Abstract Among the paintings and engravings found in the Chauvet-Pont d’Arc cave (Ardèche, France), several peculiar spray-shape signs have been previously described in the Megaloceros Gallery. Here we document the occurrence of strombolian volcanic activity located 35 km northwest of the cave, and visible from the hills above the cave entrance. The volcanic eruptions were dated, using 40Ar/39Ar, between 29 ± 10 ka and 35 ± 8 ka (2σ), which overlaps with the 14C AMS and thermoluminescence ages of the first Aurignacian occupations of the cave in the Megaloceros Gallery. Our work provides the first evidence of an intense volcanic activity between 40 and 30 ka in the Bas-Vivarais region, and it is very likely that Humans living in the Ardèche river area witnessed one or several eruptions. We propose that the spray-shape signs found in the Chauvet-Pont d’Arc cave could be the oldest known depiction of a volcanic eruption, predating by more than 34 ka the description by Pliny the Younger of the Vesuvius eruption (AD 79) and by 28 ka the Çatalhöyük mural discovered in central Turkey.

Citation: Nomade S, Genty D, Sasco R, Scao V, Féruglio V, Baffier D, et al. (2016) A 36,000-Year-Old Volcanic Eruption Depicted in the Chauvet-Pont d’Arc Cave (Ardèche, France)? PLoS ONE 11(1): e0146621. https://doi.org/10.1371/journal.pone.0146621 Editor: Michael D. Petraglia, University of Oxford, UNITED KINGDOM Received: October 5, 2015; Accepted: December 18, 2015; Published: January 8, 2016 Copyright: © 2016 Nomade et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability: All relevant data are within the paper and its Supporting material. Funding: PHD funding for Romain Sasco (2012-2014) was provided by the ED “MIPEGE” from the Université Paris-Sud XI (France). Competing interests: The authors have declared that no competing interests exist.

Introduction Volcanic eruptions are among the most impressive geological events on the surface of the earth. It is interesting to notice, however, that the oldest testimony of such an event in human history dates back only to about 9 ka [1]. Indeed it is only in 2013 that an Holocene eruption from the Hasan Däg (Central Turkey) dated at 8.97 ± 0.64 ka [1] strengthened the hypothesis made in the early 1960s by the archaeologist James Mallaart [2] that the Çatalhöyük mural coeval with the archeological level VII depicted a volcanic eruption. It has so far been considered the oldest known painting of a volcanic eruption. The second oldest one is found in Armenia but is more than 2 ka younger [3]. At this site, located in the Syunik upland, a group of six petroglyphs dated at 7 ka ago (5th millennium BC) portrays the eruption of the Porak volcano [3]. These two sites predate by, at least, five millenniums the observations and testimony made by the Roman administrator and poet Pliny the younger of the AD 79 Vesuvius eruption (i.e. Letters 6.16 and 6.20). About 340 Paleolithic caves with parietal art have been discovered in Europe, the large majority of them in South France and Northern Spain with the oldest dating back between 40 to 36 ka [4,5]. This period coincides with the arrival in Western Europe of anatomically modern humans (Homo sapiens [6]) and associated to the Aurignacian culture. The Upper Paleolithic European iconography combines figurative depictions of mainly wild animals with a predominance of herbivores (e.g. bison, horse, reindeer…) and less frequent human representations as well as diverse abstract patterns. Drawings of humans are usually schematic compared to quasi-naturalistic drawings of animals. So far, and despite the large number of caves studied since the early 19th century, no painting, petroglyphs or engravings depicting natural scenery or geological phenomena from the Upper Paleolithic period have been found in Europe. Discovered on December 18, 1994, the Chauvet-Pont d’Arc cave (Ardèche, France; Fig 1) provides some of the earliest manifestations of prehistoric art and, as such, it was granted World heritage status by the United Nations (UNESCO) in 2014. Although the age of the paintings found in this cave has long remained controversial, radiocarbon dates have now robustly constraint the oldest occupations and drawings to between 37 and 34 ka cal BP [5]. The Chauvet-Pont d’Arc bestiary is particularly renowned for the predominance of so-called "dangerous animals" (e.g. cave lions, mammoths, rhinoceros), which are rather uncommon in Upper Palaeolithic iconography from Western Europe [7]. This bestiary also contains more classical animal drawings (e.g. horse, bison, megaloceros, ibex…) and human representations (negative and positive hands, vulvas, female lower body). This figurative bestiary coexists with a wide range of engraved or painted abstract signs (schematic “W”, "butterfly" and “spray-shape”) some of them unique to the Chauvet-Pont d’Arc cave [7,8]. The meaning of some of these signs is still unknown or subject to several hypotheses including, as we suggest here, depictions of volcanic eruptions. Hereafter we examine the possible meaning of the spray-shape signs (Fig 1C) in the light of new 40Ar/39Ar ages obtained on the Bas-Vivarais strombolian volcanoes located at 35 km northwest of the Chauvet-Pont d’Arc cave (Fig 1B). Indeed, the strombolian cones are visible from the hills located only few kilometers away from the cave entrance (Fig 1D). PPT PowerPoint slide

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larger image TIFF original image Download: Fig 1. The Chauvet-Pont d’Arc cave and the Bas-Vivarais volcanic field. (A) Digital elevation model of France (Courtesy NASA/JPL-Caltech) showing the MIS 2–3 active volcanoes and the Chauvet-Pont d’Arc cave; C.P: Chaîne de Puys; B.V: Bas-Vivarais. (B) Digital elevation model of the Bas-Vivarais and Ardèche (Courtesy NASA/JPL-Caltech). The volcanic centers investigated are highlighted in bold italic fonts. (C) Detail of the spray-shape sign engraving from the Megaloceros panel. (D) View from the plateau above the Chauvet-Pont d’Arc cave showing several strombolian cones located 35 km Northwest (Courtesy NASA/JPL-Caltech). https://doi.org/10.1371/journal.pone.0146621.g001

The Bas-Vivarais Volcanism The Bas-Vivarais volcanic field (Southeast end of the French Massif Central) is dispersed over 500 km² [9] and constituted by seventeen eruptive centers aligned along NW-SE faults (Fig 1B). This French region is an iconic place for volcanologists because in 1778 the geologist Faujas de Saint-Font has linked for the first time prismatic basaltic flows and volcanic activity at the Coupe d’Aizac cone [10,11]. Since 2014, the Bas-Vivarais region that evidences 500 Ma of the Earth history is recognized as World Geopark by United Nations Educational, Scientific and Cultural Organization. The Bas-Vivarais volcanism is characterized by phreatomagmatic eruptions (maars) preceded or followed by strombolian activity associated with the emission of lava flows filling pre-exiting valleys [12] (Fig 1B). The volcanic products are mainly alkali basalts derived from a unique enriched mantle source [13,14]. This activity has always been considered as one of the most recent in the entire Massif Central and suggested to be as young as the Chaîne des Puys volcanic field [10,11,15] (Fig 1A). Despite several attempts, the chronological framework of this volcanic activity remains poorly constrained. Only eight volcanic centers have been dated by thermoluminescence and 14C [12,15]. The volcanic activity is currently divided into three distinct phases. The oldest one, developed at the north of the area, in the high plateau, predates the last interglacial with a mean age of 166 ± 15 ka [12]. South of the studied area, more recent eruptive centers, associated with the valley filling lava flows, are found (Fig 1). The ages corresponding to this recent activity are clustered into two age groups respectively centered at 79 ± 5 ka and 45 ± 3 ka [12]. Because of the frequent occurrences of mantle and lower crust xenoliths in the lavas [12] no radiometric age determination of the recent activity is currently available. To improve the chronology of this young volcanic activity a study [16] has provided the first 40Ar/39Ar ages on the youngest activity of the Bas-Vivarais. We will present for the first time below some of these new radio-isotopic constraints.

Material and Methods All samples presented hereafter (i.e. Suc de Bauzon, Coupe d’Aizac, and le maar de Ray-Pic) were collected in June 2012, two years before the UNESCO labeled the Bas-Vivarais as World Geopark. Therefore, at the time, no specific permission was required for all the locations we investigated. Moreover, the field study did not involve endangered or protected species. 40Ar/39Ar ages were obtained by step-heating experiments on groundmass (120 to 150 mg) at the LSCE argon facility (France) using a high-sensitivity noble gas GV5400 instrument operated in ion counting mode. Irradiation procedures, extraction and gas cleanup, mass spectrometric measurements and blank corrections, are fully described in [17]. Ages are calculated using ACs-2 standard at 1.193 ± 0.01 Ma [18] and the total decay constant of Steiger and Jäger [19]. Several proposed calibrations of the 40Ar/39Ar chronometer are currently in use, yielding ages that vary by ~1% [20,21]. However, this implied difference in calibrated age of 250 to 300 years; thus negligible compared to the individual plateau age uncertainty (e.g. 11 ka, Fig 2). Correction factors for interfering neutron reactions were determined on pure compounds (K 2 O, CaF 2 ) irradiated in the same position and were: (39Ar/37Ar) Ca = 8.050 10−4, (36Ar/37Ar) Ca = 3.765 10−4, (40Ar/39Ar) K = 6.560 10−4; (38Ar/39Ar) K = 1.120 10−2. Mass discrimination was assessed by analysis of Air pipette throughout the analytical period, and was calculated relative to a 40Ar/36Ar ratio of 298.56 [22]. 40Ar/39Ar full analytical dataset and furnace blanks are provided as supporting material (S1 and S2 Tables). PPT PowerPoint slide

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larger image TIFF original image Download: Fig 2. Plateau spectra for the three volcanic centers dated. Uncertainties are given at the 2σ level. Plateau steps are plotted at the 1σ level. https://doi.org/10.1371/journal.pone.0146621.g002

Conclusion New 40Ar/39Ar constraints in the Bas-Vivarais (Ardèche, France) provides radiometric evidence for a volcanic activity between 30 and 40 ka, coeval with the Aurignacian occupation of the Chauvet-Pont d’Arc cave, only 35 km southwest. Spray-shape signs specific to this cave art are dated between 36.7 and 34.1 ka cal BP. They overlapping the age of the local volcanic activity. We propose that humans are likely to have witnessed one or several eruptions and depicted them using these complex signs. If this hypothesis is correct, these depictions predate over 34 millennia the observation by Pliny the Younger of the AD 79 Vesuvius eruption and by 28 ka the Çatalhöyük mural (Turkey), currently considered the oldest eruption painted by a human hand.

Supporting Information S1 Table. 40Ar/39Ar full dataset. Data are corrected from the blanks and discrimination. Data in red are not used to calculate plateau or inverse isochron ages. https://doi.org/10.1371/journal.pone.0146621.s001 (PDF) S2 Table. 40Ar/39Ar blanks dataset. https://doi.org/10.1371/journal.pone.0146621.s002 (PDF)

Acknowledgments Authors would like to thank Jean-Louis Joron (Laboratoire Pierre Süe, Saclay, France) for sample irradiation using the OSIRIS nuclear reactor of the Commissariat à l’Énergie Atomique et aux Énergies Alternatives (CEA Saclay). Authors would like also to thank Dr. J. Nomade, Dr. G. Guérin and Dr. H. Bertrand that provided use with a lot of information concerning the Bas-Vivarais volcanic field. We additionally thank Cecilia Garrec and Mathieu Daëron (LSCE) for the English editing. This is LSCE contribution N° 5670

Author Contributions Conceived and designed the experiments: RS SN VS HG. Performed the experiments: RS SN VS HG. Analyzed the data: SN DG RS VS HG VF. Contributed reagents/materials/analysis tools: SN DG VF JMG CB HV HG ER ED JFP DB. Wrote the paper: SN DG RS VF HG CB JMG.