Gargano cherts: Multiparametric protocol for provenance determination.

In recent decades, archaeometric research about obsidian sources and circulation in Central Mediterranean area has achieved good results, despite what has happened with other knappable materials. Detailed archaeometric literature on cherty materials is poor and discontinuous in time and space. Difficulties in unambiguous characterisation to identify distinguishing features of chert for sourcing, makes it relatively hard to compare materials from different regions and retrace ancient trade routes. Current archaeological knowledge about the circulation of chert in the central Mediterranean Sea identifies Gargano Promontory as one of the main sources. In addition, the Gargano Promontory is located along one of the supposed routes of the spread of the Neolithic in southern Italy, which is the “bridge” of Adriatic islands connecting southern Croatia to the north of Apulia. In the current state of research, the geography of the Early Neolithic landscape of the promontory shows that only the area exploited for chert sources was inhabited. Early Neolithic sites and mines lie along the coast in a well-defined area, and no other site is present within a radius of about 25 km. This fact suggests an interpretation of the Neolithic mining area as an “island” area and thus the establishment of maritime expedition for the supply of Gargano chert, just as the Mediterranean islands were rich in obsidian. This suggests the possibility of a special status in the Neolithic of these territories rich in lithic raw material. In general terms, our analytical approach focuses on the correlation among quantitative data of texture or structure, colorimetry, reflectance or gloss and chemistry (through LA-ICP-MS) obtained from geological chert samples and mine debris from Gargano Promontory. Three out of the four geological formations investigated (i.e. Calcare di Peschici Formation, Maiolica Formation, and Scaglia Formation) were mined in the past, whereas traces of mining in the Marne a Fucoidi Formation are unknown to-date. In this work we present our results based on macroscopic and chemical analysis of a selection of 151 samples of chert to understand the variability of the intrinsic features and use them as potential discriminant factors for provenance. In each formation, cherts with different features and quality coexist. Among multiple sampling in outcrops with several chert layers, macroscopic and chemical results show lateral homogeneity and vertical heterogeneity. The chemical variability of chert samples is influenced by the distance from the cortex, when present. Geochemistry and colorimetry are not able to distinguish cherts of the four formations investigated. However, we observed some chromatic and chemical homogeneity on the level of sites (e.g., Defensola, Arciprete, Tagliacantoni for Peschici Formation, and Martinetti, Guariglia or Valle Sbernia, Bosco della Risega for Maiolica Formation).