Imprints of paleo-environmental conditions and human activities in mineral magnetic properties of fired clay remains from Neolithic houses

Fire as a global phenomenon plays crucial role in the Earth's climate feedbacks and forcing. However, human's influence is becoming increasingly important during the Anthropocene epoch. Burnt Neolithic houses are among the most impressive remains from fire-related ancient human activities. Mineral magnetic properties and firing temperature estimates using magnetic susceptibility method were carried out on a collection of burnt clay remains from house destructions originating from 18 Neolithic sites from Bulgaria. All of the sites/dwellings ended their existence after extensive fire. The general aim of the study was to explore the mineral magnetic properties of fired clay materials against the most important environmental factors. The main magnetic minerals identified in the burnt structures were magnetite, maghemite and hematite, as well as recently reported in several studies epsilon-Fe2O3. The latter evidences high intensity fire since this specific mineral can be synthesized at temperatures exceeding 900 degrees C. Magnetic susceptibility and percent frequency dependent magnetic susceptibility at site level were considered in relation to the climatic conditions, as defined in the published anthracological studies involving most of the sites. The major difference in lithology of the outcropping rock formations between North and South Bulgaria may influence variations in magnetic enhancement of the burnt clay across the sites at similar other conditions. Firing temperature estimates vary in wide range - between 580 degrees C and 1050 degrees C. Estimated average firing temperatures at site's level showed higher values in Early Neolithic sites (Tfire average = 815 degrees C) as compared to Late Neolithic ones (Tfire average = 746 degrees C and 713 degrees C). We suggest that possible hypotheses for the trend observed could be: difference in climate regimes across the territory, leading to different fire weather; or difference in the vegetation fuel used in house construction; and intentional burning of Early Neolithic houses.