La fouille des enclos circulaires de l'âge du Bronze : une nouvelle approche ? Contribution géopédologique à l'étude des monuments arasés sur substrat limo-neux de Lauwin-Planque
Résumé
The layer of carbonated silt (loess) found in Northern France is the result of wind sedimentation which developed during the periglacial climate of the Pleistocene. The decarbonatation of loess, active since 16,000 BP, is mainly climate-related. This process, noticed on the circular enclosure from the Bronze Age at Lauwin-Planque (Nord) is extremely interesting. Fieldwork allowed the discovery of 10 funeral enclosures, one of them not yet excavated. Five of them are really close and could belong to a coherent group. Two others are not very far from the first group and the last two seem isolated. The enclosures are simple, from 19 to 34 m in diameter. The idea expressed here is that, in a thick enough sedimentary sequence, the limit of decarbonatation preserves the image of the topography, contemporary to that process. In the case of anthropic activity, the features and the presence of organic material related to human occupation could have an impact on the decarbonatation. If they lasted long enough, their implementation could have modified the level of decarbonatation (higher under a built-up feature and lower under dug-out features). In order to collect information on mounds associated with funeral enclosures, a specific excavation method has been developed. First, it is important to know the sedimentary context extremely well. The best solution is the presence of a specialist in the field at the beginning of the work to observe the nature of the ground. After that, all the features which appear on the surface inside and around the enclosure have to be studied, before test pits are placed regularly and all the material collected, with the data recorded in a classic manner. Then four trenches are dug in order to create a cross, in staggered rows from the centre of the circle to several metres outside it. These trenches have to reach the level under the limit of carbonated silt. Observation of the cross-sections provides information regarding potential mounds present inside or outside the enclosures. Finally, the whole enclosure is emptied. In Lauwin-Planque, the excavation allowed a modification of the level of decarbonatation to be observed under the circular Bronze Age enclosures. For enclosure 1, a central mound combined with an embankment is suggested. For enclosures 2 and 5, we can guess at a central mound (which is confirmed by the absence of decarbonatation under the central tomb in enclosure 2). There are two embankments, inside and outside the enclosure. The study of the third and the fourth enclosures showed the presence of a central mound inside and one embankment for the fourth. But these two enclosures do not have embankments outside. A central mound and an external embankment was observed for enclosure 6. The seventh was extremely levelled but the presence of an external embankment was seen. For the last one where observations were made, it is possible to confirm an embankment outside the enclosure and a probable mound inside but the whole area was levelled and a modern path passed through the monument. This entire method provides an opportunity to widen our knowledge of this type of feature by gathering data equivalent to those from Britain. The silt context is really important in collecting this information. The monumental aspect of these enclosures is brought to light by the presence of mounds and embankments. It is thus possible to consider the conception of funeral features in the Bronze Age
La couverture de limon carbonaté (loess) présente dans les régions du nord est issue de la sédimentation éolienne qui s’est développée sous climat périglaciaire au cours du Pléistocène. La décarbonatation des loess, active depuis 16000 BP, est essentiellement liée au climat. Ce processus, dans le contexte d’enclos circulaires de l’âge du Bronze sur le site de Lauwin-Planque (Nord), a montré un grand intérêt. Nous exposons ici l’idée selon laquelle, dans une séquence sédimentaire suffisamment épaisse, la limite de décarbonatation conserve l’image de la topographie contemporaine de ce processus. Dans le cas d’occupations anthropiques, les structures et la présence de matière organique liées aux activités humaines sont potentiellement capables d’influencer la décarbonatation. Si les structures ont été utilisées assez longtemps, elles ont pu modifier la profondeur de décarbonatation (en négatif dans les structures en creux et en positif pour les élévations). Afin de découvrir des informations relatives aux élévations des enclos funéraires, une méthode de fouille spécifique a été développée. Elle permet d’enrichir notre connaissance de ces vestiges dans une région où ils ne sont pas conservés, apportant des données équivalentes à celles connues en Angleterre où ils le sont.