engleski

PALEOLANDSCAPES OF KARST RIVERS ZRMANJA, KRKA, CETINA, AND NERETVA IN THE EASTERN ADRIATIC COAST SUBMERGED AS A CONSEQUENCE OF THE HOLOCENE SEA-LEVEL RISE

Large areas of the Adriatic shelf were exposed during the Last Glacial Maximum (LGM) lowstand. At that time relative sea level (RSL) was at least 125m lower than present (Lambeck et al., 2011 ; Benjamin et al., 2017), enabling formation of lakes, river valleys and their floodplains. Those areas were consecutively submerged during Holocene transgression (Vacchi et al., 2016). We present a palaeohydrological study of karst rivers Zrmanja, Krka, Cetina and Neretva located along the Eastern Adriatic Coast. Well-preserved submerged river valleys are detected using acoustic geophysical methods (sub-bottom profiler, SBP) coupled with bathymetric data. We compared interpreted SBP data to RSL curve for the Adriatic region (Benjamin et al., 2017, Lambeck et al., 2011). SBP data for paleo-Zrmanja River shows channels incised into Pleistocene clastic rocks exposed during the early Holocene. Larger valley, flowing from east, joined Zrmanja and continued into Velebit Channel. Numerous channels visible in SBP data point to the existence of braided river system. Western part of the depression in today’s Novigrad Sea hosted a small lake. RSL rise caused marine sediments to overlie fluvial and terrestrial sediments at depth 35, 7 m below sea level (b.s.l.), an event dated at 11440 BP (Hasan, 2017). Submerged Krka river valley is visible in SBP data recorded in the Prokljan lake located approximately 10 km from the Krka estuary. River valley was incised up to 32 m b.s.l. indicating that fluvial sediment deposition started after 9400 BP (Lambeck et al., 2011). SBP records suggest existence of submerged tufa barrier at the northern part of the Prokljan lake. Fluvial sediments are overlain by up to 7 m thick marine sediment sequence. Present floodplain of Neretva River extends over 10 km. SBP data shows similar floodplain formed approximately 60 km to the west, between islands Hvar, Šćedro and Korčula, at sea depth of 65-70 m b.s.l. Fluvial sediments with parallel to subparallel stratified reflectors onlap on the basin edges and overlie limestones. According to RSL curve (Lambeck et al., 2011) fluvial sedimentation began approximately 13900 BP at 85 m b.s.l. After the basin was filled up to 70 m b.s.l. floodplain widened into a 10 km wide floodplain. Two meters of marine sediments overlie fluvial sediments. Cetina river mouth is located at the canyon exit in the town of Omiš. SBP data reveals 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. During the postglacial period Cetina created over 15 m deep and 350 m wide river valley. River valley was incised up to 81 m b.s.l. indicating that deposition of fluvial sediments started after 13800 BP (Lambeck et al., 2011). Due to a Holocene RSL rise, channel was infilled with retrogradational fluvial sediments. As sediments filled in the channel, Cetina created a 3 km wide floodplain overlain by 3-5 m thick marine sediment sequence. This work was supported by the Croatian Science Foundation Project “Lost Lake Landscapes of the Eastern Adriatic Shelf” (HRZZ-IP-2013-11-9419).

sub-bottom profiler, submerged landscape, Holocene climate change, Eastern Adriatic

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