Upper Campanian volcanoclastics in the Scaglia-type limestones of the Adria continental margin

Upper Campanian Scaglia-type limestones in the transition zone between the Internal and External Dinarides (Placer 2008) contain two layers of bentonitic clays. The first 110 cm thick, and the second 10 cm thick. The geochemical composition of the bentonites indicates a rhyolitic volcanic source within an active continental margin. According to the mineralogy of the clay, the layers can be interpreted as deposition of volcanic-ash in a marine sedimentary environment with admixture of carbonates. The encompassing carbonate succession was deposited in a deeper marine environment of the Slovenian Basin. The limestones are composed of (hemi)pelagic mudstones to wackestones and thin- to medium-grained calcarenites, originating from the adjacent Adriatic Carbonate Platform. Similar Upper Cretaceous successions containing Campanian bentonitic clay horizons have been described in the Central Apennines (Graziano and Adabbo 1996; Bernoulli et al. 2004). The most likely source of these volcanoclastics is the bimodal rhyolitic/basaltic magmatic activity within the Sava suture zone, located in the present day Dinarides (Ustaszewski et al. 2009; Cvetković et al. 2014; Prelević et al. 2017; Schmid et al. 2020).

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