Naslov
Chemical and textural composition of the Krka River tufa deposits from the Dinaric Karst region of Croatia

Autori
Medunić, Gordana ; Juranović Cindrić, Iva ; Pivčević, Nina ; Kampić, Štefica ; Prohić, Esad ; Goreta, Gordana ; Čobić, Andrea

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

Izvornik
Protected karst territories - monitoring and management / Yordanova, Marina ; Stefanova, Dilyana ; Mikhova, Dimitrina - Sofija : TerArt, 2012, 57-59

ISBN
978-954-9531-17-6

Skup
Protected karst territories - monitoring and management. The international scientific-practical conference

Mjesto i datum
Shumen, Bugarska, 16.09.2012. - 20.09.2012

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
tufa; mossy deposits; algal laminations; single extraction; trace element; calcite

Sažetak
The Krka National Park is situated near the city of Šibenik on the Adriatic Coast of southern Croatia (Fig.1). The Krka River with its series of spectacular waterfalls and cascades (i.e. carbonate barriers), as well as the lakes behind them, and the estury, represents a well-known karst phenomenon. The most prominent features of this specific biotop are rapid current and sprinkling water abounding in dissolved bicarbonates, together with the micro- and macro-biological communities which flourish on the tufa barriers, contributing to the build-up of the dams (Matoničkin & Pavletić, 1961). The locality has been investigated for a number of years, mainly using isotope methods (Horvatinčić et al., 2000 ; Lojen et al., 2004), whereas elemental analyses (Fe, Mn, Sr, Mg, Pb, etc.) were carried out on composite samples (i.e. carbonate phase together with insoluble residue) by means of XRF (Frančišković-Bilinski et al., 2004) and ICP-AES (Cukrov & Lojen, 2010) ; there have been no petrographic studies. Due to the paucity of research concerning the integration of geochemical data from the Krka River tufa deposits with their textural and mineral composition, this study has been initiated to characterise them by chemical, petrographical and mineralogical analyses. Hereby, this paper presents data on geochemical and petrographic features of the Krka River tufa deposits. Tufa samples were collected at the location Skradinski Buk waterfall which is 49 km downstream of the spring, at an altitude of 20 m above sea level. A total of six samples were taken either from the river bank or from the crest of the cascade. Calcite is the predominant mineral in the deposits, as determined by x-ray powder diffraction, whereas quartz, 10 Å phyllosilicate (illite and/or mica), chlorite, K-feldspar, amphibole, and smectite were detected in the insoluble residue. Commonly, freshwater carbonates exhibit a great variety of structures, textures, and morphologies, containing a wide diversity of constituents. On the basis of a framework of encrusted plant remains and porosity type, the studied tufas (Fig.1) are similar in texture and composition to deposits reported by Love & Chafetz (1988). Four specimens were extremely friable, except the two shown on Fig.1, having brown to light brown colours. Broadly, two major morphologies of sampled tufas distinguished in this active system are encrusted mossy deposits (Fig.1, a) and algally laminated crusts (Fig.1, b). Aquatic mosses abound at the Skradinski Buk waterfall, constructing the bulk of highly porous deposits. Hereby, moulds (Fig.1, a) readily visible in the form of numerous irregular cavities present in the rock testify as to their former existence. In thin-section, mossy-type encrustations consist of microcrystalline aggregates composed of peloidal, clotted or structureless micrite. Additionally, scarce occurrences of recrystallization and pore-filling cements are also present. In hand specimen, algally laminated crust (Fig.1, b) is a hard and compact stratified rock composed of alternating dark and light laminations up to 2 and 4 mm thick, respectively. On a microscopic scale, these laminae are micritic and microsparitic as a result of seasonal encrustation by algal filaments. Trace element concentrations in carbonate phase were measured after a single extraction with 1M Na-acetate (Tessier et al., 1979 ; Cook, 1992) by a Prodigy High Dispersive ICP-AES spectrometer (Teledyne Leeman, Hudson, NH, USA), working in a simultaneous mode, and equipped with a glass concentric nebuliser. All measurements were run in triplicate. The precission of the method expressed in RSD ranged from 0.4 to 6%, whereas the accuracy evaluated on the basis of the analyte recoveries by spiking experiments ranged from 77 to 103%. The concentrations of Ag, Al, Ba, Co, Cu, and Ni were below their detection limits as follows: 0.0746, 0.0257, 0.0405, 0.0311, 0.116, and 0.0782 µg/g, respectively. The organic matter content was determined by loss on ignition at 550oC for 2.5 hours. A rough inspection of the measured variables values (Tab.1) demonstrates a chemical heterogenity of the precipitates comparable to their petrographic diversity. This finding is in agreement with above statements regarding the diversity of environments and microenvironments existing within the overall tufa-depositing environment.

Izvorni jezik
Engleski

Znanstvena područja
Geologija, Kemija

POVEZANOST RADA