engleski

LATE QUATERNARY SEABED GEOMORPHOLOGY OF THE PROKLJAN LAKE (KRKA RIVER ESTUARY)

A multiproxy investigation has been carried out to study the seabed geomorphology of the Krka River estuary located in the central Dalmatia. A detailed multibeam survey (MBES bathymetry and MBES backscatter), side scan sonar imaging, subbottom acoustics coupled with piston sediment cores and bottom samples were used to characterize 6.2 km2 of submerged paleolandscape of the Krka River valley and the Prokljan Lake. The bathymetry and side scan sonar indicate that the submerged paleolandscape is well perserved and consists of partly buried tufa barrier system with small lakes and carbonate mounds. Geophysical survey consisted of a total of 70 km of seismic profiles, whereas 5 long (4–9 m long) piston sediment cores were collected in the lake area. We identified three sedimentary units, fluvial, brackish and marine, spanning up to 9000 y BP and with thickness up to 15 m. Ground truth data, in the form of grab samples and video transects, were collected at 36 locations in order to create geomorphological and geological classifications of the seabed. Sediment samples were processed for grain size, magnetic susceptibility, bulk density, carbon and nitrogen concetrations and mineralogical analysis. A map of seabed classification was produced using Object- Based Image Analysis (OBIA) by integrating information obtained from multibeam and ground truth data. Tufa barriers are unique karst features and great paleoclimate indicators. They enabled formation of lakes and had a predominant influence on the Holocene flooding of the river canyon. They can be used as an indicator of sea level given their morphology, i.e. depth of each barrier, in connection to the onset of marine sedimentation in the Lake. The results of this study reinforce the idea that submerged tufa barriers in the Prokljan Lake began forming during early Holocene or even during the transition from the Pleistocene into Holocene. Flooding of the river canyons (Guduča River and Krka River) due to sea level rise in the Prokljan Lake started at about 9300 y BP and the formation of estuary at approx. 7500 y BP. Consequently, this multiproxy study allowed a reconstruction of the seabed geomorphology and paleoenvironmental evolution of the upper part of the Krka estuary since the Holocene sea level rise. This work was supported by the Croatian Science Foundation Project “Sediments between source and sink during a late Quaternary eustatic cycle: the Krka River and the Mid Adriatic Deep System” (QMAD) (HRZZ IP04-2019- 8505).

eastern Adriatic coast ; submerged paleolandscape ; seabed mapping ; karstic estuary ; Holocene

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