Automated mineralogical profiling of soils as an indicator of local bedrock lithology: a tool for predictive forensic geolocation

The use of soil evidence to identify an unknown location is a powerful tool to determine the provenance of an item in an investigation. We are particularly interested in the use of these indicators in nuclear forensic cases, whereby identification of locations associated with for example, a smuggled nuclear material, may be used to indicate the provenance of a find. The use of soil evidence to identify an unknown location relies on understanding and predicting how soils vary in composition depending on their geological / geographical setting. In this study, compositional links between the mineralogy of forty soils and the underlying bedrock geology were established. The soil samples were collected from locations with broadly similar climate and land use across a range of geological settings in a ‘test bed’ 3500 km2 area of South West England. In this region, the soils formed through chemical weathering of the bedrock, representing a worst case for this type of forensic geolocation due to the high degree of alteration of the parent rock during soil formation. The mineralogy was quantified using automated SEM-EDX analysis. The soil mineralogy and texture are consistent with the underlying geology as indicated by regional-scale geological mapping.