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Decalcification In Loess Of Ivanić-Grad Area, Croatia

Karst in general and loess of Ivanić-Grad area in Croatia are very different terrains, but they are connected with a basic karst process. Loess is an aeolian sediment, characteristic for the Pleistocene glacial period. It is one of the most complete records of climate change during the Quaternary. Its dominant size fraction is silt (0.063 to 0.002 mm), in average 60-90%, while sand fraction (> 0.063 mm) is less frequent, as well as clay fraction (<0.002 mm) (Muhs 2007). Mineralogically, loess is uniform and consists of quartz, plagioclase, mica, carbonates and clay minerals (smectite, chlorite, kaolinite, vermiculite). The study area is located nearby Ivanić-Grad in central Croatia. The soil, the transition zone and loess were sampled in Čazma, Velika Ludina, Bunjani and Kloštar Ivanić. The study employed qualitative and quantitative phase analysis by X-ray powder diffraction, granulometric analysis, determination of organic matter, cation exchange capacity (CEC) and Fe-Mn-Al oxyhydroxides content. The results showed absence of carbonate mineral components, thus making this loess something different compared to the average loess composition. Evidence of former existence of carbonate components in loess of the study area is suggested in general geological map – sheet Bjelovar (Korolija et al., 1986). It states that above the loess without carbonate there is "real" loess with carbonate component (Basch, 1983). The carbonate component of the loess area of Ivanić- Grad disappeared in same process that is dominant in karst – dissolution and removal of carbonate minerals, decalcification. Karst geology is a term that generally refers to the carbonate rocks, limestone and dolomite. During karstification the carbonate rocks are weathered by physical and chemical processes. Thus, these rocks are denuded and lowered on their surfaces, or, what is even more distinctive, they build various characterictic geomorphological features. It is assumed that the dissolution of carbonates in loess has been dominantly affected by atmospheric precipitation and groundwater flows. So, karst rocks and loess, totally different in origin, in this case are connected by the same karst process.

loess ; Ivanić-Grad ; karst ; decalcification

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