Naslov
Holocene environments of Mljet Island: mineralogy and geochemistry of lake, marine, brackish and terrestrial sediments

Autori
Razum, Ivan ; Ilijanić, Nikolina ; Miko, Slobodan ; Hasan, Ozren ; Hajek Tadesse, Valentina, Brunović, Dea ; Rohl, Ursula

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
5. HRVATSKI GEOLOŠKI KONGRES s međunarodnim sudjelovanjem/5th CROATIAN GEOLOGICAL CONGRESS with international participation Osijek 23.– 25.09.2015. Knjiga Sažetaka/Abstracts Book / Marija Horvat & Lara Wacha - Zagreb : Hrvatski geološki institut, 2015, 224-225

ISBN
978-953-6907-50-2

Skup
5. HRVATSKI GEOLOŠKI KONGRES s međunarodnim sudjelovanjem/5th CROATIAN GEOLOGICAL CONGRESS with international participation

Mjesto i datum
Osijek, Hrvatska, 23.09.2015. - 25.09.2015

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Domaća recenzija

Ključne riječi
Holocene ; Mljet ; μ-XRF ; mineralogy ; environmental changes

Sažetak
This study presents the preliminary results obtained by analyzing cores from four locations on the Island of Mljet. The core retrieved from the Veliko jezero has a length of over 450 cm. In the marsh Sobra as well as in the bay Stupa core length was over 550 cm and in Pomena, on the mainland, its depth was over 350 cm. The μ- XRF analyses were performed on the core retrieved from the Veliko jezero. We used a resolution of one centimeter on the entire length of the core, two millimeters in the section of the core that is laminated and 0.3 mm in some laminated parts of the core. Obtained geochemical data indicate changes in the conditions of deposition and the presence of four tephra layers (Fig. 1), two of them are categorized as cryptotephra. Ca and Sr vary because of the marine influence and aragonite precipitation (Figs. 1 and 2). Changes in Al concentrations are mainly related to terrestrial influence and partially to the presence of tephra, while Zr indicates clearly the presence of the tephra. Relative concentrations of the Br can be linked to the marine influence (Ziegler et al., 2008). Mineralogical analysis (XRD) show that the most common minerals are aragonite and calcite. As a result of changing conditions, portions of aragonite and calcite vary along the core (Wunsam et al., 1999). SEM images indicate that the aragonite morphology is similar to present day aragonites which precipitate in the Malo jezero during annual whitenings (Fig. 2) (Sondi & Juračić, 2010). On the core Pomena, which is taken on the mainland, the analysis of heavy and light mineral fraction was made. Heavy minerals indicate polygenetic character of the sediment with contributions from different sources. Minerals from epidote group and garnets indicate possible contribution from the flysch, mafic minerals such as hypersthene and bronzite can be linked to plesistocene aeolian sands (Babić et al., 2013). High portion of the sanidine in light mineral fraction is also intriguing, this sanidine could originate from Colli Albani Volcanic District (Durn et al., 2007). Absence of orthopyroxenes and occurrence of apatite in third meter of core can be indicator of a provenance shift or it can be ascribed to specific geochemical conditions which caused dissolution of apatite and preservation of orthopyroxenes in the upper parts while in the lower parts of the core situation was opposite (Fig. 3) (Lang , 2000). In the Sobra, which is marsh today, we can trace changes from peatlands to wetlands environments. Clear boundaries between the marine, lake, wetland and terrestrial sediments sequence are visible in the core section from Stupa bay. Cores from the Stupa bay and Sobra are dated with 14C, so that depth-age models for these sites are obtained. Magnetic susceptibility is recorded for all cores and its values can be brought in connection with the occurrence of tephra layers and amplified erosion. All the sites have different developments at the same time making it possible to monitor the different conditions of their formation and to compare them with each other, which facilitates reconstruction of the environment.

Izvorni jezik
Engleski

Znanstvena područja
Geologija

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