Chernozem relics in the Hellweg Loess Belt (Westphalia, NW Germany) - Natural or man-made?

摘要

Chernozems and Chernozem-like soils are widespread e.g. in Central Germany but its formation is still controversially discussed. Clustered findings of Luvic Phaeozems and buried dark soil horizons in the Westphalian Hellweg Loess Belt (North Rhine-Westphalia) are traditionally interpreted as relics of early Holocene Chernozems. More recent research raised the question whether these soils are of (pre-) historic anthropogenic origin.Field observations in the east of Dortmund revealed the existence of buried black horizons in hillslope hollows. The underlying Stagnic Luvisol was penetrated by darkish clay illuviation veins forming a polygonal pattern. This feature was also found below the plough horizon in Luvisols beyond the hillslope hollows. A multianalytical approach was used in order to clarify whether the black soil horizons are natural relics or man-made. In order to identify fire-derived black carbon (microcharcoal), benzenepolycarboxylic acids were used as molecular markers.Beside the position of the fossil black horizons on top of a well-developed Stagnic Luvisol, micro-morphological thin section analysis confirmed the colluvial origin of the black horizons. Total organic carbon contents of the black horizons were only similar to 1%, whereas high black carbon concentrations indicate large amounts of fire derived organic matter. High concentrations of black carbon were also found in the clay illuviation veins, testifying to a formerly more widespread occurrence of black carbon enriched soils.Radiocarbon ages of charcoal particles from the black horizons prove fire activities during the late Neolithic and Bronze Age (e.g. slash-and-burn). Finally, our results strongly indicate that the Chernozem-like soils in the study area are man-made and natural Chernozem formation can be excluded.