III). Greyish-brownish palaeosol layers, which show characteristics of Gelic Gleysols, built the uppermost part of unit III. Above this complex, the sequence consists of relatively unaltered loess (unit IV). This loess is also the fill material for massive ice-wedge pseudomorphs approx. 3 m left of the sampled section, which pierces the below-lying units until the top of the lowermost layer (Fig. 2). A humic, finely layered colluvial unit covers the loess (unit V). This reworked sediment contains small pebbles and charcoal flitters. The uppermost 90 cm of the sequence is anthropogenically disturbed.
The SID LPS was sampled in May 2021 after exposure during construction works of the Zeelink natural gas pipeline. Prior to description and sampling, several decimetres of exposed sediments were removed to avoid contamination with weathered and relocated material. The sequence was described in detail from the bottom to the top. Samples for sedimentological, geochemical, and colorimetric analyses were taken in a continuous sampling trench. Sampling was conducted using freshly cleaned tools and sterile plastic bags. The anthropogenically disturbed uppermost 90 cm was not sampled. The colluvial unit (0.9–1.7 m) was sampled in 10 cm increments, whereas the rest of the sequence was sampled every 5 cm.
For luminescence dating, six samples were taken horizontally with steel cylinders from selected units (for position of samples, see Fig. 2). Subsequently, the sediment within a 30 cm distance to the cylinders was sampled for dose rate determination.
The samples were dried at 35
Heatmap visualisation of grain size distribution displayed with various sedimentological, geochemical, and spectrophotometric proxies of the Siersdorf LPS. Stratigraphic units (I–V) are shown for orientation.
Heatmap visualisation of the difference between two optical models (
Inorganic geochemistry was analysed using energy dispersive x-ray
fluorescence (EDPXRF) using a SPECTRO XEPOS. This device detects 50
elements from sodium (Na) to uranium (U), excluding erbium and ytterbium.
The samples were sieved to the silt fraction (
Spectrophotometric analysis was conducted using a Konica Minolta CM-5
spectrophotometer, following previously published methodologies
(Eckmeier and Gerlach, 2012;
Vlaminck et al., 2016). This device uses the diffused reflected light from a
standardised source (2
Sample preparation and measurements were conducted in the Cologne
Luminescence Laboratory (Cologne, Germany) and included pre-processing under
red light conditions. Standard procedures of fine-grain preparation included
chemical treatment with HCl (10 %), H
Equivalent dose measurements were performed on an automated Risø TL/OSL
DA-15 reader (DTU Nutech, Roskilde, Denmark) equipped with a calibrated
The suitability of both measurement protocols for the samples of this study
was tested based on preheat plateau (only for quartz samples) and
dose recovery tests (for all samples). Furthermore, laboratory residual
doses after solar simulator bleaching for 24 h and laboratory fading
following Auclair et al. (2003) were determined for pIRIR
Dose rates were determined by measuring uranium, thorium, and
potassium contents using high-resolution gamma spectrometry (Ortec
PROFILE M-Series GEM P-type Coaxial HPGe Gamma-Ray Detector). Dosimetry and
age calculation were conducted in the DRAC environment (version 1.2; Durcan
et al., 2015) using typical water contents of European loess (i.e.
15
The grain size distributions (GSDs) of SID show typical patterns for central European loess deposits. Figure S3 shows the distribution curves for all main units identified during fieldwork. The lowermost unit I shows a unimodal GSD with a mode in the middle-coarse silt fraction. The contents of fine particles, especially fine silt and clay, are elevated. The laminated loess unit shows high variations in GSDs. The overlying cryoturbated loess layers show less variations, with strong modes in coarse silt and varying clay and sand contents. The GSD of the brownish-greyish palaeosol also shows a unimodal shape with a mode in coarse silt. Since other fractions, especially clay, are increased, this mode does not show as high values as the other layers. The uppermost loess layer shows a strong coarse silt mode, whereas the colluvial unit is relatively clay rich.
The geochemical results (Figs. 3–5) were utilised to calculate the Chemical
Index of Alteration (CIA; Nesbitt and Young, 1982) to
determine phases of enhanced chemical weathering. The basal complex does not
show any variations in the CIA with all values being lower than 70. The
laminated loess package shows higher values of
A–CN–K ternary diagram according to Nesbitt and Young (1984) for
the Siersdorf LPS. The Chemical Index of Alteration is displayed on the
The results of the luminescence experiments are presented in the Supplement. All parameters relevant for age calculation and calculated ages for the six luminescence samples are presented in Table 1. Palaeodoses were calculated based on De measurements of 5–10 aliquots that were all accepted for data analysis (the very low scatter between De values did not require a larger number of aliquots). Given the absence of significant over-dispersion (Figs. S11 and S12), the arithmetic mean was chosen as the appropriate age model.
For polymineralic samples, burial doses range from 77
Age depth plot with feldspar ages and quartz ages. Age estimates for the Middle Pleniglacial (MPG), early Upper Pleniglacial (UPGa), late Upper Pleniglacial (UPGb), and the Holocene according to Zens et al. (2018).
The Siersdorf LPS is a valuable archive for Weichselian Pleniglacial landscape dynamics. Combined sedimentological, geochemical, and spectrophotometric methods reveal distinct changes of environmental conditions and associated geomorphic processes during the formation of the investigated LPS, indicating a more heterogeneous environment in the LRE than previously assumed.
Unit I shows uniform patterns in most of the analysed proxy data. Especially
the GSD and
The unit's bright-greyish hues, shown by high
Besides macroscopic similarities between the two units of SID and RGE, the respective sedimentological evidence also points to similar environmental conditions. Both LPSs show unimodal GSDs, dominated by medium-coarse silt with slightly elevated clay contents (Fig. S3). These distributions indicate input of aeolian dust. Increased sand contents indicate additional but considerably less input by surface runoff. The water-saturated conditions are imprinted not only in greyish colours and sedimentology but also in wavy, flaky structures reported from field observations, indicating a micro-layering in a quiescent depositional environment. In RGE and BOB, the sediment is completely bleached and shows signs of intense reduction of ferruginous compounds, namely blueish-greyish hues. In SID, however, the lower intensity of reduction processes indicates shorter phases of semi-terrestrial conditions compared to the former sites. However, another plausible explanation is that the unit did not develop under proper lacustrine conditions comparable to BOB or RGE but in a marshy wetland situation, presumably with seasonal drying phenomena.
Within around 10 %, the carbonate content within unit I allowed the
preservation of a high number of mollusc shells and shell fragments.
Although no samples according to proper malacological protocols were taken,
some cautious interpretation of malacofauna is feasible, always against the
backdrop of the methodological issues. For this rough screening, bulk
sediment samples from unit I were wet sieved (2 mm mesh) to separate the
molluscs from the sediment. The tentative analyses show a poor species
community with only two species comprising a high number (
From a geomorphogenetic point of view, the position of SID in an incised channel favours both sediment accumulation and moisture availability (Lehmkuhl et al., 2016). Especially during times with waterlogging, e.g. induced by permafrost conditions, moisture became concentrated in such depressions. These conditions led to the formation of wetlands, with temporary flooding within the channel caused by increased precipitation. As the Late Pleistocene was characterised by several phases of relatively enhanced dust fluxes (Zens et al., 2018; Fischer et al., 2021), and the SID site is located near potential dust sources, mainly the Pleistocene braided systems of the Meuse and the Rhine, as well as their tributaries (Lehmkuhl et al., 2018), these ponds were subjected to periodical inputs of aeolian dust. Although unit I partially shows slightly elevated sand contents (Fig. 3), the generally fine and particular unimodal GSD indicates input of aeolian dust into this marshy environment as the major sedimentological process.
After the marshy environment was covered with aeolian dust, formation of
unit II began. This unit's main characteristics are a distinct layering with
alternating dark brown and ochre-beige bands as well as small ice-wedge
pseudomorphs permeating the layers. Generally, the transition from unit I to
unit II shows sharp decreases or increases in most analysed proxies (Figs. 3 and
4). Especially the GSD from a medium-coarse silt mode to a mode bordering
the fine-sand fraction may indicate erosional processes during this
transitional period. Layered units in LPSs are well known from the ELB
(Lehmkuhl et al., 2021; Antoine et al., 2016, 2001, 2013). They are usually correlated to the Upper Pleniglacial Hesbaye loess (Haesaerts
et al., 2016; Schirmer, 2016) and are explained by a shift towards colder,
more humid climatic conditions, including extensive snow covers during
winter. Dust sedimentation on snow covers leads to a fine lamination, which
is most likely due to micro-sorting processes during snowmelt. These
laminations are usually a few millimetres thick with sandy bases fining-up
upwards (Antoine et al., 2001). The laminations in SID,
however, are partly several centimetres thick and show distinct differences
in both colour and grain size. These differences show up by the reflectance
data and the grain size patterns: generally, unit II is coarser than unit I.
Additionally, it shows larger GSD variations with sandier bands. These
sandier bands usually show higher
Unit III of the SID LPS shows a characteristic succession of an orange layer
and two distinct palaeosol layers (Fig. 2). The sediments of unit III
generally have finer GSD modes compared to unit II, paired with a slightly
decreased U ratio and GSI. The entire unit shows evidence of heavy
reworking by cryoturbation, especially wavy-layer contacts and low
Unit IV is composed of relatively unaltered loess. The unit is well sorted
and is characterised by a typical GSD for central European loess deposits,
showing a strong mode in the coarse silt fraction (Fig. S3). The high
carbonate contents of approx. 20 % and
The uppermost unit V shows a combination of no carbonate, high
In combination with the luminescence dating results (see Sect. 3.2), the
formation processes of the Siersdorf LPS draw a detailed picture of regional
imprints of the late MPG–UPG transition in the western ELB. The Pleniglacial
dynamics of the SID site are summarised in the following conceptual model
(see also Fig. 7). The correlation of unit I to the MPG–UPG transition
(Fig. 7a and b) is based on one sample (SID L6) near the upper boundary of
the unit. Luminescence analyses yield ages of 24.9
Schematic model of the Middle and early Upper Pleniglacial site
formation of the Siersdorf LPS.
The MPG, closely correlated with the MIS 3, was a phase of severe environmental
fluctuations in the ELB. Periods of climatic ameliorations and pedogenesis,
due to higher moisture availability (Fischer
et al., 2021; Antoine et al., 2013; Schirmer et al., 2012; Hošek et al.,
2017; Vinnepand et al., 2020), alternated with periods of erosion and
(re-)deposition of soils and sediment (Meszner et al., 2011, 2013). Phases of
soil formations can be traced in proxy data, as the
The silting up of the marshy environment lasted during the MPG–UPG transitions until the early UPG (UPGa sensu; Zens et al., 2018). This phase of rapid climatic deterioration is in European loess landscapes coupled with a strong increase in dust production and subsequent loess formation (Meszner et al., 2013; Meyer-Heintze et al., 2018; Lehmkuhl et al., 2016; Antoine et al., 2013, 2009). This period is considered the phase with the highest dust accumulation rates in Europe (Zens et al., 2018; Frechen et al., 2003). In the LRE and other oceanic-influenced loess regions, the loess deposits of the beginning UPG, the so-called UPGa (Lehmkuhl et al., 2016; Zens et al., 2018, 2017), are named Hesbaye loess, (Schirmer, 2016) after the Belgian loess region (Haesaerts et al., 1997, 1981). The layered Hesbaye loess is often characterised by fluvial reworking or by dust deposition and loess formation under snow-influenced conditions. This feature is typical for the ELB and can be found from France towards the East European Plain (Antoine et al., 2009; Zens et al., 2018; Lehmkuhl et al., 2021). In SID, the layered unit II is dated by the quartz ages of samples SID L4 and L5 to 36.7–26.5 ka (Fig. 6). These calculated ages are stratigraphically inconsistent compared to SID L6, indicating deposition of older material after the formation of unit I. The inherited older ages of L4 and L5 as well as slightly older feldspar ages point to incomplete bleaching due to the relocation of the sediment, which points to a short transport range during sediment transport by surface runoff. The erosional processes during the MPG–UPG transition and the early UPG are widespread phenomena within the ELB (Meszner et al., 2013), often removing large parts or even entire MPG successions. The proxy data of unit II, in combination with the luminescence properties, allow for a reconstruction of short-scale transport of Middle Pleniglacial soil material during the UPGa, particularly to the steppe phase (Zens et al., 2018; Sirocko et al., 2016). The relocated material was frequently subjected to harsh, periglacial conditions, as indicated by a multitude of small ice-wedge casts (Fig. 2). Based on these geomorphological features, the periglacial overprinting is correlated to the tundra stage of the UPGa (Zens et al., 2018; Sirocko et al., 2016) where cold, dry conditions prevailed.
The later UPG succession (UPGb;
Lehmkuhl et al., 2016; Zens et al., 2018, 2017) is also known as the
Brabant member in the regional stratigraphy and mostly reflects loess
formation during fully glacial conditions (Schirmer, 2016,
2000). Samples L4 and L3 bracket the orange and brownish-greyish complex of
unit III, with ages between 30 and 21 ka. The ages, especially derived
from quartz minerals (L4: 29.6
As the geomorphological setting is crucial not only for dust accumulation
but also for preservation of LPSs especially (Lehmkuhl et al.,
2016; Antoine et al., 2016; Marković et al., 2018), the favourable
position of SID in a channel incised into an old Meuse River terrace led to a
relatively thick accumulation of most likely Middle but especially Upper
Pleniglacial sediments. Although LPSs in other extraordinary geomorphological
situations such as loess dunes, so-called
The LRE was strongly affected by anthropogenically induced soil erosion
since the Early to Middle Holocene (Gerlach, 2006; Gerlach et al., 2006;
Protze, 2014; Schulz, 2007; Gerz, 2017). However, the feldspar age
calculated from the sample SID L1, taken from the base of the colluvial
unit, yields a late glacial age (16.2
The sedimentary sequence of SID shows a complex interplay of various depositional milieus together with proposed active tectonic setting. It is a valuable archive for landscape dynamics in the LRE and suggests that the area was highly diverse during the Late Pleistocene. The high-resolution sedimentological, geochemical, and spectrophotometric analyses reveal a change from wetter conditions with ephemeral ponds and wetlands to a silting up of these wetlands and highly erosive conditions towards typical subaerial loess formation. The SID sequence, therefore, is a crucial addition to the framework of the landscape analyses of the Pleniglacial western ELB.
The Siersdorf LPS is an important site for Late Pleistocene dynamics of the Lower Rhine Embayment, indicating changing depositional environments during the period covered. The combination of sedimentological, geochemical, and spectrophotometric data with luminescence dating and tentative malacological tests shows that the sequence was under the influence of a marshy wetland environment during the late MPG and early UPGa, a unique feature for the LRE. Observed permafrost-induced conditions show the strong influence of the geomorphological setting and related processes on characteristics of sedimentary sequences. The UPGb was influenced by long-lasting erosional processes, which, however, were constrained to short-range transport mechanisms. The typical subaerial formation processes of the upper part of the sequence correlated to the UPGa, with typical regional marker horizons such as the Eben Zone, point to cold-arid conditions during this time, as observed for large parts of the European loess belt. Overall, this study stresses the importance of the geomorphological setting and related sedimentological and post-depositional processes in relation to the formation, preservation, and resulting characteristics of LPSs. Our results show not only that the LRE was subjected to fluctuating climate during the Pleniglacial but also that the area was more fragmented than previously thought, especially regarding the environmental setting.
Data are available upon request to the corresponding author.
The supplement related to this article is available online at:
SP designed the study together with FL and PS. PS, MK, FL, and SP took the analysed samples during two separate fieldwork campaigns in 2020. KS and DB performed luminescence dating and laboratory tests and compiled and discussed the results within the scientific framework. CR analysed the mollusc shells and fragments, which were provided by MK, and discussed their interpretability. SP wrote the initial draft of the manuscript with helpful comments and suggestions from the other authors. All authors discussed the data and participated in its interpretation.
The contact author has declared that none of the authors has any competing interests.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
This article is part of the special issue “Quaternary research from and inspired by the first virtual DEUQUA conference”. It is a result of the vDEUQUA2021 online conference in September/October 2021.
We thank Marianne Dohms, Renate Erdweg, and their team for the laboratory framework and Klaus Reicherter for his helpful comments on the tectonic evolution of the Lower Rhine Embayment in the field. We also thank the three anonymous reviewers for their constructive comments and remarks, which substantially improved this manuscript, and the editorial team for the uncomplicated handling of the manuscript.
The investigations were carried out in the frame of the CRC 806 Our way to Europe – funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation, grant no. 57444011-SFB 806).This open-access publication was funded by the RWTH Aachen University.
This paper was edited by Julia Meister and reviewed by three anonymous referees.