Naslov
Tertiary carbonate breccia conundrum in the Karst Dinarides of Croatia: very massive and very neglected

Autori
Vlahović, Igor ; Tišljar, Josip ; Velić, Ivo ; Enos, Paul ; Matičec, Dubravko ; Pletikosić, Nikola ; Perković, Dario ; Prtoljan, Božo ; Velić, Josipa ; Mrinjek, Ervin ; Mikša, Goran

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

Izvornik
Abstracts, 28th IAS Meeting of Sedimentology 2011 / Bádenas, Beatriz ; Aurell, Marcos ; Alonso-Zarza, Ana M. - Zaragoza : IAS, 2011, 460-460

Skup
28th IAS Meeting of Sedimentology

Mjesto i datum
Zaragoza, Španjolska, 05.07.2011. - 08.07.2011

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
Tertiary carbonate breccia; Karst Dinarides

Sažetak
The Karst Dinarides are part of the Alpine chain that parallels the NE Adriatic coast, formed during Oligocene and Miocene deformation of a thick succession of predominantly carbonate rocks, Carboniferous to Eocene in age. A remarkable lithological unit of the Karst Dinarides is a massive Tertiary carbonate breccia. It covers 1011 km2 ; the three largest outcrops are 695, 115 and 22 km2, respectively (82% of a total area). The rest comprises more than 400 smaller outcrops. Thickness data on the breccia are few, but in places it is more than 500 m thick. The breccia is massive, clast-supported, non-bedded, and lacks visible sedimentary structures. Clasts are mostly angular and poorly sorted, ranging in size from less than 1 mm to several centimetres with sporadic cobbles and boulders. Almost all clasts were tectonized before final deposition, as shown by truncated, calcitefilled fractures. Rare clasts of similar older breccia indicate a polyphase origin. Clasts were mostly derived from the surrounding rocks. The grey, yellowish, or reddish carbonate matrix is composed of small lithoclasts and recrystallized calcite. It contains no fossils or structures indicative of subaqueous deposition. A significant criterion for differentiating this breccia from others within the Dinarides are generally steeply inclined, gradational contacts with adjacent rocks. Transitional zones up to several meters wide extend from undisturbed to gradually more tectonized limestones through completely cataclastic limestones and monomict breccia composed of clasts from adjacent limestones to ± polymictic breccias. Significantly, breccia occurrences are mostly along faults and overturned folds with NE vergences, which are very atypical for the Dinarides. The Tertiary carbonate breccia was traditionally interpreted as talus breccia shed from the front of inferred reverse faults or overthrusts. This interpretation ignores several important facts: (i) subvertical and gradational contacts with surrounding rocks, instead of the expected inclined, irregular, sharp contacts, (ii) breccias crop out at hypsometrically highest points, and (iii) stratigraphic succession does not indicate reverse faulting. The breccia was probably initiated by intense in-situ fracturing during compression/transpression, disintegrating the carbonate rocks into cm-sized clasts within km-wide zones. Subsequent extension within overturned structures opened a complex system of deep fractures within the central portion of the breccia. Other breccias formed locally on the surface and portions were reworked into the underlying breccia by surficial processes. The resulting breccias were subsequently tectonized, further altered diagenetically, and intensely karstified and denuded during the long post- emplacement exposure, therefore resulting in a very complex appearance.

Izvorni jezik
Engleski

Znanstvena područja
Geologija

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