The impact of OAE2 and Late Turonian events on calcareous nannofossil evolution. Implication for calcareous nannofossil biochronology

Calcareous nannofossils originated in the Triassic, but it is during the Late Cretaceous that they reached their highest diversity and abundance. During this period, they became a predominant component of the oceans. However, especially in the Cretaceous, some species of this group used for biostratigraphic purposes appear to exhibit pronounced provincialism and consequential diachronism, that could blur their biostratigraphic potential. To investigate whether this diachronism is real (attributed to varying paleoenvironmental conditions) or merely apparent (resulting, for example, from different taxonomic concepts used by various authors), this thesis examined four stratigraphic successions located in different paleoenvironmental settings (e.g., varying latitudes or basins). Specifically, this study explored the associations of calcareous nannofossils in the Quero section (Belluno Basin, northeastern Italy), Breonio section (Trento Plateau, northeastern Italy), Bottaccione section (Umbro-Marche Basin, central Italy), and Poigny section (Paris Basin, France). Subsequently, the obtained data were compared with those from the study of planktic foraminifera associations and stable carbon isotopes conducted by co-authors (for the Quero and Breonio sections) or with data available in the literature (for the Bottaccione and Poigny successions). For each analysed section, the results were then compared with available literature to assess whether the identified bioevents could be considered more or less synchronous and, therefore, reliable, not only within the analysed sections but also in a broader context. In addition, it has been accurately date the lastame an important fossil lagerstatten of the Veneto region ed it has explored its paleoenvironmental meaning. Unexpected result from Quero and Poigny section has been the highlighting of a sea water stratification phase between the Round Down and the Pewsey Events.