# Abrupt changes in continental sedimentation triggered by monsoon-type event during EECO hyperthermals, Minervois Basin, Southern France

Cindy Boyrie, Flavia Girard, Johan Yans, Grégory Ballas, Fabrice Lihoreau, Mouloud Benammi, Hélène Bourget, Géraldine Garcia, Christine Leredde, Aimée Pellissier-Tanon, et al.

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## ► To cite this version:

Cindy Boyrie, Flavia Girard, Johan Yans, Grégory Ballas, Fabrice Lihoreau, et al. Abrupt changes in continental sedimentation triggered by monsoon-type event during EECO hyperthermals, Minervois Basin, Southern France. Sedimentary Geology, 2025, 486, pp.106923. 10.1016/j.sedgeo.2025.106923. hal-05300426

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# Abrupt changes in continental sedimentation triggered by monsoon-type event during EECO hyperthermals, Minervois Basin, Southern France

Cindy BOYRIE<sup>a,b</sup>, Flavia GIRARD<sup>b,*</sup>, Johan YANS<sup>c</sup>, Grégory BALLAS<sup>b</sup>, Fabrice LIHOREAU<sup>a</sup>, Mouloud BENAMMI<sup>d</sup>, Hélène BOURGET<sup>a</sup>, Géraldine GARCIA<sup>d</sup>, Christine LEREDDE<sup>b</sup>, Aimée PELLISSIER-TANON<sup>b</sup>, Xavier VALENTIN<sup>d</sup>, Dominique VIDALENC<sup>e</sup>, Rodolphe TABUCE<sup>a</sup>

## ARTICLE INFO

Editor: Dr. Massimo Moretti

**Keywords:**

Ypresian
Climate warming
Palustrine shallow-lacustrine
Ephemeral multistorey braided channel plain
Upper-flow regime
Carbon isotope

## ABSTRACT

Recent studies on Early Eocene climate have established that global climatic warming, characterized by negative carbon isotopic excursions (CIE, hyperthermals) in the atmosphere, are responsible for drastically changes in the terrestrial sedimentary record of sub-tropical basins. Here we present a key sedimentary record to understand geological and climatological changes in order to evaluate the impact of hyperthermals on sediment transport and deposition in continental setting during the Early Eocene Climatic Optimum (EECO) in Europe. Based on an integrative study combining sedimentology, sequential stratigraphy, magnetostratigraphy and chemo-stratigraphy (carbon isotopes, δ¹³Corg), the study proposes a detailed constrained chronostratigraphic framework of continental sedimentary series of the Minervois Basin (South of France). Using facies association analysis, the sedimentary succession is divided into three continental sequences bounded by subaerial unconformity deposited through the development of an endoreic underfilled basin. The sequences are composed of floodplain to palustrine-shallow lacustrine carbonate deposits reflecting arid climatic conditions during the EECO. They are cyclically punctuated by the sudden arrival of detrital fluxes with deposits of supercritical bedforms associated to an ephemeral multistorey braided channel plain, reflecting intense and extreme rainfall events in the hinterland. The latter coincides to CIEs corresponding to hyperthermals identified as C24n.1nH1/K (ETM3), C23rH2 (M), and C23n.2nH1-C23n.2nH2 (N—O) interval. Extreme monsoon-type events triggered by intense warm-ups during hyperthermals are proposed to explain sudden detrital inputs in the basin. This work confirms that transient hyperthermals can generate drastic hydrological changes in the sedimentary record.

## 1. Introduction

The stratigraphic sedimentary record is an undeniable archive for identifying and understanding climatic changes over geological time. The Early Eocene Climate Optimum (EECO – 53.26 Ma–49.14 Ma; Westerhold et al., 2018, 2020) refers to a greenhouse epoch when the poles were completely ice-free and subtropical to tropical climate extended to high latitudes (Zachos et al., 2001; Westerhold et al., 2020; The Cenozoic CO₂ Proxy Integration Project (CenCO₂PIP) Consortium et al., 2023). This period corresponds to the warmest hothouse phase of the Cenozoic, when global temperatures were ~10 °C higher than today

(Westerhold et al., 2020) and atmospheric CO₂ concentrations were simultaneously high (Zachos et al., 2008). During the EECO, several carbon isotope excursions (CIEs) associated with more transient but brief, widespread and extreme warmings corresponding to hyperthermals, were overprinted (40–200 kyrs; Westerhold et al., 2018). Such short- and long-term warming events have particularly influenced the Earth's climate during the Ypresian, involving oceanic and terrestrial modifications, an intensification of the hydrological cycle, and impacting sedimentation fluxes as well as the evolution of flora and fauna (Alegret et al., 2009; Woodburne et al., 2009; McInerney and Wing, 2011; Carmichael et al., 2016; Foreman and Straub, 2017; Cramwinckel

<footnote><sup>a</sup> Institut des Sciences de l'Evolution, Univ-Montpellier, CNRS, IRD, Montpellier, France</footnote>

<footnote><sup>b</sup> Géosciences Montpellier, Univ-Montpellier, CNRS, Montpellier, France</footnote>

<footnote><sup>c</sup> Département de Géologie, Institut of Life, Earth and Environment, ILEE, Université de Namur, Belgium</footnote>

<footnote><sup>d</sup> Laboratoire Paléontologie Evolution Paléoécosystèmes Paléoprimatologie, Poitiers, France</footnote>

<footnote><sup>e</sup> 103 Avenue François Mitterand, 31800 Saint-Gaudens, France</footnote>

<footnote>* Corresponding author.
E-mail address: flavia.girard@umontpellier.fr (F. GIRARD).</footnote>
et al., 2018; Harper et al., 2020; Miller et al., 2020; Rush et al., 2021; Cooley et al., 2022; Elson et al., 2022; Filippi and Luciani, 2025; Lihoreau et al., 2025). Studying this type of ancient warming event offers an analogue of the anthropogenic warming that the Earth is currently undergoing (Zachos et al., 2008; Payros et al., 2022), providing an understanding of inherent present-day processes and contributing to the calibration of future climate models.

The impact on sedimentation of such warming events have been extensively studied in recent decades, particularly in marine environments (Robert and Kennett, 1994; Lourens et al., 2005; Zachos et al., 2005, 2010; Vimpere et al., 2023), to a reduced extent in the continental domain for the most significant Paleocene Eocene Thermal Maximum (PETM; Kraus et al., 2013; Manners et al., 2013; Chen et al., 2018; Duller et al., 2019; Arévalo et al., 2022; Basilici et al., 2022; Del Papa et al., 2022; Payros et al., 2022; Pujalte et al., 2022; Prieur et al., 2024), and even less for following Eocene Thermal Maxima (ETM; Schmitz and Pujalte, 2007; Foreman et al., 2012; Foreman, 2014; Kraus et al., 2015; Abels et al., 2016), and EECO transient warmings (Bataille et al., 2016; Owen et al., 2017; Birgenheier et al., 2020; Honegger et al., 2020). Some authors associate these hyperthermals with an increase in detrital discharges linked to a strengthening of intense rainfall episodes (Schmitz and Pujalte, 2007; Arévalo et al., 2022; Payros et al., 2022). Additionally, it is well-established that monsoonal events can trigger extreme rainfall, leading to the appearance and development of ephemeral rivers experiencing high-magnitude floods, especially close to mountainous hinterland, as demonstrated for ancient and present-day systems (Plink-Bjorklund, 2015, 2015b).

In southwestern France, the Minervois Basin provides wide extensive and continuing outcrops of sedimentary series of Ypresian age which are very rich in fossil remains, especially mammalian species (Marandat, 1986; Comte et al., 2012; Danilo et al., 2013; Godinot et al., 2018). Noiret et al. (2016) yet highlighted the occurrence of hyperthermal events (C24rH8/ETM2/H1 and C24n.1nH1/ETM3/K), and EECO interval in this area. The present study focuses on a data set analyzed through sedimentology, sequence stratigraphy, carbon isotope (δ¹³C on organics – δ¹³Corg) and magnetostratigraphy on a continental sedimentary succession. This multidisciplinary research provides new criteria for identifying hyperthermals in sedimentary archives and assesses the sedimentary signal in alluvial setting for transient hyperthermals. The

objective of this study is to develop a model for continental sedimentary response to critical climatic shifts during the EECO. This will be achieved by describing and comparing the impact of such phenomena on continent in a geologic period which is scarcely represented by long sequence in ancient European basins (Payros et al., 2009; Lihoreau et al., 2025).

## 2. Geological setting

### 2.1. Tectonic framework

The Minervois area is located in the Occitanie region (Southern France), between cities of Carcassonne and Béziers (Fig. 1A). This area corresponds to the easternmost part of the Aquitaine-Carcassonne Basin formed in the retro-foreland context of the Pyrenean Orogeny (Ford et al., 2022). The latter is related to the shortening caused by the north-south convergence of the Iberian and European plates, from the Late Cretaceous to the Oligocene (Ford et al., 2016; Rougier et al., 2016; Grool et al., 2018). In the study area, the thickness of sedimentary layers and their growth strata geometry, detected at the front of local thrusts such as those of the Alaric, Tourouzelle or Oupia (Grelaud et al., 2000; Martín-Martín et al., 2001; Christophoul et al., 2003; Al Reda et al., 2021; Fig. 1B), reveals that the most active tectonic phase occurred in the Eocene (Ford et al., 2022). The northern side of the Minervois Basin shows a large south-dipping monocline structure with sedimentary deposits resting unconformably on the folded Paleozoic-age rocks of the Montagne Noire Massif (Martín-Martín et al., 2001; Fig. 1B). This basin is limited to the east and south-east by the Corbières transfer zone, linking the Pyrenees Massif to the Saint Chinian arc and the Languedoc-Provençal thrust belt (Arthaud and Seguret, 1981; Seguret and Benedicto, 1999; Espurt et al., 2012). This transfer zone is reactivated during the Mediterranean Oligocene-Miocene rifting, related to the opening of the Gulf of Lion southeastward (Maerten and Séranne, 1995; Séranne et al., 1995; Benedicto et al., 1996; Mascle et al., 1996).

### 2.2. Stratigraphic setting

The stratigraphic succession of the Minervois Basin is composed of five sedimentary formations (Fm.) of Eocene age. Since this sedimentary

<figure><img src="image_5.png" /><figcaption>**Fig. 1.** A) Location of the Minervois Basin, south of France - B) Geological map of the Minervois Basin (modified from the 1/50000 Lézignan-Corbières geological map; Berger et al., 1990) - C) Simplified stratigraphic succession of the Minervois showing global successive depositional environments from basal Ilerdian deposits to Aigne Fm. on top.</figcaption></figure>
succession is very rich in mammal remains, numerous historic and
recently discovered localities (which are currently being studied) enable
the dating of the sedimentary rocks (Marandat, 1986; Comte et al., 2012;
Noiret et al., 2016; Godinot et al., 2018). Mammal Paleogene Reference
Scale (MP Levels) are used to propose direct correlation with reference
localities from Europe including MP7 (Dormaal, earliest Ypresian), MP8
+ 9 (Avenay, Mid-Ypresian) and MP10 (Grauves, late Ypresian;
Schmidt-Kittler et al., 1987; BiochroM'97, 1997).

From the base to the top, the sedimentary formations are (Fig. 1C):

(1) Ilerdian Fm.: This formation consists of limestones-prone suc-
cession with mostly alveolina foraminifera corresponding to an
inner shelf marine environment (Alveolina Limestone: e3bC on
Fig. 1). The limestone succession is capped by blue marls (e3bM
on Fig. 1) and oyster-rich sandstones related to a brackish envi-
ronment and marking a regressive phase (Genna, 1989), in which
Noiret et al. (2016) highlighted the C24rH8 (ETM2/H1) on the
basis of chemostratigraphy.

(2) Ventenac Fm.: This formation corresponds to lacustrine-
palustrine carbonates, Ypresian in age. At the base of the for-
mation, the Fournes fossil locality was first considered close to
MP7 (Marandat, 1991), and then to the MP7-MP8 + 9 interval
(Marandat et al., 2012). It was attributed to nannofossil zone
NP11, and positioned just after the C24rH8 (ETM2/H1).

(3) Assignan Fm.: Also known as the “Assignan Molasse”, this for-
mation is composed of sandstone-dominated fluvial channels and
silty-dominated floodplain deposits. The Sainte-Eulalie fossil lo-
cality is within the upper part of this formation, closely related to
MP8 + 9 (Danilo et al., 2013; Godinot et al., 2018) and thus mid-
Ypresian in age.

(4) Agel Fm.: This formation corresponds to palustrine-lacustrine carbonates. It is of upper Ypresian age, as evidenced by the Azillanet fossil locality close to the MP10 (Marandat, 1989), and the positive long-term trend in EECO δ¹³Corg recognized in these deposits in Noiret et al. (2016).

(5) Aigne Fm.: This formation is composed of sandstone-dominated fluvial channels and silty-dominated floodplain deposits. The mammal faunas from the fossil locality La Livinière 2, at the base of this formation is considered latest Ypresian in age or near the Ypresian-Lutetian transition (MP10–11; Comte et al., 2012; Godinot et al., 2018; Remy et al., 2019; Luccisano et al., 2020; Solé et al., 2020).

This study focuses on a stratigraphic framework starting at the upper part of the Assignan Fm. including the entire Agel Fm. and ending at the basal part of the Aigne Fm. (Fig. 1C) thus supposed to represent the youngest part of the Ypresian. The topography of the field corresponds to vineyards, hillsides, and *garrigue* landscapes. The marl-silt intervals are either located in ploughed vineyards or are heavily vegetated. The harder carbonates and sandstones outcrop in mounds across fields and roadsides. The geographical characteristics of the study area have thus a significant impact on both fieldwork and mapping studies. The selection of seven study sections was made with consideration for the constraints outlined (Fig. 2 and supplementary Fig. S1).

**3. Methods and material**

The study combines detailed sedimentological analysis, field map-
ping and chemo- and magneto-stratigraphic analysis. Biostratigraphy
based on mammal fossil (see 2.2) only enabled us to roughly identify
part of the Ypresian. This integrated, multi-disciplinary methodology
makes it possible to refine the age of the studied deposits.

Seven sedimentological sections (named sections 1 to 7, Fig. 2) were
logged. The number of sedimentary sections is defined by the constraints
of the field, and by the possibility of having fairly continuous sedi-
mentological measurements sections for chronostratigraphic analysis.
The aim is to build up the detailed architecture of the Minervois area, to
achieve a sequence stratigraphic framework, and to gain an under-
standing of the spatiotemporal variations of deposition within the basin.
This also ensures high, robust accuracy when generating correlations.
The sedimentological analysis is based on the lithological facies at
macroscopic and microscopic (petrography analysis, 40 thin sections)
scales and on the architecture of the deposits. This analysis includes the
study of texture, bedforms, bed surfaces, pedogenetic alterations, grain
size, grain type (composition/shape), and sedimentary bodies and bar-
forms. The outcrops were mapped on the field and using aerial mapping
techniques (Fig. 2), and were combined with stratigraphic staking
pattern analysis for an optimal correlation framework.

Carbon isotope (δ¹³Corg) analyses were conducted on dispersed organic matter (OM) of 151 samples obtained using a drill bit at a depth of ~10 cm to avoid potential influences from recent weathering processes. Samples for these chemostratigraphic analysis were taken from Sections 1–2 and 6, as these are almost continuous sedimentary sections with biochronostratigraphic constraints at various points (base, middle and top; MP: see 2.2. Stratigraphic setting and Fig. 2). In addition, these sections are located at the western and eastern ends of the study area,

<figure><img src="image_6.png" /><figcaption>**Fig. 2.** Mapping and location of sedimentological cross-sections (Sections 1 to 6, see Figs. 9 and 10 for detailed sedimentological sections) of the studied Ypresian strata in the northern part of the Minervois Basin on the Historical 1950's aerial images (IGN, *Remonter le temps* dataset), highlighting the correlation capacity between sedimentological log survey areas.</figcaption></figure>
<table><caption>**Table 1**
Table of facies of carbonates and detrital continental deposits.</caption><caption>CONTINENTAL CARBONATE FACIES</caption><thead><tr><th>Facies</th><th>Lithology</th><th>Primary structures</th><th>Early modifications</th><th>Interpretation - Depositional processes and environments</th></tr></thead><tbody><tr><td>C1</td><td>Beige, yellow, orange, purple or green marls (Figs. 3C, 8E)</td><td>C1a: massive</td><td>C1b: Mottling - Pedogenesis</td><td>Suspension - Alternation of phreatic and vadose conditions with early-stage mottling pedogenesis - Wetland, palustrine (Freytet, 1984)</td></tr><tr><td>C2</td><td>C2a: Mudstone with or without organic debris (gastropods, ostracods or lamellibranchs, charophytes - Fig. 3G)</td><td>-</td><td>-</td><td>Inorganic physicochemical and/or organic precipitation of carbonate - Low-energy lacustrine environment (Roemers-Oliveira et al., 2024)</td></tr><tr><td>C3</td><td>Mudstone with or without organic debris</td><td>-</td><td>&lt;cm cavities empty or crystallised with mosaic sparry calcite or coated with iron oxide corresponding to rootlets or roots marks - Pedogenesis</td><td>Inorganic physicochemical and/or organic precipitation of carbonate - Shallow lacustrine to palustrine environment (Alonso-Zarza, 2003; Roemers-Oliveira et al., 2024)</td></tr><tr><td>C4</td><td>Wackestone to packstone - organic debris (gastropods, ostracods or lamellibranchs, charophytes) and/or intraclasts (Figs. 3E-F, 8E)</td><td>-</td><td>&lt;cm cavities empty or crystallised with mosaic sparry calcite or coated with iron oxide corresponding to rootlets or roots marks - Pedogenesis</td><td>Inorganic physicochemical and organic precipitation of carbonate - Low to moderate energy - Alternating phreatic and vadose conditions - Periodically flooded shallow lake margin to palustrine environment (Freytet et al., 1982; Roemers-Oliveira et al., 2024)</td></tr><tr><td>C5</td><td>Wackestone - organic debris (gastropods, ostracods or lamellibranchs, charophytes - Figs. 3H, 8A)</td><td>-</td><td>Cm vertical roots to rhizome marks and/or irregular microscopic desiccation cracks (coated with iron oxide) - Pedogenesis</td><td>Inorganic physicochemical and organic precipitation of carbonate - Root actions and alternating conditions of emersion and flooding in a vadose palustrine environment (Freytet et al., 1982)</td></tr><tr><td>C6</td><td>Composite wackestone to packstone including sand-size grains quartz and organic debris (gastropods, ostracods or lamellibranchs, charophytes - Fig. 8D)</td><td>-</td><td>Mottling - Pedogenesis</td><td>Inorganic physicochemical and organic precipitation of carbonate - Low to moderate energy - Very low detrital input and early-stage mottling pedogenesis - Alternating phreatic and vadose conditions - Periodically flooded lake margin environment (Freytet et al., 1982; Roemers-Oliveira et al., 2024)</td></tr><tr><td>C7</td><td>Nodular-brecciated mudstone to wackestone - Irregular bed surfaces - Angular to rounded cm to dm monogenic intraclasts - With or without organic debris (gastropods, ostracods or lamellibranchs, charophytes - Fig. 3D)</td><td>-</td><td>Desiccation cracks and early in situ brecciation - Emersion processes</td><td>Inorganic physicochemical and organic precipitation of carbonate - In situ formation of breccia by alternating wet and dry cycles driven by episodic fluctuations of the water table - Palustrine environment (Freytet, 1984; Marty and Meyer, 2006; Alonso-Zarza and Wright, 2010)</td></tr><tr><td>C8</td><td>Pseudomicrokarstic wackestone - Organic debris (gastropods, ostracods or lamellibranchs, charophytes - Fig. 3I)</td><td>-</td><td>Cm to dm root cavities/marks filled with granular texture including &lt;cm intraclasts and sometimes organic debris (gastropods, ostracods or lamellibranchs, charophytes) - Pedogenesis</td><td>Inorganic physicochemical and organic precipitation of carbonate - Cavities from root action and desiccation - Infill comprising granular texture from grainification processes occurring during alternating wet and dry cycles driven by episodic fluctuations of the water table - Palustrine environment (Freytet et al., 1982; Freytet, 1984; Alonso-Zarza and Wright, 2010; Roemers-Oliveira et al., 2024)</td></tr></tbody></table>

<table><caption>CONTINENTAL DETRITAL FACIES</caption><thead><tr><th>Facies</th><th>Lithology</th><th>Primary structures</th><th>Early modifications</th><th>Interpretation - Depositional processes and environments</th></tr></thead><tbody><tr><td>S1</td><td>Argillites - S1a: Green, grey, brown or black colour - S1b: Red to orange, or beige colour. Sporadic mottling (Fig. 3A)</td><td>Massive or faint horizontal lamination</td><td>S1b: Sporadic mottling - pedogenesis</td><td>Suspension - S1a: in a reducing water level - S1b: associated with pedogenesis over oxidizing conditions - Floodplain environment (Miall, 1996)</td></tr><tr><td>S2</td><td>Beige, yellow, orange, purple silts.</td><td>Massive or faint horizontal lamination</td><td>Sporadic mottling - pedogenesis</td><td>Suspension or lower-flow regime current, followed by pedogenesis processes - Floodplain environment (Miall, 1996)</td></tr><tr><td>S3</td><td>Heterogranular to well-sorted, very fine to medium-grained sandstone - Occasionally organic debris (shells, plants, and organic matter (Figs. 4A, 8A-C))</td><td>S3a: cm to dm scale oblique laminations - S3b: Trough-cross laminations - S3c: Climbing laminations</td><td>Sometimes sporadic mottling - pedogenesis</td><td>Unidirectional current with traction to saltation processes - Lower-flow regime - S3a: 2D current ripples to megaripples - S3b: 3D current ripples to megaripples - S3c: Climbing ripples to megaripples, high-depositional rate - Top of channel bars to overbank environments sometimes affected by pedogenesis (Miall, 1978)</td></tr><tr><td>S4</td><td>Well-sorted, very fine to medium-grained sandstone (Figs. 3B, 4, 5, 6A-B, 8B-D)</td><td>S4a: Humpback, sigmoidal and low-angle cross lamination - S4b: Flat lamination - S4c: Aggrading flat- to low-angle convex-up lamination (0.4 &lt; &lambda; &lt; 3 m) - S4d: Backflow low-angle cross-</td><td>-</td><td>Unidirectional current with traction to saltation processes - Upper-flow regime - S4a: Humpback megaripples to dunes, transition between lower- and upper-flow regime - S4b: Parting lineation - S4c: Stable antidunes, high-</td></tr></tbody></table>

(continued on next page)
<table><caption>**Table 1 (continued)**</caption><thead><tr><th colspan="5">CONTINENTAL DETRITAL FACIES</th></tr><tr><th>Facies</th><th>Lithology</th><th>Primary structures</th><th>Early modifications</th><th>Interpretation - Depositional processes and environments</th></tr></thead><tbody><tr><td></td><td></td><td>lamination - S4e: Concave-up lamination in asymmetrical scours</td><td></td><td>depositional rate - S4d: Stable to unstable antidunes, low-depositional rate - S4e: Chute-and-pools to cyclic steps, high-depositional rate - Poorly developed barforms of ephemeral braided channel environment (Miall, 1978; Fielding, 2006; Cartigny et al., 2014; Tan and Plink-Björklund, 2024)</td></tr><tr><td>S5</td><td>Heterogranular polygenic conglomerate (Figs. 8C-D)</td><td>Structureless or large-scale oblique cross-bedded or large-scale trough cross-bedded</td><td>-</td><td>Unidirectional current with traction processes - Lower-flow regime, 2D linear crested bedforms or 3D sinuous to linguoid crested bedforms - Basal lag of ephemeral braided channel environment (Miall, 1978)</td></tr><tr><td>S6</td><td>Well-sorted, very fine to medium-grained sandstone (Figs. 4F, 6)</td><td>Not interpretable but still visible lamination</td><td>S6a: Convolute to overturn bedding - S6b: Dish structures - Soft-sediment deformation</td><td>Water escape processes. High pore-fluid pressure, due to rapid and high-depositional rate - Poorly developed barforms of ephemeral braided channel environment (Plink-Björklund, 2015b)</td></tr></tbody></table>

providing additional constraints which enable to discuss lateral variations in deposition (e.g. sedimentation and accommodation). The location of these samples is reported on the corresponding sedimentary sections (Fig. 2, sections 1, 2 and 6; respectively 17, 72 and 62 samples). The isolation of sedimentary OM was done at the University of Namur, according to the methodology outlined in Yans et al. (2010) and refined by Storme et al. (2012). These organic carbon isotope analyses were carried out using an elemental analyser (Carlo-Erba 1110) connected online at the University of Erlangen to a ThermoFinnigan Delta V Plus mass spectrometer. The accuracy and reproducibility of the analyses were verified by repeated measurements of the international standards USGS40 and USGS41, with a reproducibility of ±0.1 ‰ (1σ). The Bernard calcimeter was used to determine the CaCO₃ (%) content of each sample.

A total of 102 samples were collected for paleomagnetic measurements. Sampling was conducted exclusively on very fine to coarse sandstone and limestone lithologies on Sections 1 and 2 only. These sections are complementary and constitute a reference section on which the biochronostratigraphic constraints have already been defined at various points (MP – base, middle and top; see 2.2. Stratigraphic setting and Fig. 2) and the chemostratigraphic analyses have been performed. Consequently, the finer sedimentary levels, in terms of granulometry, are devoid of data. Remanent magnetization was measured using a JR6 Magnetometer (AGICO) in a magnetically shielded room. Samples were subjected to thermal or alternating field demagnetization in steps of 5 to 10 mT (25 to 50 °C). The maximum field was 40 or 70 mT (600 °C). Principal component analysis (Kirschvink, 1980) was used to determine magnetic components, while Fisher analysis was used to determine directions.

# 4. Results

## 4.1. Sedimentological analysis: Facies associations and depositional environments

Facies are listed in Table 1 for continental carbonates and detrital rocks and illustrated in Figs. 3–6. Fossil localities have delivered continental vertebrate faunas such as reptiles (chelonians and crocodiles), mammals (metatherians, primates, perissodactyls, artiodactyls, rodents, chiropterans, primitives “insectivores”, etc.), and fishes (lepisosteiforms) (Hartenberger et al., 1968; Danilo et al., 2013; Noiret et al., 2016). Subaquatic invertebrates, pulmonated gastropod molluscs (limnaeids and planorbids; Fig. 3E), were also commonly found in the studied limestone deposits as well as algae illustrated by charophytes (gyrogonites and thalli; Fig. 3G). The vertical arrangement of the facies

forms five facies associations (FA1 to FA5; Figs. 7–8) related to ephemeral fluvial and palustrine to shallow-lacustrine environments.

### 4.1.1. FA1, Floodplain

#### 4.1.1.1. Description.
FA1 (Fig. 7) consists of argilaceous to silt-prone deposits, such as argillites and mottled siltstones (S1b, S2). Some centimetres to pluricentimetre-thick beds of very fine to fine sandstones (S3) of variable lateral extent but with limited continuity are also present in this association. These sandstones occasionally exhibit root traces and sedimentary bedforms indicative of both lower- (ripple marks, S3a, S3b) and upper-flow regime (parting lineation, S4b). In some instances, poorly structured centimetre-thick beds of carbonate mudstones with rootlets or roots marks (C3) are also present.

#### 4.1.1.2. Interpretation.
The argilaceous and mottled character, and the presence of root marks suggest a subaqueous, low-energy settling environment, subsequently colonized by vegetation and thus subjected to pedogenesis. This environment is interpreted as a continental floodplain (Fig. 7; Miall, 1996). The sandstone facies with variable depositional energies indicates sand influxes into the floodplain and is interpreted as fluvial overbank and/or crevasse-splay deposits. The parting lineation facies suggests waxing sheet-flood deposits occurring during crevasse spreading on the floodplain. The carbonate beds with rootlets and roots indicate either (1) carbonate precipitation in an ephemeral shallow water body environment (pond) with limited lateral extent (hundreds of metres) subsequently subjected to pedogenesis or (2) carbonate precipitation through an evaporation process in the vadose zone and calcrete formation (Alonso-Zarza and Wright, 2010).

#### 4.1.2. FA2, Ephemeral narrow braided channel

##### 4.1.2.1. Description.
FA2 (Fig. 7) is present in narrow several-metres wide sandstone bodies which are associated with FA1 floodplain deposits (Fig. 8A). FA2 comprises pluricentimetre to metre-scale fining-upward beds showing irregular and slightly erosive basal surfaces (Fig. 8A). The association often comprises a fining upward succession <3 m thick. At the base, structureless conglomerates (S5) to cut-and-fill structures in coarse-sandstone can be stacked and amalgamated over less than a metre thick. These coarse deposits are followed by medium-grained sandstones showing possibly parting lineation (S4b), or are directly superimposed by linear crested megaripples (S3a) or 3D sinuous to linguoid crested megaripples to ripples (S3b, Fig. 8A), and followed by 2D current ripples in fine to very fine-grained sandstones. Megaripples to ripples bedforms may be aggrading over a few metres in
<figure><img src="image_7.png" /><figcaption>**Fig. 3.** Illustrations of facies (see Table 1) A) Outcrop view: faint horizontal laminated brown and beige argillites (S1a) – B) Pluricentimetric-scale reworked oncolites in fine-grained sandstone (S4c), hammer handle for scale – C) Outcrop view: yellow to purple marls with mottling (C1b) – D) Nodular-brecciated limestone (C7)- E) Gastropod inner mold (Planorbidae) in wackestone (C4) – F) Thin section: wackestone showing debris of lamellibranchs and ostracodes (C4) – G) Thin section of mudstone with charophytes (arrows, C2b)– H) Outcrop view: centimetric vertical roots marks in a wackestone (C5)- I) Macroscopic sample: pseudomicrokarstic limestones (C8), see the root cavity infilled by granular texture formed from grainification processes.</figcaption></figure>
<figure><img src="image_8.png" /><figcaption>**Fig. 4.** Photographs illustrating lower- and upper-flow regime bedforms in sandstones of Section 1, associated with FA3 (see Part. 4.1.3) and the base of T1 (see Part. 4.2). A) Facies of parting lineation (upper-flow regime, S4b) overlaid by megarides (S3b) - B) Facies of humpback megaride (S4a) at the base of FA3 - C) Facies of stable antidune with high-depositional rate (S4c), showing aggrading flat- to low-angle convex-up lamination (wavelength = λ = 1,5 m), supercritical flow - D) Facies of stable to unstable antidune associated with high-depositional rate (S4c to S4d), supercritical flow - E) Facies of stable antidune associated with high-depositional rate (S4c), showing aggrading flat- to low-angle convex-up lamination (λ < 50 cm), supercritical flow - F) Facies of stable antidune associated with high-depositional rate (S4c, λ < 30 cm) showing dish structures (S6b, formed by water-escape processes) and overlain by parting lineation (S4b).</figcaption></figure>
<figure><img src="image_9.png" /><figcaption>(caption on next column)</figcaption></figure>

**Fig. 5.** Photographs illustrating critical to supercritical flow bedforms in fine-grained sandstones of Section 1, associated with FA3 (see Part. 4.1.3) and the base of T1 (see Part. 4.2). A) From base to top: facies of stable antidune associated with high-depositional rate (S4c, λ < 50 cm) changing to unstable antidune associated with lower-depositional rate (backflow low-angle cross-lamination (S4d) then back to stable antidune (S4c) - B) Facies of unstable antidune (backflow low-angle cross-lamination; S4d) associated with low-depositional rate - C) Concave-up lamination in asymmetrical scours corresponding to facies of chute-and-pools to cyclic steps (S4e) associated with high-depositional rate.

thickness. Occasionally mottled siltstone (S2) overlies deposits on the top of the association. All sedimentary bedforms indicate a current direction to the north. The fossil locality named La Livinière 2 (Section 2, Fig. 9; Hartenberger et al., 1968) including terrestrial vertebrate remains is located within FA2.

#### 4.1.2.2. Interpretation.
The basal erosion and fining-up succession are characteristics of the formation of a channel (Fig. 7; Miall, 2014). The succession with erosion, amalgamation and underlying sedimentary bedforms indicating decreasing energy and decreasing grain size is typical of stacked mobile bar deposits infilling sandy braided channels (Miall, 1978). In such systems, upper-plane regime bedforms indicate also a consistent high-hydrodynamic flow velocity of short duration, and can be linked to flash-flood type episodes (Miall, 1982; Plink-Björklund, 2015). This type of sedimentation evokes ephemeral braided streams that develop from seasonal sheetfloods in semi-arid to arid fluvial plain (Miall, 1978; Olsen, 1989; Fillmore et al., 2010; Priddy and Clarke, 2020). Scarce mottled siltstones indicate an early paleosol occurring during the receding flood phase and then the emergence of channel bars (Miall, 1996).

#### 4.1.3. FA3, Ephemeral multistorey braided channel plain

##### 4.1.3.1. Description.
FA3 (Fig. 7) extends over an amalgamated strata mapped across a minimum of fifteen kilometres wide and up to 10 m thick. The association starts with a slightly erosive irregular basal surface overlain by a conglomerate to coarse to medium-grained sandstone lag (S5), structureless over a few tens of centimetres (Fig. 8C-D). These coarse deposits are followed by fine- to medium-grained sandstone over several metres thick showing several types of lower- and upper-flow regime bedforms, including a very high percentage (>60 %) of bedforms relating to a supercritical-flow regime (Froude Number > 1). The bedforms correspond to climbing ripples to megaripples (S3c, Fig. 6C), humpback megaripples to dunes (S4a, Fig. 4B), parting lineation (S4b, Fig. 4A, F), aggradational stable antidunes with high depositional rate (S4c, Figs. 4C-F, 5A, 8C), stable to unstable antidunes with lower depositional rate (S4d; Figs. 4D, 5A-B, 6A-B, 8C-D) and chute-and-pools to cyclic-steps (S4e, Figs. 5C, 6A-B). These bedforms may follow one another vertically in the order described above, or alternate in an unorganized way. These facies sometimes show soft-sediment deformations and water-escape structures such as convolute to overturn bedding (S6a; Fig. 6) and dish structures (S6b, Fig. 4F). Such structures were already described by Genna (1990) in the nearby site of Felines Minervois. On the top of FA3, centimetre to decimetre either linear crested megaripples (S3a) or 3D sinuous to linguoid crested megaripples to ripples (S3b, Figs. 4A, 8B) in fine-grained sandstones are sometimes present. In this case, megaripples to ripples bedforms may be aggrading and can reach up to a few metres in thickness. Occasionally mottled siltstone (S2) overlies deposits on the top of the association. All sedimentary bedforms indicate a current direction to the north. Laterally, the amalgamated strata are disorganized, lateral variation of supercritical bedforms are frequent, possibly displaying discrete macroform or barform architectures. In place, sandstone bodies are sometimes organized into several superimposed inclined beds (ranging from 10 to 20° relative to the bedding, Fig. 8C). Lenticular argillite levels (beige or
<figure><img src="image_10.png" /><figcaption>**Fig. 6.** Photographs illustrating critical- to supercritical- flow and soft-deformation structures in sandstones of Section 1, associated with FA3 (see Part. 4.1.3) and the base of T1 (see Part. 4.2). A) Outcrop showing upper-flow bedforms (S4c to S4d) reflecting changes in flow and depositional rate, associated in place with soft-sediment deformation (S6a)- B) Facies of unstable antidune (S4d) to chute-and-pools (S4e) showing convolute to overturn bedding on top (S6a) - C) Facies of climbing ripples (S3c) showing convolute to overturn bedding on top (S6a).</figcaption></figure>

black colour, S1, Fig. 3A) less than several decimetres thick may be intercalated between these inclined bodies directly on top of the upper-flow regime bedforms. In some places, flat or dome-shaped stromatolite or oncolites (ranging from centimetre to metric sizes) are present beneath these argillite levels, lying directly on top of the upper-flow regime bedforms. Oncolites may also be present in upper-flow-regime bedforms (Fig. 3B). Plant debris may be associated with black argillite levels. The fossil locality named Sainte-Eulalie (Section 2, Fig. 9; Danilo et al., 2013; Noiret et al., 2016) including terrestrial vertebrate remains is located within FA3.

### 4.1.3.2. Interpretation.
The succession consisting of a basal erosion and the overlying lag, followed by highly aggradational deposition rate of fine-grained sandstone showing an abundance of supercritical bedforms, indicates basal channel erosion and infill channel by ephemeral flash-flood deposits occurring mainly during waxing and peak flood stage (Miall, 1982; Plink-Björklund, 2015). Such deposits reflect high-magnitude floods in seasonal river (Fielding, 2011) that may be associated with monsoon-type precipitation (Plink-Bjorklund, 2015b). In these types of rivers, barforms are often poorly developed and deposits are poorly organized laterally as observed in FA3 succession. Inclined bodies could however indicate either accretion or compensation of such

barforms (Fielding, 2011; Lowe and Arnott, 2016; Alpheus and Hajek, 2024). The decrease in flow velocity evidenced by the change from upper- to lower-flow regime, the deposition recording the aggradation of upper-flow regime facies and high-sediment flux, and both variability in the strata and inclined accretional body architecture, reflect the formation of both very rapid deposition due to flow expansion and possible mobile sand bars from an extended ephemeral sandy-braided system (Fig. 7; Miall, 1978; Lowe and Arnott, 2016). In the case of the wide extended amalgamated strata composed of FA3, we hypothesize the development of a multistorey braided channel plain in semi-arid to arid fluvial plain (Olsen, 1989; Fielding, 2011; Lowe and Arnott, 2016), which could be of a fluvial fan type (Plink-Björklund, 2015). Upper-flow regime bedforms reflecting highly aggradational depositional rate indicate that the flow is linked to brief, ephemeral, intense flash flood (Miall, 1982; Plink-Björklund, 2015) allowing high pore-fluid pressure during and after the deposition. Although the resulting structures (S6a; Fig. 6 and S6b, Fig. 4F) were previously associated with variations in the intensity of early Pyrenean deformation in the study area (Genna, 1990), the depositional process of sand evoked latter is sufficient to form synsedimentary soft-sediment and water-escape deformations (Lowe, 1975; Plink-Björklund, 2015). The oncolites and stromatolites indicate a change in conditions and a rapid cessation of flooding in favour of
<figure><img src="image_11.png" /><figcaption>**Fig. 7.** Profile showing fluvial and palustrine to shallow-lacustrine depositional environments (not to scale), and corresponding lithological sections of the facies associations defined in Part. 4.1 (modified from Freytet, 1984 and Alonso-Zarza, 2003).</figcaption></figure>

carbonate production in a remaining shallow slice of water under semi-arid to arid condition. The presence of oncolites in upper-flow regime facies indicate reworking during a subsequent high-magnitude flash-flood episode. The intercalated lenticular argillite levels also reflect rapid waning of flood and decantation processes. The fine intercalations reflect periods of flood standstill. They show that several episodes of ephemeral and very rapid flooding follow one another, reminiscent of seasonal monsoon-type rainfalls (Plink-Bjorklund, 2015, 2015b).

### 4.1.4. FA4, palustrine deposits: Wetland (FA4A) and palustrine shallow lake margin (FA4B)

#### 4.1.4.1. Description.
Wetland (Figs. 7, 8A): FA4A comprises beds of mudstone or wackestone ranging from centimetres to plurideimetres (or even metre-scale) in thickness, and exhibiting sometimes lateral facies variations. These previous facies show rootlet or root or rhizome marks (either empty or crystallised with mosaic sparry calcite or coated with iron oxides – C3, C5, Figs. 3H, 8A) and/or desiccation cracks. Nodular-brecciated limestones (C7; Fig. 3D) and pseudomicrokarstic limestones (sensu Freytet et al., 1982; C8, Fig. 3I) are also predominant facies.

Palustrine lake margin (Figs. 7, 8A, D): FA4B is almost identical to the previous one (FA4A), but the facies show less mature root marks (no rhyzomes) and contain a much larger quantity of debris such as fragments or whole tests of gastropods, ostracods, lamellibranchs and charophytes (C2-C3, C5-C6). Such fauna and flora are preferably preserved along the lake margin (Freytet, 1984).

In the two sub-associations, all the facies are sometimes intercalated with dark laminated wackestones rich in shell debris (gastropods; C4, Fig. 3D), and/or grey to dark lignitic marls to argillites (S1a, C1, Figs. 3A, 8D). The marl levels are however less frequent in FA4B. The fossil locality named Azillanet, which corresponds to five fossiliferous levels with terrestrial vertebrate remains (Section 7, Fig. 9; Marandat, 1991), is located within these previous facies.

#### 4.1.4.2. Interpretation.
These two sub-associations correspond to a palustrine continental domain (Fig. 7), located in the vadose zone between the minimum and maximum groundwater table levels of either an existing lacustrine domain with variable depth and highly variable extensions (from a few tens of metres to kilometres), or a wetland setting (a shallow water body surrounded by vegetation). This type of

environment is characterized by microtopographic variations in the soil ranging from centimetres to decimetres, allowing subdivision into areas that are more or less flooded, more or less deep, and therefore more or less subject to emersion, with vegetation and pedogenesis varying according to seasonal or longer climatic cycles.

The wetland environment (FA4A, Fig. 7) is defined rather by the presence of weakly to strongly pedogenized carbonates (development of rootlets, roots and rhizomes) and represents a marsh-swamp environment (Plaziat, 1984). The formation of nodular-brecciated and pseudomicrokarstic limestone results from successive phases of wetting and drying of the carbonate mud and impacted by root systems (Alonso-Zarza and Wright, 2010). The presence of grey argillites indicates an anoxic depositional environment exposed to the deposition of terrigenous and organic fraction, while marls represent a relatively oxygenated flooded environment. An anoxic zone is induced by water stagnation associated with the presence of large quantities of plant debris on the water surface (Plaziat, 1984) in shallow marshy areas interpreted as ponds. When these water bodies are more oxygenated, gastropod fauna can thrive. In these marshy environments, vegetation susceptible to eutrophication thrives until potential desiccation occurs.

Palustrine shallow lake margin (FA4B, Fig. 7) depositional setting is directly adjacent to the lacustrine domain (see FA5 below). FA4B, displays less mature variable pedogenesis and much larger quantity of fauna and flora debris. It represents an area that is periodically flooded by the fluctuating groundwater table level of an interfluve or a permanent lake (Freytet, 1984; Alonso-Zarza and Wright, 2010). At certain times, the water body may remain stagnant, allowing the development of very shallow anoxic environments (as in the wetland domain), favouring the formation of deposits rich in organic matter (lignitic marls to argillites).

These two sub-environments, whose deposits record wide pseudomicrokarst development and a lack of profundal lake deposits are commonly associated with a semi-arid climate with strong seasonality, allowing carbonate precipitation in palustrine setting or shallow lakes, water supply, periods of intense desiccation, and vegetation activity to act as an important modifier of previous sediments (Sanz et al., 1995; Gierlowski-Kordesch, 1998; Alonso-Zarza, 2003; Alonso-Zarza and Wright, 2010).
<figure><img src="image_12.png" /><figcaption>**Fig. 8.** Illustration of facies associations from outcrop views: A) Outcrop showing sandstone deposits of a slightly erosive ephemeral narrow braided channel (FA2) on palustrine wetland carbonate deposits with vertical root marks (FA4A), Section 6 - B) 3D current ripples and megaripples (S3b), Section 7 - C) Outcrop showing sandstone bodies that form the ephemeral multistorey braided channel plain (FA3); the basal erosion surface here corresponds to the SU1 sequence boundary (see Part 4.2), note a basal lag (S5) overlaid by inclined bodies composed of sandstones with antidune bedforms; the yellow dotted lines delimiting the bodies correspond to bar accretion or compensation surfaces, Section 7 - D) Palustrine lake-margin deposits (FA4B) eroded by ephemeral braided channel sandstone body (FA3) showing both lower and upper-flow regime like antidune bedforms; the basal erosion surface of the channel here corresponds to the SU3 sequence boundary (see Part 4.2), Section 6 (rock hammer for scale) - E) Beige marls overlaid by carbonates palustrine beds (FA4B), illustrating a palustrine shallow-lacustrine margin setting, including 3 fossiliferous levels of the Azillanet fossil locality, Section 7 - F) Thick and massive beds of palustrine to shallow-lacustrine deposits (FA4 to FA5), Section 6.</figcaption></figure>
<figure><img src="image_13.png" /><figcaption>**Fig. 9.** Sedimentological logs (sections 1 to 7) and correlation framework along a 10 km long, W-E profile across the north Minervois Basin, interpreted as depositional environments. The succession is subdivided into 3 stratigraphical T-R sequences (T1, T2, T3-R3), bounded by subaerial unconformity surfaces (SU, in red). Sampling for carbon isotope and paleomagnetostratigraphy was carried out on sections 1, 2 and 6 (green numbers).</figcaption></figure>
### 4.1.5. FA5, Lacustrine deposits: Shallow lacustrine domain (interfluve lake or permanent shallow lake)

4.1.5.1. **Description.** FA5 (Figs. 7, 8F) includes mudstone (C2, C3), wackestone and packstone (C4, Fig. 3E-G), with or without rootlets, sometimes containing organic debris such as freshwater gastropod shells (shells, lymnaeids or planorbids whole tests or fragments) or debris of unidentified lamellibranchs and/or ostracods, and charophyte fragments (mainly gyrogonites and thalli). These facies successions form decimetre to metre-scale beds deposited in a subaqueous domain.

4.1.5.2. Interpretation. FA5, notable for the lack of mottling or root marks, is interpreted as forming in a shallow lacustrine domain (Fig. 7). Relative depth variations of the water body are observed due to the presence of freshwater gastropods or charophytes or the variability of the carbonate textures (Fig. 7; Gierlowski-Kordesch, 2010). The presence of rootlets indicates a typical subaqueous flora in these shallow environments. A lake depth of a few metres is estimated (<< 10 m), as the presence of rootlets in the limestone indicates deposition above the thermocline, and no deep lake-type deposits such as varves are observed.

### 4.2. Stratigraphic architecture and sedimentary systems evolution

The stratigraphic framework is based on the distribution and correlation of vertical and lateral facies variations interpreted as depositional environments defined in facies associations on sections 1 to 7 (Fig. 9). The stratigraphic stacking patterns using a stratigraphic sequence (sensu Catuneanu and Zecchin, 2013) were analyzed on the basis of successive continental Trangression-Regression (T-R) sequences, bounded by two subaerial unconformity surfaces (SU, sensu Catuneanu et al., 2009), and corresponding to medium- to high-frequency cycles. The sequences reflect accommodation changes and relative variations in base level corresponding to the groundwater table level in this particular case study.

In the succession studied, the T-R continental sequences are often incomplete (Fig. 9). The succession is composed of two successive asymmetrical continental T sequences recording two single transgressive units, followed by one T-R sequence. These three sequences record three phases of continental base level rise and drop (Fig. 9). The three sequences are bounded at the base by the basal erosion surface of the ephemeral multistorey braided channel plain (FA3), correlated over the entire study area (> 15 km), which corresponds to SU1, SU2 and SU3. Over the SU, the bases of the T sequences are then composed of sandstone-dominated deposits that develop and fill the ephemeral multistorey braided channel plain (FA3).

For T1, these deposits are overlain by localised ponds of palustrine deposits (FA4A) and narrow fluvial channels (FA2) to the west. While towards the east, these deposits evolve laterally into fluvial setting composed of floodplain deposits (FA1) and narrow braided fluvial channels (FA2). This evolution indicates an overall rise in relative base level throughout this sequence, reflecting an increase in accommodation.

For T2 sequence, the basal FA3 is overlain by stable stacked palustrine environments (FA4A) where fluvial inputs (FA2) are still sporadically present on the western part. To the east, the T2 sequence is composed of fluvial (FA2) to floodplain (FA1) deposits which grade vertically towards palustrine deposits, first wetland (FA4A) and then palustrine shallow lake margin deposits (FA4B). These vertical variations indicate an overall rise in relative base level throughout this sequence, reflecting an increase in accommodation. The vertical succession showing the development of shallow-lake margin (FA4B) environment in the eastern part also indicates greater accommodation in this area.

The T3 sequence, above FA3, is composed of wetland palustrine

deposits (FA4A) to the west and by extended shallow-lake margin to shallow-lacustrine deposits (FA4B) to the east. A thin R3 regressive sequence, corresponding to new palustrine deposits, covers the T3 deposits. The boundary between T3 and R3 has been positioned at the point where the deepest shallow-lake deposits were recorded, even if the depth does not exceed a few metres. This complete T3-R3 sequence then shows an increase and following decrease of accommodation.

The upper sequence boundaries of T1, T2 and T3-R3 are always also defined by the SU evidenced by the arrival of detrital material from sudden high-magnitude flash-flood (FA3). This indicates a sudden drop in relative base level at the end of each sequence. The studied sedimentary succession records a general trend towards increased accommodation and a rise in the relative base level during T1, T2 and T3. This is evidenced by the whole vertical evolution from a fluvial to a carbonate-dominated shallow-lacustrine systems, more pronounced in the eastern part of the studied area during T3 (MFS, Fig. 9). This general trend is cyclically interrupted by phases of sudden drops in the base level, evidenced by weak erosion (SU) of the carbonate deposits and the development of an ephemeral multistorey braided channel plain (FA3). The succession of deposits across the sequences with the development of palustrine and shallow lacustrine deposits, as well as ephemeral braided channels, suggests a semi-arid to sub-humid local climate. Potential causes of these patterns and controls on sedimentary record will be discussed further in detail with regard to the results developed in the chronostratigraphic framework (Part. 5.1, 5.2).

### 4.3. Paleomagnetostratigraphy

The studied section (Section 2, Fig. 10) records the presence of both normal and reverse magnetic polarities. Analyses conducted at relatively high temperatures (to 600 °C) suggest that the Natural Remanent Magnetization (NRM) is primary. The average declinations and inclinations were used to calculate the positions of the Virtual Geomagnetic Poles (VGP, Fig. 10 and Supplementary Tables S1 and S2).

The presence of grey areas indicates that the chron has not been sampled, or that the values obtained are not clear enough to identify the polarity of the chron.

Thus, the paleomagnetic study reveals at least five distinct magnetic polarity zones within this section.

### 4.4. Carbon isotopes

Carbon isotopic values on dispersed organic matter (δ¹³Corg) range from -27.4 to -23.5 ‰ on the Section 1; from -27.2 to -22.6 ‰ on the Section 2 and from -27.6 to -22.8 ‰ on the Section 6 (Fig. 10; Supplementary Tables S1, S2 and S3). These values are consistent with the expected δ¹³C ranges for organic material from the early Eocene in southern France (Yans et al., 2014; Noiret et al., 2016; Maufrangeas et al., 2020; Lihoreau et al., 2025). In the studied sections, sediments are only terrestrial, allowing us to consider that potential marine contribution of organics is absent. The isotope signature of plants was preserved in the terrestrial organic matter (OM) found in sediments. Measuring the carbon isotope in organic matter (OM) from sediments of continental paleoenvironments is thought to represent the carbon isotope composition of the vegetation (e.g. Hayes, 1983; Sinha and Stott, 1994). For this study, it is accepted that only C3 plants must be considered in the Eocene interval (Koch et al., 1992; Stott et al., 1996). OM from the studied sections were previously characterized by the pioneering chemostratigraphic work of Noiret et al. (2016). In this article, Rock-Eval analyses and palynofacies observations prove that the OM originates from a homogeneous type III terrestrial input. The Tmax values derived from the Rock-Eval method average at 437 °C, indicating that the organic matter is immature or slightly mature, suggesting minimal to no influence from strong burial diagenesis. Palynofacies analysis indicates that opaque phytoclasts predominate in all palynofacies slides, with minor proportions of translucent phytoclasts.
<figure><img src="image_14.png" /><figcaption>**Fig. 10.** A) Mammal faunas, paleomagnetostratigraphy (VGP latitude) and carbon isotope chemostratigraphy (δ¹³Corg curve) results for sections 1, 2 and 6, and correlations between them based on physical tracking and aerial mapping of the beds as already defined in Fig. 9. - B) Identification of hyperthermals by global correlation with the Ypresian time scale, standard marine carbon isotope records (from Westerhold et al., 2020), international magnetic polarities data and Mammals Paleogene Level. Continental T/R sequences are also positioned on Section 2.</figcaption></figure>
Phytoclasts of an opaque and translucent nature are sourced from terrestrial wood tissues. These data indicate that the degradation of OM as a consequence of potential diagenesis is negligible in the examined sections.

Carbon isotopic values reveal successive negative and positive trends along the studied sedimentary sections (Fig. 10). These trends, observed on the three studied sections, are correlated at certain points by physical tracking of the sedimentary beds directly in the field and/or by aerial mapping. Implications for stratigraphy and sedimentology will be discussed below.

# 5. Discussion

## 5.1. Identification of EECO and hyperthermal events with
*chroonostratigraphy analysis*

All the faunal, magnetostratigraphic, and isotopic data are compared with the CENOGRID chart (Westerhold et al., 2020) in order to i) refine the dating of the studied succession, ii) highlight the various recorded events and iii) correlate them with the Ypresian hyperthermals (Fig. 10). Indeed, considering a homogeneous input of terrestrial organic matter (type III) as suggested by palynofacies and Rock-Eval pyrolysis on some same samples, Noiret et al. (2016) already demonstrate that the isotopic curve of organic carbon from the continental-dominated Ypresian of the Minervois corresponds closely to the isotopic curve of standard marine carbonate carbon.

The lowermost part of the studied succession shows positive carbon isotope values (δ¹³Corg), rapidly followed by a short-term negative excursion, from 10.9 m to the top on Section 1 and from base to 27.1 m on Section 2. This latter encompasses the Sainte-Eulalie fossil site (Section 2, Fig. 10) attributed close to the MP8 + 9 mammalian reference level (Danilo et al., 2013).

The correlations highlight that the level with minimal δ¹³Corg values in the lowermost part (first 27.1 m) of Section 2 is correlated with the levels showing minimal δ¹³Corg values following the negative trend from -23.5 ‰ at 10.9 m to -23.8 ‰ at the top of Section 1. Associated magnetostratigraphic results show that these levels are comprised in the normal paleomagnetic period N1 (Fig. 10). Following Noiret et al. (2016), chron N1 is interpreted as chron C24n.1n. These data refine the position of the Sainte-Eulalie fossil locality at the start of the positive shift (recovery) of ETM3 (C24n.1nH1/K; Fig. 10) and dated between 52.844 Ma and 52.762 Ma (end of the recovery; Westerhold et al., 2020).

For post C24n.1nH1/K (ETM3) events, we consider sedimentation to be fairly continuous, as no significant hiatus, such as an angular unconformity or several metre-scale incisions of channels, is observed along the studied sections. We can thus interpret the magnetostratigraphic and isotopic results in a relative stratigraphic continuity.

In Section 2, the hyperthermal C24n.1nH1/K (ETM3) is followed by two less prominent negative excursions within chron C24n.1n, here correlated with negative excursions not named in CENOGRID (see dashed lines in Fig. 10; Westerhold et al., 2020). The chron C24n.1n is followed by a reverse paleomagnetic period R1 (41.2 m to 55.6 m), thus considered as the chron C23r. The related isotopic trend shows positive values between 41.2 m and 49.3 m, followed by a very short-term excursion also observed in the correlated deposits in Section 6. Given that this isotopic excursion occurs at the end of the reverse period of the chron C23r and follows positive values, we interpret it as the C23rH2/M transient hyperthermal (Fig. 10). Note that isotopic data showing negative excursions below the excursion of this C23rH2/M event are not in a reverse polarity and therefore cannot correspond to the C23rH1/L event. This implies that the latter event must be part of the succession where sampling was impossible on Section 2 and Section 6, lying just below the event interpreted as the C23rH2/M.

The following geomagnetic reversal to a normal paleomagnetic period N2 is interpreted as chron C23n.2n. The negative δ¹³Corg

excursion observed between 53.7 m to 74.6 m on Section 2 is correlated with the negative excursion on Section 6 between 49.1 m and 58.2 m. This negative excursion is observed before a period of significantly positive carbon-isotope values: we attribute this excursion to the C23n.2nH1/N transient hyperthermal. The C23n.2nH2/O event, located in a significant positive δ¹³C shift associated to chron C23n.2n, is consequently not recorded in Minervois sections. This absence could be explained by several phases of amalgamation and stacking of poorly developed sand barforms which compose the ephemeral multistorey braided channel strata (FA3, see 4.1) and can lead to sampling bias. In the same stratigraphic interval, the C-isotopes data do not clearly reveal the positive δ¹³C shift associated to chron C23n.2n, previously proposed by Noiret et al. (2016). This trend is scarcely identifiable on sections 2 and 6, and confirms the condensed level of sedimentation in the ephemeral multistorey braided channel deposits (FA3).

The short subsequent reverse period R2 can only be interpreted as chron C23n.1r. The record of such very short duration chron in the continental deposits (one sample) provides a reference point for future hyperthermal events such as C23n.1nH1/P or posterior. It is worth noting that capturing this chron is rare, even in marine records (e.g., Rodríguez-Pintó et al., 2013; Lauretano et al., 2016; Galeotti et al., 2019; Lihoreau et al., 2025). In the stratigraphic continuity, N3 normal period is interpreted as the chron C23n.1n. This period shows a negative trend culminating in a negative isotopic excursion, around 119.5 m in Section 2 and 103.4 m in Section 6, so just below the Azillanet fossil locality (Section 7). Because this locality is considered close to the MP10 reference level (Marandat, 1986, 1991) and that it displays a fauna similar to that of the Mas de Gimel and Le Lien (Lihoreau et al., 2025), we tentatively interpret this excursion as the C23n.1nH1/P event. In consequence, Azillanet fossil locality would be dated between 50.996 Ma and 50.767 Ma (older than the chron C22r). The boundary between the chron C23n.1n and the chron C22r is not identifiable in the studied sections, making the latter hypothesis of C23n.1nH1/P event uncertain.

Considering the CENOGRID (Fig. 10), the chron C23n.1n appears strongly dilated in the studied succession compared to underlying chrons (although not fully recorded here). This suggests an increase in the rate of sedimentation compared to underlying deposits.

To summarize, the studied succession records at least four hyperthermals C24n.1nH1/K(ETM3), C23rH2/M, C23n.2nH1/N and C23n.1nH1/P, from the chron C24n.1n to the chron C23n.1n (Fig. 10). This confirms that a large part of the EECO is recorded in the studied sections.

## 5.2. Tectonic and eustatic controls on sedimentation

The evolution of the sedimentary systems over time through the analysis of depositional sequences and the chronostratigraphic framework reveals significant variations in relative base level, accommodation, sedimentation rate and sources. This evolution raises questions about potential tectonic and/or eustatic controls on the sedimentation. The eustasy does not seem to play a significant role on the accommodation. Comparison of the eustatic level variation curve (data from Miller et al., 2020) with the defined stratigraphic sequences (Fig. 11) reveals that the continental T or R sequences do not correlate with periods of eustatic transgression or regression, respectively. This is consistent with the relatively rare impact of eustasy on conventional palustrine to shallow-lacustrine environments that are not clearly connected to the oceans (Alonso-Zarza and Wright, 2010), and with the inferred distance of around 200 km between the study site and the marine paleo-coastline to the west during this period (Plaziat, 1981; Tambareau et al., 1995; Gély and Sztràkos, 2000). On the contrary, the tectonic context, i.e. retro-foreland basin related to the Pyrenean belt, controls the accommodation and the sediment rate. A general increase in accommodation is obtained from the base to the top of the studied succession (Fig. 12). This increase is thus interpreted as related to the foreland basin context. Indeed, we notice the classical acceleration of
<figure><img src="image_15.png" /><figcaption>**Fig. 11.** A) Integrated framework for the Ypresian period including geological time-scale, international magnetic polarities data, standard marine carbon isotope records (from Westerhold et al., 2020), sea-level curve (from Miller et al., 2020), and showing EECO period and superimposed hypethermals. - B) Schematic depositional and sequential model of the studied sedimentary strata correlated with all the standards in A), highlighting the link between hyperthermals events and bases of the continental T-sequences. - C) and D), Models of depositional conditions for inter-hyperthermal periods and hyperthermal event intervals respectively.</figcaption></figure>
<figure><img src="image_16.png" /></figure>

**Fig. 12.** Graphic showing the curves of accommodation for sections 2 and 6 (Age/Thickness), dots are constrained by paleomagnetic chron limits and CIEs corresponding to identified hyperthermals. The phases of high detrital input (blue arrow), subaerial unconformity surfaces (SU), continental T/R sequences and the various tectonic constraints and events are positioned in accordance with the defined age of the deposits. The sediment thickness was not uncompacted since the overloading remains poorly constrained.

subsidence with time in such basin (Sinclair and Naylor, 2012; Ford et al., 2016; Rougier et al., 2016), the northward migration of the forebulge (to the Montagne Noire sector during Eocene; Christophoul et al., 2003), and the development of local tectonic structures (Alaric Thrust and Oupia-Tourouzelle Thrust; Martín-Martín et al., 2001). The difference in accommodation from west to east could be related to such local tectonic structures: the thicker T1 sequence to the west is potentially related to the activity of the Alaric Thrust (Fig. 1), located about 20 km to the southwest (Christophoul et al., 2003; Fig. 12), whereas the higher accommodation to the east in the T2 and T3 sequences could be related to the Tourouzelle Thrust (Fig. 1), located about 5 km south-eastward. Only a limited deepening of the shallow-lacustrine environment is recorded in the T3 unit (of the T3-R3 sequence) before a regressive unit (R3) associated with high accommodation (Fig. 9). This suggests an increase in sedimentation rate during this sequence in the whole study area and a phase of sedimentary basin infilling during the final regression (Fig. 12).

As the sedimentation rate appears relatively constant before the C23n.2nH1/N-C23n.2nH2/O interval and then increasing after it, a phase of tectonic quiescence or a pulse-induced positive inflection of the forebulge domain is envisaged as triggering a change in the accommodation of the study sector during this interval of about 500 kyrs (Fig. 12).

The tectonic events seem to have no effect on the variation of sediment sources evidenced in stratigraphic sequences. Palustrine to shallow-lacustrine systems (dominant in the studied succession) are prevalent in closed-basin infilling where the carbonate-dominated deposits onlap the basin margin, due to progressive decrease of tectonic activity along the basin margins and reduction in relief or modifications of topography (Alonso-Zarza and Wright, 2010). However, the development of palustrine to shallow-lacustrine deposits in the studied succession suggests that this part of the Minervois basin infilling corresponds rather to an underfilled lake basin environment (Bohacs et al., 2000) for at least the transgressive (T) sequences. Indeed, they occur during increased accommodation and are associated with alternating drying and wetting (recharge of the water table) phases coupled with a low input of detrital material. Such basin layout could be linked to the establishment of endoreic sedimentation conditions triggered by the development of low-relief thrusts located in south and east part of Minervois Basin. Indeed, the uplift of the forebulge to the north, and the potential damming structures to the west, disconnect periodically the

Minervois Basin from the whole Aquitaine Basin and the main Pyrenean belt. These conditions lead to a reduction in detrital input hence favouring carbonate production. The associated low reliefs favour direct recharge of the basin by shallow groundwater, and thus the development of shallow lakes or wetlands (Alonso-Zarza and Wright, 2010). In such a context, the arrival of detrital sediments is then related to sedimentation pulses that momentarily break the endoreic conditions. This break enables the hydrographic network of the hinterland (main Pyrenean belt) to the south to be connected to the basin. We precise that local low-relief tectonic structures (Alaric, Oupia-Tourouzelle) cannot be the source of such episodic inputs of detrital materials, since the growth strata and the southward unconformity they triggered (see the Agel Fm. disappearance to the south along the Oupia anticline, Fig. 1) are developing continuously throughout the sedimentary succession, and so without forming reliefs high enough to produce a detrital source (Martín-Martín et al., 2001; Christophoul et al., 2003). A step later in the stratigraphic framework, the R3 shallow-lacustrine regression sequence relates to an assumed period of increased sedimentation rate concurrently with an increase of accommodation (Fig. 12). This regression trend is interpreted as being related to the increase of exhumation and tectonic activity in the Pyrenean belt, leading to a progressive infilling of the Minervois Basin and to the transition to the Aigne Fm. (Fig. 12), as evidenced by the introduction of granitic pebbles in the conglomerates stratigraphically just above the studied succession (Al Reda et al., 2021). Consequently, tectonics plays a role in the accommodation and rate of sedimentation recorded in the Ypresian sediments of the studied series but does not exert a decisive influence on the sedimentation changes observed along the studied succession, and therefore cannot be responsible for the sudden influx of detrital material into the north Minervois Basin.

### 5.3. Climatic record and control on sedimentation: A model for continental settings

Integrated chronology allows to identify EECO and associated hyperthermals in the Ypresian continental sections of the Minervois Basin and analyze this climatic pattern with respect to sedimentological and stratigraphical sequence (Fig. 11). The following model in Fig. 11 shows that defined hyperthermal intervals match with T-R sequence framework. Indeed, the SU1 (see Part. 4.2) and overlying sandstone-
dominated deposits associated to ephemeral multistorey braided channel plain (FA3) are contemporary with the hyperthermal C24n.1nH1/K (ETM3, Fig. 11). Likewise, the SU2 and overlying FA3 deposits are contemporary with the hyperthermal C23rH2/M. The SU3 and overlying FA3 deposits are contemporary with the hyperthermal C23n.2nH1/N-C23n.2nH2/0 interval. For the C23n.1nH1/P event, even if the data cannot fully validate its position (see Part. 5.1), it would be located in the regressive unit of the T3-R3 sequence, midway between the maximum flooding surface separating the T3 and R3 sequences and the upper SU4 sequence boundary (Fig. 11). In addition, all the other deposits associated with the transgressive T1, T2, T3 sequences were then formed during the inter-hyperthermal periods. These correlations indicate that sudden development of FA3 corresponds to hyperthermal events. This substantiates the fact that climate was a determining factor in sedimentation in the studied basin. Hence, a global climatic control of the change in sedimentation type is clearly considered.

A climatic control on sedimentation during hyperthermal events has already been established in the literature for the PETM in the continental domain (Foreman, 2014; Bataille et al., 2016; Piedrahita et al., 2024). Indeed, this period of extreme warming had induced a change in fluvial architecture, but more importantly, a rapid increase in detrital fluxes and a coarser sedimentary discharge including upper-flow regime bedforms in the continental parts (rather proximal) of foreland basins (connected to the ocean or not), associated with thicker alluvial clastic deposits in Tremp Basin in south Pyrenees in Spain (Schmitz and Pujalte, 2007; Chen et al., 2018; Arévalo et al., 2022; Prieur et al., 2024) and in several basins related to the Laramide orogeny in the USA (Piceance Creek Basin, Colorado: Foreman et al., 2012; Bighorn Basin, Wyoming: Foreman, 2014; Tornillo Basin, Utah: Bataille et al., 2016). This type of major sedimentation changes in the continental domain in similar geologic contexts has also been described associated to following ETMs, much less frequently for the C24rH8/H1 (ETM2) and C24n.1nH1/K (ETM3) (Tornillo Basin, Utah: Bataille et al., 2016; Uinta-Piceance Basin, Colorado: Birgenheier et al., 2020), and for transient hyperthermal events C24rH9/H2, C24n.3nH1/I1, C24n.3nH2/I2 and C24n.2rH1/J (Uinta-Piceance Basin, Colorado: Birgenheier et al., 2020). The previous authors link this enhanced clastic input in the basins to an intensification of hydrologic cycle and then of humidity gradient. Such modification of conditions led to a dramatic change and intensification of flow in the hydrographic system resulting from a rapid change in the much more intense rainfall regime in the hinterland (Foreman, 2014; Schmitz and Pujalte, 2007; Bataille et al., 2016; Arévalo et al., 2022; Payros et al., 2022; Prieur et al., 2024) and changes in vegetation cover (Smith et al., 2014; Bataille et al., 2016). Some of them associate these intense rainfall regime with monsoon-type events on uplands triggering high-magnitude rapid flash-floods and the increase of erosion in the reliefs and the basin, since the change in vegetation allows greater diffusivity of the flow and increases the transport capacity of coarse sediments in the rivers (Foreman et al., 2012). In Minervois study, despite the fact that the hyperthermal events are of lower amplitude in terms of carbon isotopic excursion (CIE) than the PETM, and because the type of sedimentation associated with the recorded hyperthermals is typical of deposits triggered by monsoon-type rainfall (see FA3, Part. 4.1), a model of continental sedimentation based on this type of monsoon rainfall is proposed. Indeed, the subtropical latitudes of the Minervois Basin during the Ypresian (between 30° and 40°N latitude; Plaziat, 1981; Baceta et al., 2011) coincide with latitudes of above mentioned Spanish and American basins, as well as the present-day subtropical monsoon climate type. It is accepted that monsoon phenomena are related to alternating and changing seasonal air masses formed by thermal contrasts between oceans and continents on different scales (regional/global; An, 2015). In a regional context, relief plays an important role in triggering rainfall events. In warmer periods, sea surface temperatures increase evaporation and promote the formation of warm, moist air masses that enter the land and rise along the relief to then condense and give raise to heavy monsoon-type rainfall. On a larger

scale, the displacement of the inter-tropical convergence zone in relation to the equator also produces changes in air masses, leading to monsoon-type precipitation. These phenomena, which are constrained by air mass thermal contrast and geographical conditions (relief), could have occurred during the Ypresian period in the Minervois. During the EECO, the Pyrenees begin to form a relief and are surrounded to the west and south-west by the sea of the Basque country and to the south-east by the Tethys (Calvet et al., 2021). At these latitudes, average seawater temperatures are around 30 °C (Carmichael et al., 2017; Zhang et al., 2020) and the global mean surface temperatures are estimated ~27 °C (Inglis et al., 2020). Both favour the development of sea-surface evaporation and semi-arid conditions in the subtropical continental interior domain, thus promoting the development and accumulation of palustrine then shallow lacustrine carbonate limestone in an endoreic basin as well as ephemeral high-magnitude floods. These semi-arid to sub-humid climatic conditions have already been demonstrated in southern Europe over the considered period (Plaziat et al., 1987). In this context, conditions are therefore optimal for the formation of monsoon-type precipitation.

The proposed model is based on the record of alternating phases of changes in sedimentation and deposition during (1) inter-hyperthermal and (2) hyperthermal events (Fig. 11).

(1) Inter-hyperthermal periods are highlighted by floodplain siltstones and carbonate production developing progressively in palustrine and then shallow-lacustrine domain (FA4 to FA5; Fig. 11C) reflecting gradual climate warming with strong seasonality. Such conditions have drastically reduced rainfall in the uplands and activity in alluvial/fluvial systems but have nonetheless favoured alternating dry and wet periods, as well as groundwater recharge and fluctuation. It is these fluctuations that regulate carbonate production and vegetation development in such environments over extended periods of permanence of water masses thereby promoting the development of vertically stacked palustrine/lacustrine sequences (Alonso-Zarza, 2003; Armenteros and Edwards, 2012). This period corresponds to the major part to the end of the T sequences.

(2) Hyperthermal events are emphasized by the sudden arrival of detrital sediment (FA3) in the endoreic basin (Fig. 11D), through high-magnitude flash-flood triggered by episodes of extreme monsoon-rainfall intermittently accentuated in areas of high relief (i.e. main Pyrenean belt). Such events promote erosion and detrital flows to drain into the basin and subsequent deposition of sandstone bodies forming an ephemeral multistorey braided channel plain (FA3, Fig. 11D). Nowadays, these types of extreme monsoon episodes can last for several months during summer season (Plink-Bjorklund, 2015). An analogy with this duration, even if the worldwide climatic context is different, helps to explain the extent and cover of detrital material over a minimum of fifteen kilometres wide. This phase corresponds to the SU sequence boundaries and the early stages of continental T sequences.

By the end of the hyperthermals, conditions had become less extreme in the functioning of the hydrological cycle. This change of conditions causes the ephemeral multistorey braided channel plain to be abandoned. Consecutively, stable palustrine and then shallow-lacustrine carbonate systems developed for almost the studied part of the EECO period and during a phase of generally increasing subsidence. Extreme and intense rainfall episodes on the upland reliefs during the hyperthermal events must have been of much greater magnitude than the seasonal ones occurring during inter-hyperthermal periods (not restricted to the reliefs and more spread out in time). Foreman et al. (2012) and Foreman (2014) argue that the sedimentation changes previously cited for PETM reflect an increase in mean annual precipitation. Payros et al. (2022) suggest that changes are rather associated with an
increase in the frequency and intensity of rainstorms in autumn, but without a significant variation in the volume of averaged total annual precipitation. For the early Paleogene period, it is defined that 70 % of the annual rainfall of hyperthermal event occurs during wet seasons (Huber and Goldner, 2012; Bataille et al., 2016; Carmichael et al., 2016). Here, despite the drastically differences between more stable seasonal regime during inter-hyperthermal event and high-magnitude extreme events during hyperthermal, it is hypothesised that the mean annual precipitation remained virtually identical for both periods. Indeed, sufficient rainfall is still needed to recharge the groundwater table, which enables the accumulation of the palustrine and shallow-lacustrine carbonates. As the detrital sedimentation is active almost exclusively during a hyperthermal interval, this implies that, during these warm-ups, only intense monsoon episodes are recorded in the sedimentation and superimposed on one another, for several thousand years. Sediments were probably transported and deposited only throughout the monsoon season, whereas river beds may remain dry or with very little water for oncolites development between these extreme rainfall events during the rest of the year and possibly for multiple years (Plink-Björklund, 2015). In semi-arid tropic such event has a recurrence frequency of multiple years or even decades (Plink-Björklund, 2015), this could also apply to Minervois deposits, although it is not possible to assert this. In any case, the sedimentological data prove that ephemeral multistorey braided channel plain record at least more than one extreme rainfall episode. The simulated global- and regional-scale hydrological response to warming during Early Eocene in the subtropical regions suggests a drier climate in these latitudes, but also an increase in mean annual precipitation (Cramwinckel et al., 2023). The climatic model proposed for the Minervois deposits corresponding to high-magnitude monsoon-type rainfall phenomena in semi-arid domains generalized over periods of hyperthermals, could explain the hypothesis that annual precipitation increases despite the drier climate. Although it is complex to assess, the frequency of these high-magnitude monsoon events could help determine the paleo-average annual precipitation in these regions, as this parameter certainly plays a decisive role in the quantity of rains.

The proposed model shows that climatic control is therefore domi-
nant for sedimentation during the C24n.1nH1/K (ETM3), C23rH2/M,
and C23n.2nH1/N-C23n.2nH2/O hyperthermals. For the hyperthermal
C23n.1nH1/P, which occurs in the Minervois during a regressive phase
of the continental sequences, there is no notable variation in associated
sedimentation. This could be explained by the increase of subsidence at
this time, preventing the arrival of detrital material in this area of the
basin. This means that recording the effect of hyperthermal events as a
modifier of sedimentation is facilitated in an endoreic foreland basin
with medium to low subsidence (Fig. 12). A favourable accommodation
and sedimentation rate ratio, depending on the type of depositional and
tectonic context, is thus required to identify hyperthermal events
directly in the continental sedimentary archive. When these conditions
are fulfilled, the sedimentary response of hyperthermal events of lower
amplitude in terms of carbon isotopic excursion (CIE) appears almost
identical (albeit attenuated) to that of the PETM extreme episode.

6. Conclusions

The study focuses on depositional systems formed in an endoreic
foreland basin developed during EECO in the Minervois Basin. The aim
of this study was to identify and refine the impact of hyperthermal
events on continental sedimentation within a robust chronostratigraphic
framework. Results of detailed facies and stratigraphical sequence
analysis, both in time and space, constrain the depositional environ-
ments and their correlation with C24n.1nH1/K (ETM3), C23rH2/M,
C23n.2nH1/N-C23n.2nH2/O interval and C23n.1nH1/P hyperthermal
events which some transients are documented for the first time in the
study area. The present study puts forward the hypothesis that climatic
control exerts a significant and substantial influence on changes in
sedimentation patterns. The model highlights sudden and intense

monsoonal episodes triggering high-magnitude flash-flood during pe-
riods of hyperthermal warming evidenced by subaerial unconformity
surface, supercritical bedforms and ephemeral multistorey braided
channel plain. These episodes cause drastic rainfall on the reliefs,
allowing detrital sediments to arrive in the palustrine shallow-lacustrine
domain previously disconnected from hydrological networks. These
results illustrate that such transient hyperthermals manifest a conti-
nental sedimentary response in alluvial settings that is nearly identical
to that observed for more intense events, such as the PETM. The data set
also demonstrates that the impact of such climatic events on continental
sedimentation is favourably recorded in low tectonic subsidence,
underfilled basin, disconnected to eustatic influence.

In the present context of global warming linked to the anthropisation
of the planet, at a time when the society is becoming increasingly ur-
banized, leading to significant soil sealing, the study of past periods of
climatic warming highlights that they can be associated with intense
rainfall events in areas not accustomed to this type of extreme event,
such as the Earth has already experienced in recent years.

Supplementary data to this article can be found online at https://doi.
org/10.1016/j.sedgeo.2025.106923.

CRediT authorship contribution statement

**Cindy BOYRIE:** Writing – original draft, Visualization, Resources, Methodology, Investigation, Formal analysis, Data curation. **Flavia GIRARD:** Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Resources, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization. **Johan YANS:** Writing – original draft, Visualization, Validation, Resources, Methodology, Investigation, Formal analysis, Data curation. **Grégory BALLAS:** Writing – original draft, Visualization, Validation, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. **Fabrice LIHOREAU:** Writing – original draft, Visualization, Validation, Resources, Methodology, Investigation, Formal analysis, Data curation. **Mouloud BENAMMI:** Writing – review & editing, Visualization, Validation, Methodology, Investigation, Formal analysis, Data curation. **Hélène BOURGET:** Investigation, Data curation. **Géraldine GARCIA:** Investigation, Funding acquisition. **Christine LEREDDE:** Writing – review & editing, Validation, Resources, Investigation, Formal analysis. **Aimée PELLISSIER-TANON:** Investigation, Data curation. **Xavier VALENTIN:** Investigation, Data curation. **Dominique VIDALENC:** Investigation. **Rodolphe TABUCE:** Writing – review & editing, Writing – original draft, Validation, Resources, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization.

Declaration of competing interest

The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.

Acknowledgements

We would like to thank M. Seranne and N. Saspiturry for their
constructive discussions and D. Legrand for his assistance during the
field mission. We would also like to thank J-Y. Storme, G. Rochez and Y.
Sinquin who helped us for the processing and manipulation of
geochemical protocol and C. Nevado and D. Delmas for their lith-
opreparative qualities. This research was initiated by the help of late H.-
P. Labarrere, we are very grateful to him. We thank the two anonymous
reviewers and the journal's editor Massimo Moretti for their constructive
comments that help to greatly improve the quality of the manuscript. We
benefited from A. Genna's advice on the field. This research was sup-
ported by grant ANR-20-CE02-0007 and by the Tellus Program of
## Data availability

Data will be made available on request.

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