Studio biostratigrafico e risposta paleoecologica delle associazioni a Nannofossili Calcarei durante il Middle Eocene Climatic Optimum (Meco) al Site ODP 929, (Ceara Rise, AtlanticoEquatoriale)

This Master degree thesis aims to perform a biostratigraphic study and a paleoenvironmental reconstruction based on the response of calcareous nannofossils assemblages to the Middle Eocene Climatic Optimum (MECO). The MECO is a global and relatively long - lasting (ca. 500 kyr) warming event, occurred at about 40 Ma (Sexton et al. 2006; Bohaty et al., 2009). Up to now just few data are available on the response of calcareous nannoplankton to this profound climate change. Calcareous nannofossils are useful paleontological proxies because several taxa show different responses to paleoenvironmental conditions, such as temperature and paleofertility (e.g.: Toffanin et al., 2011). Sediments studied here were recovered during ODP Leg 154, in particular, the material comes from Site 929, Hole E. The main scientific objectives of this expedition were to construct a depth transect of coring sites distributed down the north-eastern flank of Ceara Rise (equatorial Atlantic), in order to better constrain the Cenozoic history of deep-water circulation and chemistry. A high resolution calcareous nannofossil biostratigraphy is provided and this results in precise biostratigraphic classification of the studied interval at Site 929E. The succession spans Zone NP16 and the lowermost part of NP17 (Martini, 1971). According to the biozonation of Agnini et al. (2014), the succession spans from Zone CNE14 to Zone CNE15. The biostratigraphic results at Site 929E are generally consistent with other data available from literature (Fornaciari et al., 2010; Agnini et al., 2014), reaffirming the validity of the additional events recently proposed for the middle Eocene (Fornaciari et al., 2010; Agnini et al., 2014). We also documented the presence of samples with no carbonates, which obviously are barren of nannofossils. This interval is likely related to the CCD shoaling globally recorded during the MECO event. This datum with others coming from the same area (e.g.; Site 1260) could in fact serve to depict the history of the CCD evolution of the equatorial Atlantic before, during and after the MECO.