Application of fuzzy clusters to quantify lithological background concentrations in stream-sediment geochemistry

Fuzzy c-means clustering of multivariate stream-sediment geochemistry in a geologically complex area of the Eastern Alps (Austria) allows to separate four dominant associations of lithologies. Weak geochemical contrasts betwe en the involved lithotypes minimize the assignment variances by using a fuz zy coefficient of 1.3. The residual component of the geochemical signal, wh ich is not explained by cluster membership, is interpreted as concentration exceeding the geogene induced background. Therefore, it is possible to spe cify the background concentration for all lithotypes. Elemental enrichment is visualized by mapping the Geoaccumulation index of Muller [1979. Schwerm etalle in den Sedimenten des Rheines-Veranderungen seit 1971. Umschau 79, 7 78-785]. This technique detects anomalous (maybe contaminated) areas within a geochemical landscape. (C) 2000 Elsevier Science B.V. All rights reserve d.