engleski

A sedimentary record of Late Pleistocene and Holocene environmental changes from lakes on the Eastern Adriatic coast

Lake sedimentary record was used to reconstruct paleoenvironmental changes during Late Pleistocene and Holocene along the Croatian karst region on the Eastern Adriatic. Lake sediments were studied using multidisciplinary approach, combining sedimentological, mineralogical and geochemical analysis with paleontological proxies like pollen, ostracods or diatoms and dated using radiocarbon absolute dating. The most of the lakes cover the end of Pleistocene and beginning of the Holocene and show the evolution of the lakes and environmental changes during the last 12.000 years. Paleolimnological research was conducted on lake sediments on the eastern Adriatic coast (Lake Vrana on the Island Cres, Bokanjačko blato, Lake Vrana near Biograd and Lake Baćina- Crniševo) and they enabled reconstruction paleoenvironmental conditions from the late Pleistocene until present. Due to the proximity of the sea and permeable karst, the lake levels are influenced significantly by the sea level rise during the Holocene. Lakes represent typical karst lakes dominated by carbonate sedimentation, with periodic siliciclastic input. In every lake, three periods can be distinguished, the beginning of the Holocene with increased erosion and higher concentrations of siliciclastic material, middle Holocene with formation of deeper lakes and carbonate sedimentation, and Late Holocene characterised by erosion of siliciclastic material as a result of deforestation and human impact. Deposition of the siliciclastic material in Lake Vrana near Biograd lasted until 9.1 ka BP, when carbonate lake sedimentation started and the lake was formed. At the end of the period from 9.6 to 9.1 ka BP the dark organic rich sediment was deposited. The marine influence on the Lake Vrana sediments is evident after 6.1 ka BP. The present lake water conditions (alternating seasonal changes in the salinity, freshwater- brackish) were established at 3.8 ka BP. Deposition of homogenous carbonate mud (lake marl) started at 3 ka BP. In Lake Baćina deposition of the siliciclastic material was very intense from 11.7 to 10 ka BP, and then gradually decline until 7.5 ka BP. Dominant carbonate deposition lasted from 7.5 until 4.5 ka BP, when intensive changes in the sediments began, observed by the high sand fraction until 2.5 ka BP, and in between the alternate intervals were developed with calcite and quartz and those in which only calcite is present. In Bokanjačko blato the deposition of siliciclastic material lasted from 10.3 to 6.1 ka BP and then gradually decreases until 5.2 ka BP, when carbonate deposition began. In Lake Vrana on the Island Cres, the beginning of the Holocene is characterized by the deposition of the siliciclastic material, but which continues to the middle Holocene, until 4.5 ka BP when the carbonates appear. During the Holocene contrasting climate pattern has been identified in the central Mediterranean. Paleoenvironmental reconstructions of investigated lakes on the Eastern Adriatic coast correlate well with the lakes situated north of around 40°N of latitude, which are characterised by a wetter early Holocene, followed by relatively drier conditions during the middle Holocene and gradually increased moisture in the Late Holocene. South of 40°N of latitude there is opposite trend, very dry conditions in the first half of the Holocene and wettest period during the Mid Holocene followed by a progressive aridification, evident in lakes Preola and Pergusa on Sicily.

Holocene; lake sediments; multiproxy analysis; environmental changes

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