engleski

A mathematical model relating stream sediment geochemistry and the Kupa River drainage basin lithology

This study (from planned dissertation of author) constitutes the first geochemical investigation of stream sediments in the Kupa River drainage basin, which area covers 10052 km2 and is situated in three countries (Croatia, Slovenia, Bosnia and Herzegovina). In order to assure the same sedimentary conditions, sediments have been sampled during the dry season in June - August 2003. Major- (8) and trace- (45) elements were determined by ICP-MS method (in Actlabs, Canada) in fraction <63 ľm at 63 locations. Bedrock lithology (44 units), which represents the parent material for the sediments, was determined for each of the 63 drainage subcells, using Geological map 1:500000, sheet Zagreb. The drainage basin was delineated in such a way that each basin segment corresponded to the area upstream and upslope of each sampling site. As a result of vectorization, topology and calculated surfaces, percentage of lithological units were obtained for each subcell. Basic statistics (program Statistica 6.0) was used to find marked positive correlations of major and trace elements with corresponding lithologies. From 44 lithological units, 8 reduced lithologic variables were specified and used in factor analysis. The geochemical variables included a selection of 8 major and 17 minor and trace elements, similarly as performed by Halamić et al. (2001) for Medvednica Mt. To illustrate how computers could help the modern geologists and how difficult it is to get exact information from a multivariate method, such as factor analysis, 4 calculation experiments have been performed. Lithologic variables were specified in different ways: 1. according to age of formation 2. according to related rocks, independent on age 3. according to related rocks, but taking into account correlation of elements and all 44 lithological units 4. according to computer based clustering of lithological units. Results will be presented for all 4 cases, showing relationships of elements and lithologic units, reduced into several geologically meaningful factors. The differences presented for 4 cases will be discussed and the best model suggested. LITERATURE: Halamić, J., Peh, Z., Bukovec, D., Miko, S., Galović, L. (2001): Geologia Croatica 54/1, 37-51.

Kupa River; geochemical investigation; stream sediments; multivariate method; factor analysis

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