Abstract
A study of the chert nodules found in the Escalada Formation (Carboniferous, Ponga region, Cantabrian Zone) was carried out as a means to characterise a number of lithic raw materials found in several prehistoric sites of the Cantabrian Mountains (NW Spain). This study comprises fieldwork aimed at locating the outcrops and obtaining samples. Some selected samples from two localities were used for both petrological (macroscopic and microscopic analyses from thin sections) and geochemical (X-ray fluorescence and powder diffraction) analysis. The macroscopic study shows a rather homogeneus coloration and a conchoidal fracture although two extreme types of cherts with a variety of intermediate forms can be differentiated according to the matrix composition. The microscopic analysis shows a high heterogeneity in carbonate versus silica percentage and gentle differences in some other features such as type of silica, origin of carbonates, occurrence of organic matter and type of skeletal components. The results of several geochemical analysis suggest that there are not geochemical features neither in the major elements nor in the traces that allows us to clearly distinguish between the analysed samples. All these studies allow us to define the main features of these chert nodules and to establish several types and varieties among them. Those varieties with high percentage of silica and with a more homogeneous matrix are the most suitable samples for knapping. These results together with the study of the geological and geographical location of archaeological sites suggest that the nodules from the Escalada Formation likely were lithic material supply sources used in knapping activitiesWhen aiming to demonstrate the use of these materials at archaeological sites the sole macroscopic analysis of the pieces does not suffice; further analyses, such as those involving thin sections, are necessary. The absence of chert from Escalada Formation in some Mesolithic sites in the area was confirmed via these additional analyses.
Highlights
The potential lithic raw material supply sources in the central-western area of the Cantabrian Mountains, especially those from Paleozoic area are poorly known (Arias et al 2009; Tarriño et al 2015)
For some years a team from the University of León has been studying these potential local sources especially in relation with the study of a number of Mesolithic sites in the region (El Espertín and La Uña caves - León, Spain). It is worth noting the occurrence of radiolarite and two kinds of black chert amongst the raw materials used at these sites (Fuertes Prieto et al 2010; Herrero 2014; Neira et al 2015)
This study focuses on the research in the Escalada Formation, a Carboniferous limestone locally bearing black chert nodules that outcrops in the Cantabrian Mountains
Summary
The potential lithic raw material supply sources in the central-western area of the Cantabrian Mountains (north of the Iberian Peninsula), especially those from Paleozoic area are poorly known (Arias et al 2009; Tarriño et al 2015). For some years a team from the University of León has been studying these potential local sources especially in relation with the study of a number of Mesolithic sites in the region (El Espertín and La Uña caves - León, Spain) It is worth noting the occurrence of radiolarite and two kinds of black chert amongst the raw materials used at these sites (Fuertes Prieto et al 2010; Herrero 2014; Neira et al 2015). Following common methodological frameworks for this kind of studies (Mangado 2005; Tarriño 2006), and in addition to the analyses carried out on the archaeological materials, we reviewed all available literature on these geological formations referencing the presence of chert This information was used when planning our fieldwork so at to best locate the outcrops of these formations in the field. This will enable us to determine whether this chert was used at these Mesolithic occupations and, on the other, to incorporate a new lithology, from a regional point of view, to the map of potential raw materials
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