Rock magnetic study of grave infill as a key to understanding magnetic anomalies on burial ground

Magnetic prospecting of burial grounds is still a great challenge in the field of archaeological geophysics. Some graves appear as positive anomalies, whereas others do not generate any traces or even show up by negative anomalies. This study involves ground magnetic survey, rock magnetic and magnetic mineralogy examinations of soils to determine factors responsible for the formation of magnetic anomalies on Late Roman time burial grounds of Chernyakhiv-Santana de Mures archaeological culture located in the forest-steppe of Ukraine. We surveyed these sites by a total magnetic field caesium magnetometer in order to target the archaeological excavations. We sampled infill from graves excavated under positive anomalies and profiles of background soils to analyse the enhancement of induced and remanent magnetization. In the laboratory, we examined magnetic mineralogy and measured various magnetic parameters and ratios characterizing concentration and granulometry of ferrimagnetic phase of soils. For further explanations of the magnetic anomalies, we created 3D synthetic magnetic models of the studied objects and compared the calculated total field anomalies with field measurements by their intensity and size. Here, we show how positive magnetic anomalies of destroyed burials are generated when a destruction pit remains open and later topsoil material gradually refilled it with aid of precipitation water. In this case, the infill layers acquire detrital remanence of the same intensity as the topsoil. Such burials are the best targets for magnetic survey. However, archaeological excavations revealed both intact and destroyed inhumations that caused no magnetic disturbance. Obviously, they were refilled immediately after digging/destruction, so that natural remanence of the infill remains mechanically destroyed. The study of this specific category of archaeological monuments brought us closer in the understanding the formation of magnetic anomalies in soil-filled features and showed the potential and limitations of magnetic prospection.

Automated summary

Magnetic prospecting of burial grounds in the forest-steppe of Ukraine is challenging, with positive magnetic anomalies indicating destroyed burials as ideal targets for magnetic survey, while intact burials filled immediately after excavation causing no magnetic disturbance, highlighting the potential and limitations of magnetic prospection.