engleski

Mineralogical and geochemical characterization of Quaternary lacustrine sediments in Rečica clay deposit (Croatia)

Remnant lacustrine sediments are preserved in the Karlovac depression, Crna Mlaka basin, in the central part of Croatia. This area represents the margin of the Adriatic Carbonate Platform. The Rečica clay deposits developed as Quaternary deposits in Crna Mlaka basin, the River Kupa Valley. Crna Mlaka basin is filled with Quaternary lacustrine/wetland sediments. Its edges are bordered and surrounded by Neogene (Pliocene) lacustrine sediments. Three types of lacustrine deposits are present. Regularly layered and gently inclined, fine- grained sediments (clay and silt) are spatially dominant. The second type is composed of coarse gravels and sands and the third one is composed of colluvial material. Fine-grained argillaceous sediments, generally referred to Pleistocene age, form Rečica clay deposit. The major part of the clays in Rečica clay deposit is represented by grey and yellow clays, brown clays and they are underlain by greenish-grey and grey-blue clays. The clay deposits are 8-12 m thick and overlay karstified limestone bedrock. A total of 171 samples were taken from 36 boreholes covering the entire area of the deposit. These samples, representing 1 to 3 m depth intervals, were used for determining mechanical properties of the material. Complete analyses, including mineralogical and geochemical analyses, were done on 12 composite samples. Clay minerals are dominated by smectite and illite, while chlorite and kaolinite are present in minor amounts. They are associated with quartz and in minor amount feldspar, occasionally goethite. Calcite is absent in lacustrine clays, indicating predominance of siliciclastic river supply. Abundance of smectite decreases in the surface sediments. SiO2 and Al2O3 dominate the clay geochemistry among other oxides. Geochemical and mineralogical analyses of the fine-grained varieties of lacustrine clays showed that their composition primarily depends on geology of the catchment area and secondarily on environment of deposition. The material was probably supplied by river. A montmorillonite-illite association is expected in closed lakes. Discovery of lake system bears on idea of river network in the Early Quaternary. These landform sequences provide an archive of long term fluvial and lake landscape development. The existence of the lakes in Crna Mlaka continental basin can be related to the period of the Pliocene-Pleistocene-Holocene. The basin is mainly characterized by fluvio-lacustrine sedimentation.

lacustrine sediments, clay deposit, clay minerals

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