Archaeomagnetic Tools Applied to the Study of Middle Palaeolithic Hearths: The Level R (ca. 60 ka BP) at Abric Romaní (NE Iberian Peninsula)

Abstract Due to its long occupation throughout the Middle Palaeolithic and the abundance of its pyrotechnological evidence, the Abric Romaní rockshelter (Capellades, Barcelona) provides an ideal setting for studying Neanderthal fire use. We conducted an archaeomagnetic study of four hearths from Level R ( ca. 60 ky BP). Rock magnetism experiments, including hysteresis loops, and backfield, isothermal remanent magnetisation acquisition and thermo-magnetic curves, were conducted on three specimens per hearth to investigate their magnetic mineralogy. To explore the raw material’s ability to become magnetised, we performed a laboratory-induced partial thermo-remanent magnetisation acquisition in a 50μT field at various increasing temperatures. Our results indicate that the material is predominantly diamagnetic, but contains a small proportion of low coercivity magnetic minerals, likely magnetite. A total of 106 oriented specimens underwent progressive thermal demagnetisation up to 580 °C. Directional results at the specimen level show either a single component or two: one between 250 and 420 °C and another between 300 and 550 °C. Three out of the four hearths yielded normal-polarity archaeomagnetic directions, within the range of secular variation expected for their estimated age; the poor quality of the data prevented any analysis of the remaining structure. These findings suggest that, despite the hearths’ low content in ferromagnetic minerals, they are able to acquire a thermal or thermochemical-remanent magnetisation, accurately recording the Earth’s magnetic field though their high-temperature component. The low-temperature component may reflect a subsequent thermo-chemical or chemical alteration that partially remagnetised the original direction.