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Palaeocene subaerial exposure surface – the end of the Adriatic Carbonate Platform deposition, island of Brač (Croatia)

The end of the Adriatic Carbonate Platform (AdCP) deposition is recognized by regional emergence between the Cretaceous and Palaeogene, marking a shift from Mesozoic large semi-isolated carbonate platform to Palaeogene complex carbonate ramps system. Regional Cretaceous/Palaeogene (K/Pg) stratigraphic hiatus was of variable duration and emergence in the southern part of the AdCP commenced mostly during Santonian. However, in farthest NW parts of the platform sedimentation was more or less continuous across the K/Pg boundary, and the same was confirmed in the studied Likva Cove section (island of Brač).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 strontium- isotope stratigraphy. The section indicates deposition on a very shallow inner platform with coexisting rudists and scleractinian corals during the late Maastrichtian. Benthic foraminifera assemblage as well as Sr-isotope dating confirmed latest Maastrichtian age. 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 biostratigraphic evidence of a possible short-lasting hiatus at the K/Pg boundary, but it is characterized by a soft sediment bioturbation and a 2-cm-thick reddish-brown clayey mudstone intercalation. The latest Cretaceous beds are covered by Palaeocene burrowed micritic limestones with discorbids, ostracods and very rare planktonic foraminifera (tentatively indicating basal Danian Zones P0– Pɑ) as a consequence of decreased shallowmarine depositional rate and a brief episode of more open marine influence. Top of the section comprises the largest and best developed coral patch reef exposed and intensely karstified during a relatively long regional stratigraphic hiatus between the oldest Palaeocene and the overlying latest Palaeocene/Eocene deposits. The emersion surface shows irregular, karstified and brecciated relief with reworked lithoclasts (with nodular fabrics, circumgranular cracking, alveolar- septal fabrics, rhizocretions, and Microcodium aggregates), and reddish bauxitic grains imbedded within yellow-brownish to reddish clayey calcareous matrix.The Likva section with prolonged shallow-marine deposition across the K/Pg boundary represents an important addition to the AdCP stratigraphy, indicating that its upper stratigraphic limit should be locally extended to the earliest Paleocene. Therefore, it may be concluded that in the SE part of the AdCP shallow-marine carbonate deposition lasted longer, and that the overlying stratigraphic hiatus before the establishment of carbonate ramp deposition was much shorter than in the other parts. Support by the Croatian Science Foundation (IP-2014-09- 9541) is acknowledged.

Platform carbonates, subaerial exposure surface, Late Cretaceous, Early Palaeocene, Brač

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