Chemical composition of the organic matter in neolithic soil material as revealed by CPMAS 13C NMR spectroscopy, polysaccharide analysis, and CuO oxidation

The archaeological site in Murr, Upper Bavaria, was settled throughout the entire Neolithic period, between 5500 and 2700 BC. Various pits and a ditch found in the area are distinct from the surrounding loamy soil because of the dark brown color of their filling materials. Although several artifacts have been discovered, at the present stage of research neither the nature of the filling material nor the function of pits and the ditch are well understood. Thus, the organic matter composition of 30 filling layers from 11 Neolithic pits found in this settlement was investigated and compared with that of a nearby Luvisol profile and two A horizons from contemporary Phaeozems. All samples were subjected to C and N analysis, soil lightness measurements, solid-state C-13 CPMAS nuclear magnetic resonance (NMR) spectroscopy, and polysaccharide and lignin analysis. The organic carbon contents are higher in the Neolithic samples than in the Luvisol horizons, but they are generally lower than in the A horizons of contemporary phaeozemic soils developed from loess. The Neolithic samples have a much higher intensity in darkness than do the surrounding Luvisol horizons. The organic carbon content of the Neolithic samples correlates with the lightness value. Solid-state C-13 NMR measurements revealed that this correlation is primarily because of their aromatic C content, which is considerably higher in the Neolithic samples than in the contemporary soils. Small polysaccharide amounts and no lignin-derived phenols were found in the Neolithic samples. Thus, the organic material filling the Neolithic pits is significantly different in overall chemical composition from the surrounding soil. It represents a highly altered, highly aromatic material showing no evidence of lignin degradation products and probably deriving from non-soil origins.