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Early Holocene marine drowning of the "karst lake" Pirovac Bay (coast of Dalmatia, Croatia) (CROSBI ID 632721)

Prilog sa skupa u zborniku | sažetak izlaganja sa skupa | međunarodna recenzija

Brunović, Dea ; Miko, Slobodan ; Ilijanić, Nikolina ; Hasan, Ozren ; Bakrač, Koraljka ; Hajek Tadesse, Valentina Early Holocene marine drowning of the "karst lake" Pirovac Bay (coast of Dalmatia, Croatia) // Proceedings of the International Congress GeoSUB - Underwater geology, Trieste 2015 / Furlani, Stefano ; Antonioli, Fabrizio ; Anzidei, Marco et al. (ur.). Trst, 2015. str. 26-27

Podaci o odgovornosti

Brunović, Dea ; Miko, Slobodan ; Ilijanić, Nikolina ; Hasan, Ozren ; Bakrač, Koraljka ; Hajek Tadesse, Valentina

engleski

Early Holocene marine drowning of the "karst lake" Pirovac Bay (coast of Dalmatia, Croatia)

Eastern Adriatic shelf along Croatian coast is dominated by karst relief that is submerged and covered with thick succession of sediments. Pirovac Bay is a great example of such type of environment. It is a relatively large submerged shallow karst doline located in the central part of the eastern Adriatic shelf. High- resolution seismic study coupled with multyproxy (geochemical, grain-size, mineralogical and paleontological) sediment core analysis was carried out in order to reconstruct paleoenvironmental evolution of the area in relation to climate variability and the sea-level fluctuations during the Late Glacial and Holocene. Karst bedrock of Pirovac Bay is covered with up to 12 m of sediments in the deepest part of the bay and six distinct seismic units were identified. Four of them can be confidently correlated with analysed sediment cores. Unit 3 in the geophysical profiles represents the remnants of the loess- like sediments that appear in the outcrops on the surrounding islands, mostly in the south- western part of the area. This unit is well preserved in the deepest part of the bay and in the Murter Channel. The deposition of sediments from seismic Unit 4 commenced with the formation of the floodplain/alluvial fan in the bay. Furthermore, results also indicate that Pirovac Bay was a lacustrine environment (Unit 5). Seismic reflections show laminated lacustrine deposits with total thickness of ~3, 5 m in the deepest part of the bay. The topmost unit (Unit 6) contains ~3 m thick sequence of marine sediments that have almost uniform thickness at the water depth from 20-25 m. In the shallower, NW and SE part of the bay thickness of this sequence is 1 m or less. The seismic units correlate with the existing 7.2 m long sediment core extracted from the central part of the bay (25 mbsl) and 1.3 m long core extracted from the NW part of the bay (6 mbsl). The bottom of the 12 m long sedimentary package remains to be retrieved. Multiproxy analysis of the longer core, which spans to the last ~14.000 years, confirmed that the lake sediments preceded marine deposits. Typical lake ostracod assemblage was found at 5 mbsf, which corresponds to 11.000 cal years BP, followed by mixed fauna-brackish to freshwater with typical marine fauna at 2.5 mbsf which is dated to 7.500 cal years BP. „Karst lake” Pirovac Bay existed from 12.000 cal years “GeoSUB – Underwater geology” – Trieste, 13-14 October 2015 27 BP until 8.000 cal years BP when the karst relief was inundated by marine waters. Inundation by the sea was restricted until that time by a sill that is located in the northern part of the bay. Further sea-level rise allowed marine waters to reach the elevation of the sill. This caused marine flooding of lacustrine environment and development of fully marine conditions. Marine sediments accumulated in the bay from 8.000 cal years BP to the Present. The share of Sr and Sr/Ca also indicates that transgression of the sea started 8.000 years ago. Additionally, grain size distribution shows that marine sediments are coarser than lake sediments. Mineralogical composition reflects catchment karst area. Following mineral phases are present: calcite, quartz, dolomite, small amount of Mg-calcite and aragonite. Domination of endogenic calcite is typical for lake sediments and deep lake water environment. Clay mineral composition of the sediments from 7.2 to 5 mbsf has signature of loess sediments that appear on the islands that surround the bay. Sedimentary succession in Pirovac Bay was highly influenced by climatic conditions and sea-level rise that enabled development of different depositional environments during the Late Glacial and Holocene. It is possible to track the evolution of the bay, from alluvial, lacustrine, brackish to fully marine environment. Pirovac Bay is significant in terms of its position as well. It is situated close to the Lake Vrana (Dalmatia), separated only by the karstified limestone ridge (800 to 2500 km wide) through which the connection between the two systems exists, so as through the artificial channel Prosika, excavated in the 18th century in the southeastern part. The evolution of the Pirovac Bay had strong influence on the formation of the Lake Vrana, and the two lakes coexisted for about 1000 years in the Early Holocene, before the drowning of the „karst lake“ Pirovac Bay due to the sea-level rise. We thank Innomar Technologie GmbH for granting the equipment (SES-2000 subbottom profiler system) and techical support for the seismic survey.

Eastern Adriatic coast ; seizmic acoustic profile ; sediment core ; geochemistry ; ostracods

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Podaci o prilogu

26-27.

2015.

objavljeno

Podaci o matičnoj publikaciji

Proceedings of the International Congress GeoSUB - Underwater geology, Trieste 2015

Furlani, Stefano ; Antonioli, Fabrizio ; Anzidei, Marco et al.

Trst:

Podaci o skupu

International Congress GeoSUB - Underwater geology

predavanje

13.10.2015-14.10.2015

Trst, Italija

Povezanost rada

Geologija