engleski

Subaerial exposure surface within Paleocene carbonates as a regional event marking the end of Adriatic Carbonate Platform deposition on the island of Brač, Croatia

The end of Adriatic Carbonate Platform (AdCP) deposition is marked by regional emergence between the Cretaceous and Paleogene, marking a shift from Mesozoic large semi-isolated carbonate platform to Paleogene complex carbonate ramps system. Stratigraphic hiatus of variable duration in the southern part of AdCP commenced mostly during Santonian. However, in the farthest NW parts of the platform sedimentation was more or less continuous up to the Maastrichtian and even across the K/Pg boundary, and the same has been indicated recently for the SE part of the platform, including the Likva Cove section (island of Brač). The section indicates deposition on a very shallow inner platform with coexisting rudists and scleractinian corals during the late Maastrichtian. The latest Cretaceous beds are covered by Paleocene burrowed micritic limestones with discorbids, ostracods and very rare planktonic foraminifera (tentatively indicating basal Danian Zones P0–Pɑ) as a consequence of decreased shallow-marine 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 Paleocene and the overlying latest Paleocene/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. Diagenetic features point to deposition during warm humid climate (paleokarst features and bauxite occurrences) which changed to semi-arid conditions during the earliest Paleocene (fragments of calcretes). 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 AdCP shallow-marine carbonate deposition lasted longer, and that the overlying stratigraphic hiatus before establishment of carbonate ramp deposition was much shorter.

subaerial exposuresurface ; Paleocene ; regional event ; Adriatic carbonate platform ; Brač ; Croatia

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