Lower Cretaceous carbonate gravity-flow deposits from the Bohinj area (NW Slovenia): evidence of a lost carbonate platform in the Internal Dinarides

In the Bohinj area (NW Slovenia), a distinctive interval of carbonate gravity-flow deposits overlying the pelagic Biancone limestone was analyzed for microfacies and dated with radiolarians. This interval, newly described as the Bohinj Formation, consists of a 3 m thick carbonate breccia capped by a 4 m thick massive calcarenite. The breccia is composed of clasts of carbonate platform facies, isolated ooids and oncoids, and bioclasts of shallow-marine benthos. Intraclasts of pelagic calpionellid wackestone and rare chert clasts are also present. Radiolarians from the pelagic limestone below indicate a latest Tithonian to earliest Berriasian age, and those above indicate a Berriasian to Early Valanginian age. Paleogeographically, the area was part of the Bled basin, which had a relatively distal position on the Adriatic continental margin. This position is suggested by flysch-type deposits in the area that are Early Cretaceous in age and thus correlate with the Bosnian Flysch in the central Dinarides. The Bohinj Formation provides evidence of a carbonate platform that must have been located more internally but is now not preserved. This inferred platform (named the Bohinj Carbonate Platform) may have developed on top of a nappe stack, which formed during the early emplacement of the internal Dinaric units onto the continental margin. The platform correlates regionally with genetically similar isolated carbonate platforms of the Alpine – Dinaride – Carpathian orogenic system, e.g., with the Plassen Carbonate Platform in the Northern Calcareous Alps and the Kurbnesh Carbonate Platform in Albania.