Patch reefs with scleractinian corals and layered domical and bulbous growth forms (calcified sponges?) in the upper Maastrichtian and lowermost Palaeocene platform carbonates, Adriatic islands of Brac and Hvar (Croatia)

New findings of numerous levels with scleractinian corals and layered domical and bulbous growth forms (calcified sponges?) within the upper Maastrichtian-lowermost Palaeocene shallow marine carbonates from the Adriatic islands Brac and Hvar (Croatia) are described. They indicate the existence of patch reefs developed on the Adriatic Carbonate Platform in the western Tethys area shortly before and after the Cretaceous/Palaeogene (K/Pg) boundary mass extinction event. Studied sections comprise reef remains preserved in situ with the remains of reef organisms in growth positions, but intense neomorphic alteration and weathering prevented determination to generic or species level. Observed coral morphology can be compared to the columnar coral growth form of modern scleractinian corals. Both the larger and smaller digitate corals described, have built small coral knobs scattered in the shallow waters of the inner carbonate platform. Layered micritic domical and bulbous growth forms that appear either as individual forms or sheet-like crusts around coral colonies are tentatively designated as possible calcified sponges. The in situ preserved fossil association reflects the once-living community and reveals palaeoecological succession within the thicker reef levels. Layered domical and bulbous growth forms prevail in the lower parts, while both corals and layered domical and bulbous growth forms in the middle and upper parts of reef levels indicate similar, but somewhat different palaeoecological requirements for the two groups. Many reef levels in the Brac sections overlie subaerially exposed limestones, following their irregular morphology, implying patch reef development during relative sea-level rise after subaerial exposure. Fossil remains described from the uppermost Maastrichtian and lowermost Danian reef levels on the island of Brac are very similar, indicating that despite the biotic crisis related to the K/Pg boundary events the reef biota from the latest Maastrichtian crossed the K/Pg boundary into the early Danian.