Origin and composition of organic matter in pits from the Neolithic settlement at Murr, Bavaria

The archaeological site in Murr, Upper Bavaria, was settled over the whole Neolithic period between 5500 and 2700 BC. Various pits and a ditch were found in the area, distinct from the surrounding loamy soil by the dark-brown colour of their filling materials. Although numerous artefacts were found, at the present stage of research neither the nature of the filling material nor the function of pits and ditches are well understood. Thus, the organic matter composition of 30 filling layers from 11 Neolithic pits of this settlement was investigated and compared to that of a close-by Luvisol profile and two A horizons from contemporary Phaeozems in southern Germany. The samples were subjected to C and N analysis, soil colour measurements, solid-state 13C CP MAS nuclear magnetic resonance (NMR) spectroscopy, combined fractionation/highenergy ultraviolet (UV) photo-oxidation/13C CPMAS NMR spectroscopy, polysaccharide and lignin analysis. The organic carbon contents are higher in the Neolithic samples than in the Luvisol horizons, but are generally lower than in the A horizons of contemporary phaeozemic soils developed from loess. The Neolithic samples show much higher colour intensity in darkness than the surrounding Luvisol horizons. The organic carbon content of the Neolithic samples can be correlated with the colour lightness value. Solid-state 13C NMR measurements revealed that this correlation is mostly due to their aromatic carbon content, which is considerably higher in the Neolithic samples compared to the contemporary soils. Low polysaccharide contents and no lignin-derived phenols are found in the Neolithic samples. Between 29 and 77% of soil organic carbon survived UV photo-oxidation, mostly present as aromatic structures. Dipolar dephasing NMR spectroscopy indicated a high degree of condensation for the aromatic rings, while scanning electron microscopy showed that the material had a plant-like morphology. Summarizing, the organic material filling the Neolithic pits shows significant differences in the overall chemical composition compared to the surrounding soil. It represents a highly altered, highly aromatic material, with no evidence for lignindegradation products, probably deriving from non-soil origin. There is strong evidence that the aromatic carbon is derived from charcoal. The material either originated from soil material that has undergone vegetation fires or from other charred organic material, e.g. residues from cooking or Neolithic fire places.