Sediments vs. Historical narratives: The use of soil magnetic properties to evaluate the existence of a historical fire in an 18th century Spanish fort (Patagonia, Argentina)

•Only an adobe-wall foundation showed magnetic signals of a thermoalteration process.•Experiments show superparamagnetic formation at 220 °C after 1-hour oxidizing heating.•A thermomagnetic curve reversibility at ~400 °C is observed in experimental samples.•A circumscribed and low-magnitude fire (<400 °C) likely took place in 1810 AD.•Magnetic analyses question historical narratives which describe a massive fire.