Unveiling “Mid-Pliocene Warm Period” dynamics through multiproxy stratigraphic analysis: The Valdelsa Basin in Northern Apennines – Italy as a key archive

Neogene marine marginal basins are important archives for reconstructing Pliocene depositional, paleogeographical and paleoenvironmental evolution. This study focuses on a key succession from the Valdelsa Basin (Tuscany, Italy), which represents a significant example within the Southern Tuscan Neogene basin system, to provide new insights into the mid-Pliocene Warm Period (m-PWP ~3.3–2.9 Ma). To achieve this, a multiproxy integrated stratigraphic approach was applied to a succession of shallow marine, paralic, and continental deposits. The methodology combined physical stratigraphy, sedimentary facies analysis, micro- and macropaleontological content, planktonic foraminiferal biostratigraphy, paleomagnetism, and chemical investigations. The studied succession has been deposited during the Piacenzian, from the upper part of the MPL4b to the MPL5a of the Mediterranean planktonic foraminiferal zonal scheme, including the m-PWP. The integration of bio- and magnetostratigraphic data, allowed the identification of two magnetic inversions: C2An.2r to C2An.2n and C2An.2n to C2An.1r. The integration of litho- and biofacies correlations allows to outline the detailed stratigraphic architecture with significant paleoecological and paleoenvironmental insights, while the new bio- and magnetostratigraphic proxy data have refined the chronostratigraphic framework. Furthermore, comparing of the updated chronological framework with global δ18O benthic stack allows a more precise identification of the main climatic events that led the Basin depositional evolution. The complex and articulated architecture of the shallow-marine to continental succession, along with the distribution of biofacies, show that depositional evolution in the basin occurred mainly under the control of eustatic fluctuations even though the basin was tectonically active. These fluctuations led to alternating transgressive and regressive phases that correlate clearly with major global climatic events, as evidenced by the δ18O stack. This study thus identifies climatic forcing as the primary control on the Valdelsa Basin's Piacenzian depositional evolution.