Geochemical mapping using a geomorphologic approach based on catchments

The Extended Sample Catchment Basin (ESCB) mapping technique, discussed in this paper, can be used to display the spatial distribution of geochemical variables measured in stream sediments taking into consideration the geomorphologic settings and the hydrographic patterns of surveyed areas. This approach is based on the association of an area of statistical representativeness with each sample, and on the assumption that the concentrations measured in the stream sediments can be considered as average reference values for this area.ESCBs can be easily identified considering the position of the sampling points within the hydrographic network and using the confluences between the streams of highest rank as break points for representing changes of the geochemical background. This approach, different from the traditional geostatistical and deterministic ones, does not consider the Euclidean distance among the sampling points as a measure of geochemical similarity but only refers to their functional relationship along the streams (following the water and the sediment flow) to measure their proximity.ESCBs can be seen as a specific development of previous techniques based on catchments and proves to be especially useful for supporting land planning in a preliminary survey phase while it is not specifically suitable for the identification of point sources of geochemical anomalies.Due to the fractal nature of the hydrographic network, all the procedures can be driven in a GIS environment by using digital terrain models apart from their spatial resolution.