The Guinardera quarry (Sant Marti de Tous, Barcelona): A new chert exploitation location during historical times

In 2014, an anthropic accumulation of chert material was discovered in La Guinardera area, at the southwest of the Sant Marti de Tous town (Barcelona, NE Iberian Peninsula). In 2018 a first archaeological intervention was carried out in two locations: La Guinardera and La Guinardera Nord. After the fieldworks, these two accumulations were interpreted as chert workshops. These workshops are in the St. Genis Formation, included within La Noguera lacustrine system and dated to the Priabonian age (upper Eocene). The St. Marti de Tous area presents shallow lacustrine conditions typical of sabkha environments, in which layers of gypsums and sandy lutites are interspersed with tabular red sandstone levels, yielding different varieties of chert. The Guinardera chert is characterized by a fairly homogeneous matrix, presenting a fine texture, with a microcrystalline and spherulitic length-slow chalcedony matrix, and a combination of grey colours, in general of dark hues, with an opaque diaphaneity but translucent at the edges. The archaeological assemblage from La Guinardera Nord site allows us to identify a chert workshop for the production of gunflints. The heterogeneity of the assemblage at La Guinardera site precludes assigning it to any single chrono-cultural period or function. The technological characterization of La Guinardera Nord site reveals distinctive attributes of a gunflint workshop that can be differentiated from prehistoric workshops. The presence of square and thick preforms, oxide traces on butts and ventral faces, marked bulbs and thick platforms, together with fresh edges on flakes and blades and the near-absence of patinated materials, corroborate it. The presence of these two deposits within the above-mentioned formation shows us a repeated landscape exploitation pattern for raw material extraction, since references chert use range from the Middle Palaeolithic (e.g., Abric Romani) to historical times (e.g., La Guinardera Nord).