Archaeomagnetic colluvial sediments

Pilot study on the applicability of the archaeomagnetic dating method on colluvial sediments from the western Cologne Bay area via paleomagnetic sampling and analysis

Collaboration between LIAG (Elisabeth Schnepp, Christian Rolf) and LVR Amt für Bodendenkmalpflege (Renate Gerlach). The project is funded by the foundation for archaeology in the Rhinish lignite field (application number 230).

Colluvial sediments are unconsolidated sediments which are transported over short distances mostly by water, but also by wind, and then resedimented. The colluvial sediments in the western Cologne Bay area are a valuable geoarchaeological sedimentary archive covering the past 7000 years which enables the influence of people on sedimentation, geomorphology and landscape change to be studied. Layers with archaeological finds are also frequently covered with colluvial sediments, which can therefore be roughly dated on the basis of the relative chronology of the colluvial sediments. However, precise absolute dating of these archaeological horizons is still difficult independent of the material found because there have so far been no suitable high-resolution dating methods. 

The pilot project represents the first attempt to date this kind of sediment with the help of paleomagnetics. Two vertical profiles are being tested using different methods in the Weissweiler opencast mine. The figure on the left shows two stacked trenches of which the younger (G1) is dated as being of Latèna age (480 − 30 BC). Previous experiments revealed that the samples are characterised by stable magnetisation, and that the magnetisation directions within the colluvial horizons have only a minor amount of scatter (right-hand figure). The stable directions of the colluvial sediments correlate well with the archaeomagnetic secular variation curve. These sediments therefore appear to be suitable in principle for paleomagnetic dating.