Occupations humaines et chronostratigraphie du gisement pléistocène d’Illiers-Combray (Eure-et-Loir, France) De nouveaux éléments pour le SIM 5b

Abstract

EnglishBetween 2012 and 2015, five successive archaeological campaigns were led by the Department of archaeology of Eure-et-Loir, on the Illiers-Combray plateau, 1 km to the east of the river Loir. Middle Palaeolithic remains were discovered in a Pleistocene loess-palaeosoils sequence, extending over an area of more than 10 km?. This Early Weichselian site constitutes a major discovery, due to the good preservation of the artefacts and the sparse data in the south-west of the Paris basin. During the archaeological survey, trenches were dug down to the bedrock every 25 m to 50 m, which revealed lithic remains over the entire research area, while neither bones nor organic remains were preserved due to the low pH value of the soils. The geoarchaeological approach combines sedimentology, micromorphology and luminescence dating (OSL, post-IR IRSL, TL) of sediments and burned flint artefacts. Lithic artefacts were found isolated or in clusters of dozens of pieces at a depth comprised between 0.70 m and 2 m. Three main sectors were identified. The sector n° 1, situated to the north-east of the town, comprises of 59 lithic artefacts in small clusters of about 10 pieces per square meter over an area of 4500 m? area. The sector n° 2, 500 m to the south, delivered 261 artefacts spread over an area of 3.6 ha. The third sector, covering an area of 0.4 km?, is the largest of the three sectors and is located to the south-east of the two other areas. 186 lithic artefacts were found in this area. The Pleistocene loess-palaeosoil sequence is homogeneous and well preserved on the plateau. It covers at least three glacial-interglacial cycles (Saalian, Eemian and Wechselian) and can be divided into 15 units. At the base, the Saalian strata (unit 11 to 15) are above the ?€?argile a silex?€? tertiary formation (unit 16). The OSL age of the unit 11 is 218.6 ± 49.6 ky. Saalian strata are marked by huge ice wedges and hydromorphy. The Eemian strata show a well preserved pseudomorph of an ancient tree windthrow (unit 9) located in a luvisol (unit 8 and 10). OSL dating of the unit 10 gives 121.0 ± 15.7 ky. The Early Weichselian strata are comprised of three units 7.1, 7.2 and 7.3. The majority of the artefacts is contained in the unit 7b, which is rich in ferro-manganic nodules. However, some artefacts were also found in the 7a and 7c units, as well as in the ice wedges which cut through the Early Weichselian strata. The top of the sequence is characterised by decarbonated loess deposits in which a luvisol has developed. The lithic material is in excellent condition and numerous refi ttings testify a good preservation within the archaeologi- cal layers. The analysis of these remains suggests a concomitance of several operating production chains, to manufac- ture fl akes, blades and points as well as an operating chain for bifacial shaping. The identifi ed production methods are convergent unipolar, parallel unipolar, Levallois and discoid debitage. However, tools made out of fl akes are rare. They consist of side scrappers and retouched artefacts. Two burned artefacts from unit 7.2 were dated by TL at 88.9 ± 6.9 ky and 89.7 ± 6.9 ky, which place the lithic industry in the MIS 5b. The preliminary results show that the site constitutes a new reference for the Pleistocene and the Middle Palaeolithic of the Centre and the North of France, in addition to the reconstruction of the palaeoenvironmental and archaeological history of this area. Finally, the extensive excavation could become important in reconstructing Middle Palaeolithic history, since the site itself is located on the divide between the watersheds of the Seine and the Loire and, thus, in a key area for understanding the cultural palaeogeography of the Neanderthal populations. francaisCinq operations de diagnostic successives, conduites a Illiers-Combray de 2012 a 2015 par le Service d'archeologie du departement d'Eure-et-Loir, ont permis l'identification de vestiges paleolithiques compris dans une sequence limoneuse de plateau, sur une aire de plus de 100 ha, fouille manuellement sur 60 m². La decouverte de ce site vient enrichir les connaissances sur le Paleolithique moyen du Centre de la France, encore tres peu documente, et ajouter un jalon manquant pour le stade isotopique 5b dans le Nord de la France. Les decouvertes ont ete faites grâce au creusement de 453 sondages, d'une profondeur allant jusqu'a 7 m, jusqu'au substratum rocheux, tous les 25 m a 50 m. Les vestiges lithiques sont presents a une profondeur comprise entre 0,70 m et 2 m, repartis sur l'ensemble de l'aire, isoles ou concentres en plusieurs dizaines de pieces. Les vestiges organiques ne sont pas conserves, du fait de l'acidite des sediments. La sequence pleistocene est bien representee sur la majorite du plateau. Elle se caracterise notamment par le developpement de sols lessives, la presence de pseudomorphoses de fentes de gel, ainsi que de fosses pleistocenes de deracinement d'arbre. L'approche geoarcheologique combine des analyses sedimentologiques, micromorphologiques et des datations OSL et post-IR IRSL sur limon loessiques et TL sur artefacts chauffes. Les premiers resultats confirment l'interet du site. La sequence limoneuse presente trois cycles glaciaire-interglaciaire, dont les plus recents couvrent le Saalien, l'Eemien et le Weichselien. La serie lithique regroupe 931 pieces, dont la majorite a ete identifiee dans un meme horizon argilo-limoneux riche en concretions ferro-manganiques. L'aspect tres frais des vestiges et la presence de nombreux remontages et raccords temoignent de la bonne preservation des niveaux archeologiques. L'analyse de ce mobilier suggere la concomitance de plusieurs chaines operatoires de debitage, orientees vers la production d'eclats, de lames et de pointes. Une chaine operatoire de faconnage est egalement attestee par la presence de bifaces. L'outillage sur eclat est faiblement represente. Il se compose principalement de racloirs et de quelques pieces sommairement retouchees. Au regard des donnees deja collectees lors des diagnostics, il semble que la fouille de ce gisement pourrait constituer un jalon important pour la connaissance du Paleolithique moyen. La localisation de ce site, a la charniere entre les bassins versants de la Seine et de la Loire, viendrait avantageusement documenter un secteur clef pour la comprehension de la paleogeographie culturelle des populations neandertaliennes.