The Monte Postale section (Bolca, northern Italy), one of the most famous Lagersta ̈tten of the Eocene, has been investigated to reconstruct the sedimentary succession and to determine both the larger foraminiferal and the calcareous nannofossil biozones. The results allowed us to ascribe the Monte Postale limestones to the Shallow Benthic Zone 11 and to the calcareous nannofossil Zone CNE 5-?6 (1⁄4 NP 13-?14a). The direct correlation of the SB and CNE Zones is consistent with the current biostratigraphic schemes and allows assignment of the deposition of the succession to the interval between 50.7 and 48.9 Ma, in the late Ypresian (early Eocene). According to the available biostratigraphic data, the uppermost portion of the Monte Postale section should correlate with the Pesciara limestones

The Monte Postale and Pesciara di Bolca sites are well-known Eocene Fossil-Lagerstätten. The origin of these deposits has been previously related to a lagoon environment, protected from the open sea by a barrier formed by some kind of reef. However, no detailed description of a bioconstructed system has ever been reported in the area. This study provides the first detailed characterization of the upper Ypresian Monte Postale reef, made of in situ corals, calcareous algae, and encrusting foraminifera. Three main facies associations have been recognized: (1) a coralgal rim, roughly E/W oriented, (2) lagoon deposits in the south and (3) fore-reef sediments towards the north. The coralgal rim is represented by a wave-resistant framework made of heavily calcified organisms associated to Alveolina accumulations; the adaptation of most of these organisms to the euphotic zone promoted their growth in proximity to the sea level, allowing this structure to act as an effective barrier. In particular, during relative sea-level lowstands or highstands, the coralgal rim could have limited the water exchange between the lagoon and the open sea, reducing the oxygenation in the lagoon and allowing the formation of the Fossil-Lagerstätten. During relative sea-level transgressions, the water could have risen well above the margin, establishing normal oxygenation and hampering the fossils’ preservation. The Monte Postale succession represents one of the few examples of lower Eocene bioconstructions. The description of this biotic assemblage provides new data for the characterization of reef communities during a crucial climatic phase, near the end of the early Eocene climatic optimum global warming

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