Naslov
Authigenic siliceous-carbonate concretions in Cenomanian–Turonian carbonates of southern Croatia ; geochemical and biotic record

Autori
Posilović, Hrvoje ; Fio Firi, Karmen ; Sremac, Jasenka ; Cvetko Tešović, Blanka ; Brajković, Marija

Izvornik
Facies (0172-9179) 62 (2016); 28-1

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
Concretions ; Silica-carbonate ; Diffusion ; Late Cretaceous ; Oceanic Anoxic Event ; Southern Croatia

Sažetak
Numerous regular and irregular shaped concretions were discovered in southern Croatia within the Upper Cretaceous carbonate deposits, which consist mostly of bioclastic wackestones and packstones. The size of the concretions varies from two to 25 cm in diameter for the regular and up to 40 cm in length for the irregular ones. The concretions have different internal structures and compositions which vary from those of the host rocks. Some concretions are entirely siliceous, while the others exhibit alternating opal silica and carbonate rich zones. Silica is derived from opal-A secreting marine biota, mostly sponges, whose spicules can be found within the concretions and in the surrounding limestones. The regular shape and alterations of zones are the result of the diffusive supply and fast "consummation" of silica at the growth site. Determined fossil community and bitumen found in the surrounding limestones, indicate deposition in oxygen depleted deep marine environment of the Adriatic Carbonate Platform, which belong to the Sveti Duh Formation (latest Cenomanian–Early Turonian). The carbon isotope composition of the concretions corresponds to the globally known Cenomanian–Turonian ′Oceanic Anoxic Event′ (OAE 2).

Izvorni jezik
Engleski

Znanstvena područja
Geologija

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