engleski

Holocene sedimentary record of the environmental changes in Lake Vrana near Biograd (Croatia)

The sediment core was recovered from the Lake Vrana near Biograd on the Eastern Adriatic coast. The 11 m of the core covers the last 12000 cal yr BP. Based on combining geochemical with palynological proxies, Lake Vrana was formed at around 9.1 ka BP (8.1 m), when the sea level rose and the water from the lake could no longer run through the karstified underground in an approximately 1 km long zone on the southeastern side of the lake. Higher concentrations of the lithogenic elements and presence of quartz in carbonate sediment from 12.3 to 9.1 ka BP, indicate increased erosion and input of the material from the catchment. Clay minerals are dominant by smectite, which originate from flysch material from the basin. We assume that in that period the periodic ponds or wetland existed, and by the end of the period from 9.6 to 9.1 ka BP the dark organic rich sediment was deposited (sapropel). Dominant carbonate sedimentation started at 9.1 ka BP, and the lake was formed. In sediments from the 6.1 ka BP it is evident gradually increase of siliciclastic components, because of the settlements as a result of deforestation, which allowed increased soil erosion and input of the siliciclastic material. These sediments are composed of following clay minerals: HIV, kaolinite and illite, and they originate from the terra rossa from the basin. Also, the pollen analysis showed assemblage of the typical Mediterranean holm oak vegetation from 6.1 ka BP. The influence of the sea on the sediments of Lake Vrana is visible after 6.1 ka BP, with increased proportions of the Mg and Sr in the sediments, so appearance of aragonite. The present lake water conditions were established at 3.8 ka BP. At 3 ka BP, started the deposition of the homogenous carbonate mud.

Holocene ; lake sediments ; environment

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