The hearth of the matter: A high-resolution magnetic microarchaeological study of a Neanderthal combustion feature utilizing Quantum Diamond Microscopy

Abstract

This study presents an integrative geoarchaeological and microarchaeological case study of combustion features, employing a multi-method analytical approach incorporating archaeomagnetic, rock magnetic, and soil micromorphological methods, alongside Quantum Diamond Microscopy (QDM). The case study focuses on a combustion feature from the Middle Palaeolithic site of El Salt (80 to 45.2ka). The primary aim is to reconstruct the depositional and post-depositional history of this combustion feature, identifying human activities and environmental processes using high-resolution magnetic and micromorphological data. The combustion feature H89/90 was studied as part of the research into a large palimpsest of combustion features located within Unit XI. Archaeomagnetic and rock magnetic microarchaeological analyses of the combustion feature demonstrates that it is relatively well-preserved and in situ. This integrative approach reveals clear evidence of anthropogenic behaviours, including hearth maintenance, the use of grass-based fuels, and potentially the active sustaining of fire through the successive addition of these fuels. Furthermore, the study highlights maghemite as the primary magnetic carrier within the combustion feature. This mineral is not commonly reported as a dominant magnetic phase in archaeological hearths. Its presence suggests either previously unrecognized burning conditions, microenvironmental factors unique to this feature, or a broader need to improve the resolution at which hearth mineralogy is studied. These interpretations are possible through high-resolution rock magnetic analysis, enhanced by QDM's micrometer-scale magnetic field mapping. Representing the first known application of QDM in archaeological science, this method allows researchers to visualize internal magnetic fabrics directly within thin sections, enabling the identification of specific microfacies and magnetic structures that are typically invisible to traditional micromorphological analysis. As a result, this method not only deepens our understanding of the magnetic architecture of the hearth but also strengthens behavioural interpretations of its formation and use. Overall, the study demonstrates the value of a deeply integrated magnetic microarchaeological approach for investigating human behaviour associated with fire use.