Facies development and paleoecology of rudists and corals: an example of Campanian transgressive sediments from northern Croatia, northeastern Slovenia, and northwestern Bosnia

At six localities in northern Croatia (Donje Oresje, Gornje Oresje), Slovenia (Stranice, Slovenj Gradec), and Bosnia (Bespelj and Kober), successions of shallow-water Campanian deposits transgressively covered a tectonically uplifted and eroded paleorelief. They constitute different lateral parts of a transgressive subtidal environment, where rudists and corals are typical macrofossils. At the investigated localities, two types of succession were distinguished: (a) clastic and (b) carbonate. Most localities are within the extended chronostratigraphic range of Calveziconus cf. lecalvezae (80.5–79.03 Ma), which comprises the upper part of the Vaccinites alpinus interval zone (for Stranice and Slovenj Gradec localities) and beginning of the Pironaea polystyla interval zone (for Bespelj and Kober localities). In clastic successions, corals are the most abundant macrofossils, whereas rudists predominate within carbonate sections. The depositional setting of the investigated localities results from rapid relative sea-level rise with a tectonic overprint, which covered different types of paleorelief. In cases when the paleorelief is gentle, a transgressive succession starts with clastic coral-rich sediments or carbonates with radiolitids. In areas of steeper paleorelief carbonate sediments were deposited with a mixed radiolitid-hippuritid community, and the rudists, as the major macrofossils, indicate higher sedimentation rates in comparison with the clastic situations.