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

Between 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.