Research concerning chemical constitution of alluvial sediments was done in the lower course of the Obra River (Western Poland). The fragment of vertical profile, which consisted of various alluvial sediments (fine sands, peats and sandy silts) was chosen lor detailed analysis. Main research problem was to determine if lithology and chemical constitution or alluvial deposits arc interconnected in a distinct way within studied section of' the Obra river valley, and if changes of chemical clements concentration could be used to i I lustratc depositional processes which take place in river bed and floodplain. Concentrations ofFe, Mn, Cu, Zn, Ca, Mg and K were determined in collected sediment samples. Investigated changes of chemical clements concentration show that there is a distinct border between the organic sediments, which mark the place of former functioning of the Obra river bed, and sandy silts, which were deposited within floodplain during floods. Besides, dependence between lithologic variability of alluvial sediments and their chemical constitution was observed. However, this dependence is not clear in some cases. The authors concluded that it is necessary to use statistic analyses to define connection between lithology and chemical constitution or alluvial deposits (distinguishing geochemical groups of alluvial sediments).

Research concerning changes or chosen chemical elements concentration in alluvial sediments was conducted in the lower course or the Obra river valley. The analyses of Fe, Mn, Cu, Zn, Ca, Mg and K concentration were done in a fragment or vertical profile, which was characterized by variable lithology. On the basis of statistical analysis (cluster analysis) an attempt was made to distinguish geochemical groups of alluvial sediments of the Obra river valley. Six geochemical groups, which represent reductive conditions within peat deposits, the environment ofllood sediments (inserts of fine sands within peats and sandy silts in the top of the profile) and the environment or river bed sediments (fine sands in the bottom part ofthe profile), were singled out. Results of the study show that it is possible to distinguish the above mentioned depositional environments on the basis of variations of sediments' chemical constitution.