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Facies and biostratigraphy of the latest Maastrichtian to earliest Palaeocene platform carbonates of the Island of Brač (Croatia)

Regional Cretaceous/Palaeogene (K/Pg) emergence of the Adriatic Carbonate Platform (AdCP) was of variable duration and emergence in its southern part commenced mostly in Santonian. However, in farthest NW parts of the platform sedimentation was already recognized to be more or less continuous across the K/Pg boundary, and the same was confirmed in the studied Likva Cove section (island of Brač). The Maastrichtian–Palaeocene Likva section was examined to reconstruct environmental changes and describe coral patch reefs across the K/Pg transition. A continuous, 50-m-thick section of shallow-water platform carbonates encompassing the K/Pg boundary was studied to determine biostratigraphy of larger benthic and planktonic foraminifera, microfacies, sedimentology, and geochemistry (strontium- isotope stratigraphy). The boundary is constrained between the last occurrence of Maastrichtian larger benthic foraminifera and the first occurrence of Danian planktonic and benthic foraminifera. Studied interval does not show clear sedimentary and biostratigraphic evidence of a possible short- lasting hiatus at the K/Pg boundary ; however, it is characterized by soft sediment bioturbation and a 2-cm-thick reddish-brown clayey mudstone. The Cretaceous strata comprise: (1) lower part made of wackestone and floatstone with rudist fragments, peloids, ostracods, benthic foraminifera, and fenestral laminites deposited in low-energy restricted shallow subtidal and intertidal environments ; (2) middle part containing similar rocks but with several levels indicating short-lasting subaerial exposures followed by small coral patch reefs with preserved globular and domal growth fabrics ; and (3) upper part composed of laminated fenestral micritic limestones with peloids, ostracods, discorbids, and rare thin- shelled rudist fragments overlain by grain- supported limestones with miliolids, peloids and intraclasts immediately below the K/Pg boundary level, indicating higher energy shallow subtidal conditions. Benthic foraminifera assemblage (Rhapydionina liburnica, Laffiteina mengaudi, Fleuryana adriatica, Bolivinopsis spp., Cuvillierinella aff. salentina, Dargenioella sp.) as well as isotope dating confirm the latest Maastrichtian age. Latest Cretaceous beds are covered by Palaeocene burrowed micritic limestones with discorbids, ostracods and very rare planktonic foraminifera as a consequence of short episode of more open marine influence. Planktonic foraminifera (Eoglobigerina sp., Parasubotina sp., Praemurica sp., Globanomalina sp.) tentatively indicate basal Danian Zones P0–Pɑ. Above this only 2 m thick horizon with pelagic influence (probably indicating short-term sediment starvation rather than deepening of the environment), a sudden return to micritic limestones with discorbids, ostracods and charophytes indicates re-establishment of low- energy shallow subtidal conditions with nearshore brackish and freshwater influence and benthic foraminifera assemblage (Bangiana hanseni, Valvulina triangularis, Kayseriella sp., Kartalina sp.), and confirms SBZ 1. Top of the section comprises the largest and best developed coral patch reef exposed and karstified during following relatively long regional exposure event between these oldest Palaeocene and the overlying Palaeocene/Eocene deposits. The Likva section with prolonged shallow-marine deposition across the K/Pg boundary is important addition to the knowledge on the AdCP, indicating that its upper stratigraphic limit should be locally extended to include Palaeocene deposits capped by regional emergence.

facies ; biostratigraphy ; late Maastrichtian ; early Palaeocene ; Brač

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