engleski

Comparison of the mineralogy and origin of clay minerals of the lake sediments of eastern Adriatic coast (Vrana Lake, Bokanjačko blato and Baćina Lake)

Mineralogical and clay mineral composition was determined on long cores (approx. 7-10 m long) from karstic lakes along a 300 km NW-SE transect of the eastern part of the Adriatic Sea. Comparison was made between three locations: Vrana Lake (northern Adriatic), Bokanjačko blato (central Adriatic) and Baćina Lakes (southern Adriatic). The transition of the Late Glacial to the Holocene can be tracked. Basic studies included change in clay composition between glacial and interglacial sediment samples assuming transformation processes in the soils from the catchments. Lake sediments are made of two components: allochthones material, derived from outside the lake by erosion or aeolian acitivity ; and auchthonous material, producesd within the lake itself (biogenic in origin or inorganic precipitation). These material can be useful in paleoclimatic reconstruction. Analysis included X- ray diffraction (XRD) for bulk and clay mineralogy, grain size analysis, analysis for magnetic properties of sediments and pollen analysis. Dominant clay mineral phases are illite, chlorite and kaolinite. Clay mineral abundances and clay-mineral ratios are used to reconstruct the weathering conditions. Mineralogical results are compared with palaeomagnetic-derived time scale. Clay data are further compared with diatom and pollen core material. The evolution of clay derived climate proxies (kaolinite/chlorite ratio) is compared between locations. The cold and dry periods during the glacial times were responsible for physical weathering and thus contribution of higher amounts of chlorite and illite, as they are less sensitive to chemical weathering. The abundance of kaolinite is good indicator of warm and humid interglacial period caused by extensive chemical weathering. Lakes accumulate sediments from their surrounding environment and so sediment cores can provide a record of sediment source.

lake sediments; clay minerals; Late Glacial; Holocene

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