hrvatski

Geomorphology of the lakebed and sediment deposition during the Holocene in Lake Visovac

Lake Visovac is a tufa barrier lake on the Krka River between Roški slap (60 m asl) and Skradinskibuk (46 m absl) waterfalls, included in the Krka national park as primarily unaltered area ofexceptional natural value. Paleolimnological research was conceived to address a lake evolutionand depositional environments through the geophysical survey and collection of the lake sedimentcores. A high- resolution bathymetric map was obtained using a multibeam sonar. The averagelake depth varies between 20 and 25 m. Sediment cores were investigated to extract physicalproperties, sedimentological, mineralogical, geochemical and paleoecological records constrainedby the radiocarbon chronology, to understand what was happening to both the landscapes andlakescapes of Lake Visovac during the last 2.000 cal yr.Significant findings of the project are geomorphological features on the lake bottom: submergedsinkholes of various sizes (up to 40 m deep) ; submerged tufa barriers in the area of Kalički kuk(southern part of Lake Visovac) at the depths of 15 and 17 m, followed by a series of buriedcascade tufa barriers at the depth of 25 m covered with up to 10 m of Holocene lake sediments ; submerged vertical tufa barrier up to 32 m-high near the mouth of Čikola River ; submergedlandslides, small (river) fan structures characterized by sediment waves. Ground-penetrating-radar(GPR) data have been acquired due to the presence of gas-saturated sediments over a large areaof the lake, that limited the use of high-resolution acoustic profiling. A total thickness of sedimentsis up to 40 m. High resolution paleoenvironmental record through the Late Holocene givesevidence of high sedimentation rates in Lake Visovac, variable soil erosion impact on lakesediment composition and carbonate authigenic sedimentation. Higher organic carbon isobserved in the last 50 years due to changes in land cover and reforestation. Pleistocene lakesediment outcrops occur up to 20 m above the present lake levels indicating higher lake levels as aconsequence of higher elevation of tuffa barriers. Kalički kuk, which lies up to 20 m above presentlake level, is a remnant of these barriers which have been dated to MIS5. Results allow us tointerpret the environmental and evolutionary dynamics of Lake Visovac in the following way: lakelevel more than 20 m higher than today in mid-Pleistocene with significantly larger lake volume inLake Visovac, with active Kalički kuk and Skradinski buk waterfalls ; lower lake-level at the beginningof the Holocene when several small lakes existed in isolated basins in the area of Lake Visovac.

Holocene ; Lake Visovac ; geomorphology

nije evidentirano