Human impact on the environment as derived from colluvial deposits – example from the La Tène Period until the Middle Ages in the Siegerland (Germany)

Human impact on the environment as derived from colluvial deposits – example from the La Tène Period until the Middle Ages in the Siegerland (Germany)

Reetz, K¹., J. Kirch¹, J.J. Birk^1,2, A. Stobbe³ and S. Fiedler¹

¹ Johannes Gutenberg-University Mainz

² recent adress Georg - August - University Göttingen

³ Goethe - University Frankfurt am Main

The Siegerland is one of the most cohesive mining regions in the Iron Age in Central Europe. While the number of settlement and smelting sites has been increasingly better researched over the last few years, it was basically unknown which impacts by the La Tène iron production on the primary forests have to be considered, and how are such correlated with other activities and soil erosion. Below a smelting site in the southwestern part of the Siegerland, we made a rare find of colluvial deposits in the valley of the Obersdorfbach. It tells about the human impact between the Earlier Iron Age and the heyday of iron production during the La Tène period and the Middle Ages. In addition to pollen and NPP analysis, we used element contents, and molecular markers (n-alkanes, steroids).

The small stream has cut in sections in meanders up to 180 cm deep into the relatively narrow floodplain. There, they lie on a gravel bed with embedded peat (Obersd 1, 170 – 153 cm, calibrated age 700/500 – 350 BC). In the uppermost 10 cm of the fen peat, the proportion of mineral components increases and pebbles are intercalated (Obersd 2, 153 – 145 cm, 350 – 200 BC).  On top are multi-textured sandy-clayey colluvial/floodplain loams with charcoal bands (Obersd 3, 145 – 125 cm, 200 BC – unknown). It is followed by a sandy colluvium from the Middle Ages (Obersd 4, 125 – 110 cm).

In the 7th to the middle of the 4th century BC the forests near Obersdorf consisted mainly of beech and linden trees. Nevertheless, non-arboreal pollen provides evidence of anthropogenic impact (Obersd 1). According to the mountain-archaeological picture, at first iron was produced only on a small scale and the interventions in the vegetation were still small. Although the area should have been sparsely populated at the time, fecal markers suggesting human presence can be found. However, human influence on the landscape increased significantly from about 350 cal. BC (zone Obersd 2). Pollen and n-alkanes show a distinct impact into the vegetation. Forest clearing led to erosion and the accumulation of thick colluvial deposits. Pollen from ruderal places increase significantly, cereals and coprophilous spores occur. The strong anthropogenic influence in zone Obersd. 2 can be correlated with the archaeologically known smelting site. In addition to wood for firing the furnaces, large quantities of clay were needed for their construction. During the transformation of the landscape, erosion increasingly occurred on the slopes. The result is clayey silt sediments with intercalated charcoal bands (Obersd 3). The following sandy colluvium (Obersd 4) from the early Middle Ages shows a dominance of beech, hornbeam, and rye. Steroids show the presence of humans and livestock here.