engleski

Stratigraphy of the Latest Cretaceous to Palaeocene platform carbonate succession of the Likva section, island of Brač, Croatia

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 succession 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). Studied succession indicates deposition within very shallow inner platform environments with coexisting rudists and scleractinian corals during the late Maastrichtian. The Cretaceous strata consist of: (1) lower part composed of wackestone and floatstone with rudist fragments, peloids, ostracods, discorbid and large benthic foraminifera, and fenestral laminites deposited in the low-energy restricted shallow subtidal and intertidal environments ; (2) middle part containing a brecciated surfaces with speleothems and blackened lithoclasts, indicating multiple subaerial exposures, accompanied by coral patch reefs with preserved globular and domal growth fabric characterised by intense weathering and reddish color ; (3) upper part composed of the laminated fenestral micritic limestones with peloids, ostracods, discorbids, and rare thin-shelled rudist fragments overlain by grain-supported limestones with miliolids, peloids, intraclasts and rare planktonic foraminifera immediately below the K/Pg boundary level indicating temporary open marine influences. The boundary is constrained between the last occurrence of the Maastrichtian larger benthic foraminifera and the first occurrence of the Danian planktonic and benthic foraminifera. The K/Pg boundary is characterized by a sediment bioturbation and a 2-cm-thick reddish-brown clayey mudstone, but due to the low biostratigraphic resolution question on existence of a possible short stratigraphic hiatus remained open. The lowest 2-m-thick interval of the Palaeocene strata consists of burrowed micritic limestones with discorbids, ostracods and planktonic foraminifera deposited in more open marine environments. Planktonic foraminifera tentatively indicate basal Danian Zones P0–Pɑ. Above the 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 the low-energy shallow subtidal conditions with nearshore brackish and freshwater influence comprising benthic foraminifera assemblage of the SBZ 1. Top of the section is characterised by the largest and best developed coral patch reef exposed and karstified during the following relatively long regional exposure event between these oldest Palaeocene and the overlying Palaeocene/Eocene deposits. The Likva section with its prolonged shallow- marine deposition across the K/Pg boundary represents an important addition to the knowledge of the Adriatic Carbonate Platform stratigraphy, indicating that its upper stratigraphic limit is locally extended to the earliest Palaeocene.

Stratigraphy ; Latest Cretaceous ; Palaeocene ; Carbonate succession ; Brač ; Croatia

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