Etude micromorphologique de matériaux de construction et de surfaces d'occupation de la Motte médiévale de Werken (Flandres, Belgique)

International audienceThe "Hoge Andjoen," an early medieval motte (860-960 A.D.) is an artificial hill made up of at least eight man-made "ground raising/leveling" layers. Each layer is associated with a stabilization level and a well-preserved occupation surface with evidence such as living floors, traces of cultivation, and goat/sheep trampling. The presence of this hill generated a local rise in the original groundwater table present in the natural, buried soil of the site. In some parts of the hill, and with little relation to the sedimentary boundaries, this process generated permanent water stagnation with pronounced anaerobic conditions and locally strong gradients of oxidoreduction. These gradients created a series of particular migrations and accumulations of iron, manganese, and phosphorus components. All organic artifacts, such as oak posts, wooden floors, leather, and seeds remained well preserved in the strongly reduced parts of the hill; they are completely decayed in the aerated zones of the hill. The soil moisture regime within the motte further influenced a series of postdepositional migrations/accumulations of clay and organic matter. The micromorphological study of this archaeological site allows verification of hypotheses developed during field surveying. These hypotheses relate mainly to the origin and mode of dumping of the various types of earthy material, the human activities related to the nine successive living floors, and the traces of numerous postdepositional processes observed throughout this archaeological structure. INTRODUCTION The "Hoge Andjoen" Medieval Motte (Werken, West Flanders, Belgium; Figure 1) is a flat artificial hill about 6 m in height and 50 m in base diameter (Figure 2), surrounded by a ditch several meters wide (Figure 3[a]). The site is constructed on the boundary between the occasionally inundated Holocene polder area and the upland with Weichselian coversands resting on a Tertiary sandy to clayey substratum (Figure 1). The archaeological excavation (Vanthournout, 1991) revealed a complex stratigraphy of successive layers. On the basis of the field investigations, eight construction phases (CP1-8) and nine occupation layers (OL1-9) (Figure 3[b]) can be identified. The total occupation and raising of the site lasted approximately 1 century (860-960 A.D.). The purpose of this micromorphological study is threefold: 1. To characterize further the various features, such as types of earth and types of occupation layers described during the field study (Langohr, 1991). 2. To test the various hypotheses formulated during the macromorphological study. These concern mainly the origin of the earth used to construct the hill and the human activities related to the occupation layers. 3. To study further the various characteristics related to diagenetic pedogenetic processes