Black adzes in the Early Neolithic of Belgium: Contribution of the Raman microspectrometry and petrography in characterization and sourcing

Abstract

Early Neolithic (Linear Pottery Culture) adzes originate from settlements and workshops accompany the neolithization of Belgium. They are made from a wide range of extraregional lithic raw materials such as metamorphic green rocks (amphibolite) and black volcanic rocks (“basalt’) beside more local or regional raw material as flints, light-coloured (sedimentary and lightly metamorphic) quartzites, black lydites (Cambrian nodular phtanite of Céroux-Mousty and Lower Namurian banded phtanites) and dark grey Lower Namurian silicified sandstones previously called “Micaceous sandstones of Horion-Hozémont’. The discovery of the workshop of Noirfontaine near the city of Liège in the 1970s and 1980s provides exceptional assemblage available for updating analytical studies. This research focuses on the multi-scale characterization, the discrimination and sourcing both Cambrian and Namurian black sedimentary rocks rich in secondary silica composing Early Neolithic adzes found in Belgium. Their black colour results from finely dispersed organic matter, but the absence of palynomorphs does not allow a biostratigraphic ascription. Additional petrographical analyses (Optical Petrography, Scanning Electron Microscope), X-ray diffraction, chemical analyses (Energy Dispersive Spectroscopy) and measuring the degree of graphitization of the organic matter through Raman microspectrometry have been decisive in identifying the geological and geographical provenances by comparing the acquired results with geological reference samples collected in the field or through reference collections. Cambrian lydites are coming from a very restricted area and were preferred to other more local rock sources.