A laboratory characterization of black limestones (Neri Antichi) from Zeugitania (Tunisia)

Black limestones, as well as black marbles, have not so far been sufficiently investigated archaeometrically in spite of the great importance of their use and wide distribution in ancient times for architectural elements and sculptures. Especially in Roman times these materials were exploited in many countries such as Italy (Latium), Greece (Mani and the island of Chios), Asia Minor (Adapazari) and Tunisia. In this latter country, three particularly important sources of black limestone of good quality have been found by the author: Ain El Ksir (Chemtou, ancient Simitthus), Djebel Azeiza and Djebel Oust (south of Tunis) where the quarries have been studied (see the relative abstract in this volume) and sampled in preparation for a reference database. A total of 40 samples were subjected to detailed minero-petrographic (OM, XRD) examination and to the analysis of C & O stable isotopes by mass-spectrometry. The results obtained indicate that the nero antico from Chemtou is a carbonaceous biomicrite (carbonatic radiolarians and sponges), sometimes slightly dolomitic; that of Djebel Azeiza is a carbonaceous micrite, slightly dolomitic, often with a micro-brecciated fabric and passing to a pelmicrite, sometimes with intra-and bio-clasts; the marble from Djebel Oust is a very pure biopelmicrite, often quite similar to that of Djebel Azeiza. The isotopic ratios of the last two limestones are very similar, with overlapping areas in the isotopic diagram, whereas the black from Chemtou is quite different showing much lower 13C values. These values coincide perfectly with those reported in the literature for the famous group of female caryatids known as the “Canephorae” preserved in the Palatine Museum, Rome, the material of which had not been previously identified with certainty.