Forensic provenance investigations of soil and sediment samples

Abstract

AbstractIn recent decades, the polarizing light microscope has been slowly phased out of the geology curricula of many universities in the United States. This is unfortunate, as the polarizing light microscope is an instrument that is particularly well suited to overcoming problems typically encountered in forensic scenarios. Its versatility makes it uniquely powerful in provenance investigations in which sample size is limited and sample history is unknown. The polarizing light microscope can be used to determine the source rock type(s) of a sample of unconsolidated grains, either based on the mineral assemblage present in the sample or on properties observed for individual mineral grains or lithic fragments. Biological particles including pollen, spores, diatoms and botanical macerals can be identified and used to constrain the possible source of a sample. In addition, individual particles observed in the sample (geological, biological or anthropogenic) can be isolated and re-mounted for subsequent analyses that are useful for provenance determination. The inferences made can be used to produce maps illustrating potential source regions by means of geographical information systems (GIS). Several examples are provided to illustrate the various capabilities of the polarizing light microscope and its contributions to forensic soil analysis, specifically in forensic provenance investigations.