Alfredo Mayoral
email: alfredo.mayoral@uca.fr

Jean-François Berger

Jean-Luc Peiry

Paul Ledger

Yannick Miras

Miras

Five millennia of human-environment interactions reconstructed from pedosedimentary archives of the Lac du Puy wetland (Corent, Fr.)

Keywords: Human-environment interactions, Pedo-sedimentary archives, Geoarchaeology, Soil Micromorphology, Palaeosoils, Limagne, Holocene

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

1-Introduction

Long-term human-environment interactions and the gradual 'anthropogenization' of natural systems are topics that have been widely investigated and discussed in geoarchaeological, palaeoenvironmental and environmental archaeological studies, from western Europe in recent decades (e.g. [START_REF] Van Der Leeuw | Climate, hydrology, land use, and environmental degradation in the lower Rhone Valley during the Roman period[END_REF][START_REF] Dearing | Climate-human-environment interactions: Resolving our past[END_REF][START_REF] Berger | Nouveau regard sur La dynamique des paysages et l'occupation humaine à L'Âge du Bronze en moyenne vallée du Rhône[END_REF][START_REF] Butzer | Geoarchaeology, Climate Change and Sustainability: A Mediterranean perspective[END_REF]Notebaert A c c e p t e d M a n u s c r i p t & Berger, 2014;[START_REF] Carozza | Society and environment in Southern France from the 3rd millenium BC to the beginning of the 2d millenium BC a tipping point?[END_REF][START_REF] Arnaud | Erosion under climate and human pressures : An alpine lake sediment perspective[END_REF][START_REF] Cremaschi | Climate change versus land management in the Po Plain (Northern Italy) during the Bronze Age: New insights from the VP/VG sequence of the Terramara Santa Rosa di Poviglio[END_REF][START_REF] Lespez | Rapid climatic change and social transformations Uncertainties, adaptability and resilience[END_REF].

More recently renewed research momentum has been stimulated by the emergence of the hotly debated 'anthropocene' paradigm [START_REF] Crutzen | The "Anthropocene[END_REF][START_REF] Foley | The Palaeoanthropocene -The beginnings of anthropogenic environmental change[END_REF][START_REF] Cremaschi | When did the Anthropocene begin? A geoarchaeological approach to deciphering the consequences of human activity in pre-protohistoric times: Selected cases from the Po Plain (northern Italy)[END_REF][START_REF] Butzer | Anthropocene as an evolving paradigm[END_REF][START_REF] Lewis | Defining the Anthropocene[END_REF][START_REF] Verstraeten | Quantification of human-environment interactions in the past[END_REF][START_REF] Ruddiman | Defining the epoch we live in. Is a formally designated[END_REF][START_REF] Ruddiman | Geographic evidence of the early anthropogenic hypothesis[END_REF][START_REF] Bauer | The Anthropocene Divide: Obscuring Understanding of Social-Environmental Change[END_REF].

Off-site palaeoenvironmental and geoarchaeological research (e.g. in lakes, peatlands, floodplains etc.) continue to provide valuable records of human impacts in environmental dynamics (e.g. [START_REF] Miras | Multi-disciplinary approach to changes in agro-pastoral activities since the Sub-Boreal in the surroundings of the "Narse d'Espinasse" (Puy de Dome, French Massif Central)[END_REF][START_REF] Brown | Geomorphology of the Anthropocene: Timetransgressive discontinuities of human-induced alluviation[END_REF][START_REF] Arnaud | Erosion under climate and human pressures : An alpine lake sediment perspective[END_REF][START_REF] Berger | A fluvial record of the mid-Holocene rapid climatic changes in the middle Rhone valley (Espeluche-Lalo, France) and of their impact on Late Mesolithic and Early Neolithic societies[END_REF][START_REF] Peña-Monné | Geoarqueología aplicada a la reconstrucción paleoambiental : La evolución del Holoceno superior en el NE de España[END_REF][START_REF] Dubois | First human impacts and responses of aquatic systems: A review of palaeolimnological records from around the world[END_REF]. In addition, progress in site-based geoarchaeological approaches is producing large amounts of detailed archaeometric data related to human-environment interactions [START_REF] Butzer | Challenges for a cross-disciplinary geoarchaeology: The intersection between environmental history and geomorphology[END_REF].

Improvements in our understanding of Holocene palaeoclimatic change are allowing the development of detailed analyses of the interaction between climate and society (Magny et al., 2009;[START_REF] Armit | Rapid climate change did not cause population collapse at the end of the European Bronze Age[END_REF][START_REF] Lespez | Rapid climatic change and social transformations Uncertainties, adaptability and resilience[END_REF][START_REF] Roberts | Mediterranean landscape change during the Holocene: Synthesis, comparison and regional trends in population, land cover and climate[END_REF]. Together, these new data contribute to feed scientific discussion and to improve our understanding of the progressive anthropogenic forcing of natural systems through the Middle to Late Holocene. Despite these achievements some "grey zones" remain in human-environment interaction studies, often neglected by palaeoenvironmental and geoarchaeological works. This is typically the case for human-environment interface halfway between site-based and off-site contexts, as researchers regularly focus on areas suitable for the formation and preservation of "optimal" sedimentary records, that are able to provide unambiguous interpretations. Intermediate, or "site-proximal" contexts are often neglected due to their sometimes incomplete sedimentary records, signal complexity or poor taphonomic conditions (Ledger et al., 2015[START_REF] Ledger | Competing hypotheses, ordination and pollen preservation: Landscape impacts of Norse landnám in southern Greenland[END_REF].

These "site-proximal" contexts are nevertheless crucial for developing an integrated understanding of the complex nature of long term human-environment interactions. They provide unique and sensitive records of processes characteristic of transitional zones, displaying a mixture of natural and A c c e p t e d M a n u s c r i p t cultural features. This makes them useful for characterizing human-environment interaction, such as locally increased impacts related to proto-urban emergence [START_REF] Kaniewski | Early urban impact on Mediterranean coastal environments[END_REF][START_REF] Danielisova | OPPIDA AND AGRICULTURAL PRODUCTION -STATE OF THE ART AND PROSPECTS[END_REF]Ledger et al., 2015;[START_REF] Styring | Centralisation and long-term change in farming regimes: Comparing agricultural practices in Neolithic and Iron Age south-west Germany[END_REF]. Formation processes of pedosedimentary sequences on the periphery of archaeological sites, often marked by hiatuses and cumulated dynamics, are valuable yet complex palimpsests that present a real geoarchaeological challenge, and are fertile ground for multi-proxy approaches. Wetlands under human influence are similar case and they have been widely studied from a palaeoenvironmental and geoarchaeological perspective in rural areas (e.g. [START_REF] Martín-Puertas | The Iberian-Roman Humid Period (2600-1600 cal yr BP) in the Zoñar Lake varve record (Andalucía, southern Spain)[END_REF][START_REF] Macaire | Quantitative analysis of climate versus human impact on sediment yield since the Lateglacial: The Sarliève palaeolake catchment (France)[END_REF][START_REF] Bernigaud | Ancient canals in the valley of Bourgoin-La Verpillière (France, Isère): morphological and geoarchaeological studies of irrigation systems from the Iron Age to the Early Middle Ages (8th century bc-6th century ad)[END_REF][START_REF] Hausmann | Direct push sensing in wetland (geo)archaeology: High-resolution reconstruction of buried canal structures (Fossa Carolina, Germany)[END_REF][START_REF] Haas | Roman-driven cultural eutrophication of Lake Murten, Switzerland[END_REF], but site-proximal or intra-site wetlands are rare and consequently less frequently studied.

Geographical Settings and Archaeological Background

The Lac du Puy is typical of these rare contexts. The small wetland is situated within the extension of the large protohistoric archaeological site of Corent, located on a volcanic plateau dating from the Pliocene [START_REF] Greffier | Aspects géomorphologiques et stabilité des versants au sud de Clermont-Ferrand[END_REF][START_REF] Nehlig | Les volcans du Massif central[END_REF][START_REF] Mayoral | Geoarchaeology and chronostratigraphy of the Lac du Puy intraurban protohistoric wetland[END_REF]. The plateau is located in a commanding position, controlling the north-south axis of the valley of the River Allier, 20 km south of Clermont-Ferrand (French Massif Central, see Fig. 1). The southern part of the plateau is a scoria cone with moderate slopes, while the Lac du Puy basin is situated in the northern area of the plateau, a basaltic lava flow with gentle topography. It is a closed circular depression (c. 2 Ha) interpreted as a pseudo-sinkhole [START_REF] Mayoral | Geoarchaeology and chronostratigraphy of the Lac du Puy intraurban protohistoric wetland[END_REF], nowadays occupied by a dry (but seasonally wet) agricultural field with a small drained pond (20x20m) fed by runoff and subsurface flow. Aerial photography and historical maps suggest that before drainage operations in the early XIX th century (Ledger et al., 2015), the open water area in the depression was probably more extensive (c. 100x80m) and could perhaps have been a valuable water source.

Extensive archaeological excavation at Corent since the 2000's has shown human occupations spanning from Middle Neolithic to Roman period. The Middle Neolithic, dated c. 4200-3700 BCE A c c e p t e d M a n u s c r i p t (Before Common Era), is characterized by a large fortified settlement and ditched structures (Poux et al., 2018). Later, a collective burial was installed in the summit of the plateau [START_REF] Daugas | Une fosse à inhumations néolithique à Corent (Puy-de-Dôme)[END_REF], maybe in the Late Neolithic (c. 3000-2400 BCE). The Bronze Age is characterized by several occupations. The most studied is a Late Bronze Age III (950-800 BCE) agglomerated settlement with proto urban features, which given its hilltop position and size is unique in France (Milcent et al., 2014a;Ledger et al., 2015). Centuries later in the Early Iron Age (Hallstatt D1, 625-510 BCE) a proto-urban settlement developed as is seen elsewhere in Western Europe (Milcent et al., 2014b;[START_REF] Fernández-Götz | Urbanization in Iron Age Europe: Trajectories, Patterns, and Social Dynamics[END_REF].

The most celebrated phase of the site is undoubtedly the Late Iron Age oppidum (La Tène D1-2 140-30 BCE). This was an immense, monumental and wealthy urban centre including public, artisanal, religious and commercial buildings, which was probably the capital of the Arverni [START_REF] Poux | Corent, Voyage au coeur d'une ville gauloise[END_REF]Milcent et al., 2014b;[START_REF] Poux | Corent, Fouille pluriannuelle 2014-2016[END_REF]. After the Roman conquest, the site became a welldeveloped secondary agglomeration (30 BCE-300 CE , [START_REF] Poux | Corent, Fouille pluriannuelle 2014-2016[END_REF]. This trajectory of successive occupations makes Corent an important site in European protohistory with rich potential for analyzing long-term socio-environmental interactions, and human impacts during proto-urban and urban episodes of the 1 st millennium BCE. Surprisingly, the palaeoenvironmental and geoarchaeological potential of the wetland has long time been neglected, aside from a restricted archaeological survey in the early 1990s [START_REF] Guichard | 1D sequential inversion of portable multiconfiguration electromagnetic induction data[END_REF].

Summary of recent research and Objectives

In the framework of the AYPONA palaeoenvironmental program, begun in 2013, palynological research (Ledger et al., 2015) and geoarchaeological survey [START_REF] Mayoral | Lac du Puy de Corent-Opération 2015: Sondages Géoarchéologiques-Rapport de prospection thématique[END_REF][START_REF] Mayoral | Geoarchaeology and chronostratigraphy of the Lac du Puy intraurban protohistoric wetland[END_REF] were undertaken within this wetland. The objectives were to investigate long-term humanenvironment interaction, impacts of human settlements since the Neolithic, and localized impacts during the proto-urbanization episodes of the I st millennium BCE.

A c c e p t e d M a n u s c r i p t

Palynological investigations analyzed (pollen and NPPs) half of a sedimentary core extracted in the Lac du Puy basin and developed an age-depth model based on radiocarbon dating (see Ledger et al., 2015). The results indicated more or less continuous human impact from the Neolithic until the Roman era. The Neolithic to Middle Bronze Age was characterized by a classical pattern of woodland clearance and landscape opening, coupled with the gradual intensification of agriculture, and development of pastoral activity. From the end of the Late Bronze Age, there is evidence of increased biodiversity, plants indicative of ruderal environments and limited evidence of agriculture. These patterns, together with other key features such as occurrences of non-native plant taxa, were interpreted as those of emerging proto-urban areas in the Late Bronze Age and the Late Iron Age (Ledger et al., 2015). Further geoarchaeological research involved trench-based survey, developed in 2015 [START_REF] Mayoral | Geoarchaeology and chronostratigraphy of the Lac du Puy intraurban protohistoric wetland[END_REF]. The infilling of the basin, divided in 12 Stratigraphic Units (SU), is in general clayey and ranges from 30 cm to 2m in deeper central sectors of the basin, with very variable depth and often sharp lateral changes of pedo-sedimentary facies (Fig. 1F).

Geomorphology and stratigraphy from logs and cross-sections, geophysics, radiocarbon dating and archaeological findings were used to build a first chrono-stratigraphic framework at the scale of the basin, and ultimately to outline the main phases of its complex pedo-sedimentary and hydrological evolution (Fig. 1F&G, adapted from [START_REF] Mayoral | Geoarchaeology and chronostratigraphy of the Lac du Puy intraurban protohistoric wetland[END_REF]. The first phase of the infilling of the basin starts somewhere at the end of the Early, or in the beginning of the Middle Neolithic (before 4500 cal. BCE). Sparse pools in the irregular basaltic bedrock revealed by geophysics (Fig. 1D) received strong runoff bringing scoria and clays (SU6A/B), whereas a weathering profile had started to develop over basalts in higher areas (WB). By the Middle Neolithic (circa or after 4500 cal. BCE), an oscillating water table and detrital sedimentary inputs smoothed the irregular topography of the basin (SU5A-B-C, Fig. 1F&G). Fragmentary archaeological remains are indicative of human activity in the area, maybe related to contemporaneous occupations of the plateau. Following this phase, a very low deposition rate, or even a hiatus between SU5 and SU4, makes interpretation of the depositional environment difficult [START_REF] Mayoral | Geoarchaeology and chronostratigraphy of the Lac du Puy intraurban protohistoric wetland[END_REF]. A new sedimentary phase, beginning in the A c c e p t e d M a n u s c r i p t

Early to Middle Bronze Age (1900-1600 cal. BCE), was characterized by low-energy environment and high watertable level (clayey gleysol, SU4-4a1-4b; see Fig. 1F&G). At the top of this unit, is an archaeological soil containing in-situ structures dating to the Late Bronze . This unit is almost certainly associated by the contemporaneous LBA3 occupation of the plateau and indicates human activity in the basin at this time. Following this period, and until the fifth century BC, sedimentation was interrupted coinciding with a soil stability phase in the plateau. However shortly after (600-425 BCE), the digging of c. one thousand storage pits, probably associated by the neighboring Hallstatt D settlement, massively disturbed pedo-sedimentary and hydrological dynamics of the basin (Fig. 1F&G). After abandonment of these pits, the disturbance period was followed by deposition of SU3, characterized by ephemeral flooding, detrital inputs and vertisol-type dynamics (seasonal shrink-swell processes). In the late Iron Age (La Tène D, 100-40 BCE) at least two phases of soil leveling and backfilling affected southern parts of the basin (SUA1-A2), followed by a generalized leveling and backfill of the Lac du Puy (50/40-30 BCE, SU2). These backfill layers, always associated with archaeological structures, are characterized by heterogeneous grain-size, very frequent basaltic and amphorae inclusions, homogeneous thickness in all their extent, and abnormal or erosive stratigraphic contacts (Fig. 1F). Indeed, they partly truncate positive reliefs on SUs 3 and 4 (Fig. 1F&G). These earthworks were caused by the gradual extension of the Gallic oppidum and were certainly accompanied by drainage [START_REF] Mayoral | Geoarchaeology and chronostratigraphy of the Lac du Puy intraurban protohistoric wetland[END_REF]. After Antiquity, sedimentation slowly covered antique backfill and a topsoil with incipient vertic features developed (SU1) as wet conditions gradually returned, until the depression was drained in recent centuries.

In summary, previous palynological and geoarchaeological research provided the first chronostratigraphic framework for the basin, and revealed the human influences likely driving its development since the Neolithic. However, the precise relationship between changing pedosedimentary processes and human activity remains unclear. For instance, were Neolithic detrital inputs connected with woodland clearance detected by palynology and with occupation phases of the plateau? Were the gleyic conditions at the onset of the Bronze Age related to human activity?

A c c e p t e d M a n u s c r i p t How did the vertisolization processes following the abandonment of storage pits in the Iron Age develop? Similarly, the hiatus/low-deposition phases were hindering comprehensive understanding of the sequence, and required more detailed examination. This work aims to resolve these questions by applying an integrative and high-resolution geoarchaeological approach to the rich but complex pedo-sedimentary archives of the Lac du Puy. A multi-proxy geoarchaeological analysis was performed on a sedimentary core from the deepest area of the basin (Fig 1D ), well-representative of the pedo-sedimentary sequence of the lower areas of the Lac du Puy (Fig. 1E&G). New micromorphological analyses, completed with high-resolution sedimentological and geochemical data, were integrated with previous palynological and archaeological information. Results were interpreted within a refined chrono-stratigraphic framework based on a compilation and integration of available radiocarbon, archaeological and stratigraphic evidence.

2-Materials and Methods

Coring and pedo-sedimentary description.

Coring was performed in the basin in November 2012 following a hand auger survey, using a Geotool GTR 790 corer (diameter of 7 cm, for location see Fig. 1D). Half of the obtained 186 cm core (COR13-4) was used for palynological analysis and radiocarbon dating (see Ledger et al., 2015 for details). In the summer of 2015 geoarchaeological prospection based on geophysics and systematic trenching [START_REF] Guichard | 1D sequential inversion of portable multiconfiguration electromagnetic induction data[END_REF][START_REF] Mayoral | Lac du Puy de Corent-Opération 2015: Sondages Géoarchéologiques-Rapport de prospection thématique[END_REF][START_REF] Mayoral | Geoarchaeology and chronostratigraphy of the Lac du Puy intraurban protohistoric wetland[END_REF] confirmed that COR13-4 was representative of the complete natural pedo-sedimentary sequence of the Lac du Puy, with limited or no truncation (Fig. 1F &G). The remaining half was used for multi-proxy geoarchaeological analyses which are described in the present study: sampling and pedosedimentary description were performed in laboratory using a Munsell color chart (see Log in Fig. 2, for detailed description see Table 3 in Appendix). Detailed laboratory descriptions and macro observations were correlated with exhaustive field description of stratigraphic units and pedo-lithofacies of the basin, already established from exposures and logs [START_REF] Mayoral | Geoarchaeology and chronostratigraphy of the Lac du Puy intraurban protohistoric wetland[END_REF].

Construction of chrono-stratigraphic framework

Radiocarbon dates from previous studies were inform the COR13-4 core and a series of stratigraphic sections across the basin (Table 1). Dates 1-6 are in COR13-4 core and dates 7-11 in a stratigraphic log in the centre of the basin (Log 4). Dates 7 and 8, taken in SU2 base (interpreted as anthropogenic backfill, see introduction), were inconsistent with the well-established typo-chronological dating of this unit (100-40 to 50-30 BCE) and were then rejected (see Mayoral et al. 2018 for details). Dates 12 and 13 were on a small ditch excavated in SU5A. Finally, dates 14-19 were at the base of storage pits A c c e p t e d M a n u s c r i p t dug through SU5A and Weathered Basalt (WB), except date 15 which was in the infilling of a pit (SU4). Dated materials include bulk sediment (11 samples), macrocharcoal (>125µm, 2 samples), microcharcoal (<125µm, 3 samples) and pollen (1 sample). Of the dated materials macrocharcoal can be considered the most accurate, whereas microcharcoal and pollen often show larger age discrepancies (relative to their stratigraphic position) owing to reworking of sediment. While bulk sediment is notoriously unreliable owing to uncontrolled ageing due to the contamination by older carbon (e.g. [START_REF] Grimm | The magnitude of error in conventional bulk-sediment radiocarbon dates from central North America[END_REF], but introduction of younger organic material can also distort radiocarbon dates. To assess potential reservoir effects or disturbance by pedological processes some of the dates were paired (dates 1-2, 3-4 and 9-10).

Given the scattering of dates, the possibility of sharp changes in accumulation rate and lateral variability of facies, and possible contaminations or reservoir effects, we used a broad chronological approach based on the assignment of radiocarbon dates to a SU, and when possible, to a part of this SU (base, middle or top, see Table 1). Well-dated archaeological levels or structures with a clear stratigraphic position were also used, such as archaeological layers from the Late Bronze Age 3 (950-800 BCE), La Tène D1B-D2A (100-40 BCE) and La Tène D2B to Gallo-Roman (50-30 BCE) [START_REF] Mayoral | Geoarchaeology and chronostratigraphy of the Lac du Puy intraurban protohistoric wetland[END_REF]. For a graphic summary of the relative stratigraphic positions of all available radiocarbon dates and archaeological landmarks, see Fig. 1G.

The seventeen AMS radiocarbon dates where calibrated with Calib 7.0 using Intcal 13 [START_REF] Stuiver | Extended 14C database and revised Calib 3.0 14C Age Calibration program[END_REF][START_REF] Reimer | IntCal13 and Marine13 Radiocarbon Age Calibration Curves 0-50,000 Years cal BP[END_REF], and their probability distribution was plotted using CLAM [START_REF] Blaauw | Methods and code for 'classical' age-modelling of radiocarbon sequences[END_REF]. The obtained plot was then integrated with litho-stratigraphic and archaeological data following the assignment of dates to SUs. The resulting chrono-stratigraphic diagram proposes a maximum age-range for each SU of COR13-4, which can be used as a robust chronological framework to discuss multi-proxy data (Fig. 2

Micromorphological analysis 250

The half-section of COR13-4 core between 40 and 144 cm was cut in 10 blocs (9 to 12.5 cm length, 7 251 cm width). Micromorphological thin sections were prepared from these blocks at Ghent University 252 (B). Descriptions of thin sections from macro-to microscale were performed with a Leica M80 253 A c c e p t e d M a n u s c r i p t binocular microscope (x2.5 to x60), a Leica DMLP polarizing microscope (x16 to x400), and a Leica DM 2500M (x500). A Leica built-in camera was used to take microphotographs and measurements.

Minerals and alteration were identified and described following petrography references [START_REF] Mackenzie | Atlas of Igneous Rocks and Their Textures[END_REF][START_REF] Delvigne | Atlas of Micromorphology of Mineral Alteration and Weathering[END_REF][START_REF] Loaiza | Manual de micromorfología de suelos y técnicas complementarias[END_REF]. Micromorphological features were semiquantitatively described and recorded, according to reference works [START_REF] Bullock | Handbook for soil thin section description[END_REF][START_REF] Stoops | Guidelines for Analysis and Description of soil and Regolith Thin Sections[END_REF][START_REF] Loaiza | Manual de micromorfología de suelos y técnicas complementarias[END_REF][START_REF] Macphail | Applied Soils and Micromorphology in Archaeology. Cambridge A c c e p t e d M a n u s c r i p t Manuals in Archaeology[END_REF]. Interpretation was based on international standards [START_REF] Nicosia | Archaeological Soil and Sediment Micromorphology[END_REF]Stoops et al., 2010a). The reconstruction of the pedostratigraphic sequence and the pedo-sedimentary processes is based on a hierarchical approach of pedofeatures [START_REF] Fedoroff | Paléosols et sols reliques. Miskovsky JC Géologie la préhistoire[END_REF][START_REF] Fedoroff | Palaeosoils and Relict Soils[END_REF].

Geochemistry and Magnetic Susceptibility

The geochemistry of the COR13-4 core was analyzed using an AVAATECH XRF core-scanner at EDYTEM laboratory (Université Savoie Mont-Blanc, F). The core was analyzed at a resolution of 10 mm under 10 Kv and 30 Kv beams generated by a rhodium anode, providing results in counts per second (cps) for 24 elements. A Principal Component Analysis (PCA) was performed on selected elements using XLSTAT software, in order to bring to light relationships between elements and with sedimentary units of the infilling [START_REF] Birks | Multi-proxy studies in palaeolimnology[END_REF][START_REF] Sabatier | Clay minerals and geochemistry record from northwest Mediterranean coastal lagoon sequence: Implications for paleostorm reconstruction[END_REF][START_REF] Bajard | Erosion record in Lake La Thuile sediments (Prealps, France): Evidence of montane landscape dynamics throughout the Holocene[END_REF]. On this base, elements and ratios were selected as palaeoenvironmental proxies and interpreted.

The Magnetic Susceptibility (MS) of the core was measured (unit: SI.10 -5 ) using a Bartington MS2E susceptibilimeter. Four measurements were taken each cm and the mean value was retained in order to integrate signal variability [START_REF] Dearing | Magnetic susceptibility[END_REF]. Measurements were focused on the clayey sedimentary matrix avoiding coarse basaltic particles, because their strong magnetic properties obscured the sedimentary signal.

A c c e p t e d M a n u s c r i p t

3-Results

3.1-Stratigraphic Units and chrono-stratigraphic framework

Seven Stratigraphic Units (SU) were identified in COR13-4, consistent with those described in the basin infilling by previous works (see Introduction,and Fig. 1E & G; for detailed pedosedimentological description at the scale of the basin see also [START_REF] Mayoral | Geoarchaeology and chronostratigraphy of the Lac du Puy intraurban protohistoric wetland[END_REF]. Several subunits were detected within these SU, drawing a more detailed stratigraphy for SU4, 5A, 6A and 6B (see log in Fig. 2, see also Table 3 in Appendix for detailed description of COR13-4).

The chronostratigraphic framework in Fig. 2 includes radiocarbon dates belonging to three SU (SU5A, SU4, SU3) and archaeological data at the contacts between SU4-SU3, SU3-SU2 and SU2-SU1. From these data, the chronology of SU1, SU6A and SU6B can only be estimated. Furthermore, caution must be exercised in interpreting the chronology of SU5A which was established from data drawn from multiple profiles. In the case of the Lac du Puy sequence, a reservoir effect due to old lithogenic carbon is unlikely for bulk radiocarbon samples: the geology of the basin includes exclusively volcanic materials such as basalt and scoria [START_REF] Mayoral | Geoarchaeology and chronostratigraphy of the Lac du Puy intraurban protohistoric wetland[END_REF] which are not prone to release significant quantities of lithogenic carbon in the sedimentary environment. However, the pedogenic nature of this relatively short sedimentary sequence suggests that bulk could be subject to contamination from upper levels due to pedoturbation. From a macroscopic perspective, SU3, 4 and 5A seem not have been subject to major disturbance, but the action of rootlets, cracks due to posterior vertisolization processes or other pedogenic sedimentary inputs is not easily discernible [START_REF] Mayoral | Geoarchaeology and chronostratigraphy of the Lac du Puy intraurban protohistoric wetland[END_REF].

A detailed analysis of the paired dates on same samples (1-2, [START_REF] Trément | Un ancien lac au pied de l'oppidum de Gergovie (Puy-de-Dôme)[END_REF][START_REF] Jongmans | Soil formation in a Quaternary terrace sequence of the Allier, Limagne, France. Macro-and micromorphology, particle size distribution[END_REF][9][10] shows that bulk sediment provides slightly younger ages than microcharcoal or pollen. This could be due to a limited incorporation of modern carbon from above, but microcharcoal and/or pollen could also have a small reservoir effect (Ledger et al., 2015). This is especially the case with paired dates at the top of SU3 (1-2): bulk seems slightly too young respect the corresponding archaeological landmark (100-40 BCE), whereas microcharcoal is slightly too old. When comparing other paired dates, such as at the top of A c c e p t e d M a n u s c r i p t SU4 [START_REF] Trément | Un ancien lac au pied de l'oppidum de Gergovie (Puy-de-Dôme)[END_REF][START_REF] Jongmans | Soil formation in a Quaternary terrace sequence of the Allier, Limagne, France. Macro-and micromorphology, particle size distribution[END_REF] with archaeological landmarks (950-800 BCE), it appears that both bulk and pollen dates can be considered reliable. A similar case is evident for paired dates 9-10 at the base of SU3. Bulk dates therefore appear more reliable in SU4 (massive gleysol) that in SU3 (especially towards its top), maybe due to vertisolization processes in the unit and posterior disturbance related to SU2 [START_REF] Mayoral | Geoarchaeology and chronostratigraphy of the Lac du Puy intraurban protohistoric wetland[END_REF]. Bulk dates 6 and 11 in SU4 are then considered as broadly correct.

Dates 5 and 15 are older than other SU4 dates and deserve detailed analysis: nº 5 is clearly too old considering its position at 87-88 cm in the middle of SU4 (Fig. 2, Table 3). A potential cause for this would be lateral erosion of unit SU4b (see Fig 1 .), bringing to the centre of the basin pedogenic materials which could include some older carbon. Date 15 corresponds to the infilling of a storage pit after its abandonment (600-425 BCE), certainly using SU4 sediment extracted when digging a new neighboring pit [START_REF] Mayoral | Geoarchaeology and chronostratigraphy of the Lac du Puy intraurban protohistoric wetland[END_REF]). In the process older or younger carbon could have been incorporated, but the date is nevertheless roughly consistent with others in SU4.

The situation is more complicated in SU5A. Here, a comparison of dates 12 and 13 (macrocharcoal) from two levels of a structure dug in this SU, with quasi-identic date 14 (microcharcoal) and slightly younger date 19 (bulk), both from adjacent levels, indicates that bulk dating is relatively accurate in SU5A. Therefore dates 16, 17 and 18 can also be considered as broadly correct. However, these dates are all situated in profiles where SU5A is in gradual transition with underlying WB, and both are almost always difficult to distinguish. Dates 16-18 therefore cannot be considered an "exact" age of SU5A, but rather provide an indicative terminus post quem (TPQ) and terminus ante quem (TAQ) for its long-term formation since first weathering stages of basaltic bedrock, a process probably initiated in early phases of the evolution of the basin from a pseudo-sinkhole [START_REF] Mayoral | Geoarchaeology and chronostratigraphy of the Lac du Puy intraurban protohistoric wetland[END_REF].

In light of this uncertainty and the high lateral variability in stratigraphy, a direct transposition of these SU5A/WB dates to SU5A in core COR13-4 is inadvisable. Particularly given the presence of the underlying SU6A/B, which was absent in a majority of the dated profiles. Indeed, translocation of dates from elsewhere in SU5A to COR13-4 would imply ages older than 4.5-5 kyr. cal. BCE for the A c c e p t e d M a n u s c r i p t lower part of the palynological sequence (see Fig. 1). This would be in marked disagreement with pollen data and with well-known regional vegetation history. Indeed, assemblages from the base of COR13-4 (Ledger et al., 2015) are clearly coherent with a landscape typical of the Mid/Late Holocene boundary in the Auvergne region, which is characterized by recognizable vegetation dynamics such as rarefaction of Tilia pollen frequencies, absence of Ulmus and increasing trends of Abies and Fagus values, amongst other significant taxa [START_REF] Trément | Un ancien lac au pied de l'oppidum de Gergovie (Puy-de-Dôme)[END_REF][START_REF] Miras | Addressing the complexity of the paleoenvironmental impact of Prehistoric settlement and Protohistoric urbanism in the Auvergne Mountains (Massif Central, France)[END_REF].

This apparent 2000 yr mismatch between radiocarbon dates and vegetation history is undoubtedly related to the complex chrono-stratigraphic relation between SU5A/WB and SU6A/B. These stratigraphic ensembles are at the same time in lateral transition and overlaid depending on the previous (and irregular) topography (see Fig 1). This indicates that SU5A is non-isochronous, but rather temporally-and spatially-transgressive. The development of SU5A was likely dependent on topography, in a context of differentiated micro-scale sedimentary environments in high-and lowrelief areas of the basin. In this scenario, a first stage SU5A would have formed slowly on WB in higher areas, whereas SU6A/B deposited simultaneously in lower areas. In a second phase SU6A/B inputs decreased or eventually ceased, and SU5A extended to lower areas overlying them. In later stages (after SU5 deposition) the basin was leveled by sedimentary accumulation and chronostratigraphy becomes significantly more uniform (Fig. 1). The temporal envelope provided by radiocarbon dates in SU5/WB in high-topography areas corresponds not only to SU5A in the lower areas where COR13-4 is located, but probably also to SU6A/B. As a consequence, the younger date obtained in SU5A (nº18) is a reliable TAQ for its deposition in both low and high areas of the basin, and also for SU6A/B. The older date obtained in SU5A (nº16) must be contemporary with the first weathering stages of basalt in high-topography areas of the basin, and is likely close to the age of the base of SU6A/B in contact with the bedrock in lowtopography areas. Despite its uncertainties and limitations, this refined chrono-stratigraphic A c c e p t e d M a n u s c r i p t interpretation of basal units of the pedo-sedimentary sequence satisfactorily incorporates radiocarbon, stratigraphic and palynological evidence.

Ultimately, integration of all the radiocarbon assays with archaeological data allowed to constrain the maximum age ranges for SUs 6A/B, 5A, 4 and 3 in COR 13-4 (Fig. 2, down) which will be used to discuss multi-proxy data in this core. The inception of SU6A/B is unclear, although it is likely around 5200 cal. BCE. Its deposition is followed by SU5A until 3500 cal. BCE. SU4 dates range from 2000 to 800 cal. BCE approx., however considering that dates 15 and 5 could be subject of reservoir effect the interval 2000-1700 to 800 cal. BCE is proposed in order to integrate this uncertainty. SU3 age ranges from 500 cal. BCE approx. to 100-40 BCE. SU2 age, exclusively from archaeological data, is dated between 100-40 and 50-30 BCE. Two major hiatus or very slow sedimentation periods are outlined between 3500 and 2000-1700 cal. BCE, and between 800 and 500 cal. BCE. This chrono-stratigraphic framework highlights the non-linear nature of the sedimentary chronology in COR13-4 and nuances previous age-depth model used for palynological analysis, which included only 6 dates and was very imprecise for SU5A and 6A (Ledger et al., 2015). Only minor changes affect upper units (SU2, 3, 4), which are now better constrained, especially the base of SU3 (c.500 cal. BCE, implying a short hiatus after the top of SU4) and SU4 (c. 2000-1700 cal. BCE) which are both slightly younger than previously estimated. By contrast, SU5A and SU6A/B appear slightly older (c. 5200-3500 cal. BCE). Considering this, chronology of previous data (Ledger et al., 2015;[START_REF] Mayoral | Geoarchaeology and chronostratigraphy of the Lac du Puy intraurban protohistoric wetland[END_REF] for these SUs was revised in the discussion. The apparent hiatus between 3200 and 2000-1700 cal. BCE (Fig. 2) is certainly due to a very low sedimentation phase between the top of SU5A and the base of SU4A.

A c c e p t e d M a n u s c r i p t Chrono-stratigraphy resulting from the integration of dates grouped by SU and archaeological data (centre) is represented as maximum age ranges for each SU (down). Note that SU5 is not isochronous between higher and lower areas of the basin before its leveling. Note also the existence of chrono-stratigraphic hiatus or very low sedimentation phases (dotted lines).

Corent chrono-cultural periods follow [START_REF] Mayoral | Geoarchaeology and chronostratigraphy of the Lac du Puy intraurban protohistoric wetland[END_REF] Bell-Beaker period, MBA: Middle Bronze Age, GR: Gallo-Roman). Grey-shaded periods and grey lines indicate known settlements (dashed line: imprecise chronology or partial evidence). For detailed description of Stratigraphic Units and subunits, and archaeological data, see Table 3 (Appendix), and [START_REF] Mayoral | Geoarchaeology and chronostratigraphy of the Lac du Puy intraurban protohistoric wetland[END_REF].

A c c e p t e d M a n u s c r i p t

Micromorphology

General features

A detailed micromorphological description is synthetized in Table 2, and a gallery of outstanding features is shown in Figs. 3 to 5. The pedosedimentary sequence of the Lac du Puy is particularly complex due to the low accretion rate and the overlapping of successive pedological processes and features (gleyfication, vertisolization, illuviation, weathering, etc.) since the Neolithic. The coarse lithogenic fraction is strictly composed of volcanic materials such as basalt and scoria, given the limited lithology of the plateau [START_REF] Bouiller | Minute de la carte Géologique de la France à[END_REF][START_REF] Greffier | Aspects géomorphologiques et stabilité des versants au sud de Clermont-Ferrand[END_REF][START_REF] Nehlig | Les volcans du Massif central[END_REF]Mayoral et al., 2017). Chert or quartz occur as very small rock fragments (typically coarse silt to fine sand fraction) and in very small quantities, and can be difficult to distinguish from small plagioclases.

These small lithogenic fragments are not native in the volcanic geology of the plateau, and can only derive from inputs related to human activities. They are therefore considered as indicators of anthropogenic influence. Micromass is composed of abundant smectitic matrix as indicated by noticeable macroscopic swelling, but also clayey domains organization and a typical yellowish color under microscope [START_REF] Bullock | Handbook for soil thin section description[END_REF][START_REF] Loaiza | Manual de micromorfología de suelos y técnicas complementarias[END_REF]. This matrix is often dotted with dark opaque particles sometimes difficult to identify, generally magnetite and microcharcoal (<125um) or small organic debris.

Larger organic features are uncommon and macrofaunal activity traces are extremely rare. Clusters of small channels with regular diameter (100-200µm) and smooth walls, sometimes digitated or in fork, are present in some layers. Studies dealing with these morphologies [START_REF] Retallack | Soils of the past. An introduction to paleopedology[END_REF][START_REF] Kooistra | c e p t e d M a n u s c r i p t Micromorphological Features of Soils and Regoliths[END_REF] allowed us to identify them as traces of rootlet mats of grasslands. Silicified microfossils as phytoliths or sponge spicules (Fig. 4G) appear in some SUs: we interpreted them as indicators of grasslands and wet environments respectively following literature (Gutiérrez-Castorena A c c e p t e d M a n u s c r i p t and Effland, 2010; [START_REF] Vrydaghs | Opal Sponge Spicules[END_REF]. Masses of translucent filaments, similar to fungal hyphae but much smaller (0.5µm diameter, see Fig. 3I), were identified as silicified streptomyces-type bacteria (e.g. [START_REF] Néraudeau | Palaeontology of the upper Turonian paralic deposits of the Sainte-Mondane formation, Aquitaine basin, France[END_REF][START_REF] Néraudeau | Upper Cretaceous amber from Vendée, north-western France: Age dating and geological, chemical, and palaeontological characteristics[END_REF]. Development of these bacteria requires aerobic conditions and abundant organic matter [START_REF] Mayfield | Studies on the ecology of actinomycetes in soil IV. Observations on the form and growth of Streptomycetes in soil[END_REF][START_REF] Ringrose-Voase | Soil Micromorphology: studies in management and genesis[END_REF][START_REF] Gutiérrez-Castorena | Pedogenic and Biogenic Siliceous Features[END_REF], their presence was therefore interpreted as an indicator of surface horizons from a palaeosoil.

Pseudomorphs and alterorelics usually result from a high degree of minerals in situ-weathering (e.g. Fig. 3) and subsequent pedoplasmation processes [START_REF] Delvigne | Atlas of Micromorphology of Mineral Alteration and Weathering[END_REF][START_REF] Stoops | Pedoplasmation[END_REF]. We interpreted them as an indirect indicator of strong alteration processes in the soil profile due to hydrological variability, drainage conditions or mechanical constraints [START_REF] Fedoroff | Paléosols et sols reliques. Miskovsky JC Géologie la préhistoire[END_REF].

Weathering of scoria fragments in acid conditions is known to produce neoformation of aluminium silicate clays such as allophane coatings (AC) and infillings. This neoformation is characteristic of andic soils [START_REF] Baize | Référentiel Pédologique. Quae[END_REF] and has already been described in the region [START_REF] Jongmans | Micromorphology and mineralogy of weathering and neoformation phenomena in a quaternary terrace sequence of the Allier, Limagne, France[END_REF][START_REF] Anthony | Handbook of mineralogy[END_REF][START_REF] Jongmans | Soil formation in a Quaternary terrace sequence of the Allier, Limagne, France. Macro-and micromorphology, particle size distribution[END_REF][START_REF] Ringrose-Voase | Soil Micromorphology: studies in management and genesis[END_REF]. However, the Lac du Puy pedosedimentary sequence does not include andic horizons [START_REF] Mayoral | Geoarchaeology and chronostratigraphy of the Lac du Puy intraurban protohistoric wetland[END_REF]: therefore we interpreted these features (Fig. 5H andI) as inherited from other soil profiles with andic features outside the basin. Additionally, small and rounded fragments of clay coatings (CC) and allophane coatings (200-300µm) are present throughout the sequence. Taken together, these indicators can be interpreted as evidence of the erosion of mature surrounding soils with andic properties. Indeed, even clay-rich volcanic soils are especially prone to runoff erosion when exposed to excessively dry or wet conditions, and especially under cultivation [START_REF] Legrand | Spécificités des sols volcaniques du Massif Central: bénéfices et contraintes pour la gestion forestière[END_REF].

Clay translocation is quasi ubiquitous in the pedosedimentary sequence, however it is much more complex in lower SUs. Various generations of clay coatings (CC) and clay infillings (CI) with different with Fe oxides, seem to be the result of local redox processes and can be found in all the SUs; B)

Large, irregular, brownish nodules, with abundant organic fragments, come likely from upper superficial units, i.e. SU2 or SU1 (brown humic clay, see Fig. 2) and are translocated in underlying US3 and 4; C) Smectitic nodules, with abundant bright clayey domains and highly similar to SU4 matrix, come certainly from this unit (SU4); D) Greyish rounded aggregates form the matrix of lower units (SU5a and 6a). Their micromass, rich in microcharcoal, organic fragments and feldspar (Fig. 5)

suggests that they result from erosion of former organo-mineral horizons, belonging to the soils of the plateau surrounding the pond. Amongst these, some (E) are particularly rich in organic microdebris and charcoal, giving them a dark brown color and a relatively humic aspect.

All these anorthic or disorthic pedogenic aggregates in the profile, except those from SU5A and 6A, are reworked downwards due to vertisolization processes. In general terms vertisolization affects SU2 to 4 as indicated by prismatic macro-structure, grano-porostriation of the fine clay matrix, mixed and phytolith-rich matrix and ferromanganic nodules [START_REF] Kovda | Vertic Features[END_REF], however several phases could be superimposed due to these layer-crossing processes. To disentangle this complexity the established nodule types were used, as several are original from one specific layer. When appearing downwards in older layers, they served as Terminus Post Quem for a given vertisolization phase. Their vertical distribution in the profile allowed then to distinguish in relative chronological order several vertisolization phases. However, when nodules appeared in levels younger than their A c c e p t e d M a n u s c r i p t

Processes and hierarchy

After identification, micromorphological features have been grouped and interpreted as processes affecting one or more SUs, and finally organized in a relative chronology based on hierarchy concept [START_REF] Fedoroff | Palaeosoils and Relict Soils[END_REF], presented on Fig. 6.

SU6A and SU5A

Micromorphological results show that SU5A and 6A have highly similar composition and microstructure, and are mainly differentiated by post-depositional processes. Blocky subangular microstructure, overlaid to a granular microstructure exclusively composed by stacked greyish aggregates (D-and E-type) and coarse mineral fraction (Table 2, Fig. 5) suggests soil re-aggregation after deposition of granules and coarse fraction by intense and concentrated hydrosedimentary fluxes [START_REF] Fedoroff | Palaeosoils and Relict Soils[END_REF]Stoops et al., 2010b).

Volcanic minerals in these granules are strongly degraded (presence of pseudomorphs and hyaline allophanes), causing a differential enrichment in plagioclase probably due to long-term weathering [START_REF] Delvigne | Atlas of Micromorphology of Mineral Alteration and Weathering[END_REF][START_REF] Stoops | Pedoplasmation[END_REF], which can be interpreted as a result of prolonged pedogenic evolution. Some of these pedogenic aggregates (E-type) have dark brown micromass, very rich in small organic fragments and microcharcoal, suggesting an origin in organo-mineral or in humic soil horizons.

With these evidences, SU6A and 5A can be interpreted as pedosediment, i.e. the resulting deposit of erosion of upper and middle horizons of mature andic soils from the lower and upper parts of the plateau, transported to the basin by concentrated hydro-sedimentary fluxes as small and rounded pedogenic aggregates. Erosion of these upper horizons was probably followed by dismantling of Organic microparticles (mainly microcharcoal, <125u) are especially abundant in granules at the base of SU6A, and are associated to macrocharcoal (>125um) which are indicative of local fires [START_REF] Deák | Soils Disturbed by Vegetation Clearance and Tillage[END_REF]. This, together with the presence of chert and quartz subangular microfragments at the base of SU6A, indicate anthropogenic activity in these eroded soils around the basin.

Furthermore, the coarse fraction in SU6A and 5A shows a marked weathering gradient towards the top of SU5A. Indeed, the abundant weathered scoria fragments (alterorelics) are much more disaggregated and their pedoplasmation is generally more advanced upwards. This indicates that deposition of pedosediment and soil re-aggregation (see above) was followed by post-depositional in situ-weathering and pedoplasmation processes affecting especially SU5A and the base of SU4 (Fig. 8).

This evidence supports the development of a well-drained and stable palaeosoil level when sedimentary inputs ceased (see also SU4 analysis below).

Illuviation is abundant and complex in SU6A and 5A, with three main phases (see Table 2, Fig. 6 and Fig. 5B-E, G, and J-L) affecting both units. A first illuviation concerns the base of SU5A and SU6A.

Massive and poorly oriented CC and CI partially clogging the stacking voids of the pedosediment can be interpreted as syn-sedimentary "flood coatings". They are likely formed by a relatively fast downwards translocation of the fine fraction of the hydrosedimentary fluxes which deposited the granules [START_REF] Brammer | Coatings in seasonally flooded soils[END_REF][START_REF] Buurman | Clay illuviation and mechanical clay infiltration -Is there a difference?[END_REF]Fedoroff & Courty, 2002 ;[START_REF] Kühn | Textural Pedofeatures and Related Horizons[END_REF][START_REF] Vliet-Lanoë | Frost Action[END_REF].

The second generation of illuvial features, with abundant thin, well-oriented and microlaminated CC clog quasi completely remaining structural porosity in SU6A and especially in SU5A. Thin microlaminations of CC suggest stable, well-drained soil as it occurs for example under arboreal vegetation which controls illuviation (Fedoroff & Courty, 2002 ;[START_REF] Kühn | Textural Pedofeatures and Related Horizons[END_REF][START_REF] Sedov | Regoliths and Soils on Volcanic Ash[END_REF][START_REF] Vliet-Lanoë | Frost Action[END_REF]. Therefore it can be interpreted as a palaeo-Bt the relatively dark color of the D-type pedogenic aggregates rich in plagioclase. F: Micromass of a D-type pedogenic aggregate, rich in charcoal and in small reddish particles resulting from quasi-total weathering and pedoplasmation of volcanic materials (SU6A, OIL). G: Massive clayey infilling, moderately laminated, limpid and well oriented, between a basalt fragment and a dark pedogenic aggregate (SU6A, XPL). H: Strongly weathered scoria granule, with reddish pseudomorphs and abundant bluish-grey neoformed hyaline allophanes (white arrow) in the vacuoles (SU6A, OIL). I: same granule in PPL, note opaque volcanic minerals, and fine and dusty layered illuviation in the center of the scoria fragment (black arrow) vs.

limpidity of surrounding hyaline allophanes. J: microlaminated coating in crescent, between several basaltic fragments.

Each lamination has sharper and darker base. Over imposed Fe-Mn impregnation occurs posteriorly (SU5A, PPL). K: Dark and dusty clay coating in residual interstitial porosity, formed within illuvial clays between two pedogenic nodules (SU5A, PPL). L: same area in XPL, note high birefringence of smectitic clays despite a poor orientation.

A third phase of illuviation consists in abundant thin, roughly laminated, brownish and very dusty CC deposited above the textural features of the precedent phases, but also in biogenic voids developed within them. These « dusty coatings » (rich in dark opaque microparticles, including microcharcoal and small organic debris, e.g. Fig. 5K andL) indicate soil disturbance, even disappearance of vegetation cover previously developed. They are often linked to agricultural activity [START_REF] Jongerius | Some morphological aspects of regrouping phenomena in dutch soils[END_REF][START_REF] Macphail | A reply to Carter and Davidson's "an evaluation of the contribution of soil micromorphology to the study of ancient arable agriculture[END_REF][START_REF] Adderley | Anthropogenic Features[END_REF][START_REF] Kühn | Textural Pedofeatures and Related Horizons[END_REF][START_REF] Deák | Soils Disturbed by Vegetation Clearance and Tillage[END_REF], even if their interpretation remains complex and subject to controversy [START_REF] Carter | Diatom-oxygen isotope record from high-altitude Lake Petit (2200 m a.s.l.) in the Mediterranean Alps: Shedding light on a climatic pulse at 4.2 ka[END_REF][START_REF] Davidson | Micromorphological evidence of past agricultural practices in cultivated soils: the impact of a traditional agricultural system on soils in Papa Stour, Shetland[END_REF][START_REF] Macphail | A reply to Carter and Davidson's "an evaluation of the contribution of soil micromorphology to the study of ancient arable agriculture[END_REF][START_REF] Usai | Textural Pedofeatures and Pre-Hadrian's Wall Ploughed Paleosols at Stanwix, Carlisle, Cumbria[END_REF][START_REF] Fedoroff | Paléosols et sols reliques. Miskovsky JC Géologie la préhistoire[END_REF].

Redox pedofeatures, mainly superimposed to illuvial features or developed in residual porosity, indicate relatively important phases of water saturation [START_REF] Lindbo | Redoximorphic Features[END_REF] and changing hydrological conditions after the last illuviation phase. This suggests a progressive drainage deterioration gradually leading to typical reductic conditions.

SU4

Despite apparently homogeneous conditions at macroscopic level, micromorphological analysis revealed sharp vertical changes in microstructure and voids pattern throughout SU4. These changes are also noticeable in groundmass, coarse fraction and pedofeatures (see Table 2). Redox

A c c e p t e d M a n u s c r i p t pedofeatures show, in general terms, absence of ferric iron and persistence of saturated reducing conditions in all the SU4 [START_REF] Lindbo | Redoximorphic Features[END_REF], which can be interpreted as permanently high groundwater level. Superimposition of textural pedofeatures shows different phases of illuviation, whose characteristics (e.g. thin and limpid clay coatings) indicate that clay translocation process is generally weak and slow probably under dense vegetal cover [START_REF] Fedoroff | Paléosols et sols reliques. Miskovsky JC Géologie la préhistoire[END_REF][START_REF] Kühn | Textural Pedofeatures and Related Horizons[END_REF]. Based on micromorphological descriptions (Table 2), SU4 has clearly different characteristics in its lower (102-115 cm), central (80-102 cm) and upper (73-80 cm) sections.

Microstructure and redox pedofeatures of the lower section of the SU4 (102-115 cm, see Table 2)

suggest weak and relatively short saturations (Fedoroff & Courty, 2002 ;[START_REF] Lindbo | Redoximorphic Features[END_REF]Stoops, Marcelino, & Mees, 2010b). This indicates a relative degradation of porosity and drainage following SU5 well-drained conditions. Composition of coarse fraction (basalt and scoria)

suggests sedimentary inputs resulting of relatively low-intensity soil erosion affecting extensively the plateau.

Weathering is moderate to strong in all the SU4, but is especially intense at its base (105-115 cm), with abundant and very disaggregated alterorelics of scoria fragments coming from the upper slopes of the plateau. This indicates very strong in situ chemical and/or mechanical weathering [START_REF] Delvigne | Atlas of Micromorphology of Mineral Alteration and Weathering[END_REF]), which appears to be a layer-crossing process affecting also underlying SU5A. The advanced state of pedoplasmation of these alterorelics suggests prolonged exposition to surface bio-climatic agents [START_REF] Fedoroff | Paléosols et sols reliques. Miskovsky JC Géologie la préhistoire[END_REF]. A dense streptomyces mass indicates well-drained, aerobic conditions. These elements support the interpretation of the base of SU4 (105-115 cm) as the upper horizon of a well-drained palaeosoil level developing downwards into SU5A and 6A, which was certainly allowed by less detrital and wetter conditions in the basin.

Massive, limpid and poorly oriented CI indicate very strong illuviation under a stable surface with vegetation cover. These characteristics suggest that clay translocation may have occurred here faster that in the underlying SU5A. This is probably due to runoff inputs into the basin with abundant clayey A c c e p t e d M a n u s c r i p t suspended load, as previously described for soils subject to seasonal flooding [START_REF] Brammer | Coatings in seasonally flooded soils[END_REF][START_REF] Buurman | Clay illuviation and mechanical clay infiltration -Is there a difference?[END_REF]Fedoroff & Courty, 2002 ;[START_REF] Fedoroff | Palaeosoils and Relict Soils[END_REF][START_REF] Kühn | Textural Pedofeatures and Related Horizons[END_REF]. This thick illuviation phase quickly causes the clogging of the porosity at the base of the SU, sealing the soil profile and strongly degrading the drainage conditions.

This subsequently resulted in the rising of the watertable and the gleyfication of the profile: this process can be understood as secondary hydromorphy [START_REF] Begon | Sur la genese de sols limoneux hydromorphes en France[END_REF][START_REF] Jamagne | Les processus pédogénétiques dans une séquence évolutive progressive sur formations limoneuses loessiques en zone tempérée froide et humide[END_REF].

Microstructure and voids in the central section of the SU4 (80 to 102 cm, Table 2) show a collapsed porosity, very weak detrital inputs, and redox pedofeatures (Fe nodules, hypocoatings and coatings, Mn nodules), indicating a strong and quasi-permanent saturation [START_REF] Lindbo | Redoximorphic Features[END_REF]. This is interpreted as a result of an intensification of previously started drainage degradation. The beginning of wetter conditions is clearly marked by formation of several ferromanganic nodules c. 102 cm, superimposed to CC of SU5A. Clay illuviation features (CC and CI) are gradually whiter, thinner and less abundant upwards. These evidences support the interpretation of a microstructure closure and a weakening of illuviation processes due to the installation of gleyic conditions (Fig. 8).

Indicators of soil erosion inputs by runoff (coarse mineral grains) also become gradually weaker in central and upper parts of the SU4. An increase in the content of microcharcoal could be interpreted as erosion of soils in the catchment or as local fires on grasses, however the presence of some macrocharcoal (>125µm) between 93 and 102 cm, which are usually considered as local [START_REF] Deák | Soils Disturbed by Vegetation Clearance and Tillage[END_REF], supports the latter hypothesis.

The upper section of the SU4 (72-80 cm, see

SU3

The microstructure of SU3 (prismatic with grano-porostriation, see Table 2) These data suggest a frame of generalized erosion of evolved andic soils in all the plateau including the Lac du Puy itself and highly variable hydro-sedimentary conditions under human influence.

SU2

This unit has an abundant and heterogeneous volcanic coarse fraction rich in feldspar, including chert, pottery fragments (Fig. 4), allochtonous quartz grains and a micromass rich in charcoal, which point to detrital origin under strong human influence. Abundant dusty CC and CI are indicators of rapid illuviation from a bare or disturbed surface (Fedoroff & Courty, 2002 ;[START_REF] Fedoroff | Palaeosoils and Relict Soils[END_REF][START_REF] Deák | Soils Disturbed by Vegetation Clearance and Tillage[END_REF]. A marked lack of biogenic voids could be indicator of surface A c c e p t e d M a n u s c r i p t compaction and an absence of vegetation [START_REF] Adderley | Anthropogenic Features[END_REF][START_REF] Deák | Soils Disturbed by Vegetation Clearance and Tillage[END_REF]. Granoporostriation of the unit and presence of sponge spicules indicate that SU2 is at some point affected by temporary flooding [START_REF] Kovda | Vertic Features[END_REF][START_REF] Lindbo | Redoximorphic Features[END_REF], and suggests vertisolization processes. Some redox features superimposed to the granular structure (Fig. 4A) indicate subsequent moderate saturation phases. This unit had already been interpreted as backfill in precedent studies, based on its litho-stratigraphic characteristics (see introduction, and [START_REF] Mayoral | Geoarchaeology and chronostratigraphy of the Lac du Puy intraurban protohistoric wetland[END_REF].

Micromorphological features indicating detrital

Geochemical endmembers and selected elementary proxies

In general, the results of geochemical analysis of COR13-4 were well correlated to the different SU of the core. Nevertheless, the signal is relatively noisy due to complex pedo-sedimentary evolution of the sequence and the relatively homogeneous lithology of the plateau, making its interpretation far from straightforward. PCA shows a relatively good separation of the variables, with 70% of the variability explained by the two first components (represented by dimensions 1 and 2, Fig. 7A). Two endmembers of chemical elements can be identified, positively correlated respectively with first and second components of the PCA. The first endmember includes several lithogenic and detrital elements such as Ti, Zr, Fe, K, Si, Al, Rb and Pb, which show generally good correlation between each others in most sections of the core. The second endmember groups other elements such as Cu, Mn, Sr and Ca (Fig. 7A).

A c c e p t e d M a n u s c r i p t

The distribution plot shows a relatively clear separation of the dataset by SUs (Fig. 7B). SU pedosedimentary and micromorphological information (see previous sections) provide some clues for components and related endmembers interpretation. Taking into account characteristics of SUs, the primary dimension of the PCA seems to represents a gradient between lithogenic sedimentary influx (positive loadings, SU3 and 4) versus pedo-sedimentary influx (negative loadings, SU6B and SU1). The second dimension likely reflects finer grain-size deposits in saturated conditions (negative loadings, mainly SU4), versus better drained conditions or irregular saturations with coarser grain-size of deposits (positive loadings, mainly SU6B). Therefore the two endmembers represent very different sedimentary inputs: elements of the first endmember are likely related to relatively fine lithogenic detrital inputs, whereas elements of second endmember to coarser inputs richer in pedo-sediment.

Elements such as Ti, Zr, Si or Fe are lithogenic and representative of the dynamics of the first endmember along the core (Fig. 7C). Zr and Ti display a very noisy signal with relatively high values at the base of the core (SU6B, 6A, 5A), followed by a very sharp drop at the base of SU4. Their values then exhibit less variability and are lower in this SU, but tend to increase gradually to the top of the unit, and reach maximum values in SU3 before dropping again in SU2 and SU1. Zr, Ti and Fe are abundant in most volcanic rocks and derived detrital materials, however Zr tends to be more abundant in coarser sediment (and is often used to describe grain-size of flood layers, e.g. [START_REF] Corella | Annuallyresolved lake record of extreme hydro-meteorological events since AD 1347 in NE Iberian Peninsula[END_REF], whereas Ti and Fe are usually more related to fine detrital fraction [START_REF] Mielke | Composition of the Earth's crust and distribution of the elements[END_REF][START_REF] Salminen | FOREGS Geochemical Atlas of Europe, Part I* Background Information, Methodology, and Maps[END_REF][START_REF] Davies | Micro-XRF Core Scanning in Palaeolimnology: Recent Developments[END_REF]. Considering the basaltic and scoriaceous geology of the catchment of the Lac du Puy, we interpret Zr, Ti and Fe as indicative of lithogenic detrital inputs, and propose to use the Zr/Fe ratio as a proxy of an increase in their grain-size. This interpretation of the ratio appears consistent with the grain-size observed in litho-stratigraphy (Fig. 2, Table 3). weathering of basaltic rock. Colloidal Si is known to be mobile in wet, organic rich and acid environments [START_REF] Anthony | Handbook of mineralogy[END_REF][START_REF] Kabata-Pendias | Trace elements in soils and plants[END_REF][START_REF] Salminen | FOREGS Geochemical Atlas of Europe, Part I* Background Information, Methodology, and Maps[END_REF]. Anoxic degradation of organic matter can also lead to a low pH [START_REF] Osman | Soils: Principles, properties and management[END_REF][START_REF] Blume | Scheffer/Schachtschabel Soil Science[END_REF], making concentrations of biogenic silica more stable (e.g. phytoliths, or sponge spicules observed in thin section). These considerations suggest that exceptionally high values of Si in the sequence can be interpreted as a proxy of reducing conditions.

Fe is also a particular case, as it is an element very sensitive to redox conditions, especially mobile in very wet environments [START_REF] Salminen | FOREGS Geochemical Atlas of Europe, Part I* Background Information, Methodology, and Maps[END_REF]. This suggests that although a part of Fe in the Lac du Puy is detrital, Fe concentrations are also increased in units with reducing conditions (e.g. SU4, Fig. 7C). Mn is also sensitive to changes in soil moisture, but is more readily mobilized in less saturated conditions than Fe, and is then a good marker of oxic conditions [START_REF] Lindbo | Redoximorphic Features[END_REF][START_REF] Kylander | High-resolution X-ray fluorescence core scanning analysis of Les Echets (France) sedimentary sequence: new insights from chemical proxies[END_REF]. The very sharp peaks in SU3 (Fig. 7C), a unit characterized by vertic processes, suggest that high Mn values can be due to ephemeral flood and drying cycles. However, as Mn can also be of lithogenic origin, we propose to use Mn/Ti ratio to discriminate this hydrological signal.

Furthermore, given the opposite sensitivity to redox conditions in the Lac du Puy of Fe and Mn, their ratio could therefore be a proxy very sensitive to redox variability and especially the intensity of reducing conditions (e.g. [START_REF] Haberzettl | Lateglacial and Holocene wet-dry cycles in southern Patagonia: chronology, sedimentology and geochemistry of a lacustrine record from Laguna Potrok Aike, Argentina[END_REF][START_REF] Cuven | Mid to Late Holocene hydroclimatic and geochemical records from the varved sediments of East Lake, Cape Bounty, Canadian High Arctic[END_REF][START_REF] Corella | The 1.5-ka varved record of Lake Montcortès (southern Pyrenees, NE Spain)[END_REF]), which appears consistent with previous litho-stratigraphic and micromorphological observations.

Ca variability provides information of the dynamics of the second endmember: its values are especially high at the base of SU6B, and then gradually decrease upwards in SU6A and 5A (Fig. 7C). A drop is also clearly visible at the base of SU4, followed by slowly and regularly increasing values from SU4 to SU1. In volcanic contexts, Ca often derives from the chemical weathering of plagioclases [START_REF] Wedepohl | Handbook of geochemistry[END_REF][START_REF] Mielke | Composition of the Earth's crust and distribution of the elements[END_REF][START_REF] Salminen | FOREGS Geochemical Atlas of Europe, Part I* Background Information, Methodology, and Maps[END_REF]. This process can result in relative Caenrichment of volcanic soils [START_REF] Kabata-Pendias | Trace elements in soils and plants[END_REF][START_REF] Salminen | FOREGS Geochemical Atlas of Europe, Part I* Background Information, Methodology, and Maps[END_REF]. At the scale of the basaltic plateau of Corent, we propose to interpret high Ca values of soils as the result of their where micromorphological analysis revealed abundant pedosediment (see 3.2.). Ca/Fe can hence be seen as an indicator of soil erosion in the plateau (especially if it covariates with other proxies of detrital inputs), however it could also indicate in situ pedogenetic processes.

Finally MS (see Fig. 7C), a measurement sensitive to magnetization, can be sensitive to different natural processes including soil genesis, fires, detrital influx or volcanic fallouts [START_REF] Dearing | Magnetic susceptibility[END_REF][START_REF] Dalan | Susceptibility[END_REF]. In the basaltic context of the Lac du Puy, MS signal is likely sensitive to fine detrital influx (partly obscured by coarse fraction rich in magnetite grains). However, given high values in SU5A and base of SU4A, it could also be indicating pedogenic sediment influx and/or local soil genesis. MS can hence be combined with Zr/Fe and Ca/Fe to interpret complex processes where detrital lithogenic inputs of variable grain-size, pedosediment influx and local soil genesis are entangled.

Following the interpretations and proposed elementary ratios developed above, a clear differentiation between SUs can be detected, indicating broadly different environmental dynamics between lower (SU5A and 6A/B), middle (SU4 and 3) and upper (SU2 and 1) sections of the sequence (Fig. 7C).

Pedogenic inputs are high (Ca/Fe) but diminishing upwards in SU6A and 6B, as shown by micromorphological analysis. Relatively dry conditions seem permanent through the SU (Fe/Mn, Mn/Ti). MS increase and lower values of Zr/Fe and Ca/Fe in SU6A suggest less pedosedimentary and more lithogenic inputs in the basin, in slightly wetter conditions (higher Fe/Mn and Si). However, the highly detrital nature of the unit demands caution in data interpretation. SU5A and the base of SU4

show stronger lithogenic detrital inputs and pedogenic influx signal (high MS, Zr/Fe, Ca/Fe). This is roughly consistent with detrital inputs followed by pedogenesis and Bt horizon formation shown by A c c e p t e d M a n u s c r i p t micromorphological analysis (see 3.2). Changing redox conditions suggest a relatively dry phase followed by wetter conditions from the top of SU5A (sharp increase of Fe/Mn and fall of Mn/Ti c. 120 cm), also consistent with litho-stratigraphic and micromorphological data.

In the middle and upper part of SU4, geochemical proxies show a clear break: ratios indicating lithogenic and pedogenic detrital inputs fall dramatically and remain quasi-stable, with only a faint increase towards the top of the SU, and the fine fraction becomes dominant (low Ca/Fe, Zr/Fe, and MS). Hydrological conditions become highly and quasi-permanently saturated (Fe/Mn, Mn/Ti), and reductic (gleyic) processes broadly dominate save for two short slightly drier phases, one intercalated in the middle-upper section of the SU (92-86 cm approx.) and the other at its top (75-72 cm), associated with minor detrital pulses. Lithogenic and pedogenic detrital inputs increase sharply at the transition to SU3 (Zr, Ti, Ca/Fe, Zr/Fe, MS), and continue to rise gradually upwards. The general trend towards less reducing (drier) conditions is punctuated by very sharp drying episodes recorded in the upper part of the unit (peaks of Mn/Ti), consistent with recurrent seasonal flooding and vertisolization observed in thin section (see 3.2). Geochemical data are lacking for SU2, and SU1

represents subactual to actual pedo-sedimentary dynamics.

A c c e p t e d M a n u s c r i p t ) and XRF values in counts per second (CPS).

Ratios are dimensionless.

A c c e p t e d M a n u s c r i p t

4-Discussion

4.1 The Early and Middle Neolithic (Mid-Holocene period)

SU6A/B and SU5A likely date to the late Early and Middle Neolithic period (c. 5200-3500 cal. BCE, Fig. 8). The period from the base of SU6B is characterized by marked detrital influx including abundant scoria and pedological aggregates, suggesting significant erosion across the plateau. The lack of palynological and micromorphological data, as well as chronological data limits interpretation for this period, which is based on geochemical and sedimentological proxies. Detrital influx increases toward the top of SU6B accompanied by slightly moister conditions. However, the pedogenic fraction is less abundant suggesting that mature andic soils of the plateau were gradually eroded and replaced by younger, more lithogenic materials.

Numerous proxies (Ca/Fe and Zr/Fe ratios, MS in Fig. 8) suggest a second phase characterized by a slight reduction in soil erosion and detrital inputs (SU6A) accompanied by a minor increase in moisture (Fe/Mn, Mn/Ti). Micromorphology indicates recurrent flooding of the basin due to intense hydro-sedimentary fluxes from the plateau. These inputs, rich in detritic and pedogenic elements embedded in fine clayey matrix, imply that despite a relative lull the erosion of soils of the plateau remains intense. The presence of allochtonous microfragments of chert and quartz, accompanied by micro and macrocharcoal indicate anthropogenic activity close to the basin. Palynological data (Fig. 8) indicate the possibility of local cereal cultivation associated with an opening of the local pine woodlands, which were developed around the depositional basin, from the beginning of SU6A as

shown by lower half of LPAZ (Local Pollen Assemblage Zone) COR-1b (Ledger et al., 2015).

The end of the period (SU5A) is characterized by renewed soil erosion (higher values of Ca/Fe, Zr/Fe, MS and Glomus), also evidenced by micromorphological analyses (abundant pedo-sedimentary A c c e p t e d M a n u s c r i p t aggregates). This suggests an increase of the anthropogenic impact on soils. Palynological data indicate an intensification of woodland clearance (decrease of arboreal pollen, increase of Poaceae) perhaps associated with pastoralism (presence of coprophilous fungi), corresponding to the upper half of LPAZ COR-1b and start of COR-2a (Ledger et al., 2015, see Fig. 8).

These geoarchaeological and palaeonvironmental data reflect a more or less continuous impact on soils and maintained erosion during the Late Early and Middle Neolithic. The opening of its first phase (SU6B) c. 5200 cal. BCE fits well with the earliest evidences of Neolithic activity at Corent (5200 to 4300 BCE, [START_REF] Poux | Corent, Fouille pluriannuelle 2014-2016[END_REF], and suggests soils of the plateau were affected by human activities from their beginning. During later phases (SU6A, 5A), micromorphological and palynological data indicate that soil erosion and detrital inputs are more certainly linked with human activities such as forest clearance and agropastoralism. The two separated episodes of impact on vegetation detected by previous palynological study (Ledger et al., 2015) become here more clearly differentiated as they roughly correspond to SU6A and SU5A. Due to chronological uncertainties, it is difficult to say if the first is associated with Early or Middle Neolithic impacts. However, the second and more intense impact episode affecting vegetation and soils (SU5A) seems more clearly related to the Middle Neolithic fortified camp dated 4200-3700 BCE approx. [START_REF] Poux | Corent, Rapport de fouille programmée[END_REF][START_REF] Poux | Corent, Fouille pluriannuelle 2014-2016[END_REF]. This latter phase can be seen as the culmination of long-term environmental impact history started in the Early Neolithic.

Recent to Late Neolithic and transition to Early Bronze Age (Middle to Late

Holocene shift)

The period covering Recent to Late Neolithic and the transition to the Early Bronze Age corresponds to the base of SU4 in the COR13-4 sequence, between 117,5 and 102 cm approx. (c. 3500 to 2000-1700 cal. BCE, see Fig. 8). Two different phases can be distinguished within this relatively short core A c c e p t e d M a n u s c r i p t section. In its lower half, micromorphological and litho-stratigraphic data show increased landscape stability, however geochemical data temper this interpretation, suggesting continued mineral and pedogenic detrital inputs (MS, Ca/Fe, Zr/Fe, Glomus) while soil hydrological conditions become more saturated (Fe/Mn, Mn/Ti, Fig. 8). Palynological data point to continued opening of the landscape and general disturbance (peak of Poaceae and presence of apophytes; end of COR-2a in Fig. 8, see also Ledger et al., 2015). Relatively mild climatic conditions prevailed during the Recent and Late Neolithic in Western Europe, although bounded by two Rapid Climate Change periods of 5.6-5.3 and 4.2-3.9 kyr. cal. BP [START_REF] Mayewski | Holocene climate variability[END_REF][START_REF] Magny | Tripartite climate reversal in Central Europe 5600-5300 years ago[END_REF][START_REF] Wang | Abrupt climate changes of Holocene[END_REF][START_REF] Carozza | Society and environment in Southern France from the 3rd millenium BC to the beginning of the 2d millenium BC a tipping point?[END_REF]. Thus, increased saturation of the basins soils was unlikely to have been climatically driven, but rather a result of gradual soil profile sealing and slight drainage deterioration due to sedimentary accumulation.

The upper half of the 117.5-102 section shows clearly different dynamics. Despite a data hiatus, geochemical and sedimentological proxies (MS, Zr/Fe, Ca/Fe, Fig. 8) indicate reduced lithogenic and pedogenic detrital inputs. This decrease is also supported by a reduction in the content of Glomus fungal spores, which are indicative of soil erosion (Ledger et al. 2015). Soil saturation remains moderate and comparable to the previous period. Micromorphological analysis revealed that this phase corresponds to the development of a well-drained palaeosoil (top of surface horizon c. 102 cm, Fig. 6 and Fig. 8) certainly under vegetal cover, consistent with palynological data which indicate local pine and oak woodlands recovery and decline of human activity suggested by the fall of Poaceae and apophytes (LPAZ COR-2b in Fig. 8, see also Ledger et al., 2015). The high degree of weathering of coarse fraction in the profile of this palaeosoil, and the well-developed clay illuviation features below its upper horizon (see Fig. 6) are traits usually needing several centuries or even millennia to develop (Courty & Fedoroff, 2002 ;Fedoroff & Courty, 2002 ;[START_REF] Kühn | Textural Pedofeatures and Related Horizons[END_REF]. This strongly suggests that this palaeosoil remained stable (and so the surrounding environmental conditions) over a long period, implying a marked demise of anthropogenic impact in the Lac du Puy and in the surrounding plateau. This palaeosoil is also crucial to understand the basin [START_REF] Daugas | Une fosse à inhumations néolithique à Corent (Puy-de-Dôme)[END_REF]Milcent et al., 2014b;[START_REF] Poux | Corent, Fouille pluriannuelle 2014-2016[END_REF], roughly dated c. 3000-2400 BCE.

After this, archaeological data become scarcer as the site is all but abandoned from the end of the Bell-Beaker period (c. 2400-2200 BCE), until the first centuries of the Bronze Age [START_REF] Poux | Corent, Fouille pluriannuelle 2014-2016[END_REF].

The rather warm and dry climate of the Middle Holocene period prior to the 4.2 kyr BP climatic event [START_REF] Wanner | Mid-to Late Holocene climate change: an overview[END_REF][START_REF] Carozza | Society and environment in Southern France from the 3rd millenium BC to the beginning of the 2d millenium BC a tipping point?[END_REF]Bini et al., 2019;[START_REF] Carter | Diatom-oxygen isotope record from high-altitude Lake Petit (2200 m a.s.l.) in the Mediterranean Alps: Shedding light on a climatic pulse at 4.2 ka[END_REF], suggests that the primary cause of this marked abandonment has to be found in social dynamics (e.g. local changes in settlement pattern ), perhaps combined with pronounced andic soils deterioration after centuries of strong soil erosion due to anthropogenic activities.

The Bronze Age

Central and upper sections of SU4 (102-83 and 83-72 cm respectively in COR13-4) broadly correspond to the Bronze Age (BA), perhaps excepting its first centuries (2000/1700 to 800 cal. BCE

A c c e p t e d M a n u s c r i p t approx.). The distribution of radiocarbon dates on COR13-4 (Fig. 2 and Table 1) indicates that central section of SU4 represents likely end of Early and Middle Bronze Age, whereas upper section of the unit records roughly the Late Bronze Age.

From the opening of central section of SU4 (102-83 cm in COR13-4, Early to Middle Bronze Age) major hydro-sedimentary changes occur: sedimentary inputs become dominated by the clayey fraction, and water saturation of the soils of the basin becomes permanent (high Fe/Mn, low Mn/Ti in Fig. 8). Despite the apparently low activity of sediment transport indicators (MS, Zr/Fe, Glomus), micromorphological analysis indicates sedimentary sources extended through the plateau. This suggests generalized erosion requiring, paradoxically, increased energy to ensure sedimentary connectivity and sedimentary transfer from upper to lower areas of the plateau. Micromorphological features also indicate sudden changes affecting soils of the basin (dusty coatings, macrocharcoal), likely anthropogenic disturbance of soils, land clearing and local fires [START_REF] Deák | Soils Disturbed by Vegetation Clearance and Tillage[END_REF]. Towards the top of the central section of SU4, micromorphology and geochemistry suggest that reductic conditions decrease with more irregular and oscillating water saturation (Fe/Mn, Mn/Ti, Fig. 8), and a slight increase of detrital inputs intensity (MS, Zr/Fe, Ca/Fe).

Palynological data from previous studies indicate here a second significant episode of woodland clearance (Arboreal Pollen (AP) falls to minimum values, Fig. 8) probably fire-induced (substantial rise of microcharcoal concentrations throughout the SU) and evidences of an arable and pastoral agriculture (maximum values of Cerealia pollen-types, pollen evidences from weeds, significant rise of coprophilous fungi, see LPAZ COR-3a in Fig. 8, and also Ledger et al., 2015). Towards the end of the phase, pronounced landscape opening after a minor woodland recovery and sustained agricultural activity (continuous presence of cereal pollen type) are accompanied by a minor microcharcoal peak (LPAZ COR-3b in Ledger et al., 2015).

Geoarchaeological and palaeoenvironmental indicators co-variation suggests that human activity increased at Corent during the end of Early and Middle BA: this situation runs contrary to the A c c e p t e d M a n u s c r i p t regional pattern for this period, where climatic deterioration [START_REF] Burga | Swiss localities of early recognized Holocene climate oscillations: Characterization and significance[END_REF][START_REF] Siklosy | Middle bronze age climate change recorded in a Hungarian stalagmite : triggering by volcanic activity ?[END_REF][START_REF] Gauthier | Le lac du Bourget ( Savoie , France ) à l ' Age du Bronze : végétation , impacts anthropiques et climat[END_REF]Magny et al., 2009) seems contemporaneous to a marked cultural decline and re-location of sites in peripheral areas respect to the previous settlements (e.g. [START_REF] Berger | Nouveau regard sur La dynamique des paysages et l'occupation humaine à L'Âge du Bronze en moyenne vallée du Rhône[END_REF][START_REF] Pétrequin | xve siècle av. J.-C. : la reprise de la croissance démographique dans le Jura[END_REF]Milcent et al., 2014b). Understanding the reasons for these particular dynamics at Corent, perhaps related to its hilltop situation, would require more robust archaeological and palaeoenvironmental data at the scale of the southern Limagne region.

The discrepancy between probable important impacts on soils across the plateau and extremely lowenergy hydrosedimentary signal in the Lac du Puy, which persists in all the SU4, is another major issue raised by our results. It can only be explained by a constrained sedimentary connectivity, i.e.

restricted to finer particles. A hedge-type structure bordering the basin, linked to specific pastoral land use of this wet area is therefore plausible, perhaps similar to the current situation. It is worthwhile noting that it is also during the BA when the first traces of agricultural plots demarcations are noted in France [START_REF] Carozza | Les travaux et les jours : la lente transformation des sociétés paysannes de l'âge du Bronze en France métropolitaine[END_REF]. Even a simple vegetal structure can have efficiently filtered hydrosedimentary inputs into the basin [START_REF] Rey | Efficacité des ouvrages de génie biologique pour le piégeage des sédiments dans des ravines incisées dans des marnes (Alpes du Sud, France)[END_REF]. It likely caused that exclusively fine suspended load supplied the basin, despite probable intensive impacts on surrounding soils and enhanced erosion and runoff. However contribution of other factors to this buffering, such as improved agropastoral management (e.g. reduced splash erosion on grasslands) since the Late Neolithic [START_REF] Barker | Prehistoric Farming in Europe[END_REF][START_REF] Rösch | The history of crops and crop weeds in south-western Germany from the Neolithic period to modern times, as shown by archaeobotanical evidence[END_REF][START_REF] Rösch | Land use and food production in Central Europe from the Neolithic to the Medieval period: change of landscape, soils and agricultural systems according to archaeobotanical data[END_REF]) cannot be excluded.

These hydrosedimentary inputs rich in fine fraction are also presumably the cause of soil porosity clogging shown by micromorphological analysis. Clays deposited in the basin were probably also illuviated into underlying soil porosity, already partly obstructed by previous illuviation phases (see 4.1 and 4.2). The consistent rise of microscopic charcoal from the base of SU4 (Fig. 8) and micromorphological evidence of local fires (macrocharcoal) indicate that burning was probably used to maintain open grasslands for agro-pastoral activity in the basin, a practice whose efficiency is attested by experimental archaeology [START_REF] Pavelka | AN INTERDISCIPLINARY TILLAGE EROSION EXPERIMENT : ESTABLISHING A NEW FIELD IN GRASSLANDS WITH RECONSTRUCTED ARD PLOUGH OF THE BRONZE AGE -IRON AGE[END_REF]. This kind of management could have A c c e p t e d M a n u s c r i p t favored clay illuviation [START_REF] Slager | Soil formation in archaeological pits and adjacent loess soils in Southern Germany[END_REF][START_REF] Huisman | Ashes to ashes, charcoal to dust: Micromorphological evidence for ash-induced disintegration of charcoal in Early Neolithic (LBK) soil features in Elsloo (The Netherlands)[END_REF][START_REF] Deák | Soils Disturbed by Vegetation Clearance and Tillage[END_REF].

This certainly resulted in complete obstruction and collapse of soil porosity, drainage deterioration, and subsequent development of vertic conditions, quickly followed by true reductic, permanently saturated conditions. Hence, our data suggest that agropastoral management practices since the end of Early BA have indirectly but strongly contributed to the sealing of the soil profile and provoked a marked change in environmental conditions in the basin. Increasingly wetter conditions could have encouraged this kind of pastoral management, then generating a feedback effect.

In the upper section of SU4 (83-72 cm in COR13-4, Late Bronze Age, Fig. 2 Ledger et al., 2015). However, at the end of this phase (Late BA3, 9 th century BCE) indicators are again similar to the top of central section of SU4, with suddenly drier conditions and slightly higher detrital inputs, but also biological activity on stable and aerobic soils revealed by micromorphology (see 3.2). Palynology notes a slight woodland increase, agricultural practices are less intensive or are more distant from the Lac du Puy basin, and pastoralism markers such as coprophilous fungi slightly increase, suggesting the local presence of livestock in the basin (LPAZ COR-3d in Ledger et al., 2015).

Therefore, two similar cycles of palaeoenvironmental impact can be distinguished during the BA, despite a relatively imprecise chronology. The first one (central section of SU4, 102-83 cm in COR13-4) covers likely the end of Early and Middle Bronze Age, and the second one the Late Bronze Age.

Both start with impacts linked to pastoral and arable agriculture, while archaeological traces of human activity remain weak for these periods (Milcent et al., 2014b ;[START_REF] Poux | Corent, Fouille pluriannuelle 2014-2016[END_REF]. Then, impacts on the basin increase with a roughly similar signature (dryer conditions, increased detrital inputs), during the end of the Middle Bronze Age (c. 1450-1300 BCE), and more clearly in the Late Bronze Age 3 (950-800 BCE). Situation of the end of LBA has been connected with extensive and dense settlement developed in the plateau, including an extended archaeological layer in the centre of the Lac du Puy (Milcent et al., 2014a;Ledger et al., 2015;[START_REF] Mayoral | Geoarchaeology and chronostratigraphy of the Lac du Puy intraurban protohistoric wetland[END_REF]. Considering that environmental conditions of the basin appear dependent on human activity, these parallel impact signatures allow proposing that relatively large settlement on the plateau perhaps developed during the end of the Middle BA. This hypothesis suggested by our results is also supported by recent archaeological finds suggesting a hitherto underestimated scale of settlement in the middle BA at Corent, even if the period remains poorly known [START_REF] Poux | Corent, Fouille pluriannuelle 2014-2016[END_REF]. This highlights how palaeoenvironmental studies in "site-proximal" contexts can efficiently complement more classical archaeological approaches.

The Iron Age and the Romanization

The Iron Age approximately corresponds to SU3 in COR13-4 (Fig. 8). However, radiocarbon probability distribution associated with results from previous works (Fig. 2) are indicative of a hiatus in the pedo-sedimentary sequence. This encompasses most of the Hallstatt period, and is associated with the construction of a battery of storage pits (c. 1000 structures estimated) in the VI th or V th century cal. BCE [START_REF] Mayoral | Geoarchaeology and chronostratigraphy of the Lac du Puy intraurban protohistoric wetland[END_REF]. Sedimentary accumulation restarted only after this disturbance of the basin. Therefore SU3 records only the end of the Hallstatt and La Tène periods (500 to 100-40 cal. BCE aprox.). Additionally, the low chronological resolution, poor quality and homogenization of the sedimentary signal (see 3.2), together with anthropogenic destabilization of hydrosedimentary functioning of the basin associated with the pits excavation [START_REF] Mayoral | Geoarchaeology and chronostratigraphy of the Lac du Puy intraurban protohistoric wetland[END_REF] imposes caution on interpretation. In general terms, sedimentological and micromorphological data (see 3.2) suggest a strong increase in discontinuous hydrosedimentary detrital inputs arriving into the A c c e p t e d M a n u s c r i p t basin. Considering the maturity of observed vertic pedofeatures of SU3 [START_REF] Kovda | Vertic Features[END_REF], active vertisolization due to these discontinuous inputs occurred for at least four to five centuries.

Two phases with different trends can nevertheless be distinguished in SU3. The first one starts from the base of the SU: the geochemical signal becomes much more detrital than in SU4, and richer in the pedogenic fraction (higher values of MS, Zr/Fe, Ca/Fe, Fig. 8). Chemical proxies indicative of redox (Fe/Mn, Mn/Ti) suggest generally drier and less saturated conditions than in previous phases.

Palynological data point to a slight vegetation recovery despite continued evidence of anthropogenic activity such as microcharcoal or pollen of disturbance-related plants. However, strong postdepositional disturbances such as marked erosion or seasonal flooding indicated by increased records of algal spores of Zygnema-type (and also supported by presence of sponge spicules, see 3.2) make interpretation complex (LPAZ COR-4 in Ledger et al., 2015). Suddenly increased hydrosedimentary activity, soil erosion and intermittent hydrology from our results can be considered as specific environmental consequences of strong disturbance induced by Hallstatt settlement and battery of storage pits excavation, followed by their rapid abandonment [START_REF] Mayoral | Geoarchaeology and chronostratigraphy of the Lac du Puy intraurban protohistoric wetland[END_REF]. In addition, the abundance of microcharcoal at the base of SU3 noted both by palynology and micromorphology (Fig. 8, Table 2) can be interpreted as traces of dismantling of first Iron Age soils from the archaeological site, likely destroyed by fire (Milcent et al., 2014b). Anthropogenic pressure weakens during this period, consistent with partial site abandonment during late Hallstatt and early La Tène periods [START_REF] Poux | Corent, Fouille pluriannuelle 2014-2016[END_REF]. However, the persistence of these hydrosedimentary dynamics over several centuries suggests a relative continuity of human impacts on soils.

In a second phase, detrital fluxes intensify towards the top of SU3 including coarser particles and pedogenic fractions coming from distant areas of the plateau, indicating intense and widespread soil erosion (high values of MS, Zr/Fe, Ca/Fe, Glomus fungal spores, microcharcoal, fragments of textural pedofeatures and scoria fragments). Some markers of human activity such as bone or pottery fragments (see Fig. 4) appear for the first time in the sequence. Micromorphology and geochemical A c c e p t e d M a n u s c r i p t

proxies suggest short and violent cycles of saturation (flooding) and drying of soils. Intensified and extended erosion processes and irregular hydro-sedimentary activity are indicative of renewed anthropogenic disturbance and intensified impacts on soils and hydrology. This signal is consistent with the gradual emergence of the huge Gallic oppidum covering the entirety of the plateau towards the end of the Iron Age [START_REF] Poux | Corent, Voyage au coeur d'une ville gauloise[END_REF]. Surprisingly, only the margins of the Lac du Puy are occupied during this period [START_REF] Mayoral | Geoarchaeology and chronostratigraphy of the Lac du Puy intraurban protohistoric wetland[END_REF]. Geoarchaeological results from this study suggest that the basin probably formed part of the sanitation/drainage system of the oppidum. At this time, the Lac du Puy was a marginal occupation zone, affected by repeated concentration of hydro-sedimentary fluxes caused by increased runoff and erosion, likely related to increased sedimentary connectivity and massive soil disturbance and artificialization in the plateau.

Interpretation of environmental dynamics in SU2 (dated 100-40 to 50-30 cal. BCE) is hindered by a gap in geochemical data, which only permits us to speculate on generally drier conditions and increased pedogenic inputs than in the preceding phase (Fig. 8). Micromorphology depicts a rather dry, compacted and bare surface, where dusty and quick illuviation occurred following deposition of sediment made of pedogenic aggregates, coarse lithogenic fraction and including abundant markers of anthropization (ceramic, bones). These features are typical of both massive deposits of pedosedimentary materials and anthropogenic deposits [START_REF] Fedoroff | Palaeosoils and Relict Soils[END_REF][START_REF] Deák | Soils Disturbed by Vegetation Clearance and Tillage[END_REF]. Thus, geochemical and micromorphological data strongly support the previous hypothesis derived from field evidence, i.e. artificial and massive backfill of the basin probably accompanied by drainage works in the Late Iron Age or early Roman period [START_REF] Mayoral | Geoarchaeology and chronostratigraphy of the Lac du Puy intraurban protohistoric wetland[END_REF], certainly to remediate the degraded situation of the wetland and extend the urban space. The post-Antiquity evolution of the basin is probably represented by SU1, however a lack of analytical and chronological data, and the interaction with present pedological activity prevent any detailed interpretation.

A c c e p t e d M a n u s c r i p t ). AP: Arboreal Pollen. NAP: Non-Arboreal-Pollen. Pollen data are given as % of TLP (Total Land Pollen) -Lactuceae.

A c c e p t e d M a n u s c r i p t

5-Conclusions

The general objective of this paper was to analyze long-term human-environment interactions at the Lac du Puy of Corent, a small wetland with a unique intra-urban setting within the protohistoric site of Corent. Building on previous studies, this paper employed a multi-proxy geoarchaeological approach of pedo-sedimentary archives of the Lac du Puy to address unresolved research questions, mainly concerning changing pedo-sedimentary processes and environmental conditions under human influence. New micromorphological, geochemical and sedimentological results were combined with existing palynological data within a refined chrono-stratigraphic framework.

Micromorphological data in particular were used to disentangle the pedo-sedimentary processes, whose traces were superimposed in the complex pedo-sedimentary record. Geochemical proxies provided valuable and complementary data where micromorphology was equivocal, and pollen evidence was especially useful when discussing the impact of human activities on vegetation and soils. Data obtained in this, and previous studies were combined to provide a comprehensive understanding of complex human-environment interaction around the Lac du Puy since the Neolithic.

Here we have significantly refined previous interpretations, revealing anthropogenic impacts on vegetation, soil erosion and geomorphological processes probably began in the Early Neolithic, contemporary with the first traces of human activity on the plateau. These impacts gradually intensify until a shift at the end of the Middle Neolithic, associated with the development of a fortified settlement in the plateau.

In the Recent and Late Neolithic, anthropogenic impacts on soils tend to decrease and ultimately cease as human traces in the site become rare. Results of this study suggest that this abandonment is perhaps due to centuries of cumulated soils degradation. Our findings revealed a "hidden" phase of this wasted space for urban area extension, however the function of this new space could not be determined. Later evolution of the basin after the Antiquity remains uncertain due to the lack of analytical and chronological data.

Results of this study draw a detailed multi-proxy picture of the complex evolution of socioenvironmental interaction and human impacts on natural systems at Corent since the Early Neolithic.

It contributes to refining our perceptions of the environmental impacts of prehistoric societies in Western Europe and highlights the crucial importance of keeping a long term perspective when dealing with past human-environment interactions.

6-Acknowledgements

This A c c e p t e d M a n u s c r i p t

7-Conflicts of interest

The authors declare no conflict of interest. The funding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results. Dark grey clayey silt, slightly mottled aspect with rare fine sands and small granules of scoria and basalt, weathered. Dark grey or brown small clayey-silty granules, rounded.

8-Appendix

135-144

Dark grey clayey silt, mottled aspect with fine sands and small granules of scoria and basalt, weathered. Dark grey or brown small clayey-silty granules, rounded.

Figure 1 .

 1 Figure 1. A) Location of study site in central France. Black line delineates Auvergne region. B) Location (black frame) of archaeological site and the Lac du Puy pond in lower part of the plateau of Corent. C) Aerial view of the Lac du Puy and the archaeological excavation (2013), with the known oppidum extent (red dashed line). Image credits: B. Dousteyssier. D) Depth model of the clayey infilling of the Lac du Puy basin (Mayoral and Depreux, 2017) with location of core COR13-4 and cross-section shown in F. Clayey infilling is thicker in red areas. No data are available on the today water body and its drainage (central part of the basin). E) Profile section corresponding exactly to core COR13-4. F) Stratigraphic cross-section of the Lac du Puy, modified from Mayoral et al. 2018. G) Chrono-stratigraphic synthesis of the Lac du Puy pedosedimentary

247

  Macrocharcoal: >125µm. Dates have been placed in their stratigraphic context on Fig 1G.

Figure 2 .

 2 Figure 2. Chrono-Stratigraphic framework for Stratigraphic Units in COR13-4. Chronological data (probability distribution of radiocarbon dates and archaeological landmarks, left) from all the Lac du Puy basin are correlated to the Stratigraphic Units present in COR13-4 (right) and Local Pollen Assemblage Zones (LPAZ) from Ledger et al. (2015). Note that radiocarbons 1-6 are in COR13-4 itself. Relative position of dates in each SU is indicated when available (left). Dated material (bulk sediment, microcharcoal, macrocharcoal or pollen) is also noted. Red rectangle and diamonds indicate archaeological tie points.

  A c c e p t e d M a n u s c r i p t characteristics can be observed (

  s c r i p t original layer, they were rather interpreted as indicators of lateral erosion from nearby areas[START_REF] Fedoroff | Palaeosoils and Relict Soils[END_REF].

Figure 3 .

 3 Figure3. Micromorphological features common in all the pedosedimentary sequence of the Lac du Puy. A: scoria with allophane hyaline coatings in rock vesicles. The coatings, neoformated as a weathering product, are microlaminated and well oriented (SU6a, XPL). B: Black-colored scoria fragment with its left part strongly weathered, in process of pedoplasmation (alterorelic). Note several pseudomorphs and an abundant clay matrix, probably in part neoformed (SU5a, PPL). C: Polyphased pedogenic aggregate, made of A-type reddish nodule embedded in a B-type greyish-brown nodule, both anorthic in a grano-porostriated clayey matrix (SU4, XPL). D: Variety of A-and B-type pedogenic aggregates, all anorthic in a grano-porostriated clayey matrix (SU4, XPL). E: C-type smectitic aggregate from SU4, anorthic in the clayey matrix of SU2 (XPL). F: Pseudomorph in boxwork, probably from hornblende, with strong peripheral grano-porostriation (SU3, XPL). G: abundant small channels (rootlets) and dark mass composed by streptomyces, marking an aerobic palaeosoil level (SU4, PPL). H: Basalt fragment (white arrow) and moderately iron impregned A-type nodule (black arrow), disorthic to anorthic, in a grano-porostriated matrix (SU3, XPL). I: zoom into a streptomyces cluster, in the micromass. Note the small diameter (0.5 to 1um) of filaments (SU4, PPL).

Figure 4 .

 4 Figure 4. Micromorphological features of SU2 (brown labels), SU3 (black labels) and SU4 (green labels). A: pottery fragment, note pedogenic nodules around the fragment, the reddish thin CCs and the abundance of small feldspar or quartz crystals (SU2, XPL). B: Laminated and very dusty CC in a channel void (SU2, PPL). C: Anorthic B-type pedogenic nodules (central and upper parts of the picture) and two orthic ferromanganic nodules (lower part of the picture), with peripheral granoporostriation (SU3, XPL). D: Macrocharcoal and ferromanganic nodules impregnated in the groundmass (SU3, PPL). E:

  s c r i p t deeper horizons (presence of anorthic papules in SU5A), indicating progressive erosion and land degradation on the plateau.

Figure 5 .

 5 Figure 5. Micromorphological features of SU5A (yellow labels) and SU6A (purple labels). A : Basaltic coarse sand to gravel, subangular to rounded, in a clayey granoporostriated matrix (SU6A, XPL). B and D: Closed granular structure, formed by Dtype pedogenic aggregates, and poorly separated due to posterior illuviation. Note the abundance of dark organic particles in pedogenic aggregates (SU6A, PPL). C and E: same areas in XPL, note high birefringence of clay coatings and infillings, and

  , the marked weathering of an otherwise heterogeneous coarse fraction, and the presence of phytoliths accompanied by sponge spicules are all indicators of highly variable hydrological inputs and intense shrink-swell processes[START_REF] Kovda | Vertic Features[END_REF], which clearly denote vertisolization. Redox pedofeatures such as developed dendritic Fe-Mn nodules are indicative of strong redox oscillations in this SU[START_REF] Kovda | Vertic Features[END_REF][START_REF] Lindbo | Redoximorphic Features[END_REF], and their distribution suggests weaker saturation but more erratic hydrology towards the top of the unit. Textural features indicate that illuviation is weak to moderate, and occurs probably under incomplete vegetal cover. Presence of fragments of well-developed and laminated CC, abundant fragments of hyaline allophanes, some smectitic C-type nodules (from SU4) and a general increase in coarse fraction towards the top of the unit are all indicators of surrounding soil erosion and increasing detrital inputs. Sustained micro-and macrocharcoal concentration together with a bone fragment could be indicative of human activities.

  sediment including abundant human activity markers, and a bare, compacted and disturbed surface at the top of the unit, are largely consistent with this previous interpretation. Moreover, they indicate a local origin of sediment from densely occupied soils of the surrounding plateau, and they also outline hypothetic posterior phases of flooding and saturation. Despite the lack of thin sections in SU1, some of its characteristics could be inferred from available data. Presence of B-type nodules (likely from SU1 and/or SU2) in SU2-3-4, and shrink-swell cracks observed on the surface of the Lac du Puy basin during fieldwork, suggest that vertic processes affected a part of the sequence posteriorly to SU2 deposition and until recent times (Fig 6).

Figure 6 .

 6 Figure 6. Pedo-stratigraphy and hierarchized interpretation of micromorphological observations of COR13-4, summarizing successive pedo-sedimentary processes distinguished in the Lac du Puy sequence.

Fe

  and Si signals are very similar to Zr and Ti (Fig. 7C), which indicates a similar relation with detrital inputs. However, both show much higher relative values than Ti and Zr in units such as SU4 or SU6A, suggesting sensibility to other factors. In the Lac du Puy catchment, Si results certainly from A c c e p t e d M a n u s c r i p t

  s c r i p t long-term evolution under relatively moist conditions facilitating weathering, versus raw detrital products richer in Fe or Ti. In the Lac du Puy basin, we can therefore interpret that high Ca/Fe ratio values indicate predominantly pedogenic instead of lithogenic sedimentary inputs. This interpretation is clearly supported by higher values of Ca and Ca/Fe in SU5A and 6A-B (Fig.7C),

Figure 7 .

 7 Figure 7. Selected geochemical results of COR13-4. A) PCA correlation circle according to dimensions 1 and 2 and identified endmembers. B) Plot with SU distribution C) detailed geochemical diagram of COR13-4 with selected elements and elementary ratios selected as environmental proxies. MS values are in SI (10 -5

  s c r i p t chrono-stratigraphy, as it explains the almost negligible sedimentary accretion between the top of SU5A and the base of SU4 (3500-2000/1700 cal. BCE). Hence, the Recent and Late Neolithic are represented in the sequence by only a few centimeters, and SU4 truly starts at 102 cm, c. 2000/1700 cal. BCE (see Fig.8).Geoarchaeological and palaeoenvironmental data show a clear trend towards a decreased human activity and reduced impact on palaeoenvironments between 3500 and 2000/1700 cal. BCE. A first phase of apparent stabilization and incipient slowdown is followed by a second and prolonged phase of more marked demise with vegetation recovery, reduced sedimentary accretion and soil stabilization in the Lac du Puy, indicating a long period of very limited soil erosion of the plateau. This two-phased pattern of decreasing human influence on environments appears consistent with the archaeological record. During the Recent Neolithic (3700-3000 BCE) signs of occupation at Corent are limited. However significant environmental impacts are recorded in COR13-4, suggesting archaeological data may be underestimating human activity from this period. Our knowledge of human activities at Corent during the Late Neolithic comprises a collective burial in the summit of the plateau

Figure 8 .

 8 Figure 8. Synthetic multi-proxy diagram of COR13-4. Palynological, microcharcoal data and palynozones (LPAZ) are extracted from Ledger et al. (2015). Chronological landmarks are taken from chrono-stratigraphic framework, see Fig. 2. MS: Magnetic Susceptibility (SI.10 -5

  s c r i p t pedogenesis in the Lac du Puy basin between Recent Neolithic and the first centuries of the Early Bronze Age, with very low sedimentation rate. This phase of soil stability and vegetation recovery in the basin, and reduced erosion in the plateau, coincides with long-term abandonment of the occupation at Corent.During the Early Bronze Age, human agropastoral reappraisal of the plateau brings specific land use and management of the Lac du Puy. Micromorphology revealed that these new practices are certainly the anthropogenic catalyst of soil profile sealing and drainage degradation of the basin, which probably becomes a very stable wet grassland maintained by a feedback effect between agropastoral management, hydrosedimentary fluxes and pedogenic processes. From our results, two cycles of environmental impact can be distinguished in the later evolution of the basin during the Bronze Age. The first covers Early and Middle Bronze Age, and second the Late Bronze Age. Both start with reduced anthropogenic impacts characterized by pastoral and arable agriculture, and finish with drier and more detrital conditions. The clear association of the end of the later cycle with settlement expansion during Late Bronze Age 3 suggests that similar signal at the end of the Middle Bronze Age could have analogous causes. This implies an extended settlement during this period, which is not evident in existing archaeological data.The Iron Age is harder to interpret in the pedo-sedimentary record of the Lac du Puy. A major and permanent hydro-sedimentary change is noticeable in the basin, lasting despite the apparent demise of occupation during several centuries after abandonment of the Hallstatt site and associated storage pit battery. Geoarchaeological analysis shown that these "inherited" impacts are exacerbated by development of the oppidum in the late La Tène period, which presumably increased soil disturbance, erosion and runoff nourishing hydro-sedimentary inputs of the basin. Our study suggests that the Lac du Puy then becomes part of the sanitation/drainage system of the urban environment of the plateau and is recurrently flooded by hydro-sedimentary fluxes.Micromorphology confirmed that circa 50-30 BCE the area is backfilled probably in order to reclaim A c c e p t e d M a n u s c r i p t

  work was carried out as a part of the AYPONA project (dir. Y. Miras and F. Vautier), funded by the Conseil Régional d'Auvergne, the Service Régional d'Archéologie d'Auvergne, the Maison des Sciences de l'Homme de Clermont-Ferrand, and the University Lyon 2 (Projet BQR Lyon 2, dir. M. Poux and J-F. Berger). The authors are grateful to a number of people who contributed to this work. The archaeological team of Corent, and especially the LUERN association for providing logistic support, and Florian Couderc for valuable discussions. Pierre Boivin, Morgane Liard, Carlos Arteaga and Olivier Voldoire for their help with microscopy and micromorphological analyses. Anne-Lise Develle for her support in the analysis of XRF data. Adrien Barra provided assistance in laboratory work. Olivier Voldoire, Franck Vautier, Erwan Roussel, Aude Beauger, Emmanuelle Defive, GerardVernet and Paul-Edgard Genet contributed in variable amounts to fieldwork. François-Xavier Simon and Bruno Depreux helped with geophysical and archaeological data respectively. Bertrand Dousteyssier contributed with aerial photography. We also owe our gratitude to the landowners Mme. Mioche and M. Rodriguez. Finally, we express sincere thanks to the anonymous reviewers for their remarks and critical reading of the manuscript.

12 244 Nº Loc. (Depth / Position) Position in SUs Lab. code Material 14C yr. BP Cal. BP (2σ) Cal. BCE/CE (2σ

  ).

								)
	1	COR13-4 (54-57	Top of SU3	Beta-379416	Microcharcoal		2340-	390-205 BCE
		cm)				± 30	2155
	2	COR13-4 (54-57	Top of SU3	Beta-379417	Bulk sed.		1998-	48 BCE-CE 71
		cm)				± 30	1879
	3	COR13-4 (71-72	Top of SU4	Beta-377232	Bulk sed.		2769-	819-755 BCE
		cm)				± 30	2705
	4	COR13-4 (71-73	Top of SU4	Beta-379418	Pollen		2894-	944-823 BCE
		cm)				± 30	2773
	5	COR13-4 (87-88	Middle of SU4	Beta-375785	Bulk sed.		3866-	1916-1749
		cm)				± 30	3699	BCE
	6	COR13-4 (102-103	Base of SU4	Beta-379419	Bulk sed.		3638-	1688-1528
		cm)				± 30	3478	BCE
	7	Log L4 (43-47 cm)	Base of SU2	Beta-434187	Microcharcoal		6407-	4457-4339
						±40	6289	BCE
	8 9 10 11 12 13 14	Log L4 (43-47 cm) Log L4 (59-63 cm) Log L4 (59-63 cm) Log L4 (87-91 cm) Ditch (base) Ditch (middle) Pit 25604 (base)	Base of SU2 Base of SU3 Base of SU3 Base of SU4 SU5A/WB (indet.) SU5A/WB (indet.) SU5A/WB (indet.)	Beta-430610 Beta-434188 Beta-430611 Beta-430612 Beta-418695 Beta-418694 a n u s c r i p t Bulk sed. ±30 1375-1293 Microcharcoal ± 30 2492-2347 Bulk sed. ± 30 2440-2316 Bulk sed. ± 30 3407-3250 Macrocharcoal ± 30 6496-6344 Macrocharcoal 6496-± 30 6344 Poz-74925 Microcharcoal 6403-M ± 40 6277	575-657 CE 542-397 BCE 490-366 BCE 1457-1300 BCE 4546-4394 BCE 4546-4394 BCE 4453-4327 BCE
	15 16 17 18 19	Pit 25604 (fill) Pit 25677 (base) Pit 25703 (base) Pit 25699 (base) Pit 25610 (base) A c c e p t e d SU4 (indet.) Beta-425790 SU5A/WB (indet.) Beta-425426 SU5A/WB (indet.) Beta-425787 SU5A/WB (indet.) Beta-425788 SU5A/WB Beta-425789 (indet.)	Bulk sed. Bulk sed. Bulk sed. Bulk sed. Bulk sed.	± 30 ± 30 ± 30 ± 30 ± 30	3826-3593 7158-6942 6176-5921 5591-5469 6491-6322	1876-1643 BCE 5208-4992 BCE 4226-3971 BCE 3641-3519 BCE 4541-4372 BCE

Table 1. Radiocarbon database for the Lac du Puy used to build the chrono-stratigraphic framework (Fig.2), all dates have 245

	246	been previously published in Ledger et al. 2015 and in Mayoral et al. 2018. Dates 7 & 8 were rejected on a stratigraphic
		basis (italic). Dates are given in BCE/CE system (Before Common Era/Common Era). Microcharcoal: <125µm,

Table 2

 2

	), indicating overlapping processes likely resulting from

Table 2 . Detailed micromorphological descriptions of COR13-4. System: Stoops

 2 Iron and manganese pedofeatures are ubiquitous throughout the sequence (seeTable 2, and Figs. 3 to 5). Each type of these features indicate different redox conditions[START_REF] Kovda | Vertic Features[END_REF][START_REF] Lindbo | Redoximorphic Features[END_REF], therefore we used their variability to infer redox changes in the

	; * Few; **Several; ***Abundant;

2003; CF: Coarse-Fine (boundary fixed at 20 µm); Related Distribution: OP: Open Porphyric; VOP: Very Open Porphyric; DSP: Double Spaced Porphyric; SSP: Single Spaced Porphyric; Birefringence Fabric: GPS: Grano-Porostriated; CS: Circular Striated; ST: Striated/Strial; Microstructure: SB: Subangular Blocky; AB: Angular Blocky; F: Fissural; GR: Granular; PR: Prismatic; WA: Well Aggregated; WS: Well Separated; PA: Poorly Aggregated; PS: Poorly Separated; MA: Moderately Aggregated; MS: Moderately Separated; Pedofeatures and coarse fraction: CCoats. or CC: Clay Coatings; CI: Clay Infillings; A. Neof. : Neoformated Allophane; Frgts.: Fragments; Pedog. Aggr.: Pedogenic Aggregates; Qtz.: Quartz; Pseud. (B): Black pseudomorph; Pseudom. (R): red pseudomorph; coats.: coatings; hypocoats. : hypocoatings; Nods. : nodules; Colors: PY: Pale Yellow; GY: Greyish Yellow; YG: Yellowish Grey. Abundance symbols: no symbol: absence; -Rare

Table 2

 2 streptomyces mass at the top of SU4 indicates the development of a well-drained, aerobic palaeosoil level at this depth (73-85 cm) , in a similar way as in the lower section of SU4 (see above).

	) has a better developed microstructure and

  & 8) micromorphology and geochemistry indicate similar dynamics to previous phase. It is first characterized by very weak detrital inputs and marked reductic conditions. Palynological data continues to depict a very open and cultivated landscape as suggested by lowest values for woodland pollen and maximal values of cereal and Poaceae pollen types (LPAZ COR-3c in

  Dark brown clayey-silty loam, several basaltic granules, one amphorae sherd, some oxidation mottles.Very dark grey to black silty clay, rare oxidation mottles, basaltic sands and granules. Olive grey massive heavy clay, with abundant oxidation mottles in the top (above 83 cm), very rare sands and basaltic granules, one quartz gravel.Dark olive grey silty clay. Some oxidation mottles, rare sands and granules.Dark grey massive clayey silt, mottled aspect with fine sands and well-sorted small granules of scoria and basalt, weathered. Abundant dark grey and small clayey-silty granules, rounded.Dark grey massive clayey silt, mottled aspect with fine sands and well-sorted small granules of scoria and basalt, weathered. Dark grey or brown small clayey-silty granules, rounded.

	SU	Depth (cm)	Munsell color	Description
	1	0-30	10 YR 3/2	Dark brown clay loam, visible blocky to granular aggregation, basaltic granules, vegetal remains (topsoil)
	2	30-49	10 YR 3/2
	3	49-72	10 YR 2,5/1
		72-87	5 Y 4/2
		87-89,5	5 Y 4/2 to 5 Y 3,5/2	Dark olive grey massive heavy clay, with some oxidation mottles, very rare sands and basaltic granules.
	4	89,5-92	5 Y 4/2	Olive grey massive heavy clay, with several oxidation mottles, very rare sands and basaltic granules.
		92-109	5 Y 4/2	Olive grey massive heavy clay, with some oxidation mottles, very rare sands and basaltic granules.
		109-	5 Y 4/2 to
		117,5	5 Y 3,5/2
			10 YR
		117,5-	2,5/1 to
		119	2,5 Y
	5A		3,5/2
		119-129	10 YR 3/1 to 2,5 Y 3,5/2
		129-
	6A	135	10 YR 4,5/1