A Critical Evaluation of Geoforensic Sampling and Interpretation of Resultant Data.

Forensic geoscientists usually consider the inorganic particulates in soils and sediments. However, irrespective of location, these deposits invariably contain palynomorphs - biological particulates such as pollen grains, plant spores, fungal spores, algae, and fragments of micro- and meso-fauna.  Portions of whole plants, including leaves, stems, sporangia, fruits, and seeds may also be there. These non-palynomorph botanical remains may be present as minute scraps and are often ignored by the geologist but, combined with palynomorphs, they enhance considerably the proxy evidence for specific habitats or even micro-habitats.

Because the ecological preferences and specific distributions of many plants is known, “pictures” can be built up from assemblages of palynomorphs and plant remains retrieved from an object. With a good understanding of palynomorph taphonomy, such “pictures” allow visualisation of the nature of the source area(s) from which the proxy evidence was transferred.

Careful sampling is required to achieve the maximum amount of evidence from any object. Invariably, material from more than one location is transferred to objects such as footwear, clothing, digging implements, and vehicles, and the various episodes of deposition can often be detected by analysis of the biological components. This is especially important when there is more than one critical site requiring investigation. Geologists often carry out “spot sampling” on exhibits, but such an approach may give a limited view of the whole accumulated deposition, and also compromise the botanical evidence. The biological approach is to demarcate an exhibit into specific areas and to retrieve the whole of the deposit from each of those areas. These methods can reveal a sequence of contact episodes between, for example, an item of clothing and a place, or specific areas within that place. Sampling needs to be as thorough as possible, and any item needs to be considered in its entirety rather than finely targeted microsites.

When assessing the feasibility of contact between an object and a crime scene, comparator samples must be collected from every pertinent site. This is important for eliminating irrelevant places, and for assessing background noise in the data. The resolution of analytical data critically depends on the numbers of samples taken and their spatial relationships one with another. Limited police budgets, and other constraints, can influence the numbers of comparator samples collected and analysed, and every attempt must, therefore, be made to focus sampling in the most appropriate way.

Case histories will be presented which demonstrate the power of botanical trace evidence in demonstrating contact between objects and places, and for providing intelligence in searches for clandestine burials or surface depositions.