engleski

Holocene sedimentation on submerged karst: Example from the northern Adriatic

The Vinodol Channel, as a part of the Kvarner area (northern Adriatic, Croatia), is located between Vinodol coast (NE) and coast of the Krk Island (SW). Coasts of this channel have irregular triangle shape. Very narrow Tihi Channel connects Vinodol Channel with the Rijeka Bay on NE side. Toward SE the width of Vinodol Channel is more than 10 km, and it is connecte with Velebit Channel. Integrated terrestrial and marine geological research indicated interesting sedimentation pattern in this transitional environment. Carbonate rocks (Cretaceous and Paleogene limestones, dolomites and carbonate breccias) predominate in the coastal area, whereas Paleogene siliciclastic rocks (flysch) outcrops are restriced. Flysch outcrops (mostly siltstones, marls and sandstones) including Quaternary slope and fluvial deposits are found in lower parts of Vinodol valley and in narrow zone between Vrbnik and Omisalj Bay on the Krk Island. At shallow sea floor (up to 20 m depth) coarse-grained sandy and gravely sediment prevail, whereas deeper sea floor is covered by fine-grained muddy sediment. The Holocene sediments cover submerged both Paleogene flysch complex and karstified Cretaceous and Paleogene carbonate rocks. On prevalently unpermeable siliciclastic rocks covered with Quaternary deposits erosional processes prevail, and these sediments are the main source of particulates transported by water flows towards Vinodol Channel. These are Dubracina and Novaljska ricina rivers in the Vinodol valley and several creeks near Soline Bay on the Krk Island. Carbonate rocks are of low erodibility, and short torrent type flows on carbonate rocky slopes of the Vinodol Channel transport relatively low quantities of prevalently coarse-grained particles. During relatively long period in the Upper Pleistocene NE part of the Vinodol Channel was alluvial valley with karstified flanks (slopes), and due to the sea-level oscillations between 40 and 60 m below recent sea-level, periods of intense erosion altered with periods of sedimentation. Remnants of fossil river and torrent valleys can be traced up to forty meters below present sea-level. However, at the same time marine sedimentation occurred in the SW part of the Channel. After rapid sea-level rise at the beginning of Holocene, filling of estuarine river mouths of Dubracina and Novaljska ricina rivers, and of shallow Soline Bay started, due to the relatively large quantities of fine to medium grained particulates originating from flysch zones. Sub-bottom profiling indicated a progradational structure of this filling. Torrent erosion and sedimentation of coarse grained particles continues at or near sea-level along carbonate coast. Due to the current system, dispersal and sedimentation of fine grained siliciclastic material occurs in the most of the Vinodol Channel bottom area.

sediments; karst; delta; progradation; Adriatic Sea

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