Abstract:The so-called "Mucientes chert" is a variety that appears in the central area of the Iberian North Plateau, in the Duero Basin. It is widely known in the geological and archaeological literature and its use for knapping was especially important in Prehistory. From a macroscopic point of view it is a nodular chert, with white and very porous cortex, and brown to blackish or beige colour in the inner part.In this work we carried out a more accurate petrographic, mineralogical and chemical characterization of this lithology using SEM, XRD and XRF techniques in samples coming from "Las Canteras" (Mucientes village), a chert outcrop of the "Cuestas" Unit (Vallesian-Aragonian, Miocene Age). Also, we have made a review of its geological occurrence and archaeological distribution areas. It is intended to sketch the delimitation of the geographical area of occurrence taking into account the geological and archaeological references.
Abstract:This work provides the keys to the mineralogical and geochemical characterization of black chert from the Vegamián Fm. This formation crops out throughout the whole of the Cantabrian Zone (of Palaeozoic age), one of the geological zones of the Cantabrian Mountains (NW Spain). The geographical distribution of this formation is very wide, surfacing in the provinces of León, Asturias, Palencia and Cantabria.This variety of chert had been included within the group generically known as 'black chert', a macrogroup including different types of chert that appear in different Palaeozoic formations in the area and which share a characteristic black colour at the macroscopic level. The characterisation presented here has enabled us to distinguish it from other varieties. In this study, Vegamián chert has been divided into two different groups depending on their textural, mineralogical, geochemical and thermal propierties. Type 1, the most suitable for knapping, is characterized by high content in silica (>97%), laminated matrix and, occasionally, ghost of radiolarians.In addition, the characteristics specific to this chert make it suitable for lithic knapping processes. To confirm its use by prehistoric populations, this chert will be compared to that found in two Mesolithic sites, the caves of La Uña and El Espertín (León, south versant of the Cantabrian Mountains), the raw materials from which are currently under study.
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 activities When 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.
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