Article: “Aménager l’espace, exploiter les ressources minérales et transformer le paysage au Néolithique” (2019)

Céline COUSSOT, Julia WATTEZ, Tony HAMON, Grégoire BAILLEUX, Annette BAILLEUX (2019), Aménager l’espace, exploiter les ressources minérales et transformer le paysage au Néolithique : les cas des sites d’habitat en terre crue de «La Fosse Blanche» à Prasville (Eure-et-Loir, France), in F. BOSTYN, C. HAMON, A. SALAVERT, F. GILIGNY (eds.), Session 4 – L’exploitation du milieu au Néolithique dans le quart nord-ouest de l’Europe : contraintes environnementales, identités techniques et choix culturels, XXVIII^e congrès préhistorique de France – Préhistoire de l’Europe du Nord-Ouest : mobilités, climats et identités culturelles (Amiens, 30 mai-4 juin 2016), volume 3, pp. 57-75.

About the: Conference proceedings of the “XXVIII^e congrès préhistorique de France – Préhistoire de l’Europe du Nord-Ouest : mobilités, climats et identités culturelles (Amiens, 30 mai-4 juin 2016)”.

Résumé

La construction en terre au Néolithique, désormais bien attestée dans le sud et l’ouest de la France est longtemps demeurée peu documentée dans le centre du Bassin parisien. Ce n’est que récemment que des diagnostics archéologiques menés sur le plateau beauceron, dans la commune de Prasville (Eure-et-Loir) ont mis au jour trois sites d’habitat comportant des restes d’architecture en terre crue. Ils sont associés à des vestiges céramiques et lithiques qui attribuent l’occupation au Néolithique final. Le caractère relativement inédit des éléments en terre crue, dans les sites établis en contexte de limons de plateau, a conduit à les considérer dans un premier temps comme des anomalies sédimentaires et, pour les caractériser au mieux, une démarche interdisciplinaire alliant les méthodes conventionnelles de l’archéologie et de géoarchéologie (géomorphologie et micromorphologie) a été mise en oeuvre. Les résultats obtenus, malgré les limites d’observations imposées par les interventions de diagnostic, ont permis d’aborder la question des modes d’aménagement, d’exploitation et de transformation du paysage en relation avec la construction en terre. Ainsi, les propriétés morphologiques et pédo-sédimentaires des anomalies sont conformes à celles qui caractérisent les matériaux façonnés en terre crue et peuvent permettre de servir de base à la difficile détection de la construction en terre. Sur le plan technologique, la micromorphologie montre que les techniques de façonnage relèvent de la terre massive et que la terre à bâtir a été préparée à partir de limons et d’argiles provenant de différents horizons de sol brun lessivé, formation pédologique locale. Différents types de structures de terre crue ont été identifiées de façon préliminaire, comme des murs, des effondrements et des sols aménagés. L’approche géomorphologique a mis en évidence des terrassements probablement liés à l’implantation de l’habitat, les structures en terre crue étant établies sur le substrat calcaire, ce qui suggère que les formations sédimentaires, volontairement arasées, ont pu être exploitées pour la construction. Elle montre enfin que la dynamique d’occupation a produit une stratification suffisamment dilatée pour conduire à la formation d’anomalies topographiques, tels que des bombements, qui marquent encore le paysage actuel.

Mots-clés : Néolithique, Structures de terre crue, Terre massive, Géomorphologie, Micromorphologie des sols, Diagnostic archéologique, Sedimentary ressources, Paysage.

Abstract

The Neolithic earthen construction is actually well documented in southern and western France. The archaeological and geoarchaeological researches have been focused on construction techniques and raw materials provenance. The nature of raw materials is a relevant issue to recognize earth architectural remains, sometimes not easily detectable on the field. At the same time, the analysis of raw materials helps to identify the sources of supply of building materials and to outline the construction techniques. Up to now, the researches show that the used materials come from the sedimentary deposits of the site itself or from its surroundings. Concerning the south-west of Parisian basin, the question of the existence and the degree of preservation of earthen architectures was still open and was badly documented for a long time. During the last years, thanks to preventive archaeological diagnosis on the plateau of the Beauce region, this hiatus of information has, partially, been completed. The archaeological diagnosis conducted on agricultural plots in the district of Prasville (Eure-et-Loir), revealed three settlements characterized by earthen architectural remains in association with Final Neolithic ceramics and lithic artifacts. These sites are placed on a Miocene calcareous plateau in a pedological context of Luvisol. The earthen architectural remains were first considered and treated on the field as sedimentary anomalies, due to the originality and the unknown characteristics of earthen architectures in these plateau contexts. In order to better characterize these sedimentary anomalies and define their topographic, geomorphologic and pedological context, an interdisciplinary approach including archaeology and geoarchaeology (geomorphology and micromorphology) was established. The field observations are done on horizontal surfaces in a large number of trial trenches and vertically on the stratigraphic sequences visible in the sections of some deep test pits. Even if the stratigraphic characteristics and the organization of artifacts show the presence occupation surfaces preserved in situ, two alternative hypotheses are raised in order to test the formation dynamics of the observed stratigraphy: the first one suggests the possibility that the observed layers have been deposited by colluvial dynamics, while the second one suggests that anthropogenic (cultural) formation processes are largely responsible for their deposition. The first hypothesis has been rejected because of the topographic position of the sites: they are placed in the centre or at the edge of a plateau which is limited by two palaeo-valleys and the archaeological stratigraphy is quite thick at the edge of this plateau. Effectively, the morphogenetic processes that are naturally dominant in these kinds of quite high topographic positions lead to the erosion of the surface deposits rather than to the accumulation of sediments. In order to test the second hypothesis, we had to identify the morphological, sedimentological and pedological characteristics of theses stratigraphic anomalies. They have been described, recorded and drawn in section and in plan and recorded as stratigraphic units, in order to allow the correlation between them and with the recovered artifacts. At the macroscopic scale, theses anomalies often have an angular shape which form, in plan view, square or rectangular lumps from 5 cm to more than 30 cm of length. Differences in color and texture of these elements allow us to identify several “sedimentary construction facies”. However, all of them are characterized by an high compactness and by a platy structure (more fine and continuous than the one related to frost action) or a granular structure. Both of these kinds of sedimentary structure could be related to the mixing of earth material. The different technological characteristics identified by the micromorphological analysis, show that earthen lumps were hand-shaped using local silt and clay from different horizons (Bt and E) of Luvisol. The morphological and sedimentological characteristics of raw earth lumps, as well as their compactness and their different reaction to moist (marked by a different drying from the nearby sediments) are important criteria which contribute to the detection of earthen construction, which is a critical issue in archaeology. The organization of the observed hand-shaped lumps allowed the identification of different types of earthen structures: constructed floors, wall remains and rests of collapsed buildings. However these are still hypothesis which have to be tested with more precise excavations. The presence of construction facies, either in form of lumps or earthen building debris, constitutes an evidence of the anthropisation degree of the pedo-stratigraphic sequences of the agricultural plots. The recording of their position allowed delimiting at least three Neolithic settlements and their spatial extension. The analysis of the cross-sections of the deep test pits shows that the earthen structures were built directly on the calcareous bedrock. This fact suggests that the luvisol horizons has been intentional removed by the Neolithic communities and shows a huge work of leveling at the moment of the site establishment. The material removed during the leveling could be used for the construction, confirming once more the use of local sources for the earthen construction. These processes prove the high impact of Neolithic societies on the local landscape. Concerning the taphonomy, the main post-deposition transformations observed are due to recent agricultural activities. The earthen structure are truncated and reworked under the modern ploughed horizon (L horizon). It seems that the anthropogenic formation processes related to earthen architecture sedimentation linked to earthen architecture sedimentation could generate a stratigraphy sufficiently thick to make topographic anomalies (i.e. bulges and topographic convexities), which are visible in the landscape even nowadays. The results of this study open new perspectives on the analysis of architectural practice, buildings’ form, settlements organization and land use patterns, even if field observations are spatially limited by the methods used in the preventive archaeology diagnosis (trenches and test pits). Archaeological sites showing earthen architectures could be considered as an additional documentary source to better understand the lifestyle of Neolithic societies and their role on the landscape evolution.

Keywords: Neolithic, Earthen building, Cob, Geomorphology, Soil micromorphology, Preventive diagnosis, Sedimentary resources exploitation, Landscape.

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