Rock art taphonomy in Lesser Antilles: study of wall weathering and engravings preservation in two preColumbian caves on Marie-Galante Island.

International audienceThe islands of Guadeloupe deliver some caves and rock shelters occupied in precolumbian times, including rare engraved caves whose age of occupation remains unclear and some burial caves used in the Late Ceramic Age. Question arises whether the absence of engravings in these latter sites reflects an archaeological reality or, in contrast, is linked to poor conditions for the preservation of cave art. Here we present a study carried out to determine the conditions of conservation of precolumbian rock art. This study was conducted in two sites of Marie-Galante, the cave Blanchard, without obvious engravings but with a funeral dimension, and the Morne Rita cave, rich in engravings. This work includes a series of hygrothermal measurements, the determination of authigenic minerals, and the study of both cave sediments.Two types of cavities can be opposed in terms of micro-climate pattern and transformation of the walls. Caves acting as trap cold air, like Morne Rita cave, have a high humidity which causes a light corrosion of the rock and mineral crust formation. Engravings modification proceeds mainly by their recovery by mineralization and the petroglyphs are relatively well preserved. In contrast, sites acting as warm air traps, like Blanchard cave, are characterized by an unstable air mass that promotes the entrance of drying air rich in salt-sprays, especially when sites are not far from the coast, which is the most frequent case in the Lesser Antilles. As a result, rock is exposed to salt weathering, and walls retreat caused by this phenomenon has been estimated in the order of a millimeter per century. This rate is sufficient to result in the disappearance of engravings that could exist in such sites. The walls of the Blanchard cave were examined in detail to find any traces of weathered petroglyphs, and we present here a wall morphology that could be explained by this hypothesis.This study highlights the control of site microclimatic pattern on the preservation of petroglyphs and concludes, therefore, on the existence of a bias in the distribution of rock caves in the Lesser Antilles where decorated caves were probably many more that which is currently found. The implications of this result on precolumbian cave occupation models are finally discussed

Were they engraved? Cave art taphonomy in the Lesser Antilles - Working hypotheses

Here we present the working hypotheses of a project dedicated to the taphonomy of cave rock art in the Lesser Antilles, based on results provided by the preliminary study of two Amerindian-occupied caves in Marie-Galante, FWI. In the caves of Guadeloupe, it is sometimes possible to observe wall morphologies that resemble pre-Columbian petroglyphs, but without engraved lines. The question arises then whether these morphologies are engraved pictures. Blanchard Cave (S coast of Marie-Galante), contains such wall morphologies that can be thought to represent weathered petroglyphs, especially when considering the pre-Columbian burials preserved in the cave entrance. The study of physical processes acting in the site provides an understanding of mechanisms that could have caused the engravings' disappearance. Site microclimatology, assessed by hygrometric and thermic measurements, reveals an unstable regime due to air currents that bring cold air deep into the cave. The result is a limited hygrometry and, above all, a transport of sea spray. The marine aerosol inputs highlight the occurrence of salt and gypsum minerals on the walls that trigger salt weathering of the rock. The resulting sediment is typically loose, very light tan silt that accumulates on the cave floor. Test pits were used to characterize and to date sediments deposited in the cave. Taking into account the rate of accumulation of sediments produced by weathering allows estimates of mean wall weathering of up to 0.6 cm/century. Such a rate would explain the alteration and even the disappearance of Amerindian carvings that are several centuries old. The questionable morphologies observed in Blanchard Cave have been compared to the Pre-Columbian petroglyphs preserved in the nearby cave of Morne Rita through photogrammetric recording. This comparison shows that the wall morphologies observed in the first site have a size and shape that fall into the variability of Pre-Columbian artworks, although they are characterized by a blurred surface and an enlargement of the outline and the cupules ascribable to the wall alteration by salt weathering. Based on these observations, it can be hypothesized that the Blanchard cave is a degraded petroglyph site. These preliminary results also help to identify the factors leading to certain types of degradation (size, morphology, nature of the rock and location). Considering that such factors are common in Lesser Antilles caves, a more general theory can be proposed that a number of engraved caves of the Lesser Antilles have not been identified as such. These hypotheses, if proven true, have two important implications for the interpretation of the pre-Columbian decorated caves distribution: 1) an under-representation of the number of known sites and 2) a bias, in the preserved sites, favoring "wet" caves where salt weathering of the cave walls does not occur.Aquí presentamos la hipótesis de trabajo de un proyecto dedicado a la tafonomía de arte de cuevas en las Antillas Menores, basada en el estudio preliminar de dos cuevas en Marie-Galante, FWI, ocupadas por amerindios. En las cuevas de Guadeloupe, a veces se puede observar morfologías de la pared que parecen indicar la presencia de petroglifos precolombinos, pero no dejan reconocer líneas grabadas. La pregunta es si realmente se trata de creaciones humanas. La cueva de Blanchard (costa sur de Marie-Galante) muestra este fenómeno, hacemos notar que en este sitio también existen tumbas precolombinas. El estudio de los procesos físicos que actúan en el sitio provee un entendimiento de los mecanismos que podrían haber causado la desaparición de los grabados. La microclimatología del sitio, evaluada por medidas higrométricas y térmicas, revela un régimen inestable debido al corriente de aire que trae aire frío al interior de la cueva. El resultado es una higrometría limitada y, sobre todo, el ingreso de rociada de agua del mar. El efecto de "aerosol marino" favorece la ocurrencia de sal y minerales de yeso en la pared que resulta en un desgaste por sales y un sedimento suelto de color claro que acumula en el suelo de la cueva. Se excavaron sondeos para caracterizar y datar los sedimentos depositados en la cueva. Tomando en cuenta el grado de acumulación producido por el desgaste permite estimaciones del desgaste de pared de hasta 0,6 cm / siglo. Esto podría explicar la alteración y aún la desaparición de grabados amerindios que tienen una antigüedad de varios centenares de años. Comparamos loas morfologías en cuestión de la cueva de Blanchard a petroglifos precolombinos preservados en la cueva cercana de Morne Rita a través de la documentación fotogramétrica. Esta comparación muestra que las morfologías de la pared en el primer sitio tiene un tamaño y una forma que caen dentro de la variabilidad de arte precolombino aunque se caracterizan por una superficie borrosa y un tamaño mayor del contorno y depresiones que pueden ser adscritos a los efectos de desgaste por sal. Basado en estas observaciones, sugerimos que la cueva de Blanchard es un sitio de petroglifos erosionados. Estos resultados preliminares pueden ayudar a identificar los factores que conducen a ciertos tipos de erosión (tamaño, morfología, naturaleza de la roca y ubicación). Considerando que estos factores son corrientes en las cuevas de las Antillas Menores, proponemos que una cantidad de cuevas con grabados no fueron identificadas como tales. Si esta hipótesis puede ser comprobada, hay dos implicancias importantes para la distribución de cuevas decoradas precolombinas: 1- una sub-representación de la cantidad de sitios conocidas y 2- un prejuicio en los sitios preservados, ya que se favorecen cuevas "húmedas" donde el desgaste por sales no ocurre

Le plus vieil objet de fer d’Europe occidentale est-il landais ?

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Utilisation du microscope confocal pour la caractérisation des états de surface lithiques : Application au niveau châtelperronien de la Roche à Pierrot (Saint-Césaire, Charente-Maritime)

International audienceLes vestiges lithiques font partie des témoins matériels principaux nous permettant d’étudier les modes de vie des populations paléolithiques. Le site de la Roche à Pierrot, actuellement soumis à une révision archéostratigraphique, suscite de nombreux questionnements à propos des modalités de transition entre le Paléolithique moyen et récent. Cette période charnière, représentée par le niveau châtelperronien, est reconnue pour ses états de surface complexes qui posent question quant à l’intégrité technique de cet ensemble. Cependant, les processus post-dépositionnels affectent l’aspect des artefacts et entrainent de multiples modifications connues sous le nom « d’états de surface ». Actuellement, la plupart des travaux taphonomiques et tracéologiques analysent ces états de façon empirique. Notre travail consiste en l’élaboration d’une nouvelle méthodologie afin de dépasser la subjectivité de ces études grâce à l’acquisition de mesures de rugosité au moyen du microscope confocal. Un référentiel géologique, composé de deux types de silex locaux, a été constitué afin de comparer l’impact des processus post-dépositionnels dans l’environnement immédiat du site ainsi qu’à l’intérieur de la surface de fouille. Le protocole novateur élaboré dans le cadre de cette étude a permis la distinction de divers degrés d’altération au sein des échantillons géologiques et archéologiques, notamment en ce qui concerne la patine blanche et le lustre localisés sur la surface des objets. Les résultats de ce travail exploratoire confirment la possible utilisation du microscope confocal dans l’étude taphonomique des ensembles lithiques

Technological and functional analysis of 80–60 ka bone wedges from Sibudu (KwaZulu-Natal, South Africa)

Fully shaped, morphologically standardized bone tools are generally considered reliable indicators of the emergence of modern behavior. We report the discovery of 23 double-beveled bone tools from ~ 80,000–60,000-year-old archaeological layers at Sibudu Cave in KwaZulu-Natal, South Africa. We analyzed the texture of use-wear on the archaeological bone tools, and on bone tool replicas experimentally used in debarking trees, processing rabbit pelts with and without an ochre compound, digging in sediment in and outside a cave, and on ethnographic artefacts. Debarking trees and digging in humus-rich soil produce use-wear patterns closely matching those observed on most Sibudu tools. This tool type is associated with three different Middle Stone Age cultural traditions at Sibudu that span 20,000 years, yet they are absent at contemporaneous sites. Our results support a scenario in which some southern African early modern human groups developed and locally maintained specific, highly standardized cultural traits while sharing others at a sub-continental scale. We demonstrate that technological and texture analyses are effective means by which to infer past behaviors and assess the significance of prehistoric cultural innovations

Technological and functional analysis of 80–60 ka bone wedges from Sibudu (KwaZulu-Natal, South Africa)

Fully shaped, morphologically standardized bone tools are generally considered reliable indicators of the emergence of modern behavior. We report the discovery of 23 double-beveled bone tools from ~ 80,000–60,000-year-old archaeological layers at Sibudu Cave in KwaZulu-Natal, South Africa. We analyzed the texture of use-wear on the archaeological bone tools, and on bone tool replicas experimentally used in debarking trees, processing rabbit pelts with and without an ochre compound, digging in sediment in and outside a cave, and on ethnographic artefacts. Debarking trees and digging in humus-rich soil produce use-wear patterns closely matching those observed on most Sibudu tools. This tool type is associated with three different Middle Stone Age cultural traditions at Sibudu that span 20,000 years, yet they are absent at contemporaneous sites. Our results support a scenario in which some southern African early modern human groups developed and locally maintained specific, highly standardized cultural traits while sharing others at a sub-continental scale. We demonstrate that technological and texture analyses are effective means by which to infer past behaviors and assess the significance of prehistoric cultural innovations.publishedVersio

À la découverte de la plus ancienne sépulture africaine datant de 78 000 ans

Depuis plus d’un an, la pandémie a bouleversé le regard que nous portons sur la mort. Pour la première fois dans l’histoire de l’humanité, les décès ont été transformés en chiffres et en graphiques anonymes que chacun peut explorer, pays par pays, jour après jour, au réveil, sur l’écran de son téléphone portable. Mais cette nouvelle réalité ne change pas le sentiment de chagrin qui nous saisit lorsque la mort nous touche de près, affectant un proche. Quand nos ancêtres ont-ils ressenti pour la première fois ce désespoir ? Quand l’ont-ils transformé en un fait social, codifié par des normes transmises de génération en génération

Dynamics and sources of last glacial aeolian deposition in southwest France derived from dune patterns, grain-size gradients and geochemistry, and reconstruction of efficient wind directions

Dune pattern, grain-size gradients and geochemistry were used to investigate the sources and dynamics of aeolian deposition during the last glacial in southwest France. The coversands form widespread fields of low-amplitude ridges (zibars), whereas Younger Dryas parabolic dunes mainly concentrate in corridors and along rivers. Spatial modelling of grain-size gradients combined with geochemical analysis points to a genetic relationship between coversands and loess, the latter resulting primarily from dust produced by aeolian abrasion of the coversands. The alluvium of the Garonne river provided also significant amounts of dust at a more local scale. The geochemical composition of loess shows much lower scattering than that of coversands, due to stronger homogenisation during transport in the atmosphere. Overall, sandy loess and loess deposits decrease in thickness away from the coversands. Dune orientation and grain-size gradients suggest that the efficient winds blew respectively from the W to the NW during the glacial, and the W-SW during the Younger Dryas. A comparison between the wind directions derived from the proxy data and those provided by palaeoclimatic simulations suggests a change of the main transport season. Ground surface conditions and their evolution throughout the year, i.e. the length of the season with snow and frozen or moist topsoil, and the seasonal distribution of wind speeds able to cause deflation are thought to have been the main factors that controlled the transport season in the study area

Chronostratigraphy of two Late Pleistocene loess-palaeosol sequences in the Rhône Valley (southeast France)

International audienceA sedimentological and chronostratigraphical investigation was carried out on two loess sections located in the Mediterranean area in southeast France along the Rhône River (Lautagne) and the lower reach of a tributary of the Rhône River (Collias). High-resolution sampling (5–20 cm) for magnetic susceptibility, grain size distribution (including non-parametric end-member modelling), colour reflectance and geochemistry was performed. The chronology was based on luminescence dating of quartz grains and radiocarbon dating of small gastropod shells, coupled with hierarchical Bayesian modelling. The Collias section (~8 m thick) records the whole last climatic cycle. It comprises a thick red basal pedocomplex S1 developed during the Last Interglacial and the Early Glacial, similar to that observed elsewhere in southern and southeastern Europe. Loess deposition occurred during the Lower (L1L2) and the Upper Pleniglacial (L1L1). It was interrupted by soil formation during the Middle Pleniglacial, of which a brown Bwk horizon has been preserved (L1S1). By contrast, the ~5 m thick Lautagne section provides a detailed record of the Upper Pleniglacial. Weakly developed hydromorphic soils are correlated with the Greenland Interstadials GI-4 to GI-2, while the main period of coarse loess sedimentation corresponds to the Greenland Stadials GS-5 to GS-2. At a regional scale, the time of loess deposition ranges between 38.5 ka and 12 ka, with a peak at ~28–24 ka, overlapping with the maximal advance of the Alpine Ice Sheet (AIS). This strongly suggests that regional glacier dynamics was the main driver of loess sedimentation