Climatostratigrafia ad alta risoluzione durante la transizione Plio-Pleistocene nella successione Monte San Nicola (Sicilia):uno studio multidisciplinare

The present study aims to unravel the climatic variability across the Plio-Pleistocene transition, in the time interval between 2.5-2.7 Ma, close to the intensification of North Hemisphere glaciation. The Plio-Pleistocene transition is of great interest for paleoclimatic studies since it is a witness of major shift of the global climate with significant expansion of Northern Hemisphere glaciation which had profound impacts on Earth's ecosystems. The Gelasian Global Stratotype Section and Point (GSSP), dated at 2.58 Ma, marks the base of the Pleistocene Series and of the Quaternary System, and is formalized in the Monte San Nicola section in Sicily. From a stratigraphic perspective the section has been widely studied over time, although with a low resolution detail. On the other hand, a high-resolution climatostratigraphic study, to investigate the climate variability during the Plio-Pleistocene transition in the Gelasian type section was lacking. Considering this lack of knowledge, a multidisciplinary and international program, the GELSTRAT Project (Head and Caruso, 2022), has been set up with the aim to restudy the Gelasian Stage GSSP with a high-resolution detail. In this context, as part of the GELSTRAT Project, the present study focuses on surface water proxies in order to improve the paleoenvironmental reconstruction of the Monte San Nicola type section (MSNt-s). The multiproxy approach has been performed at high temporal scale (~770 years), with special attention to the response of calcareous nannofossil assemblage, the major component of marine calcifying phytoplankton in the modern oceans. Quantitative analysis on calcareous nannofossil assemblage has been performed to identify main changes in surface water features and their relationship with climate variability. The response of calcareous nannofossil assemblage to climate induced surface water variations has been evaluated in terms of changes in total coccolith concentration (N), relative abundances of key taxa, assemblage diversity (Shannon index), nutricline depth fluctuation (N ratio). The study of alkenones was addressed for the reconstruction of paleoproductivity (C37 total concentration) and of sea surface water temperature (SST) in °C. The δ18O record on the planktonic foraminifera Globigerina bulloides has provided a high-resolution oxygen isotope stratigraphy to frame the study record within a regional and global climatostratigraphic contest. Spectral and wavelet analyses of selected proxies have provided main periodicities recorded in the section. Calcareous nannofossil assemblage, alkenone analysis and isotopic record have been integrated with additional marine proxies, such as planktonic foraminifera and geochemical data acquired simultaneously in the MSNt-s through various collaborations. The overall results provide new data on the climate impact over the calcareous nannofossil assemblages, identification of several climate phases at orbital and sub-orbital scale and their effects in Central Mediterranean, and recognition of the main oceanographic and atmospheric forcings. The results provide evidence that the paleoclimate and stratigraphic signals are very well preserved in the type-section and further improve the correlation potential of the GSSP outside the type-area.