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Subaerial exposure surface in the Palaeocene carbonates of the Likva Cove, the Island of Brač

Discontinuity surfaces are common in successions of carbonate platforms, including the Adriatic Carbonate Platform (AdCP). The end of AdCP deposition is marked by regional unconformity between the Cretaceous and Paleogene, but in some parts of the platform sedimentation was more or less continuous at the K/Pg boundary, like in the Likva Cove, NW part of the Island of Brač. In the Likva Cove the youngest deposits of the Sumartin formation belong to the early Palaeocene, corresponding to the lower part of the Liburnian deposits of Slovenia and marking the Maastrichtian–Palaeocene transition. The studied section of the Palaeocene part of the Sumartin formation is 15.70 m thick and is characterized by lacustrine and shallow marine carbonates with freshwater influence. These carbonates are poor in fossil remains, such as benthic foraminifera, which would enable age determination, but the younger Palaeocene–Eocene? age is assumed since the studied section overlies the youngest Palaeocene (Danian) strata previously dated. In its lower part, the studied section comprises subaerial exposure surface characterized by the processes of soil formation in a terrain rich in vegetation and in conditions of semiarid climate. The surface itself is characterized by irregular relief, biogenic calcretes with rhizoliths, Microcodium aggregates, alveolar septal fabric, micrite nodules, black pebbles, laminated calcretes and pisoids, indicating long-term subaerial exposure. It may be assumed that a complete meteoric diagenetic zone has been developed under the emerging surface. The subaerial exposure was followed by the transgression resulting in incorporation of fragments of terrestrial carbonates into the clayey calcareous matrix forming transgressive breccia (including bauxite occurrences) most likely preserved in the palaeodepressions. Above the transgressive breccias brackish to freshwater limestones with ostracods, gastropods, cyanobacteria and charophytaceans have been deposited, indicating very shallow and restrictive lacustrine environments, as well as certain marine influence. Within the brackish and freshwater limestones several subaerial exposure surfaces have been identified, probably as a consequence of a synsedimentary tectonic activity. The studied subaerial exposure and erosion surface probably formed under the influence of the Late Cretaceous synsedimentary tectonics caused by initial stages of the collision of the Adriatic microplate and Eurasian plate, and is recognized as a regional event over the entire Adriatic Carbonate Platform, marking the end of the typical carbonate shallow-marine sedimentation.

subaerial exposure surface ; Palaeocene carbonates ; Adriatic Carbonate Platform ; Island of Brač

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