Marlène Lavrieux
email: marlene.lavrieux@univ-fcomte.fr.

Jean-Robert Disnar

Emmanuel Chapron

Jean-Gabriel Bréheret

Jérémy Jacob

Yannick Miras

Jean-Louis Reyss

Valérie Andrieu-Ponel

Arnaud G Fabien

6,700-year sedimentary record of climatic and anthropogenic signals in Lake Aydat (French Massif Central)

Keywords: Lake sediments, French Massif Central, Detrital input, Climate, Anthropogenic activities, Holocene

A 19-meter-long sedimentary record retrieved in Lake Aydat (French Massif Central) covers the last 6700 yrs at a high-resolution. A multi-proxy approach (density, magnetic susceptibility, XRF, Rock-Eval, pollen and non-pollen palynomorph analyses and a historical archives study) was used to characterise and propose a model of sedimentation. The high deposition rate results from the combined effects of the high suspension load of the river, autochthonous production and the narrow shape of the incised fluvial valley dammed by a lava flow ca. 8550 years ago. Two contrasted periods (6700±200 -3180±90 cal. BP, and 1770±60 cal. BP-now) were characterized. The lower unit (mid-Holocene) displays a fine and regular lamination and holds a single, major, flood deposit. This unit is capped by an erosive mass wasting deposit triggered ca. 1770±60 cal. BP. The upper unit (late-Holocene) is made of organic rich and fine grained faintly laminated sediment, with numerous interbedded flood deposits and diatom blooms. The sedimentation was principally controlled by climatic forcings until ca. 1100 cal. BP, accompanied by detrital events linked to human activities around the lake. Then, a more detrital input attested by numerous and recurrent flood deposits can be linked to the intensification of a persistent anthropogenic impact on the catchment. Two phases of lake eutrophication are highlighted: 1200-1130 cal. BP, as a result of increased anthropogenic pressure, and the current phase that could have started ca. 150 cal. BP.

Introduction

Anthropogenic activities are now universally considered as having a strong impact on natural systems (e.g. [START_REF] Dearing | Climate-human-environment interactions: resolving our past[END_REF] and on the whole terrestrial environment (IPCC, 2007), including geological processes (e.g. [START_REF] Crutzen | Geology of mankind[END_REF][START_REF] Wilkinson | Humans as geologic agents: A deep-time perspective[END_REF]. It is therefore crucial to comprehend the complex inter-relationships linking societies, climate and environments.

Unravelling such interactions entails studying natural records, which provide information that allows the consequences of current global change to be anticipated [START_REF] Costanza | Sustainability or collapse: what can we learn from integrating the history of humans and the rest of nature?[END_REF].

Among various natural archives having a well-proven preservation potential, lacustrine sediments can provide high quality information. Like marine pelagic sediments, they generally constitute continuous records, but in contrast to the former they can deliver local information about the natural (climate, topography, vegetation...) and anthropogenic conditions prevailing at the limited spatial scale of a drainage basin (e.g. [START_REF] Zolitschka | Lacustrine and marine archives of environmental variability across South America[END_REF][START_REF] Battarbee | Palaeolimnology and its developing role in assessing the history and extent of human impact on lake ecosystems[END_REF]. The mid-altitude mountainous configuration of the French Massif Central, at the boundary of oceanic and continental climatic influences, confers on this region a relatively high sensitivity to climatic changes coupled with marked anthropization. However, so far, only a few studies have been devoted to the interactions between the environment, humans and climate in this region, with the notable exception of its northern plain, the Limagne (e.g. [START_REF] Ballut | Evolution environnementale de la Limagne de Clermont-Ferrand au cours de la seconde moitié de l'Holocène[END_REF][START_REF] Fourmont | Contrasted Late Glacial and Holocene hydrology of Sarlieve paleolake (France) from sediment geoetry and detrital versus biochemical composition[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].

Earlier palaeoenvironmental studies performed on the mountainous part, the Chaîne des Puys, focused mainly on vegetation history and tephrostratigraphy [START_REF] De Beaulieu | Zonation automatique appliquée à l'analyse pollinique : exemple de la narse d'Ampoix (Puy-de-Dôme)[END_REF][START_REF] Juvigné | Ages de traits polliniques et chronozonation du Tardiglaciaire et de l'Holocène dans le Massif Central (France)[END_REF]. Multiproxy analyses on Auvergne mountain areas combining palaeoecology, archaeology and historical sources still remain scarce (e.g. [START_REF] Michelin | Variations des teneurs en éléments minéraux dans un basmarais holocène : la Vezolle (Chaîne des Puys), premières recherches des manifestations anthropiques[END_REF][START_REF] Miras | Multi-disciplinary approach to changes in agropastoral activities since the Sub-Boreal in the surroundings of the "narse d'Espinasse" (Puy de Dôme, French Massif Central)[END_REF][START_REF] Prat | Systèmes agropastoraux et milieux périurbains en Basse Auvergne au cours des trois derniers millénaires : contribution de l'analyse palynologique à l'étude des interactions sociétés-milieux[END_REF][START_REF] Surmely | Occupation and land-use history of a medium mountain from the Mid-Holocene: A multidisciplinary study performed in the South Cantal (French Massif Central)[END_REF][START_REF] Ballut | Landscape human shaping and spatial mobility of the agropastoral practices in the Chaîne des Puys during the historical times (Massif Central, France)[END_REF], especially when compared to regions such as the NW Alps, where lacustrine archives are numerous and have been extensively studied (e.g. [START_REF] Chapron | Climatic variability in the northwestern Alps, France, as evidenced by 600 years of terrigenous sedimentation in Lake Le Bourget[END_REF][START_REF] Magny | Holocene climate variability as reflected by mid-European lake-level fluctuations and its probable impact on prehistoric human settlements[END_REF][START_REF] Arnaud | 7200 years of Rhône river flooding activity in Lake Le Bourget, France: a high-resolution sediment record of NW Alps hydrology[END_REF][START_REF] Leroux | Late Glacial-Holocene sequence of Lake Saint-Point (Jura Mountains, France): Detrital inputs as records of climate change and anthropic impact[END_REF][START_REF] Debret | Northwestern Alps Holocene paleohydrology recorded by flooding activity in Lake Le Bourget, France[END_REF]. The Massif Central did not benefit from the same interest, although it contains a notable number of lakes, including crater lakes that are remnants of its Tertiary to Quaternaryincluding Holocene -volcanic activity. While the sediment infill of some of these lakes has been investigated for various purposes (e.g. to track erosion fluxes or highlight natural hazards: [START_REF] Macaire | Effets climatiques et anthropiques sur l'érosion mécanique en montagne cristalline de région tempérée pendant le Tardiglaciaire et l'Holocène. Un exemple, le bassin du Lac Chambon (Massif Central, France)[END_REF][START_REF] Gay | Estimation of Late Glacial and Holocene chemical erosion rates, Lake Chambon watershed, Massif Central, France[END_REF][START_REF] Chapron | Multidisciplinary characterisation of sedimentary processes in a recent maar lake (Lake Pavin, French Massif Central) and implication for natural hazards[END_REF], up to now no high-resolution multidisciplinary study of a long-term lake sediment record has been conducted in this region. The history of human occupation in the surroundings of Lake Aydat has already been explored [START_REF] Miras | Multi-disciplinary approach to changes in agropastoral activities since the Sub-Boreal in the surroundings of the "narse d'Espinasse" (Puy de Dôme, French Massif Central)[END_REF] and thus represents a suitable target to partly fill this gap. Moreover its recent sedimentation and (bio)chemical characteristics have recently been studied to apprehend its current eutrophic functioning (e.g. [START_REF] Sarazin | Sedimentation rate and early diagenesis of particulate organic nitrogen and carbon in Lake Aydat (Puy-de-Dôme, France)[END_REF][START_REF] Sarazin | Organic matter mineralization in the pore water of a eutrophic lake (Lake Aydat, Puy de Dôme, France)[END_REF][START_REF] Alfonso | Etude de paléoenvironnements littoraux. Contribution à l'établissement d'une échelle chronostratigraphique à partir des retombées atmosphériques de métaux lourds[END_REF][START_REF] Stefanova | Composition and early diagenesis of fatty acids in lacustrine sediments, lake Aydat (France)[END_REF][START_REF] Michard | Annual budget of chemical elements in a eutrophic lake, Lake Aydat (Puy-de-Dôme)[END_REF][START_REF] Ogier | Neutral carbohydrate geochemistry of particulate material (trap and core sediments) in an eutrophic lake (Aydat, France)[END_REF]. In this perspective, this paper reports the results of the investigations carried out on a 19 meterlong Lake Aydat sedimentary sequence that covers the last 6700 years. The establishment of an age-depth model and comparison with other studies are used to highlight climatic and anthropogenic contributions to the sedimentary signal, approached through density, magnetic susceptibility (MS), X-ray fluorescence spectrometry (XRF), organic bulk analyses, pollen and non-pollen palynomorph (NPP) analyses and a study of historical archives.

General setting

Lake Aydat (N 45°39.809' / E 2°59.106') is located in the French Massif Central, ca.

25 km SW from Clermont-Ferrand, at the southern boundary of the Chaîne des Puys volcanic range (Figure 1), where it forms a plateau sharply incised by V-shaped valleys. The lake is at an altitude of 837 m a.s.l. and originates from the damming of the Veyre River by a basalt flow dated from 8551± 400 cal. BP that issued from the Puy de la Vache and Puy de Lassolas volcanoes [START_REF] Boivin | Volcanologie de la Chaîne des Puys (with map). Aydat (France)[END_REF]. The lake surface is 6.10 5 m². Its water volume is of ca. 5.2.10 6 m 3 , with an average depth of 7 m and a maximum depth of 15 m. The mean residence time of waters is ca. 7.5 months [START_REF] Michard | Annual budget of chemical elements in a eutrophic lake, Lake Aydat (Puy-de-Dôme)[END_REF]. The lake is eutrophic and is mainly fed from the West by the Veyre River (75%), completed by a lateral supply through the shores and direct precipitation (25%). The river constitutes the main outlet for the waters (85%), the rest (15%) percolating through the basaltic flow (Bouchet, 1987). An earlier study estimated the recent (last 50 years) sedimentation rate at ca. 0.46 cm/yr in the deepest part of the basin [START_REF] Sarazin | Sedimentation rate and early diagenesis of particulate organic nitrogen and carbon in Lake Aydat (Puy-de-Dôme, France)[END_REF]. The lake's catchment is located upstream the Loire River basin and is mainly fed by precipitation brought from the Atlantic Ocean depressions. Its surface is ca. 30 km² and extends from 837 m a.s.l. to 1300 m a.s.l. (West, top of the volcanoes; Figure 1). It develops on a plutonic and metamorphic substratum (mainly granodiorites), partially covered by late glacial to Holocene volcanic deposits [START_REF] Boivin | Volcanologie de la Chaîne des Puys (with map). Aydat (France)[END_REF]. Nowadays, the catchment is mainly covered by grasslands and pastures, and by human-sowed secondary forests (principally coniferous: Picea sp.), mainly on the top of volcanoes. Andisols constitute the typical type of soil covering the catchment.

(Figure 1 here)

Material and methods

A high-resolution seismic reflection survey, carried out prior to the coring, failed to reveal the detailed structure of sedimentary deposits because of a high content of methane, but confirmed previous bathymetric measurements (Figures 2a,b). Accordingly, the coring site was chosen in the central and deepest part of the basin, close to the Veyre River delta. A continuous sequence (AYD09) was retrieved in 2-and 3-meter long sections at 14.5 m water depth (Figure 1) with a UWITEC coring platform. A set of core sections at two nearby locations allowed the recovery of a 19 m long sedimentary record (Figure 3), once the core sections had been opened, described and correlated based on the identification of key lithological horizons on each core section. The core was divided into 1-cm-thick slices for analytical purposes. The chronology of the top 20 cm of the sequence is based on 137 Cs and 241 Am measurements (Table I; Figure 4). 25 samples from the top of the core were measured by ultra-low background, high-efficiency gamma-spectrometry at the "Laboratoire Souterrain de Modane" as described in [START_REF] Reyss | Large, low background well-type detectors for measurements of environmental radioactivity[END_REF]. 137 Cs and 241 Am were measured together with 210 Pb and 7 Be. 17 AMS radiocarbon dates distributed over the core, based on leaf and wood fragment analyses and obtained at the Laboratoire de Mesure du Carbone 14 (Gif-sur-Yvette, France) and calibrated (2σ) using CalPal Online [START_REF] Danzeglocke | CalPal-2007online[END_REF]Table I; Figure 3) constitute the base of the whole core chronology. The scarcity of datable organic material in the top 7 meters was counterbalanced by the detection of numerous mm-to cm-scale flood deposits [START_REF] Mulder | Flood deposits in continental and marine environments: Character and significance. Sediment transfer from shelf to deep water -Revisiting the delivery system[END_REF]) that were correlated with historically-described flood events that are well documented in the Loire River catchment and allowed validation of the age-depth model (Champion, 1858(Champion, -1864;;[START_REF] Deblaère | Inventaire des situations à precipitations remarquables en Auvergne, Bourgogne et Rhône-Alpes[END_REF][START_REF] Genêt | Indomptable Loire[END_REF]Table II; Figure 3; see 4.1 for the identification of flood deposits). Loire River floods mainly originate from its upstream part (i.e. Massif Central), as a result of numerous factors (hydrologic conditions, slopes, impermeable geology...; [START_REF] Genêt | Indomptable Loire[END_REF], so they can be reliably compared to those recorded in Lake Aydat sediments. MS and XRF-based element composition were measured following a step of 1 cm using a Bartington MS2E point sensor on a Geotek Multi-Sensor Core Logger System (MS; Chrono-Environnment, Besançon, France) and a Avaatech Core Scanner (XRF; Environnements et Paléoenvironnements Océaniques et Continentaux, Bordeaux, France), respectively. Density was appraised by continuous measurements using a Hologic densitometer (dual energy X-ray absorptiometry; Institut de Prévention et de Recherche sur l'Ostéoporose, Orléans, France), and SEM pictures were acquired from a LEO, Gemini, Zeiss DSM 982. Bulk organic matter (OM) analyses were carried out with a Rock-Eval6 (RE6) on ca. 60 mg of dried and crushed sediments. The Rock-Eval parameters used in this study are Total Organic Carbon (TOC, %), Hydrogen Index (HI, mg hydrocarbons.g TOC -1 ), and Oxygen Index (OI, mg CO 2 . g TOC -1 ; [START_REF] Espitalié | La pyrolyse Rock-Eval et ses applications[END_REF][START_REF] Lafargue | Rock-Eval 6 applications in hydrocarbon exploration, production, and soil contamination studies[END_REF]. Samples were taken every 2.5 cm for pollen and non-pollen palynomorph (NPP) analysis, and prepared using standard procedure [START_REF] Faegri | Textbook of Pollen Analysis[END_REF]. Minimum counts of 500 dry land pollen grains per sample were made. Pollen and NPP values were calculated as the percentage of total land pollen excluding Cyperaceae, fern spores and aquatic plants.

As this article aims at dealing with Holocene sedimentation, pollen and NPP assemblages are interpreted here in broad terms with added curves presenting the Arboreal Pollen / Total Pollen (AP/T) ratio, crops, Anthropogenic Pollen Indicators (API) including pollen taxa indicative of human impact [START_REF] Behre | The interpretation of anthropogenic indicators in pollen diagrams[END_REF] and those underlined by the modern pollen assemblages study carried out in the Massif Central [START_REF] Surmely | Occupation and land-use history of a medium mountain from the Mid-Holocene: A multidisciplinary study performed in the South Cantal (French Massif Central)[END_REF] and coprophilous fungi that are useful to assess local grazing activity [START_REF] Van Geel | Palaeoecology and stratigraphy of the Lateglacial type section at Usselo (The Netherlands)[END_REF][START_REF] Ejarque | Pollen and non-pollen palynomorph indicators of vegetation and highland grazing activities obtained from modern surface and dung datasets in the eastern Pyrenees[END_REF].

(Figure 2 and Tables I andII here) 4. Results [START_REF] Ogier | Diagenèse précoce en domaine lacustre : étude des composés minéraux et organiques des sédiments récents du lac d'Aydat (Puy de Dôme[END_REF] showed that sediments of the Veyre River are rich in Rb, Ti and K that can thus be used as markers of detrital inputs. This characteristic is also attributable to density and MS measurements in the core that highly correlate with these three elements (Figure 3). Any increase in these physical parameters inside a rapidly deposited layer (RDL) can therefore be considered as resulting from an amplification of the erosion flux, and thus to hyperpycnal flood events, as expanded by [START_REF] Mulder | Flood deposits in continental and marine environments: Character and significance. Sediment transfer from shelf to deep water -Revisiting the delivery system[END_REF]. The siliceous endogenic phase is the main constituent of the background sedimentation, half of the dissolved Si that comes into the lake being finally stocked as opal A in diatom frustules [START_REF] Sarazin | Diagenèse précoce de la matière organique dans la colonne d'eau et le sédiment d'un lac eutrophe : le lac d'Aydat (Puy-de-Dôme)[END_REF][START_REF] Ogier | Diagenèse précoce en domaine lacustre : étude des composés minéraux et organiques des sédiments récents du lac d'Aydat (Puy de Dôme[END_REF].

Background sedimentation and origin of detrital inputs

(Figure 3 here)

Sedimentological features

Based on sedimentological features, the record is divided into three main units (Figures 3 and4):

-The lower unit (1076-1914 cm depth) shows laminations consisting of alternating beige diatom blooms and dark detrital levels. Despite these two major sources the sediment is rich in OM (generally 8-10% TOC), with moderate HI and OI values (250-300 mgHC.g -1 TOC and 100-150 mgO 2 .g -1 TOC, respectively). It also contains one major flood deposit, the thickest one of the whole core (1248-1254 cm depth). The background MS value of this unit is mostly < 10.10 -5 , but can reach up to 40.10 -5 S.I., and is highly correlated to XRF (Ti, K) measurements. In the upper part, laminae are noticeably affected by microfaults, thus attesting to a destabilization of the sediment after deposition.

-The upper unit (0-829 cm depth) contrasts strongly with the lower one. It is constituted by a background of dark and faintly laminated OM rich sediment (3-5.5 % TOC) also showing moderate HI and OI values (200-300 mgHC.g -1 TOC and 100-200 mgO 2 .g -1 TOC, respectively), frequently interrupted by diatom blooms and flood deposits (1-5 cm thick;

Figure 3). The latter are darker and characterized by high density and high MS (up to 800.10 -5 S.I), reflecting increased erosional inputs from the catchment ( § 4.1).

Background MS mostly ranges between 40 and 100.10 -5 S.I, and shows the same trends as the Rb, Ti and K ones.

-Between the two previous units (829-1076 cm depth), the correlation between the two twin cores was impossible. 1 m of the sedimentary sequence appeared exactly repeated in only one of the twin cores, while particular MS fluctuations were unique to the other one (this one illustrated in Figure 3). Naked eye observation allowed the distinction of disturbed layers at the boundaries. Combined with the presence of the micro-faults at the top of the lower unit, these indices were interpreted as a mass wasting deposit (MWD; [START_REF] Mulder | Classification of offshore mass movements[END_REF]) that reworked ca. 2.5 m of sediment. Consequently, this unit is not discussed further here.

(Figure 4 here)

Depth-age model and accumulation rate

Due to its short half-life (53 days), the detection of 7 Be in the uppermost layers of the core attests to a well-preserved sediment interface (Figure 4). From the artificial radionuclides profile (Table I, Figure 4; [START_REF] Appleby | Radiometric dating of sediment records in European mountain lakes[END_REF] two events were dated: (i) the 1986 AD Chernobyl accident at 16.5 cm depth (corrected depths, i.e. without flood events) characterized by the high activity of 137 Cs; (ii) the 1963 AD maximum fallout resulting from atmospheric nuclear bomb tests at 24.5 cm depth indicated by the high activities of both 137 Cs and 241 Am. Then the recent sedimentation rate was estimated after removing a RDL individualized between these two bounds (21-22 cm depth; Table II) to establish the recent part of the depth-age model. In this chronological frame, this RDL correlates with the 1976 AD major local flood event [START_REF] Deblaère | Inventaire des situations à precipitations remarquables en Auvergne, Bourgogne et Rhône-Alpes[END_REF], confirming the assignation of this type of sedimentary event to flood deposits. 210 Pb failed to give reliable results. Previous work carried out in the same lake [START_REF] Sarazin | Sedimentation rate and early diagenesis of particulate organic nitrogen and carbon in Lake Aydat (Puy-de-Dôme, France)[END_REF] attributed this failure to the very low compaction of the sediment.

Among the 17 AMS radiocarbon dates, 2 were excluded from the depth-age model (1 gave an aberrant age, and 1 belonged to the repeated part of the MWD). 58 RDLs (56 flood events in the upper unit, 1 flood event in the lower one, plus the MWD) were removed from the sequence prior to the establishment of the age-depth model, entailing a shortening of the considered section. Finally, the background sediment record of the upper and lower units expanded between 0-774.5 and 774.5 -1597.5 cm depth, respectively. These depths are used as reference in the following discussion. The whole sequence covers the last 6730 years (Figures 3 and4). The mean background sedimentation rate is 0.20 cm.yr -1 for the lower unit, and also for the basal part of the upper unit (i.e. in the 774.5-660 cm depth interval). It suddenly increases to reach 0.52 cm/yr from 660 cm depth up to the top. This value is close to the rate of 0.46 cm/yr estimated by [START_REF] Sarazin | Sedimentation rate and early diagenesis of particulate organic nitrogen and carbon in Lake Aydat (Puy-de-Dôme, France)[END_REF] for the last 50 years, which validates the recent part of the depth-age model. The sedimentation rate reaches 0.6 cm.yr -1 when flood events are considered in the calculation. A transversal altitudinal profile, deduced from the bathymetric map and extended to the slopes of the lake sides, highlights the narrow V-shaped morphology of the valley (Figure 2c). A longitudinal profile allows extrapolation of the substratum surface from two checkpoints (location of the substratum outcropping upstream the Veyre delta, and the depth at which the substratum was reached in a drilling in the basaltic flow; [START_REF] Auriat | Etude des sondages et captages dans plusieurs coulées de la Chaîne des Puys (Balmet, Côme, Louchadières, Aydat, Tiretaine)[END_REF], in order to roughly estimate the depth of the substratum directly below the coring site of this study. The information provided by these profiles is consistent with the maximum plausible sediment accumulation at the coring site of this study (ca. 23 m, calculated from the supposed age of the lake and the sedimentation rate). In this hypothesis, the substratum should be located at ca.780 m a.s.l. (Figure 2d). This indicates that the core was probably retrieved close to the deepest point of the paleovalley, where the sediment accommodation potential is maximal. The thickness of the deposits, originating from (1) the high suspension load of the river, especially during flood events, associated to (2) a high organic productivity in the lake (diatom blooms…), itself depending on the chemical erosion coming from the catchment [START_REF] Sarazin | Diagenèse précoce de la matière organique dans la colonne d'eau et le sédiment d'un lac eutrophe : le lac d'Aydat (Puy-de-Dôme)[END_REF][START_REF] Ogier | Diagenèse précoce en domaine lacustre : étude des composés minéraux et organiques des sédiments récents du lac d'Aydat (Puy de Dôme[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], is thus reinforced by the particular geometry of the lacustrine basin, which effectively constrains this clastic sediment to accumulate in the deepest part of the lake [START_REF] Mulder | Flood deposits in continental and marine environments: Character and significance. Sediment transfer from shelf to deep water -Revisiting the delivery system[END_REF].

Pollen data

Pollen data that were obtained from background sediment samples (i.e. without flood deposits; Figures 5,6) show that Arborean pollen are largely dominant throughout the lower unit (AP/T generally > 90%; Figure 5). Pinus sharply decreases as Fagus increases, from ca. 5600 cal. BP. Evidence of anthropogenic activities are recorded through indices of crops and coprophilous fungi. A similar pattern is observed at the base of the upper unit (Figure 6), but crop pollen occurrences become continuous. AP/T suddenly decreases from 1500 cal. BP, when anthropogenic indicators (API) -Poaceae, crops and coprophilous fungiincrease sharply. 150 cal. BP clearly signs the renewal of Pinus, to the detriment of crops and coprophilous fungi indicators. These general trends follow those observed through physical (MS, density, XRF) and bulk geochemical (TOC, HI, OI) analyses, and allowed the recognition of different phases covering the whole lower unit, and four in the upper one (1770-1500 cal. BP, 1500-1200 cal. BP, 1200-150 cal. BP, 150 cal. BPpresent).

(Figures 5 and 6 here)

Discussion: climatic and anthropogenic influences on the sedimentary record

Rb, Ti and K signatures recorded in the sediments come from the erosion of andisoils, themselves deriving from a minor contribution of the granodioritic substratum added to the material originating from volcanic formations [START_REF] Ogier | Diagenèse précoce en domaine lacustre : étude des composés minéraux et organiques des sédiments récents du lac d'Aydat (Puy de Dôme[END_REF]. This detrital imprint is recorded in flood deposits, and to a lesser extent in the background sedimentation. Natural / anthropogenic contributions to the sedimentary record were evaluated by comparing the background detrital input (i.e., MS without instantaneous deposits) and pollen data with previously studied climatic and anthropogenic records, as shown in Figures 5 and6. Local human impact was mostly estimated from pollen and NPP analyses acquired during the current study, compared to the former high-resolution palynological and multi-disciplinary study performed on the 5000-year-long record of the "Narse d'Espinasse" [START_REF] Miras | Multi-disciplinary approach to changes in agropastoral activities since the Sub-Boreal in the surroundings of the "narse d'Espinasse" (Puy de Dôme, French Massif Central)[END_REF], a peat marsh located in the lake's catchment (Figure 1), that certainly constituted up to now one of the most complete palaeoenvironmental Holocene records for the whole Massif Central.

Lower unit (6730-3200 cal. BP)

All along this unit the OM contents appeared to remain stable both from a quantitative (TOC: 8-10%) and qualitative point of view (HI and OI,, 250-300 mgHC.g -1 TOC and 100-150 mgO 2 .g -1 TOC, respectively). These geochemical characteristics sign an OM classically derived indistinctly from terrestrial plants [START_REF] Meyers | Lacustrine sedimentary organic matter records of Late Quaternary paleoclimates[END_REF] and from diatoms which appear to produce rather similar HI and OI values [START_REF] Ariztegui | Lacustrine organic matter and the Holocene paleoenvironmental record of Lake Albano (central Italy)[END_REF].

Throughout this unit, 6 phases of relatively higher background detrital input are depicted on the basis of MS variations (Figure 5), in particular on long-term increasing tendencies and more short-term but highly significant increases in MS. These major features seem to coincide with the general pattern of the climate-driven Lake Accesa level evolution (Tuscany, North-Central Italy, reflecting the whole West-European pattern; [START_REF] Magny | Holocene climate changes in the central Mediterranean as recorded by lake-level fluctuations at Lake Accesa (Tuscany, Italy)[END_REF], and more generally with periods of lower solar activity [START_REF] Wanner | Mid-to Late Holocene climate change: an overview[END_REF], the latter inducing climatic variations (with cooler and more humid conditions) considered to favour enhanced soil erosion on catchments [START_REF] Arnaud | 7200 years of Rhône river flooding activity in Lake Le Bourget, France: a high-resolution sediment record of NW Alps hydrology[END_REF][START_REF] Debret | Northwestern Alps Holocene paleohydrology recorded by flooding activity in Lake Le Bourget, France[END_REF]. However, this comparison is not sufficient to explain the amplitude of variation of the detrital input observed at ca. 5900 cal. BP, which is much greater than the other ones in this unit, or the 3800 cal. BP increase of detrital input that is not correlated with a climatic event. Other factors must be invoked, such as human impact that can be assessed from pollen and NPP analyses (Figure 5). At ca. 6000 cal. BP, the slight decrease in the AP/T ratio, associated with an increase in herbaceous taxa and dung-related fungi, evidence the first, moderate woodland opening accompanied by local grazing activity. Together with a favorable climatic context, these putative slight human impacts likely influenced detrital inputs. The corresponding catchment occupation was most probably occasional, as pollen and NPP indices of abandonment are observed immediately after (renewal of heliophilous trees such as Pinus, decline of coprophilous fungi). This lapse of time is immediately followed by a well-known abrupt climate change, dated to ca. 5600 cal. BP [START_REF] Magny | Tripartite climate reversal in Central Europe 5600-5300 years ago[END_REF]. This change is not recorded by an increase of detrital input in Lake Aydat but pollen clearly attest to the development of a beech grove, characteristic of a cooler and wetter climate [START_REF] De Beaulieu | Apport des longues séquences lacustres à la connaissance des variations des climats et des paysages pléistocènes[END_REF]. A higher human pressure is recorded in the catchment by pollen and NPP data (fall of Fagus, increase of Poaceae and API) between ca. 4900-4600 cal. BP. This coincides with a high MS value denoting stronger detrital inputs. The latter that were favored by a higher erodibility of the soils subsequent to the change of vegetation, are also in agreement with previous work by [START_REF] Miras | Multi-disciplinary approach to changes in agropastoral activities since the Sub-Boreal in the surroundings of the "narse d'Espinasse" (Puy de Dôme, French Massif Central)[END_REF] which showed an important phase of fire-clearing at this period. The major flood event of the whole core is evidenced at ca. 3800 cal BP. Its thickness (6 cm), reflecting its intensity, is unusual compared to the other ones. This event happened during a period of increasing human landscape management (ca. 3900-3500 cal BP). Indeed, a marked woodland opening is associated with an extension of grassland and heliophilous taxa during this period, also described in the neighbouring site of the Narse d'Espinasse [START_REF] Miras | Multi-disciplinary approach to changes in agropastoral activities since the Sub-Boreal in the surroundings of the "narse d'Espinasse" (Puy de Dôme, French Massif Central)[END_REF]. The rise of API is associated with a significant increase in dung-related fungi, especially Sporormiella, attesting to the local presence of animals [START_REF] Davis | Sporormiella fungal spores, a palynological means of detecting herbivore density[END_REF]. This points to the highly probable role of anthropogenic activities as a trigger of this flooding event. Then, a lesser anthropogenic pressure (revealed by a decrease in anthropization indices and a renewal of the forests, ca. 3500-3200 cal. BP) on the catchment allowed us to better distinguish a climatic imprint during the last phase of higher detrital input.

Thus, from the beginning of the sedimentary record to the Final Bronze period, detrital input variations were already under the joint influence of climate and of human activities, the effects of the latter being indeed punctually perceptible from the Middle Neolithic (ca. 5900 cal. BP).

Upper unit (1770 -0 cal. BP): general overview

MS variations in the upper unit enabled 6 phases of higher background detrital input to be distinguished, at ca. 1510-1210 cal. BP, ca. 1130-1000 cal. BP, ca. 950-670 cal. BP, ca. 620-500 cal. BP, ca. 430-150 cal. BP, and ca. 90-50 cal. BP (Figure 6). The MS values reached during these events are 2-4 times higher than in the lower unit. These phases of high detrital input coincide neither with known periods of climatic variations, nor with general trends of level fluctuations in Western Central Europe (Figure 6; [START_REF] Magny | Holocene climate changes in the central Mediterranean as recorded by lake-level fluctuations at Lake Accesa (Tuscany, Italy)[END_REF][START_REF] Magny | Orbital, ice-sheet, and possible solar forcing of Holocene lake-level fluctuations in west-central Europe. A comment on Bleicher[END_REF]. Conversely and strikingly, phases of lower detrital input occur when solar activity is lowsuch as during Wolf and Spörer [START_REF] Delaygue | An Antarctic view of Beryllium-10 and solar activity for the past millennium[END_REF] that are supposedly characterized by enhanced erosional fluxes [START_REF] Magny | Holocene climate variability as reflected by mid-European lake-level fluctuations and its probable impact on prehistoric human settlements[END_REF][START_REF] Magny | Orbital, ice-sheet, and possible solar forcing of Holocene lake-level fluctuations in west-central Europe. A comment on Bleicher[END_REF]. This inconsistency prompted us to invoke other factors than climate to explain these particular variations in detrital input. It is worth noting that detrital input and the frequency of flooding events increase when palynological data attest to a global increasing trend of local human impact throughout the last two millennia, as discussed below (Figure 6). Otherwise, diatom blooms are encountered all along this unit, and they are sometimes highly prominent (Figures 3,6).

As already mentioned above, HI and OI values are most probably due to a mixture of terrestrial OM and diatoms. Along the whole core, as is generally observed (e.g. [START_REF] Disnar | Microbial mat development and dolomite formation under pre-evaporitic conditions during the Atlantic in a temperate area: the Sarliève Lake (French Massif Central)[END_REF], TOC and HI remain correlated, whereas HI and OI are anticorrelated. Thus, the simultaneous variation in these different parameters delineates different sedimentation phases.

The top of the mass wasting deposit, dated from ca. 1770 cal. BP, delimits the beginning of the upper unit. This period coincides with a phase of higher lake levels in the Alps and the Jura mountains [START_REF] Magny | Holocene climate variability as reflected by mid-European lake-level fluctuations and its probable impact on prehistoric human settlements[END_REF]. In the absence of other evidence, this suggests that the gravitary event might have been triggered by a rise in the level of Lake Aydat, leading to an increase in hydrostatic pressure on a substantial and unstale accumulation of sediments that provoked the destabilization of the latter at the front of the Veyre River delta, as suggested by a morphological anomaly on sub bottom acoustic profiles (Figure 2).

1770-1500 cal. BP

MS and organic indices (HI, OI) are in the same range as in the lower unit and are thus highly comparable, apart from TOC that show lower values. On the contrary, pollen and NPP data support the beginning of continuous crop cultivation. Woodlands are also attested as in the neighbouring site of the Narse d'Espinasse where deforestation is dated from the transition of the 2 nd Iron Age-Roman period [START_REF] Miras | Multi-disciplinary approach to changes in agropastoral activities since the Sub-Boreal in the surroundings of the "narse d'Espinasse" (Puy de Dôme, French Massif Central)[END_REF].

1500-1200 cal. BP

During this first outstanding phase of detrital input (#1, Figure 6), the background sedimentation increases sharply: when compared to previous periods, MS values are multiplied by 2 around 1500 cal. BP, and by 4 around 1250 cal. BP. This abrupt and definitive change in the detrital input pattern matches a marked decrease in solar activity [START_REF] Wanner | Mid-to Late Holocene climate change: an overview[END_REF]. Neither TOC nor HI or OI values undergo marked variations (TOC ~5.5%, HI ~250 mgHC.g -1 TOC, OI ~125 mgO 2 .g -1 TOC). Palynological data clearly evidence a sharp increase in the human pressure during this period. The drop in the AP/T ratio and the increase in herbaceous taxa values indicate large and repeated woodland openings associated to the extension of grasslands. The increase in API, crop pollen and a significant rise in coprophilous fungi prove the local presence of livestock in the surroundings of the lake, and attest to a land-use system that included crop cultivation. The end of this first phase of detrital input (at ca. 1200 cal. BP) is accompanied by the doubling of the sedimentation rate, which then reaches more than 5 mm/yr (background sedimentation), a much greater value than that of the deeper parts of the sediment record. This change takes place at the end of a wetter period, in a context of high anthropogenic pressure. These two factors could have favored the development of primary productivity in the lake, as testified by the numerous diatom blooms observed from this period (the amount of which is sufficient to explain the doubling of the sedimentation rate; Figure 3) that could sign the beginning of the first eutrophication of the lake.

1200-150 cal. BP

The beginning of this period (ca. 1200-1130 cal. BP) records a transitory but marked decrease in MS (< 50.10 -5 S.I.) accompanied by an increase in TOC (up to ca. 10%) and simultaneously in HI, with a coeval decrease in OI. Pollen and NPP do not record any substantial change in human pressure on the catchment, which remains globally high.

However, the observation of the core reveals the pervasiveness of diatom blooms during this interval (Figure 3) that is confirmed by the rise in the TOC and HI values. Accordingly, this short period indicates the maximum of the eutrophication initiated from 1200 cal. BP, probably favoured by increased nutrient inputs linked to strong anthropogenic pressure and to more favorable climatic conditions [START_REF] Hilfinger | A 2500 year sediment record from Fayetteville Green Lake, New York: evidence for anthropogenic impacts and historic isotope shifts[END_REF]. This short primary period is followed by a transitory trend, leading to the outstanding detrital phase #2, marked by a sharp decrease in TOC and HI values, and an increase in OI values (Figure 3). Then the stabilisation of TOC at around 4%, of OI and HI at 160 mgO 2 .g -1 TOC and 210 mgHC.g -1 TOC, respectively, are observed, these values testifying to a more oxidized and biodegraded OM than before [START_REF] Disnar | Assessment of peat quality by molecular and bulk geochemical analysis; application to the Holocene record of the Chautagne marsh (Haute Savoie, France)[END_REF]. The mean MS value reaches ca. 75.10 -5 S.I. Between ca. 1100 and 890 cal BP, human occupation (mainly based on grazing and cereal cultivation) is signed by crop pollen values above 10%, associated to moderate woodland clearances, confirming the maximum anthropogenic pressure reported by [START_REF] Miras | Multi-disciplinary approach to changes in agropastoral activities since the Sub-Boreal in the surroundings of the "narse d'Espinasse" (Puy de Dôme, French Massif Central)[END_REF] in the Espinasse peat marsh. The recording of more or less regularly spaced and thick flood deposits begins from this time period, underlining the probable role of human activities as triggers (at least partly) of such events. Four flood deposits are detected during the 9 th century, at the beginning of the 2 nd phase of detrital input (Figure 3). MS values decrease once more just after the detrital phase #3 (Figure 6), during the Wolf solar minimum (680-600 cal. BP), together with higher HI and TOC, lower OI, and again with a dominance of diatom blooms.

The latter are still associated to a slight decline in human activities, with a moderate renewal of tree taxa evidenced by the slight increase in the AP/T ratio. Comparably, another significant diatom bloom phase is observed between 500-450 cal. BP (between detrital phases #4 and #5), with the same consequences in terms of MS, and to a lesser extent of TOC, HI and OI. The greatest flood event frequency of the core is reached during the detrital phase #5 (9 events during the XVIII th century). The intensity of detrital input and the frequency of flood events do not decrease between 300-150 cal. BP. During this period, pollen and NPP data reveal the existence of a complex land-use system combining grazing and diversified cultures. Forestry is also in use as the AP/T ratio presents minimum values (ca 15%), confirmed by historical sources [START_REF] Georlette | Quelques aspects de l'histoire des forêts françaises depuis la fin du moyen-âge jusqu'à la promulgation de l'Ordonnance de 1669[END_REF][START_REF] Michelin | Les jardins de Vulcain. Paysages d'hier, d'aujourd'hui et de demain dans la chaîne des Puys du Massif Central français[END_REF]. All this leads to an amplification of erosion and of detrital input, apparently independent of any climate forcing.

150 cal. BP -present

This last phase initially displays a similar trend in MS to the previous one, before an abrupt decrease in the signal intensity. This phase also differs from the previous ones by a significant increase in TOC (up to 6% in the most recent sediment), whereas OI reaches 125 mgO 2 .g -1 TOC and HI 300 mgHC.g -1 TOC. This indicates a substantial supply of OM that has still not suffered extensive alteration. These values are also comparable to those observed between ca. 1200-1130 cal. BP, and that were interpreted as indices of eutrophication of the lake. Considering that the lake is currently under this status, the shift of the considered parameters probably signs the change in trophic status of the lake, the beginning of which is dated from ca. 150 cal. BP in this hypothesis. Accordingly, a major landscape change is observed during this period with a renewal of tree dynamicsmainly pioneer trees such as Pinus which colonize abandoned areas. The regression of the main API and coprophilous fungi evidence locally a decrease in the anthropogenic pressure, which is well documented [START_REF] Michelin | Les jardins de Vulcain. Paysages d'hier, d'aujourd'hui et de demain dans la chaîne des Puys du Massif Central français[END_REF]. Crop cultivation is more affected than grazing activity. This new land-use system includes reforestation with exotic trees (Picea) that is observed since ca. the beginning of the 20 th century [START_REF] Michelin | Les jardins de Vulcain. Paysages d'hier, d'aujourd'hui et de demain dans la chaîne des Puys du Massif Central français[END_REF].

General discussion: drivers of environmental changes

Thus, Lake Aydat sediments archive a succession of detrital phases of both climatic and anthropogenic origin:

-From 6730 to 3200 cal. BP, climate appears most of the time as the principal driver of detrital input. However, every occasional human occupation around the lake results in a well-marked increase in detrital input. For instance, the first punctual human activities in the catchment and the cooler and wetter climatic period at ca. 5900 cal. BP probably reinforce each other, entailing an intensification of detrital input.

-Then, the role of the climate on the evolution of the detrital input becomes less obvious as anthropogenic pressure increases. The latter reaches the threshold necessary to definitely disrupt the detrital input pattern: the major changes in land management initiated ca. 1500 cal. BP lead to the definitive change of this pattern.

-This is followed by (1) the doubling of the background sedimentation rate (ca. 1200 cal. BP), caused by the increase in the occurrences of diatom blooms and most of all (2) by the appearance of recurrent and numerous flooding events from 1100 cal. BP, all of these features being certainly linked to the growing pressure of anthropogenic activities on the local environment. Thus, through time, human activities have overtaken climate forcing and dictated a new sedimentary dynamics that still prevails. The periods of bloom predominance partially complicate the signal arising from the catchment. Consequently, MS records the catchment evolution, together with the autochthonous signal. What underlies the sharp transitions from blooms to intense detrital phases is not clearly established, but probably results from a threshold effect. The general trend of the last few centuries had also been previously observed in the sediments from the Pavin crater lake over the last 700 years (ca. 20 km SW Aydat; [START_REF] Stebich | Vegetation history, human impact and climate change during the last 700 years recorded in annually laminated sediments of Lac Pavin, France[END_REF], which suggests an anthropogenic regional control on the lacustrine sedimentation dynamics. Comparison of the Aydat record with others in the area is much more difficult due to the lower temporal resolution of the previous studies (e.g. maar Lake Le Bouchet; [START_REF] Reille | History of the Würm and Holocene vegetation in western velay (Massif Central, France): A comparison of pollen analysis from three corings at Lac du Bouchet[END_REF]; Lake Chambon, [START_REF] Gay | Estimation of Late Glacial and Holocene chemical erosion rates, Lake Chambon watershed, Massif Central, France[END_REF]; Sarlieve marsh, [START_REF] Macaire | Quantitative analysis of climate versus human impact on sediment yield since the Lateglacial: The Sarliève palaeolake catchment (France)[END_REF]. This problem is not specific to the area studied here, since the majority of studies available on the Holocene climate, covering either the last centuries or millennia at a high resolution, or a multi-millenial scale at a low resolution, make any comparison with high-resolution sedimentary records on multi-millenial time scales difficult [START_REF] Wanner | Mid-to Late Holocene climate change: an overview[END_REF].

Conclusions

The sedimentary sequence retrieved in Lake Aydat covers the last 6700 yrs, constitutes a high-resolution hydrologic record unique in the Massif Central and reflects the dynamics of a lake that is very sensitive to environmental changes. The particular morphology of the valley favored the development of a strongly dilated and high quality series. Low amplitude variations of detrital input until 1500 cal. BP are interpreted as mainly climatedriven and seem connected to solar activity. They are punctually interrupted by human-driven phases of higher detrital input. Later on the sedimentation is much more disturbed by human activities that induced, in a favorable climatic context, (i) recurrent flooding events since the Middle Ages (ca. 1100 cal. BP) and (ii) the doubling of the background sedimentation rate.

Different phases of eutrophication of the lake were also distinguished. According to the sedimentary archive, the current one was probably initiated ca. 150 cal. BP. The strong anthropogenic imprint on the sedimentary record complicated its comparison with other palaeoclimatic records. But this multi-proxy study documents major environmental changes during the mid-and late-Holocene, and constitutes a remarkable example of agropastoral dynamics leading to a definitive change in the detrital input pattern of a lake. [START_REF] Wanner | Mid-to Late Holocene climate change: an overview[END_REF] and Lake Accesa level fluctuations [START_REF] Magny | Holocene climate changes in the central Mediterranean as recorded by lake-level fluctuations at Lake Accesa (Tuscany, Italy)[END_REF]. Phases of higher detritism are indicated by the horizontal grey strips. MWD: mass wasting deposit.

Figure 6: Background signal of the upper unit -MS, TOC, OI, HI, pollen and NPP analyses, occurrence and frequency of flood events and eutrophication phases compared to West-Central European (WCE) lake-level records [START_REF] Magny | Holocene climate variability as reflected by mid-European lake-level fluctuations and its probable impact on prehistoric human settlements[END_REF], Lake Accesa level fluctuations [START_REF] Magny | Holocene climate changes in the central Mediterranean as recorded by lake-level fluctuations at Lake Accesa (Tuscany, Italy)[END_REF], and solar activity [START_REF] Delaygue | An Antarctic view of Beryllium-10 and solar activity for the past millennium[END_REF][START_REF] Wanner | Mid-to Late Holocene climate change: an overview[END_REF]. MWD: mass wasting deposit.

Figure 1 :

 1 Figure 1: Location of Lake Aydat and its geological setting (after Boivin et al., 2004). Dashed lines locate topographic profiles presented in Fig. 2.

Figure 2 :

 2 Figure 2: (a) Bathymetric map of Lake Aydat and location of the coring site and of the seismic profiles shown in (b). (c): Altitudinal profile transverse to the lake and extrapolation showing the morphology of the valley (location: see Fig. 1). (d): Schematic representation of a longitudinal profile, from the palaeodelta to the coring in the basaltic flow. Dashed line: approximate outline of the supposed location of the substratum of the lake, estimated from the river profile tendency.

Figure 3 :

 3 Figure 3: Core description, lithology and physical parameters (density, MS, and XRF -Rb, Ti, K), stratigraphic location of the 137 Cs and 14 C ages and of the historical floods. Mass

Figure 4 :

 4 Figure 4: Age-depth model, correlation with historical floods, sedimentation rates and sedimentological units. Stars and diamonds locate the depths of the pictures presented. 137 Cs, 241 Am and 7 Be of the top of the core are provided on the right.

Figure 5 :

 5 Figure 5: Background signal of the lower unit -MS, TOC, OI, HI, pollen and NPP analyses, compared to solar activity[START_REF] Wanner | Mid-to Late Holocene climate change: an overview[END_REF] and Lake Accesa level fluctuations(Magny

Table I :

 I AMS radiocarbon dates and 137 Cs results obtained from the Lake Aydat core.

	Event nr	Master core depth (cm)	Depth-Age model Age AD Age cal. BP Uncertainty	Historical flood events	Event nr	Master core depth (cm)	Depth-Age model Age AD Age cal. BP Uncertainty	Historical flood events
	# 1	21-22			1973		-23		5		1976			# 29	409-410	1280	670	50	-
	# 2	58-59			1900		50		40		1907			# 30	412-416	1275	675	50	-
	# 3 # 4 # 5 # 6	Datation method 85-87 116-117 Type of material 1849 1791 121-122 1782 Uncorrected Corrected 101 Master core depth (cm) 159 168 123-125 1778 172	40 Radiocarbon 1846 age (BP) 40 1790 40 1782 40 1778	# 31 Calibrated age # 32 (2σ; years cal. BP) # 33 # 34	416-420 428-430 Laboratory 435-436 Name 450-451	1273 1245 1216	677 693 705 734	50 50 50 50	1271 1258 --
	# 7 # 8 # 9	137 Cs 127-128 sediment Bulk 1772 137 Cs 132-133 1763 Bulk sediment 144-148 1740	16.5 25.5	178 187 210	16.5 24.5	40 40 40	--	1770 1766 1740	-36 (1986 AD) # 35 # 36 -13 (1963 AD) # 37	462-463 474-475 479-480	--	1193 1171 1161	757 779 789	50 50 50	-1174 -
	# 10	14 C 149-150	Twig	1736	349.7	214	332.7	40	520 ± 30 1733			570 ± 40 # 38	SacA 21687 481-482	1157	793	50	-
	# 11	14 C 160-161	Twig	1715	387.7	235	370.7	40	700 ± 30 1716			650 ± 50 # 39	SacA 21688 492-493	1136	814	50	-
	# 12	14 C 164-165	Twig	1707	467.5	243	433.2	1330 ± 30 40 1707		1270 ± 80 # 40	SacA 16355 502-503	Excluded (reworked debris) 1117 833	50	-
	# 13	14 C 172-174	Twig	1692	705.8	258	656.8	1265 ± 30 40 1697		1230 ± 40 # 41	SacA 21685 504-505	1113	837	50	1109
	# 14	14 C 175-176	Twig	1688	782.1	262	727.5	1575 ± 30 40 -		1480 ± 40 # 42	SacA 21686 509-511	1104	846	50	-
	# 15	14 C 186-187	Twig	1667	790.1	283	735.5	1630 ± 30 40 1668		1520 ± 60 # 43	SacA 21689 511-513	1102	848	50	-
	# 16	14 C 195-196	Leaf		1651	820.3	299	766.5	1825 ± 30 40 1651		1780 ± 40 # 44	SacA 21690 515-517	1096	854	50	-
	# 17	14 C 214-215	Leaf		1615	1056	335	-	2440 ± 30 40 1615		2530 ± 260 # 45	SacA 16356 526-527	Excluded (intermediate unit) 1077 873	50	-
	# 18	14 C 240-243 Charcoal 1565	1094.2	385	780.5	3005 ± 30 40 1565		3210 ± 100 # 46	SacA 16357 530-531	1069	881	50	-
	# 19	14 C 256-258	Leaf		1538	1136.5	412	823.5	3190 ± 30 40 1536		3420 ± 60 # 47	SacA 16362 549-550	1034	916	50	1037
	# 20	14 C 303-306	Leaf		1449	1297.2	501	979.5	3605 ± 30 40 -		3920 ± 80 # 48	SacA 16363 552-553	1028	922	50	1029
	# 21	14 C 319-321	Leaf		1422	1389.2	528	1071.5	3840 ± 30 40 1428 ?	4260 ± 140 # 49	SacA 16364 557-558	1020	930	50	-
	# 22	14 C 323-324	Twig	1416	1401.2	534	1083.5	4000 ± 30 40 1414		4480 ± 80 # 50	SacA 16358 593-594	952	998	50	966 ?
	# 23	14 C 334,5-336,5 Seed (?) 1395	1576 ± 5 555	1258.7 ± 5 4615 ± 30 40 1394		5380 ± 120 # 51	SacA 16365 600-605	939	1011	50	-
	# 24	14 C 340-343	Leaf		1388	1644.7	562	1327.5	4750 ± 30 40 1389		5510 ± 120 # 52	SacA 16359 621-622	906	1044	50	-
	# 25	14 C 344-346 Leaf (?) 1384	1685.2	566	1368	4800 ± 35 40 1384		5540 ± 100 # 53	SacA 16360 633-634	885	1065	50	886
	# 26	14 C 348-349	Twig	1378	1767.7	572	1449.5	5280 ± 30 40 -		6080 ± 140 # 54	SacA 16366 635-637	882	1068	50	-
	# 27	359-360			1357		593		50		-			# 55	642-644	870	1080	50	868
	# 28	365-366			1345		605		50		-			# 56	658-659	843	1107	50	-

Acknowledgements

We thank ARTEMIS program for AMS radiocarbon dating, B. Vannière and A. Stock (Chrono-Environnement, Besançon) for MS measurements, I. Billy (EPOC, Bordeaux, France) for XRF measurements, IPROS (Orléans, France) for density pictures, G. Ledoux and P. Lajeunesse (CEN Université Laval, Québec, Canada) for the seismic survey, B. Fanget and E. Malet for their help during the coring, and J. Granja, V. Janvier and A. Foucher for having contributed to the comprehension of the sedimentary infill, and the anonymous reviewers for their constructive comments.

Funding

This study was supported by the Erode project funded by the INSU/CNRS (Institut National des Sciences de l'Univers / Centre National de la Recherche Scientifique). M.L. also acknowledges the Région Centre for the attribution of a Ph.D grant.