engleski

Seabed geomorphology of the karst estuaries in the Eastern Adriatic Coast (Dalmatia)

During the Last Glacial Maximum (LGM) lowstand, large areas of the Adriatic shelf were exposed. At that time, relative sea level (RSL) was at least 125m lower than present (FAIRBANKS, 1989 ; LAMBECK et al., 2011 ; BENJAMIN et al., 2017). This enabled formation of lakes, river valleys and their floodplains that were subsequently submerged during Holocene transgression (VACCHI et al., 2016 ; ANTONIOLI et al., 2009). Here we present a study of three karst estuaries, Zrmanja, Krka and Cetina, located along the Eastern Adriatic Coast. High resolution acoustic geophysical methods (sub- bottom profiler) coupled with multibeam bathymetry were gathered during the projects QMAD and LOLAdria. Interpreted geophysical data are compared to RSL curve for the Adriatic region (BENJAMIN et al., 2017, LAMBECK et al., 2011). Zrmanja River in northern Dalmatia flows into semi-isolated basin Novigrad Sea, forming 14 km long estuary that ends at tufa barrier/waterfall Jankovića Buk. Geoacoustical survey in the Zrmanja river estuary revealed several tufa barriers located in the narrow canyons connecting Novigrad Sea with open waters and with Karin Sea. During the Holocene lowstand those barriers prevented marine flooding into Novigrad Sea and later to Karin Sea, consequently forming present day estuary. Krka River, located 45 km east from Zrmanja River creates a 23 km long estuary extending to the tufa waterfall Skradinski buk. Geoacoustical survey revealed many submerged tufa barriers similar to present barriers formed upstream the Skradinski buk, as well as a submerged river canyon filled with three sedimentary units: marine, brackish and fluvial. Barriers enabled formation of lakes, as well as prevented a marine flooding during the Holocene sea-level rise. During the Holocene lowstand Krka River formed a river fan some 17 km south of the today’s river mouth, right at the edge of the Mid Adriatic Deep. Present day Cetina river mouth is located at the exit from the canyon in the town of Omiš. Seismic data reveal that during the LGM river did not flow in NW direction as a continuation of today’s flow but created a valley along the coast in SSE direction. In the postglacial period river eroded flysch sequences deposited on the steep hillslopes of Omiška Dinara mountain, and created over 15 m deep and 350 m wide river valley. Due to a Holocene RSL rise, channel was infilled with retrogradational fluvial sediments. Submerged bottom of the valley along Omiška Dinara mountain stands at 81 m b.s.l. Deposition of fluvial sediments started after 13800 BP (LAMBECK et al., 2011). As sediments gradually filled in the channel, Cetina created a 3 km wide floodplain. Thickness of fluvial sediment is 20 m. Fluvial sediments are overlain by 3-5 m thick marine sediment sequence. This work was supported by the Croatian Science Foundation Projects “Sediments between source and sink during a late Quaternary eustatic cycle: the Krka River and the Mid Adriatic Deep System” (HRZZ IP-04- 2019-8505) “Lost Lake Landscapes of the Eastern Adriatic Shelf” (LOLAdria) (HRZZ-IP-2013-11- 9419).

acoustic geophysical methods, submerged landscape, Holocene, eastern Adriatic coast

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