Study of the Middle Pliocene Warm Event through multiproxy stratigraphy. A case study of Valdelsa Basin (Tuscany, Italy) and comparison with global changes

The mid-Pliocene Warm Period (mPWP, between 3.3 ~ 2.9 Ma) is the most recent period in Earth history during which the estimated temperatures were approximately 2 ~ 3 °C higher than at present days (Lisiecki & Raymo, 2005; Haywood et al., 2021). In Southern Tuscany, and in particular in the Valdelsa Basin, there are deposits dated to this period, and their analysis provides us hints and new useful proxy data of warm period of the past, highly potentially comparable to the near future and provide potential indicators of how the Earth might respond to future warming (Hill et al., 2014). This PhD thesis investigates the pliocene infill of the central-eastern and south-western sector of the Valdelsa Basin, mostly deposited during the climatic Optimum of mid-Pliocene, through traditional geological field survey and several analytical methods such as biostratigraphy, magnetostratigraphy, p-XRF proxy data, cyclostratigraphy, facies analysis, petrography, anisotropy of magnetic susceptibility, magnetic mineralogy, Sr isotopes stratigraphy performed in the frame of the ongoing of the field mapping for the realization of the CARG 286-Sheet “Poggibonsi”. In the central-eastern sector of the Basin, various analytical methodologies were applied on the Pliocene sediments mainly deposited in coeval shallow-water marine, transitional and continental environments. The application of p-XRF as proxy-data for cyclostratigraphy has been targeted to identify on some selected key-sections, through signal analysis performed in space and time domain, the orbital Milankovian periodicities recorded by geochemical data-series and to detect the astronomical forcing. The studied successions respond to the precession periodicity as for other Southern Tuscany Pliocene sections (Riforgiato et al., 2011). Geochemical, facies analysis and micropaleontological data, all combined, allow us to define changes in the depositional environment and their relationship to the climate forcing driven by the orbital configuration. The results show the high potential of the p-XRF analysis for the cyclostratigraphical application integrated with other chronostratigraphic, paleoclimatic and paleoecological proxy data and its efficacy in detecting changes in depositional conditions. The chronostratigraphic high-resolution calibration of the studied successions has allowed the outline of an evolutive paleoclimatic, paleoenvironmental and paleogeographical model of the investigated sectors of the Valdelsa Basin. In the south-western margin of the Basin, the Pliocene sediments of the mPWP transgression, are represented by basal deposits consisting of coarse-grained facies, passing upward and laterally to shallow-water clastic carbonates, marine sands and clays. Data on new stratigraphic sections were collected and compared with data from the literature to provide new chronological and paleoenvironmental constraints, which are useful to understanding the depositional history of this sector of the Basin. Presented data of the vertical and lateral distribution and main lithological-textural features of these carbonate bodies testify the onset of small carbonate factories and show the interplay between sedimentation and controlling factors as global climate forcings and local tectonic in the Valdelsa Basin within the mPWP. New data of the composition, vertical and lateral, lithological-textural features and paleogeographical distribution of these carbonate bodies of the Valdelsa Basin are presented. The research investigates the complex stratigraphic relationships and chronostratigraphic calibration of the Pliocene deposits and explores the potential of p-XRF analysis for cyclostratigraphical applications. The results of this study will contribute to the realization of the 286-Poggibonsi Sheet at 1:50.000 scale, providing new insights into the evolution of the Valdelsa Basin during the m-PWP, and offer useful proxy data for understanding a warmer world than modern.