Une nouvelle utilisation du concept Trifacial durant une phase ancienne du Paléolithique moyen de la vallée de l’Isle : le niveau 2 de Petit-Bost (Neuvic, Dordogne)

EnglishThe Trifacial lithic system is a concept combining flaking and shaping, mainly identified in Southwestern France, and characteristic of the Southern Acheulean. The Southern Acheulean was initially defined by F. Bordes in the lower layers of Combe-Grenal and Pech-de-l'Aze II (Dordogne). This lithic facies was considered to be different from the Acheulean from the North of France (Bordes, 1971), mainly because of the (core-like) biface morphology and the presence of flake cleavers. Since then, the initial definition of this techno-complex has been widely debated, with particular emphasis on raw material availability and a reappraisal of the presence of flake cleavers (Villa, 1981, 1983; Mourre, 2003; Mourre and Colonge, 2007; Turq et al., 2010). The last definition of this Southern Acheulean, referred to as an early Middle Palaeolithic, mentions " the absence of cleavers (sensu stricto), the presence of bifacial shaping (sensu lato) and a trifacial concept of production and/or shaping (Boeda, 1989) associated with varied core reduction methods " (Turq et al., 2010, p. 390). Thus, the presence of Trifacial production appears to be an important criterion. Most of the time, the aim of this production is to obtain flake blanks and a tool at the same time (Boeda et al., 1990). The triface can thus be considered as a core and a tool (named combined matrix). The flakes produced are generally similar to those from algorithmic systems (SSDA). The trifacial concept was first described by E. Boeda in levels 8 and 9 of Pech-de-l'Aze II in Dordogne (Boeda, 1989). It has since been identified in several sites in the same area, such as Barbas C'4 sup, Combe-Grenal level 59, or open-air sites such as Combe Brune 2 and 3 (Boeda et al., 1990; Turq, 1992; Chevrier, 2006; Brenet, 2011). The site of Petit-Bost (Neuvic, Dordogne) is an open-air site in the Isle valley, excavated in 2001 during a preventive archaeology operation. This study focuses on level 2, dated to MIS 9/8 by TL, between 340 and 270 ky (Bourguignon et al., 2008). This layer yielded evidence of bifacial shaping and SSDA, Quina, on flakes and Levallois flaking. Tools on flakes are poorly represented, and consist mainly of side scrapers (some with Quina retouch). Faunal remains were not preserved and solifluction processes affect the layer. As a consequence, the strict contemporaneity of the lithic concepts is uncertain, even though some artefacts were refitted. Here, we performed a new technological analysis, with particular focus on cores and tools. The aim was to identify the lithic concepts used and to reconstruct the reduction processes and their production goals. Shaped or retouched tools were analysed following a techno-morphological method, comprising a detailed description of edge morphologies and the relationships between supposed cutting edges and prehensile parts. This part of the analysis is based on present-day tool repositories, ethnographical data and traceological studies. It constitutes a hypothesis and a basis for reflection for further developments. Through this analysis, an original use of the Trifacial concept in the Isle valley area was identified in level 2. Ten artefacts in local flint and chalcedony were attributed to this concept. Three methods were identified: a single production method, a flaking/shaping method (which corresponds to a combined matrix) and a flaking/retouching method (selection of a core as a blank for retouch). The most frequent method is the combined matrix one, with six pieces. Four are considered as cores and one of these cores was subsequently retouched. Shaping/flaking processes display high variability and raw material morphologies play an important role. The functionalisation of blanks occurs during the reduction process. Most of the time, retouch is limited, and generally serves to regularise edge morphology (for both active and prehensile parts). In one case, a notch is part of the final morphology of the tool. The main objective of these tools seems to be morphology of the robust point of trifaces (high edge angles), although single linear edges can also be used in association with the point. Two general section morphologies were identified: symmetrical triangular and asymmetrical triangular sections. This morphology may have an impact on the final tool and on the position of the prehensile part and supposed active edges. A comparison with other trifaces published in Dordogne highlights the high variability of this concept. The poor quality or morphology (gelifract) of raw materials used in several sites, such as Combe-Grenal, was cited to explain its use (Turq, 1992). As a matter of fact, the use of this concept and its variability may be due to the initial morphology of the raw materials, but also to other factors. The sought-after tool may also influence the application of the lithic system. Moreover, this system produces a robust punctiform tool with a trihedral morphology in section, which is more difficult to obtain with bifacial shaping systems. Almost all the known trifaces come from south-western France, but according to the literature, some also exist or may exist in other areas in the South (Chalosse area, Deux-Sevres, Ardeche and maybe in Alpes-de-Haute-Provence). They also occur in Dordogne in sites attributed to the Southern Acheulean, but they are marginal compared to the other components of lithic assemblages. Indeed, in most of sites, there are only few trifaces. Thus, a definition of the Southern Acheulean based solely on this lithic concept does not seem relevant. Moreover, the absence of the trifacial system in assemblages with similar composition may result from taphonomic processes, site functions or activities. A more in-depth study of several former collections may enhance our understanding of the variability of this concept and links between the techno-complexes of Southern Europe during the final Middle Pleistocene. francaisLa presence de trifaces au sein des assemblages lithiques fait partie des caracteristiques des series de l'Acheuleen meridional du Sud-Ouest de la France. Le Trifacial est un concept dont les methodes peuvent etre orientees vers la production de supports, ou dans certains cas etre mixtes, c'est-a-dire melant debitage et faconnage. Le niveau 2 de Petit-Bost (Neuvic, Dordogne), date du MIS 9/8, livre un exemple inedit de son utilisation dans la vallee de l'Isle. Dans cet assemblage, differentes methodes trifaciales sont presentes. Des matrices uniques de production coexistent avec des matrices presentant une phase de fonctionnalisation dans le schema operatoire. Trois methodes ont ainsi ete identifiees : debitage strict, debitage/faconnage et debitage/confection. Selon la structure trifaciale presente (symetrique, asymetrique) une gamme d'outils diversifies peut etre produite. C'est toutefois la recherche d'outils appointes (contacts de type pointe ou bord-pointe) qui est dominante. La presence du concept Trifacial au sein d'une serie de plein air d'une phase ancienne du Paleolithique moyen de Dordogne permet d'accroitre nos connaissances sur ce concept encore peu reconnu dans les series lithiques. Il permet notamment une reflexion sur l'Acheuleen meridional au sens large et les specificites des series du Sud-Ouest de la France au Pleistocene moyen recent.