# A record of Late Pleistocene environmental conditions at the transition from central to southern Europe from the Baix loess paleosol sequence (Rhône Rift Valley, SE France)

Nora Pfaffner, Annette Kadereit, Sebastian Kreutzer, Thomas Kolb, Alexander Varychev, Sebastian Cionoiu, Tianhao Wang, Pascal Bertran, Mathieu Bosq, Christine Hatté, et al.

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Nora Pfaffner, Annette Kadereit, Sebastian Kreutzer, Thomas Kolb, Alexander Varychev, et al. A record of Late Pleistocene environmental conditions at the transition from central to southern Europe from the Baix loess paleosol sequence (Rhône Rift Valley, SE France). Quaternary Research, 2026, pp.1-20. 10.1017/qua.2025.10053. hal-05475537

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Distributed under a Creative Commons CC BY 4.0 - Attribution - International License
Research Article

A record of Late Pleistocene environmental conditions at the
turnition from central to southern Europe from the Baix loess
paleosol sequence (Rhône Rift Valley, SE France)

Nora Pfaffner<sup>a</sup>, Annette Kadereit<sup>b</sup>, Sebastian Kreutzer<sup>b</sup>, Thomas Kolb<sup>c</sup>, Alexander Varychev<sup>d</sup>, Sebastian Cionoiu<sup>d</sup>, Tianhao Wang<sup>e</sup>, Pascal Bertran<sup>f,g</sup>, Mathieu Bosq<sup>g</sup>, Christine Hatté<sup>h,i</sup> and Daniela Sauera<sup>i</sup>

Abstract

Loess–paleosol sequences (LPSs) provide valuable archives of Quaternary paleoenvironments. Here we present new data from the Baix LPS, comprising the entire Late Pleistocene. The Baix LPS is located at the western edge of the Rhône Rift Valley, France, in the transition zone from the presently temperate to the Mediterranean region of Europe. This LPS provides a missing link between the analyzed LPSs in the presently temperate regions farther north and those in the Mediterranean region. Reddish Btg horizons of a Stagnic Luvisol at the base of the Baix LPS represent the remains of an MIS 5 pedocomplex formed under warm and, at least temporarily, relatively moist conditions. Two brown Bw horizons of truncated Cambisols have been preserved in the overlying MIS 5a/4 to MIS 3 deposits. The upper Bw horizon is associated with large carbonate nodules, indicating that considerable amounts of calcium carbonate were leached from a former MIS 3 Cambisol and accumulated in the underlying loess unit. This truncated MIS 3 Cambisol is very similar to the MIS 3 paleosol remains in the LPS Collias that we investigated 87 km farther south in the present Mediterranean climate. No paleosols were observed in the late MIS 2 deposits.

**Keywords:** Loess; Paleosols; Late Pleistocene; Paleoenvironment; Paleopedology; France

Introduction

Loess–paleosol sequences (LPSs) represent valuable archives of
paleoenvironmental changes in response to Quaternary climatic
shifts. During glacial periods, larger riverbeds that seasonally dried
up, provided dust deflation areas, while river terraces and slopes
were the main sites of dust accumulation (Fig. 1). LPSs typically
display alternating phases of predominantly dust accumulation
and phases of predominantly soil formation, reflecting changes in
regional and paleoenvironmental conditions (Pye, 1995). Thereby,
several LPSs in central Europe provide high resolution paleoen-
vironmental records, with distinct indicators of climatic shifts
such as paleosol horizons and permafrost features (Semmel, 1968;
Bibus and Semmel, 1977; Guenther, 1987; Antoine et al., 1999,
2016, 2021; Frechen et al., 2007; Schirmer 2012, 2016; Fischer
et al., 2021; Lehmkuhl et al., 2021). In contrast, LPSs in south-
ern Europe (presently with Mediterranean climate) typically have
lower chronological resolution, because their loess deposits have

been relocated by slope wash processes, and their paleosol units are
usually reworked by bioturbation. Frost-related features are scarce
in Mediterranean LPSs (Bonifay, 1965; Brunnacker, 1974; Ferraro,
2009; Wacha et al., 2011a, b; Boixadera et al., 2015; Zerboni et al.,
2015; Costantini et al., 2018; Wolf et al., 2019; Bertran et al., 2021;
Lehmkuhl et al., 2021).

LPSs in the transition zone along a N–S gradient from central to southern Europe have remained understudied. However, given the currently ongoing climate change, it is crucial to understand past environmental responses of such sensitive transition zones to climate changes, particularly in areas of expected northward shift of the boundary between Mediterranean and temperate climates (Ottlé et al., 2001; Gao and Giorgi, 2008; Giorgi and Lionello, 2008). Most Mediterranean LPSs are disconnected from those in central Europe by high mountain ranges (e.g., the Pyrenees, Alps, Apennines, Dinaric Alps, Pindus mountains) (Fig. 1). Thus, the LPSs along the Rhône Rift Valley in SE France represent unique archives, as the N–S orientated Rhône Rift Valley is presently marked by a change from temperate to Mediterranean climate conditions with the climatic transition around 45°N, near Valence (Météo-France, 2020).

Loess along the Rhône Rift Valley was studied in the past by
Suen (1934), Mazenot (1956), Bourdier (1958), Bonifay (1965),

<footnote><sup>a</sup>Department of Physical Geography, University of Göttingen, 37077 Göttingen, Germany; <sup>b</sup>Heidelberg Luminescence Laboratory, Institute of Geography, Heidelberg University, 69120 Heidelberg, Germany; <sup>c</sup>Department of Geography, University of Giessen, 35390 Giessen, Germany; <sup>d</sup>Institute of Earth Sciences, Heidelberg University, 69120 Heidelberg, Germany; <sup>e</sup>Dalian University, College of Life and Health, 116622 Dalian, China; <sup>f</sup>Inrap, 33130 Bègles, France; <sup>g</sup>PACEA, UMR 5199 Université de Bordeaux CNRS, 33615 Pessac, France; <sup>h</sup>Laboratoire des Sciences du Climat et de l'Environnement, UMR CEA CNRS UVSQ 8212, Université Paris-Saclay, 91191 Gif-sur-Yvette, France and <sup>i</sup>Institute of Physics, Silesian University of Technology, 44-100 Gliwice, Poland</footnote>

<footnote>**Corresponding author:** Nora Pfaffner; Email: nora.pfaffner@protonmail.com

**Cite this article:** Pfaffner N. et al., 2026. A record of Late Pleistocene environmental conditions at the transition from central to southern Europe from the Baix loess paleosol sequence (Rhône Rift Valley, SE France). *Quaternary Research*, 1–20. https://doi.org/10.1017/qua.2025.10053</footnote>
<figure><img src="image_2.png" /><figcaption>**Figure 1.** Map of aeolian deposits in middle Europe based on dataset from Bertran et al. (2021) (loess, sandy loess, coversand) and Lehmkuhl et al. (2021) (loess and loess derivates, sandy loess, aeolian sand), including the locations of the Baix and Collias loess-paleosol sequences (LPSs) (Bosq et al., 2020b; Pfaffner et al., 2024), and selected NW-France LPS (including Havrincourt, Renancourt, Saint-Acheul, Saint-Illiers, Saint-Pierre-lès-Elbeuf, Saint-Sauflieu, Villiers-Adam; Antoine et al., 1999, 2016, 2021), Belgium LPS (including Harmignies, Kesselt, Rocourt, Remicourt; Frechen et al., 2001; Antoine et al., 2016; Haesaerts et al., 2016), the Rhine Valley LPS (including Achenheim, Garzweiler, Grafenberg, Nussloch, Schwalbenberg I-II, Remagen, Schatthausen; Antoine et al., 2001, 2009; Rousseau et al., 2002; Schirmer, 2002, 2012, 2016; Frechen et al., 2007; Gocke et al., 2014; Fischer et al., 2019, 2021), the Ebro Valley LPS (including Guiamets, Tivissa, Mas de l'Alerany, Batea, Almenara; Boixadera et al., 2015), the Po Valley LPS (including Bagaggera, Monte Netto, Val Sorda; Ferraro et al., 2004; Ferraro, 2009; Zerboni et al., 2015; Costantini et al., 2018), Susak LPS (including Sand Pit, Bok, Savudrija; Wacha et al., 2011a, b, 2018; Zhang et al., 2018). Data: Digital Elevation Model of Europe (1 km × 1 km) and shapefile of the Mediterranean biogeographic region (from the 11 biogeographic regions of Europe defined by the European Environment Agency (EEA), 2021).</figcaption></figure>

Dubar (1979) and, more recently, by Franc et al. (2017) and Bosq et al. (2018, 2020a, b). According to loess maps by Haase et al. (2007) and Lehmkuhl et al. (2021), the distribution of aeolian sediments is patchy in the southern Rhône Rift Valley, whereas the map of Bertran et al. (2021), derived from particle size distributions of topsoils (thus, also including shallow completely pedogenized loess deposits), suggests a more widespread distribution of loess and sandy loess. Furthermore, the map of Bertran et al. (2021) and observations by Bosq et al. (2018, 2020b) suggest a southward change from loess to sandy loess, whereby the region near Valence (~45°N) again represents a transition area. The Baix LPS is located within that transition area, 25 km southwest of Valence (Fig. 1).

A preliminary chronostratigraphic framework and field observations on the lower part of the Baix LPS have been introduced previously (Pfaffner et al., 2024). Here, we present an improved chronology for the entire LPS, as well as soil-color measurements, particle size analyses, chemical and micromorphological analyses,

and we derive a reconstruction of the paleoenvironmental changes at the site over the Late Pleistocene. The improved chronology includes ages by accelerator mass spectrometry (AMS) radiocarbon dating on gastropod shells from the upper part of the LPS and optically stimulated luminescence (OSL) dating on coarse feldspar grains, polymineral fine grains, and quartz fine grains from six sediment blocks (OSL blocks). The results of these analyses are then used to answer our main research questions: (1) which sedimentation dynamics can be inferred from granulometric characteristics, (2) which paleoenvironmental interpretation can be derived from the geochemical characteristics of Baix LPS, (3) in what chronological frame the inferred paleoenvironmental took place, and (4) how Baix LPS compares to other European LPSs.

We hypothesize that during the last interglacial period (Eemian, MIS 5e), the Mediterranean conditions extended farther north, compared to the present boundary of Mediterranean conditions. The location of the Baix LPS is ideal to test this hypothesis, because
<figure><img src="image_3.png" /><figcaption>**Figure 2.** (A) Profile sketch of main profile Baix and "Baix_west" with soil horizon designations. Green boxes mark sample positions for optically stimulated luminescence (OSL) dating, black rectangles mark positions of thin-section samples. (B) Profile photo of main profile Baix (Photos: D. Sauer, 2017–2020).</figcaption></figure>

it is located at the present northern boundary of Mediterranean conditions, which means that its paleosol of the last interglacial period should be a Mediterranean paleosol, if the hypothesis is true. Furthermore, we test how the texture of the Baix LPS fits into the earlier postulated change from loess to sandy loess in the Valence area (Bosq et al., 2020b; Bertran et al., 2021).

## Regional setting

The Baix LPS (44°42′36.30″N, 4243′20.80″E, 155 m asl) is located in a former loess pit, 25 km southwest of Valence, at the western flank of the Rhône Rift Valley (Fig. 1). Bounded by the Massif Central to the west and the Alps to the east, the Rhône Rift Valley is mainly filled with Oligocene to Pleistocene deposits (BRGM, 2021). It is characterized by an alternation of wide basins and narrow passages, interspersed with several smaller side basins.

According to its geochemistry, loess in the Rhône Rift Valley originated mainly from glacial and fluvioglacial deposits from the Alps, with only minor contribution from other local alluvium (Bosq et al., 2020a). The loess mainly covers the plateaus, large basins, and terraces of the Rhône River and its tributaries (Suen, 1934; Mazenot, 1956; Bosq et al., 2018). The valley is drained by the Rhône River, to which the eastern tributaries of the Rhône River (e.g., Isère, Drôme, Durance), originating in the Alps, deliver more sediment to the Rhône River than do the shorter tributaries (e.g., Ardèche, Gardon, Cèze) from the Massif Central (Olivier et al., 2009).

The present-day climate in the Rhône Rift Valley is characterized by a gradual change from temperate climate conditions in the north to Mediterranean conditions in the south. The temperate climate of the northern rift valley is characterized by warm summers (up to three dry months) and cold, humid winters. The mean annual temperature (MAT) is ~13°C, mean annual precipitation

(MAP) ranges between 800 mm and 900 mm (Météo-France, 2025a, b). The mountainous areas and regions to the west of the valley reach higher MAP of 1200–1400 mm and summer storms are common (Diodato et al., 2016).

The Mediterranean climate in the southern part of the rift valley is characterized by hot, dry summers with five arid months and humid winters, MAT is ≥ 14°C and MAP is ≥ 700 mm (Météo-France, 2025c, d). The wind system of the valley is influenced by advective air masses of different origins (Mediterranean, maritime, polar maritime, and subtropical), which lead to high yearly and seasonal variability of precipitation and wind intensities (Diodato et al., 2016). The dominating wind system is the Mistral, blowing from the northwest through the Rhône Rift Valley, which acts as a channel, accelerating the wind, before opening into the Mediterranean Sea (Obermann et al., 2018).

The Baix LPS is situated in the wind shadow, behind a small hill at the edge of an opening in the western shoulder of the Rhône Rift Valley, where a small side basin, filled with debris of Cretaceous limestone and basalt feeds into the Rhône Rift Valley (Pfaffner et al., 2024). Its topographic position explains the occurrence of a loess patch just at the Baix LPS. The source of the loess at the Baix LPS was the temporarily dried-out riverbed of the Rhône River, as has been proven for other loess sites along the Rhône Rift Valley (Bosq et al., 2020a). This does not exclude some possible component of material from more proximal sources such as riverbeds of smaller local rivers (e.g., Payre, l'Ouvèze).

## Material and methods

### *Sampling and profile description*

We cleaned and described the main profile “Baix” with a total thickness of 13.7 m (Fig. 2) during three field campaigns between 2018
and 2020 (Pfaffner et al., 2024). An additional profile, “Baix_west” (thickness 8.5 m; Fig. 2), was cleaned to assess the spatial variability of the upper sediments and paleosol horizons.

The main profile was sampled in 10-cm increments for ana-
lyzing chemical composition and particle size distribution. Where
horizon boundaries occurred in less than 10-cm distances, the
sampling increments were decreased accordingly, to avoid sam-
pling across horizon boundaries. Baix_west was sampled by taking
mixed samples per horizon and horizons thicker than 30 cm were
subdivided. The samples were air-dried, sieved (< 2-mm mesh
size) and homogenized. Four undisturbed samples for micromor-
phological analysis were taken from the paleosol horizons Bw1,
5 Bw2, 6 Bw3, and 7 Btg. For this purpose, Kubiëna boxes were
carved into the profile wall by a knife (Fig. 2).

Ten samples of bulk sediment, each of approximately 10 L, were taken at regular intervals from the upper 7 m of the main profile to collect mollusc shells for ¹⁴C-AMS dating at the Laboratoire des Sciences du Climat et de l'Environnement (LSCE) de Gif-sur-Yvette (France). The samples were wet sieved through a 425-mm mesh, and the mollusc shells were cleaned by ultrasonic treatment.

Six block samples for conventional OSL dating at the Heidelberg Luminescence Laboratory were taken. Three samples (OSL 1<sub>2020</sub>, OSL 2<sub>2020</sub>, OSL 3<sub>2020</sub>) from the 7 Bt1, 6 BCk/Btg, and 5 BCk5 horizons of the main profile Baix (Figs. 2, 6b) were collected. The other three samples (OSL 6<sub>2018</sub>, OSL 7<sub>2018</sub>, OSL 8<sub>2018</sub>) were collected from the 5 Bw2, 3 BCk3, and 2 BCk2 horizons from profile Baix_west (Figs. 2, 6a, 6b).

Paleosol horizons were described according to the FAO guide-
lines for Soil Description (FAO, 2006), and the paleosols were after-
wards tentatively classified according to the World Reference Base
for Soil Resources (IUSS Working Group WRB, 2022). Horizon
designations, detailed descriptions of the field characteristics, and
stratigraphic sequences of the main profile Baix are in Pfaffner et al.
(2024, Table 1).

Based on the preliminary results in Pfaffner et al. (2024), we distinguished from bottom to top: a last interglacial to early glacial paleosol complex (IG-EP-PSC), an early pleniglacial paleosol (EPG-PS), a middle pleniglacial paleosol complex (MPG-PSC), and the Holocene soil (Figs. 3, 6a, 6b). These paleosol complexes are intercalated by units of unweathered or only slightly altered, yet sometimes reworked (by slope wash), loess deposits with varying degrees of weathering.

By correlating the previously designated horizons and strati-
graphic sequences of the main profile (Pfaffner et al., 2024) with
the profile Baix_west, small differences in the positions of the upper
horizons suggest a gentle southwestern inclination of the sediment
layers, which matches with the local relief. However, the main
trends of the weathering proxies of Baix_west match well with
those of the upper part of the main profile down to the MPG-PSC
at 8.5 m below ground level (Fig. 3). Because of this great similarity,
we focus on the results of the main profile Baix.

**Laboratory analyses**

Particle size distribution and related proxies

High-resolution particle size distribution (PSD) data provide
valuable information about the transport distance of aeolian
sediments under consideration of the respective environmental
factors such as topography, microclimate, vegetation, and influ-
ence of post-depositional processes (Pye, 1995; Rousseau et al.,

2002; Vandenberghe, 2013; Lehmkuhl et al., 2016; Újvári et al., 2016a; Schulte et al., 2018; Vandenberghe et al., 2018; Varga et al., 2019). PSD was measured with a laser diffraction particle size analyzer (Beckman Coulter LS 13320), from samples that were prepared following ISO 11277 (International Standards Organization, 2020a) and 13320 (International Standards Organization, 2020b). For PSD determination, an optical model according to the Mie theory with RI 1.55i-0.01 suitable for quartz was applied (International Standards Organization, 2020a, b). The statistical parameters, such as mean and mode of particle size of the 116 particle size classes from 0.04 µm to 2000 µm were calculated. The percentage PSD and their shifts over depth were visualized in heatmaps. For reconstructing paleoenvironmental conditions, the GSI (26–52 µm/<26 µm) and the U ratio (16–44 µm/5.5–16 µm) were used, each influenced by different factors (e.g., wind speed, distal and local transport, post-depositional processes) (Vandenberghe et al., 1985; Antoine et al., 2009; Újvári et al., 2016a; Schulte et al., 2018; Schulte and Lehmkuhl, 2018). Additionally, the fine to coarse clay (< 0.04 µm/0.63–2.0 µm) ratio was applied as proxy for illuvial clay paleosol horizons.

Soil chemical analysis, weathering indices and soil color

Total contents of Fe, Al, Ca, Mg, Si, and Mn were obtained by mixing the samples with lithium meta-tetraborate (ratio 1:4), fusing this mixture, dissolving the fused samples with 5% HNO3 and analyzing them by inductively coupled plasma optical emission spectrometry (ICP-OES, iCAP 7000, Thermo Scientific). The total contents of Na and K were determined by flame spectrometer (Elex 6361, Eppendorf). Major element concentrations were used to calculate geochemical indices based on their molar ratios to identify the loss of bases from silicate weathering and subsequent element leaching due to pedogenesis. The following indices were used: the WIMER (Weathering Index based on Molar Element Ratios) calculated as WIMER = (Ca (after subtraction of Ca in CaCO3) + Mg + K + Na)/Al (Sauer, 2016) and the CPA index (Chemical Proxy of Alteration), calculated as CPA = Al2O3/(Al2O3 + Na2O)*100 (Sheldon and Tabor, 2009; Buggle et al., 2011). The Si/Al ratio was applied as a proxy of the aluminosilicates/quartz ratio (Liang et al., 2013). Fe, Al, and Mn contents in the form of pedogenic oxides/hydroxides (Fe<sub>d</sub>, Al<sub>d</sub>, and Mn<sub>d</sub>) were extracted by sodium dithionite Na<sub>2</sub>S<sub>2</sub>O<sub>4</sub> (Schwertmann, 1964; Sparks et al., 1996) and analyzed by ICP-OES (iCAP 7000, Thermo Scientific). Fe<sub>d</sub>/Fe<sub>t</sub> ratio and Mn<sub>d</sub>/Mn<sub>t</sub> ratio as depth functions were used to reflect the degree of weathering and hydro-morphic influence (Torrent and Nettleton, 1979; Arduino, 1984; McKenzie, 1989; Durn et al., 2001). Furthermore, the formation of manganese oxides (Mn<sub>d</sub>) is related to seasonal water logging in soils, thus reflects the degree of intensity of paleo-redox processes (McKenzie, 1989).

Carbonate contents were measured by the gas-volumetric
method using a Scheibler apparatus and calculated as calcium
carbonate equivalents in wt% (Blume et al., 2011). Soil organic
carbon (SOC) contents were estimated by quantifying total car-
bon (C) contents by use of a CHN elemental analyzer (TruSpec
Micro, LECO) in wt%, and subtracting the CaCO3 carbon contents
from the total C contents. This approach only allows for obtaining
trends, while an exact calculation of SOC contents is not possi-
ble, given the error of the Scheibler method and the high CaCO3
contents of the loess in this region.

Color changes with depth in LPS reflect varying degree of pedo-
genesis and changing paleoenvironmental conditions (Pécsi and
<figure><img src="image_4.png" /><figcaption>**Figure 3.** Stratigraphic sections of the main Baix loess–paleosol sequence (LPS) and Baix_west LPS, Rhône Rift Valley, SE France. Gray horizontal bars mark positions of paleosols. Depth curves of geochemical data (CaCO₃, SOC), ratios (CPA, WIMER, Si/Al, Fe₉/Fe₇, Mn₆/Mn₇), and color parameters (L, a, b, a/b) of both profiles. IG-EG-PSC = last interglacial to last early glacial paleosol complex; EPG-PS = last early pleniglacial paleosol; MPG-PSC = middle pleniglacial paleosol complex; Holocene-S = Holocene soil; ED = erosional discontinuity.</figcaption></figure>

Richter, 1996; Sprafke, 2015; Wang et al., 2016). Quantitative color determination has received more attention recently (e.g., in LPS studies of Chen et al., 2002; Gocke et al., 2014; Sprafke, 2015; Wang et al., 2016; Zeeden et al., 2017; Sprafke et al., 2020; Krauss et al., 2021; Laag et al., 2023). We used a handheld spectrophotometer CM-700d (Konica Minolta) for the color measurements. Fine-grained earth samples were measured three times (10° standard observer, SCI) and the mean results were converted into the CIE color index, presenting the colors as L*a*b* values by SpectraMagic NX software (CIE, 1976). L (metric lightness function) represents the brightness or luminance (range 0–100); a and b represent the chromaticity coordinates opponent red–green scales (a) and opponent blue–yellow scales (b) (Viscarra Rossel et al., 2006). Although it is not possible to separate between in-situ and reworked soil material or secondary carbonate enrichments based

on color values, the chromatic parameters and derived ratios are valuable tools to detect units that have been altered by pedogenic processes, as already minor decarbonatation, accumulation of soil organic matter, or iron oxide formation will lead to measurable changes of these values.

For thin section preparation the pore water of the undis-
turbed, orientated blocks was gradually exchanged with acetone.
The blocks then were impregnated with resin (Palatal), hardened
over six weeks, cut into slices that were then cut into smaller
blocks, which were glued on glass slide (28 mm × 48 mm) and
ground to < 25-µm thickness (first by machine, in the end by
hand). The thin sections were described according to Stoops (2021)
and microphotographs were taken with a Keyence VHX-7100/-
E100 digital microscope in plane polarized and cross polarized
light.
# Chronostratigraphic framework

## AMS radiocarbon dating

Two small mollusc taxa (Pupilla musorum and Trochulus hispidus) were selected for dating because of their abundance in the samples. These species live on vegetation and are assumed to be suitable for chronological investigations (e.g., Pigati et al., 2010; Újvári et al., 2016b). The conversion mode of the sample to CO₂ and, if required, to Cgraphite, the introduction mode BCA for the carbonate line and GG for the graphitization line followed Tisnérat-Laborde et al. (2001, 2015), Hatté et al. (2024) and Thil et al. (2024). Ages (BP) derive from F¹⁴C and are reported following the recommendations of Stuiver and Polach (1977), particularly rounding off. Radiocarbon ages were calibrated to calendar ages with the IntCal20 calibration curve (Reimer et al., 2020) using the software Calib version 8.2 (Stuiver et al., 2021) (Supplement 1 – Table S1.1). Calibrated ages are reported as age ranges with a 95.4% confidence level.

## Luminescence dating

For the present study, we subjected the six block samples to optically stimulated luminescence (OSL; Huntley et al., 1985) dating (HDS-1776 to HDS-1778 = OSL 6₂₀₁₈ to OSL 8₂₀₁₈ and HDS-1799 to HDS-1801 = OSL 1₂₀₂₀ to OSL 3₂₀₂₀). Fine grains (4–11 µm) and coarse grains (125–212 µm) were available, but quartz coarse grains were too scarce for luminescence dating (details of the sample preparation are given in Fig. S2.2.1 in Supplement 2). The single aliquot regeneration (SAR) approach was applied (Murray and Wintle, 2000). While quartz fine grains were measured with a blue-light stimulated (BLSL) SAR protocol (Murray and Wintle, 2000) detecting the ultra-violet luminescence emission around 340 nm, feldspar coarse grains and polymineral fine grains were measured with a post-infrared (at 60°C) infrared (at 225°C) stimulation (pIR₆₀IR₂₂₅) protocol (Thomsen et al., 2008) detecting the blue-violet emission around 410 nm. Details on measurement configurations, pretests for adapting the protocols to the Baix samples, parameters of data analyses, and results of the equivalent doses (Dₑ) of individual aliquots and the Dₑ distribution of a sample are given in Supplement 2 (S2.3–S2.5). For the quartz fine grains, we also provide the results of a series of tests in Supplement 2 (S2.4), which were conducted to investigate possible reasons for the unexpectedly high quartz fine grain ages. The analyses of the feldspar coarse grain measurements were accomplished by tests investigating the suitability of the Tₓ/Tₙ sensitivity curves as a proxy of (1) material source or (2) poor bleaching (Chen et al., 2013; S2.3.9–S2.3.10). For dose rate estimation (S2.6), the contents of radionuclides were determined with the µDose system in the luminescence laboratory at Gießen University (Tudyka et al., 2018; Kolb et al., 2022).

# Results

## Particle size distribution and related sedimentological indices

The heatmap of Fig. 4A showed highest contents of coarse silt and the lowest clay contents for the unweathered to slightly weathered units, whereas the paleosol horizons were marked by considerably higher clay contents. The ΔGSD (Fig. 4B) displayed the main mode in the coarse silt fraction (~44–50 µm), thus a PSD typical for aeolian sediments and two subordinate maxima in the fine to medium silt fraction and in the fine to medium clay fraction. Throughout the profile, the mean particle size ranged between 29 µm and 65

µm with an average of 36 µm, while the median particle size ranged from 23 µm to 41 µm, and the average median was 30 µm (Fig. 4A).

In the field, no laminations indicative of slope wash were observed. However, most of the horizons contained minor amounts of small rock fragments (Pfaffner et al., 2024, Fig. 11) suggesting gentle erosion and subsequent re-accumulation of sediment at the foot slope position where the Baix LPS is located. Apart from this observation, all paleosol horizons consisted of homogenous silts. In contrast, the intercalated unweathered and slightly weathered loess horizons showed an increase of the GSI towards the top, accompanied by a constant decrease of the silt fraction and an increase of the fine sand fraction. This trend is also reflected by higher mean and median PSD values (Fig. 4A). The U-ratio (1.55–3.03), GSI (0.34–0.79), and Si/Al (4.55–6.64) showed maxima within the unweathered and slightly weathered units and decreased in the paleosol horizons, whereas fine clay/coarse clay (0.16–0.57) ratios acting oppositely (Figs. 3, 4A).

## Colors and chemical characteristics

Generally, the paleosol horizons showed lower L values than the unweathered to slightly weathered units (Fig. 3). Above the MPG-PSC, the L values followed a steady upward increase, similar to the upward increase in carbonate content and WI<sub>MER</sub>. The paleosol horizons also exhibited maximum a and b values, with a = 11 and b = 32, attributed to the pedogenic iron oxide formation, while the unweathered to slightly weathered units showed much lower a and b values, with minima of a = 5 and b = 22. The lowest a and b values coincided with the least weathered units (e.g., the Ck horizons).

Carbonate contents showed maxima around 23 wt% CaCO₃ equivalent, which were reached in the Bk1 horizon of the Holocene soil and 5 BCk4 horizon of MPG-PSC (Fig. 3). In addition to these carbonate contents of the fine earth, hard carbonate nodules of various sizes were observed in most parts of the profile, from the Bk1 horizon down to the 7 Btg horizon, indicating steady carbonate dissolution and reprecipitation during the accretion of the loess. The MPG-PSC displayed considerable carbonate leaching, with carbonate contents as low as 0.3–2.5 wt% CaCO₃ equivalent. The soil organic carbon (SOC) contents fluctuated between 0 and 0.5 wt%. As expected, the maximal values are highest in the Holocene soil and decrease with depth, except for the 5 Ck2 horizon (0.5 wt%).

The weathering indices of the least-weathered units exhibited minimum values for the CPA (68) and Fe₉/Feᵢ (0.45) and Mn₉/Mnᵢ (0.86) ratios, and maximum values for the WI<sub>MER</sub> (0.95) and Si/Al (6.6) ratio. These weathering indices all highlighted the most advanced pedogenesis of the IG-EP-PSC, showing the maximum values for CPA (80) and Fe₉/Feᵢ (0.90) Mn₉/Mnᵢ (1.3), and minimum values for WI<sub>MER</sub> (0.49) and Si/Al (4.5). The second-most advanced pedogenesis of the MPG-PSC was also expressed by a high CPA (up to 74), slightly increased Fe₉/Feᵢ ratio (up to 0.60) and Mn₉/Mnᵢ ratio (up to 1.0), and low WI<sub>MER</sub> (down to 0.70) and Si/Al ratio (down to 5.0) (Fig. 3). The WI<sub>MER</sub> also reflected the pedogenesis of the Holocene soil, which was less pronounced in the other weathering indices.

## Micromorphological characteristics of the paleosol horizons

The mineralogical composition of the matrix of the four investigated soil/paleosol horizons was dominated by quartz, feldspar, biotite, and calcite (Fig. 5a–d). The void system was characterized by predominance of biogenic pores in all studied horizons,
<figure><img src="image_5.png" /><figcaption>**Figure 4.** Stratigraphy and grain size (GS) data of main profile Baix. (A) Heatmap depiction of grain size frequency [vol%], vertical curves present GS variations and ratios GSI (26–52 µm/<26 µm), U ratio (16–44 µm/5.5–16 µm), fine clay/coarse clay (< 0.2 µm/0.63–2 µm). (B) Heatmap of Δ grain size distribution [vol%]. fC = fine clay (0.04–0.2 µm), mC = medium clay (0.2–0.63 µm), cC = coarse clay (0.63–2 µm), fSi = fine silt (2–6.3 µm), mSi = medium silt (6.3–20 µm), cSi = coarse silt (20–63 µm), fS = fine sand (63–200 µm), mS = medium sand (200–630 µm), cS = coarse sand (630–2000 µm). IG-EG-PSC = last interglacial to last early glacial paleosol complex; EPG-PS = last early pleniglacial paleosol; MPG-PSC = middle pleniglacial paleosol complex; Holocene-S = Holocene soil; ED = erosional discontinuity.</figcaption></figure>

mainly by channels, chambers, and some vugs. Passage and bio-
turbation features, and calcite earthworm granules were observed
in all studied soil/paleosol horizons (Fig. 5a, e, f). Illuvial clay and
clay–silt coatings occurred along the voids and on aggregate sur-
faces in all studied horizons (Fig. 5g, i, k, s). Primary carbonates

are absent in all paleosol horizons, however secondary carbon-
ates are present in the form of micrite hypocoatings (Fig. 5p). In
all studied horizons, orthic and disorthic Fe/Mn nodules occurred
(Fig. 5k, m). The 6 Bw3 and 7 Btg horizons showed two large red-
dish rounded aggregates containing iron oxides and fragments of
limpid clay coatings (Fig. 5c, d). The broken clay coatings and the varying degree of rounding indicating that the aggregates had been relocated or reworked to varying degrees (5o). The brown paleosol Bw horizons displayed a stippled-speckled to poro-striated b-fabric (Fig. 5j, l, n), whereas the 7 Btg horizon showed a poro-striated b-fabric (Fig. 5r, t).

In detail, the Bw1 horizon in the main profile Baix (43–51 cm) was characterized by a subangular blocky structure and abundant channels, few vugs, micrite hypocoatings along voids, dense calcite infillings, calcite earthworm granules (Ø 670 µm), root residues (Fig. 5a), and a crystallitic and speckled b-fabric (Fig. 5f, h). A large, round passage feature was present in the upper left corner of the thin section (Fig. 5a), including a calcite earthworm granule (Fig. 5e, f). Also, infillings of needle–fiber calcite and clay–silt coatings along voids were observed (Fig. 5g, h).

The 5 Bw2 horizon in the profile Baix_west (734–742 cm) exhibited a massive to weakly subangular blocky microstructure, many channels that were partially infilled with rounded aggregates, few vugs, abundant disorthic, rounded, elongated, digitated Fe/Mn nodules, and typic, digitated orthic Fe nodules (Ø 580 µm) (Fig. 5b). Moreover, rounded compound micro-aggregates with clay-silt coatings along the edges of the aggregates were observed (Fig. 5i, j).

The 6 Bw3 horizon in the main profile Baix (1133–1141 cm) was characterized by a massive to channel microstructure, whereby the channels were partially filled with porous microaggregates. Orthic and disorthic, rounded and digitated Fe/Mn nodules (Ø 350 µm), and a depletion zone were observed (Fig. 5c). In-situ, dusty clay-silt coatings with abundant anorthic Fe nodules occurred along voids (Fig. 5k–o).

The 7 Btg horizon in the main profile Baix (1209–1217 cm) had a weakly subangular to angular blocky microstructure with abundant channels, large, red, rounded anorthic nodules with Fe and clay coatings, fragmented clay coatings, and common small, digitate, round to elongated, disorthic Fe/Mn nodules and larger typic orthic Fe nodules (Fig. 5d). It showed a poro-striated b-fabric, calcite hypocoatings (Fig. 5p, r, t), iron oxide coatings and infillings (Fig. 5q, r), and limpid orange clay and gray-brown clay-silt coatings along voids (Fig. 5s, t). Both, in-situ and reworked limpid, layered illuvial clay coatings were observed in the 7 Btg horizon (Fig. 5d, q, s). The layered clay coatings along the void walls started with limpid orange clay coatings, followed by dusty, grayish-brown clay-silt coatings, and finally by iron-rich coatings (Fig. 5s).

## Chronological data

### AMS radiocarbon ages

The calibrated $^{14}$C ages of mollusc shells ranged from ca. 30 ka to ca. 17 ka (Fig. 6a, Table S1.1), but exhibit substantial scatter and age inversions. Bioturbation and sediment reworking through slope wash and deflation likely contributed to this scatter. Overall, the chronological data indicate deposition of the upper unit starting from the end of MIS 3 and continuing during MIS 2, which is consistent with other regional data (Bosq et al., 2020b), as well as data from elsewhere in Europe (Antoine et al., 2016; Lehmkuhl et al., 2021).

### OSL ages

Both $pIR_{60}IR_{225}$ feldspar coarse-grain and $pIR_{60}IR_{225}$ polymineral fine-grain ages were well in line with the results of the OSL

screening presented in Pfaffner et al. (2024) (Fig. 6b). Therefore, the results of the $pIR_{60}IR_{225}$ dating provide methodically reliable single-point data that were complemented by the closely spaced OSL screening data providing a quasi-continuous chronological framework. The course of the OSL screening data and the $pIR_{60}IR_{225}$ ages met the stratigraphic expectations derived from fieldwork and pedosedimentary analyses (cf., Pfaffner et al., 2024).

In contrast, the quartz fine grain data produced age overestimates throughout the profile. This finding is surprising, because the luminescence signal of quartz is assumed to reset faster than that of feldspar (Godfrey-Smith et al., 1988). Additional investigations of the quartz fine grains showed that the thermally stimulated (TL) glow curves of the natural samples, but not of the artificially regenerated samples, exhibited a high-temperature peak, similar to a Precambrian quartz sample with a geologic dose suggesting a minimum age of ca. 1.5 Ga (published by Schmidt and Woda, 2019). This finding corroborated the assumption that geologically old fine-grained quartz from the underlying bedrock (Cretaceous marlstone) was incorporated into the Baix loess deposits, likely during slope wash processes.

Therefore, we disregarded the quartz fine grain ages based our interpretation of the results of the OSL screening (Pfaffner et al., 2024), in combination with the $pIR_{60}IR_{225}$ dating of the feldspar coarse grains and the polymineral fine grains (Fig. 6b; Supplement 2: S2.6 additional tables). As, by nature, the coarse grain ages come with a smaller error than the polymineral fine-grain ages, in the discussion we refer to the $pIR_{60}IR_{225}$ feldspar coarse grain ages.

In the interpretation and contextualization of our results, we correlated the different phases of loess deposition and soil formation with Marine Isotope Stages (MIS) assuming stage boundaries according to Lisiecki and Raymo (2005) and Railsback et al. (2015). Therefore, MIS correspond to the terrestrial periods of the last interglacial (Eemian, MIS 5e), last early glacial (MIS 5a–d), early pleniglacial (MIS 4), middle pleniglacial (MIS 3), and late pleniglacial (MIS 2) periods (Figs. 6a, 6b, 7). Possible Greenland stadials (GS) and interstadials (GI) of the INTIMATE event stratigraphy (Rasmussen et al., 2014) are cautiously proposed, especially for periods of soil formation related to the paleosol horizons, as they are expected to respond to more supra-regional climate forces.

## Discussion

### Inference of sedimentation dynamics from granulometric characteristics

The peak in the coarse silt fraction point to one regional source, most probably the riverbed of the Rhône River (Fig. 4A). This agrees with Bosq et al. (2020a, b), who suggested that the riverbed of the Rhône River, carrying meltwater and abundant outwash sediments from the Rhône Glacier during the last glacial period, was the main source of loess in Rhône Rift Valley. The location of the loess deposit at the Baix LPS, which is situated on the foot slope of a small ridge in a leeward position with respect to the strong north-ern wind (Mistral) blowing down the Rhône Rift Valley, supports this assumption (Pfaffner et al., 2024).

Bosq et al. (2018) generally attributed the change from silty loess north of Valence to sandy loess in the south to the topography of the Rhône Rift Valley. The channeled and accelerated wind transported sand- and silt-sized particles from the Rhône River south at the outlet of the valley, where the accumulation area is characterized by deposition of loess, cover sands and/or restricted/limited dune fields (Bosq et al., 2018, 2020b; Bertran et al., 2021). Thus,
<figure><img src="image_6.png" /><figcaption>**Figure 5.** Photomicrographs of paleosol horizons and paleosol-complex of profiles Baix (Bw1: 43–51 cm; 6 Bw3: 1133–1141 cm; 7 Btg: 1209–1217 cm) and Baix_west (5 Bw2: 734–742 cm). (a–d) Photomicrographs of whole thin sections (3 cm × 4 cm). (e–t) Photomicrographs of certain details of the horizons at various magnification. Feature relations are discussed in text section “Micromorphological characteristics of the paleosol horizons”. PPL = plain polarized light; XPL = crossed polarized light; ci = clay infilling; cc = clay coating; ch = calcite hypocoating; ci = calcite infilling; cs = clay-silt coating; dz = depletion zone; eg = earthworm granule; fcc = fragmented clay coating; Fe-c = Fe coating; Fe-n = Fe/Mn nodule; pf = passage feature; ra = rounded aggregate; rr = root residue; wr = weathered rock fragments. (a) Bw1 (Baix) Subangular-blocky microstructure and channels, partially filled with rounded, bioturbated aggregates (PPL) (b) 5 Bw2 (Baix_west) Subangular-blocky microstructure and channels, partially filled with rounded, bioturbated aggregates (PPL) (c) 6 Bw3 (Baix) Massive to channel microstructure, channels partially filled with porous microaggregates, iron depletion zone; orthic and disorthic, rounded and digitated Fe/Mn nodules (Ø 350 µm) (PPL) (d) 7 Btg (Baix) Weakly subangular to angular blocky microstructure with channels and vugs; large, red, rounded anorthic nodule with Fe and clay coatings and fragmented clay coatings; common small round, digitated, elongated, disorthic Fe/Mn nodules; larger typic orthic Fe nodule (PPL) (e) Bw1 (Baix) Large passage feature in upper left corner of Figure 5a (PPL) (f) Bw1 (Baix) Passage feature showing crystallic b-fabric with calcite earthworm granule (XPL) (g) Bw1 (Baix) Calcite fillings (needle-fiber calcite) and clay-silt coatings along voids (PPL) (h) Bw1 (Baix) Same area as Figure 5g with stippled speckled b-fabric (XPL) (i) 5 Bw2 (Baix_west) Round, brown aggregate with clay-silt coatings along the edges of the aggregate (PPL) (j) 5 Bw2 (Baix_west) Same area as Figure 5i with striated and stippled speckled b-fabric (XPL) (k) 6 Bw3 (Baix) In-situ dusty clay-silt coatings at the bottom of the void with abundant anorthic Fe nodules (PPL) (l) 6 Bw3 (Baix) Same area as Figure 5k with stippled speckled b-fabric (XPL) (m) 6 Bw3 (Baix) Dusty clay-silt coatings along voids; typic to concentric orthic and anorthic Fe nodules (PPL) (n) 6 Bw3 (Baix) Same area as (m) with stippled speckled b-fabric (XPL) (o) 6 Bw3 (Baix) Large rounded, reddish anorthic nodule (Ø 2200 µm) containing Fe and clay coatings (PPL) (p) 7 Btg (Baix) Poro-striated b-fabric; calcite hypocoatings (XPL) (q) 7 Btg (Baix) Iron oxide coatings and infillings; clay coatings along voids (PPL) (r) 7 Btg (Baix) Poro-striated b-fabric; limpid clay coatings (XPL) (s) 7 Btg (Baix) In-situ limpid orange clay and gray-brown clay-silt coatings along voids (PPL) (t) 7 Btg (Baix) Same area as Figure 5s with poro-striated b-fabric (XPL).</figcaption></figure>
<figure><img src="image_7.png" /></figure>

<figure><img src="image_8.png" /><figcaption>**Figure 6.** Chronological data of the Baix loess-paleosol section (LPS), Rhône Rift Valley, SE France. (A) Upper 7 m of main profile Baix with results of ¹⁴C ages of mollusc shells and sample positions of OSL7 and OSL8 taken from profile Baix_west (green squares). (B) Lower 7 m of main profile Baix with results of the OSL dating on feldspar coarse grains (pIR₆₀IR₂₂₅, green squares), polymineral fine grains (pIR₆₀IR₂₂₅, red circles), and quartz fine grains (BLSL, blue filled circles) from six OSL block samples (OSL 1_2020–OSL 3_2020 and OSL 6_2018–OSL 8_2018) of profiles Baix and Baix_west. The yellow squares mark the positions of the dose rate samples for the OSL screening. For comparison, OSL screening results presented in Pfaffner et al. (2024) displayed with gray diamonds. Solid vertical lines denote the boundaries of the Marine Isotope Stages (MIS), and dotted lines mark the peaks of the MIS 5 substages (MIS boundaries after Lisiecki and Rayno, 2005; Railsback et al., 2015).</figcaption></figure>

the deposits of Baix LPS correspond to the northern (silty) loess, described by Lehmkuhl et al. (2021) as subdomain IIIa (no sandy loess or aeolian sand).

Two subordinate maxima in the fine- to medium-silt and in the medium-clay fractions were identified (Fig. 4B). The observed tailing in the medium- to fine-silt and clay fractions may be attributed

either to long-term suspension in the atmosphere, temporarily weakening wind activity, or to aeolian transport of silt-sized clayey aggregates (Tsoar and Pye, 1987; Pye, 1995; Vandenberghe, 2013). It also may have been caused by post-depositional weathering (Bronger, 1976; Újvári et al., 2016a; Schulte et al., 2018; Bosq et al., 2020b; Sprafke et al., 2020), because pedogenesis in loess leads
to an increase in medium to fine silt and clay at the expense of coarse silt (Sun et al., 2000; Günster et al., 2001; Újvári et al., 2016a; Wacha et al., 2018). The latter explanation seems the most likely in this case, because other observations, such as the very dif-fuse upper boundary of the EPG-PS, also indicate accretional soil formation. This points to an increase in aeolian input while weath-ering proceeded (Pfaffner et al., 2024). This alteration effect was also reflected in the particle size distribution characteristics of the paleosol horizons and recent soil horizon of the Baix LPS, with a main mode in the coarse-silt fraction, high fine- and medium-silt contents in the Bw horizons, and increased fine clay contents in the Bt and Btg horizons (Fig. 4B).

Furthermore, the loess and reworked loess from bottom to top showed an increase in GSI and U-ratio, a decrease in the silt content, and an increase in fine sand content (Fig. 4A). Similar trends of upward coarsening were observed in the Lautagne LPS (Bosq et al., 2020b), possibly the Val Sorda LPS (Ferraro, 2009), in the LPS of Susak, Croatia (Wacha et al., 2018), and in central European LPSs (Antoine et al., 2001, 2009; Schirmer, 2016; Fischer et al., 2019). In other studies, such coarsening has been explained by increasing local wind intensity and/or by a shift from a more-distant to a somewhat nearer sediment source (Rousseau et al., 2002; Antoine et al., 2009; Wacha et al., 2018). In the case of the Baix LPS, increasing wind velocity towards the last glacial maximum (LGM) seems more likely than a change in the source material, which is assumed to be the riverbed of the Rhône River throughout the entire Late Pleistocene. Another possible explanation is the assumed persistence of a vegetation cover (Tsoar and Pye, 1987; Bosq et al., 2018; Bertran et al., 2021). Due to its southern location, the Rhône Rift Valley is thought to have served as a refugium for trees and shrubs during the last glacial maximum, as it was still somewhat milder than its higher-lying surroundings (Beaudouin et al., 2007; Tzedakis et al., 2013). This vegetational influence was also implemented in the sediment depositional models suggested by Bosq et al. (2018) (Fig. 11) and Bertran et al. (2021), who assumed a prominent link between the steep relief and taller vegetation cover trapping loess particles more effectively in the Rhône Rift Valley.

## Geochemistry of Baix LPS and paleoenvironmental interpretation

### Characteristics of the non-weathered or only slightly weathered units of loess and reworked loess

Based on field observations (Pfaffner et al., 2024), the PSD, and geochemical characteristics, the C horizons (characterized by maxima of U-ratio, GSI, and primary carbonate content and minima of b values, weathering indices, and $Mn_d/Mn_t$ ratios) represent the “least weathered sediment units” of the Baix LPS (Figs. 3, 4). This generally points to increased sediment accumulation rates, reflecting the coldest and driest conditions. In contrast, the CB and BC horizons (with slightly decreased $CaCO_3$ content and $WI_{MER}$ values, and increased CPA values) represent shifts towards somewhat milder and probably more humid climate conditions.

Both categories (5 BCk5 to 5 Ck2 and 3 BCk3 to 2 BCk2 to CBk to Ck1) were marked by bioturbation and carbonate leaching indicated by secondary carbonate nodules that mostly showed no distinct depth of accumulation, as well as gradual changes in the weathering ratios and color parameters a and b/b. Collectively, this indicates increasing predominance of loess accumulation over

weathering, and possibly decreasing humidity that slowed decarbonization and weathering processes.

LPSs from northern regions indicate conditions related to open vegetation with almost no trees (Gocke et al., 2014), the increased SOC content within the C horizons together with evidence of synsedimentary bioturbation of Baix LPS may be interpreted as reflecting persisting vegetation at the site and organic matter accumulation even during the coldest phases (Fig. 3). However, the SOC contents reported here should not be over interpreted, since they come with a considerable analytical error as explained in the methods section.

In contrast to such gradual changes, there were also two horizons (6 BCk/Btg and 4 BCk/Bw), in which material of an underlying paleosol horizon was mixed with fresh loess. These horizons were characterized by abrupt increases in the U-ratio, GSI, and Si/Al, as well as lower a and a/b ratio, lower CPA and $Fe_d/Fe_t$ ratio, and a higher $WI_{MER}$ (Fig. 3). All of these indicate abrupt climatic deteriorations at these two points in time, which triggered erosion and re-deposition of soil material, while aeolian processes intensified. These deteriorations (colder, drier conditions) are characterized by decreased evapotranspiration, also shown by a decline of temperate forest vegetation towards tundra/steppe vegetation (Reille and de Beaulieu, 1990; Beaudouin et al., 2005; Mologni et al., 2021).

Throughout the entire profile, no lamella, platy structure, cracks, ice-wedge pseudomorphs, or any other features related to severe frost-thaw were observed. This observation is in accordance with the suggested maximum southernmost occurrence of permafrost at 47°N during the coldest period of the last glacial period (does not strictly coincide with the LGM) (Andrieux et al., 2016). Thus, frost-induced mass movement (e.g., solifluction) processes in Baix could only have taken place during early spring, above the temporarily frozen subsoil. The main sediment reworking along the slope most likely took place through slope wash processes (e.g., during snowmelt). In the relief position of the Baix LPS, on the foot slope of a small ridge, only short-distance slope wash processes were possible (Pfaffner et al., 2024; Fig. 2).

## Characteristics of the paleosols

### Basal last interglacial to last early glacial paleosol complex (IG-EG-PSC)

Generally, the horizons of the basal IG-EG-PSC were characterized by complete decarbonization and an advanced stage of chemical weathering and pedogenesis, as indicated by the highest $Fe_d/Fe_t$ ratios and CPA values, and lowest $WI_{MER}$ values and Si/Al ratios. In addition, it showed a reddish color, as reflected in highest a values and a/b ratios, interpreted as slight rubefaction (Fig. 3). The lowest horizon, 8 Bt2, developed in a slope deposit of weathered material of the underlying bedrock, which explains its comparatively high clay content (Pfaffner et al., 2024). The overlying 7 Bt1 and 7 Btg horizons showed tonguing, generally upward increasing CPA values, $Fe_d/Fe_t$, and $Mn_d/Mn_t$ ratios and a values, and decreasing $WI_{MER}$ values. Highest fine-clay/coarse-clay ratios and clay coatings indicate clay illuviation (Fig. 4A, 4B). All these characteristics pointed to warm and humid conditions during the formation of this paleosol complex. The slight rubefaction of the paleosol complex matches with that of the last interglacial paleosol of central European LPSs. For instance, Antoine et al. (2001) reported a “brown red loam” in the last interglacial paleosol at Nussloch (unit 2b). In contrast, strong rubefaction generally has been reported from last interglacial paleosols in Mediterranean LPSs (Ferraro,
2009; Wacha et al., 2011b; Boixadera et al., 2015, Durn et al., 2018; Zhang et al., 2018; Bosq et al., 2020b). There are two possible explanations for the only slightly rubified last interglacial paleosol complex in the Baix LPS: (1) the last interglacial climatic conditions at Baix were similar to those in central Europe; and (2) the position of the Baix LPS at the foot slope of a small ridge resulted in increased moisture that prevented the soil from drying out during summer and, thus, hampered the rubefaction process. So far, no other last interglacial paleosol has been studied at this climatic transition. However, Mediterranean climate conditions during the last interglacial have been described from other nearby archives (de Beaulieu and Reille, 1984; Tzedakis, 2007; Valladas et al., 2008; Rivals et al., 2009; Moncel et al., 2015). Thus, given the foot slope position of the Baix LPS and high clay content of its lowermost horizon (8 Bt2), favoring interflow along the slope, the inhibition of rubefaction by enhanced soil moisture in this foot slope position seems the more likely explanation.

The comparatively weakly developed soil structure of the 7 Btg horizon, and the co-occurrence of in-situ and reworked clay coatings point to the polygenetic nature of the paleosol complex. In a first phase of pedogenesis, a Luvisol formed, from which only the 7 Bt1 and 8 Bt2 horizons have been preserved. The Luvisol E horizon was completely eroded, and the upper part of the Bt horizon was reworked, mainly by slope processes. Thus, climatic deterioration must have opened the vegetation cover to some extent. The reworked material again was subjected to clay migration, while enhanced moisture developed hydromorphic features, resulting in the formation of the 7 Btg horizon. This reworking and subsequent clay illuviation are indicated by the co-occurrence of broken and intact clay coatings (Fig. 5d, q, s). In addition, the formation of the stagnic color pattern might have been enhanced as the repeated clay illuviation reduced the hydraulic conductivity over time. The strong hydromorphic features, also reported from LPS between Cadarache and Saint-Estève (Durance Valley, southern Rhône Rift Valley) (Bonifay, 1965; Mologni et al., 2021), most likely reflect climatic shift towards more humid and probably cooler conditions. The observed clay-silt coatings in the absence of permafrost indicators point to the regular melting of thick annual snow covers (Fedoroff and Goldberg, 1982). This scenario seems likely for the phase when sclerophyllous taxa declined at the end of the last interglacial towards temperate deciduous forest during the following interstadial periods (MIS5 c and a) (de Beaulieu and Reille, 1984; Reille and de Beaulieu, 1990; Mologni et al., 2021).

## Last early pleniglacial paleosol (EPG-PS)

The EPG-PS was represented by a decarbonated bipartite brown 6 Bw3 horizon (Pfaffner et al., 2024). Its weathering ratios and increased fine silt proportion (~5–12 µm) reflect a moderate stage of pedogenesis (Figs. 3, 4). The lower part of the 6 Bw3 horizon still comprised some relocated reddish aggregates and depletion zones that had apparently been mixed in from the 7 Btg horizon of the IG-EG-PSC, as well as in-situ clay-silt coatings (Fig. 5c, k). Thus, the Bw formation must have started by formation of the 6 Bw3 horizon, which is a mixture of fresh sediment and pre-weathered soil material relocated from the underlying 7 Btg horizon. Pedogenesis still continued, when slow loess accumulation set in, leading to a gradual upward growth of the EPG-PS and formation of the 5 BCk5 horizon. In other words, the A horizons seemed to be transformed into B horizons as parts of the former A horizons were marked by decreasing SOC contents and an increase of biological activity. This process of accretional soil formation was also described by Kemp et al. (2001) and Constantin et al. (2021) for

the Pleistocene–Holocene climatic transition. Apparently, climatic conditions during this period were still humid enough to allow the formation of clay-silt coatings.

## Middle pleniglacial paleosol complex (MPG-PSC)

The MPG-PSC developed in a reworked loess sediment, as reflected by high variability of the clay, silt, and sand contents (Fig. 4B). The decarbonated 5 Bw2 horizon displayed similar $W_{MER}$, CPA, clay contents, fine-silt proportion, U-ratio, GIS, and silt-clay coatings along pores as the 6 Bw3 horizon of the EPG-PS (Figs. 3, 4A, 5b, j). However, in contrast to the EPG-PS, we assume a top-down soil formation, where a substantial part of the MPG-PSC was eroded. The erosion is indicated by the large carbonate nodules in the 5 BCk4 horizon, which can only be explained by a much thicker decarbonated soil horizon, which must have been overly-ing the preserved remains of the 5 Bw2 horizon that shows a major erosional discontinuity on top.

The MPG-PSC in the Baix LPS was very similar to the one in the Collias LPS farther south (Bosq et al., 2020b). In addition to the large carbonate nodules that are mainly restricted to one depth (the 5 BCk5 horizon), this paleosol in both LPSs showed smaller carbonate nodules that were distributed over a rather large depth range. At Collias, Bosq et al. (2020b) explained this observation by an interplay between relatively intensive soil formation and moderate loess deposition rates, similar to the concept of accretional soil formation (Kemp, 2001; Constantin et al., 2021). With progressive loess input, both the soil surface and the corresponding carbonate accumulation zone moved upwards. In this way, the secondary carbonate nodules were distributed over a wide depth range (Bosq et al., 2020b).

However, it must be considered that the MPG-PSC reflects successive events of pedogenesis and soil erosion, yet the complete decarbonization of the 5 Bw2 horizon and the occurrence of the large carbonate nodules at specific depths, both at Collias and at Baix, indicated at least one phase of increased humidity with soil formation without relevant loess input. However, the most strongly developed upper part of the MPG-PSC, from where the carbonates that now form the large nodules in the 5 BCk5 horizon were leached, has been eroded in both LPSs, indicating cross-regional climatic deterioration within the middle pleniglacial period.

However, it is challenging to identify a separate upper MIS 3 paleosol above the MPG-PSC (3 BCk3, 2 BCk2 horizons), because the brownish color of the slope wash loess deposits in that stratigraphic position could indicate either accretional soil formation (less intense than EPG-PS) or derivation from brown material eroded from the MPG-PSC in an upslope position and mixed in at the foot slope position of the Baix LPS. This interpretation is supported by the considerable variability in silt and sand contents within the 3 BCk3 horizon.

## Holocene soil

The recent soil at Baix is an Endocalcic Cambisol. Compared to the paleosol Bw horizons (6 Bw3, 5 Bw2), the Bw1 horizon of the recent soil is not completely decarbonated, and its weathering ratios reflect a lower degree of weathering (Fig. 5a, g). This difference most likely is not a result of less moisture and lower weathering intensity during the Holocene period, but of rejuvenation of the soil through erosion. Although the site is forested at present, human influence is obvious (with an old quarry and agricultural activities nearby).
# Chronology of Baix LPS

## Last interglacial and last early glacial period (MIS 5)

The loess unit, in which the IG-EG-PSC formed (OSL 1<sub>2020</sub>) gave a pIRIR-age of 117.5 ± 9.7 ka (Fig. 6b). However, because of the hydromorphic features in this paleosol, Pfaffner et al. (2024) assumed a higher soil water content of Δ 1.28 ± 0.05 for the lowermost part of the main profile. Adopting this value for the present study yielded an age of 128.5 ± 10.5 ka, supporting the field assumption of pre-last interglacial loess deposition and soil formation during the last interglacial (ca. 126–115 ka; in the Mediterranean likely until 110 ka, according to Sánchez Goñi et al., 1999) soil formation. Thus, formation of the 7 Bt1 horizon correlates with MIS 5e (GI 26/25c; Eemian).

The wide scatter of OSL screening data obtained for sediment of the overlying 7 Btg horizon is due to the reworking of MIS 5e soil material, involving partial bleaching of feldspar grains (Fig. 6b). The reworking phase and subsequent soil formation phase most likely took place during MIS 5d or MIS 5b and MIS 5c or MIS 5a, respectively (Fig. 7).

## Early pleniglacial period (MIS 4)

The OSL block sample (OSL 2<sub>2020</sub>) taken from the 6 BCk/Btg horizon, directly overlying the prominent erosional discontinuity above the MIS 5 paleosol complex, gave an age of 67.0 ± 5.7 ka (Fig. 6b). Thus, that erosional discontinuity and overlying reworked sediment (6 BCk/Btg horizon) apparently mark climatic deterioration at the onset of the MIS 4 (71–57 ka).

## Early to middle pleniglacial period (MIS 4 to MIS 3)

The next-upper block sample (OSL 3<sub>2020</sub>) was taken from the only slightly weathered unit (5 BCk5 horizon) above the MIS 4 Calcic Cambisol. It yielded an age of 59.8 ± 5.3 ka, roughly corresponding to the MIS 4/MIS 3 boundary around 57 ka (Fig. 6b). Thus, the accretional soil formation of the Calcic Cambisol (6 Bw3) may have continued during the milder excursions of GI 18 until GI 16/15 (Fig. 7) and must have ended at the latest by the end of MIS 4. Deposition of the overlying sediment unit probably took place mainly during the cool periods between GS 18 and GS 15 (Fig. 7).

The sedimentary material in which the truncated prominent MIS 3 Calcic Cambisol had formed, showed a pIRIR age of 54.8 ± 5.2 ka (OSL 6<sub>2018</sub>). This age overlaps within error margins with the age of 59.8 ± 5.3 ka obtained for the OSL 3<sub>2020</sub>, taken from the sediment unit below, which may suggest a very high sedimentation rate. Considering the minimum of the error margins, sedimentation rates between the times yielded from samples OSL 3<sub>2020</sub> and OSL 6<sub>2018</sub> were possibly a factor 3.6 higher compared to those between the times given by samples OSL 2<sub>2020</sub> and OSL 3<sub>2020</sub>. In contrast, considering the maximum of the error margins, it is also possible that the sediment units bracketed by samples OSL 3<sub>2020</sub> and OSL 6<sub>2018</sub> (in which the 5 BCk5 and 5 Bk2 developed) underwent a relatively short period of intensive sediment reworking that almost homogenized the pIRIR age of the whole unit. Because of the homogeneity of the material, field observation can neither confirm nor exclude this possibility. This observation of a possibly quasi-constant luminescence age of about 55 ka over a certain sediment depth is very similar to the situation at the Collias LPS, where OSL ages of 55.5 ± 4.4 ka and 55.1 ± 4.1 ka bracketed a ca. 2-m-thick sediment unit, in whose upper part the prominent MIS 3 Calcic

Cambisol had formed (Bosq et al., 2020b). Thus, the phenomenon may have occurred at the same time in the two LPSs.

Based on the sedimentation times of around 55 ka obtained in both LPSs, the formation of the MIS 3 Calcic Cambisol with the prominent carbonate nodules most likely started in the relatively long-lasting GI 14 (Fig. 7). The end of its pedogenesis and its truncation by severe erosion must pre-date the age of the overlying slope washed, weathered loess deposits (3 BCk3), which yielded an age of 37.5 ± 3.1 ka in the Baix LPS (OSL 7<sub>2018</sub>) and an age of 38.5 ± 2.5 ka in the Collias LPS. Thus, the climatic deterioration that caused the end of the period of geomorphological stability during which the Calcic Cambisol formed, may correspond to GS 9 and/or the Heinrich 4 event (40.2–38.3 ka) (Fig. 7). Hence, the truncated MIS 3 Calcic Cambisol with the prominent carbonate nodules that was present in both LPSs, Baix and Collias, represents a pedo-complex that probably developed in repeated pedogenic cycles over a period that roughly includes GI 14–GI 9, representing milder phases during that time, which allowed for enhanced soil formation.

## Middle to late pleniglacial period (MIS 3 to MIS 2)

Another time mark of ca. 35.8 ± 3.2 ka was obtained from OSL 8<sub>2018</sub>. Together with the ages obtained from the next-lower OSL 7<sub>2018</sub> (37.5 ± 3.1 ka) and OSL 6<sub>2018</sub> (54.8 ± 5.2 ka), this age supported a trend of upward-decreasing sedimentation ages for the uppermost ~4.5 m of the LPS (Fig. 6a, b).

This was important information, because the ages from the OSL screening showed such scatter for this part of the LPS that it was difficult to obtain an age trend from them (Pfaffner et al., 2024). AMS <sup>14</sup>C ages of mollusc shells from the same part of the LPS were much younger, corresponding to late MIS 3 and MIS 2 (Fig. 6a). They showed a trend of decreasing ages but with some age inversions.

# Comparison of Baix LPS with other European LPSs

Polygenetic Luvisol formation during the last interglacial (MIS 5e) to last early glacial (MIS 5d-5a) periods also has been reported from various central European and Mediterranean LPSs (Bourdier, 1958; Bonifay, 1965; Antoine et al., 1999, 2001; Rose et al., 1999; Günster et al., 2001; Ferraro, 2009; Wacha et al., 2011a, b; Boixadera et al., 2015; Haesaerts et al., 2016; Bosq et al., 2020b; Kehl et al., 2024). At Baix LPS, we assume a warm interglacial climate during MIS 5e and at least one period of sediment reworking, followed by a period of soil development involving the formation of hydromorphic features during MIS 5d-a. Similar pedo-stratigraphic units for the MIS 5 have been described from LPSs of southern France (Bosq et al., 2020b), Spain (Lachar LPS; Günster et al., 2001), and Croatia (Susak LPSs; Wacha et al., 2011b; Profe et al., 2018). In contrast, central European LPSs reflect more continental (drier) conditions during the MIS 5 interstadial periods that are typically represented by up to three humus horizons (e.g., the Mosbach humus zones, the Bettencourt soil overlying the St. Sauflieu complex, the upper Rocourt pedocomplex overlying the humus complex of Remicourt, and the upper part of the Garzweiler pedocomplex) (Antoine et al., 1999, 2016; Schirmer, 2002, 2016; Frechen et al., 2007; Lehmkuhl et al., 2021).

The erosional discontinuity above the IG-EG-PSC of Baix LPS apparently marks the climatic deterioration at the onset of the MIS 4 (71–57 ka). In the western and central European loess belt, this period is known for widespread sediment reworking (e.g., Keldach
<figure><img src="image_9.png" /><figcaption>**Figure 7.** Compiled marine and ice-core chronostratigraphy for the last 140 ka, including left: Marine Isotope Stages (MIS) derived from global benthic stack (Lisiecki and Raymo, 2005) and 1000-year average values of δ¹⁸O from NGRIP records including Greenland Interstadials (GI) from INTIMATE event stratigraphy (Rasmussen et al., 2014) and Heinrich events (H) (Allard et al., 2021). Right: Generalized loess paleosol-sequence (LPS) of Nussloch (Antoine et al., 2001, 2009; Kadereit et al., 2013; Moine et al., 2017), Baix and Collias LPS (Bosq et al., 2020b, Pfaffner et al., 2024) emphasizing soil-formation phases during chronostratigraphical stages of the Late Pleistocene with their latitudinal position, recent mean annual temperature (MAT), mean annual precipitation (MAP), and number of arid months (dwd, deutscher Wetterdienst, 2021a, b; Météo-France 2025a, c).</figcaption></figure>

discordance and Niedereschbach zone; Hermies, Harmignies col-
luvial deposit) (Semmel, 1998; Antoine et al., 2016; Lehmkuhl et al.,
2016). However, for the Rhône Rift Valley, this is the first time that
this landscape instability at the onset of MIS 4 has been precisely
identified and dated.

So far, MIS 4 paleosols such as the EPG-PS of Baix have been
reported from very few Mediterranean LPSs. Thin brown MIS 4
paleosols were observed in the Bok section in Croatia (Wacha et al.,
2011a). An orange-brown paleosol of the Bok section 1 (Wacha
et al., 2011b) that developed after 98.3 ± 7.3 ka and prior to 54.3
± 4.9 ka might correspond to the Calcic Cambisol in the Baix LPS.
In central Europe, MIS 4 to MIS 4/MIS 3 Cambisol and Regosol
relics (e.g., the Gräselberg Soil (Gräselberg LPS; Semmel, 1968); the
Jackerath Soil and Reisberg Soil (Garzweiler and Schwalbenberg
I LPS; Schirmer, 2002), the Havrincourt Soil (Havrincourt LPS;
Antoine et al., 2016), the Malplaquet Soil (Remicourt, Harmignies
LPSs; Haesaerts et al., 2016), stratigraphic units 12, 20, 23, and pos-
sibly 26 – all Bw horizons of Calcaric Cambisols (Schwalbenberg

LPS; Fischer et al., 2021) have been reported from several LPSs. The
temporal positioning of some of these paleosols seems clear (e.g.,
that of the Jackerath Soil in the MIS 4), while the allocation of oth-
ers appears less unequivocal, but is probably somewhere near the
MIS 4/MIS 3 boundary (e.g., in the case of the Lower Gräselberg
Soil; Antoine at al., 2009; the Lower Remagen Soils; Schirmer,
2012), possibly corresponding to the brown Calcic Cambisol in the
Baix LPS (Fig. 7).

An intensively red-brown soil horizon, underlain by carbonate
nodules, similar to the truncated MPG-PSC of Baix LPS has been
described on Susak Island (Wacha et al., 2011b, 2018; Zhang et al.,
2018). Furthermore, a comparably well-developed brown, trun-
cated paleosol horizon (of a Cambisol) is found in most European
LPSs (although without carbonate nodules) in northern and south-
ern France (Saint-Acheul/Villiers-Adam soil complex) (Bonifay,
1965; Antoine et al., 2003, 2016), in Belgium (Les Vaux) (Haesaerts
et al., 2016), and in Germany, where sometimes even several
brown paleosol horizons have been preserved in this stratigraphic
position (e.g., Remagen Soils, Gräselberg Soils) (Antoine et al., 2001; Schirmer, 2002, 2016; Frechen et al., 2007; Gocke et al., 2014; Fischer et al., 2021). Thus, the truncated Calcic Cambisol with the prominent carbonate nodules at Baix may be regarded as a mid-MIS 3 stratigraphic marker within the Rhône Rift Valley that also may serve for cross-regional correlation of central and south European LPSs.

Significant soil formation was not detected above the truncated MPG-PSC either at Baix LPS or at Collias LPSs. In Mediterranean LPSs, the late MIS 3 paleosols are highly diverse, depending on their geographical and geomorphological positions (Brunnacker, 1974; Coudé-Gaussen, 1990). They vary from up to three Chernozems in Italy (Ferraro, 2009) to up to four thin, brown paleosol horizons in the Susak LPS (Wacha et al., 2011a), one of the few LPSs with reliable age control for this period. For the northern Rhône Rift Valley, Franc et al. (2017) also described a possibly correlating brown paleosol, whereas in several LPSs of the southern Rhône Rift Valley the existence of a paleosol in this stratigraphic position is unclear (Bourdier, 1958; Bonifay, 1965), while in others such paleosols are missing (Bosq et al., 2020b). In addition to the MIS 3 paleosols described above, the central European LPSs typically show one or several considerably younger brown paleosol horizon(s) that formed during the milder periods GI 8 to GI 4 (ca. 38–29 ka) making up the Lohne Soil or its equivalents (e.g., the Sinzig Soils, upper part of the Saint-Acheul/Villiers-Adam soil complex) (Antoine et al., 2001; Schirmer, 2002; Kadereit et al., 2013; Moine et al., 2017; Fischer et al., 2019).

Either possible younger MIS 3 incipient soils were later mixed in with younger loess material, or the Baix LPS does not conform with the central European LPS after ca. 40 ka, but rather conforms to the south European LPS, where climatic deterioration may have been more gradual compared to the more extreme climatic fluctuations of mid-European LPSs. However, the Baix LPS apparently experienced intense loess sedimentation for the period around 40–35 ka. A comparably high sedimentation rate occurred in the Collias LPS ca. 39–37 ka.

Such high loess accumulation rates that occurred at both sites might have been related to dry conditions during Greenland stadials and especially to Heinrich events, which caused a dramatic decline of forest and led to more open vegetation (Fletcher and Sánchez Goñi, 2008). Dry conditions during Heinrich events are also assumed to have caused glacier retreat in the Mediterranean (Allard et al., 2021) as well as high sediment load of Mediterranean rivers (e.g., Woodward et al., 2008; Lewis et al., 2009), whose riverbeds provided major dust source areas when drying out. The study of Bosq et al. (2023) suggests an earlier start (approx. 42 ka – Alpine ice sheet) of enhanced loess deposition within the Alpine region compared to the mid-European region (approx. 32 ka – Fennoscandian ice sheet; Northern European Loess Belt). Thus, the lack of younger MIS 3 paleosols also may be explained by asynchronous loess deposits within the European aeolian system, in contrast to the previous assumed less-extreme climatic fluctuations for Baix LPS. The continuing loess accumulation observed at both LPSs, Baix and Collias, during MIS 2, matches with the acceleration of loess accumulation reported from many central European LPSs (Antoine et al., 2009, 2016; Ferraro, 2009).

## Conclusion

In this work, we characterized the loess and reworked loess, and the paleosol horizons of the Baix LPS based on granulometric,

geochemical, and micromorphological analyses. We also established a detailed stratigraphy of the Baix LPS with a robust chronostatigraphic framework, including the last interglacial and glacial period (MIS 5 to MIS 2). The particle size distribution of the loess and reworked loess at Baix corresponds well with characteristics of central European loess. Loess accumulation at Baix was mainly controlled by the local wind regime, topography, and vegetation cover. The main loess accumulation phases occurred during the last early pleniglacial (MIS 4) and late pleniglacial (MIS 2) periods, whereas an earlier beginning at the end of the MIS 3 at Baix LPS compared to mid-European LPSs seems highly likely.

At the base of the Baix LPS, a well-preserved record of the last interglacial to last early glacial period (Eemian, MIS 5e) is provided by a polygenetic, slightly rubified stagnic Luvisol. It indicates warm last interglacial conditions, followed by a phase of erosion and reworking caused by climatic deterioration and a subsequent phase of pedogenesis under cooler and moister conditions (due to decreased evapotranspiration and annual snowmelt). The MIS 5 paleosol complex in the Baix LPS is much less rubified than its counterpart in the Collias LPS, although the Mediterranean climate most likely expanded as far north as Baix during MIS 5e. This is probably due to the strong hydromorphic processes that overprinted the paleosol complex in the Baix LPS and prevented more intense rubefaction (Yaalon, 1997).

During the early pleniglacial period (MIS 4) accretional soil formation took place forming a Calcic Cambisol. Its brown Bw horizon is overlain by a BCk and a Ck (unweathered loess) horizon, reflecting increasing aeolian input while synsedimentary pedogenesis continued for a while and then weakened.

The middle pleniglacial period (MIS 3) allowed the formation of at least one well-developed Calcic Cambisol (top-down soil formation) with large carbonate nodules. This paleosol needed relatively mild and humid conditions to develop, which makes its development during GI 14 to GI 9 most likely. The Calcic Cambisol was then truncated, possibly during the climatic deterioration of GS 9.

During the late middle pleniglacial (MIS 3; from GS 9 on) and late pleniglacial (MIS 2) periods, loess accumulation prevailed. No soil horizons like those reported for MIS 2 in the central European LPSs (tundra gley soil; Antoine et al., 2009; cryosols and regosols; Lehmkuhl et al., 2016) were found at Baix LPS during this period. Considering an earlier beginning of pronounced loess accumulation, a milder climate at Baix, compared to central Europe, may also be a reason for the more pronounced bioturbation in the Baix LPS than in the central European LPSs. In this respect, the Baix LPS resembles the Mediterranean LPSs, for which gradual climatic changes are typical.

The recent Cambisol is only moderately developed, because anthropogenic disturbances caused its erosion and, hence, rejuvenation. Therefore, it cannot be compared to the well-developed MIS 5e paleosol, to evaluate the intensity of weathering and soil formation during MIS 5e conditions.

Overall, the Baix LPS displays characteristics of both the central European and south European LPSs and, thus, reflects its location in a climatic transition zone, as suggested by Brunnacker (1974), Bosq et al. (2018, 2020b), and Lehmkuhl et al. (2021) (subdomain IIIa to VIa). This combination of characteristics makes the Baix LPS a valuable link between the loess regions of central and southern Europe.

**Supplementary material.** The supplementary material for this article can be found at https://doi.org/10.1017/qua.2025.10053.
**Acknowledgments.** We are very grateful to Monsieur L. Garnier for allowing us to prepare the profile in his quarry. We thank Dr. Barbara von der Lühe for help in the field, and Dr. Volker Karius, Dr. Jürgen Grotheer, Anja Södje, Petra Voigt, Marius Friedrich, Jutta Asmuth, Dr. Simon Meyer-Heintze, and Dr. Phillip Schulte for the laboratory analyses and graphical support. We acknowledge the German Aerospace Centre (DLR), which provided the TanDEM-X data for the study area (DEM_GEOL1263). This work was funded by the Department of Physical Geography of the University of Goettingen. Sebastian Kreutzer was supported by the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement no. 844457 (CREDIT).

**Author contributions.** Conceptualization of the project: Daniela Sauer and Annette Kadereit; field investigation: Nora Pfaffner, Daniela Sauer, Annette Kadereit, Tianhao Wang, Pascal Bertran, Mathieu Bosq; methodology: Nora Pfaffner, Annette Kadereit, Sebastian Kreutzer, Thomas Kolb, Hans-Peter Meyer, Alexander Varychev Pascal Bertran, Christine Hatté; data validation and interpretation: Nora Pfaffner, Daniela Sauer, Annette Kadereit, Sebastian Kreutzer Thomas Kolb, Pascal Bertran, Mathieu Bosq, Christine Hatté; conceptualization of the manuscript: Nora Pfaffner; writing – original draft preparation: Nora Pfaffner; writing – review and editing: all authors. All authors have read and agreed to the published version of the manuscript.

**Conflicts of interest.** The authors declare no conflicts of interest.

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